Animal Science 434 Reproductive Physiology Lec 5 Embryogenesis
Animal Science 434 Reproductive Physiology Lec 5: Embryogenesis of the Pituitary and Sexual Development
Development of the Pituitary Gland
Germ Cell Migration begins by the 4 week of gestation in cow and human.
Migration from endoderm through mesoderm.
In birds the migration is via the blood stream.
Fetal Kidneys • Pronephros – regresses • Mesonephros – portions of reproductive tract • Metenephros – Adult kindney and urinary ducts
Development of the Metenephros and Regression of the Mesonephros (Wolffian - Male) (Mullerian - female)
The Sexually Indifferent Stage (Wolffian - Male) (Mullerian - female)
Sex Determination: The Jost Paradigm Chromosomal Sex Gonadal Sex Hormonal Sex Phenotypic Sex Brain and/or Behavioral Sex
Chromosomal Sex • Sex is environmentally determined – sea worms, fish • Single Pair of sex chromosomes – mammals, some but not all vertebrates • Multiple sex chromosomes – invertebrates, insects, reptiles • Haplodiploidy – bees, spiders
Chromosomal Sex A. Drosophila • Sex depends on the number of X chromosomes – X or XY or XO Male – XX or XXY Female B. Human (mammals) • XY or XXYY or XXXXY Male (testis) • XX or XXX Female (ovary) • XO Female with incomplete ovarian development • XXY or XXYY or XXXXY testis but impaired sperm production C. Conclusion • The primary gene that controls testicular differentiation is on the Y chromosome in mammals.
The Y Chromosome A. Region coding for testicular developement • Short arm of Y chromosome –H-Y Antigen « no longer believed to be involved –SRY « Codes for a DNA binding protein « acts as a transcription factor or assists other transcription factors « the gene products which are transcribed regulate primary sex chord differentiation (formation of seminiferous tubules), androgen production and Mullerian duct inhibiting substance (MIS) production « in the absence of the SRY protein, primary sex chord regress and secondary sex chords (egg nests) develop
The Y Chromosome Cont. B. Other genes on the Y chromosome – Spermatogenesis – androgen production – long bone growth
Problems With SRY as the Male Determining Gene • Transgenic mice studies » SRY a testis and male tract » No Spermatogenesis ! • Birds » females ZW, males ZZ » W chromosome determines sex » SRY is found on the Z chromosome !
Gonadal Sex
XY Male Testis Determining Factor (SRY gene product) Testes develop
Testicular Development Mesonephric Duct (Wolffian Duct) Mesonephric Tubules Rete Tubules Mullerian Duct Tunica Albuginea Undifferentiated Sex Chords
Mesonephric Tubules Rete Tubules Wolffian Duct Mullerian Duct Primary, Epithelial or Medullary Sex Chords Tunica • Primordial germ cells Albuginea • Sertoli Cells
Hormonal Sex
XY Male Testis Determining Factor (SRY gene product) Testes develop Sertoli cells secrete anti-mullerian hormone (AMH)
XY Male Testis Determining Factor (SRY gene product) Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate
XY Male Testis Determining Factor (SRY gene product) Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Testosterone
XY Male Testis Determining Factor (SRY gene product) Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Testosterone Development of male duct system
Wolffian Duct Cells Nucleus Testis T T TR
XY Male Testis Determining Factor (SRY gene product) Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Testosterone Development of male duct system Degeneration of Mullerian duct
Efferent Ducts Rete Tubules (Vas Efferentia) Epididymis Ductus Deferens Tunica Albuginea Seminiferous Tubules
Vas efferentia
Female Development XX Female No TDF Ovaries Develop
Female Development XX Female No TDF Ovaries Develop No Antimullerian Hormone
Female Development XX Female No TDF Ovaries Develop No AMH Mullerian ducts become the oviducts, uterus, cervix and part of the vagina
Ovarian Development Regressing Tubules Mullerian Duct Epithelial Sex Chords Future Ovarian Cortex Wolffian Duct
Regressing Tubules Mullerian Duct Regressing Epithelial Sex Chords Future Ovarian Cortex Regressing Wolffian Duct
Regressing Tubules Primordial Follicles Mullerian Duct Regressing Epithelial Sex Chords Future Ovarian Cortex Regressing Wolffian Duct Secondary or Cortical Sex Chords (egg nests)
Primordial Follicles Mullerian Duct Ovarian Medulla Regressing Wolffian Duct Ovarian Cortex
Development of the Uterus, Cervix and Vagina Mullerian Duct
Fused Mullerian Duct Hymen
Reproductive tract develops outside the peritoneum! Broad Ligament Development (transverse anterior section) Ovary Regressing Wolffian Duct Mullerian Duct
Ovary Regressing Wolffian Duct Mullerian Duct
(Posterior Transverse Section) Genital Fold (Future Broad Ligament) Regressing Wolffian Duct Mullerian Duct
Testis Determining Factor (SRY gene product) XY Male Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Testosterone Development of male duct system Degeneration of Mullerian duct No TDF XX Female Ovaries Develop No AMH Mullerian ducts become the oviducts, uterus, cervix and part of the vagina
Phenotypic Sex
XY Male Testis Determining Factor (SRY gene product) Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Degeneration of paramesonephric duct Testosterone Dihydrotestosterone Development of male duct system Development of penis scrotum and accessory sex glands
Wolffian Duct Cells Nucleus Testis T T TR
Accessory Sex Glands* and External Genitalia Cells Nucleus Testis T T D 5 Reductase DR *Prostate, Cowper’s Gland
Significance of DHT • Androgen receptor has a higher affinity for DHT • Can get effects with low levels of circulating testosterone
External Genitalia Differentiation
Testis Determining Factor (SRY gene product) XY Male Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Testosterone Degeneration of paramesonephric duct No TDF XX Female Ovaries Develop No AMH Parameonephric ducts become the oviducts, uterus, cervix and part of the vagina Dihydrotestosterone Complete Female Tract Development of male duct system Development of penis scrotum and accessory sex glands
Brain or Behavioral Sex
Brain and Behavioral Sex Differentiation Genetics Gonadal Steroid Hormones Brain Structure Experience Sexual Behavior
Brain Sexual Differentiation • Rat female – Give testosterone shortly after birth and fail to copulate or cycle like female • Sexually dimorphic nucleus • Human male and female differences in behaviors – aggression – childhood play – 3 D visual rotation
Decent of the Testis into the Scrotum
Testicular Descent Growth of testis Fusion of the tunica albuginea and peritoneum to form the visceral tunica vaginalis
Front View
Rapid growth of gubernaculum Testis is pulled down to the inguinal ring.
Gubernaculum regresses Testis pulled into scrotum
Continued regression of Gubernaculum Testis pulled deeper into Sscrotum Vaginal Process attaches to Scrotum Space between Visceral and Parietal T. V. is continuous with Peritoneum
Failure or Problems With Testicular Descent • Cryptorchid – unilateral – bilateral • Inguinal Hernia
Abnormalities in Development
5 Reductase Deficiency in an XY Individual • testis • AMH present so Mullerian ducts regress • some Wolffian ducts • psuedovagina and female external genitalia • at puberty may differentiate into phenotypic male
Testicular Feminization in an XY Individual • No androgen receptor • Testis • No testosterone response so no Wolffian duct development • AMH present so mullerian ducts regress • External genitalia is female due to lack of androgen
The Freemartin in Cattle • Female born twin to a bull • Extra embryonic membranes fuse to form a common chorion • Comon blood supply • Both fetuses share a common hormone milieu – testoterone – anti-mullerian hormone • Animals are chimeric – both express TDF
Describe the development of the reproductive tract and/or gonad in an undifferentiated • embryo that is castrated. • female embryo (XX) that has a testis transplated next to the right gonad. • female embryo (XX) that has a testosterone implant placed next to each gonad.
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