Ultraviolet-induced DNA Damage and its Subsequent Repair in Field-collected Aiptasia pallida as Monitored by Single-cell Gel Electrophoresis

Ultraviolet radiation (UVR) is a common occurring genotoxin in tropical marine environments. While shallow-water organisms have a variety of defenses against UVR, DNA damage may still occur. We documented the extent of DNA damage and subsequent repair response in the sea anemone Aiptasia pallida (pictured below) under field conditions. Samples of A. pallida were collected from Walsingham Pond, Bermuda on June 19th 2007. Subsequently, an experiment was carried out to determine the efficiency of repair from DNA damage incurred from exposure to a natural levels of Ultraviolet Radiation (UVR). It was found that field anemones produce relatively large quantities of Mycosporine-like amino acids (MAAs) and efficiently repaired DNA damage incurred from a reduced level natural UVR. Results presented here suggest that the ability of A. pallida to repair DNA damage and / or protect themselves from the detrimental effects of UVR may be an important factor for their survival. These findings provide insight into how other tropical marine cnidarians survive high levels of UVR exposure.

DNA Repair in Aiptasia pallida Following Laboratory Exposures to Ultraviolet Radiation

Cnidarians that inhabit shallow marine environments in tropical latitudes receive substantial exposure to ultraviolet radiation (UVR). It is well known that UVR damages the DNA of exposed organisms by creating cyclobutane pyrimidine dimers and 6-4 photoproducts. Damage may subsequently be repaired through nucleotide excision repair (NER) or directly by light-mediated reactions using photolyase. Neither of these mechanisms has been well-studied in cnidarians. We employed the comet assay to document DNA damage from UVR and subsequent DNA repair under laboratory conditions in the sea anemone Aiptasia pallida. Anemones cultured in the laboratory contain very low levels of UVR-absorbing mycosporine-like amino acids and thus, serve as ideal models for investigating damage due to UVR. DNA strand breaks (SBs) in aposymbiotic anemone nuclei increased in response to greater doses of UVR up to 12 hr (equivalent to 62 kJ m-2). Thereafter, total DNA SB formed in the nuclei reached an asymptote indicating a maximal amount of UVR damage had been reached. To assess the time-course of repair we subjected both symbiotic and aposymbiotic anemones to 6 hr of UVR (~ 30 kJ m-2) and then kept them in the dark. Aposymbiotic animals exhibited a delay of approximately 4 hours in the initiation of NER while symbiotic animals began repair approximately 2 hr earlier. In both cases repair mechanisms, once initiated, reduced DNA damage to near pre-exposure levels within 8 hours. Simultaneous exposure of aposymbiotic anemones to both UVR and visible light greatly reduced the amount of DNA damage after 4 hr repair. This suggests that light-mediated reactions plays an important role in DNA repair and is likely the first line of defense against cumulative DNA damage by UVR in these animals.