Movie 3.

F-actin and Myosin II are transiently enriched during the initiation phase of the AP boundary. Time-lapse movies of histoblasts in the pupal abdominal epidermis expressing utABD-GFP to visualize F-actin (left) or Sqh-GFP to visualize Myosin II (right). Times relative to the first contact between A and P cells are indicated. Large cells are larval epidermal cells (LECs). LECs extruding at the future site of the AP boundary are labeled by an ‘L’. Scale bars are 20 μm.