Programmed cell death (apoptosis) in murine blastocysts: extracellular free-radicals, polyamines, and other cytotoxic agents.

Programmed cell death can also be caused by extracellular, soluble factors, some of which are not physiologic. In vivo in the murine blastocyst, apoptosis eliminates redundant cells of unneeded phenotypes (pre-trophectoderm) from the inner cell mass. Although only a few cells die and many survive, all of the cells are exposed to the extracellular H2O2 in blastocele fluid. The specific control of life versus death is due to the developmental expression of glutathione-dependent protective mechanisms in the surviving cells. Based on recent results, a model is proposed in which apoptosis and necrosis reflect different temporal points along a single cell death program.