Tetraploid Embryo Complementation

The method of tetraploid embryonic complementation serves to verify the pluripotency of stem cells. In this method, the cells of an embryo in the two-cell stage are joined by cell fusion into a single cell. That way two cells are turned into one cell with twice the chromosome count. Thanks to a henceforth tetraploid, i.e. fourfold chromosome count these cells are no longer in a position to form a complete living organism and can but merely differentiate into cells of the trophoblast, that is to the enveloping layer of the embryo in the blastocyst stadium, which later forms the placenta and the umbilical cord. To form a living organism, though, it also needs the inner cell mass of the blastocysts, the embryoblast. The cells of the embryoblast differentiate through the course of the embryogenesis into all kinds of tissue and, thus, form the actual embryo. If the trophoblast cells that were obtained as formerly explained are then supplemented by embryonic or induced pluripotent stem cells (a method also known as “sandwiching”) a viable embryo results from them. 

Stem Cells_Tetraploid Embryo Complementation.jpg
© Stammzellnetzwerk.NRW

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).

For the study see:

Boland, M. J. / Hazen J. L. / Nazor, K. L. / Rodriguez, A. R. / Gifford, W. / Martin, G. / Kupriyanov, S. / Baldwin, K. K. (2009): Adult mice generated from induced pluripotent stem cells. In: Nature 461(7260): 91-4. doi:10.1038/nature08310 Online Version 

For further information see:

Sgodda, S. (2014): Das Kriterium der Totipotenz aus naturwissenschaftlicher Perspektive. In: Heinemann, Thomas / Dederer, Hans-Georg / Cantz, Tobias: Entwicklungsbiologische Totipotenz in Ethik und Recht: Zur normativen Bewertung von totipotenten menschlichen Zellen. Göttingen: Vandenhoeck & Ruprecht. (German)

Zhao, X. / Li, W. / Lv, Z. / Liu, L. / Tong, M. / Hai, T. / Hao, J. / Guo, C. / Ma, Q. / Wang, L. / Zeng, F. / Zhou, Q. (2009): iPS cells produce viable mice through tetraploid complementation. In: Nature 461, 86-90. Online Version 

Kang, L. / Wang, J. / Zhang, Y. / Kou, Z. / Gao, S. (2009): iPS Cells Can Support Full-Term Development of Tetraploid Blastocyst-Complemented Embryos. In: Cell Stem Cell 5 (2), 135–138. Online Version 

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