| 1. |
- Langefors, Åsa, et al.
(författare)
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Allelic polymorphism in MHC class IIB in four populations of Atlantic salmon (Salmo salar)
- 2001
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Ingår i: Immunogenetics. - : Springer Science and Business Media LLC. - 1432-1211 .- 0093-7711. ; 53:4, s. 329-336
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Tidskriftsartikel (refereegranskat)abstract
- We sequenced exon 2 of the MHC class II B gene in Atlantic salmon from the Baltic Sea and identified 17 different exon 2 alleles among 22 different restriction fragment length polymorphism haplotypes. The sequences differed at between I and 34 bases. Two different tests were used to estimate the importance of recombination in the generation of new alleles. Recombination events appear to have occurred between three and nine times. Only two pairs of sequences differed by less than five nucleotides', minimizing the importance of point mutations for generating new alleles. Phylogenetic analysis showed that sequences did not cluster according to populations, and genetic distances between populations were small compared to those obtained by allele frequency data. These results, together with the similarity found between exon 2 sequences from Baltic salmon and Norwegian salmon, indicate that all of the identified alleles were present in the ancient salmon population colonizing the Baltic rivers after the last glaciation.
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| 2. |
- Langefors, Åsa, et al.
(författare)
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Association between major histocompatibility complex class IIB alleles and resistance to Aeromonas salmonicida in Atlantic salmon
- 2001
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954 .- 0962-8452. ; 268:1466, s. 479-485
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Tidskriftsartikel (refereegranskat)abstract
- We have tested the importance of genetic variation in the major histocompatibility complex (MHC) class IIB in Atlantic salmon (Salmo salar) for survival after challenge with a highly virulent bacterial pathogen. Forty juvenile full siblings from each of 120 families were infected with the bacterium Aeromonas salmonicida, which causes high mortality in salmon due to furunculosis. Fishes from high-resistance (HR, < 35% mortality) and low-resistance (LR, > 80% mortality) families were screened for their MHC class IIB genotypes using the denaturing gradient gel electrophoresis (DGGE) technique. The exon 2 sequences, encoding the major part of the peptide-binding region, were established far each DGGE fragment. One allele, e, containing a missense single base substitution was significantly more prevalent in HR families than in LR families. An odds-ratio test showed that broods carrying this allele had a 12-fold higher chance of being HR than broods without the e allele. A second allele, i, showed significantly higher frequencies in uninfected and surviving individuals than in infected dead individuals. A third allele, j, tended to be more prevalent both in LR families and in individuals that had died of the infection. There was no correlation between MHC heterozygosity and resistance to A. salmonicida. Our results support the hypothesis that MHC polymorphism is maintained through pathogen-driven selection acting by means of frequency-dependent selection rather than heterozygous advantage.
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| 3. |
- Langefors, Åsa, et al.
(författare)
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Screening of Mhc variation in Atlantic salmon (Salmo salar) : a comparison of restriction fragment length polymorphism (RFLP), denaturing gradient gel electrophoresis (DGGE) and sequencing
- 2000
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 9:2, s. 215-219
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Tidskriftsartikel (refereegranskat)abstract
- We compared three different molecular methods currently used for screening of Mhc variation in population studies of Atlantic salmon. Restriction fragment length polymorphism (RFLP) of the entire class II gene detected 22 haplotypes. Seventeen exon 2 sequences were obtained from individuals carrying the 22 haplotypes, two of which had not been detected by RFLP. The six alleles (27%) detected by RFLP and not by exon 2 sequencing probably resulted from sequence variation outside exon 2. Within exon 2, RFLP differentiated 88% of the sequences. Alternatively, denaturing gradient gel electrophoresis (DGGE) performed under two run conditions detected 94% of the sequence variation. Both RFLP using different probes, and the two PCR-based methods using three different primer pairs, suggest that there is only a single Mhc class II B gene in the Baltic populations of Atlantic salmon.
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| 4. |
- Lohm, Jakob, et al.
(författare)
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Experimental evidence for major histocompatibility complex-allele-specific resistance to a bacterial infection
- 2002
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 269:1504, s. 2029-2033
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Tidskriftsartikel (refereegranskat)abstract
- The extreme polymorphism found at some major histocompatibility complex (MHC) loci is believed to be maintained by balancing selection caused by infectious pathogens. Experimental support for this is inconclusive. We have studied the interaction between certain MHC alleles and the bacterium Aeromonas salmonicida, which causes the severe disease furunculosis, in Atlantic salmon (Salmo salar L.). We designed full-sibling broods consisting of combinations of homozygote and heterozygote genotypes with respect to resistance or susceptibility alleles. The juveniles were experimentally infected with A. salmonicida and their individual survival was monitored. By comparing full siblings carrying different MHC genotypes the effects on survival due to other segregating genes were minimized. We show that a pathogen has the potential to cause very intense selection pressure on particular MHC alleles; the relative fitness difference between individuals carrying different MHC alleles was as high as 0.5. A co-dominant pattern of disease resistance/susceptibility was found, indicative of qualitative difference in the immune response between individuals carrying the high- and low-resistance alleles. Rather unexpectedly, survival was not higher among heterozygous individuals as compared with homozygous ones.
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| 5. |
- Lohm, Jakob
(författare)
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MHC and genomic diversity in Atlantic salmon (Salmo salar L.)
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I present studies concerning genomic diversity and genetic heterogeneity as well as the evolution and maintenance of genetic variation at a specific immune defence gene in Atlantic salmon (Salmo salar, L.). I here present data on nucleotide diversity showing that human activities as well as different post-glacial colonisation events have had considerable effects on the genomic diversity in different salmonid populations. Also, significant within-river heterogeneity in an unmanaged naturally reproducing population of Atlantic salmon is described. In this natural river, the subpopulation genetic structure was significantly correlated to the geographical distance between subpopulations suggesting that gene flow between subpopulations within this natural Atlantic salmon population corresponds to an isolation-by-distance process. However, major histocompatibility complex (MHC) alleles, encoding molecules crucial for the presentation of foreign antigens to T-cells in the adaptive immune system, are homogeneously distributed along the same river. This indicates that selection maintains genetic homogeneity at this specific MHC locus over large areas, probably due to a uniformly distributed pathogen fauna within the river, which is not the situation at neutral loci where genetic drift is counterbalanced by migration. Moreover, the within-river spatial genetic heterogeneity was almost as large as between-river differentiation showing that significant local adaptation probably exists even between regions within rivers. In this thesis I also show that genetic variation at specific genes may have pronounced fitness effects. Different alleles within the MHC rendered significant differences in disease resistance during controlled experimental infections of Atlantic salmon. Nucleotide differences as small as one single base substitution between different MHC alleles had considerable effects on susceptibility. Since MHC heterozygosity did not affect disease resistance these findings suggest that frequency-dependent selection, rather than overdominant selection, is acting at on the MHC. These results are in opposition to the widely assumed hypothesis that overdominant selection is the main contributor to maintenance of MHC diversity.
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| 6. |
- Olsen, K Håkan, et al.
(författare)
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Influence of mhc on sibling discrimination in Arctic char, Salvelinus alpinus (L.)
- 2002
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Ingår i: Journal of Chemical Ecology. - 1573-1561 .- 0098-0331. ; 28:4, s. 783-795
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Tidskriftsartikel (refereegranskat)abstract
- The preference of juvenile Arctic char [Salvelinus alpinus (L.)] for odors from siblings and nonsiblings with different major histocompability complex class II (MHC) genotypes was studied in two-choice fluviarium tests. In the first part of the study, test fish demonstrated no preference for water scented by a sibling with a MHC genotype different from its own versus water scented by a MHC identical nonsibling. When both donors were siblings with different MHC genotypes, however, the test fish chose the water scented by the fish with the same MHC type as the test fish. The results suggest that odors with information about kinship are dependent on MHC but also on other, unknown factors. In the second part of the study, we observed that fish isolated since fertilization did not show any behavioral discrimination towards siblings, based on MHC genotype. One reasonable explanation for this result is that Arctic char learn to discriminate between odors from individuals of different MHC types.
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| 7. |
- Olsén, K. Håkan, 1952-, et al.
(författare)
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MHC and kin discrimination in juvenile Arctic charr, Salvelinus alpinus (L.)
- 1998
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 56:2, s. 319-327
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Tidskriftsartikel (refereegranskat)abstract
- Kin recognition and discrimination ale thought to occur in several species of various taxonomic groups. In salmonid fish, juveniles can discriminate between odours of siblings and nonsiblings from the same population even if the odour donors and the test fish have been reared separately since fertilization. This indicates that some genetic factor is important in the recognition process. The mechanisms behind kin recognition and discrimination have not yet been described. In the present study, we performed fluviarium tests to examine whether kin recognition and discrimination in juvenile Arctic charr are influenced by the major histocompatibility complex (MHC). Prior to the fluviarium tests, exon 2 of an MHC class II B gene in charr was analysed with denaturing gradient gel electrophoresis (DGGE) and individual genotypes were determined. In the fluviarium, when fish had the choice between water scented by an MHC identical sibling: and a sibling with a different MHC genotype they preferred water from identical siblings. Moreover, water scented by an MHC different sibling was preferred to water from an MHC different nonsibling. However, we observed no discrimination when the test fish shared one allele with the nonsibling donor but no alleles with the sibling donor. Our results indicate that the MHC has a significant influence on the odours used for kin recognition and discrimination in juvenile Arctic charr. (C) 1998 The Association for the Study of Animal Behaviour.
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| 8. |
- Olsen, K Håkan, et al.
(författare)
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The influence of dominance and diet on individual odours in MHC identical juvenile Arctic charr siblings
- 2003
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 63:4, s. 855-862
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Tidskriftsartikel (refereegranskat)abstract
- No difference in attraction was observed in sibling Artic charr Salvelinus alpinus between water scented by dominant or subordinate major histocompability complex (MHC) identical fish observed in a two-choice fluviarium. In a second experiment, MHC identical sibling donors were given different types of food pellets before the preference test. The test fish showed a significant attraction to the sibling given the same kind of food as the test fish itself during the first 6 h of the fluviarium tests. The results suggest that diet has an influence on the odours released and can, in addition to MHC related odours, be used for information relating to group member identity. (C) 2003 The Fisheries Society of the British Isles.
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