[Oocyte apoptosis and evolution of ovarian reserve]

In mammals, the ovarian reserve of primordial follicles is constituted early in fetus, then it becomes progressively exhausted by both follicular development and oocyte apoptosis. At least two third of the oocytes present in the reserve die by apoptosis before birth. Hypotheses of mechanism underlying this process are 1) a "quality control" leading to eliminate meiotic anomalies 2) a deficit in survival factors produced by somatic neighbouring cells 3) a "self sacrifice" or "altruistic death", as previously described in Drosophila. After birth, growth factors and cytokines are main actors of the dialogue which exists between granulosa cells and the oocyte and determines oocyte survival. Mitochondrial factors belonging to bcl-2 family, metabolites of sphingolipids and the aromatic hydrocarbon receptor participate to oocyte apoptosis and can modulate numerical changes in the ovarian reserve. The reserve is quantitatively and qualitatively under both genetic and environmental control. Therapy to preserve ovarian reserve will benefit from better knowledge of molecular and cellular mechanisms regulating oocyte apoptosis. Moreover, recent identification of genes implicated in ovarian premature insufficiency will allow to propose new perspectives to prolong ovarian lifespan.