(354) KIT Signaling in Postnatal Ovarian Folliculogenesis: Insights from Oocyte-Specific Kit Knockout Mice

KIT Signaling in Postnatal Ovarian Folliculogenesis: Insights from Oocyte-Specific Kit Knockout Mice

Wonmi So¹, Amirhossein Abazarikia¹, So-Youn Kim¹

¹Olson Center for Women’s Health, Department of Obstetrics and Gynecology, College of Medicine, University of Nebraska Medical Center, Omaha, NE, USA.

Abstract Text:

KIT is mainly expressed in the oocyte membrane of primordial, primary, and early secondary follicles, as well as in ovarian endothelial cells. In the ovary, the KITL-KIT signaling pathway is known to regulate cyst breakdown and folliculogenesis, primarily through the PI3K-AKT-FOXO3a pathway. However, its function in the postnatal ovary remains unexplored. Our previous study demonstrated that oocyte-specific conditional Kit knockout (cKO) mice, generated using Gdf9-icre, exhibited normal cyst breakdown and folliculogenesis until 6 weeks of age. However, by 13 weeks, ovarian follicles were markedly decreased, and by 20 weeks, they were nearly absent compared to controls (WT). These mice also exhibited smaller ovarian size and weight, delayed folliculogenesis, and phenotypes consistent with primary ovarian insufficiency (POI), including elevated serum FSH and reduced AMH levels. In this study, we examined gene expression in the ovaries of cKO mice to investigate follicular loss resulting from the absence of KIT expression in oocytes. To identify the critical time points associated with these ovarian changes, we analyzed ovaries at 7 weeks (n=5) and 8 weeks (n=5). By 8 weeks, the total numbers of ovarian follicles were comparable between WT and cKO. However, the total number of primary follicles significantly increased in cKO, while the total number of secondary follicles declined, suggesting delayed folliculogenesis. Furthermore, primary follicles in cKO displayed abnormal phenotypes, including smaller oocytes and nuclear localization of FOXO3a, indicating impaired transition from primary to secondary follicle. To explore the underlying regulatory mechanisms, we performed RNA-seq analysis on 8-week-old ovaries (n=3). Interestingly, genes involved in WNT signaling, lipid metabolism, angiogenesis, and reactive oxygen species metabolism were dramatically upregulated in cKO, while genes associated with oogenesis, oocyte development, maturation, folliculogenesis were downregulated. Additionally, genes related to DNA damage responses were also downregulated. These findings suggest that, beyond the PI3K-AKT-FOXO3 pathway, a novel KIT-dependent regulatory mechanism is essential for postnatal folliculogenesis.