Synaptic exocytosis and nervous system development impaired in Caenorhabditis elegans unc-13 mutants.
C. elegans mutants defective in unc-13 exhibited severe behavioral abnormalities including paralyzed locomotion and slow pharyngeal pumping and irregular defecation cycle. Consistent with the phenotypes, the mutants accumulated abnormally high levels of the neurotransmitter acetylcholine and were resistant to acetylcholinesterase inhibitors. The unc-13 gene was expressed in most, if not all, neurons when analyzed by using chimeric constructs consisting of the unc-13 promoter and green fluorescence protein or beta-galactosidase reporter gene. While Ca(2+)-regulated acetylcholine release is lacking, the mutants were still able to release acetylcholine in vivo and in vitro at similar levels to that mediated by the regulated mechanism. Double mutants defective in both unc-13 and other genes involved in synaptic transmission showed the Unc-13 phenotype, rather than other mutant phenotypes, in terms of locomotion as well as of acetylcholine accumulation. Furthermore, electron microscopic reconstruction of the mutant nervous system uncovered that a majority of neurons developed and connected as those in the wild type except for subtle abnormalities including inappropriate connections through gap junctions and morphological alterations of neurons. These results demonstrate that the unc-13 gene product plays an essential role at a late stage in Ca(2+)-regulated synaptic exocytosis. Neurotransmitters released through the Ca(2+)-regulated mechanism are required for, but do not play major roles in the nervous system development. The large amount of Ca(2+)-independent neurotransmitter release observed in the unc-13 mutants suggests that there may be a distinct mechanism from evoked or spontaneous release in neurotransmission.
Maruyama
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Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Rakow
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Maruyama
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D000109:Acetylcholine / Q000235:genetics / Q000378:metabolism; D000110:Acetylcholinesterase / Q000096:biosynthesis / Q000235:genetics; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D017173:Caenorhabditis elegans / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics; D002352:Carrier Proteins; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000235:genetics*; D020233:Gait Disorders, Neurologic / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D017952:Ganglia, Invertebrate / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D017629:Gap Junctions / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D017930:Genes, Reporter / Q000235:genetics; D005838:Genotype; D015801:Helminth Proteins / Q000235:genetics* / Q000378:metabolism; D008854:Microscopy, Electron; D009046:Motor Neurons / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D009154:Mutation / Q000502:physiology*; D009421:Nervous System Malformations / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D009474:Neurons / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure; D013569:Synapses / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics*
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D002800:Cholinesterase Inhibitors; D015801:Helminth Proteins; C083141:phorbol ester binding protein; D000110:Acetylcholinesterase; D000109:Acetylcholine