Induction, distribution and repair of UV photodamage in the platyfish, Xiphophorus signum

The genus Xiphophorus is an important model for investigating the etiology and genetics of sunlight-induced melanoma as well as other cancers. We used immunological techniques to determine the induction, distribution and repa ir of cyclobutane pyrimidine dimers (CPD) and pyrimidine(6-4)pyrimidone dim ers ([6-4]PD) in different tissues of Xiphophorus signum exposed to ultravi olet-B light. We found that the (6-4)PD was induced at 5 to 10-fold lower f requency than the CPD and that scalation provided considerable photoprotect ion against both photoproducts, Photoenzymatic repair (PER) was very effici ent in X. signum with most of the lesions removed within 20 min; PER of CPD occurred at about twice the rate of (6-4)PD. Nucleotide excision repair (N ER) was much less efficient than PER and the rates of CPD and (6-4)PD remov al were comparable. PER was more efficient in the caudal fin compared to th e lateral epidermis; the opposite was true for NER. Although the initial ra te of CPD excision was five-fold faster in the lateral epidermis compared t o the caudal fin a considerable amount of residual damage remained in both tissues. The diverse photochemical and photobiological responses observed i n X, signum suggest that heritable traits governing deoxyribonucleic acid d amage induction and repair may be involved in the susceptibility of other X iphophorus species to melanomagenesis.