Cloning of a metallothionein gene and characterization of two other cDNA sequences in the Pacific oyster Crassostrea gigas (CgMT1)

Metallothionein (MT) genes encode essential metal-binding proteins involved in metallic homeostasis and detoxification in living organisms. Here, we d escribe the structure of the first Pacific oyster Crassostrea gigas metallo thionein (CgMT1) gene and the sequences of two other MT cDNA. The CgMT1 gen e sequence contains three coding exons plus a 5' entirely non-coding exon, and the predicted protein contains 21 cysteine residues organized in Cys-X- Cys motifs as classically described for MTs, The three cDNA sequences prese nt few substitutions in either coding sequence or UTRs. Induction of these MT-mRNA in heavy metal-treated oysters (i.e. cadmium) was confirmed by Nort hern blot analysis and RT-PCR and suggests a potential specific tissue expr ession rate. Southern blot analysis suggested the presence of multiple CgMT genes, and allowed the detection of restriction fragment length polymorphi sms (RFLPs). Although the CgMT1 coding sequence showed 30-73% nucleotide id entities with known sequences in other mollusks, it included the specific m otif Cys-X-Cys-X(3)-Cys-Thr-Gly-X-X-X-Cys-X-Cys-X(5)-Cys-X-Cys-Lys found in Mollusk family 2. Marine bivalves are commonly used as pollution bioindica tors, thus the development of genetic markers based on CgMT1 polymorphism w ill allow a monitoring of heavy metal exposure in anthropogenically disturb ed ecosystems. (C) 2001 Elsevier Science B.V. All rights reserved.