A quantitative real-time polymerase chain reaction method for the analysis of vitellogenin transcripts in model and nonmodel fish species

The measurement of vitellogenin (vtg) gene transcription has been shown to be a reliable indicator of exposure to estrogenic compounds. Unfortunately, the relatively poor molecular characterization of North American fish species has hindered its application to a larger number of ecologically important species. The current research aimed to demonstrate specific amplification of vtg gene transcripts in three model (zebrafish, rainbow trout, and medaka) and six nonmodel (emerald shiner, pearl dace, smallmouth bass, creek chub, white sucker, and golden redhorse) fish species. Quantitative polymerase chain reaction (QPCR) primers for model species were designed from publicly available vtg sequences. Successful amplification of vtg was demonstrated in fish exposed to 17 alpha-ethinylestradiol (EE2) for all model species. Vitellogenin primers for selected nonmodel species were designed from published sequences of closely related species. Multiple primers were developed targeting different regions of the vtg gene. The successful amplification of vtg was confirmed through size and sequence analysis for all nonmodel species with the exception of the white sucker, in which amplifications failed. Furthermore, QPCR primers and conditions were quantitative over five orders of magnitude in at least one species (pearl dace) exposed to 5 ng/L of EE2 for 24 h. The selected species are found in a wide array of ecological habitats that span the United States. Inclusion of vtg transcriptional analysis for wild, ecologically relevant fish in monitoring studies may aid in understanding the extent of estrogenic exposure in aquatic ecosystems across the United States.