[Nature of the phenotypic variability of somatic cells in culture: stable and high-frequency phenotypic changes]

The properties of stable phenotypic variants that appear with low frequency are considered. The data are presented that these variants are associated with both mutational and epigenetic changes. The properties of high frequency phenotypic variants that really appear and/or are detected in cell populations are analyzed more in detail. These variants: 1) arise accidentally and independently on the selectivity agent; 2) reproduce the phenotype that was changed in the course of cell generations constantly; 3) the frequency of the arising of such variants does not, as a rule, increase under the mutagen pressure, and 4) site-specificity of high frequency of changes is typical for those variants. The high frequency of phenotypic alterations causes intraclonal heterogeneity of somatic cell populations. This heterogeneity cannot be elicited by manifold subcloning. The properties of genetic unstable variations and accessible expression of these variations in populations of somatic cells in culture are discussed. The arising of a number of variants detected with high frequency is concluded to be generally provided by unstable genetic alterations. These alterations are suggested to be a result of the insertion of mobile genetic elements.