Practice question

Sex determination in mammalian gonad involves antagonism between testis-promoting and ovary-promoting signals. WNT4 secreted by XX bipotential gonad activates beta-catenin signaling via RSPO1-LGR5 axis stabilizing beta-catenin, upregulating FOXL2 and repressing SOX9 and FGF9 testis pathway, driving granulosa differentiation, Müllerian duct retention and oogenesis. Wnt4 null XX mice display partial masculinization with ectopic testosterone synthesis and coelomic vessel formation. Overexpression in XY can feminize gonads. Hence WNT4 is canonical ovary-determining factor opposing Sertoli fate. It does not promote testis, Leydig or Sertoli lineage but ensures female pathway dominance when SRY absent, maintaining ovarian differentiation and fertility.