title: Identification of a novel β-adrenergic octopamine receptor-like gene (βAOR-like) and increased ATP-binding cassette B10 (ABCB10) expression in a Rhipicephalus microplus cell line derived from acaricide-resistant ticks.
abstract: The cattle tick Rhipicephalus (Boophilus) microplus is an economically important parasite of livestock. Effective control of ticks using acaricides is threatened by the emergence of resistance to many existing compounds. Several continuous R. microplus cell lines have been established and provide an under-utilised resource for studies into acaricide targets and potential genetic mutations associated with resistance. As a first step to genetic studies using these resources, this study aimed to determine the presence or absence of two genes and their transcripts that have been linked with acaricide function in cattle ticks: β-adrenergic octopamine receptor (βAOR, associated with amitraz resistance) and ATP-binding cassette B10 (ABCB10, associated with macrocyclic lactone resistance) in six R. microplus cell lines, five other Rhipicephalus spp. cell lines and three cell lines representing other tick genera (Amblyomma variegatum, Ixodes ricinus and Hyalomma anatolicum).
  
  
  
  End-point polymerase chain reaction (PCR) was used for detection of the βAOR gene and transcripts in DNA and RNA extracted from the tick cell lines, followed by capillary sequencing of amplicons. Quantitative real-time PCR (qPCR) was performed to determine the levels of expression of ABCB10.
  
  
  
  βAOR gene expression was detected in all Rhipicephalus spp. cell lines. We observed a second amplicon of approximately 220 bp for the βAOR gene in the R. microplus cell line BME/CTVM6, derived from acaricide-resistant ticks. Sequencing of this transcript variant identified a 36 bp insertion in the βAOR gene, leading to a 12-amino acid insertion (LLKTLALVTIIS) in the first transmembrane domain of the protein. In addition, nine synonymous SNPs were also discovered in R. appendiculatus, R. evertsi and R. sanguineus cell lines. Some of these SNPs appear to be unique to each species, providing potential tools for differentiating the tick species. The BME/CTVM6 cell line had significantly higher ABCB10 (P = 0.002) expression than the other R. microplus cell lines.
  
  
  
  The present study has identified a new βAOR gene and demonstrated a higher ABCB10 expression level in the BME/CTVM6 cell line, indicating that tick cell lines provide a useful experimental tool for acaricide resistance studies and further elucidation of tick genetics.
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, McCall Building, Bearsden Road, Glasgow, G61 1QH, UK.
authors.forename: H H Caline
authors.initials: HH
authors.lastname: Koh-Tan
authors.affiliation: School of Veterinary Medicine, University of Glasgow, Glasgow, G61 1QH, UK.
authors.forename: Erin
authors.initials: E
authors.lastname: Strachan
authors.affiliation: School of Veterinary Medicine, University of Glasgow, Glasgow, G61 1QH, UK.
authors.forename: Katherine
authors.initials: K
authors.lastname: Cooper
authors.affiliation: The Pirbright Institute, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, UK.
authors.forename: Lesley
authors.initials: L
authors.lastname: Bell-Sakyi
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, McCall Building, Bearsden Road, Glasgow, G61 1QH, UK. Nicholas.Jonsson@glasgow.ac.uk.
authors.forename: Nicholas N
authors.initials: NN
authors.lastname: Jonsson
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D056810:Acaricides / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D060829:Arthropod Proteins / Q000235:genetics* / Q000378:metabolism; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology*; D004351:Drug Resistance; D008969:Molecular Sequence Data; D017982:Receptors, Biogenic Amine / Q000235:genetics* / Q000378:metabolism; D048494:Rhipicephalus / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D013984:Tick Infestations / Q000469:parasitology / Q000662:veterinary*; D014052:Toluidines / Q000494:pharmacology
chemical_list: D018528:ATP-Binding Cassette Transporters; D056810:Acaricides; D060829:Arthropod Proteins; D017982:Receptors, Biogenic Amine; D014052:Toluidines; C027604:norsynephrine receptor; C014983:amitraz
keywords: Acaricide resistance; Amitraz; Dieldrin; Ivermectin; Synthetic pyrethroid; Tick cell line