ISSN:0304-324X    

DOI:10.1159/000212163

出版商:S. Karger AG    

年代:1976

数据来源: Karger

ISSN:0304-324X    

DOI:10.1159/000212121

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

For logarithmically growing cultures of the human diploid cell lines WI-38 and WI-26, there is an exponential increase in the fraction of cells not incorporating [3H]dT under conditions of continuous labelling. Thymidine uptake, phosphorylation and incorporation into DNA can be correlated with cell proliferation. In addition, determination of the labelling index is reproducible within relatively broad limits of thymidine concentrations and specific activity. The plateauing phenomenon of the curve expressing percent-labelled nuclei versus time, which occurs in populations with less than 100% cycling cells, is largely due to radiation damage to the cells. The results of these studies provide insight into the population dynamics of aging fibroblast-like cell cultures. More importantly, however, the measurement of labelling index as described can be used as a reproducible and quantitative measure of the age of the diploid cell culture.

ISSN:0304-324X    

DOI:10.1159/000212122

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

The experimental evidence is reviewed which bears on the theory that aging in mammalian cells may be related to a decline in the efficiency of normal DNA repair processes. Although the data are as yet fragmentary, they do suggest that there is an age-associated decline in the capacity of cells to perform at least certain types of repair. This is particularly noticeable in human diploid cells as they reach terminal senescence in vitro. Whether this decline is causally related or even contributory to normal aging remains, however, an open question.

ISSN:0304-324X    

DOI:10.1159/000212123

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

For the biosynthesis of macromolecules in amounts sufficient for indefinite growth or survival in dividing as well as in nondividing metazoan cells, a specific serum protein is required. As the addition of this factor to the medium triggers off a chain of events which leads to RNA, DNA, and protein synthesis, we have called it the pleiotropin. Pleiotropin is taken into the cells by pinocytosis. Pinocytic uptake of pleiotropin is strongly inhibited by a mutual cell-to-cell contact; diploid cells in the stage of contact inhibition of pleiotropin pinocytosis are nutritionally limited, and some changes in life processes may be expected. In continuous culture and in tissues in vivo, these changes may accumulate and ultimately result in an irreversible damage of cells so that old cells are characterized by a low pinocytic activity and by a reduced formation of macromolecules. As pleiotropin increases the saturation density and prolongs the life span of diploid cells in vitro, it is suggested that the loss of division potential in metazoan cells is not a programmed event at the cellular level and that the ageing of static cell populations may be caused by the same nutritional deficiency as that of proliferating cells.

ISSN:0304-324X    

DOI:10.1159/000212124

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

The prolongation of the life span of human fibroblasts in vitro by hydrocortisone seems to be associated with its stimulatory action on ribosome synthesis. The sustaining effect of the hormone on the latter remains, after withdrawal of hydrocortisone, for a time which is dependent on the age of the cells. When hydrocortisone is removed from cultures that have grown beyond the life span of the controls, the cells die within two passages. Hence, the events leading to the growth decline took place in spite of the presence of the hormone which does not seem to prevent the aging process but rather to delay it. The results could be compatible with either the error hypothesis or the theory which explains aging by an increased binding of histones to DNA with the subsequent blocking of genetic information.

ISSN:0304-324X    

DOI:10.1159/000212125

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

This review discusses the molecular and cytokinetic aspects of cellular aging of human diploid fibroblasts. Despite a large amount of data, the basis of their limited life span has not been defined. A replicative defect in aging cells lies in the mechanism(s) that initiates DNA synthesis, and the control of this mechanism(s) is mediated through an alteration in the synthesis of specific RNA and protein molecules. Two major groups of hypotheses have been offered to explain these findings. The differentiation hypotheses are based on the concept of a ‘biological clock’, while error hypotheses presuppose defects in genetic transcription or translat

ISSN:0304-324X    

DOI:10.1159/000212126

出版商:S. Karger AG    

年代:1976

数据来源: Karger

ISSN:0304-324X    

DOI:10.1159/000212127

出版商:S. Karger AG    

年代:1976

数据来源: Karger

ISSN:0304-324X    

DOI:10.1159/000212120

出版商:S. Karger AG    

年代:1976

数据来源: Karger