Molecular cloning of vitellogenin cDNA in rockfish (Sebastes schlegeli) and effects of 2,2′4,4′5,5′-hexachlorobiphenyl (PCB 153) on its gene expression

Many environmental chemicals are known to affect sex steroid production and vitellogenesis through agonistic or antagonistic pathways. To investigate the estrogenic effect of 2,2′4,4′5,5′-hexachlorobiphenyl (PCB 153) on reproductive function, we have constructed a cDNA library and cloned a 320 base sequence encoding a partial VTG mRNA of rockfish (rVTG), Sebastes schlegeli. We have examined the expression level of rVTG mRNA level by northern blot analysis and measured levels of plasma estradiol-17β (E2) and testosterone (T) by radioimmunoassay (RIA). Plasma concentrations of T in female and male injected with PCB 153 were not significantly different between two dosages of 0.16 mg/kg b.w. and 0.57 mg/kg b.w. However, plasma concentrations of E2 in female fish injected with PCB 153 at 0.16 mg/kg b.w. and 0.57 mg/kg b.w. increased after 12 h and 24 h. An rVTG mRNA transcript of approximately 4.0 kilo bases was extracted from hepatic tissue for northern blot analysis, and the effects of PCB 153 on rVTG mRNA expression in vivo with both male and female juvenile rockfish were examined. The level of rVTG mRNA expression increased only in female rockfish injected with both dose levels of PCB 153 after 48 h of exposure. The results of this study suggest that PCB 153 may produce VTG in female through a synergic effect with E2 resulting in indirect disruption.