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Comments on C Gally et al. (2004) European Worm Meeting "LEV-10 ENCODES A TRANSMEMBRANE PROTEIN REQUIRED FOR ACETYLCHOLINE RECEPTOR CLUSTERING AT NEUROMUSCULAR JUNCTIONS IN C. ELEGANS" (0)
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C Gally, S Eimer, H Ung, J Richmond, & J Bessereau (2004). LEV-10 ENCODES A TRANSMEMBRANE PROTEIN REQUIRED FOR ACETYLCHOLINE RECEPTOR CLUSTERING AT NEUROMUSCULAR JUNCTIONS IN C. ELEGANS presented in European Worm Meeting. Unpublished information; cite only with author permission.
Clustering neurotransmitter receptors at the synapse is critical for efficient neurotransmission. In C. elegans genetic dissection of cholinergic neurotransmission has been greatly facilitated by the use of the antihelmintic drug levamisole: levamisole activates AChR receptors present at neuromuscular junctions (NMJs) which causes muscle hypercontraction and even death at high concentrations. Screens for mutants which exhibit strong resistance to levamisole have identified four genes encoding AChR subunits and two genes that are required for the biosynthesis of levamisole-sensitive AChRs. However, no genes required for AChR clustering were cloned. We hypothesised that impairing the function of such genes would generate subtle phenotype and screened for mutants only weakly resistant to levamisole. Using Mos-1 mediated mutagenesis, we identified a novel allele of lev-10. lev-10 mutants display subtle locomotory impairment and are paralysed on 1 mM levamisole. However, levamisole-sensitive AChRs are no longer detected at NMJs by immuno-fluorescence despite normal cholinergic innervation. Electrophysiological recordings of muscle cells indicate that functional AChRs are present at the muscle cell surface at similar levels in lev-10 and WT animals, but they no longer cluster at the synapse. lev-10 encodes a type I transmembrane protein carrying five CUB domains and one LDLa domain in its extracellular region. This protein is localised to cholinergic neuromuscular junctions and is required in body-wall muscles for AChR clustering. Furthermore, we demonstrate that the clustering activity of LEV-10 is contained in its extracellular region, thus suggesting a novel mechanism for AChR clustering which relies upon extracellular protein-protein interactions. Such a mechanism is likely to be evolutionary conserved since CUB/LDL transmembrane proteins similar to LEV-10, but lacking any assigned function, are expressed in the mammalian nervous system and may be used to cluster ionotropic receptors in vertebrates.
Affiliations:
- Ecole Normale Superieure - INSERM U497 - Paris, FRANCE
- University of Chicago, USA