Factors affecting cryotolerance of mammalian oocytes

Cryopreservation of oocytes is an important tool for preserving genetic resources and for farm animals breeding. Processes taking place during vitrification affect oocytes and result in their reduced developmental capacity and lower fertilisation rates of cryopreserved oocytes. Further improvement in cryopreservation techniques is still required. Several authors already summarized the actual state and perspectives of oocyte cryopreservation as well as potential approaches to improve their development after thawing. The aim of this review is to specify factors affecting cryotolerance of mammalian oocytes, especially bovine in vitro matured oocytes, and to identify the areas, where more efforts were made to improve the success of oocyte cryopreservation. These factors include oocyte lipid content, membrane composition, mRNA protection, cytoskeleton stabilization and application of such potential stimulators of cell cryotolerance as antioxidants, growth factors or antifreeze proteins.