Genetic Control of Ureter and Kidney Development

描述（由申请人提供）：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集管系统发育过程中输尿管芽诱导、生长和分支的正常过程的改变。这些事件在一定程度上由信号网络控制，包括分泌的生长因子、细胞表面酪氨酸激酶受体、多种细胞内信号通路和保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受体酪氨酸激酶和共受体Gfr11向输尿管芽上皮发出信号。在小鼠模型中，GDNF信号传导在输尿管和肾脏发育中起主要作用，而在人类中，RET和GDNF突变与肾脏发育有关。Ret激活多种细胞内机制，包括Erk MAP激酶途径，对Ret的反应通过细胞内蛋白Sprouty1的反馈调节来控制。虽然Sprouty1被认为主要作用于Erk MAP激酶途径，但其机制尚不清楚。然而，Sprouty1提供的负反馈很明显是至关重要的，因为它的缺失会导致多路和异位输尿管、输尿管积水、集管分支异常的多路肾脏和肾囊肿。本研究的重点是酪氨酸激酶信号网络控制输尿管芽的正常生长，形成一个单一的、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，我们采用多种遗传方法来研究三个相关问题。首先，我们研究了Sprouty1防止输尿管芽细胞对GDNF和其他生长因子（如FGFs）过度反应的机制，以及Sprouty1的缺失如何导致输尿管芽源性上皮的畸形和囊肿。接下来，我们研究了一个意想不到的发现，即当Sprouty1提供的负调控也被去除时，输尿管和肾脏有时可以在完全缺乏GDNF或Ret的小鼠中发育到晚期。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素的特定影响更重要。这也意味着其他通过不同酪氨酸激酶受体发出信号的生长因子在很大程度上必须与GDNF在促进和模式输尿管和集合管的生长和分支的能力上重叠。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。这一建议将通过提供对介导正常输尿管和肾脏发育的多层控制机制的更深入理解来推进该领域，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影响肾脏和泌尿道的缺陷。这些异常包括引起尿路阻塞的异常，以及那些使肾脏的大小和功能减小并可能导致高血压的异常。通过识别控制输尿管和肾脏从一小群细胞到一个复杂器官生长的基因和蛋白质，最终有可能预防或修复这类先天缺陷。

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.