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

总结 自我更新是创造和维持许多组织和器官，包括人类， 上皮、肌肉和血液系统。这些组织中的每一个都建立了自我更新的种群， 干细胞必须确保这些干细胞分裂，并在细胞周期中产生新的分化细胞。 适当的速度和在适当的地方;没有足够的细胞或分裂和组织将 恶化，太多的分裂和肿瘤可以形成。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 并且分化受到与邻近细胞的相互作用的影响。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 使得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。 在我们以前的工作中，我们发现三个bHLH转录因子和MAPK的组分， 在气孔发育的不连续阶段，信号通路调节分裂与分化的选择。 基于遗传、生物化学和功能测定的数据，我们提出， 在这三个人中，最早行动的bHLH，SPEECHLESS（SPCH），控制着不对称的分裂， 自我更新的人口。我们表明，SPCH是MAP激酶依赖性的直接靶点。 在体外，磷酸化改变了SPCH的行为，并且磷酸化改变了体内SPCH的行为。我们的具体 本研究的目的是：（1）阐明SPCH活性的分子机制， （2）建立气孔谱系细胞的分子谱，并在功能上鉴定 表征这些细胞中SPCH的转录靶点，以及（3）利用SPCH诱导的转录靶点， 表型，从遗传上剖析抑制干细胞所需的内源性信号网络， 分化因为bHLH类转录调节因子和MAPK途径都是 普遍保守，这些研究不仅有助于理解自我更新， 将有助于我们理解MAPK和bHLH信号传导机制的多样性， 应答

Summary 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.