Fig. 1. Myoblast fusion is severely disturbed in rols mutants. The muscle phenotype of rols mutants (C-H) is compared with the wild-type (A,B) pattern of the body wall muscles. The mesoderm is visualized with antibodies against ß3-tubulin. (C) Df(3L)BK9 embryo, stage 16, lateral view; the number of myotubes as well as their orientation is altered significantly. (D) Same embryo as in C but at a higher magnification; the disarranged myotube pattern as well as single, unfused myoblasts (arrow) are shown. (E) Df(3L)BK9 embryo, stage 16, dorsal view; the dorsal vessel is nearly undisturbed; most unfused myoblasts are arranged nearby formed myotubes. (F) Same embryo as in E, but at higher magnification; the alignment of unfused myoblasts (arrow) at individual muscles is evident. (G) rols^AD328, EMS-induced allele, late stage 16, lateral view; the pattern of the somatic muscles is also severely disturbed, however, owing to the later embryo stage, the number of unfused myoblasts is reduced in comparison with C. (H) rols^P1729ber, a P-element induced allele, stage 15, dorsolateral view. As in the other alleles, muscle number is reduced, and many unfused myoblasts are visible; also the pharynx (arrow) shows fusion defects. Again, the dorsal vessel is only weakly affected.