Worm Breeder's Gazette 14(3): 44 (June 1, 1996)
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.
The Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, Downing St., Cambridge, CB2 3EJ, UK.
Although nicotinic acetylcholine receptors (nAChR) are one of the best characterized membrane proteins, aspects of our understanding of nicotinic acetylcholine receptor-mediated fast synaptic signalling in neurons and on muscle remain superficial. For example, in no organism studied to date is the full complement of nAChR subunits known. The nematode C. elegans is one of the simplest organisms to employ ACh as a neurotransmitter and a number of genes for nAChR subunits have now been identified1,2,3. Putative subunit genes have been identified by: (a) cloning genes responsible for phenotypes such as resistance to the anthelmintic drug levamisole (lev-1, unc-38, unc-29)1,2 and neuronal degradation (deg-3)3; (b) screening libraries with probes from other organisms (acr-2, acr-3)4; (c) identifying putative receptor subunits in sequences from the C. elegans genome sequencing project (e.g. T09A5.3). Sequence alignments reveal notable differences at the putative ACh binding site, and have identified putative subunits (e.g.KO3F8.2, DEG-3) which exhibit extreme divergence from previously characterised nAChRs. Viable mutants of nAChR subunit genes are available in C. elegans. The use of comparative RT-PCR offers a powerful, simple means of exploring the diversity of nAChR subunits expressed in C.elegans. This method may make it possible to assign specific subunits to behavioural traits, by correlating the absence of subunit expression in defined mutant phenotypes. nAChR alpha subunits may be distinguished from other ligand-gated ion channel subunits by the presence of a vicinal cysteine motif at positions equivalant to 192,193 (numbering based on Torpedo alpha subunit). RT-PCR has been used to demonstrate the expression of the largest family of expressed nAChR alpha subunits currently known for any organism. Evidence is presented for the existence of an nAChR alpha subunit sub-family in C. elegans whose members have a YxxCC motif, (rather than the more common YxCC motif) at the ACh binding site. Such sequence variations might be expected to influence the pharmacology of nematode receptors, and may account for the insensitivity of certain Ascaris suum and C. elegans nAChRs to the coral toxin, lophotoxin (or its analogues)5. We have begun to study the in vivo expression of these receptors using the green fluorescent protein reporter gene, and are investigating the physiology of an alpha subunit (T09A5.3) which shows a high degree of similarity to the homo-oligomer forming chick alpha7 subunit. 1. Lewis J A et al. (1987) Mol. Pharmacol. 31, 185-193 2. Fleming J T, Tornøe C, Riina H A, Coadwell J, Lewis J A and Sattelle D B (1993) In Comparative Molecular Neurobiology (ed Pichon Y) 65-80, Springer-Verlag, Berlin. 3. Treinin M and Chalfie M (1994) Neuron 14;871-877 4. Squire M D, Tornøe C, Baylis H A, Fleming J T, Barnard E A and Sattelle D B (1995) Receptors and Ion Channels 3, 107-115. 5. Tornøe C, Holden-Dye L, Bai D, Abramson S N and Sattelle D B (1994) J. Physiol. (Lond.) 480, 96