Assessment of Transgenic Fish as a New Model for UV Mutagenesis

The λ transgenic medaka, a fish model carrying the cII target gene, was used to evaluate ultraviolet radiation (UV)-induced mutagenesis. Mutant frequency induction (MF) was assessed 21 days after treatment of embryos with either UVB or UVA, and a 24 hour light or dark interval. Early (stage 6), middle (stage 25) or late stage (stage 38) embryos were exposed to 0, or 400 J/m UVB (280320 nm). Stage 25 and 38 embryos were also exposed to 0, 400, 800, or 1000 J/m UVB. Additional embryos were treated with 0, 400, 800 or 1600 J/m UVA (321-400 nm). MFs were obtained using the cII mutation assay in which the cII gene was recovered from genomic DNA and transferred into indicator bacteria to distinguish mutant and non-mutant genes. Significant mortality, deformities and MF inductions were observed only in stage 25 embryos exposed to UVB. In the 400 J/m UVB + dark treatment, 68% of embryos died, 33% showed distinctive abnormalities and the MF was induced ~3-fold above controls. The survival in 400 J/m + light treatment was comparable to untreated controls, whereas the MF was induced ~2-fold. Similar relationships between survival, and MFs with light or dark treatment were observed in Experiment 2. UVB + dark treatments exhibited significant mortality and up to 12-fold MF induction. MFs were elevated up to 3.7-fold with increasing UVB + light exposure, indicating photoreactivated repair did not fully reduce UVB-induced effects. Results show this to be a suitable animal model for UV mutagenesis as it is highly responsive to UVB radiation with survival, development and MF induction dependent upon embryonic stage, dose and photoreactivated repair.