Sponsored Stem Cells Research Chair (UPSUTER), The Institute of Bioengineering (IBI), School of Life Sciences, Swiss Federal Institute of Technology, Lausanne, Switzerland.
Mol Syst Biol. 2019 Sep;15(9):e9002. doi: 10.15252/msb.20199002.
SOX2 and OCT4 are pioneer transcription factors playing a key role in embryonic stem (ES) cell self-renewal and differentiation. How temporal fluctuations in their expression levels bias lineage commitment is unknown. Here, we generated knock-in reporter fusion ES cell lines allowing to monitor endogenous SOX2 and OCT4 protein fluctuations in living cells and to determine their impact on mesendodermal and neuroectodermal commitment. We found that small differences in SOX2 and OCT4 levels impact cell fate commitment in G1 but not in S phase. Elevated SOX2 levels modestly increased neuroectodermal commitment and decreased mesendodermal commitment upon directed differentiation. In contrast, elevated OCT4 levels strongly biased ES cells towards both neuroectodermal and mesendodermal fates in undirected differentiation. Using ATAC-seq on ES cells gated for different endogenous SOX2 and OCT4 levels, we found that high OCT4 levels increased chromatin accessibility at differentiation-associated enhancers. This suggests that small endogenous fluctuations of pioneer transcription factors can bias cell fate decisions by concentration-dependent priming of differentiation-associated enhancers.
SOX2 和 OCT4 是先驱转录因子，在胚胎干细胞（ES 细胞）自我更新和分化中发挥关键作用。它们的表达水平如何随时间波动会影响谱系分化尚不清楚。在这里，我们生成了 knock-in 报告融合 ES 细胞系，允许在活细胞中监测内源性 SOX2 和 OCT4 蛋白的波动，并确定它们对中胚层和神经外胚层分化的影响。我们发现，SOX2 和 OCT4 水平的微小差异会影响 G1 期但不会影响 S 期的细胞命运决定。在定向分化过程中，升高的 SOX2 水平适度增加了神经外胚层的分化，减少了中胚层的分化。相比之下，升高的 OCT4 水平在非定向分化中强烈偏向 ES 细胞向神经外胚层和中胚层命运分化。使用 ATAC-seq 对不同内源性 SOX2 和 OCT4 水平的 ES 细胞进行门控分析，我们发现高 OCT4 水平增加了分化相关增强子的染色质可及性。这表明，先驱转录因子的微小内源性波动可以通过浓度依赖性的分化相关增强子的启动来影响细胞命运决定。
