title: Estimation of allele-specific Ace-1 duplication in insecticide-resistant Anopheles mosquitoes from West Africa.
abstract: BACKGROUND
  Identification of variation in Ace-1 copy number and G119S mutation genotype from samples of Anopheles gambiae and Anopheles coluzzii across West Africa are important diagnostics of carbamate and organophosphate resistance at population and individual levels. The most widespread and economical method, PCR-RFLP, suffers from an inability to discriminate true heterozygotes from heterozygotes with duplication.
  
  
  METHODS
  In addition to PCR-RFLP, in this study three different molecular techniques were applied on the same mosquito specimens: TaqMan qPCR, qRTPCR and ddPCR. To group heterozygous individuals recorded from the PCR-RFLP analysis into different assumptive genotypes K-means clustering was applied on the Z-scores of data obtained from both the TaqMan and ddPCR methods. The qRTPCR analysis was used for absolute quantification of copy number variation.
  
  
  RESULTS
  The results indicate that most heterozygotes are duplicated and that G119S mutation must now be regarded as a complex genotype ranging from primarily single-copy susceptible Glycine homozygotes to balanced and imbalanced heterozygotes, and multiply-amplified resistant Serine allele homozygotes. Whilst qRTPCR-based gene copy analysis suffers from some imprecision, it clearly illustrates differences in copy number among genotype groups identified by TaqMan or ddPCR. Based on TaqMan method properties, and by coupling TaqMan and ddPCR methods simultaneously on the same type of mosquito specimens, it demonstrated that the TaqMan genotype assays associated with the K-means clustering algorithm could provide a useful semi-quantitative estimate method to investigate the level of allele-specific duplication in mosquito populations.
  
  
  CONCLUSIONS
  Ace-1 gene duplication is evidently far more complex in An. gambiae and An. coluzzii than the better-studied mosquito Culex quinquefasciatus, which consequently can no longer be considered an appropriate model for prediction of phenotypic consequences. These require urgent further evaluation in Anopheles. To maintain the sustained effectiveness carbamates and organophosphates as alternative products to pyrethroids for malaria vector control, monitoring of duplicated resistant alleles in natural populations is essential to guide the rational use of these insecticides.
authors.affiliation: Institut Regional de Santé Publique de Ouidah/Université d'Abomey-Calavi, Cotonou, Benin. ldjogbenou22002@yahoo.fr.|Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK. ldjogbenou22002@yahoo.fr.
authors.forename: Luc S
authors.initials: LS
authors.lastname: Djogbénou
authors.affiliation: Institut Regional de Santé Publique de Ouidah/Université d'Abomey-Calavi, Cotonou, Benin. assobe80@yahoo.fr.
authors.forename: Benoît
authors.initials: B
authors.lastname: Assogba
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK. kwametawia@gmail.com.
authors.forename: John
authors.initials: J
authors.lastname: Essandoh
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK. edi.constant@hotmail.com.
authors.forename: Edi A V
authors.initials: EA
authors.lastname: Constant
authors.affiliation: Institut Regional de Santé Publique de Ouidah/Université d'Abomey-Calavi, Cotonou, Benin. makoutod@gmail.com.
authors.forename: Michel
authors.initials: M
authors.lastname: Makoutodé
authors.affiliation: Centre de Recherche Entomologique de Cotonou, Cotonou, Benin. akogbetom@yahoo.fr.
authors.forename: Martin
authors.initials: M
authors.lastname: Akogbéto
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK. Martin.Donnelly@lstmed.ac.uk.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Donnelly
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK. David.Weetman@lstmed.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: Weetman
mesh_terms: D000110:Acetylcholinesterase / Q000235:genetics*; D000354:Africa, Western; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000235:genetics*; D002219:Carbamates / Q000494:pharmacology; D003430:Cross-Sectional Studies; D005260:Female; D020440:Gene Duplication; D060005:Genotyping Techniques / Q000379:methods*; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D008137:Longitudinal Studies; D010755:Organophosphates / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods
chemical_list: D002219:Carbamates; D007306:Insecticides; D010755:Organophosphates; D000110:Acetylcholinesterase