Credit: ELSEVIER

Cell Stem Cell 4, 381–384 (2009); Cell Stem Cell 4, 472–476 (2009)

In 2006, researchers made cultured skin cells behave like embryonic stem cells by adding a handful of genes. But the method by which they inserted the genes — using viruses — can turn cells cancerous.

This year, two groups accomplished the same feat by delivering just the protein products of these genes into cells. Sheng Ding at the Scripps Research Institute in La Jolla, California, and his colleagues converted mouse embryonic fibroblasts into embryonic-like stem cells by using the bacterium Escherichia coli to engineer modified versions of the proteins that could cross the cellular and nuclear membranes. The cells (pictured green) were able to incorporate into early mouse embryos.

Meanwhile, Robert Lanza of Stem Cell and Regenerative Medicine International in Worcester, Massachusetts, Kwang-Soo Kim of Harvard Medical School in Boston, Massachusetts, and their colleagues reprogrammed human fibroblasts. They used a human cell line to generate the proteins, fused with a cell-penetrating peptide.

These papers are just two from this year that improved methods of stem-cell reprogramming.