Serum-differentiated GBM cells can revert back to an undifferentiated state and re-acquire stemness.

<p><b>a.</b> Serum-differentiated GSC23, GG1, GG9, GG14 and GG16 (primary) neurospheres (Nsp) reverted back to (secondary) neurospheres following exposure to neural stem cell medium (NSM). <b>b.</b> Quantification of the size of primary and secondary GG9 and GG16 neurospheres. (***<i>P</i><0.001). <b>c.</b> Western blot showing the expression level of GFAP in undifferentiated (primary Nsp), differentiated and de-differentiated (secondary Nsp) GG9 and GG16 cells. <b>d.</b> Limiting dilution assay showing the reduction in the neurosphere formation potential in GSC23, GG9, GG14 and GG16 following differentiation. Data represent the means ± SEM of 3 independent experiments and neurospheres were counted from 96 wells in each experiment (**<i>P</i><0.01, ***<i>P</i> < 0.001).