A fatal break up

Apoptosis can be short-circuited by inhibiting a protein that stimulates mitochondria to split. The finding suggests that mitochondrial fission is indispensable for programmed cell death.Most mitochondria are not the solitary, kidney bean–shaped objects you see in the textbooks, says Richard Youle (National Institute of Neurological Disorders and Stroke, Bethesda, MD). Instead, the organelles have an active social life, often linking up to form long, interconnected chains, and then sometimes splitting apart again. During apoptosis, however, networks of mitochondria shatter into small, “punctiform” blobs. The mitochondria of a dying cell also spill their guts, dumping proteins such as cytochrome c that further drive apoptosis.

To discover what spurs mitochondrial fission, Youle and colleagues focused on a protein called Drp1, a member of a class of proteins known as dynamins that are involved in...