The FCM-specific F-actin foci in sltr and kette mutants exhibit different invasive behavior. (A–D) F-actin foci in kette and sltr mutant embryos reside in FCMs. Stage 14 (A and C) and stage 15 (B and D) mutant embryos triple labeled with α-GFP (green), phalloidin (red), and α-Duf (blue). kette (A and B) or sltr (C and D) mutant embryos expressing GFP-actin in FCMs (with sns-GAL4; A and C) or in founder cells (with rP298-GAL4; B and D) are shown. GFP-negative founder cells (labeled as “f”) in A and C are outlined except at sites of cell adhesion with FCMs because the founder cell membranes at these sites cannot be delineated at this resolution. Note the colocalization of GFP- and F-actin–positive foci at muscle cell adhesion sites when GFP-actin was expressed in FCMs (A and C; arrowheads). Also note that in sltr (D), but not kette (B) mutant embryos, founder cell–expressed GFP-actin showed slight enrichment (arrows) along the cell membrane adjacent to the FCM-specific F-actin foci. Asterisks in A and C mark FCMs that are yet to express GFP-actin. (E–I) F-actin foci in sltr and kette mutants show different invasive behavior. Stage 14 wild-type (E, wt) and stage 15 sltr (F), wsp^mat/zyg (G, eliminating both maternal and zygotic WASP), kette (H), or scar^mat/zyg (I) mutant embryo triple labeled with α-Duf (red), phalloidin (green), and α-Lmd (blue). A typical “invasive” F-actin focus is shown for each genotype. Note the reduced depth of foci invasion (arrowheads) in sltr (F) and wsp^mat/zyg (G) embryos, and the similar depth of foci invasion (arrowhead) in kette (H) and scar^mat/zyg (I) embryos, compared with wt (E). Bar, 5 µm.