Molecular characterization and mRNA expression during metal exposure and thermal stress of copper/zinc- and manganese-superoxide dismutases in disk abalone, Haliotis discus discus

Complementary DNAs encoding copper/zinc superoxide dismutase (Cu/Zn-SOD; SOD1) and manganese superoxide dismutase (Mn-SOD; SOD2) were isolated from disk abalone, Haliotis discus discus. The open reading frame sequences of Cu/Zn- and Mn-SODs encoded 154 and 226 amino acids, respectively. Multiple sequence alignments using the deduced amino acid sequences revealed that both abalone SODs showed considerable sequence similarities with their orthologues from diverse aerobic organisms, in which the amino acid residues forming metal ligands were highly conserved. All phylogenetic trees for both SOD genes inferred from maximum likelihood and Bayesian inference analyses presented the monophyletic status of Teleostei and Aves/Tetrapoda clades, and recovered relatively close genetic affiliation of H. discus discus with some molluscan species. Expression of both SODs at mRNA levels were highly modulated in various tissues (gill, muscle and hepatopancreas from juveniles, and haemocytes from adults) by experimental exposures to heavy metals (copper, zinc and cadmium) and also by thermal treatments (elevation of temperature). The mRNA levels of both SODs were increased in general during the metal or thermal treatments; however, the transcriptional responses of SOD genes were quite variable depending upon isoforms and tissues based on semi-quantitative and/or real-time RT-PCR assays. (C) 2007 Elsevier Ltd. All rights reserved.