GnRH-Regulated Transcriptome in the Gonadotrope

University Of California, San Diego, La Jolla CA

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Abstract

DESCRIPTION (provided by applicant): Regulation of gene transcription in the gonadotrope is a key regulatory step that determines the levels of gonadotropin hormones and therefore, regulates gonadal function. Gametogenesis and steroidogenesis in both sexes are controlled by these two hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary, which are, in turn, regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. GnRH regulates gonadotropin synthesis through induction of the three immediate early genes: ATF3 induces the ? glycoprotein subunit, Egr-1 induces the LH? subunit, and AP-1 induces the FSH? subunit. The overall goal of this application is to determine the GnRH-regulated transcriptomes comprised of these immediate early genes in the gonadotrope cell. We propose two complimentary aims to dissect transcriptional regulation from a more comprehensive standpoint. In the first aim, we will determine the complement of direct target genes, in addition to gonadotropin subunits, of these immediate early genes by ChIP-chip, which will allow us to delineate the transcriptional regulatory network. The intersection of genes that are induced by GnRH, already identified by expression array analysis, and the direct gene targets of these three most highly induced transcription factors determined herein by ChIP-chip, will focus our analysis on the most functional binding elements. Furthermore, overlap of these data sets will identify the genes whose transcription may be regulated similarly to gonadotropins. In the second aim, using a two-hybrid screen of a cDNA library from gonadotrope-derived cells, we will identify molecules that interact with ATF3, Egr-1 or AP-1, with a special emphasis on coactivators and corepressors. These cofactors may contribute to differential expression of the three gonadotropin subunits. Additionally, we will determine whether selected target genes from the first aim have similar sets of binding sites in their promoters and/or require the same cofactors, which may contribute to regulation of their expression. This approach will help us triangulate, from a broad perspective, the differential regulation of the gonadotropin subunits and whether it is accomplished by formation of diverse complexes on their respective promoters, in addition to analyzing the more global regulation of gene transcription in the gonadotrope. The results from this proposal will also open new avenues to study chromatin remodeling and activation of basal transcriptional machinery. PUBLIC HEALTH RELEVANCE: Fertility in mammals is regulated by integration of different hormonal signals, which occurs at the level of the gonadotrope cell population in the pituitary gland. The integration ultimately results in the precisely orchestrated modulation of gene expression in the gonadotrope cell that leads to delicate balance of hormones that control reproduction. Thus, understanding the molecular mechanisms governing gonadotrope gene expression will lead to insight into the physiology and pathophysiology of the reproductive system.