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1 May 2012 Sequence Polymorphism in Acetylcholinesterase Transcripts and Genotyping Survey of BmAChE1 in Laboratory and Mexican Strains of Rhipicephalus (Boophilus) microplus
Kevin B. Temeyer, Pia U. Olafson, John H. Pruett
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Abstract

Acetylcholinesterase cDNAs, BmAChE1, BmAChE2, and BmAChE3 of Rhipicephalus (Boophilus) microplus (Canestrini) were sequenced and found to exhibit significant polymorphism. A portion of the predicted amino acid substitutions in BmAChE1, BmAChE2, and BmAChE3 were found predominantly in organophosphate-resistant strains, but most did not correlate with resistant status. Multiple transcripts were observed from individual ticks, suggesting possible gene duplication or alternative splicing to produce more than two transcripts per individual. BmAChE1 transcript polymorphisms associating with organophosphate-resistant status in laboratory strains were surveyed in laboratory and Mexican strains of R. microplus by sequencing BmAChE1 genomic DNA. Quantitative real-time polymerase chain reaction was used to determine copy numbers of BmAChE1 (eight copies/ haploid genome), BmAChE2 (16 copies/ haploid genome), and BmAChE3 (four copies/ haploid genome). Presence of at least three highly polymorphic amplified genes expressing AChE in tick synganglion suggested that ticks maintain a large and diverse assortment of AChE alleles available for rapid recombination and selection, which potentially reduces fitness costs associated with individual mutations. Elevated copy numbers for each of the BmAChEs may also explain previous failures to identify mutations resulting in insensitivity to organophosphates. It is clear that development of phenotypic resistance to organophosphates is highly complex and may be multigenic in character.

Kevin B. Temeyer, Pia U. Olafson, and John H. Pruett "Sequence Polymorphism in Acetylcholinesterase Transcripts and Genotyping Survey of BmAChE1 in Laboratory and Mexican Strains of Rhipicephalus (Boophilus) microplus," Journal of Medical Entomology 49(3), 555-562, (1 May 2012). https://doi.org/10.1603/ME11215
Received: 29 September 2011; Accepted: 20 February 2012; Published: 1 May 2012
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KEYWORDS
Acari
acaricide resistance
AChE
cattle fever tick
Ixodidae
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