UNC-119 is the first example of a novel class of protein found in both the developing and adult nervous systems of the nematode, the fly, the zebrafish (see poster by Angela Manning) and in mammals. While UNC-119 is found throughout the C. elegans nervous system, beginning around the 60-cell stage, the human and rat homologs (HRG4 and RRG4, respectively) have only been found in retinal tissue, beginning shortly after birth. The fly homolog (DmUnc-119) is expressed throughout the larval central nervous system. In the worm, four
unc-119 null alleles have been characterized in addition to the wild type. Apart from the canonical nearly paralyzed, uncoordinated phenotype, these mutants also exhibit constitutive feeding behavior even in the absence of food and are unable to enter into the dauer larva stage when subjected to overcrowding and starvation. Both the behavioral and morphological phenotypes suggest that UNC-119 plays a role in growth cone guidance in the developing nervous system. An UNC-119::GFP fusion protein is found in the cytoplasm of all cells of the nervous system. In an
unc-119 mutant the ventral nerve cord (VNC) is defasciculated and the lateral commisures, which normally project from the VNC dorsolaterally to join the dorsal nerve cord have an abnormal, highly branched structure. We have integrated GFP constructs, driven by promoters specific to subsets of neurons, into both wild-type and
unc-119 mutant strains and compared neural structures at high magnification using confocal microscopy. The projections of many neurons are unaffected by the
unc-119 mutation while abnormally long axons, abnormally branched axons and defasciculated axons are associated with neurons affected by the mutation. We have also conducted a yeast 2-hybrid screen using an
unc-119 bait construct and have found several positive interactions that are selective for UNC-119 versus a SNF-4 bait. These preliminary results are presently being confirmed using the human homolog, HRG4, as bait in a 2-hybrid experiment. Co-immunoprecipitation experiments are also underway.