DNA Loss and Related Alterations in Long-term Cultures of Diploid, Tetraploid and Octaploid Meth-A Cells

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The DNA content of polyploid cells sometimes decreases during subculturing. The mechanism of DNA reduction is not yet known. Precise measurements of DNA decay and related alterations in polyploid cells will be required to understand the mechanism. Diploid, tetraploid and octaploid Meth-A cells were continuously cultured for 244 d and the cellular DNA content was measured from the DNA histograms. The DNA content decays gradually with day t as expressed by f(t)=Ip exp{−G(t)}, where Ip is the initial ploidy, G(t)=at/{exp(−bt)+ct}, and a, b and c are the following parameters: a=0.026, b=0.01 and c=0.0175 (for tetraploid cells) or c=0.01 (for octaploid cells). The DNA content of diploid Meth-A cells was constant within the experimental errors. The DNA loss of polyploid cells was confirmed by a decrease in chromosome number. The cellular morphology changed in diploid and octaploid Meth-A cells, but not in tetraploid cells, suggesting that DNA loss and morphology alteration are independent. The doubling time shortened with culture time in the tetraploid and octaploid cells. The findings suggested that chromosomes are not independent in polyploid cells.
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