发育中PRC1调控Hh信号通路Ci/Gli转录的分子机制及功能研究

The evolutionarily conserved Hedgehog (Hh) signaling pathway plays critical functions in development. Dysregulated Hh signaling activity can cause numerous diseases, including medulloblastoma. Cubitus interruptus (Ci) is a critical transcription factor of Hh pathway, which directly controlling the target gene expression in Drosophila. Previous investigations have mainly been focusing on Ci’s stability, localization and transcriptional activity. Yet, the transcriptional regulation of Ci is largely unknown. In our preliminary work, we carried out an RNAi-based genetic screen, and surprisingly found that Pc-Sce of Polycomb Repressive Complex 2 (PRC2) plays a positive role in Ci expression and Hh signal transduction in developing Drosophila wing discs. This finding is inconsistent with previous studies that show Polycomb group (PcG) proteins usually function as repressors of a variety of developmental factors We also found that Pc-Sce binds to the transcription start site (TSS) of Ci in vivo. Interestingly, the PRC2 catalytic activity for H3K27me3, but not the PRC1 catalytic activity for H2AUb1, is required for transcription of Ci. Moreover, Pc-Sce physically and functionally interacts with a well-known transcriptional co-activator Fsh in Ci transcription. In the future study, we will further focus on the molecular mechanism of how Pc-Sce-Fsh complex regulates transcription of Ci, how this complex controls development through Hh signaling both in Drosophila and mouse.

Hh信号通路在动物组织器官发育过程中起到重要作用。Ci/Gli是Hh信号通路核心转录因子，但其自身转录调控的分子机制仍有待揭示。本项目前期研究以遗传筛选为切入点，发现表观遗传因子PRC1的Pc-Sce复合物能直接、正向地调控Ci转录；其功能依赖于PRC2及H3K27me3，但不依赖于Sce连接酶活性；Fsh蛋白与Pc-Sce形成复合物参与Ci转录调控。基于上述研究结果，我们将从分子、细胞和整体动物水平逐级研究Pc-Sce-Fsh复合物如何影响染色质结构而调控Ci/Gli转录，揭示Pc-Sce-Fsh复合物通过表观遗传调控Hh信号通路的分子机制，阐明该复合物在组织器官发育中的功能。项目的实施将回答表观遗传因子如何协同其它转录调控因子共同调控Ci/Gli的转录，进而调控组织器官发育中Hh通路活性的重要发育生物学问题，为最终理解Hh信号通路并为相关疾病的诊治及新的潜在药物靶点的发现提供理论依据。

Hh信号通路在动物组织器官发育过程中起到重要作用。Ci/Gli是Hh信号通路核心转录因子，但其自身转录调控的分子机制仍有待揭示。在项目的支持下，我们系统性地揭示了Hh信号通路转录因子Ci/Gli的调控机制及生物学功能。主要进展包括：揭示表观遗传复合物PRC1中的Pc和Sex comb extra (Sce)两个成员通过结合在Ci转录起始位点附近而正向调控Ci的转录以及Hh信号通路的活性。这一调控依赖于由PRC2催化的H3K27me3，而不依赖于由Sce催化的H2AUb1，同时Pc-Sce能够和Fsh相互结合而激活Ci转录；发现表观遗传复合物PRC1在精巢稳态维持中的调控机制及功能；发现Hh及其相关通路在组织器官形态建成过程中发挥调控的分子网络； Hh信号通路的转录因子Ci/Gli的泛素化水平及降解水平受到了特异性的E2—UbcD1的调控；Gli通过PY-NLS与KAPb-2相互作用调控了其初级纤毛的定位，从而在Hh通路活性及神经管细胞瘤的生长中发挥作用；Hh信号通路及其相关信号通路在消化道肿瘤（胃癌及肠癌）细胞生长中的生物学功能；Hh信号通路中转录因子Gli通过调控Hilnc从而在脂质代谢中的生物学功能；Ptc可以发挥PKAc的sponge作用，从而传递Hh梯度化信号；同时，为了进一步研究Hh信号的机制，我们也解析了Hh信号通路膜蛋白Ptc及DisPtc的电镜结构。相关研究成果已发表论文12篇，申请专利4项，另有3篇论文在审稿或撰写过程中。项目的实施回答表观遗传因子如何协同其它转录调控因子共同调控Ci/Gli的转录，进而调控组织器官发育中Hh通路活性的重要发育生物学问题，为最终理解Hh信号通路并为相关疾病的诊治及新的潜在药物靶点的发现提供理论依据。