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Cloning of PPAR genes and cDNAs from two marine species of fish: The sea bream (sparus aurata) and the sea bass (dicentrarchus labrax)

Genes and corresponding cDNAs encoding three distinct PPAR isotypes have been identified in sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). Of the three fish isotypes the deduced protein of PPAR beta exhibits the highest homology with its mammalian counterpart in both the DNA and ligand binding domains (DBD and LBD, respectively). Fish PPAR alpha and gamma are also highly homologous to their mammalian counterparts in the DBD. However, both isotypes have an extended LBD, as compared to mammalian PPARs.

Furthermore, in the fish PPAR gamma two important amino acid substitutions have been observed in relation to their mammalian homologue, both involving residues implicate in ligand binding in the human receptor. The above indicate the ligand binding properties of the fish PPAR gamma are potentially different from those of its mammalian homologue.

The genomic organization of the fish PPARs is remarkably different from that observed in mammalian genes in that the LBD in the fish receptors alpha and beta is encoded by three exons and that of gamma by four exons, as compared to only two exons encoding the LBD of either isotype in mammals.

This result represents the first demonstration of the existence of three PPAR isotypes in fish and suggest that the structure and function of these receptors has evolved before the divergence of the osteichtyan and amphibian/mammalian lineages. Therefore, the study of these receptors in fish can result in significant knowledge concerning fatty acid and lipid metabolism in lower vertebrates.

Reported by

National Agricultural Research Foundation-Fisheries Research Institute
Nea Peramos
64007 Kavala
Greece
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