Receptor Trafficking and the Response to Shh

描述（由申请人提供）：Sonic Hedgehog是一种形态发生素。为了实现这一作用，它必须能够通过响应组织从其合成源行进许多细胞直径。这一要求似乎与Shh的生物学特性相冲突;它含有酰基和胆固醇部分，这严重降低了它在亲水性细胞间环境中的溶解度。尽管已经鉴定出Shh的功能性、可溶性六聚体形式，但由Shh表达细胞调节的培养基不会将Shh积累到足够高的水平以引起神经板外植体的反应。然而，当这种响应组织与Shh产生细胞接触时，可以在外植体中观察到长距离Shh信号传导，表明Shh在响应组织的平面中被主动运输。据推测，这种远程运输部分是由转胞吞介导的，这得到了果蝇中的观察结果的支持，即胆固醇相关的Shh同源物Hedgehog（Hh）的输出需要专用分子Dispatched（Disp）的活性，而Shh和Hh的摄取则由Disp同源物Patched（Ptc）介导。此外，Ptc 1介导的运输Shh进入晚期内体是启动Shh反应所必需的。为了在这些应答细胞中完成转胞吞作用，Shh必须从晚期内体转运到细胞表面并使其可用于邻近细胞，并且假设这是由Disp介导的。将对假设进行检验，以确定Ptc 1介导和Disp 1介导的Shh运输是否是长程信号传导所必需的。确定Shh的替代锚定形式的长程信号传导功效。将确定晚期内体中的酸性环境是否有利于Shh与Dispatched结合，而细胞间隙中的中性环境是否允许Shh与Ptc 1结合，从而产生导致转胞吞作用的连续事件链。将通过阻断Rabs和发动蛋白的功能来测试产生长程信号对细胞内转运的需求。Shh响应耦合到胞吞作用允许产生分级的Shh响应，在组织中积极响应Shh，而不需要在细胞间隙中进行远程运输，并提供了一个解释Ptc 1和Disp 1的不寻常的活动。更好地理解长距离Shh信号形成的机制是重要的。Shh反应的不适当激活是多种癌症的原因，包括高比例的胰腺肿瘤，而正常的Shh信号传导是许多器官系统发育所必需的。

DESCRIPTION (provided by applicant): Sonic Hedgehog is a morphogen. To fulfill this role, it is necessary that it is able to travel many cell diameters away from its source of synthesis through the responding tissue. This requirement appears to be in conflict with the biological properties of Shh; it both contains an Acyl and a cholesterol moiety, which severely curtail its solubility in a hydrophilic intercellular environment. Although a functional, soluble hexameric form of Shh has been identified, medium conditioned by Shh expressing cells do not accumulate Shh to levels high enough to elicit a response in neural plate explants. However, when such responsive tissue is in contact with Shh producing cells, long-range Shh signaling can be observed in the explant, indicating that Shh is actively transported in the plane of the responding tissue. It is hypothesized that this long-range transport is mediated in part by transcytosis, which is supported by observation in Drosophila that export of cholesterol-associated Shh homolog Hedgehog (Hh) requires the activity of a dedicated molecule, Dispatched (Disp), while the uptake of Shh and Hh is mediated by the Disp homolog Patched (Ptc). In addition, the Ptc1-mediated trafficking of Shh into late endosomes is required to initiate the Shh response. To complete transcytosis in these responding cell it is necessary that Shh is transported from the late endosomes to the cell surface and made available to neighboring cells, and it is hypothesized that this is mediated by Disp. The hypotheses will be tested determining if Ptc1-mediated and Disp1-mediated trafficking of Shh are required in concert for long-range signaling. Determine the long-range signaling efficacy of alternatively anchored forms of Shh. It will be determined if the acidic environment in late endosomes favors Shh binding to Dispatched, while the neutral environment in the intercellular space allows Shh to bind to Ptc1, creating a continuous chain of events resulting in transcytosis. The requirement for intracellular transport in generating a long-range signal will be tested by blocking the function of Rabs and Dynamin. The Shh response coupled to transcytosis allows the generation of a graded Shh response, in a tissue actively responding to Shh, without the requirement for long-range transport in the intercellular space, and provides an explanation for the unusual activities of Ptc1 and Disp1. Better understanding of the mechanism by which the long-range Shh signal forms is important. Inappropriate activation of the Shh response is the cause of a wide variety of cancers, including a high fraction of pancreatic tumors, while normal Shh signaling is required for the development of many organ systems.