Characterization of Tilapia (Oreochromis niloticus) aldehyde reductase (AKR1A1) gene, promoter and expression pattern in benzo-a-pyrene exposed fish

Abstract

This study planned to isolation and characterization of AKR1A1 cDNA from Bap injected nile tilapia (Oreochromis niloticus), comparison of its characteristic structures with those of other species, characterization of AKR1A1 gene and promoter, and investigation of AKR1A1 mRNA expression in various organs of Bap injected tilapia. The cDNA was 1172 bp long which includes an open reading frame of 975 bp encoding a 324 amino acids protein and a stop codon. The sequence showed 3' and 5' non-coding regions of 179 and 18 bp. The amino acid sequence of O. niloticus AKR1A1 shows similarities of 60, 60, 60.6, 61.2 62.2, and 57.8% with mouse AKR1A1, Norway rat AKR1A1, zebrafish AKR1A1, African clawed frog AKR1A1, human, and yellow perch AKR1A1, respectively. Nucleotide sequence investigation of AKR1A1 gene and 5′-flanking region showed that the structural gene and the 5′-flanking region were approximately 2975 bp and 4006 bp in length, respectively. The protein-coding region contained eight exons, and one additional upstream exon. Real-time polymerase chain reaction (PCR) results showed that the highest level of AKR1A1 expression was found in bile (108.7), followed by kidney (77.9), muscles (37.3), and liver (24.7). mRNA levels of AKR1A1 were almost negligible in gills (0.6) while no detectable (ND) constitutive expression was detected in gut. In conclusion, our results concluded that tilapia AKR1A1 is inducible by BaP and have a significant function in the metabolism of xenobiotics and, therefore, may used as biomarker in fish