The filtered single cell suspensions were stained with AZD4547 ic50 Trypan Blue. The living cells were counted, and primary culture was completed within 2 h, followed by inoculation in simplified serum-free medium (DMEM/F12, containing 2% B27, 20 μg/L EGF and 20 μg/L bFGF), and then culture at 37°C in 5% CO2 saturated humidity incubator. The medium was changed every 3~4 days. The cells were passaged by 1:2 subculture every 7 days and observed under the inverted phase contrast microscope. The cells were passaged three times.

After the cell spheres became regularly shaped, they were dissociated into single cells with 0.25% trypsin + mechanical Caspase pathway method, and inoculated into a 96-well plate at 1 living cell/well, with each well added with 100 μL simplified serum-free medium. The wells containing only one cell were labeled under the inverted microscope, and supplemented with 100 μL simplified serum-free medium for further culture.

The formation of single cell colonies was recorded by dynamic observation. The cells were observed under the inverted microscope CT99021 nmr after culture for about one week, and the proliferated cells were collected and transferred into a culture flask for further culture and proliferation. The purified BTSCs after colony screening were used in the following experiments.   (2) Immunofluorescent identification of BTSCs: On the 5th day of passage, BTSs that grew well were re-suspended in culture medium containing a small amount

of serum (DMEM/F12 containing 10%FBS), and dropped onto a poly-L-lysine-coated coverslip. After standing still for about 4 h until the solution adhered to the coverslip, the coverslip was fixed in 4% paraformaldehyde for 30 min, blocked with normal goat serum for 20 min, incubated with rabbit anti-human CD133 antibody overnight at 4°C, and then incubated with Cy3-labeled sheep anti-rabbit IgG at 37°C for 60 min, followed by DAPI counterstaining of the nuclei and coverslipping with buffered glycerol. Following each step, the coverslip was rinsed with 0.01 mol/L PBS three times, each for 5 minutes. The coverslip was observed after mounting and pictures were taken.   (3) Assessment of the effect of ATRA on proliferation of BTSCs: The BTSCs were collected and divided into groups as described below, put into the corresponding see more culture medium, disaggregated into single cell suspensions by mechanical dissociation, and inoculated into a 96-well plate at the density of 1000 living cells/well, with 100 Ml in each well. According to the different treatments, the BTSCs were divided into: (1) control group: basic medium (DMEM/F12 with 2% B27) containing the same amount of anhydrous ethanol as in the ATRA group (the final concentration < 0.1%); (2) ATRA group: containing 1 μmol/L ATRA; (3) ATRA/growth factor group: containing 1 μmol/L ATRA, and 20 μg/L EGF and 20 μg/L bFGF; (4) growth factor group: containing 20 μg/L EGF and 20 μg/L bFGF.