To examine the alteration in cellular characteristics of polyploid embryonic stem (ES) cells during long-term culturing without leukemia inhibitory factor (LIF), mouse diploid and tetraploid H-1 (ES) cells (2H1 and 4H1 cells, respectively) were cultured without LIF for approximately 5 months. 2H1 and 4H1 cells were adapted to the medium without LIF by decreasing the concentration for several passages, and they were denoted as 2H1(⁻) and 4H1(⁻) cells, respectively. DNA content of 4H1(⁻) cells decreased gradually in the early stage, increased abruptly in the second stage, and then was maintained for a long time. 4H1(⁻) cells exhibited longer doubling time and equivalent phase fraction compared with those of 2H1(⁻) cells. The G₁ phase fractions of 2H1(⁻) and 4H1(⁻) cells were increased compared with that of 2H1 cells. Cellular morphology and pluripotency were maintained in 4H1(⁻) cells but not in 2H1(⁻) cells. 2H1(⁻) cells showed a cell population consisting of several kinds of cells, and they lost alkaline phosphatase activity, suggesting that the cells had differentiated. 4H1(⁻) cells, however, exhibited alkaline phosphatase activity and formed teratocarcinoma in mouse abdomen, suggesting that the cells maintained their pluripotency in the medium without LIF.
2010 The Authors. Human Cell 2010 Japan Human Cell Society.