Ureteric Bud Patterning

描述(申请人提供)：哺乳动物肾脏的发育依赖于输尿管芽。它的近端诱导发育中的肾脏形成肾单位，并经历分枝形态发生，形成肾内收集系统，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，这是尿流通畅到膀胱所必需的。这项建议的重点是输尿管的形态发生。在目标1中，将在Bmp4基因剂量严重下调的小鼠中分析BMP信号在限制输尿管芽沿尿路的单个位置生长和控制输尿管平滑肌分化中的作用，Bmp4基因剂量支持胚胎存活到出生，但不是更高。可诱导的Bmp4击倒将使用Cre-lox技术和现有的鼠标系列来完成。BMP4将在不同的发育阶段被下调，以分别分析该信号因子在调节输尿管数量中的作用，以及它在控制输尿管末端分化中的作用。在目标2中，我们将分析一个缺乏Hox基因辅因子Pbx1表达的小鼠株系。我们发现Pbx1对于限制Bmp4信号和输尿管的平滑肌形成是必不可少的。这一突变系将被用来剖析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(S)，输尿管交界处是新生儿最常见的尿路梗阻部位。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。与公共卫生相关：输尿管是一种肌肉管道，将废物从肾脏输送到膀胱，在人类中极易发生先天性缺陷。然而，指导胚胎发育中输尿管形成的机制仍然知之甚少。在这项提案中，我们将检验几个解释这一尿路段对缺陷易感性的假说。

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.