Lamellipodium-driven tissue reshaping: a parametric study

We recently showed that lamellipodia are able to generate forces of the right type to drive convergent extension (CE), an important class of tissue reshaping, in early stage embryos. The purpose of the present work is to quantify the mechanics of this process using parametric analyses. We use finite elements to implement a gamma-mu model in which a net interfacial tension gamma acts along each cell boundary and the cytoplasm exhibits an effective viscosity mu. The stress-strain characteristics of a rectangular patch of model tissue are investigated in terms of the rate r at which lamellipodia form and the relative strength q of their contractions. In tissues that are not constrained in-plane by adjacent tissues, the rate of tissue reshaping is proportional to r the rate of lamellipodium formation and its dependence on q is nonlinear and, near its expected value of 2 highly sensitive to q. Cell elongation, a central characteristic of CE, and stress is found to vary linearly with e the degree of kinematic restraint. Relevant "mechanical pathways" are also identified.