WHEN a young researcher recently took a closer look at embryonic stem cells, he made an astonishing finding: according to his results, the vigorously growing cells he was looking at should have been dead or dying. “I didn’t anticipate this,” says Thomas Zwaka, who works in the lab of James Thomson at the Wisconsin National Primate Research Center in Madison.
Zwaka had tested the embryonic stem cells (ESCs) for the presence of enzymes called caspases, proteins that chew up the cell from within. Their presence is usually considered a sure sign that cells are undergoing programmed suicide, or apoptosis –…
