Lack of ultraviolet-light inducibility of the medakafish (Oryzias latipes) tumor suppressor gene p53

P53 is by far the most frequently altered gene in mammalian tumors. However, so far not a single p53 lesion has been reported in malignancies of cancer model systems in lower vertebrates. For analyzing the function of p53 in lower vertebrates, the gene was cloned from the medakafish (Oryzias latipes). Despite some differences in the genomic organization, the fish p53 amino acid sequence is highly conserved. Contrary to higher vertebrates, the level of p53 mRNA in medaka embryos gradually increases during embryogenesis. High expression of the p53 mRNA was detected in melanoma cells compared to undetectable expression of the gene in embryonic stem cells and fibroblasts. No effect of ultraviolet (UV) irradiation on the expression of p53 in cell cultures as well as in medaka fry was observed, indicating a possible difference in the function of p53 in lower vertebrates.