Dodecaploid H1 embryonic stem cells abolished pluripotency in L15F10 medium both with and without leukemia inhibitory factor.

Two lines of dodecaploid H1 embryonic stem cells, 12H1 and 12H1(-) cells (mouse-originated cells), were established through polyploidization of two hexaploid H1 cells, 6H1 and 6H1(-) cells, which were cultured in L15F10 (7:3) medium with and without leukemia inhibitory factor (LIF), respectively. The G1, S, and G2/M phase fractions of 12H1 and 12H1(-) cells were almost the same as those of 6H1 and 6H1(-) cells, respectively, but the doubling time of cell proliferation was prolonged, suggesting that cell death occurred in 12H1 and 12H1(-)cells. The cell volumes of 12H1 and 12H1(-) cells were about double those of 6H1 and 6H1(-) cells, respectively. 12H1 and 12H1(-) cells showed near-negative activity of alkaline phosphatase and no ability to form teratocarcinomas in mouse abdomen, suggesting that 12H1 and 12H1(-) cells lost pluripotency. The DNA contents of 12H1 and 12H1(-) cells decayed in long-term culturing, suggesting that 12H1 and 12H1(-) cells were DNA-unstable. Possible explanations for the lost pluripotency and for the DNA decay in 12H1 and 12H1(-) cells are presented.