Fig.: Schematic illustration of tetraploid embryo complementation. (Graphic reproduced by kind permission of Stem Cell Network.NRW)

In early experiments performed with ES cells, some of the introduced pluripotent stem cells were found later on not only in the embryoblast, but also in the trophoblast. In this sense some researchers speak hence of a totipotency of these special cells in a limited manner.

By applying this method to mice, it was shown that complete organisms could emerge from induced pluripotent stem cells (iPS cells). Michael J. Boland, Jennifer L. Hazen and Kristopher L. Nazor from the Scripps Research Institute published a study in Nature in 2009 in which fibroblast cells of mice were used to prove that iPS cells could develop into all kinds of cell and could, through the help of the method of tetraploid embryonic complementation, evolve into a complete organism. At first cells of an embryo of a donor were fusioned. Pluripotent stem cells were then attached to the tetraploid cells that had been obtained using iPS technology. These, in turn, build the inner cell mass of the blastocysts, i.e. the embryoblast. These henceforth complete embryos were then transferred to the surrogate mice and some of them grew into viable mice and were born. Using the tetraploid complementation the limited efficiency of the nucleus transfer, a key hindrance for hitherto established cloning techniques, is avoided.

The process of tetraploid embryo complementation was originally developed to produce transgenic knockout mice. (See also the In Focus section on Animals in Research).