Chromatin remodeling of prostaglandin signaling in smooth muscle enables mouse embryo passage through the female reproductive tract [CHIC-seq H3K27ac & H3K4me1]

After fertilization, early mammalian development takes place as the embryo transits the oviduct prior to implantation on the wall of the uterus. This transport is precisely orchestrated by secreted oviduct fluid, unidirectional beating of epithelial cilia and smooth muscle contractions. Using multiple gene-edited mice to affect the female reproductive tract, we document that conditional disruption of Pbrm1, a component of the SWI/SNF chromatin remodeling complex, prevents embryo transport. Loss of Pbrm1 in epithelial cells lining the oviduct had no effect, but ablation in smooth muscle phenocopied the transport defect without perturbing embryogenesis. Analysis with RNA-seq, ATAC-seq, ChIC-seq and pharmacologic rescue experiments implicated prostaglandin signaling pathways. In comparison to wildtype, gene-edited mice had compromised chromatin accessibility at enhancer/promoters of Ptgs2, Pla2g16, Pla2r1 and Ptger3 (EP3) as well as decreased enhancer-promoter interactive looping critical for Ptgs2 (prostaglandin-endoperoxide synthase 2, aka Cox-2) expression in a SWI/SNF complex dependent manner in smooth muscle. These observations provide mechanistic insight into potential causes of ectopic pregnancy in fallopian tubes that is a significant cause of morbidity and mortality in human pregnancies. Overall design: CHIC-seq was performed using D2 WT primary oviductal smooth muscle cell in order to identify the directly binding sites.

受精完成后，哺乳动物早期胚胎会在子宫壁着床前经由输卵管转运。该转运过程由分泌型输卵管液、上皮纤毛的单向摆动以及平滑肌收缩精准调控。我们通过多种可影响雌性生殖道的基因编辑小鼠实验证实，作为SWI/SNF染色质重塑复合物（SWI/SNF chromatin remodeling complex）组分的Pbrm1，其条件性敲除会阻断胚胎转运过程。输卵管上皮细胞中Pbrm1的缺失并不会产生明显影响，但平滑肌内的Pbrm1敲除则可在不干扰胚胎发育的情况下，模拟出转运缺陷表型。
通过RNA-seq、ATAC-seq、ChIC-seq及药物挽救实验，我们发现前列腺素信号通路参与了该调控过程。与野生型小鼠相比，基因编辑小鼠的平滑肌中，Ptgs2、Pla2g16、Pla2r1及Ptger3（EP3）的增强子/启动子区域染色质可及性受损，同时Ptgs2（前列腺素内过氧化物合酶2，又名Cox-2）表达所必需的增强子-启动子相互作用环也出现了显著减少，且该过程依赖于SWI/SNF复合物。
上述发现为输卵管异位妊娠的潜在致病机制提供了新的见解——输卵管异位妊娠是人类妊娠中引发发病与死亡的重要诱因之一。
实验整体设计：本研究使用妊娠第2天（D2）的野生型原代输卵管平滑肌细胞开展ChIC-seq实验，以鉴定其直接结合位点。