Granulosa cell genes that regulate ovarian follicle development beyond the antral stage: The role of estrogen receptor β

Abstract

Follicle development beyond the preantral stage is dependent on gonadotropins. FSH signaling is crucial for the advancement of preantral follicles to the antral stage, and LH signaling is essential for further maturation of preovulatory follicles. Estrogen is intricately tied to gonadotropin signaling during the advanced stages of folliculogenesis. We observed that Erβ^null ovarian follicles fail to develop beyond the antral stage, even after exogenous gonadotropin stimulation. As ERβ is primarily expressed in the granulosa cells (GCs), we explored the gonadotropin-regulated GC genes that induce maturation of antral follicles. Synchronized follicle development was induced by administration of exogenous gonadotropins to wildtype 4-wk-old female rats. The GC transcriptome was analyzed via RNA-sequencing before and after gonadotropin stimulation. An Erβ^null mutant model that fails to show follicle maturation was also included in order to identify the ERβ-regulated genes involved at this step. We observed that specific groups of genes were differentially expressed in response to PMSG or hCG administration in wildtype rats. While some of the PMSG or hCG-induced genes showed a similar expression pattern in Erβ^null GCs, a subset of PMSG- or hCG-induced genes showed a differential expression pattern in Erβ^null GCs. These latter ERβ-regulated genes included previously known FSH or LH target genes including Lhcgr, Cyp11a1, Cyp19a1, Pgr, Runx2, Egfr, Kiss1, and Ptgs2, which are involved in follicle development, oocyte maturation, and ovulation. We also identified novel ERβ-regulated genes including Jaml, Galnt6, Znf750, Dusp9, Wnt16, and Mageb16 that failed to respond to gonadotropin stimulation in Erβ^null GCs. Our findings indicate that the gonadotropin-induced spatiotemporal pattern of gene expression is essential for ovarian follicle maturation beyond the antral stage. However, expression of a subset of those gonadotropin-induced genes is dependent on transcriptional regulation by ERβ.

Keywords: ERβ; Follicle maturation; Gonadotropins; Granulosa cells; Transcriptome analyses.