unc-69 is required for axonal outgrowth, guidance, branching and fasciculation in invertebrates and vertebrates. (a,b) Defect in the migration of the HSN neuron in unc-69 mutant animals. (a) In wild-type animals, the HSN axons (HSNL and HSNR) migrate ventrally until they reach the VNC, which they join and follow rostrally towards the head (arrow in (a)). (b) In unc-69 mutants, HSN axons occasionally fail to grow ventrally and instead project laterally along the body wall (arrow in (b)). Animals were stained with anti-serotonin antibodies to visualize the HSN neurons. Arrowheads indicate the vulva. Dotted lines mark the ventral margin of the body walls. (c,d) Commissures of D-type GABAergic neurons routinely reach the DNC in wild-type animals (c), but often fail in unc-69(e587) animals (d) and prematurely bifurcate (arrow). D-type GABAergic neurons were visualized with the unc-47::gfp transgene oxIs12. Asterisk in (d) marks a gap in the DNC. There are also often ectopic sprouts from the commissures (arrowheads in (d)) in unc-69(e587) mutants. (e,f) Images of the single ALM touch neuron in (e) wild-type and (f) unc-69(e602) animals. Many ectopic neurites branched out from the soma and the axonal shaft of the ALM neuron in unc-69(e602) mutant (arrowheads). (g,h) Tracings of representative electron micrographs of sections through the DNC and VNC. (g) In the wild type, the position and content of the three major fascicles are highly stereotyped (black arrows). (h) In unc-69(e587) mutants, defasciculated axons can often be found migrating separately along the body wall (open arrows). (i,j) Morphology of the bipolar AWC sensory neuron in (i) wild-type and (j) unc-69(e587) animals. Dendrites of AWC neurons in both animals reach the nose (arrows). Axonal shape is normal in wild-type worms, but abnormal in unc-69(e587) mutants, with ectopic bulges occasionally extending from the soma (arrowhead in (j)). (k,l) Expression pattern of SCOCO in stage 26 chick embryos. Sections were incubated with (k) antisense and (l) sense RNA probes for chick SCOCO. SCOCO was highly expressed in neural tissue and was most prominent in DRGs and in motoneurons of both the lateral motor column (LMC) and the medial motor column (MMC). Expression in the notochord (NC) and dermamyotome (DMT) was less pronounced. (m,n) In ovo RNAi of chick SCOCO. Embryos injected and electroporated with double-stranded RNA corresponding to (m) a yfp-containing plasmid or (n) chick SCOCO were immunostained with anti-neurofilament antibodies. (m) In control embryos, the epaxial nerves extending dorsally toward their target, the epaxial muscle, were highly fasciculated. (n) RNAi of SCOCO led to defasciculation of epaxial nerve bundles and extensive branching between muscle segments (arrows). In all panels dorsal is up. Scale bars represent: (a-j) 10 μm, (k,l) 100 μm and (m,n) 500 μm.