The Drosophila expansion Gene Controls Tracheal Tube Diameter

描述（由申请人提供）：不同的管大小对人体管状器官如肺、血管系统和肾脏的功能至关重要。发育过程中出现的异常的肾管大小会导致严重的人类疾病，如梅克尔肾病和多囊肾病。然而，调节管大小的基本机制仍然没有得到很好的理解，这阻碍了我们开发出有效的治疗方法来治疗由管大小缺陷引起的疾病。果蝇的气管为研究调节气管大小的基本机制提供了一个重要的遗传系统。在果蝇气管中发现的管大小控制机制可以随后在脊椎动物中进行研究，从而扩展我们对管状器官中管大小调节的理解。最近，通过一项靶向RNAi敲低调查，我们发现了一种进化保守的新型smad样蛋白Expansion (Exp)，它是果蝇气管管大小的重要调节因子。Smad蛋白通常作为转化生长因子- b （TGF-B）信号传导的介质。已知TGF- B信号可以控制斑马鱼颅内血管内的细胞数量，从而调节血管直径（Roman et al., 2002）。然而，我们的初步数据表明，TGF-B信号和细胞数量与exp突变体的管大小缺陷无关。相反，在exp突变体中，管腔蛋白的根尖分泌有缺陷，气管根尖膜变大。此外，磷酸化的MAP激酶（dp-Erk）水平在exp突变体中升高。此外，在exp突变体中，Erk表达的降低抑制了观察到的管径缺陷。其他研究小组表明，上皮生长因子（EGF）信号会使果蝇的Erk磷酸化（Ohshiro等人，2002），过度活跃的EGF信号会扩大气管管直径（Jeon等人，2009），这与我们对exp突变体的观察结果相似。因此，我们假设Exp减少EGF信号以控制管大小调节所需的动态细胞过程。我们将通过实现两个特定目标来检验这一假设：(1)确定由Exp调节的细胞过程；2)确定Exp如何调节EGF信号来控制管的大小。通过提出的实验，我们希望确定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大小的新作用。我们期望这项研究的结果将促进对果蝇管状器官中管道如何获得不同大小的理解，并且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由管大小缺陷引起的人类疾病的治疗方法提供新的靶点。

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.