| Epidemiological studies and evidence from wildlife and laboratory animals suggest that hormonally active agents in polluted environments are responsible for abnormalities of reproduction and development. Despite high body burdens of polychlorinated biphenyls (PCBs), a population of killifish (Fundulus heteroclitus) resident at a heavily polluted Superfund site (New Bedford Harbor MA; NBH) has survived, reproduced and developed successfully for >50 yr (∼15--20 generations). Previous studies show that NBH fish have acquired resistance to the toxic effects of PCBs and other dioxin-like chemicals (DLCs) that act via arylhydrocarbon receptor mediated pathways. To determine whether DLC, or possible estrogenic PCBs, affect estrogen signaling pathways and related reproductive and developmental parameters, we compared NBH killifish with those at a reference site (Scorton Creek MA; SC). A homology cloning approach was used to isolate complementary DNAs encoding killifish estrogen synthetases (cytochrome P450 aromatases; P450aromB and -A) and estrogen receptors (ERalpha, -betaa, and -betab). Very few site-specific polymorphisms in coding sequences were found. As determined by real time reverse transcription-polymerase chain reaction analysis, overall tissue and developmental expression patterns of each of the five genes were similar in NBH and SC fish, but site-related quantitative differences in these and other mRNAs were observed. Molecular markers of estrogen effect (P450aromB, vitellogenin) were elevated in adult NBH killifish. ERalpha mRNA, another estrogen-inducible gene, was elevated in NBH embryos, but not in NBH adults. Further, the estrogen sensitivity and responsiveness of ERalpha was reduced when compared to SC fish. Consistent with a defect in the hypothalamic-pituitary-gonadal axis, reproductively active NBH fish had reduced gonadal size, hepatic size, and plasma levels of vitellogenin and sex steroids, but other physiological and reproductive parameters (condition index, follicle size, seasonal cyclicity) did not differ in NBH and SC fish. We conclude that estrogenic contaminants are present in the NBH environment and, together with other NBH pollutants, impact estrogen signaling pathways and reproductive condition of resident killifish. Whether physiological, genetic and ecological mechanisms contribute to reproductive success of the NBH population requires further study. |
