Myosin VI is required for E-cadherin-mediated border cell migration

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Abstract
Myosin VI (MyoVI) is a pointed-end-directed, actin-based motor protein1,2, and mutations in the gene result in disorganization of hair cell stereocilia and cause deafness in mice3. MyoVI also localizes to the leading edges of growth-factor-stimulated fibroblast cells4 and has been suggested to be involved in cell motility5. There has been no direct test of this hypothesis, however. Drosophila melanogaster MyoVI is expressed in a small group of migratory follicle cells, known as border cells. Here we show that depletion of MyoVI specifically from border cells severely inhibited their migration. Similar to MyoVI, E-cadherin is required for border cell migration. We found that E-cadherin and Armadillo (Arm, Drosophila β-catenin) protein levels were specifically reduced in cells lacking MyoVI, whereas other proteins were not. In addition, MyoVI protein levels were reduced in cells lacking DE-cadherin or Arm. MyoVI and Arm co-immunoprecipitated from ovarian protein extracts. These data suggest that MyoVI is required for border cell migration where it stabilizes E-cadherin and Arm. Mutations in MyoVIIA, another unconventional myosin protein, also lead to deafness, and MyoVIIA interacts with E-cadherin through a membrane protein called vezatin6. Multiple biochemical mechanisms may exist, therefore, for cadherins to associate with diverse unconventional myosins that are required for normal stereocilium formation or maintenance.