Abstract
Invertebrates possess a diverse collection of pentameric Cys-loop ligand gated ion channel (LGIC) receptors whose molecular structures, evolution and relationships to mammalian counterparts have been intensely investigated in several clinically and agriculturally important species. These receptors are targets for a variety of control agents that may also harm beneficial species. However, little is known about Cys-loop receptors in spiders, which are important natural predators of insects. We assembled de novo transcriptomes from the central and peripheral nervous systems of the Central American wandering spider Cupiennius salei, a model species for neurophysiological, behavioral and developmental studies. We found 15 Cys-loop receptor subunits that are expected to form anion or cation permeable channels, plus a putative acetylcholine binding protein (AChBP) that has only previously been reported in molluscs and one annelid. We used phylogenetic and sequence analysis to compare the spider subunits to homologous receptors in other species and predicted the 3D structures of each protein using the I-Tasser server. The quality of homology models improved with increasing sequence identity to the available high-resolution templates. We found that C. salei has orthologous γ-aminobutyric acid (GABA), GluCl, pHCl, HisCl and nAChα LGIC subunits to other arthropods, but some subgroups are specific to arachnids, or only to spiders. C. salei sequences were phylogenetically closest to gene fragments from the social spider, Stegodyphus mimosarum, indicating high conservation within the Araneomorphae suborder of spiders. C. salei sequences had similar ligand binding and transmembrane regions to other invertebrate and vertebrate LGICs. They also had motifs associated with high sensitivity to insecticides and antiparasitic agents such as fipronil, dieldrin and ivermectin. Development of truly selective control agents for pest species will require information about the molecular structure and pharmacology of Cys-loop receptors in beneficial species.
Highlights
Pentameric Cys-loop receptors are ligand gated ion channels (LGIC) that mediate fast synaptic transmission in central and peripheral nervous systems
A recent report demonstrated that nicotinic acetylcholine receptors of the pond wolf spider Pardosa pseudoannulata are activated by neonicotinoids [8], but Cys-loop subunit genes of other spider species have not been investigated
C. salei transcriptome searches revealed a relatively small number of Cys-loop receptor subunits compared to available insect or arachnid genomes that have more than 20 such subunits [6] or C. elegans with 102 Cys-loop subunits [9]
Summary
Pentameric Cys-loop receptors are ligand gated ion channels (LGIC) that mediate fast synaptic transmission in central and peripheral nervous systems. Several invertebrate Cys-loop receptors are targets of widely used control agents, such as dieldrin, ivermectin and neonicotinoids [2,3,4,5]. Several Cys-loop receptor genes have been cloned from arachnids, mainly ticks and mites [6], but very little is known about these receptors in the largest arachnid order, the spiders [7]. A recent report demonstrated that nicotinic acetylcholine (nACh) receptors of the pond wolf spider Pardosa pseudoannulata are activated by neonicotinoids [8], but Cys-loop subunit genes of other spider species have not been investigated
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