Specific isoforms of drosophila shroom define spatial requirements for the induction of apical constriction.

Vertebrate Shroom proteins define cytoskeletal organization and cellular architecture by binding directly to F-actin and Rho-kinase and spatially regulating the activity of nonmuscle myosin II (myosin II). Here, we report characterization and gain-of-function analysis of Drosophila Shroom. The dShrm locus expresses at least two protein isoforms, dShrmA and dShrmB, which localize to adherens junctions and the apical membrane, respectively. dShrmA and dShrmB exhibit differing abilities to induce apical constriction that are based on their subcellular distribution and the subsequent assembly of spatially and organizationally distinct actomyosin networks that are dependent on the ability to engage Rho-kinase and the activity of myosin II. These data show that the differential subcellular distribution of naturally occurring isoforms of Shroom proteins can define both the position and organization of actomyosin networks in vivo. We further hypothesize that differentially positioned contractile arrays have distinct effects on cellular morphologies and behaviors.