[Oocyte apoptosis: when, how, why?]

The store of primordial follicles used for folliculogenesis is formed during oogenesis. Its size is the consequence of three processes: oogonia multiplication, time of meiosis initiation and extent of loss of germ cells (atretic oogonia, oocytes at the pachytene stage and newly formed primordial follicles). Apoptosis is causing this loss but its mechanisms are poorly documented. Both death signals (TNT alpha, Fas ligand) and survival signals (LIF, kit ligand) are present in the embryonic gonad. The apoptotic cascade then involves bclz, bax and caspases since knock out of these genes alters the store of primordial follicles. Apoptosis also exists within primordial follicles in adult ovaries and involves oocyte death. Its control has not been extensively studied.