Fig. 1: Schematic of maturation.

The oocyte is surrounded by cumulus granulosa cells (one layer only shown for simplicity). Prior to maturation, C-type natriuretic peptide (CNP) produced by the mural granulosa cells of antral follicles maintains the immature state. At ovulation, LH binds to receptors on mural granulosa cells, triggering release of EGF-like peptides. These bind to EGFR on both the mural and the cumulus granulosa. LH and EGFR activity cooperatively trigger maturation, marked by germinal vesicle breakdown (GVBD), completion of the first meiotic division and alignment of the oocyte chromosomes on the metaphase II spindle. During maturation, the cumulus granulosa cells become displaced away from the oocyte.