Condensation tendency of connected contractile tissue with planar isotropic actin network

It has been found that many types of cells form nematic symmetry on confined planar substrates. Such observation has been satisfactorily explained by modeling cells as crowded self-propelled rods. In this work, we report that rat embryonic fibroblast (REF) cells when confined in circular mesoscale patterns, form a new type of symmetry where cells align radially at the boundary. Unlike NIH-3T3 and MDCK monolayers, the REF monolayer presents a supracellular actin gradient with isotropic meshwork. In addition, the contractile REF cells present strong adhesive interactions with neighboring cells, which confers the monolayer with significant condensation tendency. We found the loss of condensation tendency by inhibiting the cell contractility or disrupting cell-cell adhesion led to the disappearance of the radial alignment. In theory, we found the prestretch due to condensation tendency with differential cell stiffness is sufficient to explain the new symmetry within a confined tissue continuum.