Cumulus Cells are an Essential Mediator of Ovulation Stimuli from Granulosa Cells to Oocyte

Abstract

In preovulatory follicles, oocytes are surrounded by numerous layers of cumulus cells in a known as the cumulus cell-oocyte complex (COC). After stimulation of ovulation by the LH surge, the morphology of COC is dramatically changed as a hyaluronan rich matrix accumulates within cumulus cell layer, and the oocyte resumes meiosis by progressing to the metaphase II. Although both changes induced by LH surge are essential for successful fertilization in vivo, the expression of LH receptors is not detected in the oocyte and is minimal (negligible) in cumulus cells compared with granulosa cells. However, cumulus cells express members of the EGF receptor family (ErbB family), prostaglandin receptors (EP2 and EP4) and cytokine family receptors that respond to specific ligands secreted by granulosa cells during the ovulation process. By these intermediary steps, the cumulus cells mediate LH signaling from granulosa cells to induce oocyte maturation. This minireview focuses on the role of cumulus cells in oocyte maturation at the physiological and molecular levels.