¾«¶«´«Ã½

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 – the body’s way of getting rid of damaged or redundant cells.

“That’s when I ran into the most confusing result,” he says. Although the cells had high levels of caspase activity, few of them were actually dying, he told a recent stem-cell meeting in Boston.

To double-check his results, Zwaka looked for, and found, two other signs of cell suicide: the presence of a chewed-up protein called PARP-1, which is abundant in suicidal cells, and the shutting down of the power factories in cells, the mitochondria, indicated by the depolarisation of their membranes.

Zwaka speculates that the process of self-renewal may have evolved alongside cell death, and some of the processes may be the same.

The fact that signs thought to be characteristic of cell suicide appear in cells that are not dying might force a lot of researchers to re-examine their work, says stem-cell researcher Margaret Goodell from the Baylor College of Medicine in Houston, Texas. “I think it is potentially incredibly exciting.”