STAG2 promotes the myelination transcriptional program in oligodendrocytes [scRNA-seq]

Cohesin folds chromosomes via DNA loop extrusion. Cohesin-mediated chromosome loops regulate transcription by shaping long-range enhancer-promoter interactions, among other mechanisms. Mutations of cohesin subunits and regulators cause human developmental diseases termed cohesinopathy. Vertebrate cohesin consists of SMC1, SMC3, RAD21, and either STAG1 or STAG2. To probe the physiological functions of cohesin, we created conditional knockout (cKO) mice with Stag2 deleted in the nervous system. Stag2 cKO mice exhibit growth retardation, neurological defects, and premature death, in part due to insufficient myelination of nerve fibers. Stag2 cKO oligodendrocytes exhibit delayed maturation and downregulation of myelinationrelated genes. Stag2 loss reduces promoter-anchored loops at downregulated genes in oligodendrocytes. Thus, STAG2-cohesin generates promoter-anchored loops at myelinationpromoting genes to facilitate their transcription. Our study implicates defective myelination as a contributing factor to cohesinopathy and establishes oligodendrocytes as a relevant cell type to explore the mechanisms by which cohesin regulates transcription. Single-cell RNA-Seq was performed on duplicates of forebrains from Stag2f/y and Stag2f/y; Cre mice黏连蛋白（Cohesin）通过DNA环挤出机制折叠染色体。黏连蛋白介导的染色体环可通过多种机制调控基因转录，其中包括塑造远距离增强子-启动子相互作用。黏连蛋白亚基及其调控因子的突变可引发人类发育疾病，此类疾病被命名为黏连蛋白病（cohesinopathy）。脊椎动物体内的黏连蛋白由SMC1、SMC3、RAD21以及STAG1或STAG2构成。为探究黏连蛋白的生理功能，我们构建了神经系统特异性敲除Stag2基因的条件性基因敲除（conditional knockout, cKO）小鼠模型。Stag2 cKO小鼠表现出生长迟缓、神经功能缺损及过早死亡的表型，该表型部分源于神经纤维髓鞘形成不足。Stag2 cKO少突胶质细胞（oligodendrocytes）存在成熟延迟及髓鞘相关基因表达下调的现象。敲除Stag2会减少少突胶质细胞中表达下调基因的启动子锚定环数量。由此可见，STAG2型黏连蛋白可在促髓鞘形成基因位点生成启动子锚定环，进而促进这些基因的转录。本研究证实髓鞘形成缺陷是黏连蛋白病的致病诱因之一，并确立了少突胶质细胞作为研究黏连蛋白调控转录机制的关键细胞类型。我们对Stag2f/y与Stag2f/y; Cre小鼠的前脑生物学重复样本开展了单细胞RNA测序（single-cell RNA-Seq）。