Estrogen responses in killifish (Fundulus heteroclitus) from polluted and unpolluted environments are site- and gene-specific

Abstract

Epidemiological, ecological, and laboratory-based studies support the hypothesis that endocrine disrupting chemicals (EDCs) in the environment are responsible for developmental and reproductive abnormalities. We have previously described a killifish population resident in a highly polluted Superfund site (New Bedford Harbor, NBH) that shows evidence of exposure to an estrogenic environment and endocrine disruption. Here, we compare NBH with a local reference population (Scorton Creek, SC) for developmental patterns and direct effects of exogenous estradiol on the estrogenic markers, brain cytochrome P450 aromatase (CYP19A2 or AroB), hepatic vitellogenin (Vtg), and hepatic estrogen receptor alpha (ERα). In contrast to our previous observation of elevated ERα in NBH embryos, developmental levels of AroB and Vtg mRNAs did not differ between the two sites, demonstrating that not all estrogen-responsive genes are upregulated in NBH embryos. A dose-response experiment showed that NBH larvae are less responsive (lower maximum induction, as measured by ERα) and less sensitive (higher EC50 for induction, as measured by AroB) to estradiol than SC larvae, changes that would be adaptive in an estrogenic environment. In contrast, induction of Vtg mRNA is similar in the two populations, indicating that the adaptive mechanism is target gene-specific. Based on the lower basal levels of ERα mRNA in several tissues from adult NBH fish vs SC fish (Greytak and Callard, 2007), we predicted estrogen hyporesponsiveness; however, induction of ERα by estradiol exposure in reproductively inactive males did not differ between the two sites. Moreover, AroB was more responsive and Vtg induction was greater (2d) or similar (5d) in NBH as compared to SC males. Worth noting is the high inter-individual variability in estrogen responses of gene targets, especially in NBH killifish, which may indicate evolving preadaptive or adaptive mechanisms. In conclusion, although multi-generational exposure to a highly polluted environment is associated with changes in basal levels of ERα mRNA, this is not a simple predictor of estrogen responsiveness. We hypothesize that adaptation of killifish to the estrogenic and polluted environment may be occurring through diverse mechanisms that are gene-, tissue type- and life-stage specific.

Decreased vitellogenin inducibility and 17β-estradiol levels correlated with reduced egg production in killifish (Fundulus heteroclitus) from Newark Bay, NJ

“…Female killifish from New Bedford Harbor, similar to those from Newark Bay, exhibit decreased vitellogenin expression (mRNA and protein), decreased gonadal somatic index, and decreased circulating 17β-estradiol levels (Greytak et al ., 2005). Challenge studies with 17β-estradiol demonstrated that larval killifish from New Bedford Harbor have a shifted dose-response for ER α expression, but exhibit normal vitellogenin inducibility (Greytak et al ., 2010). The relevance of these impacts to the formation of eggs and reproductive success of females at New Bedford Harbor are not clear because fecundity has been shown to be normal and not impacted (Black et al ., 1998).…”

When evolution is the solution to pollution: Key principles, and lessons from rapid repeated adaptation of killifish (Fundulus heteroclitus) populations

“…In addition, Atlantic Wood offspring were more susceptible to mortality associated with infectious disease (Frederick, Van Veld, & Rice, 2007), to toxicity associated with photoactivation of PAHs, and to acute hypoxia (Meyer & Di Giulio, 2003), although they were less susceptible to the model pro‐oxidant tert ‐butyl hydroperoxide than reference fish (Meyer, Smith, Winston, & Di Giulio, 2003). Altered estrogen signaling has been observed in DLC‐tolerant killifish from both Newark and NBH (Bugel et al., 2011, 2014; Greytak & Callard, 2007; Greytak et al., 2010). NBH killifish are more sensitive to the pro‐oxidant chemical tert ‐butylhydroquinone as compared to fish from a reference site (Harbeitner, Hahn, & Timme‐Laragy, 2013); however, the opposite effect was seen in ER fish, which were more tolerant of the oxidant tert ‐butylhydroperoxide than reference fish (Meyer et al., 2003).…”

Timescale effects of 17α-ethinylestradiol on behavioral consistency in male threespine stickleback

“…Our findings may indicate that individuals differ in their sensitivity to EE2 exposure. For example, greater interindividual variability in estrogen response is found in killifish populations in polluted areas than that in other areas (Greytak et al 2010), and the mechanisms underlying within-and between-population variation in sensitivity to pollutants should be explored further. It is also possible that the behavioral differences prevalent within populations may in part result from differential exposure to EDCs (Breckels and Neff 2010) and future studies should examine the degree of variation found in populations of threespine stickleback from a range of areas that differ in the amount and types of contaminants present.…”