Chromatin targeting and transcriptional control by the histone variant H2A.Z

项目摘要 表观遗传系统对于在发育期间指定细胞命运是必不可少的，因为它用于选择和 增强将在给定细胞类型中表达或沉默的基因组部分。高度 保守的组蛋白H2 A变体H2A.Z是该系统的关键组分，其是胚胎发育所需的。 在动物的发育和调节许多植物的发育过程。研究集中在 H2A.Z，因为它被认为在胰腺癌和乳腺癌细胞中起因果作用。 增殖，但其功能仍然知之甚少。H2A.Z被选择性地沉积到染色质中， SWR 1在数千个基因中重塑复合物，在那里它矛盾地促进一些转录， 基因，而其他沉默。尽管这种组蛋白变体具有生物学重要性，但关于 它的目标和功能仍然存在。例如：SWR 1复合物如何靶向特定的基因组位点， H2A.Z的证词H2A.Z抑制转录的机制是什么？考虑到植物 在历史上是告知动物表观遗传学丰富的模型系统，并且与动物不同，H2 A.Z-deficient 植物是可行的，我们的目标是使用强大的实验工具，在模式植物拟南芥 这两个问题的答案。我们最近发现了几个意想不到的SWR 1相互作用 拟南芥中先前与H2A.Z沉积无关的蛋白质，包括甲基-CpG- 结合结构域9（MBD 9）和已知结合核小体的几种其它蛋白质。我们现在已经观察到， MBD 9是H2 A. Z在一个H2 A. Z富集位点子集上掺入所必需的，这些位点共享一个共同的组蛋白 修饰谱，表明MBD 9和其他SWR 1相关蛋白提供特异性归巢 SWR 1的功能。在目标1中，我们将定义这些蛋白质在H2A.Z靶向中的作用，以便 了解形成这种变异基因组分布的机制。关于转录，我们 最近发现H2A.Z是保守的polycomb系统基因沉默所必需的。中 需要H2A.Z和polycomb系统沉默的基因是磷酸饥饿反应 基因，可以迅速从沉默转化为活跃，并再次通过转移植物之间 富磷酸盐和贫磷酸盐的生长培养基。在目标2中，我们将利用这种诱导型和 阻遏系统，以定义在H2A.Z介导的多梳沉默过程中发生的事件的顺序， 根毛细胞类型，其中磷酸盐浓度的变化首先被植物检测到。我们将遵循这些 在建立或维持阶段对各种参与者进行诱导性基因消融的研究， 为了确定H2A.Z在基因沉默中的作用，强大的基因工具， 拟南芥为理解H2A.Z靶向和功能机制提供了独特的机会， 我们预计这项工作将通过回答长期存在的关于组蛋白变体的问题来推动该领域的发展。 功能我们的研究结果也可能为操纵H2A.Z作为癌症治疗的靶点提供理论基础。

PROJECT SUMMARY The epigenetic system is essential for specifying cell fates during development because it is used to select and reinforce the portions of the genome that will be expressed or silenced in a given cell type. The highly conserved histone H2A variant, H2A.Z, is a key component of this system that is required for embryonic development in animals and regulates many developmental processes in plants. Research has focused on H2A.Z because it has been suggested to play a causal role in both pancreatic and breast cancer cell proliferation, yet its function remains poorly understood. H2A.Z is selectively deposited into chromatin by the SWR1 remodeling complex at thousands of genes, where it paradoxically promotes the transcription of some genes, while silencing others. Despite the biological importance of this histone variant, key questions regarding its targeting and function persist. For example: how is the SWR1 complex targeted to specific genomic sites for H2A.Z deposition? What are the mechanisms by which H2A.Z represses transcription? Given that plants have historically been a rich model system to inform animal epigenetics and that, unlike animals, H2A.Z-deficient plants are viable, our goal is to use the powerful experimental tools available in the model plant Arabidopsis thaliana to answer both of these questions. We recently identified several unexpected SWR1-interacting proteins in Arabidopsis that were not previously associated with H2A.Z deposition, including methyl-CpG- binding domain 9 (MBD9) and several other proteins known to bind nucleosomes. We have now observed that MBD9 is required for H2A.Z incorporation at a subset of H2A.Z-enriched sites that share a common histone modification profile, suggesting that MBD9 and other SWR1-associated proteins provide specific homing functions for SWR1. In Aim 1, we will define the roles of these proteins in H2A.Z targeting in order to understand the mechanisms that shape the genomic distribution of this variant. Regarding transcription, we have recently found that H2A.Z is required for gene silencing by the conserved polycomb system. Among the genes that require H2A.Z and the polycomb system for silencing are the Phosphate Starvation Response genes, which can be rapidly converted from silent to active and back again by shifting plants between phosphate-rich and phosphate-depleted growth media. In Aim 2 we will take advantage of this inducible and repressible system to define the order of events that occur during H2A.Z-mediated polycomb silencing in the root hair cell type, where phosphate concentration changes are first detected by the plant. We will follow these studies with inducible genetic ablation of various players during the establishment or maintenance phases of silencing in order to define the role H2A.Z in gene silencing. The powerful genetic tools available in Arabidopsis provide a unique opportunity to understand the mechanisms of H2A.Z targeting and function, and we anticipate that this work will advance the field by answering long-standing questions about histone variant function. Our results may also provide rationale for manipulation of H2A.Z as a target for cancer therapy.