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

Recent discovery of the heterodimeric voltage-gated sodium channels (Na_v) 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 Na_vs in aphids and investigate whether they have unique splicing patterns. We found that the only identifiable Na_v from Toxoptera citricida consisted of two subunits, forming a heterodimeric Na_v, which carried an atypical "DENS" ion selectivity filter and a conventional "MFM" inactivation gate, confirming the heterodimeric Na_vs' conservation within aphids. These unique heterodimeric channels may form a new Na_v subfamily, specific to aphids. A more ancient member of four-domain Na_v homolog was well preserved in T. citricida, carrying a typical "DEEA" and "MFL" motif. The presence of "DENS" in mammalian Na_xs and "DEKT" in a fungus Na_v suggested that the heterodimeric Na_vs may still preserve Na⁺ permeability. Sequencing 46 clones from nymphs and adults exposed unique splicing patterns for this heterodimeric Na_v from T. citricida, revealing 7 alternatively spliced exons, evidencing that exon 5 was no longer unique to Bombyx mori, and exon k/l was semi-mutually exclusive. Two previously undescribed optional exons and a SNP site seemingly unique to aphids were identified. In conclusion, the dimeric Na_vs might form a new aphids-specific heterodimeric N_av 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.