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

Authors: Olafson, Pia; Saelao, Perot; Luecke, David; Lohmeyer, Kimberly; SCHLECHTE, KRISTIE - Retired ARS Employee; Temeyer, Kevin

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Tick control is heavily reliant on chemical acaricides, however, acaricide resistance and potentially toxic environmental effects underscore the need to develop new tick control technologies. Tick acetylcholinesterase (AChE) is the target of two classes of commonly used pesticides and the protein has been studied to develop novel compounds that may exhibit significant improvements in specificity towards pests and mammalian safety. In support of these efforts, our group used a computational approach to identify genes encoding AChE from two tick species that are of significance to animal health: the winter tick and the southern cattle tick. Our search identified 123 and 74 putative AChE-like protein sequences in the the winter tick and cattle tick genomes, respectively, and these have hallmarks consistent with a protein that is enzymatically active. In particular, AChE1 is a major AChE involved in neuronal transmission in insects, and a clade of AChE1-like sequences was identified that included representatives from these two tick species. Other genetic signatures were observed that account for the increased number of genes encoding this protein within these ticks, and a unique set of these genes were expressed in adult reproductive systems relative to whole, unfed adults and embryos. The increased 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.

Technical Abstract: Tick control is heavily reliant on chemical acaricides, however, acaricide resistance and potentially toxic environmental effects underscore the need to develop new tick control technologies. 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. 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 123 and 74 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, indicating a role for these processes in AChE diversification. Further, a clade of AChE transcripts exhibited expression that was biased in adult reproductive systems relative to whole, unfed adults and embryos; this expression was coincident with the expression of an enzyme involved in production of acetylcholine, the substrate for AChE. The increased 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.