Birth of a domestic cat kitten produced by vitrification of lipid polarized in vitro matured oocytes

The ability to cryopreserve oocytes is an effective method to retain valuable genetic material of mammals, including that of endangered animals. Embryos of domestic cats are amenable to cryopreservation, whereas their oocytes are much less cryo-tolerant. The capability of oocytes to survive cryopreservation is affected by several factors, one of which has been hypothesized to be the high concentration of intracellular lipids. To test this hypothesis, in this study we polarized lipids of cat oocytes and tested their cooling and freezing sensitivity. We found that the sensitivity of oocytes to cooling and cryopreservation does appear to be related to their high intracellular lipid content, as indicated by higher cryosurvival and development into blastocysts when intracellular lipids of in vitro matured oocytes were polarized before vitrification. However, polarization of all intracellular lipids was detrimental to development of embryos. Cell numbers in blastocysts derived from fully polarized/vitrified oocytes were significantly lower than those of partially polarized/vitrified or non-vitrified/fresh oocytes. Although embryos derived from fully polarized/vitrified oocytes developed to the blastocyst stage at higher rates than those of partially polarized/vitrified or non-centrifuged/vitrified oocytes, their in vivo developmental competence was compromised. When embryos derived from fully polarized/vitrified oocytes were transferred, although two recipients became pregnant, all implanted embryos were reabsorbed. In contrast, when embryos derived from oocytes that were only partially lipid polarized before vitrification and then were transferred, one recipient did become pregnant and produced a live healthy kitten. The present results suggest that other approaches to altering intra-cellular lipid levels in cat oocytes should be evaluated to improve their functional survival after cryopreservation.