Evolutionary origin and status of two insect acetylcholinesterases and their structural conservation and differentiation

Chromosome-level genome assembly and comparative genomics shed light on Helicoverpa assulta ecology and pest management

BACKGROUND

The Oriental tobacco budworm, Helicoverpa assulta, a specialist herbivorous insect that exclusively feeds on plants of the Solanaceae family, causes considerable damage to crops, such as tobacco and hot pepper. The absence of a genome sequence for this species hinders further research on its pest management and ecological adaptation.

RESULTS

Here, we present a high-quality chromosome-level genome of a Korean strain of H. assulta (Pyeongchang strain, K18). The total assembly spans 424.4 Mb with an N50 length of 14.54 Mb and 37% GC content. The assembled genome (ASM2961881v1) comprises 31 chromosomes, similar to other congeneric generalist species including H. armigera and H. zea. In terms of genomic assembly quality, the complete BUSCOs and repeat content accounted for 98.3% and 33.01% of the genome, respectively. Based on this assembly, 19 485 protein-coding genes were predicted in the genome annotation. A comparative analysis was conducted using the identified number of protein-coding genes in H. armigera (24154) and H. zea (23696). Out of the 19 485 predicted genes, 137 genes in 15 orthogroups were found to have expanded significantly in H. assulta, while 149 genes in 95 orthogroups contracted rapidly.

CONCLUSION

This study revealed specific gene expansions and contractions in H. assulta compared to those in its close relatives, indicating potential adaptations related to its specialized feeding habits. Also, the comparative genome analysis provides valuable insights for the integrated pest management of H. assulta and other globally significant pests in the Heliothinae subfamily. © 2024 Society of Chemical Industry.

Sequence analysis, homology modeling, tissue expression, and potential functions of seven putative acetylcholinesterases in the spider Cupiennius salei

Acetylcholine esterases (AChEs) are essential enzymes in cholinergic synapses, terminating neurotransmission by hydrolysing acetylcholine. While membrane bound AChEs at synaptic clefts efficiently perform this task, soluble AChEs are less stable and effective, but function over broader areas. In vertebrates, a single gene produces alternatively spliced forms of AChE, whereas invertebrates often have multiple genes, producing both enzyme types. Despite their significance as pesticide targets, the physiological roles of invertebrate AChEs remain unclear. Here, we characterized seven putative AChEs in the wandering spider, Cupiennius salei, a model species for neurophysiological studies. Sequence analyses and homology modeling predicted CsAChE7 as the sole stable, membrane-bound enzyme functioning at synaptic clefts, while the others are likely soluble enzymes. In situ hybridization of sections from the spider's nervous system revealed CsAChE7 transcripts co-localizing with choline acetyltransferase in cells that also exhibited AChE activity. CsAChE7 transcripts were also found in rapidly adapting mechanosensory neurons, suggesting a role in precise and transient activation of postsynaptic cells, contrasting with slowly adapting, also cholinergic, neurons expressing only soluble AChEs, which allow prolonged activation of postsynaptic cells. These findings suggest that cholinergic transmission is influenced not only by postsynaptic receptors but also by the enzymatic properties regulating acetylcholine clearance. We also show that acetylcholine is a crucial neurotransmitter in the spider's visual system and sensory and motor pathways, but absent in excitatory motor neurons at neuromuscular junctions, consistent with other arthropods. Our findings on sequence structures may have implications for the development of neurological drugs and pesticides.

Acetylcholine titre regulation by non-neuronal acetylcholinesterase 1 and its putative roles in honey bee physiology

Similar to other insects, honey bees have two acetylcholinesterases (AChEs), AmAChE1 and AmAChE2. The primary catalytic enzyme for acetylcholine (ACh) hydrolysis in synapses is AmAChE2, which is predominantly expressed in neuronal tissues, whereas AmAChE1 is expressed in both neuronal and non-neuronal tissues, with limited catalytic activity. Unlike constitutively expressed AmAChE2, AmAChE1 expression is induced under stressful conditions such as heat shock and brood rearing suppression, but its role in regulating ACh titre remains unclear. In this paper, to elucidate the role of AmAChE1, the expression of AmAChE1 was suppressed via RNA interference (RNAi) in AmAChE1-induced worker bees. The ACh titre measurement following RNAi revealed that the expression of AmAChE1 downregulated the overall ACh titre in all tissues examined without altering AmAChE2 expression. Transcriptome analysis showed that AmAChE1 knockdown upregulated protein biosynthesis, cell respiration, and thermogenesis in the head. These findings suggest that AmAChE1 is involved in decreasing neuronal activity, enhancing energy conservation, and potentially extending longevity under stressful conditions via ACh titre regulation.

Molecular and kinetic properties of three acetylcholinesterases in the Varroa mite, Varroa destructor

The Varroa mite, Varroa destructor, poses one of the most serious threats to honey bees worldwide. Although coumaphos, an anticholinesterase pesticide, is widely used for varroa mite control, little information is available on the properties of Varroa mite acetylcholinesterases (VdAChEs). In this study, three putative VdAChEs were annotated and named VdAChE1, VdAChE2, and VdAChE3. All VdAChEs possessed most of the functionally important signature domains, suggesting that they are catalytically active. Phylogenetic analysis revealed that VdAChE1 was clustered into a clade containing most arthropod AChE1s, whereas VdAChE2 and VdAChE3 formed a unique clade with other arachnid AChEs. VdAChE1 was determined to be membrane-anchored, but both VdAChE2 and VdAChE3 are soluble, as judged by electrophoresis in conjunction with western blotting. Tissue-specific transcription profiling revealed that VdAChE1 was most predominantly expressed in the synganglion. In contrast, VdAChE2 was most predominantly expressed in the legs and cuticle. VdAChE3 showed negligible expression levels in all the tissues examined. In a kinetic analysis using recombinant VdAChEs, VdAChE1 exhibited the highest catalytic efficiency, followed by VdAChE2 and VdAChE3. Inhibition experiments revealed that VdAChE1 was most sensitive to all tested inhibitors. Taken together, VdAChE1 appears to be the major synaptic enzyme with a more toxicological relevance, whereas VdAChE2 is involved in other noncatalytic functions, including chemical defense against xenobiotics. Current findings contribute to a more detailed understanding of the evolutionary and functional traits of VdAChEs and to the design of novel anticholinesterase varroacides.

Characterization of molecular and kinetic properties of two acetylcholinesterases from the Colorado potato beetle, Leptinotarsa decemlineata

The molecular and biochemical properties of two acetylcholinesterases (LdAChE1 and LdAChE2) from the Colorado potato beetle, Leptinotarsa decemlineata, were investigated in this study. Polyacrylamide gel electrophoresis in conjunction with western blotting with LdAChE1- or LdAChE2-specific antibodies suggested that LdAChE1 exists in a soluble form, whereas LdAChE2 exists in both soluble and amphiphilic forms with a glycophosphatidylinositol anchor. Both LdAChEs exist as homodimers with each monomer connected with a disulfide bond. LdAChE1 was the most highly expressed in the thorax followed by the head, leg, and abdomen, whereas LdAChE2 was the most highly expressed in the head, followed by the thorax, leg, and abdomen. The overall expression levels of LdAChE1, however, were higher than those of LdAChE2 in all examined tissues. Kinetic analysis using recombinant LdAChE1 and LdAChE2 showed that LdAChE2 has a 4.8-fold higher catalytic efficiency toward acetylthiocholine iodide compared to LdAChE1. LdAChE2 was more sensitive to organophosphorus and carbamate insecticides than LdAChE1. The addition of irreversibly phosphorylated LdAChE1 via paraoxon titration significantly reduced LdAChE2 inhibition by insecticides and glycoalkaloids, suggesting a sequestration role of soluble LdAChE1 in the chemical defense against xenobiotics. Taken together, LdAChE2 may be the main enzyme for synaptic transmission, thus serving as a toxicologically more relevant target, whereas the soluble LdAChE1 may function as a bioscavenger.

Molecular and kinetic characterization of two acetylcholinesterases with particular focus on the roles of two amino acid substitutions (Y390N and F392W) in Bemisia tabaci

Two acetylcholinesterases (AChEs) are present in Bemisia tabaci (BtAChE1 and BtAChE2). A conserved AChE mutation conferring organophosphate (OP) resistance (F392W in BtAChE1) is saturated in field populations despite its potential fitness cost, and a highly conserved amino acid residue forming the backdoor of AChE is substituted with a unique amino acid (Y390N in BtAChE1) in B. tabaci. Thus, the roles and relationships of the two amino acid substitutions in the evolutionary adaptation of B. tabaci remain to be elucidated, and little information is available on the catalytic and molecular properties of BtAChE1 and BtAChE2. To determine which AChE is a more relevant target of OPs and carbamates, the molecular and kinetic properties of BtAChE1 and BtAChE2 were investigated. Both BtAChE1 and BtAChE2 were exclusively expressed in head and thorax but not in abdomen, bound to the membrane via GPI anchoring, and present as dimeric forms. Soluble monomeric form was detected only in BtAChE2. The catalytic activity of baculovirus-expressed BtAChE1 was 19.5-fold higher than that of BtAChE2. The inhibition assay revealed that the F392W mutation in BtAChE1 enhanced resistance to OPs. The artificial substitution of N390 (wild form) to Y (putative ancient form) led to reduced catalytic efficiency and increased inhibition by glycoalkaloids, suggesting that the Y390N substitution in BtAChE1 may have been required for Solanaceae host adaptation. BtAChE1 was proven to function as a main catalytic enzyme for ACh hydrolysis, thus being the main target of OPs and carbamates.

The ACE genes in Aphelenchoides besseyi isolates and their expression correlation to the fenamiphos treatment

Aphelenchoides besseyi could cause great yield losses of rice and many economically important crops. Acetylcholinesterase (AChE) inhibitors were commonly used to manage plant-parasitic nematodes. However, nematodes resistant to AChE inhibitors have been increasingly reported due to the extensive use of these chemicals. The current study was aimed to establish the correlation between fenamiphos (an AChE-inhibitor) sensitivities and acetylcholinesterase genes (ace) by analyzing two isolates of A. besseyi (designated Rl and HSF), which displayed differential sensitivities to fenamiphos. The concentrations of fenamiphos that led to the death of 50% (LD₅₀) of Rl and HSF were 572.2 ppm and 129.4 ppm, respectively. Three ace genes were cloned from A. besseyi and sequenced. Sequence searching and phylogenic analyses revealed that AChEs of R1 and HSF shared strong similarities with those of various vertebrate and invertebrate species. Molecular docking analysis indicated that AChEs-HSF had much higher affinities to fenamiphos than AChEs-R1. Quantitative reverse transcriptase-PCR analyses revealed that expression of three ace genes were downregulated in HSF but were upregulated in Rl after exposure to 100 ppm fenamiphos for 12 h. The results indicated that the expression of the ace genes was modulated in response to fenamiphos in different nematode strains. An increased expression of the ace genes might contribute to fenamiphos-insensitivity as seen in the Rl isolate.

Two Bombyx mori acetylcholinesterase genes influence motor control and development in different ways

Among its other biological roles, acetylcholinesterase (AChE, EC 3.1.1.7), encoded by two ace in most insects, catalyses the breakdown of acetylcholine, thereby terminating synaptic transmission. ace1 encodes the synaptic enzyme and ace2 has other essential actions in many insect species, such as Chilo suppressalis and Plutella xylostella. The silkworm, Bombyx mori, has been domesticated for more than two thousand years and its aces have no history of pesticide exposure. Here, we investigated the functional differences between two ace genes, BmAce1 and BmAce2, in the silkworm. qPCR analysis indicated that BmAce1 is highly expressed in muscle and BmAce2 is more ubiquitously expressed among tissues and enriched in the head. Both genes were separately suppressed using chemically synthesized siRNAs. The mRNA abundance of the two ace genes was significantly reduced to about 13% - 75% of the control levels after siRNA injection. The AChE activities were decreased to 32% to 85% of control levels. Silencing BmAce2 resulted in about 26% mortality, faster and higher than the 20% in the siBmAce1-treated group. Silencing BmAce1 impacted motor control and development to a greater extent than silencing BmAce2, although both treatment groups suffered motor disability, slowed development and reduced cocoons. Both genes have essential, differing biological significance.

ACE: an efficient and sensitive tool to detect insecticide resistance-associated mutations in insect acetylcholinesterase from RNA-Seq data

Background

Insecticide resistance is a substantial problem in controlling agricultural and medical pests. Detecting target site mutations is crucial to manage insecticide resistance. Though PCR-based methods have been widely used in this field, they are time-consuming and inefficient, and typically have a high false positive rate. Acetylcholinesterases (Ace) is the neural target of the widely used organophosphate (OP) and carbamate insecticides. However, there is not any software available to detect insecticide resistance associated mutations in RNA-Seq data at present.

Results

A computational pipeline ACE was developed to detect resistance mutations of ace in insect RNA-Seq data. Known ace resistance mutations were collected and used as a reference. We constructed a Web server for ACE, and the standalone software in both Linux and Windows versions is available for download. ACE was used to analyse 971 RNA-Seq data from 136 studies in 7 insect pests. The mutation frequency of each RNA-Seq dataset was calculated. The results indicated that the resistance frequency was 30%–44% in an eastern Ugandan Anopheles population, thus suggesting this resistance-conferring mutation has reached high frequency in these mosquitoes in Uganda. Analyses of RNA-Seq data from the diamondback moth Plutella xylostella indicated that the G227A mutation was positively related with resistance levels to organophosphate or carbamate insecticides. The wasp Nasonia vitripennis had a low frequency of resistant reads (<5%), but the agricultural pests Chilo suppressalis and Bemisia tabaci had a high resistance frequency. All ace reads in the 30 B. tabaci RNA-Seq data were resistant reads, suggesting that insecticide resistance has spread to very high frequency in B. tabaci.

Conclusions

To the best of our knowledge, the ACE pipeline is the first tool to detect resistance mutations from RNA-Seq data, and it facilitates the full utilization of large-scale genetic data obtained by using next-generation sequencing.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-017-1741-6) contains supplementary material, which is available to authorized users.

Natural genomic amplification of cholinesterase genes in animals

Tight control of the concentration of acetylcholine at cholinergic synapses requires precise regulation of the number and state of the acetylcholine receptors, and of the synthesis and degradation of the neurotransmitter. In particular, the cholinesterase activity has to be controlled exquisitely. In the genome of the first experimental models used (man, mouse, zebrafish and drosophila), there are only one or two genes coding for cholinesterases, whereas there are more genes for their closest relatives the carboxylesterases. Natural amplification of cholinesterase genes was first found to occur in some cancer cells and in insect species subjected to evolutionary pressure by insecticides. Analysis of the complete genome sequences of numerous representatives of the various metazoan phyla show that moderate amplification of cholinesterase genes is not uncommon in molluscs, echinoderms, hemichordates, prochordates or lepidosauria. Amplification of acetylcholinesterase genes is also a feature of parasitic nematodes or ticks. In these parasites, over-production of cholinesterase-like proteins in secreted products and the saliva are presumed to have effector roles related to host infection. These amplification events raise questions about the role of the amplified gene products, and the adaptation processes necessary to preserve efficient cholinergic transmission. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Biological evaluation of synthetic α,β-unsaturated carbonyl based cyclohexanone derivatives as neuroprotective novel inhibitors of acetylcholinesterase, butyrylcholinesterase and amyloid-β aggregation

A series of new α,β-unsaturated carbonyl-based cyclohexanone derivatives was synthesized by simple condensation method and all compounds were characterized by using various spectroscopic techniques. New compounds were evaluated for their effects on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). These compounds were also screened for in vitro cytotoxicity and for inhibitory activity for self-induced Aβ1-42 aggregation. The effect of these compounds against amyloid β-induced cytotoxicity was also investigated. The findings of in vitro experiment revealed that most of these compounds exhibited potent inhibitory activity against AChE and self-induced Aβ1-42 aggregation. The compound 3o exhibited best AChE (IC50=0.037μM) inhibitory potential. Furthermore, compound 3o disassembled the Aβ fibrils produced by self-induced Aβ aggregation by 76.6%. Compounds containing N-methyl-4-piperidone linker, showed high acetylcholinesterase and self-induced Aβ aggregation inhibitory activities as compared to reference drug donepezil. The pre-treatment of cells with synthetic compounds protected them against Aβ-induced cell death by up to 92%. Collectively, these findings suggest that some compounds from this series have potential to be promising multifunctional agents for AD treatment and our study suggest the cyclohexanone derivatives as promising new inhibitors for AChE and BuChE, potentially useful to treat neurodegenerative diseases.

Genomic Analysis of Detoxification Supergene Families in the Mosquito Anopheles sinensis

Anopheles sinensis is an important malaria vector in China and other Southeast Asian countries, and the emergence of insecticide resistance in this mosquito poses a serious threat to the efficacy of malaria control programs. The recently published An. sinensis genome and transcriptome provide an opportunity to understand the molecular mechanisms of insecticide resistance. Analysis of the An. sinensis genome revealed 174 detoxification genes, including 93 cytochrome P450s (P450s), 31 glutathione-S-transferases (GSTs), and 50 choline/carboxylesterases (CCEs). The gene number was similar to that in An. gambiae, but represented a decrease of 29% and 42% compared with Aedes aegypti and Culex quinquefasciatus, respectively. The considerable contraction in gene number in Anopheles mosquitoes mainly occurred in two detoxification supergene families, P450s and CCEs. The available An. sinensis transcriptome was also re-analyzed to further identify key resistance-associated detoxification genes. Among 174 detoxification genes, 124 (71%) were detected. Several candidate genes overexpressed in a deltamethrin-resistant strain (DR-strain) were identified as belonging to the CYP4 or CYP6 family of P450s and the Delta GST class. These generated data provide a basis for identifying the resistance-associated genes of An. sinensis at the molecular level.

Acetylcholinesterases from the Disease Vectors Aedes aegypti and Anopheles gambiae: Functional Characterization and Comparisons with Vertebrate Orthologues

Mosquitoes of the Anopheles (An.) and Aedes (Ae.) genus are principal vectors of human diseases including malaria, dengue and yellow fever. Insecticide-based vector control is an established and important way of preventing transmission of such infections. Currently used insecticides can efficiently control mosquito populations, but there are growing concerns about emerging resistance, off-target toxicity and their ability to alter ecosystems. A potential target for the development of insecticides with reduced off-target toxicity is the cholinergic enzyme acetylcholinesterase (AChE). Herein, we report cloning, baculoviral expression and functional characterization of the wild-type AChE genes (ace-1) from An. gambiae and Ae. aegypti, including a naturally occurring insecticide-resistant (G119S) mutant of An. gambiae. Using enzymatic digestion and liquid chromatography-tandem mass spectrometry we found that the secreted proteins were post-translationally modified. The Michaelis-Menten constants and turnover numbers of the mosquito enzymes were lower than those of the orthologous AChEs from Mus musculus and Homo sapiens. We also found that the G119S substitution reduced the turnover rate of substrates and the potency of selected covalent inhibitors. Furthermore, non-covalent inhibitors were less sensitive to the G119S substitution and differentiate the mosquito enzymes from corresponding vertebrate enzymes. Our findings indicate that it may be possible to develop selective non-covalent inhibitors that effectively target both the wild-type and insecticide resistant mutants of mosquito AChE.