Microtubules stabilize intercellular contractile force transmission during tissue folding

Abstract

1During development, forces transmitted between cells are critical for sculpting epithelial 2 tissues. Actomyosin contractility in the middle of the cell apex (medioapical) can change 3 cell shape (e.g., apical constriction), but can also result in force transmission between 4 cells via attachments to adherens junctions. How actomyosin networks maintain 5 attachments to adherens junctions under tension is poorly understood. Here, we 6 discovered that microtubules promote actomyosin intercellular attachments in epithelia 7during Drosophila mesoderm invagination. First, we used live imaging to show a novel 8 arrangement of the microtubule cytoskeleton during apical constriction: medioapical 9Patronin (CAMSAP) foci formed by actomyosin contraction organized an apical non-10 centrosomal microtubule network. Microtubules were required for mesoderm 11 invagination but were not necessary for initiating apical contractility or adherens junction 12 assembly. Instead, microtubules promoted connections between medioapical 13 actomyosin and adherens junctions. These results delineate a role for coordination 14