PROM1 and glioblastoma: Both types of GSCs, NCH421k and NCH644, expressed high gene expression levels of PROM1, OLIG2, NOTCH, SOX10 and SOX2 that are established GSC markers.4,37,45 Differentiation marker tubulin beta-III (TUBB3) was expressed in the highest levels in differentiated GBM cells NIB140 (Figure 1).