EXTERNAL GENITALIA DEVELOPMENT AND HYPOSPADIAS

描述(由申请人提供)：包括尿道下裂在内的生殖器畸形是仅次于心脏缺陷的第二大常见男性出生缺陷。在过去的40年里，随着其他男性生殖问题的出现，尿道下裂的发生率翻了一番。据推测，胎儿接触内分泌干扰物可能是导致这种增加的原因之一。然而，一般情况下，我们对尿道下裂或生殖器发育的病因的了解仍然非常有限。我们的初步研究令人信服地证明了两个信号通路Shh和Wnt在外生殖器发育的早期雄激素非依赖性和晚期性别二型性发育中的重要性。在早期生殖器结节(GT)发育过程中，当规范的Wnt通路在尿路上皮细胞中受到干扰时，就会发生严重的生殖器畸形。在外胚层2-连环素基因敲除和在生殖器男性化过程中缺乏2-连环素的小鼠中观察到类似尿道下裂的表型。更重要的是，我们的初步数据揭示了Wnt拮抗剂的性二型性表达，以及Shh和Wnt通路在男性外生殖器男性化过程中的功能作用。这些令人兴奋的结果解决了一个高度未被研究的领域，涉及非性腺和局部产生的男性因素，例如在介导性二态外生殖器发育中的生长因子信号级联。基于这些观察，这项提议将继续揭示调控生殖器发育和男性化的信号级联，重点放在Shh和Wnt途径上。在目标I中，我们将通过尝试用FGF8挽救Wnt突变体中的GT缺陷来检验Fgf8是GT发育过程中Wnt信号的直接靶点的假设。外胚层2-连环素在GT形态发生中的作用也将被研究。在AIM II中，我们将通过详细分析Shh和平滑的条件基因敲除GT表型来验证GT构图过程中在多个步骤中需要Shh的假设。将描述GT中Shh反应的组织，并研究Shh和Wnt途径之间的相互作用。最后，在目标III中，我们将通过分析几个条件基因敲除突变体的GT表型来验证Wnt/Shh信号参与调控外生殖器有性二态发育的假设。我们的长期目标是利用小鼠分子遗传学来了解生殖器发育和男性化的过程，以及生殖器畸形的病因学，如尿道下裂。公共卫生研究成果：该项目建议研究两个信号通路Shh和Wnt在外生殖器发育的雄激素非依赖性早期和晚期的功能。包括尿道下裂在内的生殖器畸形发生率很高，但其病因在很大程度上仍不清楚。利用几个条件基因敲除小鼠，该项目将揭示这两个重要途径的下游信号事件以及它们如何相互作用，以及雄激素信号途径调节生殖器形态发生和阳性化。我们的研究将对了解外生殖器发育和尿道下裂的病因有很大帮助。

DESCRIPTION (provided by applicant): Genital malformation including hypospadias represents the second most common male birth defect after cardiac defect. In the past 40 years, hypospadias incidence has doubled along with other male reproductive problems. It is suspected that fetal exposure to endocrine disruptors may have contributed to this increase. However, our understandings of the etiology of hypospadias or genital development in general are still very limited. Our preliminary studies convincingly demonstrated that the importance of two signaling pathways, Shh and Wnt in both early androgen-independent and late sexually dimorphic phases of external genitalia development. When the canonical Wnt pathway is perturbed in the urethral epithelium during early genital tubercle (GT) development, severe genital malformations developed. Hypospadias-like phenotype is observed in ectodermal 2-catenin knockouts and in mice lacking 2-catenin during genital masculinization. More importantly, our preliminary data revealed sexually dimorphic expression of Wnt-antagonists and the functional roles of Shh and Wnt pathways during the masculinization of male external genitalia. These exciting results address a highly understudied area involving non-gonadal and locally produced masculine factors, such as growth factor signaling cascade in mediating sexually dimorphic external genital development. Based on these observations, this proposal will continue to uncover the signaling cascade regulating genital development and masculinization, focusing on Shh and Wnt pathways. In aim I, we will test the hypothesis that Fgf8 is a direct target of Wnt signaling during GT development by attempting to rescue GT defects in Wnt mutants with FGF8. The role of ectodermal 2-catenin in GT morphogenesis will also be studied. In aim II, we will test the hypothesis that Shh is required at multiple steps during GT patterning by analyzing in detail Shh and Smoothened conditional knockout GT phenotype. Shh-responding tissues in the GT will be delineated and the interaction between Shh and Wnt pathway will be studied. Finally in aim III, we will test the hypothesis that Wnt/Shh signaling is involved in the regulation of sexually dimorphic development of external genitalia by analyzing GT phenotype of several conditional knockout mutants. Our long term goal is to use mouse molecular genetics to understand the process of genital development and masculinization and the etiology of genital malformations, such as hypospadias. PUBLIC HEALTH RELEVAVANCE: This project proposes to study the function of two signaling pathways, Shh and Wnt, in both early androgen-independent and late sexually dimorphic phases of external genitalia development. Genital malformations including hypospadias occur at a very high rate but their etiology remains largely unknown. Using several conditional knockout mice, this project will reveal the downstream signaling events of these two important pathways and how they interact with each other and the androgen signaling pathway to regulate genital morphogenesis and masculinization. Our studies will contribute greatly to the understanding of external genitalia development and the etiology of hypospadias.