Natural selection on marine carnivores elaborated a diverse family of classical MHC class I genes exhibiting haplotypic gene content variation and allelic polymorphism
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Pinnipeds, marine carnivores, diverged from terrestrial carnivores ~45 million years ago, before their adaptation to marine environments. This lifestyle change exposed pinnipeds to different microbiota and pathogens, with probable impact on their MHC class I genes. Investigating this question, genomic sequences were determined for 71 MHC class I variants: 27 from harbor seal and 44 from gray seal. These variants form three MHC class I gene lineages, one comprising a pseudogene. The second, a candidate nonclassical MHC class I gene, comprises a nonpolymorphic transcribed gene related to dog DLA-79 and giant panda Aime-1906. The third is the diversity lineage, which includes 62 of the 71 seal MHC class I variants. All are transcribed, and they minimally represent six harbor and 12 gray seal MHC class I genes. Besides species-specific differences in gene number, seal MHC class I haplotypes exhibit gene content variation and allelic polymorphism. Patterns of sequence variation, and of positions for positively selected sites, indicate the diversity lineage genes are the seals’ classical MHC class I genes. Evidence that expansion of diversity lineage genes began before gray and harbor seals diverged is the presence in both species of two distinctive sublineages of diversity lineage genes. Pointing to further expansion following the divergence are the presence of species-specific genes and greater MHC class I diversity in gray seals than harbor seals. The elaboration of a complex variable family of classical MHC class I genes in pinnipeds contrasts with the single, highly polymorphic classical MHC class I gene of dog and giant panda, terrestrial carnivores.
KeywordsPinniped MHC class I Evolution Polymorphism
We thank the Sea Mammal Research Unit at the Scottish Oceans Institute for their generous help in collecting the samples. This work was supported by NIH grant AI24258 to P.P. We thank three anonymous reviewers of this paper for their constructive and insightful advice.
- Dietz R, Heide-Jørgensen MP, Harkonen T (1989) Mass deaths of harbor seals (Phoca vitulina) in Europe. Ambio 18:258–264Google Scholar
- Hall TA (1999) BioEdit: a user-friendly biological sequence alignment editor and analysis program for windows 95/98/NT. Nucleic Acids Symp Ser 41:95–98Google Scholar
- Kennedy LJ, Ollier WER, Marti E, Wagner JL, Storb R (2012) Caninine immunogenetics. In: Ostrander EA, Ruvinsky A (eds) The genetics of the dog, 2nd edn. CAB International, OxonGoogle Scholar
- Marsh SG, Albert ED, Bodmer WF, Bontrop RE, Dupont B, Erlich HA, Fernandez-Vina M, Geraghty DE, Holdsworth R, Hurley CK, Lau M, Lee KW, Mach B, Maiers M, Mayr WR, Muller CR, Parham P, Petersdorf EW, Sasazuki T, Strominger JL, Svejgaard A, Terasaki PI, Tiercy JM, Trowsdale J (2010) Nomenclature for factors of the HLA system, 2010. Tissue Antigens 75:291–455PubMedCrossRefGoogle Scholar
- Vivian JP, Duncan RC, Berry R, O’Connor GM, Reid HH, Beddoe T, Gras S, Saunders PM, Olshina MA, Widjaja JM, Harpur CM, Lin J, Maloveste SM, Price DA, Lafont BA, McVicar DW, Clements CS, Brooks AG, Rossjohn J (2011) Killer cell immunoglobulin-like receptor 3DL1-mediated recognition of human leukocyte antigen B. Nature 479:401–405PubMedCrossRefGoogle Scholar