VIABLE OFFSPRING DERIVED FROM FETAL AND ADULT MAMMALIAN-CELLS

Fertilization of mammalian eggs is followed by successive cell divisio ns and progressive differentiation, first into the early embryo and su bsequently into all of the cell types that make up the adult animal. T ransfer of a single nucleus at a specific stage of development, to an enucleated unfertilized egg, provided an opportunity to investigate wh ether cellular differentiation to that stage involved irreversible gen etic modification. The first offspring to develop from a differentiate d cell were born after nuclear transfer from an embryo-derived cell li ne that had been induced to become quiescent(1). Using the same proced ure, we now report the birth of live lambs from three new cell populat ions established from adult mammary gland, fetus and embryo. The fact that a lamb was derived from an adult cell confirms that differentiati on of that cell did not involve the irreversible modification of genet ic material required for development to term, The birth of lambs from differentiated fetal and adult cells also reinforces previous speculat ion(1,2) that by inducing donor cells to become quiescent it will be p ossible to obtain normal development from a wide variety of differenti ated cells.