Fig. 1
From: Signaling mechanisms and their regulation during in vivo or in vitro maturation of mammalian oocytes
Scheme of maintenance of meiotic arrest in mammals. cAMP inside the oocyte is produced by activation of the G-protein coupled receptor (GPR) 3 and GPR 12 activating adenylate cyclase. Natriuretic peptide precursor C (NPPC), produced by the granulosa cells, stimulates the production of cGMP via specific NPR2 receptor. cGMP diffuses through the gap junctions, inhibiting phosphodiesterase (PDE) activity and cAMP hydrolysis, maintaining a high level of cAMP in the oocytes. cAMP-dependent protein kinase regulates the activity of the maturation promoting factor MPF (CDK1-cyclin B). The high level of cAMP results in CDK1 phosphorylation and inactivation of the CDK1-cyclin B complex. Oocyte-derived paracrine factors (ODPFs) maintain meiosis arrest by stimulating NPPC and NPR2 expression and cGMP accumulation based on [82, 119] modified