Animal Science 434 Reproductive Physiology Development of the Pituitary Gland Lec 5: Embryogenesis of the Pituitary and Sexual Development Stomodeum Brain Infundibulum Rathke s Pouch
Germ Cell Migration Migration from endoderm through mesoderm. Migration begins by the 4 week of gestation in cow and human. Fetal Kidneys Pronephros» regresses Mesonephros» portions of reproductive tract Metenephros» Adult kindney and urinary ducts In birds the migration is via the blood stream. Development of Mesenephros and Metenephros Development of Mesenephros and Metenephros Early Development Flash Movie http://www.ansci.wisc.edu/jjp1/as434/powerpoint/fa07/early_dev.swf Requires the free flash player which can be downloaded from: www.adobe.com
Jost Experiments Sex Determination: The Jost Paradigm Paramesonephric s ( s) Ovary Oviduct Uterus Mesonephric s ( s) Testis Epididymis Vas Epidi Deferens dymi Seminal Vesicles s Gonadal Sex Phenotypic Sex Sex Determination: The Jost Paradigm Gonadal Sex Phenotypic Sex Gonadal Sex Hormonal Sex Phenotypic Sex Brain and/or Behavioral Sex Single Pair of sex chromosomes» mammals, some but not all vertebrates Sex is environmentally determined» sea worms, fish, reptiles Multiple sex chromosomes» invertebrates, insects, reptiles Haplodiploidy» bees, spiders A. Drosophila Sex depends on the number of X chromosomes X or XY or XO = Male XX or XXX or XXY = Female 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 = 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
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 = 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 gene that controls testicular differentiation is on the Y chromosome in mammals. Human X and Y Chromosomes X Y 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 «Causes primary sex chord (seminiferous tubule) development Development of Sertoli Cells Anti- Hormone production by Sertoli Cells «absence of SRY 2nd 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 Gonadal Sex 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
XY Male Testicular Development Mesonephric Tubules Mesonephric ( ) Rete Tubules Tunica Albuginea Mesonephric Tubules Undifferentiated Sex Chords Primary Sex Chords in Fetal Testis Rete Tubules Pre-Sertoli Primary, Epithelial or Medullary Sex Chords Tunica Primordial germ cells Albuginea (gonocytes) Gonocyte Pre-Sertoli Cells Hormonal Sex XY Male
Cells Efferent s (Vas Efferentia) Rete Tubules Nucleus Testis T T TR Epididymis Vas Deferens Tunica Albuginea Seminiferous Tubules XY Male Vas efferentia duct XX Female No Female Development No TDF Ovaries Develop Testes Determining Factor No AMH Ovarian Development Tubules Primary or Epithelial Sex Chords s Regress ducts become the oviducts, uterus, cervix and part of the vagina Future Ovarian Cortex
Tubules Epithelial Sex Chords Tubules Primordial Follicles Epithelial Sex Chords Future Ovarian Cortex Future Ovarian Cortex Secondary or Cortical Sex Chords (egg nests) Primordial Follicles 2nd Sex Chords in Fetal Ovary Ovarian Medulla Ovarian Cortex Development of the Uterus, Cervix and Vagina Fused Hymen
Reproductive tract develops outside the peritoneum! Broad Ligament Development (transverse anterior section) Ovary Ovary (Posterior Transverse Section) Genital Fold (Future Broad Ligament) XY Male XX Female No TDF Phenotypic Sex Ovaries Develop No No AMH duct duct ducts become the oviducts, uterus, cervix and part of the vagina
XY Male XY Male Dihydrotestosterone Development of penis scrotum and accessory sex glands Cells Accessory Sex Glands* and External Genitalia Cells Nucleus Nucleus Testis T T TR Testis T T D 5α - Reductase DR *Prostate, Cowper s Gland Significance of DHT External Genitalia Differentiation 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 5α-reductase
XY Male XX Female No TDF Ovaries Develop No No AMH duct Dihydrotestosterone duct ducts become the oviducts, uterus, cervix and part of the vagina Development of penis scrotum and accessory sex glands