1
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Zeng Q, Li X, Shi X, Yan S. Partial molecular characterization, expression pattern and polymorphism analysis of MHC I genes in Chinese domestic goose (Anser cygnoides). Genet Mol Biol 2024; 47:e20220252. [PMID: 39012094 PMCID: PMC11249561 DOI: 10.1590/1678-4685-gmb-2022-0252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Accepted: 05/09/2024] [Indexed: 07/17/2024] Open
Abstract
Major histocompatibility complex (MHC) allelic polymorphism is critically important for mediating antigen presentation in vertebrates. Presently, there are insufficient studies of MHC genetic diversity in domestic Anseriform birds. In this study, we analyzed the expression profile of MHC I genes and screened for MHC I exon 2 polymorphism in one domestic goose population from China using Illumina MiSeq sequencing. The results showed that four MHC I alleles (Ancy-IE2*09/*11/*13/*21) in one goose were identified based on cDNA cloning and sequencing using four primer combinations, and the varying number of cDNA clones implied that these four classical sequences showed differential expression patterns. Through next-generation sequencing, 27 alleles were obtained from 68 geese with 3-10 putative alleles per individual, indicating at least the existence of 5 MHC I loci in the goose. The marked excess of the non-synonymous over the synonymous substitution in the peptide-binding region (PBR) along 27 alleles and five positively selected sites (PSSs) detected around the PBR indicated that balancing selection might be the major force in shaping high MHC variation in the goose. Additionally, IA alleles displaying lower polymorphism were subject to less positive selection pressure than non-IA alleles with a higher level of polymorphism.
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Affiliation(s)
- Qianqian Zeng
- Qilu University of Technology, School of Bioengineering, State
Key Laboratory of Biobased Material and Green Papermaking, Jinan, Shandong,
China
| | - Xiaojie Li
- Qilu University of Technology, School of Bioengineering, State
Key Laboratory of Biobased Material and Green Papermaking, Jinan, Shandong,
China
| | - Xiaomin Shi
- Qilu University of Technology, School of Bioengineering, State
Key Laboratory of Biobased Material and Green Papermaking, Jinan, Shandong,
China
| | - Shigan Yan
- Qilu University of Technology, School of Bioengineering, State
Key Laboratory of Biobased Material and Green Papermaking, Jinan, Shandong,
China
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2
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Watson H, Drews A, Skogsmyr KH, Neto JM, Roved J, Westerdahl H. Only rare classical MHC-I alleles are highly expressed in the European house sparrow. Proc Biol Sci 2024; 291:20232857. [PMID: 38378156 PMCID: PMC10878800 DOI: 10.1098/rspb.2023.2857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2023] [Accepted: 01/17/2024] [Indexed: 02/22/2024] Open
Abstract
The exceptional polymorphism observed within genes of the major histocompatibility complex (MHC), a core component of the vertebrate immune system, has long fascinated biologists. The highly polymorphic classical MHC class-I (MHC-I) genes are maintained by pathogen-mediated balancing selection (PMBS), as shown by many sites subject to positive selection, while the more monomorphic non-classical MHC-I genes show signatures of purifying selection. In line with PMBS, at any point in time, rare classical MHC alleles are more likely than common classical MHC alleles to confer a selective advantage in host-pathogen interactions. Combining genomic and expression data from the blood of wild house sparrows Passer domesticus, we found that only rare classical MHC-I alleles were highly expressed, while common classical MHC-I alleles were lowly expressed or not expressed. Moreover, highly expressed rare classical MHC-I alleles had more positively selected sites, indicating exposure to stronger PMBS, compared with lowly expressed classical alleles. As predicted, the level of expression was unrelated to allele frequency in the monomorphic non-classical MHC-I alleles. Going beyond previous studies, we offer a fine-scale view of selection on classical MHC-I genes in a wild population by revealing differences in the strength of PMBS according to allele frequency and expression level.
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Affiliation(s)
- Hannah Watson
- Department of Biology, Lund University, 223 62 Lund, Sweden
| | - Anna Drews
- Department of Biology, Lund University, 223 62 Lund, Sweden
| | | | - Júlio Manuel Neto
- Department of Biology, Lund University, 223 62 Lund, Sweden
- Department of Biology and Centre for Environmental and Marine Studies, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
| | - Jacob Roved
- Section for Molecular Ecology and Evolution, GLOBE Institute, University of Copenhagen, Øster Farimagsgade 5, Bygn. 7, 1353 Copenhagen K, Denmark
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3
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Mellinger S, Stervander M, Lundberg M, Drews A, Westerdahl H. Improved haplotype resolution of highly duplicated MHC genes in a long-read genome assembly using MiSeq amplicons. PeerJ 2023; 11:e15480. [PMID: 37456901 PMCID: PMC10349553 DOI: 10.7717/peerj.15480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 05/08/2023] [Indexed: 07/18/2023] Open
Abstract
Long-read sequencing offers a great improvement in the assembly of complex genomic regions, such as the major histocompatibility complex (MHC) region, which can contain both tandemly duplicated MHC genes (paralogs) and high repeat content. The MHC genes have expanded in passerine birds, resulting in numerous MHC paralogs, with relatively high sequence similarity, making the assembly of the MHC region challenging even with long-read sequencing. In addition, MHC genes show rather high sequence divergence between alleles, making diploid-aware assemblers incorrectly classify haplotypes from the same locus as sequences originating from different genomic regions. Consequently, the number of MHC paralogs can easily be over- or underestimated in long-read assemblies. We therefore set out to verify the MHC diversity in an original and a haplotype-purged long-read assembly of one great reed warbler Acrocephalus arundinaceus individual (the focal individual) by using Illumina MiSeq amplicon sequencing. Single exons, representing MHC class I (MHC-I) and class IIB (MHC-IIB) alleles, were sequenced in the focal individual and mapped to the annotated MHC alleles in the original long-read genome assembly. Eighty-four percent of the annotated MHC-I alleles in the original long-read genome assembly were detected using 55% of the amplicon alleles and likewise, 78% of the annotated MHC-IIB alleles were detected using 61% of the amplicon alleles, indicating an incomplete annotation of MHC genes. In the haploid genome assembly, each MHC-IIB gene should be represented by one allele. The parental origin of the MHC-IIB amplicon alleles in the focal individual was determined by sequencing MHC-IIB in its parents. Two of five larger scaffolds, containing 6-19 MHC-IIB paralogs, had a maternal and paternal origin, respectively, as well as a high nucleotide similarity, which suggests that these scaffolds had been incorrectly assigned as belonging to different loci in the genome rather than as alternate haplotypes of the same locus. Therefore, the number of MHC-IIB paralogs was overestimated in the haploid genome assembly. Based on our findings we propose amplicon sequencing as a suitable complement to long-read sequencing for independent validation of the number of paralogs in general and for haplotype inference in multigene families in particular.
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Affiliation(s)
- Samantha Mellinger
- Department of Biology, Molecular Ecology and Evolution Lab, Lund University, Lund, Sweden
| | - Martin Stervander
- Department of Biology, Molecular Ecology and Evolution Lab, Lund University, Lund, Sweden
- Department of Biology and Environmental Science, Faculty of Health and Life Sciences, Linnaeus University, Kalmar, Sweden
- Bird Group, Natural History Museum, Tring, Hertfordshire, United Kingdom
| | - Max Lundberg
- Department of Biology, Molecular Ecology and Evolution Lab, Lund University, Lund, Sweden
| | - Anna Drews
- Department of Biology, Molecular Ecology and Evolution Lab, Lund University, Lund, Sweden
| | - Helena Westerdahl
- Department of Biology, Molecular Ecology and Evolution Lab, Lund University, Lund, Sweden
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4
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Rekdal SL, Anmarkrud JA, Lifjeld JT, Johnsen A. Do female bluethroats without extra-pair offspring have more MHC-compatible social mates? Behav Ecol Sociobiol 2023. [DOI: 10.1007/s00265-023-03311-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/05/2023]
Abstract
Abstract
Genes of the major histocompatibility complex (MHC) are crucial for adaptive immunity in jawed vertebrates, and theory predicts that there should be mate choice for optimizing MHC constitution in the offspring. In a previous study, we demonstrated a non-random female choice of extra-pair males in the bluethroat (Luscinia svecica), yielding offspring that was closer to an intermediate MHC class II (MHCII) allele count than their within-pair halfsiblings. The present study tests whether social pairs with only within-pair young (WPY) in their brood, in the same study population, had a combined MHC-constitution closer to a presumed intermediate optimum, than social pairs with extra-pair young (EPY), with a corresponding pattern in their offspring. As expected, we found that WPY from pure WPY-broods were more MHC-optimal than WPY from mixed broods, but only in broods of young (second year) males. Correspondingly, there was a tendency for social pairs with only WPY in their brood to be more MHC-compatible than social pairs with EPY in their brood, when the male was young. Older bluethroat males have considerably larger testes than young males, and their higher sperm competitiveness could help them secure paternity in their own brood, also when they are not MHC-compatible. In other words, in the sexual conflict over paternity, females may be more likely to realise their preference for a MHC-compatible mate when paired to a young male. As a possible fitness indicator, immune responsiveness to an injected antigen (PHA) was elevated for offspring closer to “the golden mean” in MHCII allele count.
Significance statement
This study contributes to our understanding of MHC-based mate choice in extra-pair mating systems, by showing that female bluethroats (Luscinia svecica) with an MHCII-compatible social mate tend to have no extra-pair young in their brood, but only when the social male is young. This elucidates a possible sexual conflict, in which older social males are able to override female preferences and prevent other males from gaining paternity in their brood through higher sperm production. Studying systems in which extra-pair paternity occurs offers an insight into the genetic benefits of mate choice, as extra-pair males, in contrast to social males, generally contribute only sperm. Further, the strict and thorough genotyping scheme applied in this study enabled us to demonstrate a preference for “the golden mean” in MHC-diversity in a species with one of the highest MHC class II-diversity known to date.
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5
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Palomar G, Dudek K, Migalska M, Arntzen JW, Ficetola GF, Jelić D, Jockusch E, Martínez-Solano I, Matsunami M, Shaffer HB, Vörös J, Waldman B, Wielstra B, Babik W. Coevolution between MHC class I and Antigen Processing Genes in salamanders. Mol Biol Evol 2021; 38:5092-5106. [PMID: 34375431 PMCID: PMC8557411 DOI: 10.1093/molbev/msab237] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Proteins encoded by antigen-processing genes (APGs) provide major histocompatibility complex (MHC) class I (MHC-I) with antigenic peptides. In mammals, polymorphic multigenic MHC-I family is served by monomorphic APGs, whereas in certain nonmammalian species both MHC-I and APGs are polymorphic and coevolve within stable haplotypes. Coevolution was suggested as an ancestral gnathostome feature, presumably enabling only a single highly expressed classical MHC-I gene. In this view coevolution, while optimizing some aspects of adaptive immunity, would also limit its flexibility by preventing the expansion of classical MHC-I into a multigene family. However, some nonmammalian taxa, such as salamanders, have multiple highly expressed MHC-I genes, suggesting either that coevolution is relaxed or that it does not prevent the establishment of multigene MHC-I. To distinguish between these two alternatives, we use salamanders (30 species from 16 genera representing six families) to test, within a comparative framework, a major prediction of the coevolution hypothesis: the positive correlation between MHC-I and APG diversity. We found that MHC-I diversity explained both within-individual and species-wide diversity of two APGs, TAP1 and TAP2, supporting their coevolution with MHC-I, whereas no consistent effect was detected for the other three APGs (PSMB8, PSMB9, and TAPBP). Our results imply that although coevolution occurs in salamanders, it does not preclude the expansion of the MHC-I gene family. Contrary to the previous suggestions, nonmammalian vertebrates thus may be able to accommodate diverse selection pressures with flexibility granted by rapid expansion or contraction of the MHC-I family, while retaining the benefits of coevolution between MHC-I and TAPs.
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Affiliation(s)
- G Palomar
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
| | - K Dudek
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
| | - M Migalska
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
| | - J W Arntzen
- Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA leiden, Leiden, The Netherlands.,Institute of Biology Leiden, Leiden University, 2300 RA Leiden, The Netherlands
| | - G F Ficetola
- Department of Environmental Sciences and Policy, University of Milano, Italy.,Laboratoire d'Ecologie Alpine (LECA), CNRS, Université Grenoble Alpes and Université Savoie Mont Blanc, Grenoble, France
| | - D Jelić
- Croatian Institute for Biodiversity, Zagreb, Croatia
| | - E Jockusch
- Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT USA
| | - I Martínez-Solano
- Museo Nacional de Ciencias Naturales (MNCN), Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - M Matsunami
- Department of Advanced Genomic and Laboratory Medicine, Graduate School of Medicine, University of the Ryukyus, Nishihara-cho, Japan
| | - H B Shaffer
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA.,La Kretz Center for California Conservation Science, Institute of the Environment and Sustainability, University of California, Los Angeles, CA 90095, USA
| | - J Vörös
- Department of Zoology, Hungarian Natural History Museum, Budapest, Hungary
| | - B Waldman
- Department of Integrative Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA.,School of Biological Sciences, Seoul National University, Seoul 08826, South Korea
| | - B Wielstra
- Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA leiden, Leiden, The Netherlands.,Institute of Biology Leiden, Leiden University, 2300 RA Leiden, The Netherlands
| | - W Babik
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
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6
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Scherman K, Råberg L, Westerdahl H. Borrelia Infection in Bank Voles Myodes glareolus Is Associated With Specific DQB Haplotypes Which Affect Allelic Divergence Within Individuals. Front Immunol 2021; 12:703025. [PMID: 34381454 PMCID: PMC8350566 DOI: 10.3389/fimmu.2021.703025] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 07/01/2021] [Indexed: 11/17/2022] Open
Abstract
The high polymorphism of Major Histocompatibility Complex (MHC) genes is generally considered to be a result of pathogen-mediated balancing selection. Such selection may operate in the form of heterozygote advantage, and/or through specific MHC allele–pathogen interactions. Specific MHC allele–pathogen interactions may promote polymorphism via negative frequency-dependent selection (NFDS), or selection that varies in time and/or space because of variability in the composition of the pathogen community (fluctuating selection; FS). In addition, divergent allele advantage (DAA) may act on top of these forms of balancing selection, explaining the high sequence divergence between MHC alleles. DAA has primarily been thought of as an extension of heterozygote advantage. However, DAA could also work in concert with NFDS though this is yet to be tested explicitly. To evaluate the importance of DAA in pathogen-mediated balancing selection, we surveyed allelic polymorphism of MHC class II DQB genes in wild bank voles (Myodes glareolus) and tested for associations between DQB haplotypes and infection by Borrelia afzelii, a tick-transmitted bacterium causing Lyme disease in humans. We found two significant associations between DQB haplotypes and infection status: one haplotype was associated with lower risk of infection (resistance), while another was associated with higher risk of infection (susceptibility). Interestingly, allelic divergence within individuals was higher for voles with the resistance haplotype compared to other voles. In contrast, allelic divergence was lower for voles with the susceptibility haplotype than other voles. The pattern of higher allelic divergence in individuals with the resistance haplotype is consistent with NFDS favouring divergent alleles in a natural population, hence selection where DAA works in concert with NFDS.
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Affiliation(s)
- Kristin Scherman
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
| | - Lars Råberg
- Functional Zoology, Department of Biology, Lund University, Lund, Sweden
| | - Helena Westerdahl
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
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7
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Qin S, Dunn PO, Yang Y, Liu H, He K. Polymorphism and varying selection within the MHC class I of four Anas species. Immunogenetics 2021; 73:395-404. [PMID: 34195858 DOI: 10.1007/s00251-021-01222-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Accepted: 06/23/2021] [Indexed: 10/21/2022]
Abstract
Ducks (Anatidae) are often vectors for the spread of pathogens because of their long-distance migrations. These migrations also expose ducks to a wide variety of pathogens in their wintering and breeding grounds, and, as a consequence, we might expect strong selection on their immune genes. Here, we studied exons 2 and 3 of the MHC class I in four species of Anas ducks (A. platyrhynchos, A. poecilorhyncha, A. formosa, and A. querquedula) using Illumina-sequencing. Both exons 2 and 3 code for the peptide-binding region of class I molecules; however, most previous studies of birds have only focused on exon 3. Here, we found stronger positive selection on exon 2 than exon 3, as indicated by more species with dN/dS > 1 and higher Wu-Kabat values. There was little evidence that divergence time influenced polymorphism, the numbers of identical alleles (partial α1 or α2 regions) among four Anas, or selection, suggesting that these widespread species might share similar levels of selection from pathogens. The high similarity of allele numbers, positively selected sites (PSS), conserved motifs, and variable protein sites (VPS) supported the persistence of trans-species polymorphism in Anas for at least 10 million years. Our study revealed exon 2 as a relatively unexplored source of variation in avian MHC class I, which should be considered in future studies.
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Affiliation(s)
- Shidi Qin
- College of Animal Science and Technology, College of Veterinary Medicine, Key Laboratory of Applied Technology On Green-Eco-Healthy Animal Husbandry of Zhejiang Province, Zhejiang Agriculture and Forestry University, Zhejiang Provincial Engineering Laboratory for Animal Health Inspection and Internet Technology, Hangzhou, China
| | - Peter O Dunn
- Behavioral and Molecular Ecology Group, Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, USA
| | - Yang Yang
- College of Animal Science and Technology, College of Veterinary Medicine, Key Laboratory of Applied Technology On Green-Eco-Healthy Animal Husbandry of Zhejiang Province, Zhejiang Agriculture and Forestry University, Zhejiang Provincial Engineering Laboratory for Animal Health Inspection and Internet Technology, Hangzhou, China
| | - Hongyi Liu
- College of Biology and the Environment, Nanjing Forestry University, Nanjing, 210037, China
| | - Ke He
- College of Animal Science and Technology, College of Veterinary Medicine, Key Laboratory of Applied Technology On Green-Eco-Healthy Animal Husbandry of Zhejiang Province, Zhejiang Agriculture and Forestry University, Zhejiang Provincial Engineering Laboratory for Animal Health Inspection and Internet Technology, Hangzhou, China.
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8
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Minias P, Włodarczyk R, Remisiewicz M, Cobzaru I, Janiszewski T. Distinct evolutionary trajectories of MHC class I and class II genes in Old World finches and buntings. Heredity (Edinb) 2021; 126:974-990. [PMID: 33824536 PMCID: PMC8178356 DOI: 10.1038/s41437-021-00427-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 03/08/2021] [Accepted: 03/15/2021] [Indexed: 02/01/2023] Open
Abstract
Major histocompatibility complex (MHC) genes code for key proteins of the adaptive immune system, which present antigens from intra-cellular (MHC class I) and extra-cellular (MHC class II) pathogens. Because of their unprecedented diversity, MHC genes have long been an object of scientific interest, but due to methodological difficulties in genotyping of duplicated loci, our knowledge on the evolution of the MHC across different vertebrate lineages is still limited. Here, we compared the evolution of MHC class I and class II genes in three sister clades of common passerine birds, finches (Fringillinae and Carduelinae) and buntings (Emberizidae) using a uniform methodological (genotyping and data processing) approach and uniform sample sizes. Our analyses revealed contrasting evolutionary trajectories of the two MHC classes. We found a stronger signature of pervasive positive selection and higher allele diversity (allele numbers) at the MHC class I than class II. In contrast, MHC class II genes showed greater allele divergence (in terms of nucleotide diversity) and a much stronger recombination (gene conversion) signal. Gene copy numbers at both MHC class I and class II evolved via fluctuating selection and drift (Brownian Motion evolution), but the evolutionary rate was higher at class I. Our study constitutes one of few existing examples, where evolution of MHC class I and class II genes was directly compared using a multi-species approach. We recommend that re-focusing MHC research from single-species and single-class approaches towards multi-species analyses of both MHC classes can substantially increase our understanding MHC evolution in a broad phylogenetic context.
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Affiliation(s)
- Piotr Minias
- Department of Biodiversity Studies and Bioeducation, Faculty of Biology and Environmental Protection, University of Łódź, Łódź, Poland.
| | - Radosław Włodarczyk
- Department of Biodiversity Studies and Bioeducation, Faculty of Biology and Environmental Protection, University of Łódź, Łódź, Poland
| | - Magdalena Remisiewicz
- Bird Migration Research Station, Faculty of Biology, University of Gdańsk, Gdańsk, Poland
| | - Ioana Cobzaru
- Institute of Biology Bucharest, Romanian Academy, Bucharest, Romania
| | - Tomasz Janiszewski
- Department of Biodiversity Studies and Bioeducation, Faculty of Biology and Environmental Protection, University of Łódź, Łódź, Poland
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9
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O'Connor EA, Westerdahl H. Trade-offs in expressed major histocompatibility complex diversity seen on a macroevolutionary scale among songbirds. Evolution 2021; 75:1061-1069. [PMID: 33666228 DOI: 10.1111/evo.14207] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Revised: 01/07/2021] [Accepted: 02/17/2021] [Indexed: 12/30/2022]
Abstract
To survive organisms must defend themselves against pathogens. Classical Major Histocompatibility Complex (MHC) genes play a key role in pathogen defense by encoding molecules involved in pathogen recognition. MHC gene diversity influences the variety of pathogens individuals can recognize and respond to and has consequently been a popular genetic marker for disease resistance in ecology and evolution. However, MHC diversity is predominantly estimated using genomic DNA (gDNA) with little knowledge of expressed diversity. This limits our ability to interpret the adaptive significance of variation in MHC diversity, especially in species with very many MHC genes such as songbirds. Here, we address this issue using phylogenetic comparative analyses of the number of MHC class I alleles (MHC-I diversity) in gDNA and complementary DNA (cDNA), that is, expressed alleles, across 13 songbird species. We propose three theoretical relationships that could be expected between genomic and expressed MHC-I diversity on a macroevolutionary scale and test which of these are best supported. In doing so, we show that significantly fewer MHC-I alleles than the number available are expressed, suggesting that optimal MHC-I diversity could be achieved by modulating gene expression. Understanding the relationship between genomic and expressed MHC diversity is essential for interpreting variation in MHC diversity in an evolutionary context.
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Affiliation(s)
- Emily A O'Connor
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
| | - Helena Westerdahl
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Lund, Sweden
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10
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Palomar G, Dudek K, Wielstra B, Jockusch EL, Vinkler M, Arntzen JW, Ficetola GF, Matsunami M, Waldman B, Těšický M, Zieliński P, Babik W. Molecular Evolution of Antigen-Processing Genes in Salamanders: Do They Coevolve with MHC Class I Genes? Genome Biol Evol 2021; 13:6121093. [PMID: 33501944 PMCID: PMC7883663 DOI: 10.1093/gbe/evaa259] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/08/2020] [Indexed: 12/16/2022] Open
Abstract
Proteins encoded by antigen-processing genes (APGs) prepare antigens for presentation by the major histocompatibility complex class I (MHC I) molecules. Coevolution between APGs and MHC I genes has been proposed as the ancestral gnathostome condition. The hypothesis predicts a single highly expressed MHC I gene and tight linkage between APGs and MHC I. In addition, APGs should evolve under positive selection, a consequence of the adaptive evolution in MHC I. The presence of multiple highly expressed MHC I genes in some teleosts, birds, and urodeles appears incompatible with the coevolution hypothesis. Here, we use urodele amphibians to test two key expectations derived from the coevolution hypothesis: 1) the linkage between APGs and MHC I was studied in Lissotriton newts and 2) the evidence for adaptive evolution in APGs was assessed using 42 urodele species comprising 21 genera from seven families. We demonstrated that five APGs (PSMB8, PSMB9, TAP1, TAP2, and TAPBP) are tightly linked (<0.5 cM) to MHC I. Although all APGs showed some codons under episodic positive selection, we did not find a pervasive signal of positive selection expected under the coevolution hypothesis. Gene duplications, putative gene losses, and divergent allelic lineages detected in some APGs demonstrate considerable evolutionary dynamics of APGs in salamanders. Overall, our results indicate that if coevolution between APGs and MHC I occurred in urodeles, it would be more complex than envisaged in the original formulation of the hypothesis.
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Affiliation(s)
- Gemma Palomar
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
| | - Katarzyna Dudek
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
| | - Ben Wielstra
- Institute of Biology Leiden, Leiden University, The Netherlands.,Naturalis Biodiversity Center, Leiden, The Netherlands
| | - Elizabeth L Jockusch
- Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut, USA
| | - Michal Vinkler
- Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Jan W Arntzen
- Naturalis Biodiversity Center, Leiden, The Netherlands
| | - Gentile F Ficetola
- Department of Environmental Sciences and Policy, University of Milano, Italy.,Laboratoire d'Ecologie Alpine (LECA), CNRS, Université Grenoble Alpes and Université Savoie Mont Blanc, Grenoble, France
| | - Masatoshi Matsunami
- Department of Advanced Genomic and Laboratory Medicine, Graduate School of Medicine, University of the Ryukyus, Nishihara-cho, Japan
| | - Bruce Waldman
- Department of Integrative Biology, Oklahoma State University, Stillwater, Oklahoma, USA.,School of Biological Sciences, Seoul National University, South Korea
| | - Martin Těšický
- Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Piotr Zieliński
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
| | - Wiesław Babik
- Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Kraków, Poland
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11
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Stervander M, Dierickx EG, Thorley J, Brooke MDL, Westerdahl H. High MHC gene copy number maintains diversity despite homozygosity in a Critically Endangered single-island endemic bird, but no evidence of MHC-based mate choice. Mol Ecol 2020; 29:3578-3592. [PMID: 32416000 DOI: 10.1111/mec.15471] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 04/14/2020] [Accepted: 05/04/2020] [Indexed: 12/30/2022]
Abstract
Small population sizes can, over time, put species at risk due to the loss of genetic variation and the deleterious effects of inbreeding. Losing diversity in the major histocompatibility complex (MHC) could be particularly harmful, given its key role in the immune system. Here, we assess MHC class I (MHC-I) diversity and its effects on mate choice and survival in the Critically Endangered Raso lark Alauda razae, a species restricted to the 7 km2 islet of Raso, Cape Verde, since ~1460, whose population size has dropped as low as 20 pairs. Exhaustively genotyping 122 individuals, we find no effect of MHC-I genotype/diversity on mate choice or survival. However, we demonstrate that MHC-I diversity has been maintained through extreme bottlenecks by retention of a high number of gene copies (at least 14), aided by cosegregation of multiple haplotypes comprising 2-8 linked MHC-I loci. Within-locus homozygosity is high, contributing to low population-wide diversity. Conversely, each individual had comparably many alleles, 6-16 (average 11), and the large and divergent haplotypes occur at high frequency in the population, resulting in high within-individual MHC-I diversity. This functional immune gene diversity will be of critical importance for this highly threatened species' adaptive potential.
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Affiliation(s)
- Martin Stervander
- Department of Biology, Lund University, Lund, Sweden.,Department of Biology and Environmental Science, Faculty of Health and Life Sciences, Linnaeus University, Kalmar, Sweden.,Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA
| | - Elisa G Dierickx
- Department of Zoology, University of Cambridge, Cambridge, UK.,Fauna & Flora International, Cambridge, UK
| | - Jack Thorley
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - M de L Brooke
- Department of Zoology, University of Cambridge, Cambridge, UK
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