Hepatic Transcriptomic Responses to Ethinylestradiol in Embryonic Japanese Quail and Double‐Crested Cormorant

Abstract

Understanding species differences in sensitivity to toxicants is a critical issue in ecotoxicology. We recently established that double‐crested cormorant (DCCO) embryos are more sensitive than Japanese quail (JQ) to the developmental effects of ethinylestradiol (EE2). Here, we explore how this difference in sensitivity between species is reflected at a transcriptomic level. EE2 was dissolved in dimethyl sulfoxide and injected into the air cell of eggs prior to incubation at nominal concentrations of 0, 3.33, and 33.3 µg/g egg weight. At mid‐incubation (JQ; 9 days, DCCO; 16 days), liver was collected from 5 embryos per treatment group for RNA‐sequencing. Data were processed and analyzed using EcoOmicsAnalyst (www.ecoomicsanalyst.ca) and ExpressAnalyst (www.expressanalyst.ca). EE2 exposure dysregulated 238 and 1987 genes in JQ and DCCO, respectively, with 78 genes in common between the two species. These included classic biomarkers of estrogen exposure such as vitellogenin and apovitellenin. We also report DCCO‐specific dysregulation of phase I/II enzyme‐coding genes and species‐specific transcriptional ontogeny of vitellogenin‐2. Twelve KEGG pathways and two EcoToxModules were dysregulated in common in both species including PPAR signaling pathway and fatty acid metabolism. Similar to previously reported differences at the organismal level, DCCO were more responsive to EE2 exposure than JQ at the gene expression level. Our description of differences in transcriptional responses to EE2 in early life stage birds may contribute to a better understanding of the molecular basis for species differences.