SoftBio Theory Seminar: Oriented flows in multi-cellular systems

Most animals display one or more body axes (e.g. head-to-tail). In our work, we demonstrate that their formation can be promoted by large-scale tissue flows. We study aggregates of mouse stem cells, called gastruloids, which are initially spherically symmetric, but later form an axis defined by the polarized expression of specific proteins. We show that advection of cells with tissue flows contribute substantially to the overall polarization, and that these flows are driven by interface and surface tension differences.

We further discuss flows in the context of anisotropic tissue deformation. From a physics perspective, anisotropically deforming tissues can be described as oriented active materials. However, such materials inherently exhibit instabilities, raising the question of how anisotropic tissue deformation during development can be robust. We show that the presence of a signaling gradient can stabilize the process, but only if it acts to actively extend the tissue along the gradient direction. Conversely, tissues are unstable if they tend to actively contract along the gradient direction. Intriguingly, developing tissues seem to exclusively use the gradient-extensile and not the unstable gradient-contractile coupling. Our work thus points to a principle of multi-cellular morphogenesis that is directly rooted in active matter physics.