Talk:BGD Lecture - Sexual Differentiation

References

--Mark Hill 11:26, 28 May 2011 (EST) This is a good recent review paper from one of the original researchers who discovered SRY. Listed below the reference are links to the review figures in various formats.

<pubmed>17237341</pubmed>| Physiol. Rev.

Figure Pages

These are links to the images with descriptive legends.

1. Signaling in genital development
2. Sex reversal in humans caused by abnormal X-Y exchange
3. Mesonephric tubules in the 11.5 dpc mouse urogenital ridge
4. Development and differentiation of the genital duct system
5. The migratory pathway of primordial germ cells
6. Structure of the early fetal testis
7. Differentiation of pre-Sertoli cells into Sertoli cells
8. Model for cell-autonomous and prostaglandin-mediated upregulation of Sox9 in pre-Sertoli cells
9. Visualization of testicular cell types
10. Ovary and follicle development and differentiation
11. Postulated molecular pathway leading to the formation of the bipotential genital ridge
12. Structure of mouse and human SRY protein
13. Postulated interaction of molecular players involved in early testicular development

Table 1. Genes implicated in sexual development in mammals

Figures

These are links to just the images.

1. Fig. 1 - Signaling in genital development
2. Fig. 2 - Sex reversal in humans caused by abnormal X-Y exchange
3. Fig. 3 - Mesonephric tubules in the 11.5 dpc mouse urogenital ridge
4. Fig. 4 - Development and differentiation of the genital duct system
5. Fig. 5 - The migratory pathway of primordial germ cells
6. Fig. 6 - Structure of the early fetal testis
7. Fig. 7 - Differentiation of pre-Sertoli cells into Sertoli cells
8. Fig. 8 - Model for cell-autonomous and prostaglandin-mediated upregulation of Sox9 in pre-Sertoli cells
9. Fig. 9 - Visualization of testicular cell types
10. Fig. 10 - Ovary and follicle development and differentiation
11. Fig. 11 - Postulated molecular pathway leading to the formation of the bipotential genital ridge
12. Fig. 12 - Structure of mouse and human SRY protein
13. Fig. 13 - Postulated interaction of molecular players involved in early testicular development

Table 1. Genes implicated in sexual development in mammals

Figure Pages and Figures

These are links to the figure pages with descriptive legends and the images alone.

1. Signaling in genital development | Fig. 1 - Signaling in genital development
2. Sex reversal in humans caused by abnormal X-Y exchange | Fig. 2 - Sex reversal in humans caused by abnormal X-Y exchange
3. Mesonephric tubules in the 11.5 dpc mouse urogenital ridge | Fig. 3 - Mesonephric tubules in the 11.5 dpc mouse urogenital ridge
4. Development and differentiation of the genital duct system | Fig. 4 - Development and differentiation of the genital duct system
5. The migratory pathway of primordial germ cells | Fig. 5 - The migratory pathway of primordial germ cells
6. Structure of the early fetal testis | Fig. 6 - Structure of the early fetal testis
7. Differentiation of pre-Sertoli cells into Sertoli cells | Fig. 7 - Differentiation of pre-Sertoli cells into Sertoli cells
8. Model for cell-autonomous and prostaglandin-mediated upregulation of Sox9 in pre-Sertoli cells | Fig. 8 - Model for cell-autonomous and prostaglandin-mediated upregulation of Sox9 in pre-Sertoli cells
9. Visualization of testicular cell types | Fig. 9 - Visualization of testicular cell types
10. Ovary and follicle development and differentiation | Fig. 10 - Ovary and follicle development and differentiation
11. Postulated molecular pathway leading to the formation of the bipotential genital ridge | Fig. 11 - Postulated molecular pathway leading to the formation of the bipotential genital ridge
12. Structure of mouse and human SRY protein | Fig. 12 - Structure of mouse and human SRY protein
13. Postulated interaction of molecular players involved in early testicular development | Fig. 13 - Postulated interaction of molecular players involved in early testicular development

Genes implicated in sexual development in mammals

Table 1. Genes implicated in sexual development in mammals

Table below modified from review article.

Gene	Protein Function	Gonad Phenotype of Null Mice	Human Syndrome
Bipotential gonad
Wt1	Transcription factor	Blockage in genital ridge development	Denys-Drash, WAGR, Frasier syndrome
Sf1	Nuclear receptor	Blockage in genital ridge development	Embryonic testicular regression syndrome
Lhx9	Transcription factor	Blockage in genital ridge development	a
Emx2	Transcription factor	Blockage in genital ridge development	a
M33	Transcription factor	Gonadal dysgenesis	a
Testis-determining pathway
Gata4/Fog2	Transcription/cofactor	Reduced Sry levels, XY sex reversal	a
Sry	Transcription factor	XY sex reversal	XY sex reversal (LOF); XX sex reversal (GOF)
Sox9	Transcription factor	XY sex reversal	Campomelic dysplasia, XX sex reversal (GOF)
Sox8	Transcription factor	XY sex reversal in combination with partial loss of Sox9 function	a
Fgf9	Signaling molecule	XY sex reversal	a
Dax1	Nuclear receptor	Impaired testis cord formation and spermatogenesis	Hypogonadism
Pod1	Transcription factor	XY sex reversal	a
Dhh	Signaling molecule	Impaired differentiation of Leydig and PM cells	XY gonadal dysgenesis
Pgdra	Receptor	Reduction in mesonephric cell migration	a
Pgds	Enzyme	No phenotype	a
Arx	Transcription factor	Abnormal testicular differentiation	X-linked lissencephaly with abnormal genitalia
Atrx	Helicase	ND	ATRX syndrome
Insl3	Signaling factor	Blockage of testicular descent	Cryptorchidism
Lgr8	Receptor	Blockage of testicular descent	Cryptorchidism
Hoxa10	Transcription factor	Blockage of testicular descent	Cryptorchidism
Hoxal1	Transcription factor	Blockage of testicular descent	Cryptorchidism
Amh	Hormone	No Müllerian duct degeneration	Persistent Müllerian duct syndrome
Misrl1	Receptor	No Müllerian duct degeneration	Persistent Müllerian duct syndrome
Pax2	Transcription factor	Dysgenesis of mesonephric tubules	a
Lim1	Transcription factor	Agenesis of Wolffian and Müllerian ducts	a
Dmrt1	Transcription factor	Loss of Sertoli and germ cells	XY femaleb
Ovary-determining pathway
Wnt4	Signaling molecule	Müllerian duct agenesis, testosterone synthesis, and coelomic vessel formation	XY female (GOF)
FoxL2	Transcription factor	Premature ovarian failure	BPES
Dax1	Nuclear receptor	XY sex reversal (GOF)	XY sex reversal (GOF)

---

^a No mutations in human sexual disorders identified to date.

^b Candidate gene for 9p deletion, XY sex reversal. BPES, blepharophimosis-ptosis-epicanthus inversus syndrome; GOF, gain-of-function mutation; LOF, loss-of-function mutation, ND, not determined; WAGR, Wilms' tumor-aniridia-genitourinary malformations-mental retardation.

2009 BGD Lecture Slide Text

Note that not all slide text shown and text out of context may not make sense to you in this bullet list form.

Internal Genitalia

• Reproductive Tract

External Genitalia

• Development

• Function

• Abnormalities

Background Notes

• Fertilization
• Week 1
• Kidney
• Endocrine

Online References

UNSW Embryology

• Gonad Development http://embryology.med.unsw.edu.au/Notes/urogen.htm

NIH Bookshelf

• Developmental Biology (Gilbert) - Chapter 17 http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=dbio.chapter.4101

• Endocrinology (Nussey and Whitehead) - The Gonad http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=endocrin.chapter.972

Textbook References

• Human Embryology (3rd ed.) Larson Chapter 10 pp266-313
• The Developing Human (6th ed.) Moore & Persaud Chapter 13 p303-346
• Before We Are Born (5th ed.) Moore & Persaud Chapter 14 p289-326
• Essentials of Human Embryology, Larson Chapter 10 p173-205
• Human Embryology, Fitzgerald and Fitzgerald Chapter 21-22 p134-152

Genital System Development

3 stages

• Differentiation of gonad (Sex determination)
• Differentiation of internal genital organs
• Differentiation of external genital organs

- 2nd and 3rd stages dependent on endocrine gonad

Long Maturation Timecourse

• Begins in embryo
• Finishes in puberty

Sex Chromosomes

X Chromosome

• 1400+ genes
• 150 million base pairs
• 95% determined

Chromosome Y

• 200+ genes
• 50 million base pairs
• 50% determined

Human Female Differentiation

• Genes such as Wnt-4 and DAX-1
• necessary for initiation of female pathway ovary development
• female not considered a default process

Sry on Gonad

• Sry gene on Y chromosome
• responsible for testis-determining function
• TDF
• expressed in a subset of somatic cells in developing gonad
• induces cells to differentiate into Sertoli cells

Sertoli cells

• produce signals that promote development of male characteristics
• suppress development of female characteristics
• induce primordial germ cells to commit to sperm development

DNA with SRY Protein - SRY protein binds DNA

• Testes determining factor (TDF)
• Transcription factor

Bends DNA 70–80 degrees

• Black

- SRY protein HMG box

• Red coil - DNA double helix (Image after Haqq et al. 1994 and Werner et al. 1995)

SRY on Gonad Development

Germ Cells Development

• Early germ line separation from somatic cells
• germ cells do not arise within gonad

Precursors primordial germ cells (PGCs)

• • arise elsewhere and migrate into developing gonads

Gametogenesis

• forming PGCs and getting them into genital ridge as gonad forms
• formation of germ plasm and determination of PGCs
• migration of PGCs into developing gonads
• process of meiosis and modifications of meiosis for forming sperm and eggs
• differentiation of sperm and egg
• hormonal control of gamete maturation and ovulation

Movie: Germ Cell Migration

Sex Determination

Humans (week 5-6)

• Germ cells migrate into gonadal ridge
• Gonads (male/female) identical at this stage

- Indifferent

• Gonad development dependent on sex chromosome
• Y testes

• No Y ovary

Movie: Germ Cell Migration

Primary Sex Cords Carnegie stage 13/14

Internal Genital Organs

All embryos form paired

• Nephric duct
• Mesonephric duct (See kidney development)
• Paramesonephric duct

- Humans 7th week

- Invagination of coelomic epithelium

- Cord grows and terminates on urogenital sinus

Male Gonad (testes) secretes

• Mullerian duct inhibitory factor (MDIF) - Causes regression of paramesonephric duct

• Testosterone - Retains mesonephric duct

Female - opposite

Carnegie stage 13/14 Movie: Mesonephros and Gonad Movie: Urogenital Sinus Male Mesonephric Duct (st22) Movie: Gonad Development Gonad Differentiation Gonadal Cell Types Differentiation of Human Gonads Germ Cells and Ovary Folliculogenesis After colonization of gonad

female germ cells enter prophase of first meiotic division as a mid-gestational hallmark of gender

Perinatally oocytes interact with granulosa cells to form primordial follicles

• cyclic periodicity enter a 3 week growth phase that culminates in meiotic maturation and ovulation
• (study in mouse)

Folliculogenesis Spermatogenesis Inactive until puberty

Seminiferous tubules

• Initially solid (cellular)
• Hollow and active at Puberty
• Cyclic sperm production along length of tubule

Movie: Internal Female Genitalia

Genital Ligaments

Movie: Gonad Descent External Genitalia

Human Sex Hormones

• Hormonal production of differentiated gonads
  • required for differentiation of internal and external genitalia during fetal life
  • development of secondary sex characteristics at puberty
• Antimullerian hormone (AMH) secreted by Sertoli cells
• Testosterone secreted by Leydig cells
• External male genitalia
  • requires transformation of testosterone to dihydrotestosterone
  • 5alpha reductase type 2 expressed in genital skin and urogenital sinus
• effects of androgens occur in presence of functional androgen receptor protein
  • Mutations of genes coding for steroidogenic enzymes, AMH, AMH receptor, AR and 5alpha reductase are all associated with impairment of sex differentiation and result in genital ambiguity

Hormone Axis

Hormone Dependent Genitalia

External Genital Organs

All embryos initially same (indifferent)

Testosterone

• Differentiates male

Fetal Development

External Genitalia Genital Abnormalities Chromosomal

Hermaphroditism

Gonadal Dysfunction

Tract Abnormalities

External Genitalia

Gonadal Descent

Gonadal Descent Cryptorchadism

• One or both testes fail to descend into scrotum

• 1:30 live male births

• May be associated with other abnormalities

Chromosomal Turner’s Syndrome

• Monosomy XO

- 99% non-viable embryos

- Fail to sexually mature at puberty

Klinefelter's Syndrome

• 47, XXY

- Begin normal male, become infertile

- Tall, mental dullness, behaviour problems

Males

• 46, XX

- Develop as male, infertile adults

- Portion of SRY gene located on one X

Sex Reversal in Humans Hermaphroditism True

• • 46,XX

• • Gonads both ovary and teste tissues

• • Ovotestes or ovary and testes

Male Pseudohermaphrodites

• • 46,XY

• • Gonads of one sex, external genitalia of opposite

• • Various causes

Female Intersex (old term Pseudohermaphrodites)

• • 46,XX

• • Gonads are ovaries, external genitalia ambiguous

• • Hyperplastic adrenals secrete androgens

Gonadal Dysfunction

• Gonads fail to develop properly

Gonadal Dysgenesis

• Swyer’s syndrome
• 46,XX

Mixed Gonadal Dysgenesis

• 45,X/46,XY

Primary Hypogonadism

• Affected females 46,XX

Primary Hypogonadism

• Defective anterior pituitary production of gonadotropin

- Lack of gonadotropin-releasing hormone

Tract Abnormalities

• Many different forms
• Uterine - Associated with other anomolies
• Vagina - Agenesis, atresia (See endocrine lecture DES)
• Ductus Deferens - Uni- or bilateral absence - Failure of mesonephric duct to differentiate

External Genitalia

Multi-factoral

• Chromosomal, single gene, environmental
• Developmental arrest gives ambiguous

Androgen Insensitivity Syndrome

XY karyotype and presence of testes

Externally - develop female secondary sex characteristics

Internally

• women lack Müllerian duct derivatives
• have undescended testes

Summary of Gonad Development

Sex Differences in Adult and Developing Brains

• not known significance of brain sex differences
• transient sex differences in gene expression in developing brains may cause permanent differences in brain structure
• may prevent as well, by compensating for potentially differentiating effects of sex differences in gonadal hormone levels and sex chromosomal gene expression

Sex Chromosomes and Brain Sexual Differentiation

Brains of males and females differ

• • in regions specialized for reproduction

• • in other regions (controlling cognition, etc) where sex differences are not necessarily expected

Differentially susceptible to neurological and psychiatric disease

2 sources of sexually dimorphic information

• • complement of sex chromosome genes

• • mix of gonadal hormones

• • sex differences in the brain have been attributed to the differential action of gonadal hormones

• • evidence for sex chromosome effects on both neural and non-neural systems

• • XX and XY cells differentiate even before they are influenced by gonadal hormones

• • even if exposed to similar levels of gonadal steroids

Molecular Signaling Cascades

Hormone Axis - Puberty LH & FSH

Factors that increase gonadotrophin secretion and stimulate gonadal maturation

Bars show proportional rise in testosterone and estradiol secretions in males and females respectively

Activation of positive feedback mechanism of estradiol in females also occurs during puberty

Hormone Axis - Reproduction

Human Sexual Differentiation

gonads, internal genital ducts, and external genital structures develop from bipotential embryologic tissues

Male or female phenotype develops through a cascade of processes which initiate with sex determination and follow with sex differentiation

Karyotype (46, XY or 46, XX)

• of embryo (genetic sex) determines whether primordial gonad differentiates into a testis or an ovary respectively (gonadal differentiation)

Historic Genital Images

• 

  Broad ligament of adult showing Epoöphoron

• 

  Urogenital Sinus of Female Human Embryo of 8.5 to 9 weeks old

• 

  Transverse section of Human Embryo 8.5 to 9 Weeks Old

• 

  Longitudinal Section of Ovary of Cat Embryo of 9.4 cm long

• 

  Section of the Ovary of a Newly Born Child

• 

  Human Embryo (3.5 cm long) Testis Section of a Genital Cord

• 

  Tail end of Human Embryo 25 to 29 Days Old

• 
• 

  Tail end of human embryo eight and a half to nine weeks old

• 

  Primitive Kidney and Bladder

• 

  Stages in the development of the external sexual organs in the male and female

• 

  Retroperitoneal structures