Chromatin Regulation of Tissue Regeneration and Stem Cell Function

再生是一个显着的现象，既普遍存在，又神秘;虽然许多不同的 动物能够替换受损和/或丢失的结构，但目前尚不清楚这些再生物种如何 保持组织完整性所需的细胞稳定性和重新激活所需的细胞可塑性 损伤后的组织发育。此外，由于再生往往是由自发的和不精确的 组织损伤时，细胞如何将广泛和突然的信号转化为细胞类型特异性的转录变化？ 基因组调节因子如转录因子和染色质修饰酶共同作用， 在发育过程中指导细胞命运。尽管有大量数据描述了这些 尽管这些因子协调胚胎发生，但对它们如何被激活以诱导再生的了解要少得多。 我的中心假设是，染色质在被触发的信号事件之间起着中介作用 通过显著的组织损失和它们诱导的细胞变化来激活再生。将查清 作为这一过程的基础分子机制，我的实验室研究了 动物再生Planarians是自由生活的扁形虫，具有惊人的再生能力。他们也是 易于通过RNAi进行遗传干扰，易于分离用于单细胞分析，并编码 与其他生物体中的染色质修饰蛋白具有很强同源性的染色质修饰蛋白。我们特别感兴趣 一些真涡虫细胞类型如何通过激活特定的、必需的再生基因对损伤做出反应， 另一些则对同样的损伤激活完全不同的一组基因座。我的实验室使用多种定制的 分离特定的真涡虫细胞类型（分化细胞和干细胞）的方法，以表征真涡虫细胞的特征。 染色质状态的这些细胞类型之前和之后的损伤。我们还利用数据表明， MLL 1/2染色质酶在涡虫Schmidtea medialacea中的表达导致其外部纤毛的丧失， 上皮此外，我们最近分离并鉴定了一种新的Planarian物种， 纤毛模式，提供了一个令人兴奋的机会，使用比较基因组方法 来鉴定与这种特殊性状相关的特定基因。结合所有这些方法，我们的目标是 剖析再生过程中特定细胞类型的功能作用和分子信号线索。 外上皮和其他分化的组织在很大程度上是涡虫再生所必需的 因为它们向维持在细胞中的异质性多能和多能干细胞群体发出信号， 成年真涡虫因为这些干细胞必须分化成所有需要的细胞类型，以应对缺失的细胞。 组织信号，它们是高度可塑性和转录异质性的，这并不奇怪。但它是 目前尚不清楚它们如何在体内产生和维持这种异质性。我们将检验一个保守的 染色质签名调节这一关键特征。这些研究将揭示潜在的重要机制 再生和其他生物过程都需要在复杂组织中进行动态基因调控。

Regeneration is a remarkable phenomenon that is both ubiquitous and mysterious; although many different animals are capable of replacing damaged and/or lost structures, it is unclear how these regenerative species maintain both the cellular stability required for tissue integrity and the cellular plasticity needed to reactivate tissue development upon injury. Moreover, as regeneration is often induced by spontaneous and imprecise tissue damage, how do cells translate broad and sudden signals into cell-type-specific transcriptional changes? Genomic regulators such as transcription factors and chromatin-modifying enzymes work together to instruct cell fate during developmental processes. Although there is substantial data describing how these factors orchestrate embryogenesis, much less is known about how they are activated to induce regeneration. My central hypothesis is that chromatin serves as a mediator between the signaling events that are triggered by significant tissue loss and the cellular changes they induce to activate regeneration. To uncover the fundamental molecular mechanisms underlying this process, my laboratory studies the planarian model of animal regeneration. Planarians are free-living flatworms with incredible regenerative capacities. They are also amenable to genetic perturbation through RNAi, easily dissociated for single cell analyses, and encode chromatin modifying proteins with strong homology to those in other organisms. We are particularly interested in how some planarian cell types respond to injury by activating specific, essential, regeneration genes, while others activate an entirely different set of loci in response to the same injury. My lab uses multiple customized methods to isolate specific planarian cell types, both differentiated and stem cells, in order to characterize the chromatin state of these cell types before and after injury. We also leverage data showing that RNAi depletion of the MLL1/2 chromatin enzyme in the planarian Schmidtea mediterranea leads to loss of cilia on its outer epithelium. In addition, we have recently isolated and characterized a new planarian species that has a unique cilia pattern on its outer epithelium, providing an exciting opportunity to use comparative genomic approaches to identify specific genes that are linked to this particular trait. Combining all these approaches, we aim to dissect the functional role and molecular signaling cues contributed by specific cell types during regeneration. The outer epithelium and other differentiated tissues are essential for planarian regeneration in large part because they signal to a population of heterogeneous multi and pluripotent stem cells that are maintained in adult planarians. Because these stem cells must differentiate into all needed cell types in response to missing tissue signals, it is not surprising that they are highly plastic and transcriptionally heterogeneous. Yet it is unknown how they create and maintain this heterogeneity in vivo. We will test the hypothesis that a conserved chromatin signature regulates this critical feature. These studies will uncover important mechanisms underlying both regeneration and other biological processes that require dynamic gene regulation across complex tissues.