Potential alterations in gene expression associated with carcinogen exposure in Mya arenaria

Gonadal cancers in soft-shell clams (Mya arenaria) have been found at high prevalences (20-40%) in populations in eastern Maine. The aetiology of these tumours is unknown. We hypothesized that gene expression would be altered in gonadal tumours and that examination of gene expression patterns would provide some information as to the mechanism of tumour development. To investigate this hypothesis, we initiated a broad search for differentially expressed genes using differential display polymerase chain reaction (dd-PCR) to compare RNA from tumour and normal gonadal tissue. We identified two classes of genes whose expression may be altered in the gonadal tumours: genes involved in biosynthetic processes and genes with possible roles in signal transduction. We also investigated the hypothesis that environmental contaminants, such as tetrachlorodibenzo-p-dioxin (TCDD), may play a role in the development of these tumours. To investigate this hypothesis, we performed a short-term exposure of M. arenaria to [3H]TCDD. Tissues were sampled up to 2 weeks after a 24-h exposure to 10 pptr or 2000 pptr of [3H]TCDD in the water. Using dd-PCR, we identified potential alterations in expression of genes associated with cell proliferation: heparan sulphate proteoglycan, E3 ubiquitinating enzyme and p68 RNAhelicase/initiation factor eIEF-4A. There were no observable histopathological alterations in gonadal or gill tissue from exposed animals. These results suggest possible early changes in gene expression indicative of environmental exposures.