Norm Sex Diff Flashcards
What is sexual determination?
→Genetically controlled process dependent on the ‘switch’ on the Y chromosome.
→Chromosomal determination of male or female.
What is sexual differentiation?
→The process by which internal and external genitalia develop as male or
female.
At what stage in embryo development does SRY gene switch on briefly?
→ >7 weeks
What are the two hormones made by the testis?
→ AMH by Sertoli cells
→Testosterone by Leydig cells
What is SRY?
→ DNA binding protein that acts as a transcription
factor
Where is the critical site of DNA binding?
→ upstream of SOX9 which is also a transcription factor
What can SOX9 do?
→ can bind its own upstream activation
site so its levels remain high even if SRY
declines
→positive feedback
What is the relationship between SOX9 and SRY?
→SRY determines executive policy and SOX9 implements it
How does SOX9 achieve its effects- 4 ways?
→Stimulates production of prostaglandin D2 (PGD2) by the pre-sertoli cells
→SOX9 stimulates production of fibroblast growth factor 9 (FGF9)
→SOX9 stimulates the production of anti-Mullerian hormone (AMH)
→Inhibition of female transcription factors WNT4 and FOXL2
How does PGD2 acts as a positive feedback in the Sertoli pathway?
→ paracrine hormone to stimulate further SOX9 production in these cells.
How does FGF9 act as a third positive feedback?
→acts as a
chemotactic factor for cell migration into the developing testis
→stimulates the production of SOX9
What are the gonadal precursors derived from?
→common somatic mesenchymal tissue precursors- the genital ridge
Where is the genital ridge located?
→ posterior wall of lower thoracic lumbar region
What are the three waves of cells that invade the genital ridge?
→primordial
→primitive
→mesonephric
What do primordial germ cells become?
→ sperm
→ooyctes
What do primitive sex cords become?
→seroli cells
→granulosa cells
What do mesonephric cells become?
→Leydig (do not express SRY)
→basement membrane continuing to form seminiferous tubules and rete testis
→Theca
Describe the primordial germ cell migration
→small cluster of cells in the epithelium of the yolk sac expands by mitosis at around 3
weeks
→migrate to the connective tissue of the hind gut region of the hind gut
What do Sertoli cells become?
→express AMH
Where do mesonephric cells originate from?
→mesonephric primordium
→lateral to the genital ridges
What do Leydig cells express?
→androgens
Why Wolfian ducts regress in females?
→lack of testosterone
Which enzyme is involved in conversion of testosterone to DHT?
→5-a-reductase
What are the three things DHT cause in male genitalia?
→Clitoral area enlarges into penis
→Labia fuse and become ruggated to form scrotum
→Prostate forms
