Mitotic clock

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The use of a structural alteration to the cells DNA to program in the number of mitoses since original stem/gamete cell division. The cell could then have mechanisms to detect such changes which might then activate apoptosis, specific differentiation or cell senescence.

There are a number of ways that this could happen but the presently understood prime mechanism is through telomere shortening which has also been termed Olovnikov's clock. Transformed cells, cancer cells, stem cells (including gamete germ cell progenitors) are thought to be able divide indefinitely due to reactivation of human telomerase reverse transcriptase which prevents 'fraying' of the telomeres.

The maximum number of cell divisions for a given cell in vitro is termed the Hayflick number, which is approximately 50.

The mitotic clock is not the only way the human organism regulates cell differentiation and apoptosis but clearly is a mechanism that will dissociate chronological age from biological age.

Historical

This concept was first proposed by Alexey M. Olovnikov in 1971[1] and explained in the english literature in 1973[2].

References

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