Unit 8 Sex Determination and Gonadogenesis Sex Determination Testis Determining Factor Pseudoautosomal region a region that has sufficient homology to allow crossovers between X and Y chromosomes Kalthoff 2e Fig 26 9 Testis determining factor TDF region a region that can be carried along with the pseudoautosomal region in rare cases Sex Determination Testis Determining Factor occasionally a sperm gets an X chromosome with the TDF region Kalthoff 2e Fig 26 9 occasionally a sperm gets a Y chromosome without the TDF region Sex Determination Testis Determining Factor Conclusion there is a region on the Y chromosome that is sufficient to confer maleness Is there one key gene in there XX but with testes male external features Kalthoff 2e Fig 26 9 XY but with no testes no male external features Sex Determination Sry and Male Determination Conclusion Sry expression is sufficient to confer maleness Gilbert 10e Fig 15 6 XY XX Sry Sex Determination Sry and One Other Gene Are Needed on the Y Chromosome Conclusion Sry and one other gene Eif2s3y a eukaryotic translation initiation factor are the only two genes needed on the round spermatids from X0 Y chromosome male in which two to generate transgenes are added to an viable offspring autosome Sry and Eif2s3y Yamauchi et al 2014 Science 343 69 female offspring from injection of round spermatid into oocyte ICSI Sox9 is not on the Y chromoso me Gilbert 10e Fig 15 7 Sox9 can lead to testis formation in XX mammals Conclusion Sox9 is sufficient to initiate important aspects of testis development Gonadal Differentiation indifferent gonads male and female gonads are largely indistinguishable Two important ducts tubing Wolffian duct M llerian duct Gilbert 10e Fig 15 3 Gonadal Differentiation In males Wolffian duct vas deferens Sex cords seminiferous tubules M llerian duct eventually degenerates Gilbert 10e Fig 15 3 Gonadal Differentiation In females Wolffian duct degenerates Surface epithelium surface of ovary M llerian duct oviduct Fallopian tube Gilbert 10e Fig 15 3 Gonadal Differentiation cloaca common opening for urinary and reproductive tracts separate later Gilbert 10e Fig 15 1 Gonadal Differentiation M llerian duct retained Gilbert 10e Fig 15 1 Wolffian duct retained Gonadal Differentiation Sry leads to Sox9 expression In males Leydig cells testosterone Sertoli cells AMH XY XX Wnt4 expression adapted from Kalthoff 2e Fig 27 3 see Gilbert 10e Fig 15 2 In females Thecal cells testosterone Granulosa cells aromatase converts to estrogen Male Gonadal Differentiation testosterone and DHT are crucial for male 2 sex characteristics adapted from Kalthoff 2e Fig 27 3 see Gilbert 10e Fig 15 2 Male Gonadal Differentiation Gilbert 10e Fig 15 12 Androgen Insensitivity Syndrome AIS androgens male sex hormones e g testosterone dihydrotestosterone AIS results from mutation in androgen receptors steroid hormone receptors Gilbert 10e Fig 15 11 Gonadal Differentiation Sry leads to Sox9 expression In males Leydig cells testosterone Sertoli cells AMH XY XX Wnt4 expression adapted from Kalthoff 2e Fig 27 3 see Gilbert 10e Fig 15 2 In females Thecal cells testosterone Granulosa cells aromatase converts to estrogen Wnt4 is required for normal ovaries Leydig cell marker Conclusion Wnt4a is necessary to promote femaleand prevent male type differentiation in females Vainio et al 1999 Nature 397 405 409 Female Gonadal Differentiation estrogen is crucial for female 2 sex characteristics adapted from Kalthoff 2e Fig 27 3