Time course of hepatic gene expression and plasma vitellogenin protein concentrations in estrone-exposed juvenile rainbow trout (Oncorhynchus mykiss)

Abstract

Estrone (E1), a natural estrogen hormone found in sewage effluents and surface waters, has known endocrine disrupting effects in fish, thus, it is a contaminant of emerging concern. Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to an environmentally-relevant concentration of E1 (24ng/L E1 [0.1nM]) for 7d and then placed in clean water for a 9d recovery period. RNA sequencing showed transcripts from numerous affected biological processes (e.g. immune, metabolic, apoptosis, clotting, and endocrine) were altered by E1 after 4d of treatment. The time course of E1-inducible responses relating to vitellogenesis was examined daily during the two phases of exposure. Hepatic gene expression alterations evaluated by quantitative polymerase chain reaction (QPCR) were found during the treatment period for vitellogenin (VTG), vitelline envelope proteins (VEPs) α, β and γ, and estrogen receptor α1 (ERα1) transcripts. ERα1 was the only transcript induced each day during the treatment phase, thus it was a good indicator of E1 exposure. Gradual increases occurred in VEPβ and VEPγ transcripts, peaking at d7. VTG transcript was only elevated at d4, making it less sensitive than VEPs to this low-level E1 treatment. Inductions of ERα1, VEPα, VEPβ and VEPγ transcripts ceased 1d into the recovery phase. Plasma VTG protein concentrations were not immediately elevated but peaked 7d into the recovery phase. Thus, elevated vitellogenesis-related gene expression and protein production occurred slowly but steadily at this concentration of E1, confirming the sequence of events for transcripts and VTG protein responses to xenoestrogen exposure.