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Tolstenkov O, Chatzigeorgiou M, Gorbushin A. Neuronal gene expression in two generations of the marine parasitic worm, Cryptocotyle lingua. Commun Biol 2023; 6:1279. [PMID: 38110640 PMCID: PMC10728431 DOI: 10.1038/s42003-023-05675-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Accepted: 12/04/2023] [Indexed: 12/20/2023] Open
Abstract
Trematodes, or flukes, undergo intricate anatomical and behavioral transformations during their life cycle, yet the functional changes in their nervous system remain poorly understood. We investigated the molecular basis of nervous system function in Cryptocotyle lingua, a species of relevance for fisheries. Transcriptomic analysis revealed a streamlined molecular toolkit with the absence of key signaling pathways and ion channels. Notably, we observed the loss of nitric oxide synthase across the Platyhelminthes. Furthermore, we identified upregulated neuronal genes in dispersal larvae, including those involved in aminergic pathways, synaptic vesicle trafficking, TRPA channels, and surprisingly nitric oxide receptors. Using neuronal markers and in situ hybridization, we hypothesized their functional relevance to larval adaptations and host-finding strategies. Additionally, employing a behavior quantification toolkit, we assessed cercaria motility, facilitating further investigations into the behavior and physiology of parasitic flatworms. This study enhances our understanding of trematode neurobiology and provides insights for targeted antiparasitic strategies.
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Affiliation(s)
| | | | - Alexander Gorbushin
- Sechenov Institute of Evolutionary Physiology and Biochemistry, St Petersburg, Russia
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2
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Phenotypic Profiling of Macrocyclic Lactones on Parasitic Schistosoma Flatworms. Antimicrob Agents Chemother 2023; 67:e0123022. [PMID: 36695583 PMCID: PMC9933704 DOI: 10.1128/aac.01230-22] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Macrocyclic lactones are front-line therapies for parasitic roundworm infections; however, there are no comprehensive studies on the activity of this drug class against parasitic flatworms. Ivermectin is well known to be inactive against flatworms. However, the structure-activity relationship of macrocyclic lactones may vary across phyla, and it is entirely possible other members of this drug class do in fact show antiparasitic activity on flatworms. For example, there are several reports hinting at the anti-schistosomal activity of doramectin and moxidectin. To explore this class further, we developed an automated imaging assay combined with measurement of lactate levels from worm media. This assay was applied to the screening of 21 macrocyclic lactones (avermectins, milbemycins, and others such as spinosyns) against adult schistosomes. These in vitro assays identified several macrocyclic lactones (emamectin, milbemycin oxime, and the moxidectin metabolite 23-ketonemadectin) that caused contractile paralysis and lack of lactate production. Several of these were also active against miracidia, which infect the snail intermediate host. Hits prioritized from these in vitro assays were administered to mice harboring patent schistosome infections. However, no reduction in worm burden was observed. Nevertheless, these data show the utility of a multiplexed in vitro screening platform to quantitatively assess drug action and exclude inactive compounds from a chemical series before proceeding to in vivo studies. While the prototypical macrocyclic lactone ivermectin displays minimal activity against adult Schistosoma mansoni, this family of compounds does contain schistocidal compounds which may serve as a starting point for development of new anti-flatworm chemotherapies.
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S Barbosa R, Ribeiro F, Dornelas ASP, de Souza Saraiva A, Soares AMVM, Sarmento RA, Gravato C. What does not kill it makes it stronger! The tolerance of the F1 larvae of Chironomus xanthus to a neonicotinoid insecticide formulation. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2023; 250:114513. [PMID: 36610296 DOI: 10.1016/j.ecoenv.2023.114513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 12/17/2022] [Accepted: 01/03/2023] [Indexed: 06/17/2023]
Abstract
Thiamethoxam (TMX) is a systemic neonicotinoid that acts as a partial agonist of the nicotinic acetylcholine receptors (nAChRs). However, target species have shown resistance to formulations based on such neonicotinoids, which can also be expected for non-target insects. This research aimed to study the effects of a formulation based on TMX [Cruiser® 350 FS (CRZ)] on the life traits of Chironomus xanthus filial generation (F1) and compare it with the parental generation (P). Environmentally relevant concentrations of CRZ significantly decreased larvae growth P generation , also slowing and decreasing their emergence. Larvae of the F1 generation were less sensitive than their parents, suggesting that the progeny were able to thrive and perform basic physiological functions better than the parental generation. Our results highlight that insect resistance to neonicotinoids may be associated with the better performance of the filial generation, which is related to the change in affinities of the active ingredient for the sub-units constituting the nAChRs subtypes of F1 organisms, inherited from P organisms that were able to survive and reproduce. Moreover, further studies using biochemical and omics tools should be performed to disentangle the specific changes occurring at the nAChRs throughout insect development.
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Affiliation(s)
- Rone S Barbosa
- Faculdade de Ciências, Universidade de Lisboa, Campo Grande 1749-016, Lisboa, Portugal; Universidade Federal do Tocantins, Campus de Gurupi, Gurupi, Tocantins 77402-970, Brazil
| | - Fabianne Ribeiro
- Universidade Federal do Tocantins, Campus de Gurupi, Gurupi, Tocantins 77402-970, Brazil; CESAM & Departamento de Biologia, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
| | | | - Althiéris de Souza Saraiva
- Instituto Federal de Educação, Ciência e Tecnologia Goiano, Campus Campos Belos, Campos Belos, Goiás 73840-000, Brazil
| | - Amadeu M V M Soares
- CESAM & Departamento de Biologia, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
| | | | - Carlos Gravato
- Faculdade de Ciências, Universidade de Lisboa, Campo Grande 1749-016, Lisboa, Portugal.
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4
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Speculation on How RIC-3 and Other Chaperones Facilitate α7 Nicotinic Receptor Folding and Assembly. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27144527. [PMID: 35889400 PMCID: PMC9318448 DOI: 10.3390/molecules27144527] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 07/07/2022] [Accepted: 07/09/2022] [Indexed: 11/17/2022]
Abstract
The process of how multimeric transmembrane proteins fold and assemble in the endoplasmic reticulum is not well understood. The alpha7 nicotinic receptor (α7 nAChR) is a good model for multimeric protein assembly since it has at least two independent and specialized chaperones: Resistance to Inhibitors of Cholinesterase 3 (RIC-3) and Nicotinic Acetylcholine Receptor Regulator (NACHO). Recent cryo-EM and NMR data revealed structural features of α7 nAChRs. A ser-ala-pro (SAP) motif precedes a structurally important but unique "latch" helix in α7 nAChRs. A sampling of α7 sequences suggests the SAP motif is conserved from C. elegans to humans, but the latch sequence is only conserved in vertebrates. How RIC-3 and NACHO facilitate receptor subunits folding into their final pentameric configuration is not known. The artificial intelligence program AlphaFold2 recently predicted structures for NACHO and RIC-3. NACHO is highly conserved in sequence and structure across species, but RIC-3 is not. This review ponders how different intrinsically disordered RIC-3 isoforms from C. elegans to humans interact with α7 nAChR subunits despite having little sequence homology across RIC-3 species. Two models from the literature about how RIC-3 assists α7 nAChR assembly are evaluated considering recent structural information about the receptor and its chaperones.
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Mitchell EL, Viscarra F, Bermudez I, Hawkins J, Goodchild JA, Jones AK. The Apis mellifera alpha 5 nicotinic acetylcholine receptor subunit expresses as a homomeric receptor that is sensitive to serotonin. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2022; 182:105055. [PMID: 35249651 DOI: 10.1016/j.pestbp.2022.105055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 01/18/2022] [Accepted: 02/10/2022] [Indexed: 06/14/2023]
Abstract
Insect nicotinic acetylcholine receptors (nAChRs) are molecular targets of highly effective insecticides such as neonicotinoids. Functional expression of these receptors provides useful insights into their functional and pharmacological properties. Here, we report that the α5 nAChR subunit of the honey bee, Apis mellifera, functionally expresses in Xenopus laevis oocytes, which is the first time a homomeric insect nAChR has been robustly expressed in a heterologous system without the need for chaperone proteins. Using two-electrode voltage-clamp electrophysiology we show that the α5 receptor has low sensitivity to acetylcholine with an EC50 of 2.37 mM. However, serotonin acts as an agonist with a considerably lower EC50 at 119 μM that is also more efficacious than acetylcholine in activating the receptor. Molecular modelling indicates that residues in the complementary binding site may be involved in the selectivity towards serotonin. This is the first report of a ligand-gated ion channel activated by serotonin from an insect and phylogenetic analysis shows that the α5 subunit of A. mellifera and other non-Dipteran insects, including pest species, belong to a distinct subgroup of subunits, which may represent targets for the development of novel classes of insecticides.
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Affiliation(s)
- Eleanor L Mitchell
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Headington, Oxford OX3 0BP, United Kingdom.
| | - Franco Viscarra
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Headington, Oxford OX3 0BP, United Kingdom.
| | - Isabel Bermudez
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Headington, Oxford OX3 0BP, United Kingdom.
| | - Joseph Hawkins
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Headington, Oxford OX3 0BP, United Kingdom.
| | - Jim A Goodchild
- Syngenta, Jealotts Hill International Research Centre, Bracknell, Berkshire RG42 6EY, United Kingdom.
| | - Andrew K Jones
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Headington, Oxford OX3 0BP, United Kingdom.
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Promethazine exhibits antiparasitic properties in vitro and reduces worm burden, egg production, hepato-, and splenomegaly in a schistosomiasis animal model. Antimicrob Agents Chemother 2019:AAC.01208-19. [PMID: 31527034 DOI: 10.1128/aac.01208-19] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The treatment and control of schistosomiasis, a neglected disease that affects more than 200 million people worldwide, rely on the use of a single drug, praziquantel. A vaccine has yet to be developed and since new drug design and development is a lengthy and costly process, drug repurposing is a promising strategy. In this study, the efficacy of promethazine, a first-generation antihistamine, was evaluated against Schistosoma mansoni ex vivo and in a murine model of schistosomiasis. In vitro assays demonstrated that promethazine affected parasite motility, viability, and it induced severe tegumental damage in schistosomes. The LC50 of the drug was 5.84 μM. Similar to promethazine, schistosomes incubated with atropine, a classical anticholinergic drug, displayed reduced motor activity. In an animal model, promethazine treatment was introduced at an oral dose of 100 mg/kg for five successive days at different intervals from the time of infection, for the evaluation of the stage-specific susceptibility (pre-patent and patent infections). Various parasitological criteria indicated the in vivo antischistosomal effects of promethazine: there were significant reductions in worm burden, egg production, and hepato- and splenomegaly. The highest worm burden reduction was achieved with promethazine in patent infections (> 90%). Taken together, considering the importance of the repositioning of drugs in infectious diseases, especially those related to poverty, our data revealed the possibility of promethazine repositioning as an antischistosomal agent.
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Suppression of Schistosoma japonicum Acetylcholinesterase Affects Parasite Growth and Development. Int J Mol Sci 2018; 19:ijms19082426. [PMID: 30115897 PMCID: PMC6121427 DOI: 10.3390/ijms19082426] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 08/10/2018] [Accepted: 08/11/2018] [Indexed: 12/17/2022] Open
Abstract
To further investigate the importance of Schistosoma japonicum acetylcholinesterase (SjAChE) in cholinergic signaling for parasite growth and development, we used RNA interference (RNAi) to knock-down its expression in adults and eggs in vitro. This resulted in its reduced transcription but also expression of other important genes involved both in cholinergic signaling and glucose uptake were impacted substantially. Significant decreases in AChE protein expression, AChE enzymatic activity, and glucose uptake were observed in the SjAChE-knockdown parasites compared with luciferase controls. In vaccine/challenge experiments, we found that immunization of mice with recombinant SjAChE (rSjAChE) expressed in Escherichia coli elicited reductions in male worm numbers (33%), liver granuloma density (41%), and reduced numbers of mature intestinal eggs (73%) in the vaccinated group compared with the control group. These results indicate AChE plays an important role in the metabolism of male worms, and impacts indirectly on female fecundity leading to increased numbers of immature eggs being released and reduced sizes of liver granulomas. Furthermore, cytokine analysis showed that immunization of mice with rSjAChE elicited a predominantly Th1-type immune response characterized by increased production of IFNγ in splenic CD4+ T cells of vaccinated mice. The study confirms the potential of SjAChE as a vaccine/drug candidate against zoonotic schistosomiasis japonica.
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You H, Liu C, Du X, McManus DP. Acetylcholinesterase and Nicotinic Acetylcholine Receptors in Schistosomes and Other Parasitic Helminths. Molecules 2017; 22:molecules22091550. [PMID: 28906438 PMCID: PMC6151654 DOI: 10.3390/molecules22091550] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Revised: 09/11/2017] [Accepted: 09/14/2017] [Indexed: 11/25/2022] Open
Abstract
Schistosomiasis, which is caused by helminth trematode blood flukes of the genus Schistosoma, is a serious health and economic problem in tropical areas, and the second most prevalent parasitic disease after malaria. Currently, there is no effective vaccine available and treatment is entirely dependent on a single drug, praziquantel (PZQ), raising a significant potential public health threat due to the emergence of PZQ drug resistance. It is thus urgent and necessary to explore novel therapeutic targets for the treatment of schistosomiasis. Previous studies demonstrated that acetylcholinesterase (AChE) and nicotinic acetylcholine receptors (nAChRs) play important roles in the schistosome nervous system and ion channels, both of which are targeted by a number of currently approved and marketed anthelminthic drugs. To improve understanding of the functions of the cholinergic system in schistosomes, this article reviews previous studies on AChE and nAChRs in schistosomes and other helminths and discusses their potential as suitable targets for vaccine development and drug design against schistosomiasis.
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Affiliation(s)
- Hong You
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia.
| | - Chang Liu
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia.
- Parasitology Laboratory, School of Animal Medicine, Northeast Agricultural University, Harbin 150030, China.
| | - Xiaofeng Du
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia.
| | - Donald P McManus
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia.
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9
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You H, Gobert GN, Du X, Pali G, Cai P, Jones MK, McManus DP. Functional characterisation of Schistosoma japonicum acetylcholinesterase. Parasit Vectors 2016; 9:328. [PMID: 27283196 PMCID: PMC4901427 DOI: 10.1186/s13071-016-1615-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/01/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Acetylcholinesterase (AChE) is an important metabolic enzyme of schistosomes present in the musculature and on the surface of the blood stage where it has been implicated in the modulation of glucose scavenging from mammalian host blood. As both a target for the antischistosomal drug metrifonate and as a potential vaccine candidate, AChE has been characterised in the schistosome species Schistosoma mansoni, S. haematobium and S. bovis, but not in S. japonicum. Recently, using a schistosome protein microarray, a predicted S. japonicum acetylcholinesterase precursor was significantly targeted by protective IgG1 immune responses in S. haematobium-exposed individuals that had acquired drug-induced resistance to schistosomiasis after praziquantel treatment. RESULTS We report the full-length cDNA sequence and describe phylogenetic and molecular structural analysis to facilitate understanding of the biological function of AChE (SjAChE) in S. japonicum. The protein has high sequence identity (88 %) with the AChEs in S. mansoni, S. haematobium and S. bovis and has 25 % sequence similarity with human AChE, suggestive of a highly specialised role for the enzyme in both parasite and host. We immunolocalized SjAChE and demonstrated its presence on the surface of adult worms and schistosomula, as well as its lower expression in parenchymal regions. The relatively abundance of AChE activity (90 %) present on the surface of adult S. japonicum when compared with that reported in other schistosomes suggests SjAChE may be a more effective drug or immunological target against this species. We also demonstrate that the classical inhibitor of AChE, BW285c51, inhibited AChE activity in tegumental extracts of paired worms, single males and single females by 59, 22 and 50 %, respectively, after 24 h incubation with 200 μM BW284c51. CONCLUSIONS These results build on previous studies in other schistosome species indicating major differences in the enzyme between parasite and mammalian host, and provide further support for the design of an anti-schistosome intervention targeting AChE.
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Affiliation(s)
- Hong You
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
| | - Geoffrey N Gobert
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.,School of Biological Sciences, Queen's University Belfast, Belfast, UK
| | - Xiaofeng Du
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
| | - Gabor Pali
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
| | - Pengfei Cai
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
| | - Malcolm K Jones
- School of Veterinary Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Donald P McManus
- Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
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MacDonald K, Kimber MJ, Day TA, Ribeiro P. A constitutively active G protein-coupled acetylcholine receptor regulates motility of larval Schistosoma mansoni. Mol Biochem Parasitol 2015; 202:29-37. [PMID: 26365538 PMCID: PMC4607267 DOI: 10.1016/j.molbiopara.2015.09.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 09/05/2015] [Accepted: 09/07/2015] [Indexed: 12/20/2022]
Abstract
The neuromuscular system of helminths controls a variety of essential biological processes and therefore represents a good source of novel drug targets. The neuroactive substance, acetylcholine controls movement of Schistosoma mansoni but the mode of action is poorly understood. Here, we present first evidence of a functional G protein-coupled acetylcholine receptor in S. mansoni, which we have named SmGAR. A bioinformatics analysis indicated that SmGAR belongs to a clade of invertebrate GAR-like receptors and is related to vertebrate muscarinic acetylcholine receptors. Functional expression studies in yeast showed that SmGAR is constitutively active but can be further activated by acetylcholine and, to a lesser extent, the cholinergic agonist, carbachol. Anti-cholinergic drugs, atropine and promethazine, were found to have inverse agonist activity towards SmGAR, causing a significant decrease in the receptor's basal activity. An RNAi phenotypic assay revealed that suppression of SmGAR activity in early-stage larval schistosomulae leads to a drastic reduction in larval motility. In sum, our results provide the first molecular evidence that cholinergic GAR-like receptors are present in schistosomes and are required for proper motor control in the larvae. The results further identify SmGAR as a possible candidate for antiparasitic drug targeting.
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Affiliation(s)
- Kevin MacDonald
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue Quebec, H9X 3V9, Canada
| | - Michael J Kimber
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Tim A Day
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Paula Ribeiro
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue Quebec, H9X 3V9, Canada.
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11
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MacDonald K, Buxton S, Kimber MJ, Day TA, Robertson AP, Ribeiro P. Functional characterization of a novel family of acetylcholine-gated chloride channels in Schistosoma mansoni. PLoS Pathog 2014; 10:e1004181. [PMID: 24945827 PMCID: PMC4055736 DOI: 10.1371/journal.ppat.1004181] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Accepted: 04/28/2014] [Indexed: 12/25/2022] Open
Abstract
Acetylcholine is the canonical excitatory neurotransmitter of the mammalian neuromuscular system. However, in the trematode parasite Schistosoma mansoni, cholinergic stimulation leads to muscle relaxation and a flaccid paralysis, suggesting an inhibitory mode of action. Information about the pharmacological mechanism of this inhibition is lacking. Here, we used a combination of techniques to assess the role of cholinergic receptors in schistosome motor function. The neuromuscular effects of acetylcholine are typically mediated by gated cation channels of the nicotinic receptor (nAChR) family. Bioinformatics analyses identified numerous nAChR subunits in the S. mansoni genome but, interestingly, nearly half of these subunits carried a motif normally associated with chloride-selectivity. These putative schistosome acetylcholine-gated chloride channels (SmACCs) are evolutionarily divergent from those of nematodes and form a unique clade within the larger family of nAChRs. Pharmacological and RNA interference (RNAi) behavioral screens were used to assess the role of the SmACCs in larval motor function. Treatment with antagonists produced the same effect as RNAi suppression of SmACCs; both led to a hypermotile phenotype consistent with abrogation of an inhibitory neuromuscular mediator. Antibodies were then generated against two of the SmACCs for use in immunolocalization studies. SmACC-1 and SmACC-2 localize to regions of the peripheral nervous system that innervate the body wall muscles, yet neither appears to be expressed directly on the musculature. One gene, SmACC-1, was expressed in HEK-293 cells and characterized using an iodide flux assay. The results indicate that SmACC-1 formed a functional homomeric chloride channel and was activated selectively by a panel of cholinergic agonists. The results described in this study identify a novel clade of nicotinic chloride channels that act as inhibitory modulators of schistosome neuromuscular function. Additionally, the iodide flux assay used to characterize SmACC-1 represents a new high-throughput tool for drug screening against these unique parasite ion channels.
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Affiliation(s)
- Kevin MacDonald
- Institute of Parasitology, McGill University, Macdonald Campus, Ste. Anne de Bellevue, Quebec, Canada
| | - Samuel Buxton
- Department of Biomedical Sciences, Iowa State University, Ames, Iowa, United States of America
| | - Michael J. Kimber
- Department of Biomedical Sciences, Iowa State University, Ames, Iowa, United States of America
| | - Tim A. Day
- Department of Biomedical Sciences, Iowa State University, Ames, Iowa, United States of America
| | - Alan P. Robertson
- Department of Biomedical Sciences, Iowa State University, Ames, Iowa, United States of America
| | - Paula Ribeiro
- Institute of Parasitology, McGill University, Macdonald Campus, Ste. Anne de Bellevue, Quebec, Canada
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12
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Molecular cloning and characterization of novel glutamate-gated chloride channel subunits from Schistosoma mansoni. PLoS Pathog 2013; 9:e1003586. [PMID: 24009509 PMCID: PMC3757052 DOI: 10.1371/journal.ppat.1003586] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Accepted: 07/15/2013] [Indexed: 12/28/2022] Open
Abstract
Cys-loop ligand-gated ion channels (LGICs) mediate fast ionotropic neurotransmission. They are proven drug targets in nematodes and arthropods, but are poorly characterized in flatworms. In this study, we characterized the anion-selective, non-acetylcholine-gated Cys-loop LGICs from Schistosoma mansoni. Full-length cDNAs were obtained for SmGluCl-1 (Smp_096480), SmGluCl-2 (Smp_015630) and SmGluCl-3 (Smp_104890). A partial cDNA was retrieved for SmGluCl-4 (Smp_099500/Smp_176730). Phylogenetic analyses suggest that SmGluCl-1, SmGluCl-2, SmGluCl-3 and SmGluCl-4 belong to a novel clade of flatworm glutamate-gated chloride channels (GluCl) that includes putative genes from trematodes and cestodes. The flatworm GluCl clade was distinct from the nematode-arthropod and mollusc GluCl clades, and from all GABA receptors. We found no evidence of GABA receptors in S. mansoni. SmGluCl-1, SmGluCl-2 and SmGluCl-3 subunits were characterized by two-electrode voltage clamp (TEVC) in Xenopus oocytes, and shown to encode Cl−-permeable channels gated by glutamate. SmGluCl-2 and SmGluCl-3 produced functional homomers, while SmGluCl-1 formed heteromers with SmGluCl-2. Concentration-response relationships revealed that the sensitivity of SmGluCl receptors to L-glutamate is among the highest reported for GluCl receptors, with EC50 values of 7–26 µM. Chloride selectivity was confirmed by current-voltage (I/V) relationships. SmGluCl receptors are insensitive to 1 µM ivermectin (IVM), indicating that they do not belong to the highly IVM-sensitive GluClα subtype group. SmGluCl receptors are also insensitive to 10 µM meclonazepam, a schistosomicidal benzodiazepine. These results provide the first molecular evidence showing the contribution of GluCl receptors to L-glutamate signaling in S. mansoni, an unprecedented finding in parasitic flatworms. Further work is needed to elucidate the roles of GluCl receptors in schistosomes and to explore their potential as drug targets. Schistosomiasis is a debilitating disease caused by blood flukes in the genus Schistosoma that afflicts over 200 million people worldwide. Treatment relies almost exclusively on a single drug, praziquantel. Reports of sub-optimal efficacy of praziquantel raise concerns about the prospect of drug resistance and highlight the need to develop new schistosomicidal drugs. Neuroactive receptors are recognized targets of insecticides and anthelmintics. Likewise, neuronal receptors of schistosomes are attractive targets for drug development. Lacking a coelom and a proper circulatory system, schistosomes are thought to lack the capacity for endocrine signaling, and therefore depend entirely on neuronal modulation to control functions vital to their survival and reproduction. We characterized a novel family of glutamate-gated chloride channel (GluCl) receptors from S. mansoni that are pharmacologically and evolutionarily distinct from GluCls in nematodes, insects and snails. Our phylogenetic analyses suggest that these receptors are also widely distributed in other flukes and tapeworms. This study provides the first molecular evidence for the contribution of an inhibitory component to glutamatergic signaling in S. mansoni. Our findings add to a growing body of evidence suggesting that glutamatergic signaling in schistosomes may be physiologically important, and could be targeted for chemotherapeutic intervention.
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In vivo efficacy of the anthelmintic tribendimidine against the cestode Hymenolepis microstoma in a controlled laboratory trial. Acta Trop 2012; 123:78-84. [PMID: 22487754 DOI: 10.1016/j.actatropica.2012.03.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 03/22/2012] [Accepted: 03/23/2012] [Indexed: 11/20/2022]
Abstract
Tribendimidine has been registered for the treatment of human soil transmitted helminthiases in China. In the model nematode Caenorhabditis elegans it is an agonist of L-subtype nicotinic acetylcholine receptors and therefore shares its mode of action with levamisole and pyrantel. Besides its broad spectrum of nematicidal efficacy, tribendimidine is efficacious against several trematodes and has been attributed to have anti-cestodal effects. However, there are few published data available for the latter. The efficacy of tribendimidine and its nematicidal metabolite deacylated amidantel against Hymenolepis microstoma were examined for their anti-cestodal potential. Doses of 50 and 100mg/kg body weight deacylated amidantel and 10, 25, 50, and 100mg/kg tribendimidine were administered orally on three consecutive days to mice experimentally infected with eight cysticercoids. Necropsy was performed and the worm burdens were determined one day after the last treatment. Furthermore, levamisole was used in combination with tribendimidine (100mg/kg levamisole plus 10 and 25mg/kg tribendimidine, respectively) and alone (50 and 100mg/kg) to investigate any possible interactions of the partner compounds against cestodes. Tribendimidine showed a very high efficacy at dosages of 50mg/kg or higher. Surprisingly, deacylated amidantel led to no reduction of the worm burden in any of the treatments. Combinations of levamisole with tribendimidine did not augment the effects of tribendimidine alone and as expected levamisole alone also showed no anti-cestodal activity. To our knowledge, this study shows for the first time activity of tribendimidine against a cestode in a controlled laboratory study. Due to the excellent cure rates observed here, multiple tribendimidine treatments might be considered as useful scheme for treatments of cestode, nematode and trematode infections although this would significantly increase both costs and management efforts. Moreover, the differences between tribendimidine and deacylated amidantel indicate at least a strong difference in sensitivity of H. microstoma or a strong difference in drug availability.
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Taman A, Ribeiro P. Characterization of a truncated metabotropic glutamate receptor in a primitive metazoan, the parasitic flatworm Schistosoma mansoni. PLoS One 2011; 6:e27119. [PMID: 22069494 PMCID: PMC3206071 DOI: 10.1371/journal.pone.0027119] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 10/11/2011] [Indexed: 11/26/2022] Open
Abstract
A novel glutamate-binding protein was identified in Schistosoma mansoni. The protein (SmGBP) is related to metabotropic glutamate receptors from other species and has a predicted glutamate binding site located within a Venus Flytrap module but it lacks the heptahelical transmembrane segment that normally characterizes these receptors. The SmGBP cDNA was cloned, verified by 5' and 3' Rapid Amplification of cDNA Ends (RACE) and shown to be polyadenylated at the 3'end, suggesting the transcript is full-length. The cloned cDNA was subsequently expressed in bacteria and shown to encode a functional glutamate-binding protein. Other studies, using a specific peptide antibody, determined that SmGBP exists in two forms, a monomer of the expected size and a stable but non-covalent dimer. The monomer and dimer are both present in the membrane fraction of S. mansoni and are resistant to extraction with high-salt, alkaline pH and urea, suggesting SmGBP is either an integral membrane protein or a peripheral protein that is tightly associated with the membrane. Surface biotinylation experiments combined with western blot analyses and confocal immunolocalization revealed that SmGBP localized to the surface membranes of adult male schistosomes, especially the dorsal tubercles. In contrast, we detected little or no expression of SmGBP either in the females or larval stages. A comparative quantitative PCR analysis confirmed that the level of SmGBP expression is several-fold higher in male worms than cercariae, and it is barely detectable in adult females. Together, the results identify SmGBP as a new type of schistosome glutamate receptor that is both gender- and stage-specific. The high-level expression of this protein in the male tubercles suggests a possible role in host-parasite interaction.
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Affiliation(s)
- Amira Taman
- Institute of Parasitology, McGill University, Macdonald Campus, Sainte Anne de Bellevue, Quebec, Canada
| | - Paula Ribeiro
- Institute of Parasitology, McGill University, Macdonald Campus, Sainte Anne de Bellevue, Quebec, Canada
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15
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Prole DL, Taylor CW. Identification of intracellular and plasma membrane calcium channel homologues in pathogenic parasites. PLoS One 2011; 6:e26218. [PMID: 22022573 PMCID: PMC3194816 DOI: 10.1371/journal.pone.0026218] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 09/22/2011] [Indexed: 11/29/2022] Open
Abstract
Ca2+ channels regulate many crucial processes within cells and their abnormal activity can be damaging to cell survival, suggesting that they might represent attractive therapeutic targets in pathogenic organisms. Parasitic diseases such as malaria, leishmaniasis, trypanosomiasis and schistosomiasis are responsible for millions of deaths each year worldwide. The genomes of many pathogenic parasites have recently been sequenced, opening the way for rational design of targeted therapies. We analyzed genomes of pathogenic protozoan parasites as well as the genome of Schistosoma mansoni, and show the existence within them of genes encoding homologues of mammalian intracellular Ca2+ release channels: inositol 1,4,5-trisphosphate receptors (IP3Rs), ryanodine receptors (RyRs), two-pore Ca2+ channels (TPCs) and intracellular transient receptor potential (Trp) channels. The genomes of Trypanosoma, Leishmania and S. mansoni parasites encode IP3R/RyR and Trp channel homologues, and that of S. mansoni additionally encodes a TPC homologue. In contrast, apicomplexan parasites lack genes encoding IP3R/RyR homologues and possess only genes encoding TPC and Trp channel homologues (Toxoplasma gondii) or Trp channel homologues alone. The genomes of parasites also encode homologues of mammalian Ca2+influx channels, including voltage-gated Ca2+ channels and plasma membrane Trp channels. The genome of S. mansoni also encodes Orai Ca2+ channel and STIM Ca2+ sensor homologues, suggesting that store-operated Ca2+ entry may occur in this parasite. Many anti-parasitic agents alter parasite Ca2+ homeostasis and some are known modulators of mammalian Ca2+ channels, suggesting that parasite Ca2+ channel homologues might be the targets of some current anti-parasitic drugs. Differences between human and parasite Ca2+ channels suggest that pathogen-specific targeting of these channels may be an attractive therapeutic prospect.
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Affiliation(s)
- David L Prole
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom.
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16
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Taman A, Ribeiro P. Glutamate-mediated signaling in Schistosoma mansoni: a novel glutamate receptor is expressed in neurons and the female reproductive tract. Mol Biochem Parasitol 2010; 176:42-50. [PMID: 21163308 DOI: 10.1016/j.molbiopara.2010.12.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Revised: 12/01/2010] [Accepted: 12/02/2010] [Indexed: 11/26/2022]
Abstract
l-Glutamate is a major neurotransmitter of both vertebrates and invertebrates. Earlier studies have shown that glutamate stimulates neuromuscular activity in the bloodfluke, Schistosoma mansoni, but its mode of action is unknown. Here we describe a novel glutamate receptor in S. mansoni (SmGluR), the first of its kind to be identified in a parasitic flatworm. SmGluR belongs to the G protein-coupled receptor (GPCR) superfamily and is distantly related to metabotropic glutamate receptors from other species. The full-length receptor cDNA was cloned, stably expressed in HEK-293 cells and shown to be activated by glutamate, whereas aspartate and the glutamate derivative, gamma-aminobutyric acid (GABA) had no significant effect. Among the classical (mammalian) agonists and antagonists tested, only LY341495 was able to interact with the schistosome receptor, suggesting that the pharmacological profile of SmGluR is substantially different from that of receptors in the host. The presence of SmGluR in the parasite was verified by immunoprecipitation and Western blot analyses, using a specific peptide antibody. Confocal immunolocalization studies revealed that SmGluR is strongly expressed in the nervous system of adult worms and larvae. In the adults, the receptor was detected in the longitudinal nerve cords and cerebral commissures, as well as the peripheral nerve fibers and plexuses innervating the acetabulum and the somatic musculature. Outside the nervous system, SmGluR was detected along the length of the female reproductive system, including the oviduct, ootype and the uterus. A comparative expression analysis at the RNA level revealed that SmGluR is expressed at about the same level in cercaria and adult stages, as determined by quantitative reverse-transcription PCR. The results identify SmGluR as an important neuronal receptor and provide the first molecular evidence for a glutamate signaling system in schistosomes.
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Affiliation(s)
- Amira Taman
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Sainte Anne de Bellevue, Quebec, Canada H9X 3V9
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Ribeiro P, Geary TG. Neuronal signaling in schistosomes: current status and prospects for postgenomicsThe present review is one of a series of occasional review articles that have been invited by the Editors and will feature the broad range of disciplines and expertise represented in our Editorial Advisory Board. CAN J ZOOL 2010. [DOI: 10.1139/z09-126] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Parasitic platyhelminths of the genus Schistosoma Weinland, 1858 (Trematoda, Digenea) are the etiological agents of human schistosomiasis, one of the most prevalent and debilitating parasitic diseases worldwide. Praziquantel is the only drug treatment available in most parts of the world and the effectiveness of the drug is threatened by the prospect of drug resistance. There is a pressing need to learn more about the basic biology of this organism and to identify molecular targets for new therapeutic drugs. The nervous system of schistosomes coordinates many activities that are essential for parasite survival, and as such is an attractive target for chemotherapeutic intervention. Until recently, very little was known about the molecular mechanisms of neuronal signaling in these organisms, but this is rapidly changing following the completion of the genome sequence and several recent developments in schistosome transgenesis and gene silencing. Here we review the current status of schistosome neurobiology and discuss prospects for future research as the field moves into a postgenomics era. One of the themes that will emerge from this discussion is that schistosomes have a rich diversity of neurotransmitters and receptors, indicating a more sophisticated system of neuronal communication than might be expected of a parasitic flatworm. Moreover, many of these transmitter receptors share little sequence homology with those of the human host, making them ideally suited for selective drug targeting. Strategies for characterization of these important parasite proteins will be discussed.
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Affiliation(s)
- Paula Ribeiro
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue, QC H9X 3V9, Canada
| | - Timothy G. Geary
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue, QC H9X 3V9, Canada
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18
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Jones AK, Sattelle DB. Diversity of Insect Nicotinic Acetylcholine Receptor Subunits. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 683:25-43. [DOI: 10.1007/978-1-4419-6445-8_3] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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19
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Alternative splicing of the Anopheles gambiae nicotinic acetylcholine receptor, Agamαβ9, generates both alpha and beta subunits. INVERTEBRATE NEUROSCIENCE 2009; 9:77-84. [DOI: 10.1007/s10158-009-0089-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Accepted: 07/23/2009] [Indexed: 01/01/2023]
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20
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Taman A, Ribeiro P. Investigation of a dopamine receptor in Schistosoma mansoni: functional studies and immunolocalization. Mol Biochem Parasitol 2009; 168:24-33. [PMID: 19545592 DOI: 10.1016/j.molbiopara.2009.06.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Revised: 06/05/2009] [Accepted: 06/11/2009] [Indexed: 11/15/2022]
Abstract
A dopamine receptor (SmD2) was cloned from adult Schistosoma mansoni. The receptor has the classical heptahelical topology of class A (rhodopsin-like) G protein-coupled receptors (GPCR) and shares sequence homology with D2-like receptors from other species. The full length SmD2 cDNA was expressed in the yeast Saccharomyces cerevisiae and mammalian HEK293 cells. Functional assays in both expression systems revealed that SmD2 was responsive to dopamine in a dose-dependent manner, whereas other structurally related amines had no effect. Activation of SmD2 in mammalian cells caused an elevation in intracellular cAMP but not calcium, suggesting that the receptor coupled to Gs and the stimulation of adenylate cyclase. Pharmacological studies showed that the S. mansoni dopamine receptor was inhibited by apomorphine, a classical dopamine agonist, as well as known dopaminergic antagonists, including chlorpromazine, spiperone and haloperidol. SmD2 immunoreactivity was detected in membrane protein fractions of S. mansoni cercaria, in vitro transformed schistosomula and adult parasites, using a specific peptide antibody. When tested by confocal immunofluorescence, SmD2 was detected in the subtegumental somatic musculature and acetabulum of all larval stages tested. In the adults, SmD2 was enriched in the somatic muscles and, to a lesser extent, the muscular lining of the caecum. The results suggest that SmD2 is an important component of the neuromuscular system in schistosomes.
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Affiliation(s)
- Amira Taman
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Sainte Anne de Bellevue, Quebec, Canada
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21
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El-Shehabi F, Vermeire JJ, Yoshino TP, Ribeiro P. Developmental expression analysis and immunolocalization of a biogenic amine receptor in Schistosoma mansoni. Exp Parasitol 2009; 122:17-27. [PMID: 19545530 DOI: 10.1016/j.exppara.2009.01.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2008] [Revised: 12/18/2008] [Accepted: 01/05/2009] [Indexed: 11/19/2022]
Abstract
A Schistosoma mansoni G-protein coupled receptor (SmGPCR) was previously cloned and shown to be activated by the biogenic amine, histamine. Here we report a first investigation of the receptor's subunit organization, tissue distribution and expression levels in different stages of the parasite. A polyclonal antibody was produced in rabbits against the recombinant third intracellular loop (il3) of SmGPCR. Western blot studies of the native receptor and recombinant protein expressed in HEK293 cells showed that SmGPCR exists both as a monomer (65 kDa) and an apparent dimer of approximately 130 kDa These species were verified by immunoprecipitation of SmGPCR from S. mansoni extracts, using antibody that was covalently attached to agarose beads. Further investigation determined that the SmGPCR dimer was resistant to treatment with various detergents, 4 M urea and 0.1 M DTT but could be made to dissociate at acidic pH, suggesting the dimer is non-covalent in nature. Confocal immunofluorescence studies revealed significant SmGPCR immunoreactivity in sporocysts, schistosomula and adult worms but not miracidia. SmGPCR was found to be most widely expressed in the schistosomula, particularly the tegument, the subtegumental musculature and the acetabulum. In the adult stage we detected SmGPCR immunofluorescence mainly in the tubercles of male worms and, to a lesser extent, the body wall musculature. Localization in sporocysts was mainly confined to the tegument and cells within parenchymal matrices. A real-time quantitative reverse-transcription PCR analysis revealed that SmGPCR is upregulated at the mRNA level in the parasitic stages compared to the free-living miracidium and cercariae, and it is particularly elevated during early sporocyst and schistosomula development. The results identify SmGPCR as an important parasite receptor with potential functions in muscle and the tegument of S. mansoni.
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MESH Headings
- Animals
- Antibodies, Helminth/biosynthesis
- Antibodies, Helminth/immunology
- Biomphalaria
- Blotting, Western
- Electrophoresis, Polyacrylamide Gel
- Female
- Fluorescent Antibody Technique
- Gene Expression Regulation
- Immunoprecipitation
- Male
- Mice
- Microscopy, Confocal
- RNA, Messenger/analysis
- RNA, Messenger/biosynthesis
- Rabbits
- Receptors, Biogenic Amine/analysis
- Receptors, Biogenic Amine/biosynthesis
- Receptors, Biogenic Amine/genetics
- Receptors, Biogenic Amine/immunology
- Receptors, G-Protein-Coupled/analysis
- Receptors, G-Protein-Coupled/biosynthesis
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/immunology
- Reverse Transcriptase Polymerase Chain Reaction
- Schistosoma mansoni/immunology
- Schistosoma mansoni/metabolism
- Transfection
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Affiliation(s)
- Fouad El-Shehabi
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Quebec, Canada H9X 3V9
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22
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Tan S, Johnston DA, Roberts RG. Schistosome dystrophin and dystrobrevin proteins contain large insertions. Biochem Biophys Res Commun 2007; 362:700-6. [PMID: 17764661 DOI: 10.1016/j.bbrc.2007.08.063] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Accepted: 08/08/2007] [Indexed: 11/23/2022]
Abstract
Dystrophin and dystrobrevin are distantly related proteins that form a heterodimeric membrane-bound complex in all metazoa so far studied. The signature feature of the dystrophin/dystrobrevin/dystrotelin superfamily is a highly conserved cluster of domains whose integrity and size are maintained in all known members- more than 60 sequences so far reported. We were therefore surprised to find that the analogous regions of the Schistosoma mansoni proteins bear multiple large insertions amounting to 100% (dystrophin) and 35% (dystrobrevin) of their expected size. We isolated orthologous sequences from Schistosoma haematobium and Schistosoma bovis, and found that the insertions have a 10-fold higher rate of change (Ka/Ks value) than their respective host sequences, suggesting a much lower degree of functional constraint. A survey of known S. mansoni protein sequences shows that only two other proteins (both acetylcholine receptors) share these properties. We discuss the implications of the positions and sizes of these insertions for the structure and function of the dystrophins and dystrobrevins.
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Affiliation(s)
- Sipin Tan
- Division of Genetics & Molecular Medicine, Department of Medical & Molecular Genetics, King's College London, Guy's Hospital, London SE1 9RT, UK
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23
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Ribeiro P, El-Shehabi F, Patocka N. Classical transmitters and their receptors in flatworms. Parasitology 2007; 131 Suppl:S19-40. [PMID: 16569290 DOI: 10.1017/s0031182005008565] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The flatworm nervous system employs a wide repertoire of neuroactive substances, including small chemical messengers, the so called classical transmitters, and several types of neuropeptides. A large body of research accumulated over four decades has provided a wealth of information on the tissue localization and effects of these substances, their biochemistry and, recently, their molecular modes of action in all major classes of flatworms. This evidence will be reviewed, with particular emphasis on the small (classical) transmitters and the receptors that mediate their effects. One of the themes that will emerge from this discussion is that classical transmitters regulate core activities such as movement, metabolism and transport, and thus are essential for survival of the organism. In addition, the evidence shows that flatworms have multiple neurotransmitter receptors, many with unusual pharmacological features, which make them particularly attractive as drug targets. Understanding the molecular basis of these distinctive properties, and developing new, more specific receptor agonists and antagonists will undoubtedly become a major challenge in future research.
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Affiliation(s)
- P Ribeiro
- Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue Quebec, Canada H9X 3V9.
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24
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Jones AK, Brown LA, Sattelle DB. Insect nicotinic acetylcholine receptor gene families: from genetic model organism to vector, pest and beneficial species. INVERTEBRATE NEUROSCIENCE 2007; 7:67-73. [PMID: 17216517 DOI: 10.1007/s10158-006-0039-6] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2006] [Accepted: 12/18/2006] [Indexed: 10/23/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission in the insect nervous system and are targets of a major group of insecticides, the neonicotinoids. Analyses of genome sequences have shown that nAChR gene families remain compact in diverse insect species, when compared to their mammalian counterparts. Thus, Drosophila melanogaster and Anopheles gambiae each possess 10 nAChR genes while Apis mellifera has 11. Although these are among the smallest nAChR gene families known, receptor diversity can be considerably increased by alternative splicing and mRNA A-to-I editing, thereby generating species-specific subunit isoforms. In addition, each insect possesses at least one highly divergent nAChR subunit. Species-specific subunit diversification may offer promising targets for future rational design of insecticides that act on particular pests while sparing beneficial insects. Electrophysiological studies on cultured Drosophila cholinergic neurons show partial agonist actions of the neonicotinoid imidacloprid and super-agonist actions of another neonicotinoid, clothianidin, on native nAChRs. Recombinant hybrid heteromeric nAChRs comprising Drosophila Dalpha2 and a vertebrate beta2 subunit have been instructive in mimicking such actions of imidacloprid and clothianidin. Unitary conductance measurements on native nAChRs indicate that more frequent openings of the largest conductance state may offer an explanation for the superagonist actions of clothianidin.
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Affiliation(s)
- Andrew K Jones
- MRC Functional Genetics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Le Gros Clark Building, South Parks Road, Oxford, OX1 3QX, UK.
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25
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Bentley GN, Jones AK, Agnew A. ShAR2β, a divergent nicotinic acetylcholine receptor subunit from the blood fluke Schistosoma. Parasitology 2007; 134:833-40. [PMID: 17214911 DOI: 10.1017/s0031182006002162] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
SUMMARYNicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate the fast actions of the neurotransmitter, acetylcholine. Invertebrate nAChRs are of interest as they are targets of widely-selling insecticides and drugs that control nematode parasites. Here, we report the cloning of ShAR2β, a candidate nAChR subunit from the blood fluke, Schistosoma haematobium, which is the third trematode nAChR subunit to be characterized. While ShAR2β possesses key structural features common to all nAChRs, its amino acid sequence shares considerably low identity with those of insect, nematode and vertebrate nAChR subunits. In particular, the second transmembrane domain of ShAR2β, which lines the ion channel, bears unusual amino acid residues which will likely give rise to a receptor with distinct functional properties. Phylogenetic analysis shows that ShAR2β is a divergent nAChR subunit that may define a clade of trematode-specific subunits. We discuss our findings in the context of potentially exploiting this receptor as a target for controlling schistosome parasites.
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Affiliation(s)
- G N Bentley
- The School of Biology, University of Leeds, West Yorkshire, Leeds, LS2 9JT, UK
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26
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Lazari O, Kipar A, Johnson DR, Selkirk ME, Matthews JB. Up-regulated expression of the α7 nicotinic acetylcholine receptor subunit on inflammatory infiltrates during Dictyocaulus viviparus infection. Parasite Immunol 2006; 28:429-37. [PMID: 16916366 DOI: 10.1111/j.1365-3024.2006.00873.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cholinergic signalling is known to affect immune cell function, but few studies have addressed its relevance during nematode infection. We therefore analysed the anatomical distribution and expression pattern of the nicotinic acetylcholine receptor (nAChR) alpha7 subunit in lungs obtained from Dictyocaulus viviparus-infected and uninfected control cattle. The analysis was performed on trachea and lung parenchyma from uninfected animals and animals necropsied at 15, 22 and 43 days post-infection (DPI). Localization of the alpha7 nAChR was evaluated by immunohistology and mRNA expression analysed by gene-specific reverse transcription-polymerase chain reaction (RT-PCR). In uninfected animals, tracheal, bronchial and bronchiolar epithelium and smooth muscle cells constitutively expressed the alpha7 nAChR, as did type I and II alveolar epithelial cells and alveolar macrophages and a few infiltrating leucocytes. By 15 DPI, immunohistology revealed a massive influx of alpha7 nAChR+ inflammatory cells into the lung parenchyma and tracheal wall. This was reflected in the RT-PCR results. At later time points, both parenchyma and tracheal wall contained large numbers of alpha7 nAChR+ leucocytes, but detection of transcript was restricted to the trachea. Recruitment of nAChR-containing leucocytes to the lungs of D. viviparus-infected cattle suggests that these cells may represent possible downstream targets for parasite-secreted acetylcholinesterases.
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Affiliation(s)
- O Lazari
- Veterinary Medicine Biology, Pfizer Animal Health, Sandwich, Kent CT13 9NJ, UK
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27
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Brown LA, Jones AK, Buckingham SD, Mee CJ, Sattelle DB. Contributions from Caenorhabditis elegans functional genetics to antiparasitic drug target identification and validation: nicotinic acetylcholine receptors, a case study. Int J Parasitol 2006; 36:617-24. [PMID: 16620825 DOI: 10.1016/j.ijpara.2006.01.016] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2005] [Revised: 01/16/2006] [Accepted: 01/30/2006] [Indexed: 10/24/2022]
Abstract
Following the complete sequencing of the genome of the free-living nematode, Caenorhabditis elegans, in 1998, rapid advances have been made in assigning functions to many genes. Forward and reverse genetics have been used to identify novel components of synaptic transmission as well as determine the key components of antiparasitic drug targets. The nicotinic acetylcholine receptors (nAChRs) are prototypical ligand-gated ion channels. The functions of these transmembrane proteins and the roles of the different members of their extensive subunit families are increasingly well characterised. The simple nervous system of C. elegans possesses one of the largest nicotinic acetylcholine receptor gene families known for any organism and a combination of genetic, microarray, physiological and reporter gene expression studies have added greatly to our understanding of the components of nematode muscle and neuronal nAChR subtypes. Chemistry-to-gene screens have identified five subunits that are components of nAChRs sensitive to the antiparasitic drug, levamisole. A novel, validated target acting downstream of the levamisole-sensitive nAChR has also been identified in such screens. Physiology and molecular biology studies on nAChRs of parasitic nematodes have also identified levamisole-sensitive and insensitive subtypes and further subdivisions are under investigation.
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Affiliation(s)
- L A Brown
- MRC Functional Genetics Unit, Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK
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28
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Pessôa RF, Castro NG, Noël F. Binding of [3H]MK-801 in subcellular fractions of Schistosoma mansoni: evidence for interaction with nicotinic receptors. Biochem Pharmacol 2005; 69:1509-16. [PMID: 15857615 DOI: 10.1016/j.bcp.2005.03.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Accepted: 03/03/2005] [Indexed: 11/19/2022]
Abstract
Several studies have suggested that l-glutamate is a putative neurotransmitter in Schistosoma mansoni. Recently, we detected the presence of low-affinity binding sites for [(3)H]kainic acid in the heterogeneous (P(1)) subcellular fraction of S. mansoni. In an attempt to characterize N-methyl-d-aspartate (NMDA) receptors in this worm, we performed binding assays with [(3)H]MK-801, a NMDA non-competitive antagonist, in the P(1) fraction of adult S. mansoni. In competition experiments, MK-801 (IC(50) approximately 200 microM) and ketamine (IC(50) approximately 500 microM) exhibited a low affinity for the sites labeled with [(3)H]MK-801. Along with the lack of modulation of this binding by glutamatergic agonists and antagonists and the absence of stereoselectivity for MK-801 isomers, these results suggest that [(3)H]MK-801 could label a site different from the classical NMDA receptor in S. mansoni. Based on the evidences that MK-801 interacts with mammalian muscle and central nervous system nicotinic receptors as a low-affinity noncompetitive antagonist, we have investigated the effects of MK-801 on the nicotine-induced flaccid paralysis of the worm, in vivo. The motility of S. mansoni was quantified by image analysis through a measure of displacement of the worm's extremities. In the presence of (-)-nicotine (10-100 microM), we observed an immediate paralysis of the worms, that was inhibited by 1mM MK-801. Besides nicotine, choline (10-50mM) was also able to inhibit the worm's motility. As a conclusion, we suggest that [(3)H]MK-801 binds to nicotinic receptors, and not NMDA receptors, in subcellular fractions of S. mansoni.
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Affiliation(s)
- Renata Fittipaldi Pessôa
- Departamento de Farmacologia Básica e Clínica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21941-590 Rio de Janeiro, Brazil
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Bentley GN, Jones AK, Agnew A. Expression and comparative functional characterisation of recombinant acetylcholinesterase from three species of Schistosoma. Mol Biochem Parasitol 2005; 141:119-23. [PMID: 15811534 DOI: 10.1016/j.molbiopara.2005.01.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2004] [Accepted: 01/21/2005] [Indexed: 11/20/2022]
Affiliation(s)
- Geoffrey N Bentley
- The School of Biology, University of Leeds, Leeds, West Yorkshire LS2 9JT, UK.
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