Effect of different activation modes on DNA integrity of porcine M II oocytes matured in vitro.

Summary The effect of different activation protocols on DNA integrity of porcine oocytes matured in vitro wasanalysed using the comet assay. The oocytes from ovaries of slaughtered gilts were cultured for 48hin modified M199 medium. They were then freed of cumulus cells and treated continuously orintermittently with a nitric oxide (NO) donor for 6h. Standard activation with calcium ions (Ca 2+ )and culture without any treatment served as positive and negative controls, respectively. The activationwas assessed according to the formation of pronuclei. Exposure of oocytes to Ca 2+ was associated withhigh activation efficiency, but decreased DNA integrity. The opposite, i.e. low activation efficiency buthigh DNA integrity was observed after continuous exposure to NO. Intermittent action of NO increasedthe activation rate, while the values of DNA damage remained at low levels. Our data suggest that anincreased DNA instability could be the main reason compromising the further embryonic developmentof oocytes activated by the standard protocol. The intermittent treatment with NO thus represents apromising step to optimization of parthenogenetic activation of pig oocytes.Keywords: Comet assay, DNA integrity, Nitric oxide, Oocyte, Parthenogenesis, Pig