Cell Fate Regulation of Nephron Progenitors

描述(申请人提供)：正常肾脏中的肾单位数目有很大的差异。低肾单位数与高血压和各种肾脏疾病相关。为了在发育过程中产生足够数量的肾单位，平衡肾单位祖细胞的自我更新(增殖)和分化(消耗)是至关重要的。自我更新的未分化肾单位祖细胞表达SIX2，这是维持未分化状态所必需的转录因子。这些细胞的分化包括 多种信号通路，其中最关键的两条是Wnt/β-catenin和Notch。虽然Wnt信号启动了祖细胞的分化，但Notch信号需要进一步 分化为近端小管。我们最近发表的研究表明，SIX2和β-catenin通过一组共同的基因调控元件相互对抗，从而调节肾单位祖细胞的自我更新和分化。尽管如此，人们对调控肾单位祖细胞命运的基因调控网络知之甚少。我们的初步数据表明，SIX2和Notch2通过调节共同靶基因的表达在肾脏发育过程中发挥重要作用，而Hox蛋白参与了与Notch2相同的基因调控网络。我们的目标是更好地了解SIX2、Hox和Notch2是如何调控肾单位祖细胞的细胞命运的，以及肾单位如何通过Notch组件与肾单位特有的转录因子(如SIX2和HoxD11)之间的相互作用来以特定于上下文的方式解释Notch信号。为了解决这一问题，我们建议(1)检验SIX2和Notch2在常见顺式调节元件上分别作为抑制物和激活物的假说，以及(2)检验HoxD11在肾脏形成过程中作为Notch信号介体的假说。肾单位祖细胞的细胞命运由多种转录因子和信号通路的复杂协调决定。关键是要确定哪些靶基因受转录因子的调控，并确定肾单位祖细胞如何解释来自不同信号通路的指令。此外，了解每个信号通路下游的多个转录调控因子是如何被协调的，不仅对于提高我们操纵肾祖细胞进行潜在细胞替代治疗的能力至关重要，而且对于开发更好的方法来预防或治疗肾脏发育不全或发育不全至关重要。这项研究的结果将加强我们对细胞命运决定的分子机制的了解，并将通过更好地了解肾脏发育中的基因调控网络，推动肾病学领域的发展。这项工作是与Hox基因、RNA-Seq分析和肾脏发育方面的专家Steve Potter和生物信息学专家Sunghee oh的密切合作，他们都是我在辛辛那提儿童医院的同事。

DESCRIPTION (provided by applicant): The number of nephrons in a normal kidney shows a wide variation. Low nephron number is correlated with high blood pressure and various renal diseases. In order to generate a sufficient number of nephrons during development, it is critical to balance self-renewal (proliferation) and differentiation (consumption) of nephron progenitors. Self-renewing undifferentiated nephron progenitors express Six2, a transcription factor that is required for the maintenance of the undifferentiated state. Differentiation of these cells involves multiple signaling pathways, two of the most critical being Wnt/beta-catenin and Notch. While Wnt signaling initiates differentiation of the progenitors, Notch signaling is required for further differentiation into proximal tubules. Our recent publication showed that Six2 and Beta-catenin regulate self-renewal and differentiation of nephron progenitors by antagonizing each other through a common set of gene regulatory elements. Still, little is known about the gene regulatory networks regulating the cell fate of nephron progenitors. Our preliminary data suggest that Six2 and Notch2 play important roles during kidney development by regulating expression of common target genes and that Hox proteins participate in the same gene regulatory networks as Notch2. Our goal is to better understand how the cell fate of nephron progenitors is regulated by Six2, Hox, and Notch2, and how nephron progenitors interpret Notch signaling in a context-specific manner through interaction between Notch components and nephron progenitor-specific transcription factors, such as Six2 and HoxD11. To address this, we propose to (1) test the hypothesis that Six2 and Notch2 act as a repressor and an activator, respectively, on common cis-regulatory elements and to (2) test the hypothesis that HoxD11 acts as a mediator of Notch signaling during nephrogenesis. Cell fate decisions of nephron progenitors are determined by complex coordination of multiple transcription factors and signaling pathways. It is critical to identify which target genes are regulated by the transcription factors and to determine how the instructions from various signaling pathways are interpreted by nephron progenitors. Furthermore, understanding how multiple transcriptional regulators downstream of each signaling pathway are orchestrated is essential not only to improve our ability to manipulate nephron progenitors for potential cell replacement therapies but also to develop better ways to prevent or treat renal agenesis or hypoplasia. The results of the proposed research will enhance our knowledge of molecular mechanisms of cell fate decisions and will advance the field of nephrology by providing a better understanding of gene regulatory networks in kidney development. This work is a close collaboration with Steve Potter, an expert in Hox genes, RNA-seq analysis and kidney development, and with Sunghee Oh, an expert in bioinformatics, both my colleagues at Cincinnati Children's Hospital.