Ageing of human glial cells in culture: increase in the fraction of non-dividers as demonstrated by a minicloning technique.

A minicloning technique was used to analyse quantitatively the fraction of cells incapable of division in mass populations of human glial cells at various passage levels. The percentage of non-dividers rose from 18 to 73% between passages 11 and 40 at which further subcultivation of the mass culture became impossible. The non-dividers were predominantly arrested in G1; only a minor fraction of G2 arrested cells was established. Although not conclusive, the data suggest that commitment to irreversible loss of division potential increases as a function of the number of completed cell cycles which a glial cell has completed.