Cell Culture Journals

Cell culture is the complex process by which the cells are grown under controlled conditions.A consistent presence of floating cells is a common phenomenon in cultures of human embryonic stem cells(hESCs). However, little attention has been paid to their existence. It is currently believed that unavoidableimperfections in culture conditions lead the cells to undergo senescence and apoptosis resulting in unattached cellsfloating in the culture medium. Inspired by recent studies on mitotic activities in human embryonic stem cell colonies,we believe the existence of floating cells is not simply the result of unfavorable growth conditions but an intrinsicphenomenon resulted from maintaining the pluripotency of hESCs under the culture conditions.We tested thishypothesis with a set of systematic experiments and discovered: 1) the ratio of floating cells to attached cells wassignificantly increased with culture time; 2) the number of floating cells could be manipulated. For example, we wereable to reduce the number of floating cells by providing the colonies with more horizontal or vertical cultural spacesand maintaining the cells’ pluripotency. The results open a new avenue to increase the stem cell culture efficienciesby rescuing the floating cells. On the other hand, by placing a physical barrier on the top of colonies, the number offloating cells was decreased, at the same time, hESCs also showed signs of differentiation. In addition, wheninducing cells to differentiate with retinoic acid, the number of floating cells no longer increased with prolongedculture time. Taken together, these results suggested that continuous cell division across the colonies is responsiblefor the emergence of floating cells during hESC culture. This is quite different from the bacterial colony growth wherethe cells in the center of colonies are quiescent. Our results indicated that continuous cell division, even at the costof floating cells formation, is essential for human embryonic stem cell proliferation.(Chen L, Jin Q, Gong Jand Krishna Dasa SS, The Nature of Floating Cells in Human Embryonic Stem Cell Culture)

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Last date updated on April, 2024