Characterization of an insect heterodimeric voltage-gated sodium channel with unique alternative splicing mode

Recent discovery of the heterodimeric voltage-gated sodium channels (Nay) in two aphid species, Acyrthosiphon pisum and Myzus persicae, aroused interest in exploring whether this kind of channel is conserved for aphids. Herewith, we aim to provide evidence for the conservation of heterodimeric Nays in aphids and investigate whether they have unique splicing patterns. We found that the only identifiable Nay from Toxoptera citricida consisted of two subunits, forming a heterodimeric Nay, which carried an atypical "DENS" ion selectivity filter and a conventional "MFM" inactivation gate, confirming the heterodimeric Nays' conservation within aphids. These unique heterodimeric channels may form a new Nay subfamily, specific to aphids. A more ancient member of four-domain Nay homolog was well preserved in T. citricida, carrying a typical "DEEA" and "MFL" motif. The presence of "DENS" in mammalian Na(x)s and "DEKT" in a fungus Nay suggested that the heterodimeric Nays may still preserve Na+ permeability. Sequencing 46 clones from nymphs and adults exposed unique splicing patterns for this heterodimeric Nay from T. citricida, revealing 7 alternatively spliced exons, evidencing that exon 5 was no longer unique to Bombyx mori, and exon k/I was semi-mutually exchisive. Two previously undescribed optional exons and a SNP site seemingly unique to aphids were identified. In conclusion, the dimeric Nays might form a new aphids-specific heterodimeric N(a)v subfamily. This dimeric Na-v from T. citricida was characterized with distinguishable alternative splicing modes, exemplified by the discovery of two novel alternative exons and unique usage patterns of alternative exons. (C) 2016 Elsevier Inc. All rights reserved.