The mechanics of cephalic furrow formation in the Drosophila embryo investigated using anadvanced vertex model

Cephalic furrow formation (CFF) in the Drosophila embryo is driven by a sequence of intricate cell-shape changes in the invagination region. Mechanical cell activity involves coordinated constrictions and expansions of the apical, lateral and basal cell membranes. Moreover, as evident from the membrane curvature, there is also pressure variation from cell to cell. To identify mechanical forces that drive CFF we have developed an advanced 2D vertex model that incorporates membrane curvature into the system description. Our simulations of the invagination process show that the pressure in the cells entering the invagination region from anterior and posterior directions initially decreases, which results in the enhancement of the cell flexibility. As the cells advance through the invagination region the pressure increases to produce a stiffer base of the invaginated domain. In coordination with these pressure changes, apical and lateral cell membranes first relax and then increase their tension to produce unidirectional motion towards the high-pressure base. Our simulations of a perturbed system show that precise mechanical coordination of cell activities is needed for a successful invagination.