Diagrammatic description of the molecular events leading to oocyte meiotic arrest at prophase I. The processes leading to oocyte arrest in prophase begin when natriuretic peptide precursor C (NPPC) from the mural granulosa binds to its receptor, guanylyl cyclase-linked natriuretic peptide receptor 2 (NPR2) on the cumulus cell promoting cyclic guanosine monophosphate (cGMP) synthesis. cGMP enters into the oocyte via network of connexin gap junction to stop phosphodiesterase 3A (PDE3A) enzymes from hydrolyzing cAMP. As more and more cAMP is produced, protein kinase A (PKA) becomes active to phosphorylates WEE1B kinase and prevents CDC25B phosphatase. Inactivation of CDC25B causes the inactivation of cyclin-dependent kinase 1 (CDK1) and thus, prophase arrest is sustained. Modified following (Fan and Sun, 2019; Pan and Li, 2019).