Fig. 6. A mutagenesis screen identifies sensory axon and dendrite arborization phenotypes. (A) Wild-type class IV embryonic axon scaffold visualized by ppk-eGFP. (B-D) Defects in longitudinal branch formation shown by lines isolated from the screen. Arrowheads in B-D indicate missing longitudinal tracts. (E) l(3)2332 mutants show loss of most commissural branches. (F) boojum (bum) mutants show loss of commissural axon branching in the CNS and highly reduced dendritic branching (G,H). Arrowheads in E-F indicate missing commissural branches. Arrows in H indicate stunted dendritic arbors. (I) Labeling with the axonal marker BP102 shows that despite the lack of sensory axon commissural branches, commissural tracts seem to develop normally but undergo a successive loss of labeling or integrity during development. Temporal progresssion is inferred by gut morphology and VNC length. Arrows indicate grossly intact areas of the VNC; arrowheads indicate areas that are disrupted. (J-O) Mutations disrupting axon tract coherence or position. Lines l(3)11534 (J) and l(3)1025 (K) lack a coherent longitudinal axon tract (arrowhead). (L-M) Mutations in brahma (brm), a chromatin remodeling factor, show defasciculation or thinning of longitudinal tracts. (N-O) Axon phenotype of two boa alleles. Note that axons generally branch lateral to, rather than between, longitudinal branches (arrowheads). (P) boa mutants show no obvious abnormalities in dendrite morphology. (Q) Staining of boa² mutants with the axonal marker BP102 reveals the presence of longitudinal (arrows) and commissural (arrowhead) tracts but relatively weak labeling. Anterior is up in CNS images. Dorsal is up in PNS images. Animals are stage 17 except E,P, which are hatchling larvae. Scale bars: 25 µm in I,Q.