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METALLOTHIONEIN GENE TRANSCRIPTION AS AN INDICATOR OF METAL EXPOSURE IN FATHEAD MINNOWS
Citation:
Reddy, T V., D L. Lattier, J M. Lazorchak, G P. Toth, AND M E. Smith. METALLOTHIONEIN GENE TRANSCRIPTION AS AN INDICATOR OF METAL EXPOSURE IN FATHEAD MINNOWS. Presented at Society of Environmental Toxicology and Chemistry, Philadelphia, PA, November 12-14, 1999.
Description:
Metallothionein is a cysteine rich, low molecular weight, metal binding protein. Basal levels of endogenous metallothioneins (MT) have been reported in all eucaryotes. MT has been shown to play an essential role in regulating physiological requirements of essential metals such as zinc and copper, and elimination of non-essential metals such as cadmium and lead from the system. Our objectives are to investigate metallothionein gene (Mt) expression in aquatic organisms, and use the onset of Mt gene transcription as an indicator of metal exposure. To achieve our objectives, we designed Mt-specific synthetic oligonucleotides based on the published gene sequence for common carp (Cyprinus carpio). Induction of Mt gene expression was measured in newly hatched fathead minnow larvae (Pimephales promelas) exposed to varied concentrations of zinc sulfate. Fathead minnow larvae were exposed for 48 hours to zinc concentations between 25 and 250 ug/L. Following exposure, total RNA was isolated from larvae and Mt gene transcription was analyzed by RT-PCR. Results suggest that fathead minnows express constitutive levels of Mt messenger RNA; however, the gene was inducible with zinc in a dose dependent manner. The lowest concentration at which Mt was induced (25-50 ug/L zinc) was less than that which produced effects measured in standard USEPA 7-day fathead minnow short-term chronic survival (LC50 > 240 ug/L), and growth (IC25 > 90 ug/L) tests. Mt gene transcription was induced at concentrations far below those that result in the onset of sublethal toxicity. The observed sensitivity of Mt gene expression renders this approach a sound aquatic, field-based indicator of heavy metal exposures.