TBP bookmarks and preserves neural stem cell fate memory by orchestrating local chromatin architecture (RNA-Seq)

Mitotic bookmarking has been posited as an important strategy for cells to faithfully propagate their fate memory though cell generations. However, the physiological significance and regulatory mechanisms of mitotic bookmarking in neural development remain unexplored. Here, we identified TBP (TATA binding protein) as a crucial mitotic bookmarker for preserving fate memory of Drosophila neural stem cells (NSCs). Phosphorylation by the super elongation complex (SEC) is important for TBP to retain as discrete foci at mitotic chromosomes of NSCs to effectively transmit their fate memory. TBP depletion leads to drastic NSC loss, whereas TBP overexpression enhances the ability of SEC to induce neural progenitor dedifferentiation and tumorigenesis. Importantly, TBP achieves its mitotic retention through recruiting the chromatin remodeler EP400, which in turn increases local chromatin accessibility via depositing H2A.Z. Thus, local chromatin remodeling ensures mitotic bookmarking, which may represent a general principle underlying the preservation of cell fate memory. Overall design: To investigate the biological function of TBP and H2A.Z in Drosophila neural stem cells, we compared the gene expression profiles of neural stem cells with shRNA knockdown of TBP, H2A.Z loss of function and control neural stem cells using RNA-seq.

有丝分裂书签（mitotic bookmarking）被认为是细胞在细胞世代间忠实传递其命运记忆的重要策略。然而，神经发育过程中有丝分裂书签的生理学意义及调控机制仍有待阐明。本研究鉴定出TATA结合蛋白（TATA binding protein, TBP）是维持果蝇神经干细胞（Drosophila neural stem cells, NSCs）命运记忆的关键有丝分裂书签蛋白。超级延伸复合物（super elongation complex, SEC）所介导的磷酸化修饰，对于TBP在神经干细胞的有丝分裂染色体上形成离散焦点、有效传递细胞命运记忆至关重要。敲低TBP可导致神经干细胞大量丢失，而TBP过表达则会增强SEC诱导神经前体细胞去分化及肿瘤发生的能力。值得注意的是，TBP通过招募染色质重塑因子EP400实现其有丝分裂滞留，后者通过沉积组蛋白变体H2A.Z（H2A.Z）增加局部染色质开放性。因此，局部染色质重塑可保障有丝分裂书签功能，这或许代表了维持细胞命运记忆的通用机制。实验设计：为探究TBP与组蛋白变体H2A.Z在果蝇神经干细胞中的生物学功能，本研究通过RNA测序（RNA-seq）对比了TBP shRNA敲低组、H2A.Z功能缺失组与对照组神经干细胞的基因表达谱。