Worldwide migration of amplified insecticide resistance genes in mosquitoes

The mosquito Culexquinquefasciatus (Say) is a vector of human disease and a world-wide biting nuisance. Organophosphorus insecticides (OPs) have been widely used to control C. quinquefasciatus populations and this has led to the emergence of OP-resistance. Predominantly, resistance is caused by increased production of two non-specific carboxylesterases, Estα21 and Estβ21. Increased abundance of these esterases is associated with the amplification of their respective genes. The estα21 and estβ21 genes were cloned and sequenced from OP-resistant Sri Lankan C. quinquefasciatus; the two adjacent genes are in a head to head configuration, within a single amplification unit (amplicon). The homology between the two genes suggests that they arose from an ancient duplication event. The two genes have different numbers of exons (estα21 has seven and estβ21 has four); however, the intron/exon boundaries in estβ21 are all conserved in estα21. The two genes are co-amplified in three other mosquito strains with the elevated Estα21/Estβ21 phenotype. Their complete linkage disequilibrium is explained by the location of the two genes involved in resistance within a single amplicon. In insecticide-susceptible C. quinquefasciatus, the non-amplified estα and estβ gene loci are also found in a similar head to head configuration, but the size of the intergenic non-coding region is approx. 1 kb less than in the amplicon. The smaller intergenic spacer is also found in a strain with amplified estβ11, which suggests that extensive laboratory selection for this amplified esterase has not eliminated the non-amplified genes. The intergenic spacer regions have been subcloned and sequenced. They contain numerous possible TATA boxes, promoters and a number of possible regulatory elements with high homology to the consensus sequence of the Barbie box. These latter putative regulatory elements are more numerous in the larger intergenic spacer, which differs from the non-amplified spacer by two large (> 420 bp) and one small (5 bp) insertions.

Section: Introductionmentioning

confidence: 83%

Co-amplification explains linkage disequilibrium of two mosquito esterase genes in insecticide-resistant Culex quinquefasciatus

Vaughan

Hawkes

Hemingway

1997

“…This could result from migration, coupled with worldwide selection of the amplified genes, as has been suggested for the B1 genes in mosquitoes [25]. In aphids, spread could occur naturally by longrange aerial movement [26] or perhaps more likely as a consequence of the international trade in plants and produce which harbour insect pests [27].…”

Section: Resultsmentioning

confidence: 99%

Structure and organization of amplicons containing the E4 esterase genes responsible for insecticide resistance in the aphid Myzus persicae (Sulzer)

Field

Devonshire

1997

Insecticide resistance in the aphid Myzus persicae results primarily from the amplification of genes encoding the insecticidedetoxifying esterase, E4. Here we report the analysis of flanking DNA co-amplified with the E4 gene. The 5h end of this gene has an untranslated leader sequence interspersed by two introns, and the promoter region lacks TATA and CAAT boxes. The DNA breakpoint involved in the generation of the amplification is just upstream (approx. 250 bp) of the putative E4 transcription start site ; thus the E4 gene is very close to the 5h end of the approx.

“…The most prevalent amplified esterase genes are estα2" and estβ2", which occur worldwide [1,14,15]. Some insects have variants of estβ1 (alleles of estβ2") that might or might not have a co-amplified estα3 [16].…”

Section: Introductionmentioning

confidence: 99%

Quantitative analysis of gene amplification in insecticide-resistant Culex mosquitoes

Paton

Karunaratne

Giakoumaki

et al. 2000

The amplification of carboxylesterase structural genes followed by their overexpression is the most common mechanism of resistance to organophosphorus insecticides in Culex mosquitoes. Most resistant Culex quinquefasciatus mosquitoes have coamplified estα2" and estβ2" genes. Recently, Southern, DNA dotblot analysis and phosphorimaging technology were used to quantify the est gene copy number in aphids and mosquitoes. Although more accurate than autoradiography, this method relies on probe hybridization, which can be variable. We have directly measured gene and mRNA copy number by using realtime quantitative PCRs in mosquitoes. The acquisition of fluorescence from incorporation of the double-strand-specific dye SYBR GreenI into a PCR product once per cycle is used to provide an absolute quantification of the initial template copy number. Thus it has been possible to show that estα2" and estβ2"