NUCLEAR TRANSFER IN MAMMALS - RECENT DEVELOPMENTS AND FUTURE PERSPECTIVES

A clone can be defined as a set of genetically identical animals. Smal l clones of two or occasionally up to four identical animals can be ob tained by embryo splitting or blastomere separation. Embryo cloning by nuclear transfer involves the transfer of genetic material from a don or cell (karyoplast) to the cytoplasm of an oocyte or zygote from whic h the genetic material has been removed (cytoplast). In farm animals, metaphase II oocytes are most widely used as cytoplasts. There are now many factors known to influence the efficiency of embryo cloning by n uclear transfer. These include stage of development and cell cycle of donor cells, the choice of the recipient cell, the methods for activat ion of oocytes, the cell cycle coordination between donor cell and rec ipient cytoplast, and the method for fusion between nuclear donor and recipient cytoplast. Recent progress in cloning embryos and animals fr om cultured cells of embryonic, fetal, or adult origin offers a wide s pectrum of potential applications of nuclear transfer, such as the unl imited multiplication of elite embryos or animals from selected mating s and the potential for precise genetic modification of farm animals f or gene farming or xenotransplantation. (C) 1998 Elsevier Science B.V. All rights reserved.