Abstract
Acetylcholineserase genes confer the organophosphate and carbamate resistance mechanism. A total of 46 acetylcholineserase genes in the 24 mosquito genomes were identified. In this study, all the analysed mosquito genomes have the two acetylcholinesterase genes (ace-1 and ace-2) except Aedes albopictus and Anopheles sinensis- sinensis strain. Phylogenetic tree showed the divergence of acetylcholinesterase genes among the mosquito genome. Phylogenetic tree confirmed that the ace-1 and ace-2 genes of each species were structurally different and they form the different clades. This provided data on acetylcholinesterase gene organization for 24 mosquito genome is possibly a first time and will be a starting point for the molecular characterization of the acetylcholinesterase genes which further helps to understand the organophosphate and carbamate resistance mechanism.
Introduction
Vector borne diseases are of the major public health problem due to insecticide resistance in mosquitoes. Organophosphates and carbamates kill insects by inhibiting acetylcholinesterase found in the central nervous system. Some species have ace-1 gene and many other species has both ace-1 and ace-2 genes (Kozaki et al., 2008) but only ace-1 gene involved in insecticide resistance mechanism (Liu 2015). It was reported that the mutations at codon 119 of the acetylcholinesterase (ace-1) gene that leads to a single amino acid substitution of glycine to serine may infer resistance to organophosphates and carbamates (Chang et al., 2014). In this study acetylcholinesterase genes in the 24 mosquito genome were analyzed.
Methodology
Anopheles gambiae acetylcholinesterase gene (Ranson et al., 2002) was blasted against the mosquito vector genome in VectorBase database (Giraldo-Calderon et al., 2015) using BLASTN tool. The blast resulted sequences were retrieved and multiple sequence alignment was done by using MUSCLE tool (Edgar 2004). Phylogenetic tree was constructed for the sequences by using maximum likelihood module in MEGA 6 software (Benevides et al., 2016).
Result and Discussion
VectorBase database has 24 mosquito genomes namely Aedes aegypti, Ae. albopictus, Anopheles albimanus, An. arabiensis, An. atroparvus, An. christyi, An. coluzzii, An. culicifacies, An. darlingi, An. dirus, An. epiroticus, An. farauti, An. funestus, An. gambiae, An. maculatus, An. melas, An. merus, An. sinensis-sinensis strain, An. sinensis-China strain, An. minimus, An. quadriannulatus, An. stephensi–Indian strain, An. stephensi–SDA 500 strain, Culex quinquefasciatus (Giraldo-Calderón et al. 2015). A total of 46 acetylcholinesterase gene sequences were obtained from the blast results (Illustration 1). Two acetylcholinesterase genes each were present in all genome except Ae. albopictus and An. sinensis- sinensis strain are the two genome each has only one acetylcholinesterase gene similar to Drosophila melanogaster and Musca domestica species (Kozaki et al., 2008). Phylogenetic tree showed the divergence of acetylcholinesetrase genes among the family members. Orthologous relationship is observed due to the conserved region in the genes, while paralogous relationship of the genes in the phylogenetic tree is observed due to the local gene duplication (Canoon and Young 2003). On the whole polyphyletic clades were observed in the phylogenetic tree. The species-wise observations inferred in the phylogenetic tree are explained below. Both An. culicifacies and An. minimus genes were orthologous to each other and paralogous to An. funestus. Similarly An. stephensi genes were orthologous among them and paralogous to An. maculatus. In case of An. dirus, An. atroparvus and An. albimanus genes were orthologous to An. farauti, An. sinensis and An. darlingi genes respectively forms the individual monophyletic clade. Whereas, Aedes albopictus gene was orthologous to Ae. aegypti gene and paralogous to Culex quinquefasciatus genes. The gambiae complex (Harbach 2013) species like An. arabiensis, An. gambiae, An. melas, An. merus and An. quadriannulatus are orthologous and paralogous among each other but outside this clade An. christyi and An. epiroticus genes are presented as an outlier. It was observed in the phylogenetic tree that acetylcholinesterase gene 1 (ace-1) and Acetylcholinesterase gene 2 (ace-2) were structurally different, so they both formed different clades for the different species (Illustration 2).
Conclusion
This study reported the presence of acetylcholinesterase in the mosquito genomes. A total of 46 acetylcholineserase genes in the mosquito vector were identified. All the mosquito genomes have the two acetylcholinesterase genes except Ae. albopictus and An. sinensis- sinensis strain. Phylogenetic tree confirmed that the ace-1 and ace-2 genes of each species were structurally different and they form the different clades. This provided data will be a starting point for the molecular characterization of the acetylcholinesterase genes which helps to understand the carbamate resistance mechanism.
Acknowledgement
NE sincerely thanks ICMR for the providing the Senior Research Fellowship. Authors thank Director, NIMR for all the encouragement and support in completion of this work.
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Source(s) of Funding
ICMR project fund
Competing Interests
No competing nterests
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