Functional diversity of sodium channel variants in common eastern bumblebee, Bombus impatiens

For the past decade, Colony Collapse Disorder has been reported worldwide. Insecticides containing pyrethroids may be responsible for a decline in bees, which are more sensitive to pyrethroids compared with other insects. Voltage-gated sodium channels (Na_v ) are the major target sites of pyrethroids, and the sodium channel diversity is generated through extensive alternative splicing and RNA editing. In this study, we cloned and analyzed the function of variants of the Na_v channel, BiNa_v , from Bombus impatiens. BiNa_v covers a 46 kb genome region including 30 exons. Sequence analysis of 56 clones showed that the clones can be grouped into 22 splice types with 11 optional exons (exons j, w, p, q, r, b, e, t, l/k, and z). Here, a special alternative exon w is identified, encoding a stretch of 31 amino acid resides in domain I between S3 and S4. RNA editing generates 18 amino acid changes in different positions in individual variants. Among 56 variants examined, only six variants generated sufficient sodium currents for functional characterization in Xenopus oocytes. In the presence of B. impatiens TipE and TEH1, the sodium current amplitude of BiNa_v 1-1 increased by fourfold, while TipE of other insect species had no effect on the expression. Abundant alternative splicing and RNA editing of BiNa_v suggests the molecular and functional pharmacology diversity of the Na_v channel for bumblebees. This study provides a theoretical basis for the design of insecticides that specifically target pests without affecting beneficial insects.