Transcriptomic change as evidence for cadmium-induced endocrine disruption in marine fish model of medaka, Oryzias javanicus

Abstract

We evaluated cadmium (Cd)-induced acute toxicity in Oryzias javanicus (marine medaka or Javanese ricefish) and gathered transcriptomic evidence for the Cd-induced endocrine-disrupting effect. The median lethal concentrations for the fish were determined to be 44.25 and 27.80 mg/L after exposure to Cd in seawater for 24 and 48 h, respectively, and 2.84, 1.61, and 1.20 mg/L after exposure in freshwater for 24, 48, and 72 h, respectively. The differences in the bioavailability and activity of free Cd²⁺ caused by the salt concentration in seawater could explain these dramatic differences in the toxicity of Cd between marine and fresh water system. The genes differentially expressed in O. javanicus liver tissue after exposure to 280 μg/L CdCl₂ for 48 h were profiled with a customized marine medaka cDNA microarray (HazChem Fish Array). We identified 204 differentially expressed genes; the expression of 66 genes was upregulated and that of 138 genes was downregulated (P<0.05). The total 31 genes were commonly expressed in fish exposed to Cd and two references of environmental disruptor (bisphenol A, or 17β-estradiol). These genes were used to predict the changes that occur in metabolic pathways and processes in response to Cd exposure. The database for annotation, visualization and integrated discovery (DAVID) was used for functional analysis for the differentially expressed genes. Significant changes were predicted in the steroid hormone and estrogen stimulus response, vitellogenin expression, sterol and cholesterol metabolic processes, lipid transport activity, defense response, innate immune response, and metal ion binding activity. These results extend our knowledge of the toxicity of Cd at the molecular level and indicate that Cd exposure causes endocrine disruption in aquatic organisms.