Cytoplasmic, rather than nuclear-DNA, insufficiencies as the major cause of poor competence of vitrified oocytes

To unravel the differential contributions of nuclear-DNA and cytoplasm to the poor 'competence' of oocytes after cryopreservation, reciprocal exchange of metaphase II-spindle chromosomal complex (karyoplast) between vitrified and fresh oocytes was carried out in an ovine animal model. Karyoplast exchange per se was accomplished with high efficiency and in-vitro development of oocytes reconstituted with fresh-karyoplast and vitrified-cytoplast (FK/VC) showed no improvement over VK/VC and control-vitrification oocytes. Blastocyst development of oocytes that were reconstituted with vitrified-karyoplast and fresh-cytoplast (VK/FC) approached that of fresh-controls, however, and was significantly higher than FK/VC, VK/VC, and control-vitrification (all P ≤ 0.05). These results point toward 'cytoplasmic insufficiencies' as the main cause of poor 'competence' of matured oocytes after vitrification.