Grotesque manipulations are possible, to be sure: imagine chimeric mice with nascent human brain cells developing within their tiny skulls.

The general methods for creating chimeric mice can be summarized either by injection or aggregation of embryonic cells from different origins.

The first chimeric mouse was made by Beatrice Mintz in the 1960s through the aggregation of eight cell stage embryos.

Since this discovery occurred in 1999, ES cells have become a key tool in the generation of specific chimeric mice.

Finally, chimeric mice where the modified cells make up the reproductive organs are selected for breeding.

Unfortunately, two of the four genes used (namely, c-Myc and KLF4) are oncogenic, and 20% of the chimeric mice developed cancer.

To generate chimeric mice the embryos were allowed to develop to term.

The result is a chimeric mouse, which develops with a portion of its cells containing the ES cell genome.

Groα/MGSA and IL-8 have also been shown to enhance re-epithelialization of human skin grafts in chimeric mice [ 29 38 ] .

Transgenic mice and embryos can be generated from these ES cells by standard injection into blastocysts and subsequent breeding of the resulting chimeric mice.