Mobile E-cad–Baz prevents cells from crossing the segment boundary. (A) Examples of stripes of en::Gal4 driving GFP (red), with cell outlines labeled with anti–E-cad (green). In most cases, cells do not cross the segment boundary (white line, left). When cells cross, one can see independent events with different levels of GFP (middle, arrowheads), a rare example of a cell pair in the process of crossing the boundary (right, arrow). Bars, 5 µm. (B) Quantitation of cell behavior in control cells and cells expressing CD8, EB1-DN, Spas, or baz-RNAi. (top) Percentage of stripes with cells expressing the engrailed-driven marker transgene on the other side of the segment boundary; (middle) relative rates of cell pair crossing, estimated using Poisson distribution; (bottom) percentage of rosettes, five- and six-cell contacts, between cells within the posterior compartment (the cells at the boundary and their anterior neighbors). In each case, the mean ± 95% CI is shown (error bars); for raw data and examples of fitting with Poisson distribution, see Fig. S3. (C) Examples of three-cell contact (3), four-cell contact (4), and five-cell contact rosette (R) between cells at the segment border and their anterior neighbors, indicated with asterisks in A. (D) Localization of MyoII-YFP (black/green) in wild-type cells and adjacent cells expressing CD8, EB1-DN, Spas, or baz-RNAi marked with Cherry (magenta). Bars, 5 µm. (E) Quantitation of cortical MyoII levels, see also Table S1. *, P < 0.01; **, P < 0.001; ***, P < 0.0001.