Remodeling and Spacing Factor 1 in Histone H2A Ubiquitination-Mediated Gene Silencing

组蛋白的翻译后修饰在染色质结构和细胞周期调控中起重要作用 功能。组蛋白H_2A泛素化是一种主要的修饰，对多种细胞过程都很重要。 我们先前已经发现，多梳抑制复合体1(PRC1)是一种基本的发育 调节子，作为泛素连接酶对H_2AK119泛素化(H_2AK119 Ub)起作用。这项研究将H2AK119 ub与 Prc1介导的关键发育基因的基因沉默及其在细胞识别中的重要作用 肿瘤发生和基因组印记。几种蛋白质已被证明能结合H2AK119ub；然而，如何 这种修饰引起的下游基因沉默事件在很大程度上仍然不清楚。我们最近确认了 重塑和间隔因子1(RSF1)作为一种新的H2 AK119亚基结合蛋白，为解剖提供了一个通道 H_2AK119ub的作用机理。我们发现RSF1通过以前的一种 未表征的区域被指定为泛素化的H2A结合(UAB)基序，并且RSF1是两者所必需的 用于沉默H2AK119ub靶基因并维持正常的H2AK119ub核小体模式 启动子区域。我们进一步证明，在非洲爪哇早期胚胎发育过程中，RSF1调节 中胚层细胞规格和原肠形成的方式类似于Ring1，非洲爪哇的PRC1亚单位介导 H2 AK119 ub.尽管这些研究表明，RSF1作为一种H_2AK119亚基结合蛋白，是 H2AK119ub靶基因的抑制，还有待证实的是，阅读H2AK119ub标记是 RSF1抑制基因表达的机制。在这里，我们提出了一系列的结构，体外，和在 体内研究以阐明RSF1在H2AK119ub功能中的作用机制。我们假设RSF1 是H2AK119泛素化的关键读者，该泛素化介导其在基因沉默、染色质 重塑和发展。我们建议解决对这个假设至关重要的三个问题：1)如何 RSF1特异性识别H_2AK119ub核小体？2)RSF1如何调节 H_2AK119微染色质？3)RSF1在H_2AK119亚调节生理过程中的意义 流程？考虑到在正常情况下PRC1和RSF1在细胞命运决定中的基本作用 以及PRC1和RSF1在癌症发展中的广泛参与，这些研究将 显著提高了我们对控制正常发育的表观遗传机制的理解 作为致病过程。

Posttranslational modifications of histones play important roles in the regulation of chromatin structure and function. Histone H2A ubiquitination is a predominant modification important for a variety of cellular processes. We have previously discovered that Polycomb Repressive Complex 1 (PRC1), a fundamental developmental regulator, acts as a ubiquitin ligase for H2AK119 ubiquitination (H2AK119ub). This study links H2AK119ub to PRC1-mediated gene silencing of key developmental genes and the essential roles of PRC1 in cell identity, tumorigenesis, and genomic imprinting. Several proteins have been shown to bind H2AK119ub; however, how this modification elicits downstream gene silencing events remains largely obscure. We recently identified Remodeling and Spacing Factor 1 (RSF1) as a novel H2AK119ub-binding protein, providing a gateway to dissect the mechanism of action of H2AK119ub. We discovered that RSF1 binds H2AK119ub through a previously uncharacterized region designated as the ubiquitinated H2A binding (UAB) motif, and that RSF1 is required both for silencing of H2AK119ub target genes and for maintaining the normal H2AK119ub nucleosome pattern at promoter regions. We further demonstrated that, during Xenopus early embryonic development, RSF1 regulates mesodermal cell specification and gastrulation in a fashion similar to Ring1, a Xenopus PRC1 subunit mediating H2AK119ub. Although these studies reveal that RSF1, as a H2AK119ub-binding protein, is required for H2AK119ub target gene repression, it remains to be established that reading the H2AK119ub mark is the mechanism by which RSF1 represses gene expression. Here, we propose a series of structural, in vitro, and in vivo studies to delineate the mechanism of action of RSF1 in H2AK119ub function. We hypothesize that RSF1 is a key reader of H2AK119 ubiquitination that mediates its roles in gene silencing, chromatin remodeling, and development. We propose to address three questions critical to this hypothesis: 1) how does RSF1 specifically recognize H2AK119ub nucleosomes? 2) how does RSF1 modulate the organization of H2AK119ub chromatin? and 3) what is the significance of RSF1 in H2AK119ub-regulated physiological processes? Given the fundamental roles of PRC1 and RSF1 in cell fate determination during normal development and the extensive involvement of PRC1 and RSF1 in cancer development, these studies will significantly advance our understanding of the epigenetic mechanisms controlling normal development as well as pathogenic processes.