The nicotinic acetylcholine receptor gene family of the nematode Caenorhabditis elegans: an update on nomenclature

Abstract

The simple nematode, Caenorhabditis elegans, possesses the most extensive known gene family of nicotinic acetylcholine receptor (nAChR)-like subunits. Whilst all show greatest similarity with nAChR subunits of both invertebrates and vertebrates, phylogenetic analysis suggests that just over half of these (32) may represent other members of the cys-loop ligand-gated ion channel superfamily. We have introduced a novel nomenclature system for these "Orphan" subunits, designating them as lgc genes (ligand-gated ion channels of the cys-loop superfamily), which can also be applied in future to unnamed and uncharacterised members of the cys-loop ligand-gated ion channel superfamily. We present here the resulting updated version of the C. elegans nAChR gene family and related ligand-gated ion channel genes.

Fig. 1

Alignment of cys-loop sequences from various cys-loop LGIC subunits including: a human nAChR subunit (α7); several C. elegans nAChR subunits (ACR-16, UNC-38, ACR-8, UNC-29 and DEG-3), a C. elegans nAChR-like subunit (CUP-4), C. elegans GABA receptor (UNC-49) and glutamate receptor (GLC-1) subunits; a rat serotonin receptor subunit (5HT3a); a Drosophila melanogaster histamine receptor subunit (HisCl).

Fig. 2

Tree showing the nAChR receptor gene family of C. elegans. Based on protein sequence homology, the worm nAChR subunits are divided into five ‘core’ groups whereas subunits showing substantial sequence homology with known nAChR subunits that do not fall within the core groups are designated ‘Orphan’ subunits. Acetylcholine-gated chloride channels, ACC-1 to ACC-4 (Putrenko et al., 2005), show greatest similarity with other anion channels such as GABA (UNC-49), glutamate (GLC-1) and glycine (T27A1.4) receptors The avian/mammalian nAChR gene family as well as mammalian serotonin-gated ion channels (5-HT3 receptors) are also included for comparison.