Fig. 1. The karussell phenotype. Dorsal view of dissected embryonic nervous systems stained for BP102 expression. Anterior is to the left. (A) In wild-type stage-14 embryos, commissures are established as regular axon fascicles. (B) In wild-type stage-16 embryos, the typical ladder-like axon pattern is established. Two clearly separated commissures (anterior commissure, ac; posterior commissure, pc) are found in every neuromere. Neuromeres are connected by the longitudinal connectives (lc). (C) In stage-14 hemizygous-mutant ß-spectrin^kusS012 embryos, characteristic loops are found at the point where commissural axons normally enter the connectives (arrows). (D) Stage-16 hemizygous ß-spectrin^kusS012 embryo. The longitudinal connectives are found closer to the midline and appear thinner (arrowhead); in addition, the segmental commissures are not clearly separated and appear slightly fused (arrow). (E,F) Hemizygous ß-spectrin^kusS012 embryos that express ß-spectrin under the control of the elav promoter. The axonal phenotype is rescued.