Department of Biological Sciences, Columbia University, New York, United States.
Elife. 2020 Oct 21;9:e61083. doi: 10.7554/eLife.61083.
Extracellular Hedgehog (Hh) proteins induce transcriptional changes in target cells by inhibiting the proteolytic processing of full-length Ci or mammalian Gli proteins to nuclear transcriptional repressors and by activating the full-length Ci or Gli proteins. We used Ci variants expressed at physiological levels to investigate the contributions of these mechanisms to dose-dependent Hh signaling in wing imaginal discs. Ci variants that cannot be processed supported a normal pattern of graded target gene activation and the development of adults with normal wing morphology, when supplemented by constitutive Ci repressor, showing that Hh can signal normally in the absence of regulated processing. The processing-resistant Ci variants were also significantly activated in the absence of Hh by elimination of Cos2, likely acting through binding the CORD domain of Ci, or PKA, revealing separate inhibitory roles of these two components in addition to their well-established roles in promoting Ci processing.
细胞外 Hedgehog (Hh) 蛋白通过抑制全长 Ci 或哺乳动物 Gli 蛋白的蛋白水解处理，将其转化为核转录阻遏物，并激活全长 Ci 或 Gli 蛋白，从而诱导靶细胞的转录变化。我们使用生理水平表达的 Ci 变体来研究这些机制对 wing 幼虫盘内 Hh 信号的剂量依赖性的贡献。当 Ci 抑制剂组成型表达时，不能被处理的 Ci 变体支持正常的靶基因激活模式，并发育出具有正常翅膀形态的成虫，表明在没有调节处理的情况下，Hh 可以正常信号传递。在没有 Hh 的情况下，通过消除 Cos2，处理抗性 Ci 变体也被显著激活，这可能是通过 Ci 的 CORD 结构域或 PKA 结合而发挥作用，揭示了这两个成分除了在促进 Ci 处理方面的既定作用之外，还有单独的抑制作用。
