OR08-1 Context-Specific Chromatin Binding Properties of Progesterone Receptor and Consequential Effects on Gene Expression in Mouse Reproductive Tissues

Abstract

Progesterone receptor (PGR), the nuclear receptor transcription factor responsive to progesterone, regulates diverse tissue-specific processes in the reproductive tract. Importantly, PGR expression in ovarian granulosa cell is critical for ovulation and female fertility (1). As a transcription factor, PGR modulates target gene expression through interaction with the canonical PGR response element (PRE) motif. However, evidence has shown that PGR can employ non-canonical pathways to achieve specific transcriptional regulation roles (2). In granulosa cells, the mechanism employed by PGR in order to regulate specific functions and how this relates to specialized roles in reproductive tissues are still poorly understood. To address this, we produced the first genome-wide description of PGR action in peri-ovulatory mouse granulosa cell and contrasted this with PGR properties in the oviduct and uterus. Granulosa cells were obtained from hormonally-stimulated pre-pubertal female mice sacrificed at 6 h post-hCG for PGR and H3K27ac ChIP-seq (wildtype mice) and microarray analysis (wildtype and Pgr-null mice). Using PGR ChIP-seq we found more than 15000 PGR-DNA binding sites in granulosa cells. Remarkably, 62% of sites were in proximal promoter regions (< 3 kb from TSS) and nearly 75% overlapped transcriptionally active H3K27ac-bound chromatin intervals. Motif analysis indicated that while canonical PRE binding was most common, PGR binding was also significantly enriched at other transcription factor binding motifs (TFBS) , including bZIP, Zinc Finger and RUNT families. Parallel analysis of granulosa cell and uterus PGR ChIP-seq illustrated striking differences in cistromes, with the vast majority (42%) of uterine PGR binding localized to intergenic regions and uterine PGR binding at TFBS which were not enriched for in granulosa cell. Using microarray analysis of Pgr-null mice we identified 61 PGR-regulated genes in granulosa cell, 90% of which possessed PGR binding sites. A systematic comparison of PGR action in granulosa, oviduct and uterus revealed the highly specialised PGR-dependent gene regulation, with no common genes between granulosa cell, oviduct and uterus. Our findings confirm the uniqueness of PGR action in reproductive tissues and suggest that in the reproductive tract, PGR binds to its canonical PRE and also interacts with context-specific co-modulators to exert tissue-specific functions. Reference: (1) Akison & Robker, Reproduction in domestic animals 47 (2012): 288-296. (2) Doyle et al., Molecular Endocrinology 18 (2004): 2463-2478.