Programmed cell death and Bcl-2 protection in the absence of a nucleus.

The molecular basis of programmed cell death (PCD) is unknown. An important clue is provided by the Bcl-2 protein, which can protect many cell types from PCD, although it is not known where or how it acts. Nuclear condensation, DNA fragmentation and a requirement for new RNA and protein synthesis are often considered hallmarks of PCD. We show here, however, that anucleate cytoplasts can undergo PCD and that Bcl-2 and extracellular survival signals can protect them, indicating that, in some cases at least, the nucleus is not required for PCD or for Bcl-2 or survival factor protection. We propose that PCD, like the cell cycle, is orchestrated by a cytoplasmic regulator that has multiple intracellular targets.