ARS | Publication request: Acetylcholinesterases of Rhipicephalus (Boophilus) microplus and Phlebotomus papatasi: Gene identification, expression and biochemical properties of recombinant proteins

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2012
Publication Date: N/A

Interpretive Summary: Cattle fever ticks transmit bovine babesiosis and anaplasmosis to cattle and these diseases are often fatal to infected livestock. Cattle fever ticks were eradicated from the United States in 1943. Re-establishment of the cattle ticks is prevented by the Cattle Fever Tick Eradication Program, which relies on inspection, surveillance, quarantine, and acaricide treatment of imported or infested cattle. Tick resistance to the primary acaricide utilized in this program has become an increasing threat to the U.S. cattle industry. This acaricide resistance involves mutations in genes functioning in the tick nervous system and other genes providing metabolic detoxification. Sequencing and in vitro expression of genes encoding acetylcholinesterase (AChE), the target of organophosphate acaricides, allowed biochemical characterization of three AChEs expressed in the southern cattle tick brain. Biochemical properties of the recombinant AChE enzymes confirmed their functional identity. Mutations in the tick genes specifying production of AChE were demonstrated in two of the three AChE genes. Gene silencing studies indicated that the tick AChE genes were able to fill in for one another. In addition, the ticks contained several copies and expressed different versions of each of the AChE genes allowing them to express both normal and mutant forms of the AChE enzymes, presumably allowing the ticks to express acaricide resistance without losing effectiveness of the normal AChE enzyme. Studies also identified a gene encoding AChE of the sand fly, Phlebotomus papatasi, a vector of leishmaniasis in humans and animals. Expression of recombinant P. papatasi AChE (PpAChE) enabled biochemical characterization and identification of novel inhibitors that selectively target PpAChE.

Technical Abstract: Rhipicephalus (Boophilus) microplus (Bm) is a vector of bovine babesiosis and anaplasmosis. Tick resistance to organophosphate (OP) acaricide involves acetylcholinesterase (AChE) insensitivity to OP and metabolic detoxification. In vitro expression of Bm genes encoding AChE allowed biochemical characterization of three BmAChEs expressed in tick synganglion. BmAChE1, BmAChE2 and BmAChE3 exhibited substrate preference for acetylthiocholine, high substrate inhibition and sensitivity to AChE-specific inhibitors. OP-insensitivity mutations were found in BmAChE1 and BmAChE3. Gene silencing suggested functional complementation of BmAChEs in vivo. BmAChE genes had amplified copy number and multiple transcript polymorphisms were expressed in individual tick synganglia for each of the BmAChEs, suggesting allelic diversity within individuals. Studies identified a cDNA encoding AChE in the sand fly, Phlebotomus papatasi, a vector of leishmaniasis in humans and animals. Expression of recombinant P. papatasi AChE (PpAChE) enabled biochemical characterization and identification of inhibitors selectively targeting PpAChE. USDA is an equal opportunity provider and employer.