Analysis of the sequence and expression of a second putative acetylcholinesterase cDNA from organophosphate-susceptible and organophosphate-resistant cattle ticks.
The cattle tick, Boophilus microplus, is a major pest of cattle in Australia, Central and South America, and parts of Africa and Asia. Control of ticks with organophosphates (OPs) and carbamates, which target acetylcholinesterases (AChE), led to evolution of resistance to these pesticides. Alleles at the locus studied here, AChE2, from OP-susceptible female ticks from Australia and Mexico differed at 46 of 1689 nucleotide positions (20 putative amino acid differences) whereas alleles from three strains of OP-resistant ticks from Australia differed with the allele from the Australian susceptible ticks at six to 13 nucleotide positions (three to six putative amino acid differences). However, the role, if any, of these polymorphisms in the OP-resistance phenotype is unknown. Certainly none of the polymorphisms correspond to sites in AChE that are involved in catalysis or binding of acetylcholine in other organisms. Both of the AChE loci of B. microplus, AChE1 and AChE2, are apparently expressed in synganglia; AChE1 is also expressed in salivary glands and ovaries, in OP-susceptible and OP-resistant ticks. This seems to contradict studies of enzyme kinetics, which indicated that only one form of AChE was present in the synganglia, the site of the action of OPs, in this species of tick.
Baxter
Glenn D
GD
Department of Microbiology and Parasitology, and Institute for Molecular Biosciences, University of Queensland, Brisbane 4072, Australia.
Barker
Stephen C
SC
D000110:Acetylcholinesterase / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D018076:DNA, Complementary; D015870:Gene Expression; D007305:Insecticide Resistance; D007306:Insecticides; D008969:Molecular Sequence Data; D009943:Organophosphorus Compounds; D017386:Sequence Homology, Amino Acid; D013987:Ticks / Q000201:enzymology*
D018076:DNA, Complementary; D007306:Insecticides; D009943:Organophosphorus Compounds; D000110:Acetylcholinesterase