Cellular Aging: Basic Phenomena
Changes In Cell Morphology And Contact, Senescence And Cell-cycle Progression, Growth Signals And Senescence
Development proceeds through many steps that ultimately produce germ (reproductive cells) and somatic (nonreproductive) cell lineages. The germ cell lineage population is potentially immortal, because the genes it carries can be passed on indefinitely. The somatic cells will ultimately age and die. Early studies by Carrel and coworkers suggested that, when isolated from organisms, individual somatic cells were immortal. This view remained prominent for many years, though subsequent studies showed that it was actually untrue.
Studies conducted in many laboratories have shown that after the migration of cells from tissue pieces into culture vessels there is a phase of rapid proliferation, followed by one of declining proliferative capacity, and ultimately a total loss of mitotic activity. Cultures that have entered this permanently quiescent state are termed "senescent." During this later nonmitotic phase, the cells change in size and morphology, become granular in appearance, and accumulate debris. The loss of proliferative capacity in human diploid cell culture populations is a well-regulated phenomenon. As populations of cells divide successive times, the generation time of the culture increases, and there is also failure of an increasing fraction of the population to replicate at all. There is strong evidence that substantial heterogeneity develops in populations of cells as they proliferate, with some members of the population exhibiting a high proliferative capacity while others are capable of only a small number of divisions.
Cellular senescence has been observed in a variety of cell types. Although the proliferative capacity differs between various types of cells, for any given cell type the proliferative capacity tends to be relatively constant. The inability of cell cultures to proliferate indefinitely is neither the result of technical difficulties nor of the depletion of essential metabolites. Hayflick and Moorhead (1961) concluded that the limited lifespan phenomenon observed in human diploid cells might be programmed, and/or that accumulation of genetic damage might limit proliferative capacity. They suggested that the limited proliferative lifespan of cell cultures was an expression of cellular aging in vitro.
- Cellular Aging: Cell Death - Cellular Senescence, Cell Death: Programmed, Apoptosis, And Necrosis, Cell Death Genes, Cell Death And Aging
- Cellular Aging
- Cellular Aging: Basic Phenomena - Changes In Cell Morphology And Contact
- Cellular Aging: Basic Phenomena - Senescence And Cell-cycle Progression
- Cellular Aging: Basic Phenomena - Growth Signals And Senescence
- Cellular Aging: Basic Phenomena - The Genetics Of Cellular Senescence
- Cellular Aging: Basic Phenomena - Cellular Senescence And Aging In Organisms
- Cellular Aging: Basic Phenomena - Donor Age And Proliferative Life Span
- Cellular Aging: Basic Phenomena - Biomarkers Of Cellular Aging In Vitro And In Vivo
- Cellular Aging: Basic Phenomena - Senescence And Differentiation
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