METALLOTHIONEIN INDUCTION AS A MEASURE OF RESPONSE TO METAL EXPOSURE IN AQUATIC ANIMALS

Metallothioneins (MTs) are considered central in the intracellular reg ulation of metals such as copper, zinc, and cadmium. Increased MT synt hesis is associated with increased capacity for binding these metals a nd protection against metal toxicity. Recent advances in the biochemis try and molecular biology of MTs have facilitated research on MTs in a quatic species. For the bivalve mollusc Crassostrea virginica, a speci es frequently used in studies on the toxicology and environmental moni toring of metals, the primary structure for MT has been deduced from a nalysis of the proteins and cDNA. Procedures for analysis of MT synthe sis and MT gene expression have been applied in studies of response to metal exposure. Induction of specific MT forms by Cd is concentration - and time-dependent. The levels of MT-bound metals exhibit a strong r elationship with the cytosolic metal concentrations in a metal-exposed natural population of oysters. Ribonuclease protection assays using s equence-specific antisense RNA probes have shown that the MT mRNA stru cture in this natural population exhibits considerable individual vari ability in the 3'-untranslated region. Although yet to be substantiate d, the possibility exists that the distribution of this variability ma y be related to the level of environmental metal contamination. One pr obe derived from the coding region is suitable for use in quantitative RPAs for oyster MT mRNAs.