Analysis of the developmental potential of R545-1 ES cells. (a) A hatching blastocyst derived from a breast cancer cell by nuclear transfer shows a blastocoel cavity, trophectoderm layer, and an inner cell mass. (b,c) H&E staining of teratoma sections produced from R545-1 ES cells shows differentiation into mature neurons, mesenchymal cells, and squamous epithelium (b), and columnar epithelium, chondrocytes, and adipocytes (c). (d–f) Contribution of GFP-labeled R545-1 ES cells to newborn chimeras. Shown on top are the GFP images of the head (d), heart (e), and intestine (f) of one chimera. Below are the same images under phase contrast. (g) FACS analysis of peripheral blood of a Rag2/R545-1 ES cell chimera shows the presence of B cells using antibodies FITC-IgM/PE-B220 and T cells using antibodies FITC-CD4/PE-CD8. (h) Contribution of R545-1 cells to the skin indicates differentiation into melanocytes. Arrows depict spontaneous development of tumors on the eye and neck of chimera #1 (see ). (i) Embryos produced entirely from ES cells by tetraploid complementation develop to E9.5 with obvious tail and limb buds, a closed neural tube, and a beating heart.