| Infectious hematopoietic necrosis (IHN) is one of the most serious viral diseaseto rainbow trout (Oncorhynchus mykiss) and other salmonids. The majorhistocompatibility complex (MHC) gene is highly correlated with immune response invertebrate and the polymorphisms of MHC have been closely linked with the diseaseresistance/susceptibility. In this study, polymerase chain reaction-single strandconformation polymorphism (PCR-SSCP) followed by cloning and sequencing wereused to examine polymorphisms of MHC class II β chain genes (DAB) exon2(224-bp)and analysed their association with the anti-IHN in104resistant and91susceptiblerainbow trout. The main results were as follows:(1) A total of45different alleles were identified, thirty of which were novelalleles. Individuals possessed between one and four alleles, indicating that the genomeharbors at least two closely related DAB exon2loci.(2) Homology comparison of the45Onmy-DAB alleles revealed that thevariation percentages of nucleotide substitutions and amino acid mutations were29.46%(66/224) and51.35%(38/74), respectively. The percentage of amino acidmutations in the peptide binding region (PBR) and non-PBR were66.67%(14/21)and45.28%(24/53), respectively. The rate of dNoccurred at a significantly higherfrequency (P <0.001) than that of dSin PBR and non-PBR, suggesting that balancingselection for maintaining polymorphisms at the DAB exon2locus. The dNin the PBR(0.097) was significantly higher than that in the non-PBR (0.049, P <0.001),indicating some sort of directional selection is at work on PBR.(3) Correlation analysis of polymorphism and disease-resistant revealed that theOnmy-DAB*0103, Onmy-DAB*0601and Onmy-DAB*1402are highly associated withresistance to IHN in rainbow trout (P <0.001), while the Onmy-DAB*0201(P <0.001), Onmy-DAB*0904(P <0.001) and Onmy-DAB*1102(P <0.01) are highlyassociated with susceptibility to IHN. |
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