Principal Investigator Adam Martin
risingly, myosin does not localize around the circumference of Drosoophila mesoderm cells. In contrast to the purse-string model, apical constriction appears to be driven by contraction of an actomyosin meshwork spanning the apical cortex, which pulls the cell surface inwards at discrete junctional attachments. Furthermore, apical constriction and actomyosin meshwork contraction are pulsed, with phases of rapid constriction interrupted by pauses where the constricted state is maintained. Constriction pulses are initiated in mesoderm cells at roughly the same time. However, constriction pulses are asynchronous between adjacent cells, such that cells pull back-and-forth against each other. This means that cells must resist being stretched by their constricting neighbors during a pause (the stabilization phase). Importantly, mutants for the transcription factor Twist continue to exhibit constriction pulses, but fail to constrict because cell shape is not stabilized. Thus, the cell apex constricts incrementally, like a ratchet. The step-wise nature of apical constriction provides a novel framework for thinking about how cellular force is generated and how cell shape change is coordinated because the mechanical state of each cell is dynamic. The lab is investigating the mechanisms behind this ratchet-like cell shape change.