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Department of Biological and Medical Sciences
Faculty of Health and Life Sciences
+44 (0)1865 483602
Laboratory - Sinclair 3.18; Office - Sinclair 3.22
I completed my Biochemistry undergraduate degree at Imperial College London in 1996. I was then awarded a PhD at the University of Leeds in 2000, studying acetylcholinesterase and nicotinic acetylcholine receptors of the blood fluke, Schistosoma. In 2001 I carried on research of invertebrate cys-loop ligand-gated ion channels at the MRC Functional Genomics Unit, Oxford, until 2011. After a year's postdoctoral research at the Botnar Institute, Oxford, I became Senior Lecturer in Molecular Biology and Genomics at Oxford Brookes University in 2012.
My laboratory is interested in gene diversity and the resulting functional/pharmacological properties of ligand-gated ion channels, using genome sequence analysis, molecular biology and electrophysiology. In particular, I am focusing on cys-loop ligand-gated ion channels of insects. The cys-loop ligand-gated ion channel superfamily includes nicotinic acetylcholine receptors, GABA receptors and glutamate-gated chloride channels, which play key roles in signalling and are also of interest as they are targets of pesticides.
BBSRC Oxford Doctoral Training Program iCASE studentship 2018-2022
Oxford Brookes Research Excellence Award 2017
Nigel Groome PhD Studentship 2015-2018
Higher Education Innovation Funding (HEIF), Oxford Brookes University, 2014
The Leverhulme Trust RPG-2012-602: 'Characterising the functional spectrum of the mosquito GABA receptor'.
Characterisation of insect cys-loop ligand-gated ion channels including the GABA receptor, RDL, and nicotinic acetylcholine receptors.
Investigating target-site insecticide resistance in mosquitoes from Laos.
Broflanilide, a novel meta-diamide insecticide, shows high insecticidal activity against agricultural pests and is scheduled to be launched onto the market in 2020. However, little information about its potential toxicological effects on fish has been reported. In this study, broflanilide showed low toxicity to the zebrafish, Danio rerio, with LC50 > 10 mg L-1 at 96 h and also did not inhibit GABA-induced currents of the heteromeric Drα1β2Sγ2 GABA receptor. Broflanilide showed medium bioconcentration level with a bioconcentration factor at steady state (BCFss) of 10.02 and 69.40 in D. rerio at 2.00 mg L-1 and 0.20 mg L-1, respectively. In the elimination process, the concentration of broflanilide rapidly decreased within two days and slowly dropped below the limit of quantification after ten days. In the 2.00 mg L-1 broflanilide treatment, CYP450 activity was significantly increased up to 3.11-fold during eight days. Glutathione-S- transferase (GST) activity significantly increased by 91.44% within four days. In conclusion, the acute toxicity of broflanilide was low, but it might induce chronic toxicity, affecting metabolism. To our knowledge, this is the first report of the toxicological effects of broflanilide on an aquatic organism, which has the potential to guide the use of broflanilide in the field.
The gamma-aminobutyric acid (GABA) receptor, RDL, plays important roles in neuronal signalling and is the target of highly effective insecticides. A mutation in RDL, commonly A296S, underlies resistance to several insecticides such as cyclodienes. Even though the use of cyclodienes has been banned, the occurrence of mutations substituting A296 is notably high in mosquitoes from several countries. Here we report a survey investigating the prevalence of the Rdl mutant allele in mosquitoes from Laos, a country where mosquito-borne diseases such as malaria and dengue fever are health concerns. Anopheles and Aedes mosquitoes were collected from twelve provinces in Laos. Adult bioassays on Ae. aegypti (Linnaeus) (Diptera: Culicidae) and Ae. albopictus (Skuse) showed that all the populations tested were susceptible to dieldrin (4%) following WHO protocols. Exon 7 from a total of 791 mosquitoes was sequenced to identify the amino acid encoded for at 296 of RDL. Only one of these mosquitoes, Anopheles maculatus rampae (Diptera: Culicidae) from Attapeu, carried the mutant allele being heterozygous for A296S. We therefore found a general lack of the Rdl mutant allele indicating that mosquitoes from Laos are not exposed to insecticides that act on the GABA receptor compared to mosquitoes in several other countries. Identifying the prevalence of the Rdl mutation may help inform the potential use of alternative insecticides that act on the GABA receptor should there be a need to replace pyrethroids in order to prevent/manage resistance.
Recently, Taylor-Wells et al. published evidence that the GABA receptor, RDL, from mosquitoes undergo RNA A-to-I editing to generate an extraordinarily large range of isoforms. This editing was found to impact on GABA receptor pharmacology as it influenced the potency of GABA and ivermectin. This highlights RNA editing as a species-specific mechanism to fine tune receptor function as well as possibly increase tolerance of mosquitoes to certain insecticides. This commentary also considers novel findings from analysis of Rdl transcripts from individual mosquitoes taken from different geographical areas.
Female Aedes aegypti mosquitoes infect more than 400 million people each year with dangerous viral pathogens including dengue, yellow fever, Zika and chikungunya. Progress in understanding the biology of mosquitoes and developing the tools to fight them has been slowed by the lack of a high-quality genome assembly. Here we combine diverse technologies to produce the markedly improved, fully re-annotated AaegL5 genome assembly, and demonstrate how it accelerates mosquito science. We anchored physical and cytogenetic maps, doubled the number of known chemosensory ionotropic receptors that guide mosquitoes to human hosts and egg-laying sites, provided further insight into the size and composition of the sex-determining M locus, and revealed copy-number variation among glutathione S-transferase genes that are important for insecticide resistance. Using high-resolution quantitative trait locus and population genomic analyses, we mapped new candidates for dengue vector competence and insecticide resistance. AaegL5 will catalyse new biological insights and intervention strategies to fight this deadly disease vector.
The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats.
We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits.
These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation
A mutation in the second transmembrane domain of the GABA receptor subunit, Rdl, is associated with resistance to insecticides such as dieldrin and fipronil. Molecular cloning of Rdl cDNA from a strain of the malaria mosquito, Anopheles gambiae, which is highly resistant to dieldrin revealed this mutation (A296G) as well as another mutation in the third transmembrane domain (T345M). Wild-type, A296G, T345M and A296G + T345M homomultimeric Rdl were expressed in Xenopus laevis oocytes and their sensitivities to fipronil, deltamethrin, 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT), imidacloprid and spinosad were measured using two-electrode voltage-clamp electrophysiology. Spinosad and DDT had no agonist or antagonist actions on Rdl. However, fipronil, deltamethrin and imidacloprid decreased GABA-evoked currents. These antagonistic actions were either reduced or abolished with the A296G and the A296G + T345M mutations while T345M alone appeared to have no significant effect. In conclusion, this study identifies another mutation in the mosquito Rdl that is associated with insecticide resistance. While T345M itself does not affect insecticide sensitivity, it may serve to offset the structural impact of A296G. The present study also highlights Rdl as a potential secondary target for neonicotinoids and pyrethroids.
Ticks and tick-borne diseases have a major impact on human and animal health worldwide. Current control strategies rely heavily on the use of chemical acaricides, most of which target the CNS and with increasing resistance, new drugs are urgently needed. Nicotinic acetylcholine receptors (nAChRs) are targets of highly successful insecticides. We isolated a full-length nAChR α subunit from a normalised cDNA library from the synganglion (brain) of the brown dog tick, Rhipicephalus sanguineus. Phylogenetic analysis has shown this R. sanguineus nAChR to be most similar to the insect α1 nAChR group and has been named Rsanα1. Rsanα1 is distributed in multiple tick tissues and is present across all life-stages. When expressed in Xenopus laevis oocytes Rsanα1 failed to function as a homomer, with and without the addition of either Caenorhabditis elegans resistance-to-cholinesterase (RIC)-3 or X. laevis RIC-3. When co-expressed with chicken β2 nAChR, Rsanα1 evoked concentration-dependent, inward currents in response to acetylcholine (ACh) and showed sensitivity to nicotine (100 μM) and choline (100 μM). Rsanα1/β2 was insensitive to both imidacloprid (100 μM) and spinosad (100 μM). The unreliable expression of Rsanα1 in vitro suggests that additional subunits or chaperone proteins may be required for more robust expression. This study enhances our understanding of nAChRs in arachnids and may provide a basis for further studies on the interaction of compounds with the tick nAChR as part of a discovery process for novel acaricides.
Gap junction-mediated intercellular communication influences a variety of cellular activities. In tendons, gap junctions modulate collagen production, are involved in strain-induced cell death, and are involved in the response to mechanical stimulation. The aim of the present study was to investigate gap junction-mediated intercellular communication in healthy human tendon-derived cells using fluorescence recovery after photobleaching (FRAP). The FRAP is a noninvasive technique that allows quantitative measurement of gap junction function in living cells. It is based on diffusion-dependent redistribution of a gap junction-permeable fluorescent dye. Using FRAP, we showed that human tenocytes form functional gap junctions in monolayer and three-dimensional (3-D) collagen I culture. Fluorescently labeled tenocytes following photobleaching rapidly reacquired the fluorescent dye from neighboring cells, while HeLa cells, which do not communicate by gap junctions, remained bleached. Furthermore, both 18 β-glycyrrhetinic acid and carbenoxolone, standard inhibitors of gap junction activity, impaired fluorescence recovery in tendon cells. In both monolayer and 3-D cultures, intercellular communication in isolated cells was significantly decreased when compared with cells forming many cell-to-cell contacts. In this study, we used FRAP as a tool to quantify and experimentally manipulate the function of gap junctions in human tenocytes in both two-dimensional (2-D) and 3-D cultures.
Adult house flies, Musca domestica L., are mechanical vectors of more than 100 devastating diseases that have severe consequences for human and animal health. House fly larvae play a vital role as decomposers of animal wastes, and thus live in intimate association with many animal pathogens.
We have sequenced and analyzed the genome of the house fly using DNA from female flies. The sequenced genome is 691 Mb. Compared with Drosophila melanogaster, the genome contains a rich resource of shared and novel protein coding genes, a significantly higher amount of repetitive elements, and substantial increases in copy number and diversity of both the recognition and effector components of the immune system, consistent with life in a pathogen-rich environment. There are 146 P450 genes, plus 11 pseudogenes, in M. domestica, representing a significant increase relative to D. melanogaster and suggesting the presence of enhanced detoxification in house flies. Relative to D. melanogaster, M. domestica has also evolved an expanded repertoire of chemoreceptors and odorant binding proteins, many associated with gustation.
This represents the first genome sequence of an insect that lives in intimate association with abundant animal pathogens. The house fly genome provides a rich resource for enabling work on innovative methods of insect control, for understanding the mechanisms of insecticide resistance, genetic adaptation to high pathogen loads, and for exploring the basic biology of this important pest. The genome of this species will also serve as a close out-group to Drosophila in comparative genomic studies.
The nematode Caenorhabditis elegans is an established model organism for studying neurobiology. UNC-63 is a C. elegans nicotinic acetylcholine receptor (nAChR) α-subunit. It is an essential component of the levamisole-sensitive muscle nAChR (L-nAChR) and therefore plays an important role in cholinergic transmission at the nematode neuromuscular junction. Here, we show that worms with the unc-63(x26) allele, with its αC151Y mutation disrupting the Cys-loop, have deficient muscle function reflected by impaired swimming (thrashing). Single-channel recordings from cultured muscle cells from the mutant strain showed a 100-fold reduced frequency of opening events and shorter channel openings of L-nAChRs compared with those of wild-type worms. Anti-UNC-63 antibody staining in both cultured adult muscle and embryonic cells showed that L-nAChRs were expressed at similar levels in the mutant and wild-type cells, suggesting that the functional changes in the receptor, rather than changes in expression, are the predominant effect of the mutation. The kinetic changes mimic those reported in patients with fast-channel congenital myasthenic syndromes. We show that pyridostigmine bromide and 3,4-diaminopyridine, which are drugs used to treat fast-channel congenital myasthenic syndromes, partially rescued the motility defect seen in unc-63(x26). The C. elegans unc-63(x26) mutant may therefore offer a useful model to assist in the development of therapies for syndromes produced by altered function of human nAChRs.
Members of the cys-loop ligand-gated ion channel (cysLGIC) superfamily mediate chemical neurotransmission and are studied extensively as potential targets of drugs used to treat neurological disorders, such as Alzheimer's disease. Insect cys-loop LGICs also have central roles in the nervous system and are targets of highly successful insecticides. Here, we describe the cysLGIC superfamily of the parasitoid wasp, Nasonia vitripennis, which is emerging as a highly useful model organism and is deployed as a biological control of insect pests. The wasp superfamily consists of 26 genes, which is the largest insect cysLGIC superfamily characterized, whereas Drosophila melanogaster, Apis mellifera and Tribolium castaneum have 23, 21 and 24, respectively. As with Apis, Drosophila and Tribolium, Nasonia possesses ion channels predicted to be gated by acetylcholine, γ-amino butyric acid, glutamate and histamine, as well as orthologues of the Drosophila pH-sensitive chloride channel (pHCl), CG8916 and CG12344. Similar to other insects, wasp cysLGIC diversity is broadened by alternative splicing and RNA A-to-I editing, which may also serve to generate species-specific receptor isoforms. These findings on N. vitripennis enhance our understanding of cysLGIC functional genomics and provide a useful basis for the study of their function in the wasp model, as well as for the development of improved insecticides that spare a major beneficial insect species.
Nicotinic acetylcholine receptors (nAChRs) are the members of the cys-loop ligand-gated ion channel superfamily and are formed by five subunits arranged around a central ion channel. Each subunit is encoded by a separate gene and is classified as either α or non-α depending on the presence or absence, respectively, of two adjacent cysteine residues which are important for acetylcholine binding. Here, we report for the first time a single nAChR gene encoding both α and non-α subunits. Specifically, alternative splicing of the Anopheles gambiae nAChR subunit, previously called Agamα9 and renamed here Agamαβ9, generates two variants, one possessing the two cysteines (denoted Agamαβ9α) and the other lacking the cysteine doublet (Agamαβ9β). Attempts to heterologously express functional nAChRs consisting of the Agamαβ9 splice variants in Xenopus laevis oocytes were unsuccessful. Our findings further characterise a potential target to control the malaria mosquito as well as provide insights into the diversification of nAChRs.
The resistance to dieldrin (RDL) receptor is an insect γ-aminobutyric acid (GABA) receptor, characterized by the dieldrin resistance mutation that was pivotal to understanding target based insecticide resistance. RDL is the target for various non-competitive antagonists, including dieldrin and fipronil, as well as novel acting compounds such as the meta-diamides and isoxazolines. Therefore the RDL receptor has returned to center stage as a relevant and effective insecticide target. Our understanding of the function of RDL in vivo is still unfolding, with the discovery of species specific post-transcriptional modifications such as alternative splicing and RNA editing, modifications shown to influence the pharmacology of the receptor. Exposing these receptors to insecticides also evokes ever evolving mechanisms of mutagenesis, and a number of contributory mutations have been identified both in field and laboratory resistant insects, occurring in parallel to the dieldrin resistance mutation. We present an overview of these variations and discuss the impact on the pharmacology of GABA and various insecticides.
Quotations in the press:
Independent: Bee-friendly insecticides closer to reality after breakthrough development