Immunolocalization and Expression Pattern of Gpr3 in the Ovary and Its Effect on Proliferation of Ovarian Granulosa Cells in Pigs

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Gpr3, a member of the G protein-coupled receptor superfamily, was known as a critical factor for the maintenance of meiotic prophase arrest in oocytes via a Gs protein-mediated pathway. The present studies were conducted to examine the ovarian immunolocalization of Gpr3, its expression pattern in different stages of fetal, postnatal and developmental pigs and its effect on proliferation of ovarian granulosa cells in pigs. Immunohistochemical analysis indicated that Gpr3 was localized in egg nests, oocytes and granulosa cells (GCs) of the follicle ranging from the primordial to Graafian stages and the corpora lutea. Staining was faintly present in the corpora lutea and weak in GCs but was strong in oocytes. Real-time PCR and Western blotting indicated that Gpr3 mRNA and protein were both present in the different ages of ovaries, and there were wavy changes in the expression levels from postpartum 1 to 180 days. Moreover, both the mRNA and protein levels of Gpr3 were upregulated significantly during follicle growth, suggesting that Gpr3 might play potential roles in regulating ovarian follicle development in the pig. MTT and flow cytometry analyses indicated that Gpr3 knockdown significantly promoted proliferation of porcine GCs while increasing the proportion of cells in the S phase and the expression of Cyclin B1 and Cyclin D2, providing new insights into how Gpr3 signaling regulates the proliferation of porcine GCs. In conclusion, the stage- and cell-specific expression pattern of Gpr3 in the porcine ovary suggested that Gpr3 might play an important role during the entire process of follicular development and luteinization.