Studies of the molecular basis of gonadal tumors in the marine bivalve, Mya arenaria

Epizootiological studies of gonadal tumors of Maine soft-shell clams (Mya arenaria) have shown prevalences of over 20% in certain populations in eastern Maine. The etiology of these tumors is unknown, and both environmental as well as genetic factors may play a role. In order to investigate the effect of exposure to environmental contaminants, we initiated a short-term exposure study of M. arenaria to [3H]tetrachlorodibenzo-p-dioxin ([3H]TCDD). Gill, digestive gland, foot and gonad were sampled up to two weeks after a 24-h exposure to a low dose (10 parts per trillion or pptr) or high dose (2000pptr) of [3H]TCDD in the water. In the gill, peak concentrations occurred at the beginning of depuration, whereas peak concentrations in the digestive gland and foot were found 12–24 h after exposure. In contrast, tissue concentrations in the gonad increased through the post-exposure period; at two weeks after exposure, [3H]TCDD concentrations were highest in the gonad. Examination of gill and gonad by differential display polymerase chain reaction (ddPCR) identified potential alterations in expression of genes that may be associated with increased cell cycling (heparan sulfate proteoglycan, E3 ubiquinating enzyme) or translation initiation (p68 RNA helicase/initiation factor eIEF-4A). Histopathological analysis indicated no observable alterations in gonadal or gill tissue from exposed animals.