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Le résumé fourni par la source

Abstract Major histocompatibility complex (MHC) genes are among the most polymorphic and fastest evolving genes in vertebrate genomes with more than 1,000 alleles found at some human MHC loci. In this study, MHCII genes are explored in Atlantic herring, a species that comprises one of the biggest populations among vertebrates and occurs in huge shoals providing a potential target for pathogens using whole genome, long read sequencing of 14 individuals from three different geographic regions. The analysis identified a total of nine MHC class II loci present on three chromosomes. Some of the genes show extremely high nucleotide diversity (π = 10-13%) compared with the genome average (0.3%) as well as strong signatures of positive selection (dN/dS >> 1). Furthermore, we showed a highly significant nonrandom association of alpha and beta genes, strongly suggesting coevolution of alpha and beta alleles forming the peptide binding domain of MHC class II molecules. To the best of our knowledge this is the first genetic study of MHC polymorphism in a non-model organism based on whole genome, long-read sequencing. It demonstrates that the Atlantic herring MHC class II genes are among the most polymorphic so far described. The very high degree of polymorphisms is most likely explained by the combination of the large population size minimizing loss of genetic diversity due to drift and pathogen-driven selection.

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