Regulation of Nephron Progenitor Cell Self-Renewal and Differentiation

描述(申请人提供)：这项拟议工作的长期目标是确定SALL1转录因子及其相关的染色质重塑复合体如何控制基因调控，以产生正常的肾素天赋。这将阐明人类遗传综合征和常见的零星出生缺陷的基础机制，如肾发育不全(肾单位数量减少的小肾脏)，这会导致肾衰竭。形成适当的肾单位补体需要在扩增多潜能的肾祖细胞和分化之间取得平衡。SALL1的遗传缺陷改变了发育中肾脏的基因表达，加速了肾单位的分化，导致肾单位前体细胞的枯竭和肾脏发育不全。这些未被定位的肾单位前体被称为帽间充质，它们必须对典型的Wnt/ss-catenin信号做出反应，要么经历自我更新，要么经历间充质到上皮的转变，形成肾单位的大部分管状节段。控制帽间充质的这些相反反应的转录机制尚不清楚，但目前的证据表明，SALL1在这一关键的发育决定中起着关键作用。我们最近的研究为一种新的范式提供了证据。我们认为SALL1与核小体重塑和脱乙酰酶(NuRD)染色质重塑复合体合作，通过调节Wnt/ss-catenin的转录输出来决定肾单位祖细胞的命运。此应用程序将测试 使用遗传、基因组和生化方法的组合对该模型进行关键预测。SIX2是一种肾单位分化的抑制因子。在目标1中，我们将确定SALL1是否直接上调帽间充质中SIX2的表达，以抑制祖细胞的分化。SALL1突变体中主要分化信号Wnt9b的表达增加。我们会 确定Wnt9b增加和SIX2表达减少的组合是否足以导致肾单位加速形成和自我更新的祖细胞耗尽。目的2将确定SALL1和NuRD如何控制肾单位前体细胞的转录输出，以确定未定位的前体细胞是经历自我更新还是启动肾单位分化。从这些研究中获得的机制见解将促进体外培养肾单位祖细胞和/或促进成熟肾小管上皮细胞的再生，以纠正肾单位缺陷。

DESCRIPTION (provided by applicant): The long-term goal of the proposed work is to determine how the Sall1 transcription factor and its associated chromatin remodeling complexes control gene regulation to generate a normal endowment of nephrons. This will illuminate mechanisms that underlie human genetic syndromes and common sporadic birth defects, such as renal hypoplasia (small kidneys with reduced numbers of nephrons), which result in kidney failure. Formation of the proper complement of nephrons requires a balance between expansion of multi-potent renal progenitor cells and differentiation. Genetic deficiency of Sall1 alters gene expression in the developing kidney, accelerating nephron differentiation leading to a depletion of nephron progenitor cells and renal hypoplasia. These uncommitted nephron precursors, termed cap mesenchyme, must respond to canonical Wnt/ss-catenin signals by either undergoing self-renewal or mesenchymal-to-epithelial transition to form most tubular segments of the nephron. The transcriptional mechanisms that control these opposing responses of the cap mesenchyme are not known, but current evidence argues that Sall1 is pivotal in this critical developmental decision. Our recent studies provide evidence for a novel paradigm. We propose that Sall1 cooperates with the Nucleosome Remodeling and Deacetylase (NuRD) chromatin remodeling complex, to determine nephron progenitor cell fate by regulating the transcriptional output in response to Wnt/ss-catenin. This application will test key predictions of this model using a combination of genetic, genomic, and biochemical approaches. Six2 is an inhibitor of nephron differentiation. In Aim 1, we will determine if Sall1 directly up-regulates Six2 expression in cap mesenchyme to restrain differentiation of progenitor cells. Expression of Wnt9b, the main differentiation signal, is increased in Sall1 mutants. We will determine if the combination of increased Wnt9b and reduced Six2 expression are sufficient to cause accelerated nephron formation, and exhaustion of self-renewing progenitor cells. Aim 2 will determine how Sall1 and NuRD control the transcriptional output in nephron progenitor cells to determine whether the uncommitted precursor cells undergo self-renewal or initiate nephron differentiation. The mechanistic insights gained from these studies will advance efforts to propagate nephron progenitors in vitro and/or promote regeneration of mature tubular epithelial cells in order to correct nephron deficits.