The all-powerful potential of stem cells to become any kind of cell is what makes them so promising for restoring diseased or damaged tissues throughout the body—and also what makes them so difficult for scientists to control. But several breakthroughs represent major strides toward understanding and harnessing the cells' elusive property of inherent “stemness.”
Shinya Yamanaka of Kyoto University, who transformed a regular mouse skin cell into a cell with most of the characteristics of embryonic stem cells (ESCs) by turning up the activity of just four genes, demonstrated recently a more precise way of isolating cells “reprogrammed” to an ESC-like state—and several other laboratories have replicated his results.
Coaxing cultured ESCs to go in the opposite direction—to become skin cells or some other type of tissue—is a tricky process involving the cells’ own gene activity and signals from their surrounding environment. Peidong Yang of the University of California, Berkeley, and Bruce R. Conklin of the Gladstone Institute of Cardiovascular Disease in San Francisco showed a new way to deliver those external signals by growing ESCs embedded with nanoscale silicon wires. Yang and Conklin envision the technique being used to guide the differentiation of stem cells into specific tissue types through electrical pulses or chemicals transmitted via nanowires.
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As some researchers worked on controlling the differentiation of ESCs, others were focused on finding out what keeps adult stem cells in an undifferentiated state. Frank D. McKeon of Harvard Medical School showed last year that the activity of a single gene, known as p63, is the key to a cell staying a stem, at least in epithelial cell types, which include a variety of tissues such as skin, prostate, breast and thymus.
There is no shortage of adult stem cells for investigators who want to probe their relation to health and disease, but that is not true for ESC scientists who typically must first create embryos from hard-to-procure eggs. A technique for recycling unhealthy fertilized embryos, which have no other viable use, has promise as a source of ESCs for research. Kevin Eggan of the Harvard Stem Cell Institute and his team used aberrant embryos with extra chromosome sets—which can occur naturally during in vitro embryo creation when two sperm fertilize an egg—as stand-ins for the precious eggs. They found that when the chromosomes were removed and new genetic material introduced, the resulting embryo developed successfully about as often as embryos made from eggs and yielded stem cells that were apparently normal.