Talk:BGD Lecture - Sexual Differentiation

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2017

Anomalies in human sex determination provide unique insights into the complex genetic interactions of early gonad development

Clin Genet. 2017 Feb;91(2):143-156. doi: 10.1111/cge.12932.

Bashamboo A1, Eozenou C1, Rojo S1, McElreavey K1.

Abstract Human sex determination (SD) involves complex mutually antagonistic genetic interactions of testis- and ovary-determining pathways. For many years, both male and female SD were considered to be regulated by a linear cascade of pro-male and pro-female genes, respectively; however, it has become clear that male and female development is achieved through the repression of the alternative state. A gene determining the formation of a testis may function by repressing the female state and vice versa. Uniquely in development, SD is achieved by suppression of the alternate fate and maintained in adulthood by a mutually antagonistic double-repressive pathway. Here, we review genetic data generated through large-scale sequencing approaches that are changing our view of how this system works, including the recently described recurrent NR5A1 p.R92W mutation associated with testis development in 46,XX children. We also review some of the unique challenges in the field to establish that mutations, such as this are pathogenic. The impending surge of new genetic data on human SD from sequencing projects will create opportunities for the development of mechanistic models that will clarify how the system operates and importantly provide data to understand how selection and developmental processes interact to direct the evolution of SD across species. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

KEYWORDS: NR5A1; cell-fate choice decisions; cellular models of human disease; disorders of sex development; gonadal dysgenesis; infertility; sex determination; testicular DSD PMID: 27893151 DOI: 10.1111/cge.12932

2016

Hill, M.A. (2016) Embryology BGD Lecture - Sexual Differentiation. Retrieved March 16, 2016, from https://embryology.med.unsw.edu.au/embryology/index.php/BGD_Lecture_-_Sexual_Differentiation
Hill, M.A. (2016) Embryology BGDB Practical - Sexual Differentiation. Retrieved March 16, 2016, from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Practical_-_Sexual_Differentiation
Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders. Chapter 12 http://www.unsw.eblib.com.wwwproxy0.library.unsw.edu.au/patron/Read.aspx?p=2074364&pg=329 Urogenital System
Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone. Chapter 15 http://www.unsw.eblib.com.wwwproxy0.library.unsw.edu.au/patron/Read.aspx?p=2074524&pg=393 Development of the Urinary System Chapter 16 http://www.unsw.eblib.com.wwwproxy0.library.unsw.edu.au/patron/Read.aspx?p=2074524&pg=412 Development of the Reproductive System
Hill, M.A. (2016) Embryology Genital System Development. Retrieved March 16, 2016, from https://embryology.med.unsw.edu.au/embryology/index.php/Genital_System_Development
Nussey, S and Saffron Whitehead, S. Endocrinology: An Integrated Approach. Oxford: BIOS Scientific Publishers; 2001. Chapter 6 http://www.ncbi.nlm.nih.gov/books/NBK29 The gonad

1 June 2013, at 12:53. - page has been accessed 12,947 times.
29 May 2011 at 17:18 - page has been accessed 375 times.

--Mark Hill 13:38, 28 May 2011 (EST) If you have an early print version or 2009 lecture slides, the final 2011 updated presentation may differ, as I probably won't be finished updating here until before lecture. I also remove the draft banner when I am satisfied with the content. If you cannot wait, here is a similar 2010 Science Lecture. Some useful images used in the lecture from a recent review^[1] are shown as external links and are not reproduced here, due to copyright restrictions. As always the animations will help you understand dynamic processes and will be covered again during the associated practical class.

2009 Lecture | 2009 Lecture slides PDF |

References

<pubmed>17245850</pubmed>| PDF

--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.

Table 1. Genes implicated in sexual development in mammals

Figures

These are links to just the images.

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.

Genes implicated in sexual development in mammals

Table below modified from Table 1. Genes implicated in sexual development in mammals in recent review article.<pubmed>17237341</pubmed>| Physiol. Rev.

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 female^b
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)

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

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

^b Candidate gene for 9p deletion, XY sex reversal.

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

↑ <pubmed>17237341</pubmed>| Physiol. Rev. | Figure Links

[1] <pubmed>17237341</pubmed>| Physiol. Rev. | Figure Links

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