Identification of new members of metallothionein gene family in sea urchin

Heavy metals are common marine pollutants that emanate from such sources as industrial and sewage treatment discharges and anti-fouling paints. Cadmium (Cd2+) serves no essential function in biological organisms and it is a highly toxic and carcinogenic metal. In Paracentrotus lividus sea urchin embryos cadmium causes development arrest or severe malformations. At lower doses, cadmium activates different responses (HSPs synthesis, autophagic or apoptotic processes) that can allow embryo survival. This study was conducted to elucidate the gene transcription activation/upregulation or repression/downregulation inducted in sea urchin embryos grown under cadmium stress. Comparison between transcriptomes of 30 hours embryos treated or untreated with 100 mM cadmium chloride (CdCl2) was conducted by RDA technique. Results showed increased transcription levels, in treated embryos, of metallothionein genes, and genes coding for detoxification enzymes. Bioinformatic analysis of metallothionein sequences showed at least five different transcripts (MT-4 toMT -8) and only one of them was already new (MT-8 probably corresponds to Pl-MT). Quantitative real-time RT-PCR experiments confirmed RDA results and showed the specific activation of MT-4, MT-5 and MT-6 genes and the upregulation (or mRNA stabilization) of MT-7 and MT-8 genes. To investigate the threshold for gene activation, we are going to check the variations of transcript levels in embryos exposed to different doses of CdCl2.