cr7 was identified as a viable mutant displaying a highly penetrant dorsal head bulge and a less penetrant tail bulge, somewhat similar to
vab-1,-2 , and -3 mutants. The gene represented by
cr7 is named
vab-17 . Several lines of evidence indicate that
vab-17 is essential for embryogenesis, and that
cr7 is hypomorphic.
vab-17 was genetically mapped to LGV and its physical location was refined using PCR to map deficiency breakpoints. None of the candidate cosmids rescued the
vab-17 defect, but rescue was achieved using fosmids covering a cosmid gap. A 10 kb minimal
vab-17(
cr7) rescuing fragment was found, which led to the identification of several Kohara cDNAs. These cDNAs correspond to alternatively spliced variants of
vab-17 . Additional cDNA clones were obtained by RT-PCR, and it was found that
vab-17 expresses multiple transcripts of different sizes that are alternatively spliced and have alternative 5' ends.
cr7 is a nonsense mutation in an alternative exon. The largest predicted protein encoded by the
vab-17 locus has 7-12 WD-40 repeats and a molecular mass of 180 kDa. WD-40 motifs are believed to mediate the assembly of macromolecular complexes. To obtain a preliminary picture of VAB-17 expression, an in-frame GFP fusion was constructed using the minimal
vab-17(
cr7) rescuing fragment. The fusion protein localises to the cytoplasmic face of adherens junctions, but unlike the adherens junction staining displayed by MH27, the VAB-17 fusion is not associated with embryonic hypodermal adherens junctions. In the course of genetically mapping
vab-17 , it was found that mutations in members of the GABAergic pathway exhibit synthetic lethality with
vab-17(
cr7) . We have taken advantage of this lethality to identify a series of potential
vab-17 intragenic revertants, which are weakly Vab, yet suppress the synthetic lethality.