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Extensive MHC class IIβ diversity across multiple loci in the small-spotted catshark (Scyliorhinus canicula). Sci Rep 2023; 13:3837. [PMID: 36882519 PMCID: PMC9992475 DOI: 10.1038/s41598-023-30876-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 03/02/2023] [Indexed: 03/09/2023] Open
Abstract
The major histocompatibility complex (MHC) is a multigene family responsible for pathogen detection, and initiation of adaptive immune responses. Duplication, natural selection, recombination, and their resulting high functional genetic diversity spread across several duplicated loci are the main hallmarks of the MHC. Although these features were described in several jawed vertebrate lineages, a detailed MHC IIβ characterization at the population level is still lacking for chondrichthyans (chimaeras, rays and sharks), i.e. the most basal lineage to possess an MHC-based adaptive immune system. We used the small-spotted catshark (Scyliorhinus canicula, Carcharhiniformes) as a case-study species to characterize MHC IIβ diversity using complementary molecular tools, including publicly available genome and transcriptome datasets, and a newly developed high-throughput Illumina sequencing protocol. We identified three MHC IIβ loci within the same genomic region, all of which are expressed in different tissues. Genetic screening of the exon 2 in 41 individuals of S. canicula from a single population revealed high levels of sequence diversity, evidence for positive selection, and footprints of recombination. Moreover, the results also suggest the presence of copy number variation in MHC IIβ genes. Thus, the small-spotted catshark exhibits characteristics of functional MHC IIβ genes typically observed in other jawed vertebrates.
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2
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Wong ATC, Lam DK, Poon ESK, Chan DTC, Sin SYW. Intra-specific copy number variation of MHC class II genes in the Siamese fighting fish. Immunogenetics 2022; 74:327-346. [PMID: 35229174 DOI: 10.1007/s00251-022-01255-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Accepted: 02/04/2022] [Indexed: 11/28/2022]
Abstract
Duplicates of genes for major histocompatibility complex (MHC) molecules can be subjected to selection independently and vary markedly in their evolutionary rates, sequence polymorphism, and functional roles. Therefore, without a thorough understanding of their copy number variation (CNV) in the genome, the MHC-dependent fitness consequences within a species could be misinterpreted. Studying the intra-specific CNV of this highly polymorphic gene, however, has long been hindered by the difficulties in assigning alleles to loci and the lack of high-quality genomic data. Here, using the high-quality genome of the Siamese fighting fish (Betta splendens), a model for mate choice studies, and the whole-genome sequencing (WGS) data of 17 Betta species, we achieved locus-specific amplification of their three classical MHC class II genes - DAB1, DAB2, and DAB3. By performing quantitative PCR and depth-of-coverage analysis using the WGS data, we revealed intra-specific CNV at the DAB3 locus. We identified individuals that had two allelic copies (i.e., heterozygous or homozygous) or one allele (i.e., hemizygous) and individuals without this gene. The CNV was due to the deletion of a 20-kb-long genomic region harboring both the DAA3 and DAB3 genes. We further showed that the three DAB genes were under different modes of selection, which also applies to their corresponding DAA genes that share similar pattern of polymorphism. Our study demonstrates a combined approach to study CNV within a species, which is crucial for the understanding of multigene family evolution and the fitness consequences of CNV.
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Affiliation(s)
- Anson Tsz Chun Wong
- School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Hong Kong SAR, China
| | - Derek Kong Lam
- School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Hong Kong SAR, China
| | - Emily Shui Kei Poon
- School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Hong Kong SAR, China
| | - David Tsz Chung Chan
- School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Hong Kong SAR, China
| | - Simon Yung Wa Sin
- School of Biological Sciences, The University of Hong Kong, Pok Fu Lam Road, Hong Kong SAR, China.
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3
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Hacking J, Bradford T, Pierce K, Gardner M. De novo genotyping of the major histocompatibility complex in an Australian dragon lizard, Ctenophorus decresii. T ROY SOC SOUTH AUST 2018. [DOI: 10.1080/03721426.2018.1542259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Jessica Hacking
- College of Science and Engineering, Flinders University, Bedford Park, Australia
| | - Tessa Bradford
- College of Science and Engineering, Flinders University, Bedford Park, Australia
- Evolutionary Biology Unit, South Australian Museum, Adelaide, Australia
- School of Biological Sciences, University of Adelaide, Adelaide, Australia
| | - Kelly Pierce
- College of Science and Engineering, Flinders University, Bedford Park, Australia
| | - Michael Gardner
- College of Science and Engineering, Flinders University, Bedford Park, Australia
- Evolutionary Biology Unit, South Australian Museum, Adelaide, Australia
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4
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Lighten J, Papadopulos AST, Mohammed RS, Ward BJ, G Paterson I, Baillie L, Bradbury IR, Hendry AP, Bentzen P, van Oosterhout C. Evolutionary genetics of immunological supertypes reveals two faces of the Red Queen. Nat Commun 2017; 8:1294. [PMID: 29101318 PMCID: PMC5670221 DOI: 10.1038/s41467-017-01183-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Accepted: 08/23/2017] [Indexed: 11/09/2022] Open
Abstract
Red Queen host-parasite co-evolution can drive adaptations of immune genes by positive selection that erodes genetic variation (Red Queen arms race) or results in a balanced polymorphism (Red Queen dynamics) and long-term preservation of genetic variation (trans-species polymorphism). These two Red Queen processes are opposite extremes of the co-evolutionary spectrum. Here we show that both Red Queen processes can operate simultaneously by analysing the major histocompatibility complex (MHC) in guppies (Poecilia reticulata and P. obscura) and swamp guppies (Micropoecilia picta). Sub-functionalisation of MHC alleles into 'supertypes' explains how polymorphisms persist during rapid host-parasite co-evolution. Simulations show the maintenance of supertypes as balanced polymorphisms, consistent with Red Queen dynamics, whereas alleles within supertypes are subject to positive selection in a Red Queen arms race. Building on the divergent allele advantage hypothesis, we show that functional aspects of allelic diversity help to elucidate the evolution of polymorphic genes involved in Red Queen co-evolution.
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Affiliation(s)
- Jackie Lighten
- School of Environmental Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, UK.
| | - Alexander S T Papadopulos
- Molecular Ecology and Fisheries Genetics Laboratory, Environment Centre Wales, School of Biological Sciences, Bangor University, Bangor, LL57 2UW, UK
| | - Ryan S Mohammed
- Department of Life Sciences, The University of the West Indies, St Augustine, Trinidad and Tobago
| | - Ben J Ward
- Earlham Institute, Norwich Research Park Innovation Centre, Colney Lane, Norwich, NR4 7UZ, UK
| | - Ian G Paterson
- Marine Gene Probe Laboratory, Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS, Canada, B3H 4R2
| | - Lyndsey Baillie
- Michael Smith Laboratories, University of British Columbia, 2185 East Mall, Vancouver, BC, Canada, V6T 1Z4
| | - Ian R Bradbury
- Marine Gene Probe Laboratory, Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS, Canada, B3H 4R2.,Science Branch, Department of Fisheries and Oceans Canada, 80 East White Hills Road, St. John's, NL, Canada, A1C 5X1
| | - Andrew P Hendry
- McGill University, 859 Sherbrooke Street West, Montreal, QC, Canada, H3A 0C4.,Redpath Museum, McGill University, 859 Sherbrooke Street West, Montreal, QC, Canada, H3A 0C4
| | - Paul Bentzen
- Marine Gene Probe Laboratory, Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS, Canada, B3H 4R2
| | - Cock van Oosterhout
- School of Environmental Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, UK.
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5
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Abduriyim S, Nishita Y, Kosintsev PA, Raichev E, Väinölä R, Kryukov AP, Abramov AV, Kaneko Y, Masuda R. Diversity and evolution of MHC class II DRB gene in the Eurasian badger genus Meles (Mammalia: Mustelidae). Biol J Linn Soc Lond 2017. [DOI: 10.1093/biolinnean/blx077] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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6
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Lenz TL, Spirin V, Jordan DM, Sunyaev SR. Excess of Deleterious Mutations around HLA Genes Reveals Evolutionary Cost of Balancing Selection. Mol Biol Evol 2016; 33:2555-64. [PMID: 27436009 PMCID: PMC5026253 DOI: 10.1093/molbev/msw127] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Deleterious mutations are expected to evolve under negative selection and are usually purged from the population. However, deleterious alleles segregate in the human population and some disease-associated variants are maintained at considerable frequencies. Here, we test the hypothesis that balancing selection may counteract purifying selection in neighboring regions and thus maintain deleterious variants at higher frequency than expected from their detrimental fitness effect. We first show in realistic simulations that balancing selection reduces the density of polymorphic sites surrounding a locus under balancing selection, but at the same time markedly increases the population frequency of the remaining variants, including even substantially deleterious alleles. To test the predictions of our simulations empirically, we then use whole-exome sequencing data from 6,500 human individuals and focus on the most established example for balancing selection in the human genome, the major histocompatibility complex (MHC). Our analysis shows an elevated frequency of putatively deleterious coding variants in nonhuman leukocyte antigen (non-HLA) genes localized in the MHC region. The mean frequency of these variants declined with physical distance from the classical HLA genes, indicating dependency on genetic linkage. These results reveal an indirect cost of the genetic diversity maintained by balancing selection, which has hitherto been perceived as mostly advantageous, and have implications both for the evolution of recombination and also for the epidemiology of various MHC-associated diseases.
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Affiliation(s)
- Tobias L Lenz
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School Evolutionary Immunogenomics, Department of Evolutionary Ecology, Max Planck Institute for Evolutionary Biology, Plön, Germany
| | - Victor Spirin
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School
| | - Daniel M Jordan
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School
| | - Shamil R Sunyaev
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School Program in Medical and Population Genetics, The Broad Institute, Cambridge, MA
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7
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Mable BK, Kilbride E, Viney ME, Tinsley RC. Copy number variation and genetic diversity of MHC Class IIb alleles in an alien population of Xenopus laevis. Immunogenetics 2015; 67:591-603. [PMID: 26329765 PMCID: PMC4572066 DOI: 10.1007/s00251-015-0860-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Accepted: 07/10/2015] [Indexed: 12/23/2022]
Abstract
Xenopus laevis (the African clawed frog), which originated through hybridisation and whole genome duplication, has been used as a model for genetics and development for many years, but surprisingly little is known about immune gene variation in natural populations. The purpose of this study was to use an isolated population of X. laevis that was introduced to Wales, UK in the past 50 years to investigate how variation at the MHC compares to that at other loci, following a severe population bottleneck. Among 18 individuals, we found nine alleles based on exon 2 sequences of the Class IIb region (which includes the peptide binding region). Individuals carried from one to three of the loci identified from previous laboratory studies. Genetic variation was an order of magnitude higher at the MHC compared with three single-copy nuclear genes, but all loci showed high levels of heterozygosity and nucleotide diversity and there was not an excess of homozygosity or decrease in diversity over time that would suggest extensive inbreeding in the introduced population. Tajima’s D was positive for all loci, which is consistent with a bottleneck. Moreover, comparison with published sequences identified the source of the introduced population as the Western Cape region of South Africa, where most commercial suppliers have obtained their stocks. These factors suggest that despite founding by potentially already inbred individuals, the alien population in Wales has maintained substantial genetic variation at both adaptively important and neutral genes.
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Affiliation(s)
- Barbara K Mable
- Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK.
| | - Elizabeth Kilbride
- Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Mark E Viney
- School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, UK.
| | - Richard C Tinsley
- School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, UK
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8
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Jouet A, McMullan M, van Oosterhout C. The effects of recombination, mutation and selection on the evolution of the Rp1 resistance genes in grasses. Mol Ecol 2015; 24:3077-92. [PMID: 25907026 DOI: 10.1111/mec.13213] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2014] [Revised: 03/25/2015] [Accepted: 04/09/2015] [Indexed: 01/30/2023]
Abstract
Plant immune genes, or resistance genes, are involved in a co-evolutionary arms race with a diverse range of pathogens. In agronomically important grasses, such R genes have been extensively studied because of their role in pathogen resistance and in the breeding of resistant cultivars. In this study, we evaluate the importance of recombination, mutation and selection on the evolution of the R gene complex Rp1 of Sorghum, Triticum, Brachypodium, Oryza and Zea. Analyses show that recombination is widespread, and we detected 73 independent instances of sequence exchange, involving on average 1567 of 4692 nucleotides analysed (33.4%). We were able to date 24 interspecific recombination events and found that four occurred postspeciation, which suggests that genetic introgression took place between different grass species. Other interspecific events seemed to have been maintained over long evolutionary time, suggesting the presence of balancing selection. Significant positive selection (i.e. a relative excess of nonsynonymous substitutions (dN /dS >1)) was detected in 17-95 codons (0.42-2.02%). Recombination was significantly associated with areas with high levels of polymorphism but not with an elevated dN /dS ratio. Finally, phylogenetic analyses show that recombination results in a general overestimation of the divergence time (mean = 14.3%) and an alteration of the gene tree topology if the tree is not calibrated. Given that the statistical power to detect recombination is determined by the level of polymorphism of the amplicon as well as the number of sequences analysed, it is likely that many studies have underestimated the importance of recombination relative to the mutation rate.
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Affiliation(s)
- Agathe Jouet
- School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.,The Sainsbury Laboratory, Norwich Research Park, Norwich, NR4 7UH, UK
| | - Mark McMullan
- The Genome Analysis Center, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - Cock van Oosterhout
- School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
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9
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Herdegen M, Babik W, Radwan J. Selective pressures on MHC class II genes in the guppy (Poecilia reticulata) as inferred by hierarchical analysis of population structure. J Evol Biol 2014; 27:2347-59. [PMID: 25244157 DOI: 10.1111/jeb.12476] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Revised: 08/08/2014] [Accepted: 08/11/2014] [Indexed: 11/29/2022]
Abstract
Genes of the major histocompatibility complex, which are the most polymorphic of all vertebrate genes, are a pre-eminent system for the study of selective pressures that arise from host-pathogen interactions. Balancing selection capable of maintaining high polymorphism should lead to the homogenization of MHC allele frequencies among populations, but there is some evidence to suggest that diversifying selection also operates on the MHC. However, the pattern of population structure observed at MHC loci is likely to depend on the spatial and/or temporal scale examined. Here, we investigated selection acting on MHC genes at different geographic scales using Venezuelan guppy populations inhabiting four regions. We found a significant correlation between MHC and microsatellite allelic richness across populations, which suggests the role of genetic drift in shaping MHC diversity. However, compared to microsatellites, more MHC variation was explained by differences between populations within larger geographic regions and less by the differences between the regions. Furthermore, among proximate populations, variation in MHC allele frequencies was significantly higher compared to microsatellites, indicating that selection acting on MHC may increase population structure at small spatial scales. However, in populations that have significantly diverged at neutral markers, the population-genetic signature of diversifying selection may be eradicated in the long term by that of balancing selection, which acts to preserve rare alleles and thus maintain a common pool of MHC alleles.
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Affiliation(s)
- M Herdegen
- Institute of Environmental Sciences, Jagiellonian University, Kraków, Poland
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10
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Lighten J, van Oosterhout C, Bentzen P. Critical review of NGS analyses for de novo genotyping multigene families. Mol Ecol 2014; 23:3957-72. [DOI: 10.1111/mec.12843] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 06/08/2014] [Accepted: 06/17/2014] [Indexed: 01/16/2023]
Affiliation(s)
- Jackie Lighten
- Department of Biology; Marine Gene Probe Laboratory; Dalhousie University; Halifax Nova Scotia Canada
| | - Cock van Oosterhout
- School of Environmental Sciences; University of East Anglia; Norwich Research Park; Norwich UK
| | - Paul Bentzen
- Department of Biology; Marine Gene Probe Laboratory; Dalhousie University; Halifax Nova Scotia Canada
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11
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Wright DJ, Spurgin LG, Collar NJ, Komdeur J, Burke T, Richardson DS. The impact of translocations on neutral and functional genetic diversity within and among populations of the Seychelles warbler. Mol Ecol 2014; 23:2165-77. [PMID: 24689851 PMCID: PMC4237152 DOI: 10.1111/mec.12740] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Revised: 03/06/2014] [Accepted: 03/07/2014] [Indexed: 01/10/2023]
Abstract
Translocations are an increasingly common tool in conservation. The maintenance of genetic diversity through translocation is critical for both the short- and long-term persistence of populations and species. However, the relative spatio-temporal impacts of translocations on neutral and functional genetic diversity, and how this affects genetic structure among the conserved populations overall, have received little investigation. We compared the impact of translocating different numbers of founders on both microsatellite and major histocompatibility complex (MHC) class I diversity over a 23-year period in the Seychelles warbler (Acrocephalus sechellensis). We found low and stable microsatellite and MHC diversity in the source population and evidence for only a limited loss of either type of diversity in the four new populations. However, we found evidence of significant, but low to moderate, genetic differentiation between populations, with those populations established with fewer founders clustering separately. Stochastic genetic capture (as opposed to subsequent drift) was the main determinant of translocated population diversity. Furthermore, a strong correlation between microsatellite and MHC differentiation suggested that neutral processes outweighed selection in shaping MHC diversity in the new populations. These data provide important insights into how to optimize the use of translocation as a conservation tool.
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Affiliation(s)
- David J Wright
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK; NERC Biomolecular Analysis Facility, Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK
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12
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Lighten J, van Oosterhout C, Paterson IG, McMullan M, Bentzen P. Ultra-deep Illumina sequencing accurately identifies MHC class IIb alleles and provides evidence for copy number variation in the guppy (Poecilia reticulata). Mol Ecol Resour 2014; 14:753-67. [PMID: 24400817 DOI: 10.1111/1755-0998.12225] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Revised: 12/02/2013] [Accepted: 12/20/2013] [Indexed: 11/27/2022]
Abstract
We address the bioinformatic issue of accurately separating amplified genes of the major histocompatibility complex (MHC) from artefacts generated during high-throughput sequencing workflows. We fit observed ultra-deep sequencing depths (hundreds to thousands of sequences per amplicon) of allelic variants to expectations from genetic models of copy number variation (CNV). We provide a simple, accurate and repeatable method for genotyping multigene families, evaluating our method via analyses of 209 b of MHC class IIb exon 2 in guppies (Poecilia reticulata). Genotype repeatability for resequenced individuals (N = 49) was high (100%) within the same sequencing run. However, repeatability dropped to 83.7% between independent runs, either because of lower mean amplicon sequencing depth in the initial run or random PCR effects. This highlights the importance of fully independent replicates. Significant improvements in genotyping accuracy were made by greatly reducing type I genotyping error (i.e. accepting an artefact as a true allele), which may occur when using low-depth allele validation thresholds used by previous methods. Only a small amount (4.9%) of type II error (i.e. rejecting a genuine allele as an artefact) was detected through fully independent sequencing runs. We observed 1-6 alleles per individual, and evidence of sharing of alleles across loci. Variation in the total number of MHC class II loci among individuals, both among and within populations was also observed, and some genotypes appeared to be partially hemizygous; total allelic dosage added up to an odd number of allelic copies. Collectively, observations provide evidence of MHC CNV and its complex basis in natural populations.
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Affiliation(s)
- Jackie Lighten
- Marine Gene Probe Laboratory, Department of Biology, Dalhousie University, Halifax, NS, Canada, B3H 4R2
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13
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Sepil I, Lachish S, Hinks AE, Sheldon BC. Mhc supertypes confer both qualitative and quantitative resistance to avian malaria infections in a wild bird population. Proc Biol Sci 2013; 280:20130134. [PMID: 23516242 DOI: 10.1098/rspb.2013.0134] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Major histocompatibility complex (Mhc) genes are believed to play a key role in the genetic basis of disease control. Although numerous studies have sought links between Mhc and disease prevalence, many have ignored the ecological and epidemiological aspects of the host-parasite interaction. Consequently, interpreting associations between prevalence and Mhc has been difficult, whereas discriminating alleles for qualitative resistance, quantitative resistance and susceptibility remains challenging. Moreover, most studies to date have quantified associations between genotypes and disease status, overlooking the complex relationship between genotype and the properties of the Mhc molecule that interacts with parasites. Here, we address these problems and demonstrate avian malaria (Plasmodium) parasite species-specific associations with functional properties of Mhc molecules (Mhc supertypes) in a wild great tit (Parus major) population. We further show that correctly interpreting these associations depends crucially on understanding the spatial variation in risk of infection and the fitness effects of infection. We report that a single Mhc supertype confers qualitative resistance to Plasmodium relictum, whereas a different Mhc supertype confers quantitative resistance to Plasmodium circumflexum infections. Furthermore, we demonstrate common functional properties of Plasmodium-resistance alleles in passerine birds, suggesting this is a model system for parasite-Mhc associations in the wild.
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Affiliation(s)
- Irem Sepil
- Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
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14
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van Oosterhout C. Maintenance of major histocompatibility supertype variation in selfing vertebrate is no evidence for overdominant selection. Proc Biol Sci 2013; 280:20122501. [PMID: 23303538 DOI: 10.1098/rspb.2012.2501] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Cock van Oosterhout
- School of Environmental Science, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
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15
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McMullan M, van Oosterhout C. Inference of selection based on temporal genetic differentiation in the study of highly polymorphic multigene families. PLoS One 2012; 7:e42119. [PMID: 22900006 PMCID: PMC3416836 DOI: 10.1371/journal.pone.0042119] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 07/02/2012] [Indexed: 01/12/2023] Open
Abstract
The co-evolutionary arms race between host immune genes and parasite virulence genes is known as Red Queen dynamics. Temporal fluctuations in allele frequencies, or the ‘turnover’ of alleles at immune genes, are concordant with predictions of the Red Queen hypothesis. Such observations are often taken as evidence of host-parasite co-evolution. Here, we use computer simulations of the Major Histocompatibility Complex (MHC) of guppies (Poecilia reticulata) to study the turnover rate of alleles (temporal genetic differentiation, G'ST). Temporal fluctuations in MHC allele frequencies can be ≥≤order of magnitude larger than changes observed at neutral loci. Although such large fluctuations in the MHC are consistent with Red Queen dynamics, simulations show that other demographic and population genetic processes can account for this observation, these include: (1) overdominant selection, (2) fluctuating population size within a metapopulation, and (3) the number of novel MHC alleles introduced by immigrants when there are multiple duplicated genes. Synergy between these forces combined with migration rate and the effective population size can drive the rapid turnover in MHC alleles. We posit that rapid allelic turnover is an inherent property of highly polymorphic multigene families and that it cannot be taken as evidence of Red Queen dynamics. Furthermore, combining temporal samples in spatial FST outlier analysis may obscure the signal of selection.
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Affiliation(s)
- Mark McMullan
- School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, United Kingdom.
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