The yellow catfish, Pelteobagrus fulvidraco (Siluriformes) metallothionein cDNA: molecular cloning and transcript expression level in response to exposure to the heavy metals Cd, Cu, and Zn

Abstract

Metallothionein (MT) has been used extensively as a potential molecular biomarker to detect heavy metal pollution in aquatic organisms. In order to investigate the modulation effect of heavy metals and to establish suitable biomarkers for the monitoring of heavy metal pollution, Pelteobagrus fulvidraco metallothionein gene was characterized as the first report in the family Bagridae. Pf-MT transcript was detected at high levels in liver, gonad, kidney, and brain compared to other tissues. A time-course study in response to waterborne Cd (5 ppm) revealed that a significant increase in the Pf-MT transcript abundance was observed at 6 h in gill, kidney, and liver. These elevated levels were kept for 96 h, implying that Cd distributed fast into different organs and was involved in the tissue-specific induction pattern. We observed a significant Pf-MT transcript increase in liver tissues at 48 h, followed by gill at 12 h and intestine at 48 h after Cd exposure. This indicates hepatic MT expression as a potential biomarker of acute Cd exposure in this species. Cd-binding ability of recombinant Pf-MT protein provided evidence for sensitivity to Cd and other heavy metal exposure. In the case of Zn exposure (1 ppm), a significant increase in Pf-MT transcript abundance was observed at 12 h, and a peak induction level reaching sixfold at 24 h was kept until 48 h, showing similar transcript induction patterns with Cd. A high level of Pf-MT mRNA after exposure to Cu (1 ppm) was observed at 12 h that gradually increased until 96 h with a 12-fold induction, revealing a long-lasting induction and somewhat dissimilar pattern compared to other metals in liver. Our results demonstrate that Pf-MT can be induced by heavy metals in a tissue-specific and metal-specific manner and plays probably a conserved role in metal detoxification. This study provides new information on P. fulvidraco metallothionein gene for the use of biomarkers indicating metal pollution in fish.

Characteristics, functions, and applications of metallothionein in aquatic vertebrates

“…Metal accumulation relies on tissue metabolism and differences in their chemical environment, including presence of various ligands, each with different metal-binding characteristics (Campenhout et al, 2004). Different extent of tolerance of each fish species to different heavy metals may also induce different expression level of MTs (Boeck et al, 2003;Kim et al, 2012). Notably, differential regulation of metallothionein by various metals has been revealed in many other fish species (Cho et al, 2005).…”

Cloning metallothionein gene in Zacco platypus and its potential as an exposure biomarker against cadmium

“…Using the blast algorithm of the National Center for Biotechnology Information (NCBI), we found that MT amino acids displayed high This high degree of similarity suggests that this highly conserved amino acid sequence may play the same role in Z. platypus as in other fish species. The high proportion of cysteine residues organized in Cys-Cys and Cys-X-Cys motifs is a typically specific characteristic of MT (Cho et al 2008;Kim et al 2012). In this study, MT amino acid sequence in Z. platypus also retained the specific common feature of MT.…”

“…In this study, MT amino acid sequence in Z. platypus also retained the specific common feature of MT. MT of Z. platypus consists of 20 cysteine residues among encoding 60 amino acids (approximately 33.3 %), similar to MT of yellow catfish, Pelteobagrus fulvidraco (Kim et al 2012). Cysteine motifs provide the binding capacity to heavy metals through the thiol group of its cysteine and make MT delay the acute toxicity of heavy metals (Ghedira et al 2010).…”

“…In previous studies, the 48-h exposure to Cd concentrations of 50 and 367 μg/L induced mRNA expression of MT in Persian sturgeon (Acipenser persicus) and Korean spotted barbell (Hemibarbus mylodon), respectively (Cho et al 2008;Shariati et al 2011). For yellow catfish (P. fulvidraco), significant enhancement of hepatic MT transcription was reported at 6 h of exposure to 5 mg/L Cd (Kim et al 2012). On the other hand, significant increase of MT mRNA expression in rainbow trout was observed at 10 μg/L Cd following 14-day exposure (Lange et al 2002).…”

“…Metallothionein (MT) is a cysteine-rich and lowmolecular-weight (6-7 kDa) cytoplasmic protein (Cho et al 2008) and is recognized as a sensitive and useful biomarker for exposure to heavy metals in various species (Amiard et al 2006;Cho et al 2008;Kim et al 2012). Because of its unique cysteine-rich structural characteristics, this biomolecule has high affinity to metal ions (Coyle et al 2002).…”