转录因子Ttk69与成体果蝇肠道上皮终末分化细胞命运的维持

成体组织的稳态不仅需要成体干细胞的有序增殖与分化，也有赖于终末分化细胞命运与功能的稳定维持。目前的研究多集中于调控干细胞增殖与分化过程中子细胞命运决定的分子机制，关于终末分化细胞命运维持的相关研究却相对较少。本研究以成体果蝇肠道为模型，旨在探寻维持终末分化细胞命运的分子机制。我们前期研究发现转录抑制因子Ttk69对维持肠细胞（EC）命运至关重要。在EC中敲低ttk69会导致其特征基因的下调，并启动多种肠内分泌细胞特征基因表达。我们将进一步通过遗传学研究，结合转录组，蛋白-DNA互作以及染色质开放性等分析，探究Ttk69维持EC命运的分子机制。此外，鉴于ttk的缺失只能诱导部分EC的转分化，我们也将利用单细胞转录组测序等手段，探寻导致转分化响应异质性的调控因子。总之，本研究通过研究果蝇肠细胞和肠分泌细胞的命运维持和转换机制，将为进一步理解终末分化细胞的命运维持及可塑性提供理论基础。

Tissue homeostasis driven by local stem cells requires coordinated specification of multiple cell lineages and maintenance of differentiated cell identity. Regulators modulating stem cell proliferation and differentiation have been extensively investigated, while factors safeguarding mature cell identity attract less attention. Using the Drosophila intestine as a model system, this study aims to reveal mechanisms that maintain cell fate identity of mature enterocytes (ECs) and enteroendocrine cells (EEs). Our preliminary studies have revealed that Ttk69, a master repressor of EE fate in Drosophila intestinal progenitor cells, is continuously required in differentiated ECs for their identity maintenance. Depleting ttk69 in ECs causes cell-autonomous activation of various EE-specific markers, accompanying loss of EC-specific signature genes, indicating a direct trans-differentiation process between these two terminal differentiated cell types. Next, we will collectively use genetic analysis, as well as DNA binding profiles and chromatin accessibility analysis to further illustrate the underlying mechanisms of how Ttk69 maintains EC identity and suppresses cell fate conversion. Additionally, the degree of ttk69 depletion induced cell fate transformation was highly heterogeneous within different ECs, which lead us to seek for additional factors that helps to maintain EC identity, by using approaches including ATAC-sequencing, single cell RNA-sequencing and genetic screening. To conclude, this project would clarify the interconvertibility between absorptive and secretory cells in the intestine and establish a genetic model system for further understanding cell fate maintenance and plasticity among terminal differentiated cell types, which might also occur in various physiological and pathological conditions.