Pluripotency of a polyploid H1 (ES) cell system without leukaemia inhibitory factor

Objectives: Tetraploid cells are strictly biologically inhibited from composition of embryos; by the same token, only diploid cells compose embryos. However, the distinction between diploid and tetraploid cells in development has not been well explained. To examine pluripotency of polyploid ES cells, a polyploid embryonic stem (ES)‐cell system was prepared. Materials and methods: Diploid, tetraploid, pentaploid, hexaploid, octaploid and decaploid H1 (ES) cells (2H1, 4H1, 5H1, 6H1, 8H1 and 10H1 cells, respectively) were cultured for about 460 days in L15F10 medium without leukaemia inhibitory factor (LIF). The cells cultured under LIF‐free conditions were denoted as 2H1(?), 4H1(?), 5H1(?), 6H1(?), 8H1(?) and 10H1(?) cells, respectively. Pluripotency and gene expression were examined. Results: Ploidy alteration of H1(?) cells was similar to that of H1 cells. The polyploid H1(?) cells showed positive activity of alkaline phosphatase, suggesting that they maintained pluripotency in vitro without LIF. The polyploid H1(?) cells formed teratocarcinomas in mouse abdomen, suggesting they could differentiate in mouse abdomen in vivo. 2H1, 4H1 and polyploid H1(?) cells expressed nanog, oct3/4 and sox2 genes, suggesting that they fulfilled the criteria of ES cells. Nanog gene was significantly over‐expressed in 4H1 and polyploid H1(?) cells, suggesting that overexpression of nanog gene was a characteristic of polyploid H1 cells. Conclusion: Polyploid H1 (ES) cells retained pluripotency in vitro, without LIF with nanog over‐expression.