Early development of reconstructed embryos after somatic cell nuclear transfer in a non-human primate.

To improve efficiency and assess variation in nuclear transfer techniques in non-human primates, we investigated the following factors: type of donor cell, interval between enucleation and cell injection, activation after electrical pulsing and cytokinesis inhibitors. An average of 16.4 oocytes were recovered from 91 retrievals; however, 15 (14%) additional retrieval attempts yielded no oocytes due to a failure of follicular stimulation. Oocyte maturation rates at 36, 38 and 40 h post-hCG were 46.2, 52.6 and 61.2%, respectively. The MII spindle could be seen clearly using polarized microscopy in 89.1% (614/689) of oocytes. Nuclei were seen in 42% of the NT couplets, 53% of those cleaved to the 2-cell stage and 63% of the 2-cell embryos developed to the 8-cell stage by Day 3. There was no difference in the occurrence of nuclear formation between couplets created using fibroblasts or cumulus cells, although embryos were more reliably produced with fibroblasts. The interval (2, 3 and 4 h) between enucleation and cell injection did not affect NT efficiency. Ethanol treatment after electrical pulses yielded more 2-cell NT embryos than did treatment with ionomycin, but the frequency of nuclear formation and development to the 8-cell stage was not different. Treatment of couplets with cycloheximide and cytochalasin B for 5 h after activation had no impact on NT efficiency.