FBXL19 transcriptionally primes promoters of developmental genes via CDK8-Mediator recruitment [RNA-seq]

Regulatory elements called CpG islands (CGIs) are associated with the majority of mammalian gene promoters and have been proposed to play an important role in gene expression. The regulatory capacity of CGIs is thought to rely upon a family of proteins that recognise CGIs through their ZF-CxxC DNA binding domains to recruit chromatin-modifying activities to gene promoters. Through studying FBXL19, a poorly characterized ZF-CxxC domain-containing protein, we have discovered that it specifically interacts with the CDK8-Mediator complex in mouse embryonic stem cells (ESCs). Intriguingly, FBXl19 recruits CDK8-Mediator to a subset of CGI-associated promoters of repressed developmental genes in ESCs. We show that FBXL19-dependent recruitment of CDK8 in ESCs is required for the proper induction of the associated genes during ESC differentiation. This is consistent with early embryonic lethality of in FBXl19 deficient mice. Together, our observations highlight a novel role for FBXL19 in priming developmental gene expression, via recruitment of CDK8 to their CGI promoters, in order to support normal gene induction during differentiation and development. Overall design: Gene expression analysis of wild type (Fbxl19fl/fl) and mutant (?CxxC Fbxl19) cells in pluripotent state and and during retinoic acid differentiaion performed by 4sU-RNA sequencing.被称为CpG岛（CpG islands, CGIs）的调控元件与绝大多数哺乳动物基因启动子相关联，既往研究提示其在基因表达调控中发挥关键作用。CGIs的调控活性被认为依赖于一类可通过其ZF-CxxC DNA结合域（ZF-CxxC DNA binding domains）识别CGIs的蛋白质家族，这类蛋白能够将染色质修饰活性因子招募至基因启动子区域。 通过对FBXL19——一种功能尚未得到充分阐明的含ZF-CxxC结构域的蛋白质——开展研究，我们发现该蛋白在小鼠胚胎干细胞（ESCs）中可与CDK8-中介体复合物（CDK8-Mediator complex）特异性相互作用。值得注意的是，FBXL19会将CDK8-中介体复合物招募至小鼠胚胎干细胞中一类受抑制的发育基因的CGI关联启动子子集当中。 我们证实，在小鼠胚胎干细胞内，依赖FBXL19的CDK8招募过程，对于胚胎干细胞分化过程中相关基因的正常诱导至关重要。这一发现与FBXL19缺陷小鼠呈现早期胚胎致死的表型相一致。 综上，我们的研究结果揭示了FBXL19的全新功能：通过将CDK8招募至发育基因的CGI启动子处，在分化与发育过程中支持正常的基因诱导，从而预启动发育基因的表达程序。 总体实验设计：采用4sU-RNA测序（4sU-RNA sequencing）技术，对多能状态下及视黄酸诱导分化过程中的野生型（Fbxl19fl/fl）与突变型（ΔCxxC Fbxl19）细胞开展基因表达分析。