Effects of Hedgehog Signaling on Pancreas Organogenesis

描述（由申请人提供）：Hedgehog（Hh）信号传导调节胚胎发生期间各种器官中的细胞增殖和分化。在胰腺中，该途径的作用是复杂的。在早期阶段，Hh信号传导被排除在胰腺之外，并且该途径的异位激活通过干扰间充质-上皮相互作用而损害胰腺形成。相反，这种抑制作用，我们的初步数据表明，一个积极的，细胞自主的作用，Hh信号在内分泌细胞的形成和功能。这种新颖的细胞自主活动的确切性质仍有待阐明。关于调节胰腺上皮中Hh信号传导的上游机制的信息也很少。最近的研究结果表明，初级纤毛，在许多细胞类型上发现的细胞附属物，控制Hh信号传导活性的水平。初级纤毛存在于胰腺内的成体导管和内分泌细胞上，这些细胞类型与表达Ptc（Hh信号传导的转录靶基因）的细胞类型相同。我们的初步结果表明，纤毛控制胰腺细胞中Hh信号的激活。在第一个具体的目标，我们将解决在胰腺上皮Hh信号的细胞自主的要求。这将通过分析转基因小鼠来实现，在这些小鼠中，编码Hh途径的重要组分的基因Smoothened已在胰腺上皮细胞中特异性消除。在第二个具体的目标，我们建议阐明纤毛在调节胰腺上皮细胞和内分泌细胞的Hh信号水平的作用。为此目的，已经产生了在缺乏初级纤毛的胰腺上皮和上皮细胞中异位表达GLI2（Hh信号传导的转录激活因子）的转基因小鼠。在第三个具体目标中，我们将进行细胞培养实验，以分析初级纤毛控制胰腺细胞中Hh活性的机制。总之，本申请中提出的实验将解决胰腺上皮细胞中Hh信号传导的细胞自主需求和初级纤毛在调节这些细胞中Hh活性水平中的作用。鉴于Hh信号在胰腺和内分泌细胞发育和功能的不同时间点发挥的不同作用，了解这些作用将有助于优化旨在从胚胎干细胞产生功能性细胞的策略。

DESCRIPTION (provided by applicant): Hedgehog (Hh) signaling regulates cell proliferation and differentiation in various organs during embryogenesis. In the pancreas, the role of this pathway is complex. At early stages, Hh signaling is excluded from the pancreas and ectopic activation of the pathway impairs pancreas formation by disturbing mesenchymal-epithelial interactions. In contrast to this inhibitory role, our preliminary data suggest a positive, cell autonomous role for Hh signaling during endocrine cell formation and function. The exact nature of this novel, cell autonomous activity remains to be elucidated. Little information is also available about the upstream mechanisms that regulate Hh signaling in pancreatic epithelium. Recent results have revealed that primary cilia, cellular appendages found on many cell types, control the level of Hh signaling activity. Primary cilia are present on adult duct and endocrine cells within the pancreas, the same cell types that are marked by expression of Ptc, a transcriptional target gene of Hh signaling. Our preliminary results indicate that cilia control activation of Hh signaling in pancreatic cells. In the first specific aim, we will address the cell autonomous requirement for Hh signaling in pancreatic epithelium. This will be accomplished by analyzing transgenic mice in which Smoothened, the gene coding for an essential component of the Hh pathway, has been eliminated specifically in pancreatic epithelial cells. In the second specific aim, we propose to elucidate the role of cilia in regulating the level of Hh signaling in pancreatic epithelium and in endocrine ¿-cells. Transgenic mice ectopically expressing GLI2, a transcriptional activator of Hh signaling, in pancreatic epithelial and ¿-cells that lack primary cilia have been generated for this purpose. In the third specific aim, we will perform cell culture experiments to analyze the mechanisms by which primary cilia control Hh activity in pancreatic cells. In summary, experiments proposed in this application will address the cell autonomous requirement for Hh signaling in pancreatic epithelial cells and the role primary cilia play in regulating the level of Hh activity in these cells. Given the distinct roles Hh signaling plays at different time points during pancreas and endocrine cell development and function, understanding of these effects will help to optimize strategies designed to generate functional ¿-cells from embryonic stem cells.