Couplet alignment and improved electrofusion by dielectrophoresis for a zona-free high-throughput cloned embryo production system

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Mammalian cloning by somatic nuclear transfer has great potential for developing medical applications such as biopharmaceuticals and generation of tissues for transplantation. For agricultural applications, it allows the rapid dissemination of genetic gain in livestock breeding. The maximisation of that potential requires improvements to overall cloning technology, especially with respect to increasing cloning efficiency and throughput rates in cloned embryo production. A zona-free embryo reconstruction system was developed to increase cloning throughput and ease of operation. Central to this system is a modified electrofusion procedure for nuclear transfer. Cytoplast-donor cell couplets were placed in a custom-designed ‘parallel plate’ electrode chamber. A 1 MHz sinusoidal AC dielectrophoresis alignment electric field of 6–10 kVm−1 was applied for 5–10 s. The couplets were then fused using 2×10 μs rectangular DC-field pulses (150–200 kVm−1), followed by application of the AC field (6–10 kVm−1) for another 5–10 s. Fusion was performed in hypoosmolar buffer (210 mOsm). Automated alignment of up to 20 couplets at a time has been achieved, resulting in greatly improved fusion throughput rates (2.5-fold increase) and improved fusion yields (1.3-fold increase), compared with commonly followed zona-intact protocols.