Abstract: C-type natriuretic peptide (Cnp), a member of the natriuretic peptide family of structurally related peptides, is widely distributed in animal brain, kidney, heart and vascular tissues with important roles in cardiovascular homeostasis, regulation of cell proliferation and skeletal development. It is generally believed that there are three known natriuretic peptide receptors (NPR) in mammals: NPR1, NPR1, and NPR3. Cnp exerts its biological actions by the preferentially activation of NPR2. The components of the Cnp signaling pathway mainly include ligand (Cnp), transmembrane receptor (NPR2) and cGMP. Binding of Cnp to NPR2 results in the change of receptor kinase homology domain conformation, which can further activate downstream pathway through stimulation of cGMP production by the activation of receptor guanylate cyclase. At present, some studies have shown that Cnp is expressed predominantly by mural granulosa cells, which line the inside of the follicular wall, whereas Npr2 is expressed predominantly by cumulus cells, indicating a similar pattern of Cnp and Npr2 expression in female animal ovary. In addition，the expression of Cnp and Npr2 is hormonally regulated during animal follicular growth in vivo. FSH- promoted expression of Cnp and Npr2 is mediated by estradiol. Meanwhile, Oocyte-derived paracrine factors promot expression of Npr2 in cumulus cells. LH- reduced expression of Cnp and Npr2 probably is due to activation of EGF signal pathway. Notably, research showed that Cnp, similar to FSH, can induce the expression of diverse ovarian genes important for follicle maturation and steroidogenesis, which is beneficial to cumulus oophorus formation, thereby promote follicular development, indicating that similar to the known follicle-stimulating and oocyte maturation effects of FSH, and Cnp /FSH exerts their biological actions via cGMP /cAMP signal pathway, respectively. Besides, recent studies have revealed that Cnp, secreted by mural granulosa cells, plays an essential role in maintaining meiotic arrest of oocyte. Cnp exerts its biological action as a local factor by binding to NPR2 in cumulus cells, followed by the production of cGMP via the guanylyl cyclase catalytic domains of NPR2, then cGMP diffuses into the oocyte from companion cumulus cells via gap junctions, and inhibits oocyte PDE activity and cAMP hydrolysis, at the same time, higher level of cAMP inhibits oocyte MPF activity, subsequently preventing meiotic resumption of oocyte; whereas Cnp does not affect meiotic maturation of naked oocytes, suggesting the indirect effect of Cnp on meiotic maturation of oocyte by acting as a regulator to cumulus cells. Additionally, pre-treatment of oocytes with Cnp exerts a beneficial effect on cytoplasmic maturation, thereby enhances the developmental capacity of oocyte following in vitro maturation. To sum up, Cnp produced within the ovary might maintain meiotic arrest of oocyte, as well promote cytoplasmic maturation of oocyte by affecting the physiological function of cumulus cells during animal follicular growth, which ensure the higher capability of development after oocyte maturation and fertilization. In light of the findings above, Cnp may be of special importance in the promotion of oocyte development in vitro as one meiotic inhibitor in domestic animals. Hence, this paper reviewed the structure of Cnp, its signal transduction pathway and expression in ovary as one of functional molecules that modulate ovary function in animals.

Key words: C-type natriuretic peptide , animal ovary , expression , reproduction performance