Apoptosis in preimplantation mammalian embryo and genetics

The presence of dead cells in the preimplantation mammalian embryo has been well described. Since Kerr et al. (1972), it has become apparent that thes e cells die by apoptosis, a form of programmed cell death. This review anal yses the recent morphological and biochemical evidence that apoptosis play a role in early mammalian embryo development. Normal and apoptotic (i.e. fr agmented) embryos express several apoptosis-related genes during mammalian preimplantation embryo development, with severe changes when apoptosis is a ctivated; these findings support a model in which mammalian preimplantation embryo development is regulated by the ratio of pro- and -anti- apoptotic genes. Apoptosis may be a normal feature in human preimplantation developme nt, even in vivo, and may play an active role in the developing embryo thro ugh the removal of genetically abnormal cells. Contrary to these beneficial effects, apoptosis may have detrimental effects if either the number of ap optotic cells or ratio of these cells to the normal cells is elevated. Acco rding to this value, embryos could either continue to develop or arrest.