PM02 Metals in the Environment: Aquatic Biological Perspectives
Exhibit Hall
8:00 AM - Monday, 10 November 2003
(PM036) Characterization and tissue-specific expression of three metallothionein isoforms in sea turtles.
Tanabe, S.1, Kim, E. Y.2, Kunito, T.1, 1 Center for Marine Environmental Studies, Ehime University, Matsuyama, Japan2 Ehime Prefectural Institute of Public Health and Environmental Science, Matsuyama, Japan
ABSTRACT- Sea turtles, particularly green turtles, accumulate copper and cadmium to high levels in the liver and kidney. Our previous studies revealed that these two metals mainly associate themselves with metallothioneins (MTs), suggesting that the interaction between metals and MT is crucial in the detoxification process of metals in tissues of sea turtles. It has been reported that several MT isoforms found in various animal species take part in the metal detoxification process with isoform-, and tissue-specific expression. However, in spite of the importance of this process, no data is available on the occurrence and expression of sea turtle MT isoforms. In this study, we initially cloned and sequenced cDNAs encoding MT isoforms from green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata) using RT-PCR and RACE methods, and then examined the isoform- and tissue specific expression of each MT isoform in the liver and kidney by real-time RT-PCR. The cDNA sequences of three MT isoforms (MT-A, MT-B and MT-C) were obtained from green and hawksbill turtles. Each cDNA had an open reading frame encoding 63 amino acid residues. Phylogenetic analysis revealed that the amino acid sequences of sea turtle MTs were closely related to those of avian MTs. For all the three MT isoforms, the mRNA expression pattern was similar between green and hawksbill turtles. MT-A mRNA level was higher in the liver than in the kidney, while kidney showed higher MT-C mRNA level than liver in the both sea turtles. In contrast, no significant difference was observed in MT-B mRNA level between liver and kidney. These results suggest that MT-A, -B and -C may have different biological/ ecotoxicological roles in the liver and kidney of sea turtles. To our knowledge, this is the first report of the MT cDNAs from reptiles.
Key words: copper, metallothionein isoform, cadmium, sea turtles