Control of epidermal self-renewing populations by bHLH and MAPK regulatory system

描述（由申请人提供）：自我更新是许多组织和器官包括人体上皮、肌肉和血液系统的创建和维护的组成部分。这些组织中的每一个都建立了自我更新（干细胞）的群体，并且必须确保这些干细胞以适当的速度在适当的位置分裂并产生新的分化细胞；没有足够的细胞或分裂，组织就会恶化，分裂太多，就会形成肿瘤。我们的长期目标是了解分散的自我更新种群建立的机制，以及它们的分裂和分化如何受到与邻近细胞相互作用的影响。一套强大的遗传、分子和功能基因组工具，结合可视化和跟踪细胞分裂的能力，使拟南芥气孔发育成为研究这一系列问题的一个有吸引力的系统。在我们之前的工作中，我们发现bHLH转录因子和MAPK通路的三个组成部分在气孔发育的不同阶段调节分裂和分化的选择。基于遗传、生化和功能分析的数据，我们提出这三个基因中起作用最早的bHLH （SPCH）的活性控制了产生自我更新群体的不对称分裂。我们发现SPCH在体外是MAP激酶依赖性磷酸化的直接靶点，磷酸化改变了SPCH在体内的行为。我们的具体目标是：(1)阐明SPCH活性调控的分子机制；(2)建立气孔系细胞的分子图谱，并鉴定这些细胞中SPCH的转录靶点，并对其进行功能表征；(3)利用SPCH诱导的表型，从遗传学上剖析抑制干细胞分化所需的内源信号网络。由于bHLH类转录调控因子和MAPK通路都是普遍保守的，这些研究可能不仅有助于理解自我更新，而且有助于我们理解MAPK和bHLH信号传导机制和反应的多样性。公共卫生相关性：成体干细胞被要求在损伤或疾病后再生或修复组织。然而，这些相同的茎的过度分裂会导致癌症。因此，拟议的研究将有助于提供诱导干细胞分化为特定组织的策略，同时限制癌症过度生长的可能性。

DESCRIPTION (provided by applicant): Self renewal is integral to the creation and maintenance of many tissues and organs including human epithelia, muscle and blood systems. Each of these tissues establishes populations of self-renewing (stem) cells and must ensure that these stem cells divide and create new differentiated cells at the appropriate rate and in the appropriate place; not enough cells or divisions and the tissue will deteriorate, too many divisions and tumors can form. Our long term goal is to understand the mechanism(s) by which dispersed self-renewing populations are established and how their division and differentiation is influenced by interaction with neighboring cells. A powerful set of genetic, molecular and functional genomic tools, combined with the ability to visualize and track cell divisions makes Arabidopsis stomatal development an attractive system for investigating this set of questions. In our previous work we found that a trio of bHLH transcription factors and components of a MAPK pathway modulate division vs. differentiation choices at discrete stages in stomatal development. Based on data from genetic, biochemical and functional assays, we propose that activity of the earliest-acting bHLH in this trio, SPEECHLESS (SPCH), controls the asymmetric divisions that create the self-renewing populations. We show that SPCH is a direct target of MAP kinase-dependent phosphorylation in vitro, and that phosphorylation alters the behavior of SPCH in vivo. Our specific aims in this proposal are to: (1) elucidate the molecular mechanisms by which SPCH activity is regulated (2) Create a molecular profile of stomatal lineage cells and identify and functionally characterize transcriptional targets of SPCH in these cells, and (3) Take advantage of SPCH-induced phenotypes to genetically dissect the endogenous signaling network required to repress stem-cell differentiation. Because both the bHLH class of transcriptional regulators and the MAPK pathway are universally conserved, these studies may contribute not only to an understanding of self-renewal, but will contribute to our understanding of the diversity of MAPK and bHLH signaling mechanisms and responses. PUBLIC HEALTH RELEVANCE: Adult stem cells are called upon to regenerate or repair tissues following injury or disease. However, excess division of those same stems can lead to cancer. The proposed studies will thus help to inform strategies to induce stem cells to differentiate into specific tissues while restricting the potential for cancerous overgrowth.