A phytochelatin synthase gene in the solitary tunicate Ciona intestinalis

The major thiol-containing molecules involved in controlling the level of intracellular ROS in eukaryotes, acting as a nonenzymatic detoxification system, are metallothioneins (MTs), glutathione (GSH) and phytochelatins (PCs). Both MTs and GSH are well-known in the animal kingdom. PC was considered a prerogative of the plant kingdom but, in 2001, a phytochelatin synthase (PCS) gene was described in the nematode Caenorhabditis elegans; additional genes encoding this enzyme were later described in the earthworm Eisenia fetida and in the parasitic nematode Schistosoma mansoni but scanty data are available, up to now, for deuterostomes. Here, we describe the molecular characterisation and transcription pattern, in the presence of Cd, of a PCS gene from the invertebrate chordate Ciona intestinalis, a ubiquitous solitary tunicate and demonstrate the presence of PCs in tissue extracts. We also studied mRNA localization by in situ hybridization. In addition, we analysed the behaviour of hemocytes and tunic cells consequent to Cd exposure as well as the transcription pattern of the Ciona orthologous for PCNA, usually considered a proliferation marker, and observed that cell proliferation occurs after 96 h of Cd treatment. This matches the hypothesis of Cd-induced cell proliferation, as already suggested by our previous data on the expression of a metallothionein gene in the same animal.