Edge-localized alteration in pluripotency state of mouse ES cells forming topography-confined layers on designed mesh substrates.

Self-organization of pluripotent stem cells during tissue formation is directed by the adhesion microenvironment, which defines the resulting tissue topography. Although the influence of tissue topography on pluripotency state has been inferred, this aspect of self-organization remains largely unexplored. In this study, to determine the effect of self-organized tissue topography on pluripotency loss, we designed novel island mesh substrates to confine the self-organization process of mouse embryonic stem cells, enabling us to generate isolated cell layers with an island-like topography and overhanging edges. Using immunofluorescence microscopy, we determined that cells at the tissue edge exhibited deformed nuclei associated with low OCT3/4, in contrast with cells nested in the tissue interior which had round-shaped nuclei and exhibited sustained OCT3/4 expression. Interestingly, F-actin and phospho-myosin light chain were visibly enriched at the tissue edge where ERK activation and elevated AP-2γ expression were also found to be localized, as determined using both immunofluorescence microscopy and RT-qPCR analysis. Since actomyosin contractility is known to cause ERK activation, these results suggest that mechanical condition at the tissue edge can contribute to loss of pluripotency leading to differentiation. Thus, our study draws attention to the influence of self-organized tissue topography in stem cell culture and differentiation.