Dissecting OCT4 defines the role of nucleosome binding in pluripotency maintenance

The aim of this study is to dissect the transcription factor OCT4 and reveal which parts of the protein are essential for interaction with nucleosomes and access to closed chromatin. We revealed that the DNA-binding domain mediates the interaction of OCT4 with nucleosomes. Remarkably, nucleosome-binding can be uncoupled from DNA-binding, diminishing the ability of OCT4 to access to closed chromatin, thus losing the pioneer function. We show that the pioneer function of OCT4 is not only essential during reprogramming differentiated cells to pluripotency but also during pluripotency maintenance of embryonic stem cells. Overall, this study shows how pioneer transcription factors interact with nucleosomes to engage the genome and control cellular identity, highlighting that nucleosomes are not always barriers to genome accessibility. Measuring Chromatin accessibility (ATAC-seq) during stem cell self-renewal, when endogenous OCT4 is knocked down and replaced with OCT4 wild-type or mutant.

本研究旨在解析转录因子OCT4，明确该蛋白质的哪些结构域对其与核小体的相互作用以及开放封闭染色质的能力至关重要。研究发现，DNA结合结构域（DNA-binding domain）介导了OCT4与核小体的相互作用。值得注意的是，核小体结合能力可与DNA结合能力解偶联，这会削弱OCT4开放封闭染色质的能力，进而使其丧失先驱转录因子功能。本研究证实，OCT4的先驱转录因子功能不仅在将分化细胞重编程为多能干细胞的过程中不可或缺，在胚胎干细胞的多能性维持过程中同样至关重要。综上，本研究阐明了先驱转录因子如何通过与核小体相互作用结合基因组并调控细胞身份，同时揭示了核小体并非始终是基因组可及性的阻碍。本研究在干细胞自我更新过程中开展实验：对内源OCT4进行基因敲低，随后以野生型或突变型OCT4进行替代，并通过ATAC-seq技术检测染色质可及性。