Effects of oocyte vitrification on histone modifications.

Vitrification has been widely used as an assisted reproductive technology in animals and humans, yet the impact of oocyte vitrification and warming on survival and histone modifications has to be evaluated. In the present study, the survival of mouse MII oocytes was assessed after freezing, as were changes in histone 3 lysine 9 (H3K9) dimethylation, histone 4 lysine 5 (H4K5) acetylation and histone 3 lysine 14 (H3K14) acetylation. The results show that, in oocytes subjected to vitrification, H3K9 methylation and H4K5 acetylation were increased. H3K14 acetylation could not be detected in either non-vitrified or vitrified oocytes. Oocytes are very sensitive to changes in H3K9 and H4K5 following vitrification. Both these histone modifications could be useful markers to monitor epigenetic perturbations induced by various experimental vitrification protocols and eventually for optimising the cryopreservation of human oocytes.