Cautious apoptosis

It is not easy to convince sympathetic neurons to commit suicide. Potts et al. (page 789) now show that a caspase inhibitor called XIAP acts as a safety brake so that these terminally differentiated cells do not take the death decision too lightly.

Earlier studies established that injection of cytochrome c, which is normally released from mitochondria to activate caspases and thus apoptosis, can kill most cell types but not sympathetic neurons. This resistance can be overcome by coinjection with excess Smac, which shuts down caspase inhibitors including XIAP. Potts et al. now show that cells lacking XIAP no longer need Smac, and succumb to cytochrome c injection alone.

This clean result from a single gene deletion was surprising because there are a number of XIAP-like inhibitors, or IAPs, that have until now been largely undifferentiated....