Each well was added with 20 μL simplified serum-free medium every other PLX4720 day, and the BTS formation was

observed. The sphere formation and growth rate were observed at specified times every day, and the emergence of regularly-shaped BTSs (containing over 10 cells) was considered as positive result. The time required for BTS formation and the number of BTSs were recorded and used to calculate the percentage of BTS and the time for colony formation. The formed BTSs were dropped on PLL-coated coverslips to be dried for CD133 immunofluorescence staining as described previously.   3 Statistical analysis All experimental data were expressed by mean ± RAD001 mouse standard deviation ( ± s). The software click here of SPSS version 16.0 was used for data analysis. An independent t-test was conducted for comparison between groups, and one-way ANOVA with Dunnett t test was used to compare the growth curves of different groups. P ≤ 0.05 was considered statistically significant. Results 1 BTS formation from proliferation of a single BTSC The whole process of BTS formation from the proliferation of a single BTSC by limited dilution could be observed under the inverted microscope (Fig. 1). After 1-2 days of inoculation, it could be observed that the single cells splitted to form cell colonies consisting of 2~several cells. The cells in the colonies were round, with similar

size. After 2~3 days, more cells formed colonies, and 4~5 days later, cell spheres composed of dozens to hundreds of cells were observed. The cell spheres were spherically shaped or elliptically shaped, with uniform structures and high transmittance. BTSCs are different from ordinary tumor cells due to their self-renewal and proliferation potential, and CD133 plays an important role in identifying

whether BTSCs have the characteristics of stem cells, so cell spheres formed from the proliferation of a single cell were stained with CD133. It can be found that cell spheres were CD133 positive (Fig. Unoprostone 2), proving that the cultured cell spheres were composed of BTSCs with characteristics of stem cells. They could now be called BTS, which was the colonial sphere of a great number of sub-cell lines from the same cell, so the proportion of non-BTSCs was low, and the purity was high. Figure 1 BTS resulting from the proliferation of a single BTSC(Inverted phase-contrast microscope, × 400). 1A:an hour after inoculated. 1B: 12 hours after inoculated. 1C: 24 hours after inoculated. 1D: 3 days hours after inoculated. Figure 2 Immunofluorescent identification of BTSCs for CD133 (Cy3, × 200). 2A: DAPI. 2B:CD133. 2C:Merge. It showed the cell spheres were CD133 positive. 2 Proliferation of BTSCs promoted by ATRA BTSCs in the growth factor group began to proliferate after 1~2 days of culture, forming cell spheres composed of 10~20 cells. The cells exhibited rapid suspended growth thereafter, and the cell spheres gradually got larger.