EN
Studies aimed at improving the effectiveness of cloning by nuclear transfer have shown that proper development of the majority of reconstituted embryos is secured by G1 phase of the donor nucleus or by using 'universal recipients' i.e. enucleated pre-activated oocytes. Donor nuclei for cloning may by derived from cell lines of embryonic stem cells (mouse), embryonic cells after short in vitro culture (sheep, pig, cattle) or even from fetal cells or adult cells after in vitro culture and inducing quiescence in their nuclei (sheep). The use of fetal cells for transgenesis in vitro and the production of transgenic sheep after nuclear transfer from these cells opens the way to profitable technology of cloning transgenic farm animals.