Showing papers on "Apoptosis published in 1982"

Hormone-induced cell death. Purification ad properties of thymocytes undergoing apoptosis after glucocorticoid treatment.

Abstract: A high proportion of cortical thymocytes obtained from suckling rats undergo apoptosis on exposure in vitro to the glucocorticoid methylprednisolone. The apoptotic cells can be separated from apparently normal thymocytes by isopyknic centrifugation on Percoll gradients. This experimental system provides homogeneous populations of apoptotic cells and thus permits a more incisive study of this physiologic mode of cell death than has been hitherto possible. It is shown that apoptosis involves a sharp but transient increase in buoyant density, concomitant with the appearance of characteristic morphologic changes in nucleus and cytoplasm. More than 80% fo the chromatin of apoptotic cells has a molecular weight sufficiently low to resist sedimentation at 27,000g and consists of short oligonucleosome chains, apparently as a result of endogenous endonuclease activity. By contrast, the chromatin of thymocytes that retain normal density (whether treated or control) is of high molecular weight. Apoptotic cells, unlike those of normal density, show little or no incorporation of nucleosides and amino acids into macromolecules. These investigators were unable to detect populations of cells intermediate between apoptotic and normal in buoyant density, morphologic characteristics, chromatin cleavage, or leucine incorporation, but evidence is presented suggesting that thymidine and uridine incorporation may fall prior to development of apoptosis.

Intestinal Cell Radiosensitivity: A Comparison for Cell Death Assayed by Apoptosis or by a Loss of Clonogenicity

Abstract: SummaryApoptotic and reproductive cell death have been assayed in the crypt of the small intestine. These two approaches result in survival curves with mean lethal doses (D0) that differ by a factor of 10. Widely differing doses and times of assay post-irradiation were used for the assays employing apoptosis in one case and clonogenicity in the other. The results obtained by the two approaches are compared. It is concluded that the cells that die via apoptosis represent a very sensitive subpopulation of the crypt (about 6 cells per crypt) that may or may not be clonogenic. Most clongenic cells die at a later time by some other mechanism. If the apoptoses represent dead clonogenic cells they must be either a very sensitive subpopulation or, as deduced here, a subpopulation which is part of a uniformly resistant population of cells when clonogenicity is considered, but which is very sensitive to an early form of death.