Fig. 6.
RacGAP mutants do not have general defects in the actin or microtubule cytoskeleton. (A-H) Phalloidin labeling showing LT (A-B′,E-F′) and ventral (C,D,G,H) muscles. During MAS selection, F-actin concentrates at the ends of myotubes in the wild type (A-C) and in RacGAPDH15 mutants (E-G). Magnification of LT ends shows multiple filopodia in both wild type (B,B′) and RacGAPDH15 (F,F′). At stage 16, F-actin continues to accumulate at muscle ends (D). In RacGAPDH15 mutants, F-actin accumulation occurs even when muscles attach to the wrong site (H, arrowhead) or contain ectopic extensions (H, arrow). (I-L) Anti-β3-tubulin labels microtubules (MTs) in somatic muscles. At stage 13 during myoblast fusion, wild type (I) and RacGAPDH15 (K) have a similar β3-tubulin pattern. By stage 16, wild-type MTs are organized along the longitudinal axis of each muscle (J). In RacGAPDH15 mutants, MTs are present, but muscles make inappropriate attachments (L, arrowheads).