Objective: In this experiment, we investigated the expression of Cyclin G1 in mouse ovaries and explored the role of Cyclin G1 during ovarian folicular development and oocyte maturation.
Methods: Immature female Kunming mice were treated with Pregnant Mare Serum Gonadotropin (PMSG) to induce the follicular development, with PMSG/human Chorionic Gonadotropin (hCG) to promote the ovulation and luteinization. The expression pattern of Cyclin G1 in ovary sections was determined by immunohistochemical analysis. The expression and localization of Cyclin G1 in isolated oocytes were evaluated by indirect immunofluorescence analyses.
Results: The immunohistochemical staining showed that with the development of follicles, granulose cells showed to have the gradually increased Cyclin G1 levels and the expressing protein G1 localized clearly in cell nuclei. The Cyclin G1 was observed to express at all stage follicles of oocytes by immunohistochemical analysis. The localization of Cyclin G1 in oocytes was related to the developing stage of follicle. With the development of follicle, Cyclin G1 protein in the oocytes was transferred from the cell nucleus to the cytoplasm. Following anovulatory dose of hCG, the positive reactivity of Cyclin G1 in preovulatory granulosa cells was decreased. Furthermore, the luteinized granulosa cells showed the weak staining. And the expression of Cyclin G1 in atretic follicles was very low. Indirect immunofluorescence analyses demonstrated that Cyclin G1 was present in both GV (germinal vesicle) oocytes and those after GVBD (germinal vesicle breakdown), with increasing expression in oocytes after GVBD. Cyclin G1 was also present in both metaphase II (M II) eggs and fertilized eggs. Comparing with M II eggs, the positive immunostaining was increased in fertilized eggs.
Conclusion: The expression of Cyclin G1 in mouse ovary is in spatiotemporal pattern, which indicates that Cyclin G1 may play the role as a positive modulator of cell cycle in ovarian follicular development and oocyte maturation.