Ureteric Bud Patterning

描述（由申请人提供）：哺乳动物肾脏的发育依赖于输尿管芽。它的近端在发育中的肾脏中诱导肾元形成，并经历分支形态形成肾内集合系统，而其远端或主干区域分化为输尿管。输尿管芽形态发生的异常调节可导致一系列先天性缺陷，最常见的是输尿管重复和梗阻。然而，限制输尿管数量和控制输尿管平滑肌分化的组织相互作用和信号通路仍然知之甚少，而输尿管平滑肌分化是尿液畅通无阻地流向膀胱所必需的。这一建议的重点是输尿管形态发生。在Aim 1中，Bmp信号在限制输尿管芽沿尿路向单个位点生长和控制输尿管平滑肌分化中的作用将在Bmp4基因剂量严重敲低的小鼠中进行分析，Bmp4基因剂量可支持胚胎存活至出生，但不能超过胚胎存活。可诱导的Bmp4敲除将使用Cre-lox技术和现有的小鼠品系来完成。Bmp4将在不同的发育阶段被敲低，从其控制输尿管末端分化的作用出发，分别分析该信号因子在调控输尿管数量中的作用。在目的2中，我们将分析缺乏Pbx1（一种hox基因辅助因子）表达的小鼠系。我们发现Pbx1对于限制Bmp4信号传导和输尿管平滑肌形成至关重要。这个突变系将被用来解剖控制肾脏和输尿管交界处平滑肌组织的遗传途径和细胞类型，这是新生儿尿路梗阻最常见的部位。这些实验的成功完成将有助于深入了解输尿管形态发生对先天性缺陷的易感性。公共卫生相关性：输尿管是一种将废物从肾脏输送到膀胱的肌肉管，人类很容易出现先天性缺陷。然而，在胚胎发育过程中，输尿管形成的机制尚不清楚。在本提案中，我们将检验几种解释该尿道段对缺陷易感性的假设。

DESCRIPTION (provided by applicant): Mammalian renal development is dependent on the ureteric bud. Its proximal tip induces nephron formation in the developing kidney and undergoes branching morphogenesis forming the intra-renal collecting system whereas its distal or trunk domain differentiates into the ureter. Abnormal regulation of ureteric bud morphogenesis can result in a spectrum of congenital defects, the most common being ureteral duplications and obstructions. Yet the tissue interactions and signaling pathways that limit ureter number and control ureteral smooth muscle differentiation required for the un-obstructed flow of urine to the bladder remain poorly understood. This proposal is focused on ureter morphogenesis. In Aim 1, the role of Bmp signaling in restricting ureteric bud outgrowth to a single site along the urinary tract and in controlling ureteral smooth muscle differentiation will be analyzed in mice with a severe knockdown in Bmp4 gene dosage that supports embryonic viability to birth, but not beyond. Inducible Bmp4 knockdown will be accomplished using Cre-lox technology and existing mouse lines. Bmp4 will be knocked down at different stages of development to analyze the role of this signaling factor in regulating ureter number separately, from its role in controlling terminal ureter differentiation. In Aim 2, we will analyze a mouse line lacking expression of Pbx1, a hox gene cofactor. We have discovered that Pbx1 is essential for restricting Bmp4 signaling and smooth muscle formation to the ureter. This mutant line will be used to dissect the genetic pathways and cell type (s) that control the organization of smooth muscle at the border between the kidney and the ureter, the most common site of urinary tract obstructions in newborns. The successful completion of these experiments will provide insight into the susceptibility of ureter morphogenesis to congenital defects. PUBLIC HEALTH RELEVANCE: The ureter, a muscular tube that transports waste products from the kidneys to the bladder, is highly prone to congenital defects in humans. However, the mechanisms guiding ureter formation in the developing embryo remain poorly understood. In this proposal, we will test several hypotheses explaining the susceptibility of this urinary tract segment to defects.