Characterization and differential expression of CPD and 6-4 DNA photolyases in Xiphophorus species and interspecies hybrids.

Among the many Xiphophorus interspecies hybrid tumor models are those that exhibit ultraviolet light (UVB) induced melanoma. In previous studies, assessment of UVB induced DNA damage and nucleotide excision DNA repair has been performed in parental lines and interspecies hybrids. Species and hybrid specific differences in the levels of DNA damage induced and the dark repair rates for cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine pyrimidine photoproducts (6-4PPs) have been reported. However, UVB induced DNA lesions in Xiphophorus fishes are thought to primarily be repaired via light dependent CPD and 6-4PP specific photolyases. Photolyases are of evolutionary interest since they are ancient and presumably function solely to ameliorate the deleterious effects of UVB exposure. Herein, we report results from detailed studies of CPD and 6-4PP photolyase gene expression within several Xiphophorus tissues. We determined photolyase gene expression patterns before and after exposure to fluorescent light in X. maculatus, X. couchianus, and for F1 interspecies hybrids produced from crossing these two parental lines (X. maculatus Jp 163 B×X. couchianus). We present novel results showing these two photolyase genes exhibit species, tissue, and hybrid-specific differences in basal and light induced gene expression.