A murine neural-specific homolog corrects cholinergic defects in Caenorhabditis elegans unc-18 mutants.
Caenorhabditis elegans UNC-18 protein, homologous to yeast Sec1p, is important in neurotransmitter release, because the unc-18 mutation leads to severe paralysis and presynaptic acetylcholine (ACh) accumulation. To examine the functional conservation in mammals, we tried to isolate unc-18 isoforms from mouse and human brain cDNA libraries and obtained two classes of isoforms-neural genes and ubiquitous genes. Neural genes were identical to Munc-18 (also known as n-Sec1 or rbSec1), identified in rat and bovine brains as a syntaxin-binding protein. According to "Munc-18" terminology, we call the neural genes Munc-18-1 and the ubiquitous genes Munc-18-3. These mammalian isoforms exhibit 58% (Munc-18-1) and 42-43% (Munc-18-3) amino acid sequence identity with UNC-18. Next, we constructed transgenic unc-18 mutants to test biological activity of mouse Munc-18-1 and Munc-18-3 under the control of C. elegans unc-18 promoter. Munc-18-1 compensates for severe locomotion disability and cholinergic defects, e.g., abnormal sensitivities to cholinesterase inhibitors and cholinergic receptor agonists in unc-18 mutants, but Munc-18-3 fails. These data suggest that Munc-18-1 and C. elegans unc-18 may play positive roles in ACh release and that the molecular mechanism of neuronal regulated secretion has been partially conserved from nematodes to mammals.
Gengyo-Ando
K
K
Laboratory of Molecular Oncology, The Institute of Physical and Chemical Research (RIKEN), Tsukuba, Ibaraki 305, Japan.
Kitayama
H
H
Mukaida
M
M
Ikawa
Y
Y
D000818:Animals; D030801:Animals, Genetically Modified; D000918:Antibody Specificity; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000235:genetics*; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D002799:Cholinergic Fibers / Q000737:chemistry / Q000502:physiology*; D003001:Cloning, Molecular; D005816:Genetic Complementation Test; D015801:Helminth Proteins / Q000235:genetics*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D051938:Munc18 Proteins; D009154:Mutation / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000235:genetics; D018377:Neurotransmitter Agents / Q000502:physiology; D010750:Phosphoproteins; D012333:RNA, Messenger / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D013572:Synaptic Vesicles / Q000235:genetics; D033921:Vesicular Transport Proteins; D005680:gamma-Aminobutyric Acid / Q000276:immunology
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D015801:Helminth Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D010750:Phosphoproteins; D012333:RNA, Messenger; C497937:STXBP1 protein, human; C497938:Stxbp1 protein, mouse; C497943:Stxbp3 protein, mouse; C082636:Unc-18 protein, C elegans; D033921:Vesicular Transport Proteins; D005680:gamma-Aminobutyric Acid