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Animal Science 434 Reproductive Physiology Lec 5: Embryogenesis of the Pituitary and Sexual Development Development of the Pituitary Gland Germ Cell Migration 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 Mesenephros and Metenephros Jost Experiments Sex Determination: The Jost Paradigm Chromosomal Sex Chromosomal Sex Gonadal Sex Gonadal Sex Hormonal Sex Phenotypic 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 XXX or XXY Female B. Human (mammals) • XY or XXY or XXYY or XXXY or XXXXY Male (testis) • XX or XXX Female (ovary) • XO Female with incomplete ovarian development • XXY or XXYY or XXXY 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 development • 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 AntiMullerian Hormone (AMH) 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 SRY and Birds • Birds » females ZW, males ZZ » W chromosome determines sex » SRY is found on the Z chromosome ! • SRY is not the only sex determining gene in animals 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) AMH causes leydig cells to differentiate Testosterone Development of male duct system Wolffian Duct Cells Nucleus Testis T T TR Efferent Ducts Rete Tubules (Vas Efferentia) Epididymis Ductus Deferens Seminiferous Tubules Tunica Albuginea 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 Vas efferentia Female Development XX Female No TDF Testes Determining Factor Ovaries Develop No Testosterone Wolffian Ducts Regress 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) XX Female XY Male Testes develop Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Testosterone Development of male duct system No TDF Degeneration of Mullerian duct Ovaries Develop No Testosterone Degeneration of Wolffian duct 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 Mullerian 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 5Reductase 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 • Secondary sex characteristic tissue in the male expresses 5-reductase External Genitalia Differentiation Testis Determining Factor (SRY gene product) No TDF XX Female XY Male Testes develop Ovaries Develop No Testosterone Sertoli cells secrete anti-mullerian hormone (AMH) AMH causes leydig cells to differentiate Degeneration of Mullerian duct Degeneration of Wolffian duct Testosterone Dihydrotestosterone Development of male duct system Development of penis scrotum and accessory sex glands No AMH Mullerian ducts become the oviducts, uterus, cervix and part of the vagina 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 • fail to copulate or cycle like female as adult • Sexually dimorphic nucleus • Human male and female differences in behaviors – aggression – childhood play – 3D 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 Inguinal Hernia Loop of Intestine Abnormalities in Development 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 – testosterone – anti-mullerian hormone • Animals are chimeric – both express TDF 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 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 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.