Hemocyte proliferation influences metallothionein and phytochelatin levels in Ciona intestinalis.

We studied, through semiquantitative PCR and in-situ hybridization, the activities of the newly identified metallothionein and phytochelatin synthase genes from the solitary ascidian Ciona intestinalis (Ci-MT and Ci-PCS, respectively) in response to 10 μM CdCl2. Metallothioneins (MTs) and phytochelatins (PCs) are involved in detoxification systems of many organisms. An appreciable number of data are available for metazoan, especially for vertebrate, but very few data are available for urochordates. As the latter occupy the peculiar phylogenetic position of invertebrate chordates, the research on MTs and PCs in tunicates assumes a particular significance. Cd strongly induced Ci-MT, with a maximum at 4 days. Ci-PCS showed maximum expression at the same time. This result is probably related to a cell proliferation event, rather than an effective Ci-PCS gene activation. The hypothesis is supported by the strong induction of Proliferating Cell Nuclear Antigen (PCNA) transcript after 4 days of treatment and the colocalization in the hemocytes of the different riboprobes used. In addition, in literature is reported an expression profile similar to that of CiMT for C. intestinalis mannose binding lectins (CiMBL). Collectively, our data and data from the literature support the conclusion that hemocyte proliferation occurs in tunicate immune responses.