Embryonic stem cells become mechanoresponsive upon exit from ground state of pluripotency.

Stem cell fate decisions are driven by a broad array of signals, both chemical and mechanical. Although much progress has been made in our understanding of the impact of chemical signals on cell fate choice, much less is known about the role and influence of mechanical signalling, particularly in embryonic stem (ES) cells. Many studies use substrates with different stiffness to study mechanical signalling, but changing substrate stiffness can induce secondary effects which are difficult to disentangle from the direct effects of forces/mechanical signals. To probe the direct impact of mechanical stress on cells, we developed an adaptable cell substrate stretcher to exert specific, reproducible forces on cells. Using this device to test the response of ES cells to tensile strain, we found that cells experienced a transient influx of calcium followed by an upregulation of the so-called immediate and early genes. On longer time scales, however, ES cells in ground state conditions were largely insensitive to mechanical stress. Nonetheless, as ES cells exited the ground state, their susceptibility to mechanical signals increased, resulting in broad transcriptional changes. Our findings suggest that exit from ground state of pluripotency is unaffected by mechanical signals, but that these signals could become important during the next stage of lineage specification. A better understanding of this process could improve our understanding of cell fate choice in early development and improve protocols for differentiation guided by mechanical cues.