colXIX RNA is dynamically expressed during motor axon outgrowth. (A-D′) RNA in situ hybridization using colXIX anti-sense (A-D) and sense (A2-D′) riboprobes that encompasses exons 1-27 of the zebrafish colXIX cDNA at (A,A′) 19 hpf, (B,B′) 24 hpf, (C,C′) 30 hpf and (D,D′) 36 hpf. Sections were from the mid-trunk region. (E) Histogram of colXIX RNA in situ hybridization intensity at 19 hpf for wild-type (n=8 embryos; -40 sections) and stumpy mutant embryos (n=8 embryos; -40 sections). The x-axis reflects the intensity of the colXIX expression. Spinal cord (sc) and notochord (nc) are indicated by white borders. Arrows show localization of colXIX transcripts in the myotome. Scale bar: 20 μm.

ColXIX knock down phenocopies the stumpy mutation. (A) RT-PCR shows inclusion of a 109 bp fragment in splice-blocking colXIX MO injected (MO) compared to wild-type (wt) embryos. (B-D) CaP axon phenotypes as visualized using znp-1 antibody in (B) uninjected wild-type embryos, (C) wild-type embryos injected with 9 ng colXIX MO and (D) stumpy^b393-/- mutant embryos. White dashed line indicates the horizontal myoseptum. Scale bar: 70 μm.

Mutant ColXIX acts as a dominant negative. (A-C) Examples of CaP axon defects observed in embryos injected with mutant ColXIX RNA. White dashed line indicates the horizontal myoseptum. Arrowhead denotes Stumpy-like CaP axons.

Rescue of stumpy^b393-/- mutants with mouse ColXIX RNA. (A) stumpy^b393-/- embryo. (B-D) Representative images of stumpy^b393-/- embryos co-injected with translation blocking colXIX MO and full-length mouse ColXIX RNA. Arrowheads indicate rescued CaP axons. An abnormal axon is indicated by the arrow. White dashed line indicates the horizontal myoseptum. Scale bar: 70 μm.