The Role of Bicaudal-C in Polycystic Kidney Disease

描述(申请人提供)：多囊肾疾病(PKD)是终末期肾功能衰竭的主要原因，其特征是沿整个肾单位发展肾囊肿。它们需要广泛的治疗，如透析和肾移植。由于肾囊肿形成的分子机制仍然知之甚少，目前对PKD的治疗形式有限。多年来，在鉴定人类形式的PKD突变基因以及研究这些有害疾病的发病机制的动物模型方面取得了相当大的进展。除了小鼠和大鼠的PKD模型外，更原始的非洲爪哇或斑马鱼的前肾已成为研究上皮畸形导致PKD的分子机制的替代模型系统。原肾发展迅速，分子操作简便，是研究人或小鼠PKD的理想伴侣系统。在这个方案中，我们将使用小鼠后肾和两栖动物前肾来研究RNA结合分子Bicaudal-C。缺乏Bicaudal-C蛋白的小鼠在胚胎15.5天就会出现肾囊肿。囊性形成首先在肾小球中检测到，但随后可沿整个肾单位检测到。同样，在非洲爪哇，双尾C的缺失会导致前肾出现“PKD样”表型。重要的是，肾脏发育过程中Bicaudal-C活性的分子机制及其与多囊蛋白-1、多囊蛋白-2和多囊蛋白/纤维囊蛋白基因突变的关系尚不清楚。这项提案将解决这些问题。我们将验证Bicaudal-C是多囊肾病相关基因的翻译调节因子的假设。它基于四个观察：(1)Bicaudal-C突变小鼠在囊形成开始之前就已经降低了Polycystin-2mRNA和蛋白的水平。(2)多囊蛋白-2的调控是转录后调控。(3)Bicaudal-C蛋白定位于P小体，已在果蝇和线虫中发现，在转录后水平上调节一组选定的mRNAs。(4)许多PKD基因的3‘非编码区都有进化保守的miRNA结合位点。如果成功，这项研究将为PKD肾囊肿形成的潜在生物学和生化途径提供新的见解。它将把最少被理解的PKD基因之一整合到现有的PKD范例中。因此，它将直接适用于未来对PKD的研究，并可能为治疗干预提供一个新的角度。

DESCRIPTION (provided by applicant): Polycystic Kidney Diseases (PKD) are the leading cause of end-stage renal failure and are characterized by the development of renal cysts along the entire length of the nephron. They require extensive treatments, such as dialysis and kidney transplantation. Only limited forms of therapy for PKD exist, since the molecular mechanisms underlying the formation of renal cysts are still poorly understood. Over the years, considerable progress has been made in identifying genes mutated in human forms of PKD and in the development of animal models to study the pathogenesis of these detrimental diseases. Besides mouse and rat PKD models, the more primitive pronephric kidney of Xenopus or zebrafish has emerged as an alternative model system to study the molecular mechanisms underlying the epithelial malformations causing PKD. With its fast development and ease of molecular manipulations, the pronephric kidney is an ideal companion system to the study of PKD in humans or mice. In this proposal we will use the mouse metanephros and the amphibian pronephros to study the RNA binding molecule Bicaudal-C. Mice lacking Bicaudal-C protein develop renal cysts as early as embryonic day 15.5. Cyst formation is first detected in the glomerulus, but can later be detected along the entire length of the nephron. Similarly, in Xenopus, loss-of-Bicaudal-C induces a "PKD-like" phenotype in the pronephros. Importantly, the molecular mechanism of Bicaudal-C activity in kidney development and its connection to the genes mutated in human PKD, i.e. Polycystin-1, Polycystin-2 and Polyductin/Fibrocystin is still not understood. This proposal will address these questions. We will test the hypothesis that Bicaudal-C is a translational regulator of genes involved in Polycystic Kidney Disease. It is based on four observations: (1) Bicaudal-C mutant mice have reduced Polycystin-2 mRNA and protein levels before the onset of cyst formation. (2) The regulation of Polycystin-2 is posttranscriptional. (3) Bicaudal-C protein is localized to P-Bodies and has been shown in Drosophila and C. elegans to regulate a selected group of mRNAs at the posttranscriptional level. (4) Many PKD genes have evolutionary conserved miRNA binding sites in their 3' UTR. If successful, this study will provide novel insights to the underlying biological and biochemical pathways leading to the renal cyst formation in PKD. It will integrate one of the least understood PKD genes into the existing paradigms of PKD. As such, it will be directly applicable to future studies of PKD and may provide a new angle for therapeutic interventions.