Manipulation of gametes and embryos in the pig

Several manipulation techniques including nuclear injections, nuclear transplantation, embryo splitting, chimaera production and sperm injection are discussed with special reference to their application in the pig. The nuclear injection technique is likely to be of greatest use for gene transfer. Gene transfer is feasible for pig embryos, but it is very inefficient. Efficiencies of various steps in the successful production of transgenic offspring as summarized from several published references are as follows: immediate survival of embryos following injection (60%), offspring produced from injected embryos (15%), offspring with an integrated foreign gene (24%) and offspring expressing the integrated foreign gene (60%). The overall efficiency is about 1%. Potential uses for nuclear transplantation are for the production of gynogenetic and androgenetic embryos and for cloning embryos. The feasibility of producing androgenetic and gynogenetic embryos will depend on whether in the pig, as in the mouse, the paternal and maternal genomes function differently. The feasibility of cloning by nuclear transplantation will depend upon the timing of developmental events in pig embryos and the development of methods for reprogramming nuclei. Pig embryos have been cloned by embryo splitting. Chimaera production and fertilization by sperm injection are likely to be feasible for pig embryos but have not yet found application.