Assessment of DNA damage in individual hamster embryos by comet assay

DNA damage induced by either light exposure or oxidative stress likely cont ributes to the compromised development in vitro of cultured preimplantation embryos. Using the comet assay, which entails microgel electrophoresis tha t can readily detect single-strand breaks in DNA, a significant increase in DNA damage was detected in individual one-cell hamster embryos that were t reated with either ultraviolet light or hydrogen peroxide. In addition, an increase in DNA damage also was observed following exposure of one-cell emb ryos to visible light. When the embryos were placed in drops of culture med ium that were covered with mineral oil and the dishes then placed in a port able incubator containing 5% CO2 in air at 37 degrees C, visible and UV lig ht irradiation for 30 min still induced extensive DNA damage when compared to control embryos that were kept in the dark. In contrast, infrared irradi ation did not induce an increase in DNA damage. DNA damage also was measure d in individual one- and two-cell stage embryos developed in vivo or in vit ro. The extent of DNA damage in the cultured embryos was significantly grea ter than in embryos that developed in vivo. These results highlight the use fulness of the comet assay to assess DNA damage in individual preimplantati on embryos and how the assay can be used to monitor culture conditions in v itro, (C) 1999 Wiley-Liss, Inc.