Somatic cell interspecies nuclear transfer.

摘要

The low efficiency of the nuclear transfer (NT) procedure requires large number of oocytes to produce embryos and live offspring. A series of experiments were conducted to evaluate the ability of the bovine cytoplast to reprogram nuclei from horses and llamas. In a preliminary study, equine oocytes from small (20mm diameter) follicles were either pretreated with roscovitine or placed in maturation (IVM only) prior to NT. Roscovitine pretreatment did not improve nuclear maturation rates (roscovitine pretreatment 57% vs. IVM only 66%) and no fusion was obtained from roscovitine-pretreated oocytes after NT. Another preliminary study was conducted with the objective to produce llama NT embryos and to compare their development in two in vitro culture conditions (G1.2RTM vs. CR1aa). No difference was found in the number of embryos cleaved after 2 d of culture. This resulted in the first scientific report of somatic cell NT, in vitro culture and transfer of NT embryos in the llama. In the next experiment, adult horse and llama fibroblasts were injected into enucleated cow oocytes. The results showed the cow cytoplasm is capable of partially reprogramming nuclei from other species and support mitotic divisions. However, this study also showed a consistent embryonic developmental arrest at the 8- to 16-cell stage when horse or llama donor cells were used as donor nuclei. When a more closely related species of donor cell (banteng) and recipient oocyte (domestic cattle) were used for NT, no embryonic developmental arrest was found. Embryos progressed to achieve high blastocyst rates (banteng male cell line 28% vs. banteng female cell line 15%). Two banteng interspecies NT pregnancies were established and subsequently lost from the banteng male cell line. In the final study, the effect of a mixed mitochondrial population (heteroplasmy) on early embryonic development was investigated. Ooplasmic transfer performed in combination with NT procedure indicated presence of foreign mitochondria clustered in a small portion of the cytoplasm in early stages of embryo development. When goat ooplasm was transferred into interspecies (cow oocyte-goat donor cell) NT embryos, fusion and cleave rates were reduced suggesting an increased level of heteroplasmy or nuclear-ooplasmic incompatibilities.