Int J Biol Sci 2012; 8(10):1291-1309. doi:10.7150/ijbs.4966
Multiple Sodium Channel Variants in the Mosquito Culex quinquefasciatus
1. Department of Entomology and Plant Pathology, Auburn University, Auburn AL 36849, USA;
2. Current address: College of Plant Protection, Southwest University, Chongqing, China;
3. Genomics Laboratory, Auburn University, Auburn, AL 36849, USA.
* These authors contributed equally to this work.
Voltage-gated sodium channels are the target sites of both DDT and pyrethroid insecticides. The importance of alternative splicing as a key mechanism governing the structural and functional diversity of sodium channels and the resulting development of insecticide and acaricide resistance is widely recognized, as shown by the extensive research on characterizing alternative splicing and variants of sodium channels in medically and agriculturally important insect species. Here we present the first comparative study of multiple variants of the sodium channel transcripts in the mosquito Culex quinquefasciatus. The variants were classified into two categories, CxNa-L and CxNa-S based on their distinguishing sequence sizes of ~6.5 kb and ~4.0 kb, respectively, and generated via major extensive alternative splicing with minor small deletions/ insertions in susceptible S-Lab, low resistant HAmCqG0, and highly resistant HAmCqG8 Culex strains. Four alternative Cx-Na-L splice variants were identified, including three full length variants with three optional exons (2, 5, and 21i) and one with in-frame-stop codons. Large, multi-exon-alternative splices were identified in the CxNa-S category. All CxNa-S splicing variants in the S-Lab and HAmCqG0 strains contained in-frame stop codons, suggesting that any resulting proteins would be truncated. The ~1000 to ~3000-fold lower expression of these splice variants with stop codons compared with the CxNa-L splicing variants may support the lower importance of these variants in S-Lab and HAmCqG0. Interestingly, two alternative splicing variants of CxNa-S in HAmCqG8 included entire ORFs but lacked exons 5 to18 and these two variants had much higher expression levels in HAmCqG8 than in S-Lab and HAmCqG0. These results provide a functional basis for further characterizing how alternative splicing of a voltage-gated sodium channel contributes to diversity in neuronal signaling in mosquitoes in response to pyrethroids, and possibly indicates the role of these variants in the development of pyrethroid resistance.
Keywords: Sodium channel, transcript variants, alternative splicing, insecticide resistance, Culex quinquefasciatus.
He L, Li T, Zhang L, Liu N. Multiple Sodium Channel Variants in the Mosquito Culex quinquefasciatus. Int J Biol Sci 2012; 8(10):1291-1309. doi:10.7150/ijbs.4966. Available from http://www.ijbs.com/v08p1291.htm