ABSTRACT: The genomes of three major mosquito vectors of human diseases, including Anopheles gambiae, Aedes aegypti, and Culex pipiens quinquefasciatus, have been previously sequenced. C. p. quinquefasciatus has the largest number of predicted protein-coding genes, which partially results from the expansion of three detoxification gene families: cytochrome P450 monooxygenases (P450), glutathione S-transferases (GST), and carboxylcholinesterases (CCE). However, unlike A. gambiae and A. aegypti, which have large amounts of gene expression data, C. p. quinquefasciatus has limited transcriptomic resources. Knowledge of complete gene expression information is very important for the exploration of the functions of genes involved in specific biological processes. In the present study, the three detoxification gene families of C. p. quinquefasciatus were analyzed for phylogenetic classification and compared with those of three other dipteran insects. Gene expression during various developmental stages and the differential expression responsible for parathion resistance were profiled using the digital gene expression (DGE) technique. Results: A total of 291 detoxification genes were found in C. p. quinquefasciatus, including 70 CCE, 186 P450, and 35 GST genes. Compared with three other dipteran species, gene expansion in Culex mainly occurred in the CCE and P450 families, where the genes of M-NM-1-esterases, juvenile hormone esterases, and CYP325 of the CYP4 subfamily showed the most pronounced expansion on the genome. A total of 13314 genes were expressed in five DGE libraries. Genes with signal transduction and odorant binding functions were prominently expressed during egg development. Genes involved in proteolysis, glycosphingolipid biosynthesis, and purine metabolism were preferentially expressed at the larval stage. Seventy five percent of the detoxification genes were found to be expressed. One fourth of the CCE and P450 genes were expressed at unique stages, indicating their developmentally regulated expression. Fifteen detoxification genes, including 2 CCEs, 6 GSTs, and 7 P450s, were expressed at higher levels in a parathion-resistant strain than in a susceptible strain. Conclusion: The results of the present study provide new insights into the functions and evolution of three detoxification gene families in mosquitoes and comprehensive transcriptomic resources for C. p. quinquefasciatus, which will facilitate the elucidation of molecular mechanisms underlying the different biological characteristics of the three major mosquito vectors. Raw data were deposited in SRA and assigned accession number SRA049959: http://www.ncbi.nlm.nih.gov/sra?term=SRA049959 Five DGE libraries were sequenced: the egg, third instar larval, pupal, and adult stages of the SG strain, and the third instar larval stage of the S-lab strain.
