Illuminating cell hollowing; the mysterious process of seamless tube formation

描述（由申请人提供）：癌细胞释放生长因子如VEGF，诱导其微环境中新血管的生长。新生血管为生长中的肿瘤提供氧气和营养，同时清除任何废物，并为肿瘤细胞扩散到其他器官系统提供有效途径。在没有血管生成的情况下，肿瘤的大小不能超过3-4毫米；因此，血管生成已成为一种治疗靶点。脊椎动物的血管系统和果蝇的气管系统有着相似的分支发芽和管道形成机制，因此，可管理的果蝇模型系统将为血管生成过程中的毛细血管管化提供急需的见解。超微结构研究表明，分支连接点通常由“无缝”管组成。无缝管是单细胞管，横截面呈甜甜圈状。培养的内皮细胞通过细胞内液泡的融合形成无缝管，最终与其他内皮细胞连接形成具有细胞间缝的更大的管。这些观察结果导致了无缝管形成的“细胞空化”模型，其中膜囊泡或液泡被靶向到细胞中心，在那里它们合并和融合产生内部根尖膜。本研究旨在定义无缝管形成的遗传、分子和细胞生物学机制，采用双管齐下的方法来解决果蝇气管系统中的这个问题。首先，通过研究在前向遗传筛选中发现的无缝管缺陷突变体，将阐明无缝管形成的过程。该方法的第二个方面需要活细胞成像研究，其中充分表征和荧光标记的膜运输成分被用来实时可视化体内无缝管的形成。

DESCRIPTION (provided by applicant): Cancerous cells release growth factors such as VEGF to induce growth of new blood vessels in their microenvironment. Neovascularization provides oxygen and nutrients to the growing tumor, while removing any waste products and providing an efficient route for the spread of tumor cells to other organ systems. In the absence of angiogenesis, tumors cannot develop more than 3-4 mm in size; hence, angiogenesis has become a therapeutic target. The vertebrate vasculature and Drosophila tracheal system share similar mechanisms of branch sprouting and tube formation, and therefore the tractable Drosophila model system will provide much needed insight into capillary lumenization during angiogenesis. Ultrastructural studies have shown that branch connection points are frequently comprised of "seamless" tubes. Seamless tubes are unicellular tubes that appear doughnut like in cross-section. Endothelial cells in culture form seamless tubes by the fusion of intracellular vacuoles before eventually connecting with other endothelial cells to generate larger tubes with intercellular seams. These observations have led to a "cell hollowing" model of seamless tube formation in which membrane vesicles or vacuoles are targeted to the center of the cell, where they coalesce and fuse to generate an internal apical membrane. This proposal seeks to define the genetic, molecular, and cell biological mechanisms that underlie formation of seamless tubes, taking a two-pronged approach to address this question in the Drosophila tracheal system. First, the process of seamless tube formation will be elucidated by studying mutants identified in a forward genetic screen that exhibit defects in seamless tubes. The second prong of the approach entails live cell imaging studies in which well-characterized and fluorescently-tagged membrane trafficking components are utilized to visualize seamless tube formation in vivo in real time. DIRECT RELEVANCE TO PUBLIC HEALTH: The induction of new blood vessels Is critical for many aspects of growth and development, but particularly important during wound healing and tumorigenesis. This proposal aims to describe the mechanism by which a cell can transform into a tube (such as a blood vessel) using the Drosophila trachea as a model system.