Putative acetylcholinesterase genes from a one-host tick species, the winter tick (Dermacentor albipictus)

Tick control is heavily reliant on chemical acaricides; however, acaricide resistance and potentially toxic environmental effects underscore the need to develop new tick control strategies. Tick acetylcholinesterase is the target of organophosphate and carbamate acaricides, and the protein has been studied to develop novel anticholinesterase compounds that may exhibit significant improvements in arthropod specificity and mammalian safety. In support of these efforts, we mined the chromosome-level genome assemblies of Dermacentor albipictus and Rhipicephalus microplus to identify genes encoding acetylcholinesterase and evaluated transcript expression using publicly available D. albipictus transcriptome datasets. These one-host ixodid tick species are of significance to wildlife and livestock health, and genomic comparisons between them are highly relevant given their shared lifecycle. Our in silico search identified 73 and 52 putative AChE-like protein sequences in the D. albipictus and R. microplus genomes, respectively, and these encode conserved domains and features consistent with enzymatically active cholinesterases. AChE1 is one of the major AChEs involved in neuronal transmission in insects, and a clade of AChE1-like sequences that included representatives from D. albipictus and R. microplus was observed, including the BmAChE1 protein that has been enzymatically characterized. Alternative splicing and gene duplication events were evident, including a conserved AChE gene duplication event that appears across five tick species, indicating a role for these processes in AChE diversification. Different expression patterns of AChE were observed, with indication that its expression was coincident with the expression of receptors for acetylcholine, the substrate for AChE. The notable number of AChE-encoding genes supports the diversification and specialization of this gene family in one-host tick species, emphasizing the complex role that AChEs play in tick physiology and development.