Characterization of β2m gene and its association with antibacterial trait in Megalobrama amblycephala

Beta 2-microglobulin (beta(2)m), an essential subunit of major histocompatibility complex protein (MHC) class I molecule, plays an important role in the immune system of vertebrates, but its research in fish is very limited. In order to understand the expression pattern of beta(2)m gene and its association with antibacterial trait in Megalobrama amblycephala, in the present study, the sequence of beta(2)m gene was obtained from the genome database, and its expression pattern was studied by quantitative real-time PCR, its SNPs were screened by Sanger sequencing and genotyped by High Resolution Melting method. The results showed that the beta(2)m gene was located in the genomic Linkage Group 14 of the M. amblycephala, and its ORF was 351 bp, encoding 116 amino acids. The beta(2)m gene is widely expression in various tissues of healthy M. amblycephala. After Aeromonas hydrophila infection, the expression of beta(2)m significantly increased at 24 hpi (hours post injection) in the liver and reached a peak at 72 hpi. Moreover, the beta(2)m expression in the spleen increased significantly and peaked at 4 hpi, followed by a slow decline, but still higher than the control. Four SNPs were screened from the beta(2)m gene, which are locating in exons SNP-beta(2)m + 1042 A/T and SNP-beta(2)m + 1438C/T, and introns SNP-beta(2)m + 198 A/G and SNP-beta(2)m + 408 A/C, respectively. The genotype and the alleles frequency of SNP-beta(2)m + 408 A/C were significantly different between the resistant and susceptible groups. The genotype frequency of SNP-beta(2)m + 1042 A/T was not significant different, but the alleles were significantly different between the resistant and susceptible groups. The results of this study provide certain theoretical support for the further functional study of the beta(2)m gene and for the selection breeding of new disease-resistant strains of M. amblycephala.

Automated summary

The study investigated the expression pattern of the beta(2)m gene in Megalobrama amblycephala and found significant increases in expression levels after infection with Aeromonas hydrophila. Four SNPs were identified in the beta(2)m gene, with one showing significant differences in genotype and allele frequencies between resistant and susceptible groups. These results provide theoretical support for further functional studies of the beta(2)m gene and breeding of disease-resistant strains of M. amblycephala.