Arc controls organ architecture through modulation of Crb and MyoII.

Precise orchestration of morphogenetic processes generates organs that are optimally positioned and the right size and shape to fit and maximize functionality. Here, we show that Arc, a large apical membrane-associated PDZ domain-containing protein, works through the apical determinant Crumbs to limit non-muscle myosin II (MyoII) activity during tissue invagination in the Drosophila salivary gland (SG). We show that loss of Arc, attenuation of Crumbs, and increased activation of MyoII leads to the simultaneous internalization of more precursor cells than normal. Consequently, mature SGs are shorter with more cells surrounding the lumen all along the tube. Correspondingly, overexpression of Arc or SG-specific knockdown of MyoII leads to longer SGs with fewer cells surrounding the lumen. Our findings support a model wherein plasma membrane (PM)-associated Crumbs stabilizes cellular junctions by limiting apical pools of activated MyoII and countering the destabilizing effects of MyoII at the PM, limiting how many cells internalize at any given time, shaping final tube geometry.