SoftBio Theory Seminar: Mechanics and activity in the regulation of tissue shape and the fluctuation of physical observables

Biological systems exhibit complex, non-equilibrium behaviors that emerge from the interplay between active forces and the material properties of their surroundings. In this talk, I will present two studies that explore how active mechanical forces regulate time dynamics and material deformation at different length scales—within the cell cortex and in epithelial tissue morphogenesis.
In the first study, we investigate the non-equilibrium fluctuations of an AFM tip embedded in the active cortex of HeLa cells. By quantifying time irreversibility through the Kullback-Leibler divergence (KLD) and deviations from thermal equilibrium via effective temperature, we assess how perturbations to motor activity and cytoskeletal fluidity influence non-equilibrium dynamics.  Supported by a minimal model, our findings reveal that KLD and effective temperature can follow opposite trends, questioning the validity of effective temperature as a universal measure of non-equilibrium activity. 

In the second study, we explore epithelial tissue folding by developing a coarse-grained plate theory model of the basement membrane in the presence of active stresses. We verify model assumptions using Drosophila wing disc experiments and demonstrate that local basement membrane degradation can drive epithelial folding, even in the absence of tissue growth. Our results provide a mechanistic framework for understanding epithelial morphogenesis through force balance between active cellular forces and elastic deformation.

Together, these studies highlight how active forces and mechanical constraints shape biological systems at multiple scales, from single-cell dynamics to tissue architecture.