Physics of multicellular systems

The mechanical state of a tissue emerges from the collective interactions among cells. However, this emergent physical state at supra cellular scales is controlled at cell the cell and sub cellular scales. What are the cell behaviors and sub cellular processes that affect/control the emergent mechanical state of the tissue? To address this question, we are combining experimental and theoretical approaches. We have developed 'Active Foam' models of embryonic tissues that enable the simulation of tissue dynamics in the presence of spaces between cells (confluent and non-confluent tissues), stochastic tension dynamics and complex cell shapes. These simulations allow us to study how changes in physical parameters at cell/subcellular scales control change in the emergent tissue mechanics. These models predict different kind of rigidity transitions (fluid-to-solid transition or tissue fluidization) for different control parameters. Our experimental data indicates that tissue fluidization is mainly controlled by active T1 transitions driven by actomyosin tension fluctuations at cell-cell contacts.

At very early embryonic stages, the communication between the few cells (blastomeres) composing the embryo depends critically on the topology of cell-cell contacts and the geometry of cellular packings. We are studying how the physics of cellular interactions generates the topological and geometrical patterns that characterize embryos at these early stages.