Mechano-osmotic signals control chromatin state and fate transitions in pluripotent stem cells [bulk RNA-seq]

Acquisition of specific cell shapes and morphologies is a central component of cell fate transitions. Although the signaling circuits and gene regulatory networks regulating pluripotent stem cell differentiation have been intensely studied, how these networks are integrated in space and time with morphological transitions and mechanical deformations that occur during state transitions remains a fundamental open question. Here, we discover that stem cell fate transitions are gated by two critical signals - nuclear envelope fluctuations and osmotic stress - that emanate from growth factor signaling-controlled changes in nuclear volume and nucleoplasm viscosity/density to subsequently trigger changes in nuclear architecture and transcription. We observe that fate transitions in the early human embryo and in an in vitro pluripotency exit model are guided by rapid changes in nuclear volume and nuclear envelope mechanics. These changes alter nuclear mechanosensitivity and trigger changes in nucleoplasmic viscosity and nuclear condensates that together prime chromatin for a cell fate transition. However, while this mechanical priming accelerates fate transitions, sustained biochemical signals are required for robust induction of differentiation. Our findings uncover a critical mechanochemical feedback mechanism that integrates nuclear mechanics, shape and volume with biochemical signaling and chromatin state to control cell fate transition dynamics. Total RNA sequencing was performed on iPS cells 24 h post recovery from 30 min compression, either in pluripotency maintenance conditions or in basal medium, comparing these scenarios to hypertonic shock in both media conditions.

特定细胞形状与形态的获得是细胞命运转变的核心组成部分。尽管调控多能干细胞（pluripotent stem cell）分化的信号通路与基因调控网络已得到广泛研究，但这些网络如何在时空维度上与状态转变过程中发生的形态转变及机械形变相整合，仍是一个根本性的未解问题。本研究发现，干细胞命运转变受两类关键信号调控——核被膜波动与渗透应激——此类信号源自生长因子信号通路控制的核体积与核质黏度/密度变化，进而触发核架构与转录过程的改变。我们观察到，人类早期胚胎以及体外多能性退出模型中的细胞命运转变，由核体积与核被膜力学特性的快速变化所引导。这些变化会改变细胞核的机械敏感性，并引发核质黏度与核凝聚体的改变，二者共同将染色质预编程以启动细胞命运转变。不过，尽管这类机械预编程可加速细胞命运转变，但要实现稳定的分化诱导，仍需要持续的生化信号支持。本研究的发现揭示了一种关键的机械化学反馈机制，该机制将核力学特性、形态与体积同生化信号及染色质状态相整合，以此调控细胞命运转变的动态过程。本研究对经30分钟挤压后恢复24小时的诱导多能干细胞（induced pluripotent stem cell, iPS）进行了总RNA测序，实验分别在多能性维持条件与基础培养基中开展，并将这两种条件下的样本与两种培养基环境中的高渗冲击处理组进行对比。