Hypospadias: Morphogenesis of the Proximal Urethra

描述(申请人提供)：尿道下裂是一种先天性缺陷，其特征是阴茎腹侧的异位开放的尿道口。它是男性最常见的出生缺陷之一，发病率为每125名活产儿中就有一名。目前，唯一的治疗方法是 尿道下裂是一种手术。尿道下裂的高发病率反映了其多重原因。研究发现，胚胎在环境中暴露于内分泌干扰性化学物质会增加尿路下裂的发生率。此外，还有一些由基因突变引起的综合征形式的尿道下裂。然而，尽管最近在了解外生殖器发育方面取得了进展，但仍然不清楚遗传或环境信号是如何影响外生殖器发育的。尿路由一块内胚层来源的上皮细胞组成，它被发育中的外生殖器的中胚层或生殖器结节(GT)所包围。尿道板上皮空化形成尿道管，不能保持尿道管的完整性会导致尿道下裂。在GT的发育过程中，GT底部的外胚层开口暴露出下面的尿道管，在男性和女性胚胎中都存在，但这种近端的尿道口在雄性胚胎后期关闭，而在雌性胚胎中保持，成为阴道开口。有趣的是，许多病例发生在阴茎近端，这导致了一种假说，即PUO的形态发生缺陷会导致近端的尿道下裂。为了解决这一假设，这项提议将利用三种互补的方法。这项建议的目标1将研究在雄性小鼠GT发育过程中控制PUO正常形成和关闭的细胞事件。目的2将通过检测BMP2和FGFR2突变体中基因表达和细胞事件的变化来解决PuO形态发生的分子控制。BMP2和FGFR2均在Puo区表达，FGFR2突变体的Puo形态发生存在缺陷。最后，目标3将研究导致红耳滑龟Trachemys Scripta自然出现开放尿路的细胞和分子机制。这一目标将允许确定新的机制，对维持尿道闭合很重要。这项建议的发现不仅将增加外生殖器正常发育的知识，还将确定导致尿道下裂产生的机制。这可能会对预防尿道下裂的方法的发展产生更广泛的影响。此外，T.Scripta的工作将有助于确定与尿道下裂发生有关的因素，并可能导致一种新的模型系统，用于研究卵子中的尿道下裂。 与公共卫生相关：尿道下裂是一种尿道管闭合缺陷，是最常见的出生缺陷之一，每125名男性新生儿中就有一例发生；然而，导致尿道下裂的原因尚不清楚。这项建议将研究近端尿道口的形态发生，这是一种在男性和女性中都形成的结构，但在男性的晚期通常是关闭的。由于关闭近端尿道口的缺陷会导致男性的尿道下裂，这项研究将提供对导致近端尿道下裂的分子和细胞机制的洞察。

DESCRIPTION (provided by applicant): Hypospadias is a congenital defect characterized by an ectopic opening of the urethra on the ventral side of the penis. It is one of the most common birth defects in males with an incidence of 1 in 125 live births. Currently, the only treatment for hypospadias is surgery. The high incidence of hypospadias is reflective of its multiple causes. Studies have found that environmental exposure of embryos to endocrine disrupting chemicals increases the rate of hypospadias. Additionally, there are syndromic forms of hypospadias that result from genetic mutations. However, in spite of recent progress in understanding external genitalia development it is still not clear exactly how genetic or environmental signals are influencing external genitalia development. The urethra is formed from a plate of endodermally derived epithelium that is surrounded by the mesoderm of the developing external genitalia, or genital tubercle (GT). The urethral plate epithelium cavitates to form the urethral tube, and failure to maintain the integrity of this tube leads to hypospadias. During development of the GT, an ectodermal opening at the base of the GT exposes the underlying urethral tube and occurs in both male and female embryos, but this proximal urethral opening (puo) is closed at later stages in males while it is maintained in females to become the vaginal opening. Interestingly, many cases of hypospadias occur in the proximal penis leading to the hypothesis that defective morphogenesis of the puo causes proximal hypospadias. To address this hypothesis, this proposal will utilize three complimentary approaches. Aim 1 of this proposal will examine the cellular events that control normal formation and closure of the puo during development of the male mouse GT. Aim 2 will address molecular control of puo morphogenesis through examination of changes in gene expression and cellular events in Bmp2 and Fgfr2 mutants. Both Bmp2 and Fgfr2 are expressed in the puo region, and Fgfr2 mutants show defective puo morphogenesis. Finally, Aim 3 will examine the cellular and molecular mechanisms that lead to the naturally occurring open urethra in the red-eared slider turtle Trachemys scripta. This aim will allow for the identification of novel mechanisms important for maintaining urethral closure. Findings from this proposal will not only add to the knowledge of how external genitalia normally develop, but will also identify mechanisms that lead to the generation of hypospadias. This could have broader implications in the development of methods to prevent hypospadias. Additionally, work in T. scripta will aid in determining factors that are involved in the generatio of hypospadias and may lead to a novel model system for studying hypospadias in ovo. PUBLIC HEALTH RELEVANCE: Hypospadias, a defect in urethral tube closure, is one of the most common birth defects occurring in 1 in 125 male births; however, the cause of hypospadias is not clear. This proposal will examine morphogenesis of the proximal urethral opening, a structure that forms in both males and females, but is normally closed at later stages in males. As defective closure of the proximal urethral opening would lead to hypospadias in males, this research will provide insight into the molecular and cellular mechanisms that lead to hypospadias in the proximal urethra.