C. The Indifferent Gonads Flashcards
What are the three sets of kidneys during embryonic development (in sequential order)?
1) Pronephros.
2) Mesonephros.
3) Metanephros.
What happens to the pronephros?
It degenerates, but its duct persists as the mesonephric duct.
What happens to the mesonephros?
It degenerates, except for some of the caudal tubules and the mesonephric duct.
What happens to the metanephros?
It develops into kidney and ureter.
Where do the gonads develop from?
Gonads develop from the urogenital ridge, a strip of mesenchyme adjacent to the ventromedial surface of the mesonephric kidney.
What is the mesenchyme of the urogenital ridge invaded by?
1) Coelomic epithelial cells.
2) Cells from degenerating mesonephric tubules.
What do the invading cells form?
They form the cellular cords of the indifferent gonad (the “first proliferation of the sex cords”).
This development is controlled by which four genes?
1) Wilm’s tumor predisposition gene 1 (WT1)
2) Steroidogenic factor 1 (SF-1)
3) Lhx9 (LIM-1)
4) Emx2
What are the four cell lines for the final gonads?
1) primordial germ cells (sperm vs oocytes)
2) supporting cells (Sertoli vs granulosa)
3) steroid producers (Leydig vs theca)
4) connective tissue (peritubular myoid cells, blood vessels, fibroblasts)
What are the two possible fates of the single pair of undifferentiated gonads (bipotential)?
Ovary or testicle.
What determines the fate of the bipotential gonads?
It is decided by the supporting cells (Sertoli vs granulosa).
What are the two competing genetic cascades?
Male = Sox9 and Fgf9 (fibroblast growth factor-9). Female = Wnt-4 and RSPO1 (R-spondin1).
What is SRY’s role in the genetic cascades?
SRY tips the balance in favor of the male pathway by kick-starting (up-regulating) Sox9 before the female cascade can get going.
What are the two distinct regions in lower animals?
1) Cortex.
2) Medulla.
What do the cortex and medulla become, respectively?
Cortex = ovary. Medulla = testicle.
