Gonadotropin induced transcriptional and epigenetic regulation of gene expression in ovarian granulosa cells

Abstract

Mammalian pituitary gland secretes two gonadotropins (GPNs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) that act on the gonads to regulate gonadal development and functions. In females, FSH promotes the development of ovarian follicles, and LH induces oocyte maturation, induction of ovulation, and formation of corpus luteum. Oocytes do not express the GPN receptors, FSHR or LHCGR. GPN responses are accomplished by follicular somatic cells, theca cells (TCs) and granulosa cells (GCs) that surround the oocytes and express GPN receptors. GPN signaling regulates the expression of genes in TCs and GCs, which are essential for ovarian functions. We have studied the GPN-induced regulation of genes in GCs using immature rats. Four-week-old female rats were administered with exogenous GPNs, pregnant mare’s serum GPN (PMSG), and human chorionic GPN (hCG), which act like long acting FSH and LH, respectively. GCs were isolated from the rat ovaries 48h after PMSG administration, 4hr after hCG administration following the PMSG-priming or without GPN administration. RNA-sequencing was performed to identify the differentially expressed genes in GCs following PMSG or PMSG and hCG administration. The majority (~87%) of the differentially expressed genes 48h after PMSG treatment were found to be downregulated indicating that gene repression plays a crucial role in FSH-induced follicle development. However, hCG treatment upregulated a group of the genes in GCs that was repressed by PMSG. Strikingly, hCG administration rarely impacted the expression of any GC-gene, which was not modulated by PMSG administration. This observation suggests that FSH-induced epigenetic and/or transcriptional regulation is essential for subsequent LH actions in GCs. We further investigated the mechanism of GPN-mediated gene regulation in GCs by methyl-sequencing of genomic DNA. Our results demonstrated that changes in genome-wide DNA methylation is an important epigenetic process that is vital for GPN-mediated gene regulation in GCs.