Distinct functional properties of sodium channel variants are associated with usage of alternative exons in Nilaparvata lugens.

ABSTRACT

Voltage-gated sodium channels (Nav) are essential for electrical signaling in the nervous system. They are also the primary targets of several classes of insecticides including pyrethroids. There is only one sodium channel gene in most insect species, whereas mammals possess at least nine sodium channel genes. Extensive alternative splicing and RNA editing of sodium channel transcripts have been documented in many insect species. However, the functional consequences of these post-transcriptional events have been evaluated only in DmNav and BgNav from Drosophila melanogaster and Blattella germanica, respectively. In this study, we isolated 41 full-length cDNA clones encoding 34 sodium channel (NlNav) variants from a major rice pest, the brown planthopper (Nilaparvata lugens Stål). The 34 NlNav variants represent 24 distinct splicing types based on the usage of nine alternative exons, six of which, including exon b, have been previously reported in other insect species. When expressed in Xenopus oocytes, NlNav variants lacking exon b generated significantly larger sodium currents than variants possessing exon b, suggesting an inhibitory effect of exon b on sodium current expression. A similar effect has been reported for exon b from BgNav. Mutational analysis showed that three conserved amino acid residues encoded by exon b are critical for its inhibitory effect. In addition, mutually exclusive exons k/l contribute to distinct functional properties and channel sensitivity to pyrethroids. Altogether, these results show that alternative splicing generates functional diversity of sodium channels in this insect species and that the role of exon b in regulating neuronal excitability is likely conserved among insect species.