Programmed cell death

Programmed cell death (PCD; sometimes referred to as cellular suicide^[1]) is the death of a cell as a result of events inside of a cell, such as apoptosis or autophagy.^[2][3] PCD is carried out in a biological process, which usually confers advantage during an organism's lifecycle. For example, the differentiation of fingers and toes in a developing human embryo occurs because cells between the fingers apoptose; the result is that the digits are separate. PCD serves fundamental functions during both plant and animal tissue development.

Apoptosis and autophagy are both forms of programmed cell death.^[4] Necrosis is the death of a cell caused by external factors such as trauma or infection and occurs in several different forms. Necrosis was long seen as a non-physiological process that occurs as a result of infection or injury,^[4] but in the 2000s, a form of programmed necrosis, called necroptosis,^[5] was recognized as an alternative form of programmed cell death. It is hypothesized that necroptosis can serve as a cell-death backup to apoptosis when the apoptosis signaling is blocked by endogenous or exogenous factors such as viruses or mutations. Most recently, other types of regulated necrosis have been discovered as well, which share several signaling events with necroptosis and apoptosis.^[6]