Worm Breeder's Gazette 11(1): 41
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
unc-4 appears to define the wiring diagram for a specific portion of the ventral nerve cord. In unc-4(e120), most VAn motor neurons assume a pattern of presynaptic connections normally reserved for the VBn motor neuron class; VAn's receive input from AVB and PVC interneurons as opposed to the normal sets of connections with AVA, AVD and AVE which are absent in e120 (White et al., WBG 9, p81, 1985). We have now shown that unc-4 may correspond to yet another homeobox locus in C. elegans.A spontaneous allele, unc-4(wd1), was isolated from the mutator strain TR679 in a general screen for movement-defective mutants. Blots of recombinants with flanking markers rol-6 and bli-1 identified two closely linked TC1-containing EcoRI fragments; wdP1 (2. 5 kb) is 0.12 m.u to the right and wdP3 (3.2 kb) is 0.1 m.u to the left. A phage clone overlapping wdP1 was fingerprinted in Cambridge and maps to a large contig near unc-4 on chromosome II. wdP3 includes repetitive DNA and a corresponding phage clone to mark the left side boundary is apparently not represented in our genomic library. The identification of a homeobox sequence in the region, however, suggested a likely location for unc-4. Cosmid C07E2 overlaps, ceh-4, one of 50 different homeobox loci that hybridize with a degenerate oligonuclcotidc probe (T. Burglun and G. Ruvkun, WBG 10, p35, 1988). We probed Southern blots of DNA isolated from 15 independent unc-4 alleles with random primer labeled C07E2. Alterations were detected in five of these alleles: e2314, e2320, e2308 (from M. Shen), e887 and wd-1. All of these mutations affect a 1.8 kb EcoRI fragment (see below). The e2320 mutation deletes 200 bp from the 1.8 kb fragment. In wd-1, the 1.8 kb as well as several other EcoRI fragments are absent suggesting a large deletion (~25kb). The alterations observed in e2314, e2308, and e887 have not been reconstructed but all of these mutations delete the 1.8 kb EcoRI fragment. A restriction map of the region indicates that a 1.05 kb EcoRI fragment containing the homeobox 'third helix' consensus sequence (.WFQNRR.K.R) is adjacent to the region that is altered in unc-4 mutants. We are now searching for a cDNA to determine if in fact the putative homeodomain corresponds to portion of the unc-4 coding sequence. [See Figure 1]