Efficient in vitro production of porcine blastocysts by handmade cloning with a combined electrical and chemical activation

The purpose of our work was to establish an efficient protocol for activation of porcine cytoplast-fibroblast constructs produced by the handmade cloning technique. Firstly, we investigated a combined electrical and chemical activation protocol for parthenogenetic development of in vitro matured zona-free oocytes. Oocytes were activated by one 80 μs pulse and subsequently cultured in cytochalasin B and cycloheximide. Developmental rates of blastocysts from activated oocytes were 49 ± 1 and 40 ± 2%, when using one 80 μs pulse of 0.85 or 1.25 kV/cm, respectively. The activation procedure was further confirmed by a simultaneous re-fusion and activation of bisected oocytes, resulting in a blastocyst rate of 41 ± 8%. Secondly, the activation protocol was applied in the handmade cloning technique. In vitro matured zona-free porcine oocytes were bisected and halves containing no chromatin, i.e. the cytoplasts, were selected. Reconstructed embryos were produced by a two-step fusion procedure. At the first step, one cytoplast was fused to one fibroblast by one 80 μs pulse of 1.25 kV/cm. After 1 h, the cytoplast-fibroblast pair and another cytoplast were fused and activated simultaneously by one 80 μs pulse of 0.85 kV/cm, and subsequently cultured in cytochalasin B and cycloheximide. The development of reconstructed embryos to the blastocyst stage was in average 21 ± 4%, and total blastocyst cell counts were in average 48 ± 3. Thus, the combined electrical and chemical activation procedure resulted in efficient blastocyst development in the handmade cloning technique.