Chromatin Regulation of Tissue Regeneration and Stem Cell Function

再生是一种非凡的现象，它既普遍又神秘；尽管有许多不同之处 动物能够替代受损和/或丢失的结构，目前还不清楚这些再生物种是如何 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，由于再生通常是由自发的和不精确的 组织损伤，细胞如何将广泛而突然的信号转化为特定细胞类型的转录变化？ 转录因子和染色质修饰酶等基因组调节因子共同作用 指示细胞在发育过程中的命运。尽管有大量数据描述了这些 因子协调胚胎发生，但人们对它们如何被激活以诱导再生知之甚少。 我的中心假设是染色质在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引起的细胞变化来激活再生。为了揭开 这一过程背后的基本分子机制，我的实验室研究了 动物再生。平面动物是自由生活的扁虫，具有令人难以置信的再生能力。他们也是 可通过RNAi受遗传干扰，易于分离用于单细胞分析，并编码 染色质修饰蛋白与其他生物中的染色质修饰蛋白具有很强的同源性。我们特别感兴趣的是 一些脊椎动物细胞类型如何通过激活特定的、必要的、再生基因来应对伤害，而 另一些人则会激活一套完全不同的基因座来应对相同的伤害。我的实验室使用多个定制的 方法分离特定类型的脊椎动物细胞，包括分化细胞和干细胞，以表征 损伤前后这些细胞类型的染色质状态。我们还利用数据显示RNAi枯竭 稻纵卷尾藻MLL1/2染色质酶缺失导致其外缘纤毛丧失 上皮组织。此外，我们最近分离并鉴定了一种新的脊椎动物物种，这种物种具有独特的 其外上皮上的纤毛图案，为使用比较基因组方法提供了一个令人兴奋的机会 以确定与这一特定特征相关的特定基因。结合所有这些方法，我们的目标是 剖析特定细胞类型在再生过程中的功能作用和分子信号提示。 在很大程度上，外上皮和其他分化的组织是脊椎动物再生所必需的。 因为它们向维持在体内的异质多能和多能干细胞群体发出信号 成年的行星动物。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 组织信号，它们高度可塑性和转录异质性也就不足为奇了。然而，它确实是 未知它们是如何在体内创造和维持这种异质性的。我们将检验这样的假设：一个守恒的 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跨复杂组织的动态基因调控。

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.