Abstract
BackgroundIonotropic glutamate receptors (iGluRs) are conserved ligand-gated ion channel receptors, and ionotropic receptors (IRs) were revealed as a new family of iGluRs. Their subdivision was unsettled, and their characteristics are little known. Anopheles sinensis is a major malaria vector in eastern Asia, and its genome was recently well sequenced and annotated.MethodsWe identified iGluR genes in the An. sinensis genome, analyzed their characteristics including gene structure, genome distribution, domains and specific sites by bioinformatic methods, and deduced phylogenetic relationships of all iGluRs in An. sinensis, Anopheles gambiae and Drosophila melanogaster. Based on the characteristics and phylogenetics, we generated the classification of iGluRs, and comparatively analyzed the intron number and selective pressure of three iGluRs subdivisions, iGluR group, Antenna IR and Divergent IR subfamily.ResultsA total of 56 iGluR genes were identified and named in the whole-genome of An. sinensis. These genes were located on 18 scaffolds, and 31 of them (29 being IRs) are distributed into 10 clusters that are suggested to form mainly from recent gene duplication. These iGluRs can be divided into four groups: NMDA, non-NMDA, Antenna IR and Divergent IR based on feature comparison and phylogenetic analysis. IR8a and IR25a were suggested to be monophyletic, named as Putative in the study, and moved from the Antenna subfamily in the IR family to the non-NMDA group as a sister of traditional non-NMDA. The generated iGluRs of genes (including NMDA and regenerated non-NMDA) are relatively conserved, and have a more complicated gene structure, smaller ω values and some specific functional sites. The iGluR genes in An. sinensis, An. gambiae and D. melanogaster have amino-terminal domain (ATD), ligand binding domain (LBD) and Lig_Chan domains, except for IR8a that only has the LBD and Lig_Chan domains. However, the new concept IR family of genes (including regenerated Antenna IR, and Divergent IR), especially for Divergent IR are more variable, have a simpler gene structure (intron loss phenomenon) and larger ω values, and lack specific functional sites. These IR genes have no other domains except for Antenna IRs that only have the Lig_Chan domain.ConclusionsThis study provides a comprehensive information framework for iGluR genes in An. sinensis, and generated the classification of iGluRs by feature and bioinformatics analyses. The work lays the foundation for further functional study of these genes.
Highlights
Ionotropic glutamate receptors are conserved ligand-gated ion channel receptors, and ionotropic receptors (IRs) were revealed as a new family of iGluRs
Identification and nomenclature of iGluRs in An. sinensis genome We identified 56 putative iGluR genes in the An. sinensis genome, all of which had full-length protein-coding sequences except for 5 genes (AsGluRIIb1, AsGluRIIb2, AsIR64a.1, AsIR64a.2 and AsIR75k.1)
In the 56 genes, 16 were supported by transcripts, 38 genes did not have transcript support but their amino acid sequences were characteristic of functional domains and motifs, and shared high sequence identity (> 30%) with reported insect iGluRs (Additional file 1: Table S1, Additional file 2: Table S2)
Summary
Ionotropic glutamate receptors (iGluRs) are conserved ligand-gated ion channel receptors, and ionotropic receptors (IRs) were revealed as a new family of iGluRs. Sensing the environmental small molecules is a kind of important ability for all species in bacteria, plants and animals. Diverse rapid and specific communication between cells and between individuals principally relies on chemical signals. Insects are able to sense a diversity of environmental chemicals such as bitter, sweet, salty tastants, odors, humidity, pheromones and carbonated water [1, 2]. External molecular cues are usually recognized by detecting receptor proteins on cell surface, which can trigger a series of changes like gene expression, physiology or behavior both in cells and organisms. Intercellular communication occurs between neurons at synapses. Cell terminal presynaptic membranes release diffusible neurotransmitters, and these neurotransmitters are recognized by receptor proteins in postsynaptic cell membranes, which can induce neuronal depolarization and continued propagation of action potentials
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