The pregnant myometrium is epigenetically activated at contractility-driving gene loci prior to the onset of labor in mice

Abstract

25During gestation, uterine smooth muscle cells transition from a state of quiescence to one of 26 contractility, but the molecular mechanisms underlying this transition at a genomic level are not well-27 known. To better understand these events, we evaluated the epigenetic landscape of the mouse 28 myometrium during pregnancy, labor and post-partum. We established gestational timepoint-specific 29 enrichment profiles involving histone H3K27 acetylation (H3K27ac), H3K4 tri-methylation (H3K4me3), 30 and RNA polymerase II (RNAPII) occupancy by chromatin immunoprecipitation sequencing (ChIP-seq), as 31 well as gene expression profiles by total RNA-sequencing (RNA-seq). Our findings reveal that 533 genes, 32 including known contractility-driving genes (Gja1, Fos, Oxtr, Ptgs2), are upregulated during active labor 33 due to an increase in transcription at gene bodies. Their promoters and putative intergenic enhancers, 34 however, are epigenetically activated by H3K27ac as early as day 15, four days prior to the onset of 35 active labor on day 19. In fact, we find that the majority of genome-wide H3K27ac or H3K4me3 peaks 36 identified during active labor are present in the myometrium on day 15. Despite the early presence of 37 H3K27ac at labor-associated genes, both an increase in non-coding enhancer RNA (eRNA) production, 38 and in recruitment of RNAPII to corresponding genes occur during active labor, at labor upregulated 39 gene loci. Our findings indicate that epigenetic activation of the myometrial genome precedes active 40 labor by at least four days in the mouse model, suggesting the myometrium is poised for rapid activation 41 of contraction-associated genes in order to exit the state of quiescence. 42 43 65 [16]. Selective reduction of GJA1 production in the uterine smooth muscle cells of two different mouse 66 models has been shown to significantly prolong the quiescent state during pregnancy and thereby delay 67 the onset of labor [17,18]. Reporter expression downstream of a synthetic Gja1 promoter is increased 68 by co-expression of constructs encoding members of the activator protein 1 (AP-1) transcription factor 69 FOS and JUN sub-families [19-21]. Furthermore, increased levels of FOS and FOSL2 in particular within 70 the nuclei of myometrial cells during labor raises the possibility that the FOS:JUN family acts to

MYB and ELF3 differentially modulate labor-inducing gene expression in myometrial cells

“…Nevertheless, much recent work shows promise in the targeting of genomic activity in SMCs in order to prolong pregnancy. For instance, our earlier study uncovered gestational time point-specific, genome-wide active histone mark patterns; these patterns support previous findings that the onset of labor is associated with global histone deacetylation [8,26,27]. Recently, Zierden and others have developed a mode of delivery of suspensions containing inhibitors of histone deacetylase proteins alongside the labor-stalling hormone, progesterone; their results showed that these two-target suspensions provide greater efficacy in preterm birth prevention in bacterial infection-induced mouse labor models than two prominent approved drugs [28].…”

“…Accordingly, we generated another reporter construct under the control of the endogenous murine Fos promoter. The genomic region upstream of this gene was selected in particular because of the previously observed up-regulation of Fos gene transcription in myometrial cells; the established role of FOS protein in driving labor-associated gene promoter activation; and on account of our previous findings that the Fos locus exhibits signs of elevated active transcription during active murine labor relative to late pregnancy [8,11,15,16]. Before testing the effects of either ELF3 or MYB on Fos promoter activity, however, unlike the case of the Gja1 promoter, the effects of JUN or FOS factors on this promoter had not yet been established in a myometrial context.…”

“…To pinpoint candidate factors that might contribute to the transcriptional up-regulation of labor-associated genes, we examined genes encoding transcription factors that are differentially expressed between gestational days 15 and 19 (active labor) from our previously generated mouse gestational RNA-seq dataset [8]. The expression levels of two laborupregulated gene targets, Myb and Elf3, were examined by RT-qPCR from RNA samples extracted at select late gestational time points in both murine and human myometrial tissues…”

“…Our previous work revealed that the majority of gene expression differences between late gestation SMCs and contracting SMCs in the mouse gestation model occur due to changes in active transcription. More specifically, many contraction-driving genes undergo increased primary transcript synthesis at labor onset [8]. But the mechanism by which these transcriptional changes are conferred during the SMC quiescence to contractility transition is not well understood.…”

A Novel Pregnant Rat Model for Labor Induction and Augmentation With Oxytocin

“…In contrast, we performed cesarean delivery during uncomplicated labor to facilitate sample collection. This line of thought is supported by the 4-5-fold increased myometrial expression of OxtR gene during uncomplicated labor in rodents(37, 38).…”