EMBRYONIC STEM-CELLS - DEVELOPMENTAL CAPABILITIES AND THEIR POSSIBLE USE IN MAMMALIAN EMBRYO CLONING

Mouse embryonic stem cells (ES cells) are the most pluripotent mammali an cells known. After microsurgical injection into blastocysts or moru la stage embryos, mouse ES cells can differentiate into probably all t issues of the developing fetus, including the germ line, Recent observ ations show that mouse embryonic stem cells can alone support full ter m development, It also seems that pluripotency of mouse ES cells is ex tended to their cell nuclei, since after transfer of ES cell nuclei in to enucleated oocytes and 2-cell embryos, development was obtained unt il Day 16. Sheep cells of similar origin to mouse ES cells, which come from cultured embryonic discs, also retain pluripotency. After inject ion of these cells into host blastocysts, two chimaeric lambs were obt ained.