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 endocytosis and vesicle formation. In a healthy cell, Drp1 loiters in the cytosol and regulates the division of mitochondria. But the authors found that during apoptosis, Drp1 swarms to the mitochondria, concentrating at the sites where the organelles tend to cleave. Youle believes that these Drp1 complexes hasten mitochondrial breakup. Blocking Drp1 not only slows the splitting of mitochondrial networks, it also prevents release of cytochrome c and thwarts apoptosis. The researchers plan to probe how Drp1 works and why its actions change once apoptosis begins. “It works in healthy cells to regulate mitochondrial dynamics,” Youle says, “the question is how does it change from its normal function to its proapoptotic function.” ▪


Frank, S.,...

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