In practice, persuading embryonic stem cells to differentiate into specific cell types has not proved straightforward. Researchers at the National Institutes of Health (Bethesda, MD) have now hit on a means of differentiating stem cells into the insulin-secreting cells of the pancreas, potentially providing material for islet transplants for people who have diabetes (Science 292, 1389–1394, 2001). Using a selected subpopulation of stem cells that had previously been thought to give rise to only neurons, the researchers chemically induced stem cells to differentiate into the pancreatic cells of the islets of Langerhans, which secrete the hormones insulin, somatostatin, glucagon, and pancreatic polypeptide. The islet cells released insulin in a glucose-sensitive manner and responded appropriately to insulin-modifying drugs. When injected into diabetic mice, the differentiated cells aggregated into structures not dissimilar to those created in situ in the pancreas. The islet cells secrete around 50 times less insulin than normal islets and so did not help lower the blood sugar concentration, but they controlled the animals' body weight and prolonged their life span.
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Fletcher, L. Islet transplants?. Nat Biotechnol 19, 535 (2001). https://doi.org/10.1038/89277