Translocation and interaction of PAR proteins explain oscillation and ratcheting mechanisms during Drosophila dorsal closure

We have developed a mechanochemical model that is able to recapitulate the Drosophila dorsal closure (DC) phenomenon. During DC, an opening on the dorsal side of the embryo is sealed in a great feat of coordination at the cellular and tissue scales of the embryo. The amnioserosa tissue, in the dorsal opening, exhibits three distinct phases of dynamic behavior: an early phase characterized by cellular oscillations, a late phase distinguished by dampening oscillations and loss of area, and a final late phase which is marked by rapid tissue contraction. Based on recent experimental observations, we couple the kinetics and transport of 3 key signaling proteins with cell mechanics to establish a delayed-negative feedback network that reproduces the three phases and provides a natural transition between them. In particular, the model explains the origin of the cell oscillation in the early phase, and that of the subsequent “ratcheting” action that allows the cells and tissue to shrink progressively over cycles of oscillation.