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[[File:SexualDifferentation.jpg|350px|right|thumb|The stages in sexual differentiation of the female and male reproductive system]]
 +
 
=Genital=
 
=Genital=
--[[User:Z8600021|Mark Hill]] ([[User talk:Z8600021|talk]]) 15:13, 26 August 2014 (EST) No sub-headings yet and I even had to add your project title! Get moving.
 
  
--[[User:Z8600021|Mark Hill]] ([[User talk:Z8600021|talk]]) 11:53, 6 September 2014 (EST) Just references not much else here yet.
+
==Introduction==
 +
 
 +
Genital system development occurs in both the embryonic and foetal phase of development. By the commencement of the foetal period, sexual determination and initial growth of the different gonads occur <ref name=Hill2014>Hill, M.A. (2014) Lecture - Genital Development. Retrieved October 24, 2014, from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Genital_Development</ref>. It is within the foetal period that the internal and external genital organs develop <ref name=Hill2014>Hill, M.A. (2014) Lecture - Genital Development. Retrieved October 24, 2014, from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Genital_Development</ref>. This page focuses on the foetal developmental processes, exploring the current and historical models and understanding, alongside the congenital abnormalities.
 +
 
 +
Today there is an innumerable amount of research articles focused on foetal genital growth, with some addressing the system as a whole <ref name=PMID14641326><pubmed>14641326</pubmed></ref> and others investigating certain genital organs <ref name=PMID13362960><pubmed>13362960</pubmed></ref>. Current models and understandings have been obtained from both human <ref name=PMID11315960><pubmed>11315960</pubmed></ref> and animal populations <ref name=PMID13362960><pubmed>13362960</pubmed></ref>, and this page will outline some of the important current research.
 +
 
 +
Research into foetal genital development can be traced to as early as the 16th century<ref name=PMID18462432><pubmed>18462432</pubmed></ref> with anatomists proposing theories and constructing models, proven to being critical in obtaining the in-depth information known today. This page will mention some of these historical findings in both the female and male genital system. 
 +
 
 +
This project will end with discussing some of the congenital abnormalities of the genital system, mentioning both the malformations that are most common <ref name=PMID16006950><pubmed>16006950</pubmed></ref> and those that are rare <ref name=PMID23635766><pubmed>23635766</pubmed></ref>.
 +
 
 +
 
  
 
==System Development==
 
==System Development==
{| class="wikitable"
+
 
 +
 
 +
[[File:Paramesonephric duct.jpg|300px|thumb|Paramesonephric duct development]]
 +
[[File:Infant ovary.jpg|300px|thumb|Histological image of primordial follicles in infant ovary]]
 +
 
 +
'''Timeline of Embryonic, Fetal and Postnatal Genital Development'''<ref>Hill, M.A. (2014) Lecture - Genital Development. Retrieved October 24, 2014, from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Genital_Development</ref>
 +
 
 +
{| class="wikitable"  
 +
|-bgcolor="purple"|align="centre"
 +
|'''Week''' || '''Development'''
 +
|-bgcolor="lavender"
 +
| 3-4 || Primordial germ cells migrate during gastrulation
 
|-
 
|-
! Weeks !! M A L E  !! F E M A L E
+
| 4 || Intermediate mesoderm, pronephros primordium
 +
|-bgcolor="lavender"
 +
| 5 || Mesonephros and mesonephric duct
 
|-
 
|-
| FERTILIZATION || both male and female are same at this point- only difference is presence of XY or XX chromosome
+
| 6 || Ureteric bud, metanephros, genital ridge
 +
|-bgcolor="lavender"
 +
| 7 || Cloacal divison, gonadal primordium - indifferent to first appearance of testis cords
 +
Female - Paramesonephric duct preservation or regression begins
 
|-
 
|-
|WEEKS 1-7 || GENITAL DEVELOPMENT IS UNDIFFERENTIATED. gonads derived from:
+
| 8 || Paramesonephric duct, clear gonadal differentiation
 +
|-bgcolor="lavender"
 +
| 9 || Paramesonephric duct fusion in the female forming the uterus and lack of fusion laterally forming the fallopian tubes. Also forms vagina.
 +
|-
 +
| 15 || Primary follicles (ovary)
 +
From the 26th week (between week 4 and 5), the gubernaculum starts to pull the testes down and results in descent of the testes into the scrotal sac.
 +
Both male and female gonads undergo descent. 
 +
|-bgcolor="lavender"
 +
| Puberty || Development of secondary sexual characteristics
 +
Female - start of menstruation, first egg released.
 +
Male - development of course voice, body hair and sperm formation.
 +
|-
 +
|}
  
* mesothelium lining posterior abdominal wall
+
'''Related video'''
* underlying mesenchyme
+
 
* primordial germ cells.
+
<html5media>https://www.youtube.com/watch?v=MureNA-RSZM</html5media>
 +
 
 +
 
 +
 
 +
----
 +
 
 +
 
 +
===Development of Internal Genitalia===
 +
{| style="width:100%"
 +
|bgcolor="lightskyblue"|'''MALE'''
 +
|bgcolor="violet"|'''FEMALE'''
 
|-
 
|-
| WEEK 5 || '''development of indifferent gonads'''  
+
|bgcolor="aliceblue"| The fetal development of internal genitalia is largely dependent on the endocrine functions of the fetal testes.  The fetal testes produce masculinizing hormones such as '''testosterone''' which begins its release from the interstitial Leydig cells of the primitive seminiferous tubules during the 8th week of development, and also the release of '''Mullerian Inhibiting Hormone (MIS)''' which is released at the sixth and seventh weeks by the Sertoli Cells. Testosterone acts primarily on the mesonephric ducts to stimulate the formation of the male genital ducts, whereas the MIS acts on the paramesonephric duct to stimulate its regression. <ref name=PMID11315960><pubmed>11315960</pubmed></ref> <ref name=PMID24240231><pubmed>24240231</pubmed></ref>
 +
 
 +
By the eighth week of fetal development in XY embryos, the testosterone produced in the testes results in the convolution of the proximal ends of the mesonephric ducts to form the '''epididymis''' <ref name=PMID24240231><pubmed>24240231</pubmed></ref>. The mesonephros begins to degenerate, however some of the mesonephric tubules remain and develop into efferent ductules, which then open into the duct of the epididymis. Distal to this end, the mesonephric duct begins to develop a thick lining of smooth muscle and progresses to become the ductus deferens.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
 
 +
 
 +
 
 +
''Fetal Male Glandular Development''
 +
* the seminal glands develop from lateral outgrowths from that caudal end of each mesonephric duct which nourishes the sperm and constitutes most of the fluid in the ejaculate
 +
* the endodermal outgrowths arise from the prostatic part of the urethra which grow into the surrounding mesenchyme. This acts as a base of the proliferation of the glandular epithelium of the prostate to differentiate- the associated mesenchyme will differentiate into dense stroma and the smooth muscle of the prostate. <ref name=PMID24240231><pubmed>24240231</pubmed></ref>
 +
* The bulbourethral glands are pea-sized and developed from paired outgrowths that originate from the spongy pat of the urethra. The adjacent mesenchyme gives rise to the stroma and smooth muscle fibres which will ultimately produce secretions which contribute to the semen.
 +
 
 +
 
 +
 
 +
| bgcolor="lavenderblush"| The absence of testosterone production in XX embryos results in the regression of the mesonephric duct, and conversely the absence of MIH results in the development and progression of the paramesonephric ducts. The paramesonephric ducts give rise to most of the female internal genital system- the unfused cranial aspects of the ducts give rise to a primitive '''fallopian tubes''', whilst the caudally fused portions form the uterovaginal primordium which will develop into a '''uterus''' and '''superior vagina'''. The splanchnic mesenchyme gives rise to the endometrial stromal tissue and the myometrium.<ref name=PMID11315960><pubmed>11315960</pubmed></ref>
 +
 
 +
 
 +
Female genital development during the fetal period is not dependant on endocrine contributions from the foetus. Later in fetal development, maternal oestrogen's and oestrogen derived from the placenta contribute to the development of the fallopian tubes, uterus and the superior vagina.
 +
 
 +
 
 +
''Female Glandular Development''
 +
 
 +
[[File:Kollmann454.jpg|thumb|200px|right|Internal genitalia in the female]]
  
* thickened area of mesothelium develops on medial side of mesonephros [primitive kidney]
+
* The urethra develops outgrowths which form the mucus secreting '''urethral glands''' and paraurtehral glands.
* this + proliferation of underlying mesenchyme = gonadal ridge
+
* outgrowths from the urogenital sinus form the '''greater vestibular glands''' in the lower third of the Labia Majora. These glands are also mucous secreting and are comparative to the bulbourethral glands in males. <ref name=PMID11315960><pubmed>11315960</pubmed></ref>
* fingerlike epithelial chords = gonadal chords
 
* gonad = cortex + medulla
 
 
|-
 
|-
|WEEK 8 || seminiferous tubules begin to release androgens ||
+
|- style="height:10px"
|-
+
| style="width:50%"|  
|WEEK 10 || || rudimental rete ovarii forms from indifferent gonads
+
|}
|-
+
 
|WEEK 12 ||
+
[[File:External genitalia current model.jpg|300px|right|thumb|Flow Diagram of the current model of embryonic and fetal development of the external genitalia]]
 +
 
 +
===Development of the External Genitalia ===
 +
 
  
* testosterone determining factor induces '''seminiferous chords''' from indifferent gonads --> branch to '''rete testis'''
+
{|class="wikitable mw-collapsible mw-collapsed"
* tunica albiguinea develops
+
! ''Embryonic Period – fertilisation to end of 8th week (embryonic age) = AMBISEXUAL STAGE''
|-  
+
|- bgcolor="lavender"
|WEEK 16 ||  || primordial follicles begin to develop
 
 
|
 
|
 +
# The external genitalia initially begin in the perineal region as three primordia, being the genital tubercle in the midline and the bilateral genital swellings. These three primordia arise together with the differentiation of the cloacal part of the hindgut into the urogenital sinus, rectum and anal canal. The cloacal membrane extends from the perineum cranially to the root of the umbilical cord and during development, this bilayered cloacal membrane retracts into the perineum. This is due to cranial and medial migration of mesodermal cells into the ventral body wall between the ectoderm and endoderm of the cloacal membrane. These migrating mesodermal cells line around the membrane and accumulate, forming the three primordial swellings.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
# These external features are internally related to the cloaca, which becomes divided coronally by the urorectal septum into the urogenital sinus anteriorly, and the rectum and anus posteriorly.
 +
# This division of the cloaca occurs in a specific way so the allantois, Mullerian and Wolffian ducts and ureters all empty into the urogenital sinus.
 +
# When the cloacal membrane becomes divided into the urogenital and anal membranes, the urogenital membrane is bound cranially by the genital tubercle in the midline and laterally by the urogenital folds and genital swellings. <ref name=PMID11315960><pubmed>11315960</pubmed></ref>
 +
# The urogenital membrane degenerates to allow communication between the urogenital sinus and amniotic cavity.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 
|}
 
|}
  
Genital system development is an extremely interesting area of embryology as it is not until the later stages of embryogenesis (around week 4-6) that sexual differentiation occurs in the fetus, and the sexual organs actually look very similar up until this point, and the formation of the correct sex organs depend really on whether the genital ridge releases Testosterone or oestrogen
 
  
<pubmed>24240231</pubmed>
+
----
<pubmed>24928207</pubmed>
+
 
<pubmed>24741072</pubmed>
+
 
--[[User:Z3416697|Z3416697]] ([[User talk:Z3416697|talk]]) 20:06, 26 August 2014 (EST)
+
'''The current model for fetal development of the external genitalia in humans and mice:'''
 +
{| style="width:100%"
 +
|bgcolor="lightskyblue"|'''MALE MODEL'''
 +
|bgcolor="violet"|'''FEMALE MODEL'''
 +
 
 +
|-
 +
|bgcolor="aliceblue"|'''''Fetal Period – from 8th week of development = SEXUAL DIFFERENTIATION'''''
 +
# Initially, the female and male fetuses’ external genitalia are identical and include the genital tubercle in the midline, urogenital folds (forming the urogenital ostium) and genital swellings (laterally).
 +
# In males, the genital tubercle will eventually form the penis and the genital swellings migrate caudally and a fusion event in the midline occurs, thus forming the scrotum.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
# As the genital tubercle elongates to form the penis, a groove forms on the ventral surface known as the urethral groove. The urethral folds that are continuous with the urogenital folds surrounding the urogenital ostium define the urethral groove laterally.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
# At first, the urethral groove and folds extend only part of the along the shaft of the elongating genital tubercle (known as the phallus at this stage).
 +
# Distally, the urethral groove terminates at the urethral plate, consisting of epithelial cells, and then extends into the glans of the penis, forming a channel.
 +
# As the phallus elongates, the urethral folds grow toward each other and fuse in the midline forming the midline epithelial seam, converting the urethral groove into a tubular penile urethra. The fusion of the urethral folds begins proximally in the perineal region and extends distally towards the glans of the penis.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
 
 +
[[File:Cross section of genital tubercle male.jpg|270px|right|thumb|Cross section of the male genital tubercle]][[File:Anatomical diagram of testes.jpg|300px|left|thumb|Anatomical drawing of adult male testes]]
 +
 
 +
* Hypospadias result from failure of formation or fusion of the urethral folds and this is the focus of current research.
 +
* The elongating phallus is covered externally by ectoderm that will eventually give rise to the penile epidermis.
 +
* Urethral epithelium has endodermal origins and the majority of the penis is derived from mesodermal cells.
 +
* During development, the mesoderm separates into connective tissues and dermis.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
* Dense areas of mesenchymal cells form within the shaft of the penis with the most superficial dense bodies forming the thick connective tissue capsule known as the tunica albuginae.
 +
 
 +
* Mesenchyme surrounding the urethra forms smooth muscle of the urethral mucosa and submucosa. Erectile tissues such as the corpus spongiosum and corpus cavernosum then surround these two layers.
 +
* In some species, the mesenchyme of the genital tubercle also forms an os penis, comprised of bone and cartilage.
 +
* Genital tubercle development involves an outgrowth of somatic tissue from the body surface, similar to the development of the limb.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
* Development of the external genitalia is highly regulated by the endocrine system. Sexual differentiation of the external genitalia is determined by the presence or absence of androgen receptor signaling. The fetal testes produce testosterone, which travels to the genital tubercle via the bloodstream, where it is converted into 5a-dihydrotestosterone by the enzyme 5a-reductase. This formation of the highly potent 5a-dihydrotestosterone masculinizes the developing external genitalia, as binding of the 5a-dihydrotestosterone to its androgen receptor leads to the regulation of downstream signaling genes.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
*: Sonic Hedgehog (SHH) acts as an endodermal signal that normally regulates patterning of the hindgut and is expressed in the epithelium of the cloaca, urogenital sinus and urethral plate epithelium. However this has an important signaling pathway role in development of external genitalia. The SHH gene codes for a particular protein that has important roles in organogenesis as well as structures that are dependent upon mesenchymal-epithelial interactions, such as limbs, teeth and prostate.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
| bgcolor="lavenderblush"|'''''Fetal Period – from 8th week of development = SEXUAL DIFFERENTIATION'''''
 +
# Only minor changes occur from the embryonic ambisexual stage in the female, beginning with the minimal growth of the genital tubercle to form the clitoris.
 +
# The urogenital folds remain apart and unfused to form the labia majora.<ref name=PMID11315960><pubmed>11315960</pubmed></ref>
 +
# The genital swellings also remain apart and unfused to form the labia minora.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
 
 +
* Together, these bilateral labial structures and the clitoris located proximally form the border for the urogenital ostium, thus forming the vestibule of the vagina, with vaginal and urethral openings.
 +
* The tubercle itself goes on to form the mons pubis.
 +
* Sexual dimorphism of the external genitalia in female humans is determined by the absence of androgenic pathways, however the female genital tubercle can be ‘masculinised’ as 5a-reductase and androgen recpetors are present.
 +
* The genital tubercle can not go on to form a penis as testosterone is not produced, however in some instances it is abnormally produced in excess by the suprarenal gland resulting in different degrees of masculinsation of the clitoris.<ref name=PMID11315960><pubmed>11315960</pubmed></ref>
 +
 
 +
 
 +
 
 +
 
 +
 
 +
 
 +
 
 +
 
 +
 
 +
 
 +
 
  
[[File:External Genitalia.jpg|450px]] [[File:Image.jpg|450px]]
 
  
==Current Research, Models and Findings==
 
  
===Current Research===
 
  
====Male====
 
  
• Extensive research into organogenesis of the external genitalia, mainly in males, is driven by the increasing incidence of hypospadias.
+
[[File:Clitoris.jpg|600px|thumb|center|Stages in the Development of the External Sexual Organs in the Male and Female]]
 +
|-
 +
|- style="height:10px"
 +
| style="width:50%"|
 +
|}
  
• Hypospadias are a result of the defect of fusion of the urethral folds of the lower part of the penis to fold and form the tubular penile urethra.
 
  
• The result of this in humans is the presence of an abnormal ventral urethral meatus, incomplete formation of the prepuce and an abnormal penile curvature.
 
  
• Development of the male external genitalia, which occurs in the fetal period of development, is androgen dependent and involves epithelial-mesenchymal interactions. Because of these interactions, which are very similar to limb development, research into the development of genital tubercle has utilised similar methods for both processes.
+
===Descent of the Gonads===
  
• A minority of hypospadias cases are a result of the androgenic pathways being impaired and causing this congenital defect.
+
[[File:Testis-descent end.jpg|200px|thumb|right|Descent of testes]]
  
The cell-cell interactions that allow for the development of the male external genitalia are mediated by a broad range of signaling molecules and growth factors such as fibroblast growth factors (FGFs), Sonic hedgehog (SHH) and bone morphogenetic proteins (BMPs).  
+
'''Male:''' The testis undergo transabdominal and transinguinal descent. The testis lies in the subserous fascia. The processus vaginalis evaginates into the scrotum and the gubernaculum draws it into the scrotal sac. As it descends, it traverses past the superficial (external oblique fascia) and deep (transversalis fascia) inguinal rings of the inguinal canal. This begins in between the 4th and 5th week (usually around day 26) and spans over many days. It can occur unilaterally or bilaterally, more common in premature babies and can conclude postnatally.<ref>Hill, M.A. (2014) Lecture - Genital Development. Retrieved October 24, 2014, from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Genital_Development</ref>
  
• Such signaling and growth factors are downstream of androgen receptor signaling and an understanding of the mechanisms that underlie normal penile development during the fetal period, will lead to a deeper understanding of the aetiology of hypospadias.  
+
'''Female''': ovaries undergo caudal and lateral shifts to be suspended in the broad ligament of the uterus. The gubernaculum does not shorten, attaches to paramesonephric ducts and causes medial translocation into the pelvis. The remnant in adult life of the gubernaculum is the ovarian and round ligament of the uterus, which suspend the ovaries and uterus respectively.<ref>Hill, M.A. (2014) Lecture - Genital Development. Retrieved October 24, 2014, from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Genital_Development</ref>
  
• Future research can work to decrease the incidence of hypospadias, which has more than doubled in the past 30 years.
 
  
• Current research uses mouse models and observes the development of their external genitalia, especially their penile development, which initially appears to be different to human development. However, more microscopic inspection shows that mice have very similar external genitalia and are therefore appropriate animal models for observing such fetal development. As a result, mutant mouse models can effectively be used in future research to observe molecular mechanisms underlying hypospadias and their aetiology. <ref><pubmed>14641326</pubmed></ref>
+
----
  
====Female====
+
==Current Research, Models and Findings==
  
 
===Current Models===
 
===Current Models===
  
Current model: of the cellular and molecular mechanisms of the development of mammalian external genitalia. <ref><pubmed>14641326</pubmed></ref>
+
Most current research uses mouse models and observes the development of their external genitalia, especially their penile development, which initially appears to be different to human development. However, more microscopic inspection shows that mice have very similar external genitalia and are therefore appropriate animal models for observing such fetal development. As a result, mutant mouse models can effectively be used in future research to observe molecular mechanisms underlying hypospadias and their aetiology. <ref name=PMID14641326><pubmed>14641326</pubmed></ref>
  
'''DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN'''
+
When observing the morphology and cell biology of the developing testis, it is important to note that most of the research conducted on the subject involves the use of mouse models as a result of a lack of human subjects. It can be assumed that events in the human embryo correspond to the same events in the mouse embryo, however there are some differences between the time course of certain events and anatomy. <ref name=PMID17237341><pubmed>17237341</pubmed></ref>
  
''Embryonic Period – fertilisation to end of 8th week (embryonic age) = AMBISEXUAL STAGE''
+
Some examples of different animal models used in research involving fetal development of male and female genital systems are:
  
• The external genitalia initially begin in the perineal region as three primordia, being the genital tubercle in the midline and the bilateral genital swellings.
+
* Sheep<ref name=PMID21223560><pubmed>21223560</pubmed></ref>
 +
* Mouse<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
* Dogs<ref name=PMID13362960><pubmed>13362960</pubmed></ref>
 +
* Porcine<ref name=PMID23571006><pubmed>23571006</pubmed></ref>
 +
* Rats<ref name=PMID22248293><pubmed>22248293</pubmed></ref>
 +
* Monkeys<ref name=PMID21710394><pubmed>21710394</pubmed></ref>
 +
* Bovine<ref name=PMID20347535><pubmed>20347535</pubmed></ref>
 +
* Goats<ref name=PMID22006251><pubmed>22006251</pubmed></ref>
  
• These three primordia arise together with the differentiation of the cloacal part of the hindgut into the urogenital sinus, rectum and anal canal.
+
Different models are used for different research topics; for example, research involving Polycystic ovary syndrome (PCOS) uses murine models preferable due to the developmental time frame that allows studies of inherited PCOS to be examined within an appropriate time frame. The sheep model is also beneficial to use for PCOS research as it is cost effective and their size allows them to be subjected to certain procedures such as ultrasound and neurotransmitter measures. Primates are examples of an optimal model however are limited in their accessibility and long time frame of development.<ref name=PMID21710394><pubmed>21710394</pubmed></ref>
  
• The cloacal membrane extends from the perineum cranially to the root of the umbilical cord and during development, this bilayered cloacal membrane retracts into the perineum. This is due to cranial and medial migration of mesodermal cells into the ventral body wall between the ectoderm and endoderm of the cloacal membrane.
+
It is important to note that any findings associated with an animal model should be translated appropriately to the human model, as animals differ in their anatomy and regulatory mechanisms, as well as placentation. That is, sheep, rats and mice display different placentation and ovarian development that occurs in utero in sheep, primates and humans differs to the ex utero development in murine models.<ref name=PMID21710394><pubmed>21710394</pubmed></ref>
  
• These migrating mesodermal cells line around the membrane and accumulate, forming the three primordial swellings.
+
All animal experiments must be performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. [[http://grants.nih.gov/grants/olaw/Guide-for-the-care-and-use-of-laboratory-animals.pdf | Guide for the Care and Use of Laboratory Animals]]
  
• These external features are internally related to the cloaca, which becomes divided coronally by the urorectal septum into the urogenital sinus anteriorly and the rectum and anus posteriorly. <ref><pubmed>14641326</pubmed></ref>
+
===Current Research and Findings===
 +
====Male====
 +
----
 +
{|
 +
|-bgcolor="aliceblue"
 +
|
 +
[[File:Hypospadias.jpg|400px|thumb|right|Different types of hypospadias]]
  
[[File: Flow Diagram of Fetal Development of External Genitalia.pptx|1000px|thumb|right|alt text]]
+
Extensive research into organogenesis of the external genitalia, mainly in males, is driven by the increasing incidence of hypospadias. Hypospadias are a result of the defect of fusion of the urethral folds of the lower part of the penis to fold and form the tubular penile urethra. The result of this in humans is the presence of an abnormal ventral urethral meatus, incomplete formation of the prepuce and an abnormal penile curvature.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
  
• This division of the cloaca occurs in a specific way so the allantois, Mullerian and Wolffian ducts  and ureters all empty into the urogenital sinus. <ref><pubmed>14641326</pubmed></ref>
+
Development of the male external genitalia, which occurs in the fetal period of development, is androgen dependent and involves epithelial-mesenchymal interactions. Because of these interactions, which are very similar to limb development, research into the development of genital tubercle has utilised similar methods for both processes. A minority of hypospadias cases are a result of the androgenic pathways being impaired and causing this congenital defect. The cell-cell interactions that allow for the development of the male external genitalia are mediated by a broad range of signaling molecules and growth factors such as fibroblast growth factors (FGFs), Sonic hedgehog (SHH) and bone morphogenetic proteins (BMPs). Such signaling and growth factors are downstream of androgen receptor signaling and an understanding of the mechanisms that underlie normal penile development during the fetal period, will lead to a deeper understanding of the aetiology of hypospadias.<ref name=PMID14641326><pubmed>14641326</pubmed></ref>
 +
|}
 +
 
 +
[http://npesu.unsw.edu.au/sites/default/files/npesu/surveillances/Congenital%20anomalies%20in%20Australia%202002-2003.pdf | Statistics regarding congenital abnormalities, including hypospadias and epispadias for 2002 and 2003 in Australia]
  
DRAW A PICTURE
+
----
  
• When the cloacal membrane becomes divided into the urogenital and anal membranes, the urogenital membrane is bound cranially by the genital tubercle in the midline and laterally by the urogenital folds and genital swellings.
 
  
• The urogenital membrane degenerates to allow communication between the urogenital sinus and amniotic cavity.
+
{|
 +
|-bgcolor="aliceblue"
 +
|
 +
[[File:POPs and risk of hypospadias.jpg|400px|thumb|left|Table of levels of POPs in maternal serum samples and risk of hypospadias in infants]]
  
''Fetal Period – from 8th week of development = SEXUAL DIFFERENTIATION''
+
'''A Nested Case-Control Study of Intrauterine Exposure to Persistent Organochlorine Pollutants and the Risk of Hypospadias (2012)'''<ref name=PMID23028613><pubmed>23028613</pubmed></ref>
  
• Initially, the female and male fetuses’ external genitalia are identical and includes the genital tubercle in the midline, urogenital folds (forming the urogenital ostium) and genital swellings (laterally). <ref><pubmed>14641326</pubmed></ref>
+
Hypospadias are a common congenital abnormality resulting from the failure of fusion of the urethral folds within the fetal period of development (8th-14th week of gestation). Whilst it is known that sexual differentiation of the male external genitalia depends on testosterone and its conversion into dihydrotestosterone, the risk factors of hypospadias are not thoroughly researched. This article aims to examine environmental exposure to endocrine disrupting chemicals (EDCs) and understand their potential to act as antagonists on androgen receptors, thereby disrupting the hormonal balance of the endocrine system ultimately leading to hypospadias.<ref name=PMID11469497><pubmed>11469497</pubmed></ref>
 +
More specifically, a major group of EDCs known as persistent organochlorine pollutants (POPs), for example, polychlorinated biphenyls, dioxins, pesticides (dichlorodiphenyl trichloroethane, DDT) and hexachlorobenzene (HCB). Such chemicals are lipophilic, resistant to biodegradation and are present throughout the hydrosphere and atmosphere. Although these chemicals were banned in the 1970’s and 1980’s, due to the potency of these chemicals, they are still found within humans<ref name=PMID22425898><pubmed>22425898</pubmed></ref> and are able to traverse the placenta, becoming exposed to the developing fetus<ref name=PMID6431068><pubmed>6431068</pubmed></ref>.
 +
Therefore, the aim of the present study was to investigate the linkage between exposures of the fetus to POPs and risk of developing hypospadias.
  
 +
This was a case-controlled study of the risk of hypospadias of single-born boys with regards to levels of POPs within the mothers’ blood during pregnancy. The study used 390 boys with hypospadias and controls were used. Boys with any cryptorchidisms, major malformations or even minor hypospadias were excluded from the study.
  
====Male====
+
This study concluded that EDCs such as PCBs, p,p’-DDE and HCB possess the potential to alter hormonal levels and affect the fetus, resulting hypospadias. It shows that in uterine exposure to HCB and possibly p,p’-DDE are risk factors and may affect androgen-signaling.
 +
|}
 +
 
 +
 
 +
 
 +
----
 +
 
 +
 
 +
 
 +
{|
 +
|-bgcolor="aliceblue"
 +
|
 +
'''Paracetamol, aspirin, and indomethacin induce endocrine disturbances in the human fetal testis capable of interfering with testicular descent.''' '''(2013)'''<ref name=PMID24030937><pubmed>24030937</pubmed></ref>
 +
 
 +
[[File:Male testosterone and AMH level graph.jpg|thumb|300px|right|Graph showing male testosterone and AMH levels]]
 +
 
 +
The differentiation of the gonads into male or female begins around week 6-8 and is linked to the sex-determining region of the Y chromosome. The formation and descent of the testis is determined by a number of hormones which are:
 +
*Anti-mullerian hormone (AMH) - produced by sertoli cells, which acts on the mullerian ducts.
 +
*Testosterone - produced by the fetal leydig cells, which ensures differentiation of wolffian ducts as well as the terminal phase of descent of the testis.
 +
*Insulin like factor 3 (INSL3) - is produced by the differentiated fetal leydig cells, which are involved in the transabdominal phase of descent.
 +
*Prostaglandins are also believed to be involved in the differentiation of the male genital tract and testis.
 +
 
 +
The development of the male reproductive system requires the action of different hormones and is highly susceptible for development to be altered due to endocrine disruptions.
  
• In males, the genital tubercle will eventually form the penis and the genital swellings migrate caudally and a fusion event in the midline occurs, thus forming the scrotum.
+
Cryptorchidism is the failure of descent of the testis and is the most common congenital malformation in males.
 +
Non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol are some of the most widely used drugs used. These drugs have recently been identified as potential endocrine disruptors (ED) in humans. A number of epidemiological studies have reported that exposure to NSAIDs and analgesics during pregnancy showed an increased risk of cryptorchidism.
  
• As the genital tubercle elongates to form the penis, a groove forms on the ventral surface known as the urethral groove. The urethral folds that are continuous with the urogenital folds surrounding the urogenital ostium define the urethral groove laterally.
+
This study used 62 fetuses from the first trimester between 7-12 weeks in gestation (GW) from pregnant women who obtained an abortion legally and with were given information and verbal consent was obtained according to national guidelines. The terminations were not motivated by abnormalities. The testes were cut in approximately 1mm3 pieces and drugs were used in the same concentration compared to recommended dosages in the body. The drugs used were paracetamol, aspirin, indomethacin, ketoconazole (antifungal).
  
• At first, the urethral groove and folds extend only part of the along the shaft of the elongating genital tubercle (known as the phallus at this stage).
+
Testicular cells were counted using histology and image analysis and the hormones were assayed in the medium.
 +
The results showed no changes in the architecture of the testis with the analgesic treatment whereas the ketoconazole caused the boundaries of the testis cords to become unrecognisable. The analgesics did not significantly modify the number of germ cells or sertoli cells.
 +
Ketoconazole reduced testosterone levels in contrast to indomethacin, which stimulated testosterone production. Paracetamol had no significant effect on testosterone while aspirin produced a dose response relationship with an increase in testosterone after 72 hours in the youngest fetuses (8-9.86 GW) but not the older testes (10-12GW). None of the analgesics significantly affect the number of interstitial cells.
  
• Distally, the urethral groove terminates at the urethral plate, consisting of epithelial cells, and then extends into the glans of the penis, forming a channel.
+
The results showed a consistent trend for lower INSL3 production after 48-72 hours of exposure to mild analgesics and ketoconazole. This was the first study to measure direct production of INSL3 by the testis.
 +
Aspirin strongly stimulated AMH production, whereas as paracetamol and indomethacin increased production but not significantly. The analgesics did not significantly alter the sertoli cells and Ketoconazole significantly inhibited AMH production. Aspirin and paracetamol showed significant inhibition of Prostaglandin E2 production while indomethacin had no effect.  
  
• As the phallus elongates, the urethral folds grow toward each other and fuse in the midline forming the midline epithelial seam, converting the urethral groove into a tubular penile urethra. <ref><pubmed>14641326</pubmed></ref>
+
In conclusion, the study shows that painkillers have a direct effect on various hormones, which are crucial for endocrine function and development of the human testis. The study shows that there is a direct effect with the dosages which are currently found with most medications.
 +
|}
  
DRAW A PICTURE
 
  
• The fusion of the urethral folds begins proximally in the perineal region and extends distally towards the glans of the penis.
 
  
• Hypospadias result from failure of formation or fusion of the urethral folds and this is the focus of current research.
+
----
  
• The elongating phallus is covered externally by ectoderm that will eventually give rise to the penile epidermis. Urethral epithelium has endodermal origins and the majority of the penis is derived from mesodermal cells.
 
  
• During development, the mesoderm separates into connective tissues and dermis.
 
  
• Dense areas of mesenchymal cells form within the shaft of the penis with the most superficial dense bodies forming the thick connective tissue capsule known as the tunica albuginae. <ref><pubmed>14641326</pubmed></ref>
+
{|
 +
|-bgcolor="aliceblue"
 +
|
 +
'''The Effect of Dihydrotestosterone Exposure During or Prior to the Masculinisation Programming Window on Reproductive Development in Male and Female Rats (2012)'''<ref name=PMID22248293><pubmed>22248293</pubmed></ref>
  
[[File: Labelled Drawing of Testes.jpeg|200px|thumb|left|alt text]]
+
[[File:Schematic representation of the various treatment windows and experimental design..jpg|400px|thumb|left|Schematic representation of the various treatment windows and experimental design]]
  
• Mesenchyme surrounding the urethra forms smooth muscle of the urethral mucosa and submucosa. These two layers are then surrounded by erectile tissues such as the corpus spongiosum and corpus cavernosum.
+
Whilst it is evident that some of the most common reproductive abnormalities in males occurs within the fetal stage, it is believed that disorders that affect young men later in life (such as low sperm count or testicular cancer) could also occur within this stage. Previous studies have demonstrated a critical period (masculinisation programming window - MPW) during fetal development that must transpire in order for masculinisation of the male fetus to occur. If the androgenic pathways do not occur in the correct manner, testicular dysgenisis (TD) may result. Although androgen production can be difficult to measure in humans, it can be measured by examining the anogenital distance, which is shorter in females versus males.
  
• In some species, the mesenchyme of the genital tubercle also forms an os penis, comprised of bone and cartilage.
+
Therefore, it can be established that the MPW is important in setting up normal male development and it is triggered to open by either the presence or absence of both androgens and their receptors. The aim of the present study was to investigate whether or not availability of excess androgens available to their receptors before or during the MPW could increase masculinisation and therefore, development of male and female rats.
  
• Genital tubercle development involves an outgrowth of somatic tissue from the body surface, similar to the development of the limb.
+
This study uses the highly potent dihydrotestosterone (DHT) androgen in comparison to other studies, which used testosterone, with the potential to convert to oestradiol and cause pregnancy disorders. The study used pregnant Wister rats and exposed them to DHT in two time frames: either before the MPW or during it. Relevant tissues were then extracted from the animals and certain procedures such as spectrophotometry, immunohistochemistry for AR proteins and RNA analysis were used to measure masculinisation and obtain results.
  
• Development of the external genitalia is highly regulated by the endocrine system. Sexual differentiation of the external genitalia is determined by the presence or absence of androgen receptor signaling. The fetal testes produce testosterone, which travels to the genital tubercle via the bloodstream, where it is converted into 5a-dihydrotestosterone by the enzyme 5a-reductase. This formation of the highly potent 5a-dihydrotestosterone masculinizes the developing external genitalia, as binding of the 5a-dihydrotestosterone to its androgen receptor leads to the regulation of downstream signaling genes. <ref><pubmed>14641326</pubmed></ref>
+
Results showed that exposing male fetuses to a dosage of DHT that would result in masculinisation of the female fetus had no effect on the male. More specifically, the results indicated that exposure to DHT before or during the MPW did not stimulate any male reproductive development, and female masculinisation may begin much prior to the MPW. The results also support previous evidence demonstrating the potential for testosterone and oestrogen treatment to cause adverse pregnancy effects.  
  
• Sonic Hedgehog (SHH) acts as an endodermal signal that normally regulates patterning of the hindgut and is expressed in the epithelium of the cloaca, urogenital sinus and urethral plate epithelium. However has an important signaling pathway role in development of external genitalia. The SHH gene codes for a particular protein that has important roles in organogenesis as well as structures that are dependent upon mesenchymal-epithelial interactions, such as limbs, teeth and prostate. <ref><pubmed>14641326</pubmed></ref>
+
Overall, the study concludes that genital development in male rats is not enhanced by DHT exposure before or during the MPW and that sensitivity of the female fetus to androgens can not only be refined to occurring during the MPW but also prior to. This has implications in that the female fetus is more susceptible to androgens and masculinisation of the genital system much before the male is, therefore suggesting a wider window.
 +
|}
  
 
====Female====
 
====Female====
 +
----
  
• In females, the genital tubercle will eventually form the clitoris and the genital swellings remain apart and will eventually form the labia majora. The urogenital folds forming the border for the urogenital ostium will eventually form the labia minora in the female, thus forming the vestibule of the vagina. <ref><pubmed>14641326</pubmed></ref>
 
  
===Current Findings===
 
====Male====
 
====Female====
 
  
===References===
+
{|
<references/>
+
|-bgcolor="lavenderblush"
<pubmed>18367374</pubmed>
+
|
<pubmed>15086026</pubmed>
+
'''Female External Genitalia on Fetal Magnetic Resonance Imaging (2011)'''<ref name=PMID21584884><pubmed>21584884</pubmed></ref>
<pubmed>14641326</pubmed>
+
 
<pubmed>11684660</pubmed>
+
In the past, magnetic resonance imaging (MRI) has been used in conjunction with ultrasound to diagnose prenatal complications, including urogenital abnormalities. However, no previous research yielded any data regarding normal development of female external genitalia using MRI. As a result, this study investigated labial growth and correlated it with gestational age using prenatal MRI.
<pubmed>22127979</pubmed>
 
<pubmed>24631756</pubmed>
 
<pubmed>23192465</pubmed>
 
  
==Historic Finding==
+
[[File:Ultrasound male.jpg|200px|thumb|left|Ultrasound of male fetus]]
===Female Genital Development===
 
  
[[File:Mullerian ducts development.jpeg|300px|right|thumb|Development of Mullerian Ducts into mature female organs]]
+
This study included fetal MRI results from 197 female fetuses of Caucasian background, with either normal anatomy or minor congenital abnormalities. Fetuses with major congenital abnormalities, especially with urogenital abnormalities were omitted from the study. The MRI results were used to confirm if suspected anomalies during ultrasound screening were correct. Axial and coronal images of the fetus’ lower body were used to visualise the external female genitalia, including labia and clitoris and statistical analyses were performed on all MR images.
  
The mullerian (paramesonephric) ducts, found laterally to the wolffian ducts, are the original structures of the female reproductive system. Female sexual organs (the fallopian tubes, uterus and vagina) originate from the mullerian ducts, which differentiates within the foetal developmental phase. Initially the foetus contains two mullerian ducts, however by the ninth week, fusion of the lower portion of the ducts is complete, creating the fundamental structure of the uterus and the vagina, however the these two organs are not continuous with the vagina being solid. The non-fused upper part of the ducts emerge into the fallopian tubes. It is not until the fourth and fifth month of development that the uterus becomes continuous with the vagina, with both organs developing a hollow lumen. The muscular layers of the uterus is also present by this stage. The cervix begins to form within the fifth month in between the continuous vagina and uterus. Also within the same month, the formation of the hymen occurs. The hymen is described as a pouting vertical slit and represents the remains of the mullerian eminence. <ref><pubmed>17232227</pubmed></ref> <ref><pubmed>13230915</pubmed></ref>
+
Results showed a linear relationship between bilabial diameter and gestational age, and the morphology on the MRI showed a statistically significant difference between the 20-23 weeks age group and the rest (24-36 weeks) in the visual differentiation of the clitoris and the labial structures. Between 20-23 weeks, differentiation of the clitoris from the labia was not possible. Similar to what can be identified in ultrasounds, from 24 weeks onwards, in 12% of fetuses the clitoris and labia could be differentiated as 3-5 protuberances emerging from the pelvis, with the clitoris lying in the midline.
  
===Male Genital Development===
+
The results are important as they demonstrate the MRI’s potential to be used in adjunct to ultrasound in order to assist in the diagnosis of certain genital abnormalities, such as hypospadias or micropenis. This is necessary as such conditions can mimic female external genitalia and so hypospadias especially should be determined on the basis of parallel labial lines and not exclusively on the direction of the genital tubercle.<ref name=PMID18431748><pubmed>18431748</pubmed></ref>
'''The Prostate'''
 
  
Foetal prostate differentiation begins in the 10th week of gestation, influenced by the production of testosterone that starts within the 8th week. It is discovered that the origin of the gland is from the urogenital sinus. The prostate gland continues to grow and differentiate within the foetal period and postnatally under the influence of androgens.
+
In conclusion, this study examines the morphological development of the female external genitalia in utero using MRI, proving its effectiveness as a visualiser of the female phenotype and diagnosis of genital abnormalities, and should be used in conjunction with ultrasound.
 +
|}
  
Prostate foetal development has been continuously reshaping at a slow rate since the published illustrations of the male sex organs by Andreas Vesalius in 1543. Throughout this period, various anatomical classifications have been proposed via dissection procedures, hormone responses and histological methods, attributing to the current understanding of prostate development. It was not until the following century that another anatomical description of the prostate was put forth. Gerard Blasius in 1674 introduced the gland as a structure encircling the neck of the bladder. Literature in relevance to the embryonic prostate was further published in the late 19th century. The literature was reviewed and compared within the subsequent 20th century articles. Research into the structure and development of the prostate continued, however the rate of publication steeply increased in the 20th century, where each decade saw an improvement of the understanding of the development of the gland.
 
  
In 1912, Oswald S Lowsley constructed the first detailed illustration of the anatomy of the prostate, and to an extent, began the research that led to today’s understanding of the sex gland. Lowsley created his model from researching on a 13-week old foetus, 30-week old foetus, and one at full-term. From examining the samples he proposed that the prostate can be divided into five lobes consisting of differing amounts of tubules. This concept was later rendered invalid, however a discovery from Lowsley that is still accepted today is that the prostate originates from the urogenital sinus.
 
  
Lowsley’s division of the prostate into lobes was questioned by Johnson in 1920, where in his research and reconstruction of the prostate, was has unable to produce identical results as Lowsley. Upon conclusion of his work he reshaped the anatomical illustration of the prostate, however preserved the use of the term lobe in describing the prostatic divisions.
+
----
It was not until 1954, 42 years post the introduction of the lobe terminology, that it was completely revoked by Franks. Franks, upon dissections, described the prostate in terms of three concentric regions. Today, it is clear that the prostate consists of zones and not lobes as introduced by Lowsley nor concentric regions as introduced by Franks. The concept of prostatic zones was established by McNeal in the 1980s and is still accepted today. <ref><pubmed>18462432</pubmed></ref>
 
  
'''Testicular descent'''
 
  
Testicular descent begins during the early foetal period, 8-10 weeks, and takes approximately 5 weeks for the testes to reach the inguinal region. The second phase of descent, when the testes reach the scrotum, is not complete until the 35th to 40th week. The mechanisms behind testicular descent has been debated for at least two centuries, beginning with anatomical dissections during the eighteenth and nineteenth centuries, then enhancing with endocrinological discoveries during the twentieth century.
 
  
The Scottish surgeon and anatomist, John Hunter, first documented the gubernaculum and the location of the male foetal testicles in the late 1700s. In his research, Hunter claimed that descent occurred during the 8th foetal month and was directed by the gubernaculum testis, a ligament attaching the foetal testis to the abdominal wall and the scrotum. He further proposed that the processus vaginalis closes subsequent to the decent of the testis. This is contrary to the findings of Albrecht von Haller who illustrated that foetal testis is intra-abdominal and the processus vaginalis is not closed.
+
{|
 +
|-bgcolor="lavenderblush"
 +
|
 +
'''In humans, early cortisol biosynthesis provides a mechanism to safeguard female sexual development (2011)'''<ref name=PMID16585961><pubmed>16585961</pubmed></ref>
  
Hunter described the gubernaculum as a vascular and fibrous foetal structure covered by the cremaster muscle, a muscle of unknown function. This led to more research focused on the cremaster muscle. In 1777, Palletta questioned the importance of the cremaster muscle because of its under developed state during the time of descent. This however did not stop Pancera, who in the following year, considered the muscle as the key factor in the process. Pancera’s conclusion was confirmed by Lobsetin in 1801.  
+
As sexual differentiation of the external genitalia is an event that occurs within the fetal period, it is highly important to maintain the correct intrauterine environment in terms of hormonal content. In humans, differentiation and growth of the external genitalia is triggered by the release of androgens from the fetal testis such as dihydrotestosterone. Exposure of the female fetus to these androgens results in the female developing more male sexual characteristics at birth. This results from congenital adrenal hyperplasia, due to a deficiency of cytochrome P450 21-hydroxylase (CYP21), an enzyme involved in the biosynthesis of cortisol.
  
The second phase of testicular descent to the scrotum has also seen many theories. Lobsetin suggested that this phase is complete by birth, influenced by respiration and the increased abdominal pressure that occurs at birth. The concept of increased abdominal pressure was reiterated by Robin in 1849, however he also introduced the theory that descent into the scrotum occurs due to the weight of the testes and muscles associated. Both Lobsetin and Robin’s work was refuted by Weber who highlighted the processus vaginalis, an embryonic pouch of peritoneum, as the main force of the migration.
+
A deficiency of CYP21 results in a decrease in cortisol levels, and this is believed to alleviate negative feedback at the fetal anterior pituitary. As a result, increased adrenocorticotropic hormone (ACTH) shifts steroid precursor formation towards androgen biosynthesis and therefore a balance between cortisol biosynthesis and androgen production is important for normal female external genitalia development. Therefore, this article illustrates the potential of utilising early cortisol biosynthesis to uphold normal female sexual development.
  
In 1841, Curling detailed the structure of the gubernaculum and the cremaster muscle. Curling believed that during the foetal period, the cremaster muscle was important in descending the testis, however subsequent to the descent, the fibres of the muscle everted resulting in it’s new functions of elevating, supporting and compressing of the developed testis. The eversion of the muscle fibres were denied by Cleland, who in 1856 performed dissections on foetal specimens ranging from 5-6 gestational months old. In his experiment he found that the foetal gubernaculum did not directly attach the testicle to the scrotum and was only present in the inguinal wall. In terms of the testicular descent process, Cleland presented a similar theory as Weber, in terms that the cremaster was not the primary source of descent, second to the gubernaculum, that led the descent of the testes. In 1888, Lockwood published a completely unique theory claiming that the testes remained stationary and that it was in fact the surrounding structures that developed, resulting in the changing of the testicular location. Lockwood’s hypothesis was disagreed on by many anatomists and embryologists.  
+
The study used gas chromatography and mass spectrometry to observe a 9-18 fold increase in cortisol levels within the adrenal gland during the first trimester. The capacity of the adrenal gland in the fetus to secrete androgens was also determined using assays.  
  
With the introduction of endocrinology and hormonal testing, the previous theories were tested on a cellular basis. Male androgen, controlled by the pituitary gland, was the first hormonal theory believed to influence testicular descent. It has been evidently proven that androgens are important in the descent however it is unclear if it is important in both stages. It is currently accepted that testosterone influences the gubernaculum during the second phase in which the testes reach the scrotum, however the exact method is currently debatable. The first phase theories are under high scrutiny, with theories ranging from the development of the gubernaculum and hormones such as the Mullerian inhibiting substance. <sup>[4]</sup>
+
By the time differentiation of the external genitalia occurs in the second trimester, the female fetus is well protected by high levels of placental aromatase enzymes, which convert androgens to oestrogens. Also, in order to prevent virilisation in CYP21 deficiency, dexamethasone needs to be administered at week 6.
 +
|}
  
===References===
 
<references/>
 
4. Martyn P. L. Williams, John M. Huston '''The history of ideas about testicular descent.''' Pediatric Surgery International: 1991, 6(3):180-184 [http://link.springer.com/article/10.1007/BF00176064 The history of ideas about testicular descent]
 
  
--[[User:Z3415716|Z3415716]] ([[User talk:Z3415716|talk]]) 01:10, 27 August 2014 (EST)
 
  
<pubmed>18462432</pubmed>
+
----
<pubmed>17232227</pubmed>
 
Martyn P. L. Williams, John M. Huston '''The history of ideas about testicular descent.''' Pediatric Surgery International: 1991, 6(3):180-184 [http://link.springer.com/article/10.1007/BF00176064 The history of ideas about testicular descent]
 
  
==Abnormalities==
 
  
We discuss both male and female genital abnormalities internally or externally, that may occur during fetal development. The abnormalities have been identified as disorders of sex differentiation(DSD), associated with congenital conditions in the atypical  development of chromosomal, gonadal or phenotypical sex <ref><pubmed>16882788</pubmed></ref>, <ref><pubmed>25248670</pubmed></ref>.  The content will cover most common abnormalities and then also the rare cases.
+
{|
===FEMALE===
+
|-bgcolor="lavenderblush"
 +
|
 +
'''Fibrillin-3 in the Fetal Ovary: Can it Contribute to Polycystic Ovary Syndrome? (2012)'''<ref name= Abbott>Abbott David, H. '''Fibrillin-3 in the fetal ovary: can it contribute to polycystic ovary syndrome?'''. Expert Review of Endocrinology & Metabolism: 2012, 7(1); 31-34</ref>
  
[[File:Uterus and Vagina Abnormalities.jpg|400px|right|thumb|Abnormalities of the Uterus and Vagina]]
+
Fibrillin-3 contributes to microfibril formation within the extracellular matrix of many mammals and is predominantly expressed during fetal life<ref name=PMID20970500><pubmed>20970500</pubmed></ref>. The ovary continuously remodels its stroma in order to accommodate the constantly growing follicles from fetal life through to adult life, resulting in a continuously changing extracellular matrix, and therefore, fibrillin-3. Recent studies have discovered a linkage between an allele of the fibrillin-3 gene and polycystic ovary syndrome (PCOS), where hyperandrogenic interactions result in an enlarged and hyperstromal ovary with follicles that fail to mature and get released.
Abnormalities of the Uterus and vagina are cause by inadequate fusion or regression of Mullerian duct may result as the following;
 
  
*double uterus and double vagina
+
This study obtained 29 samples of ovarian tissue from humans in first or second trimester fetuses and 6 non-PCOS adults. Fetal bovine ovaries were also obtained. mRNA expression analyses were performed, as well as PCR and indirect immunofluorescence immunochemistry.
*double uterus
 
*bicornate uterus
 
*septated uterus
 
*unicornate uterus
 
*cervical atresia
 
  
====Mullerian agenesis====
+
Results showed that in both human and bovine ovaries, fibrillin-3 mRNA is mostly expressed during the first trimester, with little to none being expressed in the adult ovaries. Localised expression of fibrillin-3 surrounding primordial and primary follicles results in fetal oocyte and adult follicle expansion within the stroma, as the ECM remodeling is necessary to support the growth of these follicles. Therefore, the fibrillin-3 gene in PCOS women displays potential for altering fetal ovarian follicle development, and since it is expressed in ECM throughout the fetus, it may result in altered development in non-ovarian organ systems in human fetuses.
  
Mullerian agenesis also known as ‘Mayer-Rokitansky-Kuster-Hauser’ syndrome, vaginal agenesis or Mullerian aplasia, is presented in the absence of the uterus or vagina or in some case even both.  This is due to the unsuccessful development of the Mullerian ducts which then causes certain parts of the reproductive system to be underdeveloped.  It is present in 1 of 4000-10 000 women. This condition also uses dilation therapy and following the neovaginal approach with the reconstruction of the vagina in its treatment strategies <ref><pubmed>23635766</pubmed></ref>.  
+
In conclusion, the study suggests that since the stroma within the ovaries is hyper developed in PCOS women, different alleles of the same fibrillin-3 gene could be expressed within the fetal ovary to overcommit the polycystic ovary to follicular growth that is unlikely to mature into preovulatory follicles.  
 +
|}
  
====Vaginal agenesis====
 
  
Vaginal agenesis is a rare condition involving the underdevelopment of the vagina.  It is commonly cause by a combination of Rokitansky (Mullerian agenesis) and androgen insensitivity syndromes <ref><pubmed>21872517</pubmed></ref>. To ensure effectiveness in treatment, it’s advised after or during adolescence, procedures consist of vaginal dilation shown a success rate of 80% and low risks.  In cases where such methods are ineffective then vaginal reconstruction is implemented as a final option for patients <ref><pubmed>17995494</pubmed></ref>.
 
  
====Turners syndrome====
+
----
  
A chromosomal disorder occurring among women due to the absence of the whole or part of the sex chromosome (X). The condition is characterized by short stature, cardiovascular malformations, amenorrhea and estrogen insufficiency <ref><pubmed>16849410</pubmed></ref>.  It is prevalent in 1 of 2000 live births among females <ref><pubmed>2037286</pubmed></ref>.  Management of the syndrome depends on the extent of the condition the individual will present. Therefore treatment will vary, for short stature biosynthetic growth hormone is utalised in growth hormone.  The most common cardiac malformations are bicuspid aortic valve, coarctation of the aorta and aortic stenosis that are all surgically treated. Generally patients are advised to see pediatricians, endocrinologists and many other clinicians depending on the severity of the condition, to discuss strategies to manage the syndrome <ref><pubmed>16714725</pubmed></ref>.
 
  
'''Also related include;'''
 
  
====Polycystic Ovarian Syndrome====
+
{|
 +
|-bgcolor="lavenderblush"
 +
|
 +
'''Expression of miRNAs in Ovine Fetal Gonads: Potential Role in Gonadal Differentiation (2011)'''<ref name=PMID21223560><pubmed>21223560</pubmed></ref>
  
A metabolic endocrine disorder with an immense variety of phenotypes presented.  The disorder has an imbalance in female sex hormones and a resistance to insulin. Most importantly it affects the female reproductive system, with issues associated with infertility and menstrual irregularities. The treatments implemented depend on the clinical manifestations each patient develops.  Insulin-sensitizing agents are among the treatments used these include Metformin, Rosiglitazone and Piglitazone all have shown to be effective <ref><pubmed>19405411</pubmed></ref>.
+
Genotype of sex is determined at the time of fertilisation, where a sperm carrying X or Y genetic material will fertilise an XX ova. This genotype that results then determines whether the genital ridge in the embryonic period will develop into the fetal testis (XY) or fetal ovaries (XX). The pathway involving testicular development includes a fine balance between genes that promote testis development and simultaneously genes that prevent ovarian development <ref name=PMID19027189><pubmed>19027189</pubmed></ref>  
  
===MALE===
+
[[File:Human Y chromosome SRY region.jpg|400px|right|thumb| Human Y chromosome showing SRY gene]]
  
====Cryptorchidism====
+
Some critical genes involved in the testicular and ovarian pathways include:
[[File:Cryptorchidism.jpg|400px|right|thumb|]]
+
*SRY gene (sex-determining region of the Y-chromosome) <ref name=PMID2247149><pubmed>2247149</pubmed></ref>
 +
*Rspol gene (R-spondin homolog)<ref name=PMID18250098><pubmed>18250098</pubmed></ref>
 +
*Wnt4 – wongless-related MMTV integration site 4)<ref name=PMID18250097><pubmed>18250097</pubmed></ref>
 +
*Beta-catenin<ref name=PMID18250098><pubmed>18250098</pubmed></ref>
  
Involves the absence of both or single testis to descend into the scrotum, the testes can be ectopic, incompletely descended, absent or atrophic. It is possible that sometimes the cryptrodism may be spontaneously corrected by 3 months of age. The abnormality can occur as a result of a number of factors including maternal, genetic or environmental <ref><pubmed>24683948</pubmed></ref>.
+
Such genes are expressed in the support cells of the fetal gonads, for example, the Sertoli cells in the testis and the granulosa cells in the ovary.<ref name=PMID18250098><pubmed>18250098</pubmed></ref>
The descendence of testis occur in two stages; in the first stage insulin like hormone attaches the testis to the inguinal ring this is through gubernaculum development. Following is the inguinoscrotal stage that requires testicular androgens <ref><pubmed>18032558</pubmed></ref>.
 
  
Treatment includes human chorionic gonadotropin or gonadotroping-releasing hormones, these are not the most beneficial or advised approach.
+
Small non-coding RNA molecules, called miRNAs are RNAs that regulate gene expression and function within many different tissue types. Whilst studies have shown that miRNAs are important for growth and development of the gonads, none have yet indicated which miRNAs.  
Surgical repair is intended to apply the safest and least invasive methods, focusing on repositioning the undescended testicle/s to their normal position in the scrotum. Such surgeries are recommended in early life and have proved to be most effective, with 75%+ success. The therapy used to relocate the testis into the scrotum is known as ‘Orchiopexy’, others include one-stage Fowler Stephens and two-stage FS Orchidopecy    . However there are concerns with long-term effects which include infertility and testicular cancer later in life as a result of the procedure <ref><pubmed>24857650</pubmed></ref>.
 
  
====Hypospadias====
+
Not much is known regarding the expression of miRNAs during fetal genital development in mammals and the purpose of this study was to identify this expression of miRNAs using the ovine as a model. Expression levels were examined and the importance of such research is to provide further understanding of human genital development on a genetic level, as well as the reproductive development of ovine, which may have economical implications as livestock.  
In males the most common congenital malformation of the external genitalia is hypospadias, it’s also the second most common developmental disorder. It occurs due to the midline fusion of the male urethra, as a result the urethral meatus is misplaced. There are several sites where this abnormality may occur: granular, penile, penoscrotal, scrotal and perineal. <ref><pubmed>16006950</pubmed></ref> Its believed that genetic factors contribute to the presence of the disorder, however endocrine and environmental factors are also of significance.
 
<ref><pubmed>24936573</pubmed></ref>
 
Treatment
 
The surgical methods currently used to treat distal hypospadias, include tabularized incised plate and meatal advancement and glansplasty intergrated repair.  For proximal forms two staged procedures are employed. <ref><pubmed>25023236</pubmed></ref>
 
  
====Klinefelter====
+
This study used sheep breeding methods and collected fetal gonads, which then underwent PCR genotyping. RNA was isolated, and miRNAs were treated with reverse transcriptase and then hybridised. These techniques were all used to detect expression levels of the relevant genes.
Klinefelter is a genetic disorder caused by the addition of an X chromosome among males (47, XXY, XXY,XXXXY, XXYY),  due to the inability of the extra chromosomes to detach throughout meiosis. It is believed to have an origin from either parent. The abnormality has a wide range of phenotypic variations, that typically include infertility, small testes, gynecomastia and hypergonadotropic hypogonadism <ref><pubmed>16342850</pubmed></ref>. An early diagnosis is important in order for treatment to be commenced right away.  The treatment implemented involves Testosterone replacement therapy, which assists in easing some of the features, although infertility is still an issue.  The fertility options consist of IVF, where males undergo testicular sperm extraction, cryopreservation of sperm containing semen or testicular tissue during adolescence <ref><pubmed>24563893</pubmed></ref>.
 
  
===BOTH===
+
From the study, it is evident that miRNAs are indeed present during fetal genital development in sheep. It is believed that miRNAs are important regulators of gene expression and function and based upon the results, the genes Let7 and miR-22 regulate oestrogen signaling during fetal genital development. Further, miR-22 may be needed for suppression of the oestrogen-signaling pathway during fetal development of the testes, as localisation of the gene in the testicular cords suggested that Sertoli cell development required such suppression of the oestrogen-signaling pathway.
 +
|}
  
====Congenital adrenal hyperplasia====
 
  
The condition is caused by a deficiency in 21-Hydroxylase, a genetic disorder of steroidogenesis. Occurs due to mutations in genes that encode enzymes that take part in adrenal steroid synthesis therefore there is a loss of function <ref><pubmed>18844712</pubmed></ref>.  The deficiency is from mutations in CYP21A2, thus the clinical characteristics may vary. In females it results in the ambiguity of the female genitalia, fused labia majora, larger clitoris and common urogenital sinus <ref><pubmed>15964450</pubmed></ref>. Steroid 21-OHD deficiency is examined in-utero and then prenatal treatment with dexamethasone is administered.  This is a safe method used and decreases the risk of ambiguous genitalia in females <ref><pubmed>20392211</pubmed></ref>. Among males symptoms aren’t present at birth a side from possible penile enlargement and slight hyperpigmentation <ref><pubmed>15964450</pubmed></ref>. Generally male patients also require the administration of glucocorticoid and mineralocorticoid therapies <ref><pubmed>18446680</pubmed></ref>.
 
  
====Hydrocele====
+
----
  
Hydrocele occurs when the space between parietal and visceral layers of tunica vaginalis accumulates an abnormal amount of serous fluid.  Normally caused by an imbalance in the processes of production and reabsorption of fluid or varicocelectomy (14).  To manage the condition treatments focus on ensuring draining any excess fluid and inhibiting reaccumulation. Techniques used involve sclerotherapy and hydrocelectomy (15).  In females it is a very rare condition, occurs in the ‘Canal of Nuck’, a part of the inguinal canal containing a section of the processus vaginalis. A swelling is present on the labia major or inguinal ring. Techniques applied to treat the condition in females involve ligation of the processus vaginalis neck and the hydrocele is surgically resected (12).
 
  
  
'''Also related include;'''
+
{| class="wikitable mw-collapsible mw-collapsed"
 +
! '''Other current research findings and interesting reads:'''
 +
|-
 +
| * A recent study investigated the ability of in vitro cultures of female fetal mouse gonads to subsequently develop in vivo. It demonstrated that premeiotic germ cells in fetal gonads possessed the capability to develop into mature oocytes using this method. <ref name=PMID19379463><pubmed>19379463</pubmed></ref>Additionally, the study showed that the longer a culture of fetal gonads was kept (>14 days), follicular and development and oocyte growth in vivo was affected, as well as the maturation of the oocytes in vitro following transplantation into kidney capsules (the capsules are an ectopic site, however have all the necessary conditions for growth of the oocytes). <ref name=PMID8882299><pubmed>8882299</pubmed></ref>
  
====Hypogonadotropic hypogonadism====
+
<pubmed>21584884</pubmed>
 +
<pubmed>18367374</pubmed>
 +
<pubmed>15086026</pubmed>
 +
<pubmed>14641326</pubmed>
 +
<pubmed>11684660</pubmed>
 +
<pubmed>22127979</pubmed>
 +
<pubmed>24631756</pubmed>
 +
<pubmed>23192465</pubmed>
 +
|}
  
====Kallmann syndrome====
 
  
===References===
+
----
<references/>
 
--[[User:Z3417458|Z3417458]] ([[User talk:Z3417458|talk]]) 21:01, 26 August 2014 (EST)
 
  
<<pubmed>24290348</pubmed>>
+
==Historic Findings==
  
<<pubmed>25064170</pubmed>>
+
Click [https://embryology.med.unsw.edu.au/embryology/index.php/2014_Group_Project_9 here] for Historical Findings
  
<<pubmed>23168057</pubmed>>
+
==Abnormalities==
  
A review on spermatogenesis and cyptorchidism a common in males, results in an absence of testes either one or both.
+
Click [https://embryology.med.unsw.edu.au/embryology/index.php/2014_Group_Project_9 here] for foetal genital abnormalities
  
<<pubmed>24829558</pubmed>>
+
==References==
 +
<references/>

Latest revision as of 00:19, 25 October 2014

2014 Student Projects
2014 Student Projects: Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6 | Group 7 | Group 8
The Group assessment for 2014 will be an online project on Fetal Development of a specific System.

This page is an undergraduate science embryology student and may contain inaccuracies in either description or acknowledgements.

The stages in sexual differentiation of the female and male reproductive system

Genital

Introduction

Genital system development occurs in both the embryonic and foetal phase of development. By the commencement of the foetal period, sexual determination and initial growth of the different gonads occur [1]. It is within the foetal period that the internal and external genital organs develop [1]. This page focuses on the foetal developmental processes, exploring the current and historical models and understanding, alongside the congenital abnormalities.

Today there is an innumerable amount of research articles focused on foetal genital growth, with some addressing the system as a whole [2] and others investigating certain genital organs [3]. Current models and understandings have been obtained from both human [4] and animal populations [3], and this page will outline some of the important current research.

Research into foetal genital development can be traced to as early as the 16th century[5] with anatomists proposing theories and constructing models, proven to being critical in obtaining the in-depth information known today. This page will mention some of these historical findings in both the female and male genital system.

This project will end with discussing some of the congenital abnormalities of the genital system, mentioning both the malformations that are most common [6] and those that are rare [7].


System Development

Paramesonephric duct development
Histological image of primordial follicles in infant ovary

Timeline of Embryonic, Fetal and Postnatal Genital Development[8]

Week Development
3-4 Primordial germ cells migrate during gastrulation
4 Intermediate mesoderm, pronephros primordium
5 Mesonephros and mesonephric duct
6 Ureteric bud, metanephros, genital ridge
7 Cloacal divison, gonadal primordium - indifferent to first appearance of testis cords

Female - Paramesonephric duct preservation or regression begins

8 Paramesonephric duct, clear gonadal differentiation
9 Paramesonephric duct fusion in the female forming the uterus and lack of fusion laterally forming the fallopian tubes. Also forms vagina.
15 Primary follicles (ovary)

From the 26th week (between week 4 and 5), the gubernaculum starts to pull the testes down and results in descent of the testes into the scrotal sac. Both male and female gonads undergo descent.

Puberty Development of secondary sexual characteristics

Female - start of menstruation, first egg released. Male - development of course voice, body hair and sperm formation.

Related video




Development of Internal Genitalia

MALE FEMALE
The fetal development of internal genitalia is largely dependent on the endocrine functions of the fetal testes. The fetal testes produce masculinizing hormones such as testosterone which begins its release from the interstitial Leydig cells of the primitive seminiferous tubules during the 8th week of development, and also the release of Mullerian Inhibiting Hormone (MIS) which is released at the sixth and seventh weeks by the Sertoli Cells. Testosterone acts primarily on the mesonephric ducts to stimulate the formation of the male genital ducts, whereas the MIS acts on the paramesonephric duct to stimulate its regression. [4] [9]

By the eighth week of fetal development in XY embryos, the testosterone produced in the testes results in the convolution of the proximal ends of the mesonephric ducts to form the epididymis [9]. The mesonephros begins to degenerate, however some of the mesonephric tubules remain and develop into efferent ductules, which then open into the duct of the epididymis. Distal to this end, the mesonephric duct begins to develop a thick lining of smooth muscle and progresses to become the ductus deferens.[2]


Fetal Male Glandular Development

  • the seminal glands develop from lateral outgrowths from that caudal end of each mesonephric duct which nourishes the sperm and constitutes most of the fluid in the ejaculate
  • the endodermal outgrowths arise from the prostatic part of the urethra which grow into the surrounding mesenchyme. This acts as a base of the proliferation of the glandular epithelium of the prostate to differentiate- the associated mesenchyme will differentiate into dense stroma and the smooth muscle of the prostate. [9]
  • The bulbourethral glands are pea-sized and developed from paired outgrowths that originate from the spongy pat of the urethra. The adjacent mesenchyme gives rise to the stroma and smooth muscle fibres which will ultimately produce secretions which contribute to the semen.


The absence of testosterone production in XX embryos results in the regression of the mesonephric duct, and conversely the absence of MIH results in the development and progression of the paramesonephric ducts. The paramesonephric ducts give rise to most of the female internal genital system- the unfused cranial aspects of the ducts give rise to a primitive fallopian tubes, whilst the caudally fused portions form the uterovaginal primordium which will develop into a uterus and superior vagina. The splanchnic mesenchyme gives rise to the endometrial stromal tissue and the myometrium.[4]


Female genital development during the fetal period is not dependant on endocrine contributions from the foetus. Later in fetal development, maternal oestrogen's and oestrogen derived from the placenta contribute to the development of the fallopian tubes, uterus and the superior vagina.


Female Glandular Development

Internal genitalia in the female
  • The urethra develops outgrowths which form the mucus secreting urethral glands and paraurtehral glands.
  • outgrowths from the urogenital sinus form the greater vestibular glands in the lower third of the Labia Majora. These glands are also mucous secreting and are comparative to the bulbourethral glands in males. [4]
Flow Diagram of the current model of embryonic and fetal development of the external genitalia

Development of the External Genitalia

Embryonic Period – fertilisation to end of 8th week (embryonic age) = AMBISEXUAL STAGE
  1. The external genitalia initially begin in the perineal region as three primordia, being the genital tubercle in the midline and the bilateral genital swellings. These three primordia arise together with the differentiation of the cloacal part of the hindgut into the urogenital sinus, rectum and anal canal. The cloacal membrane extends from the perineum cranially to the root of the umbilical cord and during development, this bilayered cloacal membrane retracts into the perineum. This is due to cranial and medial migration of mesodermal cells into the ventral body wall between the ectoderm and endoderm of the cloacal membrane. These migrating mesodermal cells line around the membrane and accumulate, forming the three primordial swellings.[2]
  2. These external features are internally related to the cloaca, which becomes divided coronally by the urorectal septum into the urogenital sinus anteriorly, and the rectum and anus posteriorly.
  3. This division of the cloaca occurs in a specific way so the allantois, Mullerian and Wolffian ducts and ureters all empty into the urogenital sinus.
  4. When the cloacal membrane becomes divided into the urogenital and anal membranes, the urogenital membrane is bound cranially by the genital tubercle in the midline and laterally by the urogenital folds and genital swellings. [4]
  5. The urogenital membrane degenerates to allow communication between the urogenital sinus and amniotic cavity.[2]




The current model for fetal development of the external genitalia in humans and mice:

MALE MODEL FEMALE MODEL
Fetal Period – from 8th week of development = SEXUAL DIFFERENTIATION
  1. Initially, the female and male fetuses’ external genitalia are identical and include the genital tubercle in the midline, urogenital folds (forming the urogenital ostium) and genital swellings (laterally).
  2. In males, the genital tubercle will eventually form the penis and the genital swellings migrate caudally and a fusion event in the midline occurs, thus forming the scrotum.[2]
  3. As the genital tubercle elongates to form the penis, a groove forms on the ventral surface known as the urethral groove. The urethral folds that are continuous with the urogenital folds surrounding the urogenital ostium define the urethral groove laterally.[2]
  4. At first, the urethral groove and folds extend only part of the along the shaft of the elongating genital tubercle (known as the phallus at this stage).
  5. Distally, the urethral groove terminates at the urethral plate, consisting of epithelial cells, and then extends into the glans of the penis, forming a channel.
  6. As the phallus elongates, the urethral folds grow toward each other and fuse in the midline forming the midline epithelial seam, converting the urethral groove into a tubular penile urethra. The fusion of the urethral folds begins proximally in the perineal region and extends distally towards the glans of the penis.[2]
Cross section of the male genital tubercle
Anatomical drawing of adult male testes
  • Hypospadias result from failure of formation or fusion of the urethral folds and this is the focus of current research.
  • The elongating phallus is covered externally by ectoderm that will eventually give rise to the penile epidermis.
  • Urethral epithelium has endodermal origins and the majority of the penis is derived from mesodermal cells.
  • During development, the mesoderm separates into connective tissues and dermis.[2]
  • Dense areas of mesenchymal cells form within the shaft of the penis with the most superficial dense bodies forming the thick connective tissue capsule known as the tunica albuginae.
  • Mesenchyme surrounding the urethra forms smooth muscle of the urethral mucosa and submucosa. Erectile tissues such as the corpus spongiosum and corpus cavernosum then surround these two layers.
  • In some species, the mesenchyme of the genital tubercle also forms an os penis, comprised of bone and cartilage.
  • Genital tubercle development involves an outgrowth of somatic tissue from the body surface, similar to the development of the limb.[2]
  • Development of the external genitalia is highly regulated by the endocrine system. Sexual differentiation of the external genitalia is determined by the presence or absence of androgen receptor signaling. The fetal testes produce testosterone, which travels to the genital tubercle via the bloodstream, where it is converted into 5a-dihydrotestosterone by the enzyme 5a-reductase. This formation of the highly potent 5a-dihydrotestosterone masculinizes the developing external genitalia, as binding of the 5a-dihydrotestosterone to its androgen receptor leads to the regulation of downstream signaling genes.[2]
    Sonic Hedgehog (SHH) acts as an endodermal signal that normally regulates patterning of the hindgut and is expressed in the epithelium of the cloaca, urogenital sinus and urethral plate epithelium. However this has an important signaling pathway role in development of external genitalia. The SHH gene codes for a particular protein that has important roles in organogenesis as well as structures that are dependent upon mesenchymal-epithelial interactions, such as limbs, teeth and prostate.[2]
Fetal Period – from 8th week of development = SEXUAL DIFFERENTIATION
  1. Only minor changes occur from the embryonic ambisexual stage in the female, beginning with the minimal growth of the genital tubercle to form the clitoris.
  2. The urogenital folds remain apart and unfused to form the labia majora.[4]
  3. The genital swellings also remain apart and unfused to form the labia minora.[2]
  • Together, these bilateral labial structures and the clitoris located proximally form the border for the urogenital ostium, thus forming the vestibule of the vagina, with vaginal and urethral openings.
  • The tubercle itself goes on to form the mons pubis.
  • Sexual dimorphism of the external genitalia in female humans is determined by the absence of androgenic pathways, however the female genital tubercle can be ‘masculinised’ as 5a-reductase and androgen recpetors are present.
  • The genital tubercle can not go on to form a penis as testosterone is not produced, however in some instances it is abnormally produced in excess by the suprarenal gland resulting in different degrees of masculinsation of the clitoris.[4]









Stages in the Development of the External Sexual Organs in the Male and Female


Descent of the Gonads

Descent of testes

Male: The testis undergo transabdominal and transinguinal descent. The testis lies in the subserous fascia. The processus vaginalis evaginates into the scrotum and the gubernaculum draws it into the scrotal sac. As it descends, it traverses past the superficial (external oblique fascia) and deep (transversalis fascia) inguinal rings of the inguinal canal. This begins in between the 4th and 5th week (usually around day 26) and spans over many days. It can occur unilaterally or bilaterally, more common in premature babies and can conclude postnatally.[10]

Female: ovaries undergo caudal and lateral shifts to be suspended in the broad ligament of the uterus. The gubernaculum does not shorten, attaches to paramesonephric ducts and causes medial translocation into the pelvis. The remnant in adult life of the gubernaculum is the ovarian and round ligament of the uterus, which suspend the ovaries and uterus respectively.[11]



Current Research, Models and Findings

Current Models

Most current research uses mouse models and observes the development of their external genitalia, especially their penile development, which initially appears to be different to human development. However, more microscopic inspection shows that mice have very similar external genitalia and are therefore appropriate animal models for observing such fetal development. As a result, mutant mouse models can effectively be used in future research to observe molecular mechanisms underlying hypospadias and their aetiology. [2]

When observing the morphology and cell biology of the developing testis, it is important to note that most of the research conducted on the subject involves the use of mouse models as a result of a lack of human subjects. It can be assumed that events in the human embryo correspond to the same events in the mouse embryo, however there are some differences between the time course of certain events and anatomy. [12]

Some examples of different animal models used in research involving fetal development of male and female genital systems are:

Different models are used for different research topics; for example, research involving Polycystic ovary syndrome (PCOS) uses murine models preferable due to the developmental time frame that allows studies of inherited PCOS to be examined within an appropriate time frame. The sheep model is also beneficial to use for PCOS research as it is cost effective and their size allows them to be subjected to certain procedures such as ultrasound and neurotransmitter measures. Primates are examples of an optimal model however are limited in their accessibility and long time frame of development.[16]

It is important to note that any findings associated with an animal model should be translated appropriately to the human model, as animals differ in their anatomy and regulatory mechanisms, as well as placentation. That is, sheep, rats and mice display different placentation and ovarian development that occurs in utero in sheep, primates and humans differs to the ex utero development in murine models.[16]

All animal experiments must be performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. [| Guide for the Care and Use of Laboratory Animals]

Current Research and Findings

Male


Different types of hypospadias

Extensive research into organogenesis of the external genitalia, mainly in males, is driven by the increasing incidence of hypospadias. Hypospadias are a result of the defect of fusion of the urethral folds of the lower part of the penis to fold and form the tubular penile urethra. The result of this in humans is the presence of an abnormal ventral urethral meatus, incomplete formation of the prepuce and an abnormal penile curvature.[2]

Development of the male external genitalia, which occurs in the fetal period of development, is androgen dependent and involves epithelial-mesenchymal interactions. Because of these interactions, which are very similar to limb development, research into the development of genital tubercle has utilised similar methods for both processes. A minority of hypospadias cases are a result of the androgenic pathways being impaired and causing this congenital defect. The cell-cell interactions that allow for the development of the male external genitalia are mediated by a broad range of signaling molecules and growth factors such as fibroblast growth factors (FGFs), Sonic hedgehog (SHH) and bone morphogenetic proteins (BMPs). Such signaling and growth factors are downstream of androgen receptor signaling and an understanding of the mechanisms that underlie normal penile development during the fetal period, will lead to a deeper understanding of the aetiology of hypospadias.[2]

| Statistics regarding congenital abnormalities, including hypospadias and epispadias for 2002 and 2003 in Australia



Table of levels of POPs in maternal serum samples and risk of hypospadias in infants

A Nested Case-Control Study of Intrauterine Exposure to Persistent Organochlorine Pollutants and the Risk of Hypospadias (2012)[19]

Hypospadias are a common congenital abnormality resulting from the failure of fusion of the urethral folds within the fetal period of development (8th-14th week of gestation). Whilst it is known that sexual differentiation of the male external genitalia depends on testosterone and its conversion into dihydrotestosterone, the risk factors of hypospadias are not thoroughly researched. This article aims to examine environmental exposure to endocrine disrupting chemicals (EDCs) and understand their potential to act as antagonists on androgen receptors, thereby disrupting the hormonal balance of the endocrine system ultimately leading to hypospadias.[20] More specifically, a major group of EDCs known as persistent organochlorine pollutants (POPs), for example, polychlorinated biphenyls, dioxins, pesticides (dichlorodiphenyl trichloroethane, DDT) and hexachlorobenzene (HCB). Such chemicals are lipophilic, resistant to biodegradation and are present throughout the hydrosphere and atmosphere. Although these chemicals were banned in the 1970’s and 1980’s, due to the potency of these chemicals, they are still found within humans[21] and are able to traverse the placenta, becoming exposed to the developing fetus[22]. Therefore, the aim of the present study was to investigate the linkage between exposures of the fetus to POPs and risk of developing hypospadias.

This was a case-controlled study of the risk of hypospadias of single-born boys with regards to levels of POPs within the mothers’ blood during pregnancy. The study used 390 boys with hypospadias and controls were used. Boys with any cryptorchidisms, major malformations or even minor hypospadias were excluded from the study.

This study concluded that EDCs such as PCBs, p,p’-DDE and HCB possess the potential to alter hormonal levels and affect the fetus, resulting hypospadias. It shows that in uterine exposure to HCB and possibly p,p’-DDE are risk factors and may affect androgen-signaling.




Paracetamol, aspirin, and indomethacin induce endocrine disturbances in the human fetal testis capable of interfering with testicular descent. (2013)[23]

Graph showing male testosterone and AMH levels

The differentiation of the gonads into male or female begins around week 6-8 and is linked to the sex-determining region of the Y chromosome. The formation and descent of the testis is determined by a number of hormones which are:

  • Anti-mullerian hormone (AMH) - produced by sertoli cells, which acts on the mullerian ducts.
  • Testosterone - produced by the fetal leydig cells, which ensures differentiation of wolffian ducts as well as the terminal phase of descent of the testis.
  • Insulin like factor 3 (INSL3) - is produced by the differentiated fetal leydig cells, which are involved in the transabdominal phase of descent.
  • Prostaglandins are also believed to be involved in the differentiation of the male genital tract and testis.

The development of the male reproductive system requires the action of different hormones and is highly susceptible for development to be altered due to endocrine disruptions.

Cryptorchidism is the failure of descent of the testis and is the most common congenital malformation in males. Non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol are some of the most widely used drugs used. These drugs have recently been identified as potential endocrine disruptors (ED) in humans. A number of epidemiological studies have reported that exposure to NSAIDs and analgesics during pregnancy showed an increased risk of cryptorchidism.

This study used 62 fetuses from the first trimester between 7-12 weeks in gestation (GW) from pregnant women who obtained an abortion legally and with were given information and verbal consent was obtained according to national guidelines. The terminations were not motivated by abnormalities. The testes were cut in approximately 1mm3 pieces and drugs were used in the same concentration compared to recommended dosages in the body. The drugs used were paracetamol, aspirin, indomethacin, ketoconazole (antifungal).

Testicular cells were counted using histology and image analysis and the hormones were assayed in the medium. The results showed no changes in the architecture of the testis with the analgesic treatment whereas the ketoconazole caused the boundaries of the testis cords to become unrecognisable. The analgesics did not significantly modify the number of germ cells or sertoli cells. Ketoconazole reduced testosterone levels in contrast to indomethacin, which stimulated testosterone production. Paracetamol had no significant effect on testosterone while aspirin produced a dose response relationship with an increase in testosterone after 72 hours in the youngest fetuses (8-9.86 GW) but not the older testes (10-12GW). None of the analgesics significantly affect the number of interstitial cells.

The results showed a consistent trend for lower INSL3 production after 48-72 hours of exposure to mild analgesics and ketoconazole. This was the first study to measure direct production of INSL3 by the testis. Aspirin strongly stimulated AMH production, whereas as paracetamol and indomethacin increased production but not significantly. The analgesics did not significantly alter the sertoli cells and Ketoconazole significantly inhibited AMH production. Aspirin and paracetamol showed significant inhibition of Prostaglandin E2 production while indomethacin had no effect.

In conclusion, the study shows that painkillers have a direct effect on various hormones, which are crucial for endocrine function and development of the human testis. The study shows that there is a direct effect with the dosages which are currently found with most medications.




The Effect of Dihydrotestosterone Exposure During or Prior to the Masculinisation Programming Window on Reproductive Development in Male and Female Rats (2012)[15]

Schematic representation of the various treatment windows and experimental design

Whilst it is evident that some of the most common reproductive abnormalities in males occurs within the fetal stage, it is believed that disorders that affect young men later in life (such as low sperm count or testicular cancer) could also occur within this stage. Previous studies have demonstrated a critical period (masculinisation programming window - MPW) during fetal development that must transpire in order for masculinisation of the male fetus to occur. If the androgenic pathways do not occur in the correct manner, testicular dysgenisis (TD) may result. Although androgen production can be difficult to measure in humans, it can be measured by examining the anogenital distance, which is shorter in females versus males.

Therefore, it can be established that the MPW is important in setting up normal male development and it is triggered to open by either the presence or absence of both androgens and their receptors. The aim of the present study was to investigate whether or not availability of excess androgens available to their receptors before or during the MPW could increase masculinisation and therefore, development of male and female rats.

This study uses the highly potent dihydrotestosterone (DHT) androgen in comparison to other studies, which used testosterone, with the potential to convert to oestradiol and cause pregnancy disorders. The study used pregnant Wister rats and exposed them to DHT in two time frames: either before the MPW or during it. Relevant tissues were then extracted from the animals and certain procedures such as spectrophotometry, immunohistochemistry for AR proteins and RNA analysis were used to measure masculinisation and obtain results.

Results showed that exposing male fetuses to a dosage of DHT that would result in masculinisation of the female fetus had no effect on the male. More specifically, the results indicated that exposure to DHT before or during the MPW did not stimulate any male reproductive development, and female masculinisation may begin much prior to the MPW. The results also support previous evidence demonstrating the potential for testosterone and oestrogen treatment to cause adverse pregnancy effects.

Overall, the study concludes that genital development in male rats is not enhanced by DHT exposure before or during the MPW and that sensitivity of the female fetus to androgens can not only be refined to occurring during the MPW but also prior to. This has implications in that the female fetus is more susceptible to androgens and masculinisation of the genital system much before the male is, therefore suggesting a wider window.

Female



Female External Genitalia on Fetal Magnetic Resonance Imaging (2011)[24]

In the past, magnetic resonance imaging (MRI) has been used in conjunction with ultrasound to diagnose prenatal complications, including urogenital abnormalities. However, no previous research yielded any data regarding normal development of female external genitalia using MRI. As a result, this study investigated labial growth and correlated it with gestational age using prenatal MRI.

Ultrasound of male fetus

This study included fetal MRI results from 197 female fetuses of Caucasian background, with either normal anatomy or minor congenital abnormalities. Fetuses with major congenital abnormalities, especially with urogenital abnormalities were omitted from the study. The MRI results were used to confirm if suspected anomalies during ultrasound screening were correct. Axial and coronal images of the fetus’ lower body were used to visualise the external female genitalia, including labia and clitoris and statistical analyses were performed on all MR images.

Results showed a linear relationship between bilabial diameter and gestational age, and the morphology on the MRI showed a statistically significant difference between the 20-23 weeks age group and the rest (24-36 weeks) in the visual differentiation of the clitoris and the labial structures. Between 20-23 weeks, differentiation of the clitoris from the labia was not possible. Similar to what can be identified in ultrasounds, from 24 weeks onwards, in 12% of fetuses the clitoris and labia could be differentiated as 3-5 protuberances emerging from the pelvis, with the clitoris lying in the midline.

The results are important as they demonstrate the MRI’s potential to be used in adjunct to ultrasound in order to assist in the diagnosis of certain genital abnormalities, such as hypospadias or micropenis. This is necessary as such conditions can mimic female external genitalia and so hypospadias especially should be determined on the basis of parallel labial lines and not exclusively on the direction of the genital tubercle.[25]

In conclusion, this study examines the morphological development of the female external genitalia in utero using MRI, proving its effectiveness as a visualiser of the female phenotype and diagnosis of genital abnormalities, and should be used in conjunction with ultrasound.




In humans, early cortisol biosynthesis provides a mechanism to safeguard female sexual development (2011)[26]

As sexual differentiation of the external genitalia is an event that occurs within the fetal period, it is highly important to maintain the correct intrauterine environment in terms of hormonal content. In humans, differentiation and growth of the external genitalia is triggered by the release of androgens from the fetal testis such as dihydrotestosterone. Exposure of the female fetus to these androgens results in the female developing more male sexual characteristics at birth. This results from congenital adrenal hyperplasia, due to a deficiency of cytochrome P450 21-hydroxylase (CYP21), an enzyme involved in the biosynthesis of cortisol.

A deficiency of CYP21 results in a decrease in cortisol levels, and this is believed to alleviate negative feedback at the fetal anterior pituitary. As a result, increased adrenocorticotropic hormone (ACTH) shifts steroid precursor formation towards androgen biosynthesis and therefore a balance between cortisol biosynthesis and androgen production is important for normal female external genitalia development. Therefore, this article illustrates the potential of utilising early cortisol biosynthesis to uphold normal female sexual development.

The study used gas chromatography and mass spectrometry to observe a 9-18 fold increase in cortisol levels within the adrenal gland during the first trimester. The capacity of the adrenal gland in the fetus to secrete androgens was also determined using assays.

By the time differentiation of the external genitalia occurs in the second trimester, the female fetus is well protected by high levels of placental aromatase enzymes, which convert androgens to oestrogens. Also, in order to prevent virilisation in CYP21 deficiency, dexamethasone needs to be administered at week 6.




Fibrillin-3 in the Fetal Ovary: Can it Contribute to Polycystic Ovary Syndrome? (2012)[27]

Fibrillin-3 contributes to microfibril formation within the extracellular matrix of many mammals and is predominantly expressed during fetal life[28]. The ovary continuously remodels its stroma in order to accommodate the constantly growing follicles from fetal life through to adult life, resulting in a continuously changing extracellular matrix, and therefore, fibrillin-3. Recent studies have discovered a linkage between an allele of the fibrillin-3 gene and polycystic ovary syndrome (PCOS), where hyperandrogenic interactions result in an enlarged and hyperstromal ovary with follicles that fail to mature and get released.

This study obtained 29 samples of ovarian tissue from humans in first or second trimester fetuses and 6 non-PCOS adults. Fetal bovine ovaries were also obtained. mRNA expression analyses were performed, as well as PCR and indirect immunofluorescence immunochemistry.

Results showed that in both human and bovine ovaries, fibrillin-3 mRNA is mostly expressed during the first trimester, with little to none being expressed in the adult ovaries. Localised expression of fibrillin-3 surrounding primordial and primary follicles results in fetal oocyte and adult follicle expansion within the stroma, as the ECM remodeling is necessary to support the growth of these follicles. Therefore, the fibrillin-3 gene in PCOS women displays potential for altering fetal ovarian follicle development, and since it is expressed in ECM throughout the fetus, it may result in altered development in non-ovarian organ systems in human fetuses.

In conclusion, the study suggests that since the stroma within the ovaries is hyper developed in PCOS women, different alleles of the same fibrillin-3 gene could be expressed within the fetal ovary to overcommit the polycystic ovary to follicular growth that is unlikely to mature into preovulatory follicles.




Expression of miRNAs in Ovine Fetal Gonads: Potential Role in Gonadal Differentiation (2011)[13]

Genotype of sex is determined at the time of fertilisation, where a sperm carrying X or Y genetic material will fertilise an XX ova. This genotype that results then determines whether the genital ridge in the embryonic period will develop into the fetal testis (XY) or fetal ovaries (XX). The pathway involving testicular development includes a fine balance between genes that promote testis development and simultaneously genes that prevent ovarian development [29]

Human Y chromosome showing SRY gene

Some critical genes involved in the testicular and ovarian pathways include:

  • SRY gene (sex-determining region of the Y-chromosome) [30]
  • Rspol gene (R-spondin homolog)[31]
  • Wnt4 – wongless-related MMTV integration site 4)[32]
  • Beta-catenin[31]

Such genes are expressed in the support cells of the fetal gonads, for example, the Sertoli cells in the testis and the granulosa cells in the ovary.[31]

Small non-coding RNA molecules, called miRNAs are RNAs that regulate gene expression and function within many different tissue types. Whilst studies have shown that miRNAs are important for growth and development of the gonads, none have yet indicated which miRNAs.

Not much is known regarding the expression of miRNAs during fetal genital development in mammals and the purpose of this study was to identify this expression of miRNAs using the ovine as a model. Expression levels were examined and the importance of such research is to provide further understanding of human genital development on a genetic level, as well as the reproductive development of ovine, which may have economical implications as livestock.

This study used sheep breeding methods and collected fetal gonads, which then underwent PCR genotyping. RNA was isolated, and miRNAs were treated with reverse transcriptase and then hybridised. These techniques were all used to detect expression levels of the relevant genes.

From the study, it is evident that miRNAs are indeed present during fetal genital development in sheep. It is believed that miRNAs are important regulators of gene expression and function and based upon the results, the genes Let7 and miR-22 regulate oestrogen signaling during fetal genital development. Further, miR-22 may be needed for suppression of the oestrogen-signaling pathway during fetal development of the testes, as localisation of the gene in the testicular cords suggested that Sertoli cell development required such suppression of the oestrogen-signaling pathway.




Other current research findings and interesting reads:
* A recent study investigated the ability of in vitro cultures of female fetal mouse gonads to subsequently develop in vivo. It demonstrated that premeiotic germ cells in fetal gonads possessed the capability to develop into mature oocytes using this method. [33]Additionally, the study showed that the longer a culture of fetal gonads was kept (>14 days), follicular and development and oocyte growth in vivo was affected, as well as the maturation of the oocytes in vitro following transplantation into kidney capsules (the capsules are an ectopic site, however have all the necessary conditions for growth of the oocytes). [34]

<pubmed>21584884</pubmed> <pubmed>18367374</pubmed> <pubmed>15086026</pubmed> <pubmed>14641326</pubmed> <pubmed>11684660</pubmed> <pubmed>22127979</pubmed> <pubmed>24631756</pubmed> <pubmed>23192465</pubmed>



Historic Findings

Click here for Historical Findings

Abnormalities

Click here for foetal genital abnormalities

References

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