Identification, sequencing and expression of selenium-dependent glutathione peroxidase transcript in the freshwater bivalve Unio tumidus exposed to Aroclor 1254

Glutathione peroxidases (GPx) and glutathione S-transferases (GST) are essential enzymes of the cellular defense system. The aim of this work was the identification of GPx transcript in a freshwater bivalve, Unio tumidus, and the effects of Aroclor 1254 on GPx and pi-class GST (pi-GST) expression pattern. The GPx full-length coding sequence was obtained by reverse transcription PCR using degenerated primers followed by 5′ and 3′ rapid amplification of cDNA ends. The GPx cDNA encodes a protein of 232 amino acids. The 72nd amino acid corresponds to a selenocysteine encoded by a TGA codon. Residues essential to the enzymatic function are conserved in GPx of U. tumidus. Specific amplifications of the Se-GPx mRNA from U. tumidus were performed on the digestive gland, the excretory system and the gills. Se-GPx expression level is highest in the digestive gland. No induction of the Se-GPx was observed at the transcriptional level in the digestive gland and the excretory system of Aroclor-treated mussels, while an increase of the pi-GST mRNA level was observed in the excretory system.