Annotation and expression of carboxylesterases in the silkworm, Bombyx mori

Abstract

BackgroundCarboxylesterase is a multifunctional superfamily and ubiquitous in all living organisms, including animals, plants, insects, and microbes. It plays important roles in xenobiotic detoxification, and pheromone degradation, neurogenesis and regulating development. Previous studies mainly used Dipteran Drosophila and mosquitoes as model organisms to investigate the roles of the insect COEs in insecticide resistance. However, genome-wide characterization of COEs in phytophagous insects and comparative analysis remain to be performed.ResultsBased on the newly assembled genome sequence, 76 putative COEs were identified in Bombyx mori. Relative to other Dipteran and Hymenopteran insects, alpha-esterases were significantly expanded in the silkworm. Genomics analysis suggested that BmCOEs showed chromosome preferable distribution and 55% of which were tandem arranged. Sixty-one BmCOEs were transcribed based on cDNA/ESTs and microarray data. Generally, most of the COEs showed tissue specific expressions and expression level between male and female did not display obvious differences. Three main patterns could be classified, i.e. midgut-, head and integument-, and silk gland-specific expressions. Midgut is the first barrier of xenobiotics peroral toxicity, in which COEs may be involved in eliminating secondary metabolites of mulberry leaves and contaminants of insecticides in diet. For head and integument-class, most of the members were homologous to odorant-degrading enzyme (ODE) and antennal esterase. RT-PCR verified that the ODE-like esterases were also highly expressed in larvae antenna and maxilla, and thus they may play important roles in degradation of plant volatiles or other xenobiotics.ConclusionB. mori has the largest number of insect COE genes characterized to date. Comparative genomic analysis suggested that the gene expansion mainly occurred in silkworm alpha-esterases. Expression evidence indicated that the expanded genes were specifically expressed in midgut, integument and head, implying that these genes may have important roles in detoxifying secondary metabolites of mulberry leaves, contaminants in diet, and odorants. Our results provide some new insights into functions and evolutionary characteristics of COEs in phytophagous insects.

Genomic and phylogenetic analysis of insect carboxyl/cholinesterase genes

“…Only one of these genes is represented in each subcluster in the phylogenetic tree; however, there are exceptions: D. melanogaster and A. aegypti each lack Nlg-5 and, interestingly, B. mori has two Nlgs that are localized in the Nlg-4 cluster, as shown previously. 10,11) The chromosomal location of nlgs is conserved among insect species, 2) but we found this is not for B. mori. 11)…”

“…The database search revealed 425 insect CCEs, including those from insects whose genomes have been completely sequenced, namely the dipterans Drosophila melanogaster, 1) Anopheles gambiae, 6) and Aedes aegypti; 7) the hymenopterans Apis mellifera 8) and Nasonia vitripennis; 9) lepidopteran Bombyx mori; 10,11) and the coleopteran Tribolium castaneum; 9) hemipteran Acyrthosiphon pisum. 12) The identified insect CCEs also included those of the lepidopterans Helicoverpa armigera and Spodoptera littoralis, in which EST clone analysis has been conducted, 13,14) and several other CCEs.…”

Functional Analysis of Insect Molting Fluid Proteins on the Protection and Regulation of Ecdysis

“…Two silkworm integument esterases were encoded by one gene in Tribolium. Integument esterases (IE1 and IE2) can degrade pheromones and detoxify xenobiotics (47). The corresponding genes in Tribolium were knocked down in larvae and pupae, respectively.…”

Esterase-based metabolic resistance to insecticides in heliothine and spodopteran pests

“…The benzoylureas have amide linkages, endosulfan is a sulfenic ester and Cry1Ac is a 3,[5][6][7] Although the functions of most of these CCEs remain unknown, several lines of evidence suggest that most of the species sequenced may have up to a dozen that could perform some role in xenobiotic detoxification. 3,[5][6][7] The cases where CCE-based metabolic resistance mechanisms have been elucidated at a molecular level to date largely involve higher and lower Diptera, plus certain Hemiptera and a wasp. No lepidopteran resistance involving an esterase has yet been fully resolved at a molecular level, despite nearly a hundred papers characterising other aspects of esterase-mediated resistances in heliothine and spodopteran pests alone.…”