INDUCIBILITY OF METALLOTHIONEIN MESSENGER-RNA EXPRESSION AND CADMIUM TOLERANCE IN LARVAE OF A MARINE TELEOST, THE TURBOT (SCOPHTHALMUS-MAXIMUS)

An acute (48-hr) lethal toxicity study of turbot at various stages fro m hatch to juveniles showed that prior to first exogenous feeding, lar vae of turbot were an order of magnitude more sensitive to cadmium tox icity than later developmental stages (LC50 of 0.18-0.23 ppm Cd versus 2-5 ppm Cd). To investigate the possible role of metallothionein (MT) in Cd tolerance, the concentrations of MT mRNA were determined in con trol and Cd-exposed animals using a plaice MT cDNA probe. MT mRNA was expressed throughout embryonic and early larval development at levels approximately twice those in juvenile turbot liver apart from the peri od around hatching, when there was a decreased level of expression. Du ring endogenous feeding, despite larval drinking, MT mRNA levels did n ot appear to be inducible by exposure to Cd in the water within 3 days of hatching but were induced three- to fivefold after 48 hr exposure to waterborne Cd at all later stages of development. The results sugge st that Cd tolerance is associated with metal induction of MT gene tra nscription and that the enhanced sensitivity of very early stage larva e is attributable to a deficiency in MT gene transcription. (C) 1996 S ociety of Toxicology