The Drosophila expansion Gene Controls Tracheal Tube Diameter

描述(申请人提供)：独特的管径对人体管状器官的功能至关重要，如肺、血管系统和肾脏。发育过程中出现的异常管子尺寸可能会导致毁灭性的人类疾病，如梅克尔肾病和多囊肾病。然而，调节管子大小的基本机制仍然不清楚，阻碍了我们开发有效的治疗由管子大小缺陷引起的疾病的方法。果蝇气管提供了一个主要的遗传系统来研究调节管子大小的基本机制。在果蝇气管中发现的管子大小控制机制随后可以在脊椎动物中进行研究，从而扩大了我们对管状器官一般管子大小调节的理解。最近，通过一项有针对性的RNAi敲除调查，我们发现Expansion(Exp)是一种进化上保守的新的Smad样蛋白，是果蝇气管管径的重要调节因子。Smad蛋白通常作为转化生长因子-B信号转导的中介。众所周知，转化生长因子-β信号可以控制斑马鱼脑血管内的细胞数量，从而调节血管直径(Roman等人，2002年)。然而，我们的初步数据表明，在EXP突变体中，转化生长因子-B信号和细胞数量并不参与管大小缺陷。相反，在exp突变体中，管腔蛋白的顶端分泌是有缺陷的，并且气管顶膜较大。此外，在EXP突变体中，磷酸化的MAPK(DP-ERK)水平增加。此外，减少ERK在EXP突变体中的表达抑制了观察到的管径缺陷。其他研究小组已经表明，上皮生长因子(EGF)信号在果蝇中使ERK磷酸化(Ohshio等人，2002)，而过度活跃的EGF信号会扩大气管直径(Jeon等人，2009)，类似于我们对Exp突变体的观察。因此，我们假设Exp通过减少EGF信号来控制管子大小调节所需的动态细胞过程。我们将通过两个具体目标的实现来检验这一假设：(1)确定Exp调控的细胞过程；2)确定Exp如何调节EGF信号来控制管径。通过拟议的实验，我们希望定义Smad家族蛋白在调节信号通路和下游动态细胞过程中控制管子大小的新角色。我们预计，拟议的研究结果将促进对果蝇管状器官中管子如何获得不同大小的理解，许多机制将与包括脊椎动物在内的其他生物共享。最终，这些知识有可能为开发治疗由管子大小缺陷引起的人类疾病提供新的靶点。

DESCRIPTION (provided by applicant): Distinct tube size is critical for the function of human tubular organs such as the lung, vascular system, and kidney. Aberrant tube sizes that arise during development can lead to devastating human illnesses such as Meckel kidney disease and polycystic kidney disease. However, the fundamental mechanisms that regulate tube size are still not well understood, preventing us from developing effective treatments for diseases caused by tube-size defects. Drosophila trachea provides a premier genetic system to investigate the fundamental mechanisms that regulate tube size. Mechanisms of tube-size control discovered in Drosophila trachea can be subsequently investigated in vertebrates, thereby extending our understanding of tube-size regulation in tubular organs in general. Recently, through a targeted RNAi knock down survey, we identified Expansion (Exp), an evolutionarily conserved and novel Smad-like protein, as an essential regulator of tube size in Drosophila trachea. Smad proteins generally function as mediators of Transforming Growth Factor-B (TGF-B) signaling. TGF- B signaling is known to control cell numbers within zebrafish cranial vessels, thereby regulating vessel diameter (Roman et al., 2002). However, our preliminary data indicated that TGF-B signaling and cell numbers were not involved in tube-size defects in exp mutants. Instead, the apical secretion of luminal proteins was defective, and the tracheal apical membrane was larger in exp mutants. In addition, phosphorylated MAP kinase (dp-Erk) levels were increased in exp mutants. Moreover, reducing Erk expression in exp mutants suppressed the observed tube-diameter defects. Other groups have shown that Epithelial Growth Factor (EGF) signaling phosphorylates Erk in Drosophila (Ohshiro et al., 2002) and that over-active EGF signaling expands tracheal tube diameter (Jeon et al., 2009), similar to our observations with exp mutants. Therefore, we hypothesize that Exp reduces EGF signaling to control the dynamic cellular processes required for tube-size regulation. We will test this hypothesis through the achievement of two specific Aims: (1) Identify the cellular processes that are regulated by Exp; 2) Determine how Exp regulates EGF signaling to control tube-size. Through the proposed experiments, we expect to define a novel role for Smad family proteins in regulating signaling pathways and downstream dynamic cellular processes to control tube-size. We expect that the results from the proposed study will advance the understanding of how tubes acquire their distinct sizes in tubular organs in Drosophila, and many mechanisms will be shared with other organisms, including vertebrates. Ultimately, such knowledge has the potential to provide novel targets for developing treatments for human diseases caused by tube-size defects.