Fig. 2. Morphological defects observed at 48 hpf in acc embryos are secondary to the abnormal behavior. Tricaine is applied to acc embryos from 24 to 48 hpf to immobilize the embryos. Wild-type sibling and a tricaine-treated acc embryo (C) display a straight trunk while an acc mutant (B) displays a bent trunk. DIC images show that the notochord in a wild-type sibling (D) and tricaine-treated acc embryo (F) are undamaged, while the notochord of an acc mutant is breaking apart (E). The normal pattern of slow twitch muscle fibers labeled with MAb F59 is seen in wild-type sibling (G) and tricaine-treated acc mutant (I), but the slow twitch fibers are disarrayed in acc mutants (H).