Roles of KIT and KIT LIGAND in ovarian function

Evidence from mouse mutants indicates that the Kit gene encoding KIT, a rec eptor present on the oocyte and theca cells, and the Mgf gene encoding KIT LIGAND, the ligand of KIT, are important regulators of oogenesis and follic ulogenesis. Recently, in vitro cultures of fetal gonads, of follicles and o f oocytes have identified specific targets for the KIT-KIT LIGAND interacti on. In fetal gonads, an anti-apoptotic effect of KIT-KIT LIGAND interaction s on primordial germ cells, oogonia and oocytes has been demonstrated. In p ostnatal ovaries, the initiation of follicular growth from the primordial p ool and progression beyond the primary follicle stage appear to involve KIT -KIT LIGAND interactions. During early folliculogenesis, KIT together with KIT LIGAND controls oocyte growth and theca cell differentiation, and prote cts preantral follicles from apoptosis. Formation of an antral cavity requi res a functional KIT-KIT LIGAND system. In large antral follicles, the KIT- KIT LIGAND interaction modulates the ability of the oocyte to undergo cytop lasmic maturation and helps to maximize thecal androgen output. Hence, many steps of oogenesis and folliculogenesis appear to be, at least in part, co ntrolled by paracrine interactions between these two proteins.