Developmental potential of aged oocyte rescued by nuclear transfer following parthenogenetic activation and in vitro...

Mouse oocyte aged in vitro cannot develop normally following activation. To investigate the roles of nucleus or cytoplasm elements in oocyte aged in vitro process and their subsequent development capability following activation, we reconstructed oocytes with MII chromosome spindle and cytoplasm from aged and fresh oocytes by nuclear transfer. The subsequent developmental potential after parthenogenetic activation (PA) or in vitro fertilization (IVF) was evaluated. After nuclear transfer, more than 75.6% of karyoplast and cytoplast pairs can be fused and reconstructed oocytes have a normal haploid karyotype. Following PA, aged oocytes cannot develop beyond four-cell stage, reconstructed oocytes from fresh nucleus and aged cytoplasm developed to blastocyst with a low percentage (9.1%). Instead, blastocyst formation rate of reconstructed oocyte from aged nucleus and fresh cytoplasm was higher (60.0%). Following IVF, zygote with diploid karyotype can be formed from zona pellucida (ZP)-free oocyte. After cultured in vitro, aged oocytes cannot develop beyond two-cell; reconstructed oocytes from fresh nucleus and aged cytoplasm developed to blastocyst with low percentage (15.0%). However, high blastocyst formation rate (86.2%) can be obtained from reconstructed oocytes from aged nucleus and fresh cytoplasm. Furthermore, after embryo transfer, three viable pups have been obtained, although the efficiency is very low. These observation demonstrated that cytoplasm is more crucial than nucleus to aging process. Fresh cytoplasm could partly rescue nucleus susceptibility to apoptosis from aging in vitro.