Cell-cycle-dependent Ca2+ transients in human induced pluripotent stem cells revealed by a simultaneous imaging of cell nuclei and intracellular Ca2+ level

Abstract

Cell cycle phase and [Ca2+]i are key determinants of self-renewal and differentiation in pluripotent stem cells. However, little is known about their relationship in human pluripotent stem cells owing to the lack of an effective method. Here, we applied an imaging-based approach for evaluating the relationship between the cell cycle and Ca2+ transients in human induced pluripotent stem (iPS) cells. Ca imaging and DNA staining was simultaneously performed at the same site. Then, individual cells were recognized and the cell cycle phase was estimated from the image of nuclei. We found that 18 ± 4% of human iPS cells exhibited spontaneous Ca2+ transients and their inter-transient interval was 119 ± 19 s. Ca wave events were observed in 64% of the sample and the [Ca2+]i elevation propagated among 47 ± 30 cells with a duration of 57 ± 22 s. With the imaging-based approach, we demonstrated that the ratio of cells exhibiting Ca2+ transients significantly decreased during cell cycle progression, suggesting that the relationship previously described in mouse cells holds true in the human context as well. These results suggest that our method is suitable for evaluating Ca2+ transients, the cell cycle phase, and their relationship with densely cultured cells.