RT-PCR and protein expression analysis in GBM core- and p-CSC. (A-B) NOTCH1 and his gene target HES1 mRNA levels are highly expressed in p-CSC3 and p-CSC4 compared to relative counterparts c-CSC. C, EGFR mRNA expression results more abundant in c-CSC of cases 1-3-4, but in case 2 occurs the opposite. (D) Custom RNA macroarray analysis performed in the first three cases reveals the up regulation of several components of Notch pathway in p-CSC3, while the opposite was detected in Cases 1 and 2. (E) Western blot analysis of more relevant RTK in GBM: EGFR (p-EGFR), PDGFRα and β isoforms and the active Notch1 (NICD1), Notch ligand delta-like 1 (Dll1) and Notch1 gene target Hes1. PDGFRα abundance is an hallmark property of all p-CSC pools which suggests the presence of a cell subpopulation in p-CSC with probably distinct growth factor response. c-Myc is abundantly expressed in all pairs of CSC examined. Arrows denote the doublet of EGFR full-length and variant III. Error bars represent the mean ± SD (n = 3).