Molecular Cloning and Analyzing of Fatty Acid Desaturase and Elongase Genes in Japanese Eel(Anguilla japonica)

Full-length cDNAs of fatty acid desaturase(FAD) and fatty acid elongase(ELO) ,which were involved in the biosynthesis of highly unsaturated fatty acids(HUFA) ,were isolated from an anadromous teleost fish Japanese eel(Anguilla japonica) by RT-PCR and RACE methods. The results revealed that the FAD cDNA was 2 456 bp,including a 3′-UTR as long as 1 046 bp,a 5′-UTR of 75 bp and a 1 335 bp ORF specifying a protein of 444 amino acids. The protein sequence contained all the characteristics of microsomal fatty acid desaturases,including three histidine boxes,two transmembrane regions,and one cytochrome b5 domain. The deduced amino acid sequence shared 70.5%-77.5% identity with other fish of different life history and it had a closer genetic relationship with anadromous migratory fish in the phylogenetic tree. The 1 239 bp cDNA of ELO included an 885 bp ORF encoding a 294 amino acid peptide that contained one single histidine box redox centre motif,one canonical ER retention signal and several transmembrane regions,in line with other fatty acid elongases. The deduced protein sequence had 87.1%-88.8% identity with other fish and the phylogenetic tree showed that it had a closer genetic relationship with North African catfish(Clarias gariepinus) and zebrafish. These results will help study the relationship between their structure and function,and elucidate the HUFA biosynthesis pathway in Japanese eel.