title: Genetic basis of pyrethroid resistance in a population of Anopheles arabiensis, the primary malaria vector in Lower Moshi, north-eastern Tanzania.
abstract: BACKGROUND
  Pyrethroid resistance has been slower to emerge in Anopheles arabiensis than in An. gambiae s.s and An. funestus and, consequently, studies are only just beginning to unravel the genes involved. Permethrin resistance in An. arabiensis in Lower Moshi, Tanzania has been linked to elevated levels of both P450 monooxygenases and β-esterases. We have conducted a gene expression study to identify specific genes linked with metabolic resistance in the Lower Moshi An. arabiensis population.
  
  
  METHODS
  Microarray experiments employing an An. gambiae whole genome expression chip were performed on An. arabiensis, using interwoven loop designs. Permethrin-exposed survivors were compared to three separate unexposed mosquitoes from the same or a nearby population. A subsection of detoxification genes were chosen for subsequent quantitative real-time PCR (qRT-PCR).
  
  
  RESULTS
  Microarray analysis revealed significant over expression of 87 probes and under expression of 85 probes (in pairwise comparisons between permethrin survivors and unexposed sympatric and allopatric samples from Dar es Salaam (controls). For qRT-PCR we targeted over expressed ABC transporter genes (ABC '2060'), a glutathione-S-transferase, P450s and esterases. Design of efficient, specific primers was successful for ABC '2060'and two P450s (CYP6P3, CYP6M2). For the CYP4G16 gene, we used the primers that were previously used in a microarray study of An. arabiensis from Zanzibar islands. Over expression of CYP4G16 and ABC '2060' was detected though with contrasting patterns in pairwise comparisons between survivors and controls. CYP4G16 was only up regulated in survivors, whereas ABC '2060' was similar in survivors and controls but over expressed in Lower Moshi samples compared to the Dar es Salaam samples. Increased transcription of CYP4G16 and ABC '2060' are linked directly and indirectly respectively, with permethrin resistance in Lower Moshi An. arabiensis.
  
  
  CONCLUSIONS
  Increased transcription of a P450 (CYP4G16) and an ABC transporter (ABC 2060) are linked directly and indirectly respectively, with permethrin resistance in Lower Moshi An. arabiensis. Our study provides replication of CYP4G16 as a candidate gene for pyrethroid resistance in An. arabiensis, although its role may not be in detoxification, and requires further investigation.
authors.affiliation: Kilimanjaro Christian Medical University College (KCMUCo), Moshi, Tanzania. johntowo@yahoo.com.
authors.forename: Johnson
authors.initials: J
authors.lastname: Matowo
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Jones
authors.forename: Bilali
authors.initials: B
authors.lastname: Kabula
authors.forename: Hilary
authors.initials: H
authors.lastname: Ranson
authors.forename: Keith
authors.initials: K
authors.lastname: Steen
authors.forename: Franklin
authors.initials: F
authors.lastname: Mosha
authors.forename: Mark
authors.initials: M
authors.lastname: Rowland
authors.forename: David
authors.initials: D
authors.lastname: Weetman
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation; D016678:Genome; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides / Q000494:pharmacology*; D020411:Oligonucleotide Array Sequence Analysis; D011722:Pyrethrins / Q000494:pharmacology*; D060888:Real-Time Polymerase Chain Reaction; D013636:Tanzania
chemical_list: D007306:Insecticides; D011722:Pyrethrins