Above, from left: Xu Luo, Xiaodong Wang, and Imawati Budihardjo.
In apoptosis, death signals from outside a cell are conveyed to various organelles inside a cell through an intricate network of molecules acting as messengers. These two Cell papers outline two independent identifications of a critical missing link in this signaling pathway. They show that the cytosolic protein Bid carries a death signal from the cell membrane to the mitochondria. Identifying Bid's signaling role allowed researchers to connect two existing stories into one big picture.

Researchers had a good idea of what happens before the death signal reaches the mitochondria. Activation of the Fas and tumor necrosis factor (TNF) death receptors on the cell surface leads to activation of caspase 8 (Casp8). Caspases cleave proteins involved in apoptosis. Researchers also had a handle on cellular events occurring after mitochondria receive the apoptotic signal. The mitochondrial outer membrane becomes permeable to...

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