The signal pathway of gonadotrophins-induced mammalian oocyte meiotic resumption

Fully grown mammalian oocytes are arrested at the first meiotic prophase until a surge of gonadotrophin at the mid-cycle. The actions of gonadotrophins, follicle stimulating hormone (FSH) and luteinizing hormone (LH), on oocyte meiotic resumption are believed to be mediated in large part through increasing the production of cyclic adenosine 3',5'-monophosphate and subsequent activation of mitogen-activated protein kinase (MAPK) in its surrounding cumulus granulosa cells. Recent findings indicate that gonadotrophins-induced epidermal growth factor-like growth factors, meiosis activating sterol and gonadal steroid hormones, possibly via protein kinase A II and protein kinase C pathways, are involved in the activation of MAPK. Another second messenger cyclic guanosine 3',5'-monophosphate induced by nitric oxide or natriuretic peptides system mediates the function of gonadotrophins during oocyte meiotic resumption. FSH and LH induced pathways may either directly overlap or each hormone may utilize redundant pathways in oocyte maturation. A detailed appreciation of different FSH and LH-activated signaling pathways in mammalian oocytes will be needed in understanding their actions in follicular development and oocyte maturation.