Generation of germ-line competent induced pluripotent stem cells

We have previously shown that pluripotent stem cells are induced from mouse fibroblasts by retroviral introduction of Oct3/4, Sox2, c-Myc and Klf4, and subsequent selection for Fbx15 expression. These iPS (induced pluripotent stem) cells are similar to embryonic stem (ES) cells in morphology, proliferation and teratoma formation. Fbx15-iPS cells, however, are different in gene expression and DNA methylation patterns and fail to produce adult chimeras. Here we show that selection for Nanog results in germ-line competent iPS cells, with more ES cell-like gene expression and DNA methylation patterns. The four transgenes were strongly silenced. We obtained adult chimeras from seven Nanog-iPS clones, with one clone transmitted through the germ-line to the next generation. Approximately 20% of the offspring developed tumors, where c-Myc transgene was reactivated. Thus iPS cells competent for germ-line chimeras can be obtained from fibroblasts, but retroviral introduction of c-Myc should be avoided for clinical application. Keywords: cell type comparison