Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 23, 2003
Publication Date: May 10, 2004
Citation: Temeyer, K.B., Davey, R.B., Chen, A.C. 2004. Identification of a third Boophilus microplus (Acari: Ixodidae) cDNA presumptively encoding an acetylcholinesterase. Journal of Medical Entomology. 41(3):259-268. Interpretive Summary: The southern cattle tick, a major pest and vector of cattle diseases, is once again a major threat to U.S. cattle producers after being eradicated from the United States in 1961. The threat is that tick strains in Mexico (and other parts of the world) have developed resistance to coumaphos, the organophosphate acaricide that is used to treat Mexican cattle prior to U.S. importation. Coumaphos kills ticks by interfering with the normal function of their central nervous system by inhibiting the action of an enzyme called acetylcholinesterase. The acetylcholinesterase in some strains of coumaphos-resistant ticks is less sensitive to the pesticide than in non-resistant ticks. Identification of the mutation and gene responsible for producing the resistant acetylcholinesterase should allow researchers to develop rapid genetic tests to identify resistant ticks and guide treatment options. Two genes were previously identified as candidates for production of the tick acetylcholinesterase, but no mutations resulting in resistance were found. New research has identified a third gene potentially encoding the tick acetylcholinesterase, and will enable further investigations to determine if mutations in this new candidate gene are found in strains of resistant ticks.
Technical Abstract: Amino acid sequences conserved in known acetylcholinesterases (AChEs) were identified by multiple sequence alignment. Reverse translation analysis of the conserved amino acid sequences was used to design PCR primers used to amplify segments of cDNA potentially encoding acetylcholinesterase of Boophilus microplus (Canestrini). Amplicons were analyzed for correspondence to expected size, specificity of the PCR reaction, and presence of nested AChE primer sequences. Primer walking and RACE were used to obtain the complete cDNA sequence, revealing an open reading frame encoding a 620 amino acid protein containing a 20 amino acid signal peptide. BLAST searches of GenBank using the presumptively encoded protein showed significant homology to known acetylcholinesterases.