Some of the ES cell-derived neuronal colonies still contain at day 14 OCT3/4 and Ki67-positive cells.

<p>(A) After 14 days of differentiation culture few colonies (less than 5%), as exemplified here, still contain OCT3/4-positive cell clusters as detected by immunofluorescence staining using a specific mAb (magnification 40×). (B) The same colony was stained by an anti-Ki67 mAb to detect proliferating cells. (C) The merged staining indicates that Ki67-positive proliferating cells exist which are not OCT3/4-positive stem cells. (D) In parallel, cells of the neuronal differentiation culture were stained at day 14 by anti-Ki67 and anti-Tuj1 mAb. The merged staining (magnification 20×) indicates that the vast majority of the cells are Tuj1-positive neuronal cells. Few Ki67-positive proliferating cells are negative for the neuronal cell marker.