In vitro manipulation of cryopreserved gametes in the domestic cat

The availability of preserved gametes would greatly enhance reproductive technologies aimed to the diffusion of valuable cat breeds or to the preservation of biodiversity in wild feline species. In the domestic cat, in vitro fertilization (IVF) or intracytoplasmic injection of frozen spermatozoa resulted in embryo development up to the blastocyst stage. By contrast, cryopreservation of oocytes has met with very little success in animals and humans, due to the unique morphological characteristics of the cells. Various types of cell damage (i.e. cytoskeleton disorganization, DNA abnormality, premature granule exocitosis, etc.) may occur during freezing and meiotic stages vary in their response to cryopreservation. In fact, IVF of frozen cat oocytes resulted in embryo development to the blastocyst stage only when mature (Metaphase II) oocytes were cryopreserved. The cryopreservation of immature oocytes, as donors of germinal vesicles (GVs) for transfer to fresh enucleated oocytes, could be an opportunity to overcome the problem of freezing injuries to the cytoplasm. The transferred GV could respond to meiosis promoting factors present in the recipient cytoplasm, as demonstrated in other species. Our recent results show that high proportions of cat immature oocytes are still viable and their GVs are well preserved after thawing. Removal and transfer of the cryopreserved GVs would allow a better understanding of the physiological mechanisms involved in cat oocyte maturation and a future application of this procedure may aid in the conservation of female valuable germplasm.