| The cytoskeleton mediates developmental changes in cell shape, adhesive properties and motility. We have characterized the function of myosin light chain/moesin phosphatase, a regulator of cytoskeletal function, in Drosophila photoreceptor development. Mutations in the gene encoding the myosin/moesin binding subunit of this enzyme cause photoreceptors to drop out of the eye disc epithelium and move towards and through the optic stalk. We show that this phenotype is due to excessive phosphorylation of the myosin regulatory light chain Spaghetti squash rather than another potential substrate, Moesin, and that it requires the non-muscle myosin II heavy chain Zipper. Myosin/moesin binding subunit mutant cells retain their epithelial character and apical-basal polarity, and do not undergo ectopic apical constriction. In addition, mutant cells in the wing disc remain within the epithelium and differentiate abnormal wing hairs. We suggest that excessive myosin activity in photoreceptors generates a traction force that pulls the cell bodies toward the axon terminals. |
