Zebrafish Have a Competent p53-Dependent Nucleotide Excision Repair Pathway to Resolve Ultraviolet B–Induced DNA Damage in the Skin

Abstract

UV light is a primary environmental risk factor for melanoma, a deadly form of skin cancer derived from the pigmented cells called melanocytes. UVB irradiation causes DNA damage, mainly in the form of pyrimidine dimers (cis-syn cyclobutane pyrimidine dimers and pyrimidine (6–4) pyrimidone photoproducts), and organisms have developed complex multi-protein repair processes to cope with the DNA damage. Zebrafish is becoming an important model system to study the effects of UV light in animals, in part because the embryos are easily treated with UV irradiation, and the DNA damage repair pathways appear to be conserved in zebrafish and mammals. We are interested in exploring the effects of UV irradiation in young adult zebrafish, so that we can apply them to the study of gene-environment interactions in models of skin cancer. Using the Xiphophorus UV melanoma model as a starting point, we have developed a UV irradiation treatment chamber, and established UV treatment conditions at different ages of development. By translating the Xiphophorus UV treatment methodology to the zebrafish system, we show that the adult zebrafish skin is competent for nucleotide excision DNA damage repair, and that like in mammalian cells, UV treatment promotes phosphorylation of H2AX and a p53 dependent response. These studies provide the groundwork for exploring the role of UV light in melanoma development in zebrafish.

UV-induced DNA damage in coral reef fish: damage levels and protection mechanisms

“…The only evidence comes again from Eckes (2009), who showed a significant decrease in the number of dead cells in tissue of UVB irradiated fish that had been exposed to photoreactivating light compared to fish deprived of these wavelengths. Similar results from polar and temperate species (Regan et al 1982, Malloy et al 1997, Vetter et al 1999) and freshwater fish (Ahmed & Setlow 1993, Uchida et al 1995, Meador et al 2000, Zeng 2009, Mitchell et al 2014,…”

“…The third protection mechanism is DNA repair via photoreactivation and dark repair, which has been shown to exist in various freshwater and temperate marine fish species (Ahmed & Setlow 1993, Uchida et al 1995, Malloy et al 1997, Vetter et al 1999, Lesser et al 2001, Armstrong et al 2002, Mitchell et al 2009, Zeng 2009, Mitchell et al 2014). …”

Does Melanoma Begin in a Melanocyte Stem Cell?

“…In zebrafish, p53 mutants are deficient in NER and are more sensitive than wild-type fish to UVB radiation [32]. Many studies show that p53 gene expression is developmentally regulated and its expression depends upon the stage of development [32–36]. Thus, p53 may play an important role in DNA damage repair in MSCs similar to what has been shown in other cells [37].…”

“…For example, it has been found that expression of the BRAF V600E mutation, the most common mutation in human nevi and melanoma, is sufficient to induce ectopic nevi in zebrafish and can collaborate with p53 mutations to promote melanoma [88, 89]. It has been discovered that zebrafish have a competent p53 -dependent NER pathway to protect cells from UVB-induced DNA damage in the skin [32]. We are using the zebrafish model in our lab to determine the effects of UVA/UVB radiation on the MSC population.…”

“…Normal stem cells have strict control of gene expression and DNA replication whereas MSCs with compromised DNA repair pathways may have altered patterns of proliferation, quiescence, and differentiation, and may be more susceptible to malignant transformation [31]. In zebrafish, p53 mutants are deficient in NER and are more sensitive than wild-type fish to UVB radiation [32]. Many studies show that p53 gene expression is developmentally regulated and its expression depends upon the stage of development [32–36].…”