Death in embryonic systems.

The principal conclusion to be drawn from the foregoing discussion is that the death of cells and the destruction of tissues, organs, and organ systems are programmed as normal morphogenetic events in the development of multicellular organisms. Death in embryonic systems may thus be explored within the same conceptual framework as growth and differentiation. The present exploration has revealed that death during embryogenesis serves utilitarian goals in some instances, at least, that its occurrence is subject to control by factors of the immediate cellular and humoral environment, and that aberrations in its normal pattern of expression provide the mechanism for realization of many mutant phenotypes. Hopefully, it has also pointed toward the appropriate formulation of some of the problems that confront us in understanding the control of death at the level of genetic transcription, the biochemical events which determine and accompany its occurrence, and the pathways of disposition and the developmental significance of disassembled cellular building blocks.