Fig. 2

Label retention in CSC. (A) Schematic representation of label retention. A bulk population of tumor cells (a) is labeled with a vital dye so that all cells become labeled (b). During the following chase period, actively dividing cells (black nuclei) progressively lose the dye by diluting it to daughter cells (c,d). In contrast, CSC (blue nucleus), due to their slow cycling rate, retain the dye much longer and can thus be identified (d). (B) Label retention during sphere formation. When labeled, single CSC (a) are cultured under low-attachment conditions they undergo asymmetric division to generate another CSC and a progenitor cell (b). While the daughter CSC enters quiescence thus retaining the dye (b), the progenitor give rise to a progeny of proliferating cells (c), which form the bulk of sphere cells, in which the dye is progressively lost (d,e). The final result, as shown in (C), is a clonal sphere with only one or very few label-retaining CSC. The image shows a sphere from primary OC cells labeled with PKH26. Scale bar, 100 μm