巨核细胞(MK)在发育过程中通过DNA的连续复制，可分化为高达128倍体的巨型细胞，将其产生血小板的效率提高1000倍。在这一多倍体化过程中，MK如何在染色体复制后，精细调控骨架蛋白而成功避免经典的细胞分裂命运，是国际前沿的根本生物学问题。我们前期发现抑制甲基转移酶SETD2可促进MK骨架蛋白延伸且高倍体增多。结合SETD2在成纤维细胞中调节微管骨架蛋白的报道，我们提出SETD2是MK多倍体化关键上游调控因子的假说。在本研究中，我们首先明确SETD2在连续多倍体化及脱胞浆生成血小板中的重要功能。通过一系列生化实验，解析SETD2对骨架蛋白的调节作用、两者相互关系和酶活性的功能位点。最终探索SETD2如何通过甲基化修饰精细调控骨架蛋白对染色质的牵引分离和胞浆缢缩，促进MK多倍体化和血小板的生成。本研究有望揭示决定细胞多倍体化或有丝分裂命运的新关键分子，对MK生物学和血小板相关疾病有重要意义。

Megakaryocyte (MK) is a highly polyploidy cell type that can efficiently generate platelets in bone marrow. During differentiation, MK undergoes endomitosis and polyploidization, which means repeated rounds of DNA replication without cell division. Mature normal MK may contain a DNA content of up to 128N to enhance the efficiency of platelet production by 1000 times. However, the mechanisms behind the polyploidization process are still incompletely understood, particularly the cytoskeletal remodeling, involving in endomitotic cell cycle regulation and defect in karyokinesis and cytokinesis, which is a biologically cutting-edge question. We previously found that suppression of methyltransferase SETD2 promotes cytoskeletal protein elongation in MKs and increases MKs with high ploidy. Interestingly, it has been reported that dynamic microtubules are methylated by SETD2 during mitosis and cytokinesis in fibroblasts. Thus, we propose that SETD2 may act as a key upstream regulator during MK polyploidization. In this study, we firstly investigate the functions of SETD2 in MK polyploidization and platelet production. Then, a series of biochemical assays will be applied to study the regulation of SETD2 on microtubules and other cytoskeletal proteins during MK development, and elucidate the interactions and functional site between SETD2 and cytoskeletal proteins. Finally, we will explore the requirement of SETD2 for cytoskeletal methylation in regulating the defect in karyokinesis and abscission to cause cytokinesis failure, which eventually promotes MK polyploidization and platelet production. This study is expected to reveal a novel key factor of SETD2 in governing the process of polyploidization or mitosis, which is of important scientific significance in MK development and platelet disorders.