S 1 1 Model description

The models referred to in the main text, simulate the coupling of mechanical and molecular forces in the early stages of the development of mammalian embryo. The assumptions made in describing single cell mechanics follow the postulates introduced in [1, 2]. As in [1, 2], we describe the cell as an incompressible ellipsoid whose elastic response is characterized by three orthogonal springs placed along the three axes of the ellipsoid. In principle, deformations of the ellipsoid are allowed. However, in our simulations we find that, since the orientation of the ellipsoidal axes constrains available degrees of deformational freedom, arbitrary (nondynamical) positioning of these axes leads to unphysical behavior or even instability of the solutions. Thus, even though the formalism presented here is applicable to ellipsoidal shapes we restrict ourselves in simulations to allowing for spherical shapes of the cells only.