Full-length cDNA cloning and tissue expression of major histocompatibility complex(MHC)-Ⅰα from cobia (Rachycentron canadum)

We cloned the MHC-Ⅰα gene from cobia (Rachycentron canadium) by homology cloning and RACE PCR. The full-length cDNA of MHC-Ⅰα comprises 1 330 bp with a 76 bp 5′ untranslated region (UTR), a 189 bp 3′ UTR and a 1 065 bp open reading frame (ORF), encoding a polypeptide of 354 amino acid residues with a predicted molecular weight of 40.10 kDa and a theoretical isoelectric point of 5.70. According to the phylogenetic tree and amino acid similarity comparison, the homology of MHC-Ⅰα amino acids between cobia and some known fishes and human (Homo sapiens) varies from 27.9% to 67.1%. The putative protein sequence shows some important features including leader peptide, α1, α2, α3, CP/TM/CYT regions and conserved cysteines, etc.. Real-time PCR result indicates that MHC-Ⅰα expresses in all detected tissues at different expression levels. High expression is detected in head kidney; moderate expression is detected in gill, spleen and intestine; while low expression is detected in heart, brain and muscle.