Worm Breeder's Gazette 12(3): 33 (June 15, 1992)
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.
Several genes were shown to be essential for the normal outgrowth or correct guidance of the neuronal axons in C. elegans. The unc-51 gene is one of such genes, and the mutants are paralyzed, egg laying defective and dumpy . Fluorescent dye uptake or monoclonal antibody staining of the neural network in unc-51 mutants have revealed that some neurons ( DD, VD and PDE ) have misdirected axons (1)(2) and other neurons (PHA, PHB and HSN ) have shortened axons without visible defects in musculature (1)(3) In unc-51 mutants, these neurons also contain large, atypical varicosities and significant enlargements in axon diameter as well as many abnormal vesicles and cisternae-like structures within axons (1)(3) similar to the phenotypes of shibire mutant of Drosophila (4). These results suggest that the primary defect of unc-51 mutants may be in the membrane structure or function, leading to abnormal axon formation (2).
A part of the presumed unc-51 gene was cloned by tagging with transposon Tc1 (5) The cloned fragment (2.7kb, EcoRI) was mapped by A. Coulson to a cosmid F43A2 in a small isolated contig. Introduction of the DNA of cosmid F43A2 rescued the phenotypes of unc-51 ( e369 )to wild type. A 13kb EcoRI - Sall fragment in the cosmid also rescued completely. A 10kb Clal - Sall fragment within this fragment rescued nearly completely, but neither left half nor right half of the 10kb fragment rescued at all. A cDNA clone of 2.9kb excluding poly A was isolated, which is encoded both by the left and right halves of, but included entirely within, the 10kb Clal - Sall fragment. This cDNA contains a single open reading frame for 856 amino acids with a serine/threonine kinase catalytic domain (6) near the N-terminus. Analysis of the corresponding genomic region of the original unc-51 ( ks38 ::T c1 )revealed Tc1 insertion within a coding region for the 856 amino acids protein. A cDNA fragment detects a single RNA band of 3.1 kb on a Northern blot of wild type N2 .These results indicate that the unc-51 gene encodes the 856 amino acids protein. The presumed kinase domain cannot easily be classified in any of the known subfamilies, and the relatively long C-terminal portion does not share significant sequence similarities with any of the proteins so far identified, suggesting that the presumed product is a novel serine/threonine kinase. These findings suggest that protein phosphorylation is important for construction of the neuronal membrane structures as well as axon formation.
(2.) McIntire, Garriga, White, Jacobson, & Horvitz, Neuron 8, 307-322 (1992)
(3) Desai, Garriga, McIntire, & Horvitz, Nature 336, 638-646 (1988)
(4) Koenig, Saito, & Ikeda, J. CellBiol. 96,1517-1522 (1983)
(5) Ogura, Mori, & Ohshima, W. B. G. 12(1), 19 (1991). 6. Hanks, Quinn, &Hunter;, Science 241, 42-52 (1988).