In Vitro Development of Reconstructed Porcine Oocytes after Somatic Cell Nuclear Transfer1

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Abstract
This study was designed to examine the developmental ability of porcine embryos after somatic cell nuclear transfer. Porcine fibroblasts were isolated from fetuses at Day 40 of gestation. In vitro-matured porcine oocytes were enucleated and electrically fused with somatic cells. The reconstructed eggs were activated using electrical stimulus and cultured in vitro for 6 days. Nuclear-transferred (NT) embryos activated at a field strength of 120 V/mm (11.6 ± 1.6%) showed a higher developmental rate as compared to the 150-V/mm group (6.5 ± 2.3%) (P < 0.05), but the mean cell numbers of blastocysts were similar between the two groups. Rates of blastocyst development from NT embryos electrically pulsed at different times (2, 4, and 6 h) after electrofusion were 11.6 ± 2.9, 6.6 ± 2.3, and 8.1 ± 3.3%, respectively. The mean cell numbers of blastocysts developed from NT embryos were gradually decreased (30.4 ± 10.4 > 24.6 ± 10.1 > 16.5 ± 7.4 per blastocyst) as exposure time (2, 4, and 6 h) of nuclei to oocyte cytoplast before activation was prolonged. There was a significant difference in the cell number between the 2- and 6-h groups (P < 0.05). Nuclear-transferred embryos (9.4 ± 0.9%) had a lower developmental rate than in vitro fertilization (IVF)-derived (21.4 ± 1.9%) or parthenogenetic embryos (22.4 ± 7.2%) (P < 0.01). The mean cell number (28.9 ± 11.4) of NT-derived blastocysts was smaller than that (38.6 ± 10.4) of IVF-derived blastocysts (P < 0.05) and was similar to that (29.9 ± 12.1) of parthenogenetic embryos. Our results suggest that porcine NT eggs using somatic cells after electrical activation have developmental potential to the blastocyst stage, although with smaller cell numbers compared to IVF embryos.