Cultured primary neurons derived from either homozygous chb2 or chb2/Df(3L)BSC553 embryos have a significantly reduced axon length compared to wild-type controls.
chb2 mutant hemocytes exhibit a delay in migration along the ventral midline. Individual hemocytes fail to distribute evenly at stage 15, indicating a defect in contact repulsion. chb2 hemocytes are frequently seen in contact with one another for more than 15 minutes (wild-type hemocytes are rarely seen in contact for more than 10 minutes). chb2 hemocytes are still capable of migration to both epithelial wounds and in response to developmental guidance cues. chb2 mutant hemocytes migrating to wounds exhibit reduced directional persistence and an increase in migration speed when compared to wild-type cells.
Microtubules in chb2 mutant cells are highly dynamic and are able to both polymerize and undergo catastrophe. However, unlike in wild-type cells, microtubule polymerization is unpolarized: no microtubules are stabilized or bundled, with no microtubule arm developing.
Homozygous and chb2/chb4 embryos show ectopic crossing of the midline by axons in the central nervous system. Sema-2b-expressing neurons show erratic trajectories both approaching the midline and along the longitudinal neuropil in the central nervous system of homozygous embryos. The Sema-2b-positive axon tracts show a significant inward shift in their lateral position.
Mitotic defects are seen in the cells of the larval central nervous system in chb2/chbS068607 flies. Polyploid metaphase figures (16%), diploid metaphase figures with hypercondensed chromosomes (40%) and circular metaphase figures (3%) are seen. The metaphase to anaphase ratio and the mitotic index is increased compared to wild type. Third instar chb2/Df(3L)Pc-9a, chb3/chb2 or chb4/chb2 larvae lack imaginal discs and have a small central nervous system. More than 80% of total metaphase figures are polyploid, and more than 30% of polyploid figures have greater than an 8N chromosome complement. Circular metaphase figures and anaphase figures cannot be detected.