Worm Breeder's Gazette 8(2): 24
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.
We have identified mutations in 5 new unc genes that lead to foreshortened or misguided PHA and PHB axons as determined by FITC uptake. PHA and PHB are bilaterally symmetric pairs of sensory neurons with cell bodies in the right and left lumbar ganglia of the tail. They have dendrites that end in the phasmid sensilla and axons that extend forward into the pre-anal ganglion (PAG) at the posterior end of the ventral nerve cord. Mutants unc(ev404)I, unc(ev416)I, and unc(ev411)V are similar to mutants of unc-33 IV, unc-44 IV, unc-51 V, and unc-76 V (Hedgecock et al, WBG 7#1 p. 70) in that the phasmid axons accurately find the ventral nerve cord but terminate prematurely, stopping just as they enter the posterior end of the pre-anal ganglion. The terminals of these neurons appear to be abnormally enlarged. In two mutants unc(ev400)X and unc(ev410)1 the phasmid axons frequently fail to reach the ventral nerve cord and instead run in various lateral positions. In cases where the phasmid axons do reach the ventral nerve cord, however, the axons appear to grow forward into the PAG normally. Thus, there are two predominant (and some minor) classes of unc(ev400) animals. 1) Animals in which the phasmid axons from right and left find the ventral nerve cord and grow forward into the PAG. These animals look like wild type in phasmid axon morphology. Animals in which phasmid axons from one side fail to find the ventral cord and are misdirected, while those on the other side find the cord and grow forward into the PAG (i.e. appear normal). In the unc-76 unc(ev400) double, two analagous classes of animals are found. 1) Animals in which the phasmid axons from right and left find the ventral cord but fail to grow forward into the PAG (equivalent to the unc-76 phenotype). 2) Animals in which phasmid axons on one side fail to find the ventral cord, while those on the other side find the cord. Surprisingly, in these one-sided animals those phasmid axons that do find the ventral cord are able to grow forward into the PAG despite the unc-76 mutation. Apparently the unc-76 phenotype is not always expressed in axons that reach the PAG in one-sided animals, presumably because the PAG is different in these individuals (for example, the axons from contralateral PHA and PHB homologs are absent).