Embryonic and somatic cell cloning.

Revolutionary opportunities in biology, medicine and agriculture arise from the observation that offspring are obtained after nuclear transfer if somatic donor cells are induced to become quiescent. Exploitation of many of these opportunities will depend upon optimizing procedures for nuclear transfer. This may come about through an understanding of the means by which factors in the oocyte cytoplasm act upon the DNA of the transferred nucleus to regulate gene expression. Similarly, research will extend the procedure to other species. This technology may be used for embryo production, the introduction of genetic change and the derivation of cells needed to treat human diseases. Groups of genetically identical animals will be used in research to control genetic variation and to allow transfer of cells between individuals. In agriculture, production of a small number of clones will separate genetic and environmental effects, whereas production of larger numbers of offspring will disseminate genetic improvement from nucleus herds. Precise genetic modification will be achieved by site specific recombination in the donor cells before nuclear transfer. In all mammals it will become possible to define the role of any gene product and to analyse the mechanisms that regulate gene expression. Medical uses of these techniques will include the production of proteins needed to treat disease and the supply of organs such as hearts, livers and kidneys from pigs. As genome mapping projects identify loci associated with traits of commercial importance in agriculture then gene targeting will be used to study this effect. Finally, cells capable of differentiation into any of the tissues of a patient will provide treatment for diseases reflecting damage to a specific cell population that neither repairs nor replaces itself.