Actomyosin contractility plays an important role in orchestrating cell shape changes and tissue morphogenesis, but the upstream signals that coordinate contractility across the tissue are less well understood. In this issue, Donald Ready and Henry Chang study the actomyosin-dependent remodelling of the Drosophila retinal floor, which is crucial for the formation and maintenance of curvature in the fly eye. The remodelling is dependent on the contraction of actomyosin stress fibres in the interommatidial cells (IOCs), which are pigment-secreting cells found between the ommatidia, the functional units of the compound eye. Because calcium signalling is a known regulator of actomyosin activity, the authors express calcium reporters in the eye and observe calcium waves sweeping across the IOCs. These waves are blocked in mutants of the inositol 1,4,5-triphosphate receptor (IP3R). IP3R is required for the release of intracellular calcium stores from the endoplasmic reticulum. IP3R mutant clones also have abnormal stress fibres and a 40% increase in the retinal floor area, indicating actomyosin contractility defects. Furthermore, levels of phosphorylated myosin regulatory light chain, a marker of activated myosin, are reduced in IP3R− IOCs, suggesting a role for calcium signalling in stress fibre contraction. Together, these data describe how calcium signalling coordinates actomyosin contractility across the Drosophila eye to promote tissue remodelling.
