Hh信号通路中Ci SUMO化修饰的作用机制及功能研究

As one of evolution conserved pathways in vertebrate and invertebrate, Hh signaling is essential for metazoan development. Its malfunction causes a series of serious human diseases, including congenital disorder and cancer. As the transcriptional factor of Hh signaling, Ci contributes to controlling downstream gene expressions, therefore the development. However, underlying mechanisms remain ill defined. In order to understand Hh signaling and the development of metazoan, investigating the regulation mechanism of Ci is very important, of which the key questions are the stability, localization of Ci and the generation of Ci75. In our study, we found that E2 and E3 of Sumoylation modification are involved in the regulation of Hh signaling transduction. In the experiment, we identified Ci as the direct Sumoylation target in Hh signaling by different methods. Protein Sumoylation modification plays very important in the regulation of protein function, especially for nuclear proteins. According facts above, we hypothesize here that Sumoylation is involved in Hh signaling by directly sumoylating Ci. In this study, we will use Drosophila as a model to investigate the mechanism which Hh signaling is regulated by Ci Sumoylation. We will also figure out the biology function of Ci Sumoylation, especially in testis germline stem cell self-renew and maintenance.

Hh信号通路是进化上最为保守的信号通路之一，控制了多细胞动物发育过程中细胞的生长及分化。Hh信号通路的异常调节将会导致包括多种癌症及出生缺陷在内的人类严重疾病。Ci作为转录因子，在Hh信号传递过程中处于最为重要的地位。然而，目前对于Ci调控机制的研究还远远不够。我们在实验中发现控制SUMO化修饰的E2/E3对Hh信号通路存在较为重要的调控作用；同时，我们在实验中确定Ci可以被SUMO化特异性地修饰。鉴于SUMO修饰在蛋白质功能调控中的重要作用，其很可能通过SUMO化修饰Ci参与了Hh信号的传递。本项目拟利用模式生物果蝇在in vitro及in vivo两方面开展Ci SUMO化修饰的作用机理的研究。同时，也将针对SUMO化修饰Ci在雄性生殖过程中的生物学功能进行研究。以期揭示SUMO修饰调控Hh信号传递的作用机理及其生物学功能，为最终理解Hh信号转导通路机制及功能调控提供坚实的理论基础。

生长调控是生物体最基本的发育过程之一，关于其机理的研究不仅是一个重大基础理论问题，也是相关疾病如肿瘤发生、发展的重要内容。此外，生殖干细胞稳态 (Homeostasis)的维持对于生殖细胞的正常产生至关重要，一旦其出现异常可能造成不孕不育等疾病的发生，严重影响到人们的生存和生活质量。细胞内信号转导通路的异常是疾病发生的重要分子基础之一。作为生物体发育过程中最为重要的形态发生素之一以及生物进化史上最为保守的信号转导途径之一，Hedgehog (Hh) 信号转导途径控制了脊椎动物以及非脊椎动物众多发育过程中细胞的生长分化，以及生殖干细胞的稳态维持。Hh信号需要通过调控转录因子Ci的活性而对下游基因的转录进行控制。因此，转录因子Ci的调节机制在Hh信号通路中占有极为重要的地位。SUMOylation是一种高度动态的翻译后修饰，其对于组织的发育以及疾病的发生起到重要作用。但是，SUMOylation在成体干细胞稳态维持中的功能尚不清楚。通过遗传学筛选，我们发现SUMOylation在果蝇精巢干细胞中维持somatic cyst stem cells (CySCs)自我更新的新功能。SUMO信号通路自主性地（cell-autonomously）控制CySCs的数目和干性维持。整体减少SUMOylation导致CySCs提前分化而减少其数量，而人工累积SUMOylation使得CySCs增多。与此一致，突变掉SUMO conjugating enzyme的CySC克隆很快就会消失。我们进一步发现SUMO信号通路通过调控Ci的SUMOylation而正向调控Hh信号通路活性，这部分介导了SUMO信号通路维持CySCs干性的功能。