A Cys-loop mutation in the Caenorhabditis elegans nicotinic receptor subunit UNC-63 impairs but does not abolish channel function.
The nematode Caenorhabditis elegans is an established model organism for studying neurobiology. UNC-63 is a C. elegans nicotinic acetylcholine receptor (nAChR) α-subunit. It is an essential component of the levamisole-sensitive muscle nAChR (L-nAChR) and therefore plays an important role in cholinergic transmission at the nematode neuromuscular junction. Here, we show that worms with the unc-63(x26) allele, with its αC151Y mutation disrupting the Cys-loop, have deficient muscle function reflected by impaired swimming (thrashing). Single-channel recordings from cultured muscle cells from the mutant strain showed a 100-fold reduced frequency of opening events and shorter channel openings of L-nAChRs compared with those of wild-type worms. Anti-UNC-63 antibody staining in both cultured adult muscle and embryonic cells showed that L-nAChRs were expressed at similar levels in the mutant and wild-type cells, suggesting that the functional changes in the receptor, rather than changes in expression, are the predominant effect of the mutation. The kinetic changes mimic those reported in patients with fast-channel congenital myasthenic syndromes. We show that pyridostigmine bromide and 3,4-diaminopyridine, which are drugs used to treat fast-channel congenital myasthenic syndromes, partially rescued the motility defect seen in unc-63(x26). The C. elegans unc-63(x26) mutant may therefore offer a useful model to assist in the development of therapies for syndromes produced by altered function of human nAChRs.
Medical Research Council Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, United Kingdom.
Andrew K
AK
Jones
Diego
D
Rayes
Adam
A
Al-Diwani
Thomas P R
TP
Maynard
Rachel
R
Jones
Guillermina
G
Hernando
Steven D
SD
Buckingham
Cecilia
C
Bouzat
David B
DB
Sattelle
D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000494:pharmacology; D000077770:Amifampridine; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D009132:Muscles / Q000378:metabolism*; D009154:Mutation; D020294:Myasthenic Syndromes, Congenital / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D009469:Neuromuscular Junction / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D017433:Protein Structure, Secondary; D011729:Pyridostigmine Bromide / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D013550:Swimming
D029742:Caenorhabditis elegans Proteins; D002800:Cholinesterase Inhibitors; D026902:Potassium Channel Blockers; D011978:Receptors, Nicotinic; C493164:Unc-63 protein, C elegans; D015761:4-Aminopyridine; D011729:Pyridostigmine Bromide; D000077770:Amifampridine