No substantial changes in estrogen receptor and estrogen-related receptor orthologue gene transcription in Marisa cornuarietis exposed to estrogenic chemicals

Estrogen receptor orthologues in molluscs may be targets for endocrine disruptors, although mechanistic evidence is lacking. Molluscs are reported to be highly susceptible to effects caused by very low concentrations of environmental estrogens which, if substantiated, would have a major impact on the risk assessment of many chemicals. The present paper describes the most thorough evaluation to-date of the susceptibility of Marisa cornuarietis ER and ERR gene transcription to modulation by vertebrate estrogens in vivo and in vitro. We investigated the effects of estradiol-17β and 4-tert-Octylphenol exposure on in vivo estrogen receptor (ER) and estrogen-related receptor (ERR) gene transcription in the reproductive and neural tissues of the gastropod snail M. cornuarietis over a 12-week period. There was no significant effect (p>0.05) of treatment on gene transcription levels between exposed and non-exposed snails. Absence of a direct interaction of estradiol-17β and 4-tert-Octylphenol with mollusc ER and ERR protein was also supported by in vitro studies in transfected HEK-293 cells. Additional in vitro studies with a selection of other potential ligands (including methyl-testosterone, 17α-ethinylestradiol, 4-hydroxytamoxifen, diethylstilbestrol, cyproterone acetate and ICI182780) showed no interaction when tested using this assay. In repeated in vitro tests, however, genistein (with mcER-like) and bisphenol-A (with mcERR) increased reporter gene expression at high concentrations only (>10(-6)M for Gen and >10(-5)M for BPA, respectively). Like vertebrate estrogen receptors, the mollusc ER protein bound to the consensus vertebrate estrogen-response element (ERE). Together, these data provide no substantial evidence that mcER-like and mcERR activation and transcript levels in tissues are modulated by the vertebrate estrogen estradiol-17β or 4-tert-Octylphenol in vivo, or that other ligands of vertebrate ERs and ERRs (with the possible exception of genistein and bisphenol A, respectively) would do otherwise.

Assessment of putative endocrine disrupters in an in vivo crustacean assay and an in vitro insect assay

Concern over endocrine disrupters in coastal ecosystems has stimulated global efforts to understand their potential impacts on fish and invertebrate communities. Given that marine crustaceans are sensitive to the effects of alkylphenols and other xenobiotics, we are currently investigating whether these responses may be caused via an endocrine mechanism. Tisbe battagliai (Copepoda: Harpacticoida) is representative of an ecologically important group of meiofauna, is sensitive to toxicants and is used as an international test species in marine ecotoxicology. A 21-day life-cycle test that incorporates assessment of survival, development, reproduction and sex ratios, has shown that populations of T. battagliai are not significantly affected by environmentally relevant levels of steroidal oestrogen agonists, or by related synthetic receptor agonists. The absence of in vivo effects due to these steroid agonists and antagonists prompted in vitro studies of ecdysteroid receptor activity of a range of reference compounds and environmental contaminants with an ecdysteroid receptor (EcR/USP)-based screening assay derived from the BII haemocyte line of Drosophila melanogaster. The implications for environmental monitoring of endocrine disrupters are discussed.