Wnt signaling dosage controlled by a Ctnnb1 enhancer balances homeostasis and tumorigenesis of intestinal epithelia [scRNA-Seq]
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beta-catenin-dependent canonical Wnt signaling plays a plethora of roles in organ development, tissue homeostasis and cancer. Here we identified an upstream enhancer of Ctnnb1 - ieCtnnb1 - that controls intestinal homeostasis. ieCtnnb1 is specifically active in crypts of small and large intestines. Single-cell sequencing revealed that ieCtnnb1 knockout (ieCtnnb1KO) biased epithelial composition and functions of small intestinal crypts leaning toward absorptive functions at the expense of secretive roles. Deletion of ieCtnnb1 hampered epithelial turnovers in physiologic and regenerative conditions. In contrast, deletion of ieCtnnb1 prevents occurrence and progression of Wnt/-catenin driving colorectal cancers. The human ieCTNNB1 specifically drives reporter in intestinal crypts and contains a SNP that is associated with CTNNB1 expression levels in human gastrointestinal epithelia. The enhancer activity of ieCTNNB1 in colorectal cancer tissues is higher than that in adjacent normal tissues and positively correlates with CTNNB1 expression levels. Key trans-factors that bind to ieCTNNB1 and regulate CTNNB1 transcription were identified. Together, these findings revealed an enhancer-dependent mechanism that controls the dosage of Wnt signaling, hence homeostasis of intestinal epithelia. Single cell sequencing of small intestinal crypts in adult wild-type and ieCtnnb1 knockout mice
β-连环蛋白（beta-catenin）依赖的经典Wnt信号通路在器官发育、组织稳态及癌症发生发展中发挥诸多关键作用。本研究鉴定出Ctnnb1的上游增强子ieCtnnb1，其可调控肠道稳态。ieCtnnb1仅在小肠和大肠的隐窝中具有特异性活性。单细胞测序结果显示，ieCtnnb1敲除（ieCtnnb1KO）会改变小肠隐窝上皮细胞的组成与功能，使其偏向吸收功能，以牺牲分泌功能为代价。敲除ieCtnnb1会阻碍生理及再生状态下的上皮细胞更新。与之相反，敲除ieCtnnb1可抑制Wnt/β-连环蛋白驱动的结直肠癌的发生与进展。人类ieCTNNB1可特异性驱动肠道隐窝中的报告基因表达，且其携带的单核苷酸多态性（SNP, single nucleotide polymorphism）与人类胃肠道上皮细胞中CTNNB1的表达水平相关。ieCTNNB1在结直肠癌组织中的增强子活性高于邻近正常组织，且与CTNNB1的表达水平呈正相关。本研究还鉴定出可结合ieCTNNB1并调控CTNNB1转录的关键反式作用因子。综上，本研究揭示了一种依赖增强子的调控机制，该机制可通过控制Wnt信号通路的剂量，进而维持肠道上皮的稳态。成年野生型与ieCtnnb1敲除小鼠的小肠隐窝单细胞测序
