Apoptosis: The history and trends of its studies.
Recent molecular studies have revealed genes which regulate cell death, especially apoptosis, or programmed cell death occurring in organogenesis during fetal life, for the maintenance of cell numbers in the body by balancing cell production with cell death, and in tumor cell turnover. As has been suggested, however, cell death is not a single entity, but is heterogeneous in morphological and metabolic mechanisms, circumstances of initiation and biological significance (Wyllie, 1981); it is at present difficult to understand the entire cascade of intracellular metabolism concerning apoptosis. The present review focuses on the description of precise morphological features characteristic of apoptosis with those of necrosis, particularly inward and outward blebbings of the cell membrane causing cell shrinkage. Special reference is given to inward blebbing, an event which has been shown in various physiological and pathological apoptotic cells. In this process, the blebs form numerous clear vesicles in the cytoplasm, which are degraded together with parts of the cytoplasm by autophagolysosomes. Analysis of the processes of the death of cells and the determination of whether it is apoptotic or necrotic in nature is important when considering the fact that the hindrance of apoptosis in embryogenesis may cause congenital disorders, whereas its prevention in pathological diseases may open the way to new therapies.
Uchiyama
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Department of Anatomy, Osaka University Medical School, Japan.
D000818:Animals; D017209:Apoptosis; D006801:Humans