Totipotency or multipotentiality of cultured cells: Applications and progress.

The stable introduction of new genetic material into breeding programmes for farm animal species requires germ line modification. One route by which to achieve this is by the combination of embryo manipulation and molecular biological techniques. In the mouse, genetic manipulation of embryonic stem (ES) cells in culture followed by the production of chimeric animals by blastocyst injection has proved a powerful tool for germ line manipulation. In contrast, the absence of proven ES lines in farm animal species has restricted similar progress, the production of transgenic animals being limited to gene addition using the technique of pronuclear injection. An alternative and desirable route to germ line modification in farm animals is to produce offspring by nuclear transfer from a cell line which can be maintained in culture. In sheep this has now been achieved with the birth of live lambs from an embryo derived, epithelial like cell line. The combination of this technology with that developed in ES cells for genetic modification will herald a new era in the germ line modification of farm animal species.