Genetic Control of Ureter and Kidney Development

描述(申请人提供)：先天性肾脏和尿路异常(CAKUT)是人类最常见的出生缺陷之一。其中许多是由于输尿管和肾脏集合管系统发育过程中输尿管芽的诱导、生长和分支的正常过程的改变。这些事件在一定程度上是由信号网络控制的，信号网络包括分泌的生长因子、细胞表面酪氨酸激酶受体、多个细胞内信号通路以及维持信号网络平衡的负反馈机制。GDNF是一种间质来源的生长因子，通过Ret受体酪氨酸激酶和辅助受体Gfr11向输尿管芽上皮细胞发出信号。在小鼠模型中，GDNF信号在输尿管和肾脏发育中起主要作用，而在人类中，RET和GDNF突变与肾脏发育不全有关。RET激活几种细胞内机制，包括Erk MAP激酶通路，对Ret的反应通过细胞内蛋白Sprouty1的反馈调节来控制。虽然Sprouty1被认为在Erk MAP激酶途径中起主要作用，但其机制尚不清楚。然而，很明显，Sprouty1提供的负反馈是至关重要的，因为它的缺失会导致多个异位输尿管、输尿管积水、多个肾脏的集合管异常分支，以及肾囊肿。这一建议侧重于酪氨酸激酶信号网络，该网络控制输尿管芽的正常生长，形成单一的、正确定位的输尿管，然后在肾脏发育过程中调节其复杂的生长和分支模式。以小鼠为模型系统，我们采用了多种遗传学方法来研究三个相关问题。首先，我们研究了Sprouty1阻止输尿管芽细胞对GDNF和其他生长因子(如FGFs)过度反应的机制，以及它的缺失如何导致输尿管芽衍生上皮的畸形和囊肿。接下来，我们调查了一项意想不到的发现，即当Sprouty1提供的负面调节也被移除时，完全缺乏GDNF或Ret的小鼠的输尿管和肾脏有时可以发育到晚期。这表明，积极刺激和消极反馈之间的平衡可能比任何一种生长因子的具体影响更重要。这也意味着，通过不同的酪氨酸激酶受体发出信号的其他生长因子在很大程度上必须与GDNF重叠，因为它具有促进输尿管和集合管的生长和分支的能力。因此，我们研究了几种候选因子，包括成纤维细胞生长因子(FGFs)和肝细胞生长因子(HGF)在这些过程中的作用。这项建议将通过提供对调节正常输尿管和肾脏发育的多层控制机制的更深入了解来推动该领域的发展，并可能提出预防或治疗CAKUT的新方法。最常见的出生缺陷类型是那些影响肾脏和尿路的缺陷。这些异常包括导致尿路梗阻的异常，以及那些缩小肾脏大小和功能并可能导致高血压的异常。通过识别控制输尿管和肾脏生长的基因和蛋白质，从一小群细胞到一个复杂的器官，最终可能预防或修复这种出生缺陷。

DESCRIPTION (provided by applicant): Congenital abnormalities of the kidney and urinary tract (CAKUT) are among the most common birth defects in humans. Many of them result from alterations in the normal processes of ureteric bud induction, growth, and branching during the development of the ureter and the renal collecting duct system. These events are controlled, in part, by signaling networks that include secreted growth factors, cell-surface tyrosine kinase receptors, multiple intracellular signaling pathways, and negative feedback mechanisms that keep the signaling networks in balance. GDNF is a mesenchymally-derived growth factor that signals to the ureteric bud epithelium via the Ret receptor tyrosine kinase and the co-receptor Gfr11. In mouse models, GDNF signaling plays a major role in ureter and kidney development, and in humans, RET and GDNF mutations are associated with renal agenesis. Ret activates several intracellular mechanisms, including the Erk MAP kinase pathway, and the response to Ret is controlled through feedback regulation by the intracellular protein Sprouty1. While Sprouty1 is thought to act primary on the Erk MAP kinase pathway, its mechanism is not well understood. However, it is clear that the negative feedback provided by Sprouty1 is critical, as its absence leads to multiple and ectopic ureters, hydroureter, multiplex kidneys with abnormal branching of collecting ducts, and renal cysts. This proposal focuses on the tyrosine kinase signaling networks that control the normal outgrowth of the ureteric bud to form a single and correctly positioned ureter, and then regulate its complex patterns of growth and branching during kidney development. Using the mouse as a model system, we employ a variety of genetic approaches to investigate three related issues. First, we examine the mechanism by which Sprouty1 prevents ureteric bud cells from over-responding to GDNF and other growth factors such as FGFs, and how its absence leads to malformations and cysts in the ureteric bud-derived epithelium. Next, we investigate the unexpected finding that ureters and kidneys can sometimes develop to an advanced stage in mice completely lacking GDNF or Ret, when the negative regulation provided by Sprouty1 is also removed. This suggests that a balance between positive stimuli and negative feedback is perhaps more important than the specific effects of any one growth factor. It also implies that other growth factors that signal through different tyrosine kinase receptors must overlap, to a large degree, with GDNF in its ability to promote and pattern growth and branching of the ureter and collecting ducts. We therefore investigate the roles of several candidates, including fibroblast growth factors (FGFs) and hepatocyte growth factor (HGF), in these processes. This proposal will advance the field by providing a deeper understanding of the multilayered control mechanisms that mediate development of a normal ureter and kidney, and may suggest new ways to prevent or treat CAKUT. Among the most common types of birth defects are those affecting the kidneys and urinary tract. These include abnormalities causing urinary tract obstruction, as well as those that reduce the size and function of the kidney and can lead to hypertension. By identifying the genes and proteins that control the growth of the ureter and kidney from a small group of cells to a complex organ, it may eventually be possible to prevent or repair such birth defects.