Oocyte Cryopreservation in Domestic Animals and Humans: Principles, Techniques and Updated Outcomes

SIMPLE SUMMARY: Oocyte cryopreservation is the most powerful technique for preserving the genetic potential of individual females. However, the recent outcomes of this technology in terms of viability, fertilizing ability, embryo development and pregnancy remain poor. The high sensitivity of the oocytes to freezing has been correlated with the profound dynamics of oocyte structures and functions. As a result, cryoinjury inevitably occurs at several cellular levels, which is indeed detrimental to cell viability and subsequent development. Advancement in the improvement of freezing technology via modifications to freezing technique and development of novel cryodevices plays a central role in mitigating cryoinjury and efficiently empowering the outcomes of oocyte cryopreservation. However, empirical study and optimizations of the techniques are generally required for cryopreservation of oocytes from particular species. ABSTRACT: Oocyte cryopreservation plays important roles in basic research and the application of models for genetic preservation and in clinical situations. This technology provides long-term storage of gametes for genetic banking and subsequent use with other assisted reproductive technologies. Until recently, oocytes have remained the most difficult cell type to freeze, as the oocytes per se are large with limited surface area to cytoplasm ratio. They are also highly sensitive to damage during cryopreservation, and therefore the success rate of oocyte cryopreservation is generally poor when compared to noncryopreserved oocytes. Although advancement in oocyte cryopreservation has progressed rapidly for decades, the improvement of cryosurvival and clinical outcomes is still required. This review focuses on the principles, techniques, outcomes and prospects of oocyte cryopreservation in domestic animals and humans.