Genetic modification of sheep by nuclear transfer with gene-targeted somatic cells

For many years the lack of germline competent embryonic stem cell lines in livestock meant that the targeted modification of endogenous genes was not possible in these species. The demonstration that livestock could be cloned by nuclear transfer from cultured somatic cells has now provided an alternative route to accomplish gene targeting. This chapter describes protocols for culturing primary sheep fibroblasts, introducing and selecting targeted modifications into them and then using these modified cells in nuclear transfer experiments.