Principal Investigator Adam Martin
Tissue movements throughout development are driven by collective cell shape changes. For example, a sheet of polarized columnar cells, called an epithelium, can bend and fold when cells constrict at their apical end, a process known as apical constriction. During Drosophila gastrulation, apical constriction is thought to drive the invagination of cells along the ventral midline, which will eventually form the mesoderm (much of which becomes the muscle) of the fly. Apical constriction was widely believed to result from the gradual purse-string-like contraction of a belt of actin filaments and myosin (type II) motors around the apical circumference of the cell. However, simultaneous live imaging of both cell shape and myosin demonstrated that a dynamic contractile meshwork of actin and myosin spans the apical cortex of these epithelial cells. Importantly, these actomyosin contractions are pulsed, with phases of rapid constriction (contraction) interrupted by pauses where the constricted state is maintained (stabilization). Using a combination of traditional cell biology and genetics, RNAi, and quantitative analysis, we showed that the cell apex constricts incrementally like a ratchet. Our lab is further investigating the molecular mechanisms of this ratchet-like constriction.