Fig. 4.
FC specification and myoblast fusion are not affected in RacGAP mutants. (A,B) In wild-type Drosophila embryos at stage 12, Eve is expressed in the founder cell (FC) for muscle 1 (DA1) and two pericardial cells (A). These cells are properly specified in RacGAPDH15 embryos (B). (C) Runt staining labels FCs for muscles 10 (DO2), 28 (VO3) and 15 (VO4) at stage 12. (D) In RacGAPDH15 embryos, Runt-positive FCs are properly specified, although some segments contain an extra Runt-positive muscle 10 nucleus (arrow), whereas FCs for muscles 28 and 15 are unaffected (arrowhead). (E,F) Anti-Vestigial labels a subset of FCs at stage 12 in the wild type (E), and this staining is normal in RacGAPDH15 mutants (F). (G,H) By stage 14, FCs have fused with fusion-competent myoblasts (FCMs), showing an increase in Vestigial-positive nuclei of wild-type dorsal muscles (G). Fusion also occurs in RacGAPDH15 mutants (H). (I,J) 5053A-GAL4/UAS-lacZ embryo stained for Muscle myosin to label all muscles (magenta) and for β-galactosidase to label nuclei (green) of muscle 12 (VL1). In the wild type (I), muscle 12 spans each hemisegment and contains ∼11 nuclei. In RacGAPDH15 mutants (J), muscle 12 is specified and contains the correct number of nuclei, but is mispositioned in 6% of hemisegments (n=52) (brackets). Asterisks mark intestinal cells that are also labeled with the 5053-GAL4 driver.