Wilding, CS and Smith, I and Lynd, A and Yawson, AE and Weetman, D and Paine, MJI and Donnelly, MJ (2012) A cis-regulatory sequence driving metabolic insecticide resistance in mosquitoes: Functional characterisation and signatures of selection. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY, 42 (9). pp. 699-707. ISSN 0965-1748
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Although cytochrome P450 (CYP450) enzymes are frequently up-regulated in mosquitoes resistant to insecticides, no regulatory motifs driving these expression differences with relevance to wild populations have been identified. Transposable elements (TEs) are often enriched upstream of those CYP450s involved in insecticide resistance, leading to the assumption that they contribute regulatory motifs that directly underlie the resistance phenotype. A partial CuRE1 (Culex Repetitive Element 1) transposable element is found directly upstream of CYP9M10, a cytochrome P450 implicated previously in larval resistance to permethrin in the ISOP450 strain of Cx. quinquefasciatus, but is absent from the equivalent genomic region of a susceptible strain. Via expression of CYP9M10 in E.coli we have now demonstrated time- and NADPH-dependant permethrin metabolism, prerequisites for confirmation of a role in metabolic resistance, and through qPCR shown that CYP9M10 is >20-fold over-expressed in ISOP450 compared to a susceptible strain. In a fluorescent reporter assay the region upstream of CYP9M10 from ISOP450 drove 10x expression compared to the equivalent region (lacking CuRE1) from the susceptible strain. Close correspondence with the
gene expression fold-change implicates the upstream region including CuRE1 as a cis-regulatory
element involved in resistance. Only a single CuRE1 bearing allele, identical to the CuRE1 bearing
allele in the resistant strain, is found throughout Sub-Saharan Africa, in contrast to the diversity encountered in non-CuRE1 alleles. This suggests a single origin and subsequent spread due to selective advantage. CuRE1 is detectable using a simple diagnostic. When applied to Cx.
quinquefasciatus larvae from Ghana we have demonstrated a significant association with permethrin resistance in multiple field sites (mean Odds Ratio = 3.86) suggesting this marker has relevance to natural populations of vector mosquitoes. However, when CuRE1 was excised from the allele used in the reporter assay through fusion PCR, expression was unaffected, indicating that the TE has no direct role in resistance and hence that CuRE1 is acting only as a marker of an as yet unidentified regulatory motif in the association analysis. This suggests that a re-evaluation of the assumption that TEs contribute regulatory motifs involved in gene expression may be necessary.
|Uncontrolled Keywords:||0601 Biochemistry And Cell Biology, 0608 Zoology|
|Subjects:||Q Science > QH Natural history > QH301 Biology|
|Divisions:||Natural Sciences and Psychology|
|Date Deposited:||20 Jan 2016 11:40|
|Last Modified:||20 Jan 2016 11:40|
|DOI or Identification number:||10.1016/j.ibmb.2012.06.003|
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