Sze Christie C, Cao Kaixiang, Collings Clayton K, Marshall Stacy A, Rendleman Emily J, Ozark Patrick A, Chen Fei Xavier, Morgan Marc A, Wang Lu, Shilatifard Ali
Department of Biochemistry and Molecular Genetics, Robert H. Lurie National Cancer Institute Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA.
Genes Dev. 2017 Sep 1;31(17):1732-1737. doi: 10.1101/gad.303768.117. Epub 2017 Sep 22.
Of the six members of the COMPASS (complex of proteins associated with Set1) family of histone H3 Lys4 (H3K4) methyltransferases identified in mammals, Set1A has been shown to be essential for early embryonic development and the maintenance of embryonic stem cell (ESC) self-renewal. Like its familial relatives, Set1A possesses a catalytic SET domain responsible for histone H3K4 methylation. Whether H3K4 methylation by Set1A/COMPASS is required for ESC maintenance and during differentiation has not yet been addressed. Here, we generated ESCs harboring the deletion of the SET domain of Set1A (Set1A); surprisingly, the Set1A SET domain is dispensable for ESC proliferation and self-renewal. The removal of the Set1A SET domain does not diminish bulk H3K4 methylation in ESCs; instead, only a subset of genomic loci exhibited reduction in H3K4me3 in Set1A cells, suggesting a role for Set1A independent of its catalytic domain in ESC self-renewal. However, Set1A ESCs are unable to undergo normal differentiation, indicating the importance of Set1A-dependent H3K4 methylation during differentiation. Our data also indicate that during differentiation, Set1A but not Mll2 functions as the H3K4 methylase on bivalent genes and is required for their expression, supporting a model for transcriptional switch between Mll2 and Set1A during the self-renewing-to-differentiation transition. Together, our study implicates a critical role for Set1A catalytic methyltransferase activity in regulating ESC differentiation but not self-renewal and suggests the existence of context-specific H3K4 methylation that regulates transcriptional outputs during ESC pluripotency.
在哺乳动物中鉴定出的组蛋白H3赖氨酸4（H3K4）甲基转移酶COMPASS（与Set1相关的蛋白质复合物）家族的六个成员中，Set1A已被证明对早期胚胎发育和胚胎干细胞（ESC）自我更新的维持至关重要。与其家族成员一样，Set1A拥有一个负责组蛋白H3K4甲基化的催化SET结构域。Set1A/COMPASS介导的H3K4甲基化对于ESC的维持和分化过程是否必要尚未得到解决。在这里，我们生成了缺失Set1A的SET结构域（Set1AΔSET）的ESC；令人惊讶的是，Set1A的SET结构域对于ESC的增殖和自我更新是可有可无的。去除Set1A的SET结构域并不会减少ESC中的整体H3K4甲基化；相反，只有一部分基因组位点在Set1AΔSET细胞中显示出H3K4me3的减少，这表明Set1A在ESC自我更新中独立于其催化结构域发挥作用。然而，Set1AΔSET ESC无法进行正常分化，这表明在分化过程中Set1A依赖性H3K4甲基化的重要性。我们的数据还表明，在分化过程中，Set1A而非Mll2作为双价基因上的H3K4甲基转移酶发挥作用，并且是它们表达所必需的，这支持了在自我更新到分化转变过程中Mll2和Set1A之间转录转换的模型。总之，我们的研究表明Set1A催化甲基转移酶活性在调节ESC分化而非自我更新中起关键作用，并表明存在调节ESC多能性期间转录输出的上下文特异性H3K4甲基化。
