C-Type natriuretic peptide maintains domestic cat oocytes in meiotic arrest

Recent studies have shown that C-type natriuretic peptide (CNP; encoded by the natriuretic peptide C (NPPC) gene) plays an essential role in maintaining meiotic arrest of mouse and porcine oocytes. However, whether CNP inhibits feline meiotic resumption is not known. In the present study we used a domestic cat model to explore the role played by CNP in feline oocyte meiotic resumption. We determined mRNA expression of genes encoding CNP and its cognate receptor natriuretic peptide receptor 2 (NPR2) in antral follicles. NPPC mRNA was primarily expressed in mural granulosa cells, whereas NPR2 mRNA was predominantly expressed in cumulus cells. Following in vitro culture for 24 h, 100 nM CNP increased cGMP levels, and maintained meiotic arrest of oocytes associated with cumulus cells. When the duration of in vitro culture increased from 24 h to 36 h, the ability of CNP to maintain meiotic arrest decreased, and this was accompanied by a decrease in the steady state levels of NPR2 mRNA in cumulus cells. In addition, CNP decreased the rate of degeneration of oocytes. These results indicate that CNP is required to maintain meiotic arrest and prevent degeneration in domestic cat oocytes.