The specialized mitotic behavior of human embryonic stem cells.

Human embryonic stem cells (hESCs) are self-renewing and pluripotent cells that originate from the inner cell mass of the blastocyst. Mitosis is fundamental to organism survival and reproduction and is responsible for the equal distribution of duplicated chromosomes into daughter cells. Mitotic dysfunction is associated with a wide variety of human diseases, not least cancer. hESCs have a unique cell cycle distribution, but it is unclear exactly how the mitotic activity of hESCs is related to their proliferation and differentiation. Here, we established a cell line of hESCs stably expressing GFP-α-tubulin and mCherry-H2B by lentiviral infection to analyze and visualize mitosis in detail. During metaphase, the mitotic spindle was smaller and wider and contained a greater proportion of astral microtubules than normal cells. In addition, spindle microtubules were more stable, and chromosome alignment was faster in hESCs than in somatic cells. We also found that the spindle assembly checkpoint was functional in hESCs. These findings thus reveal a specialized mitotic behavior of hESCs.