(A) Western blot analysis shows significantly higher pS6 activation and lower Myc expression in HN CSC lines than in HH and Myc^T58A CSC lines. (B) Western blot analysis shows significantly higher pS6 activation and, on average, lower Myc expression in tumors derived from the implantation of HN CSC lines compared with those from HH and Myc^T58A CSCs. (C) H&E staining showing classic features in HH CSC–derived MB, such as small cells intermingled with extensive neuropil (CSC line LB). Tumors from a subset of HH (CSC line L84) and from Myc^T58A CSC lines (CSC line ML9) are endowed with LC/A characteristics, such as nuclear molding, prominent nucleoli, and apoptosis; in both cases, pS6-IR cells are few (cytoplasmic staining, brown) and are double-labeled with IRF8, indicating that they are tumor stromal cells (pS6, cytoplasmic staining, blue; IRF8, nuclear staining, brown). c-Myc (nuclear staining, brown) is lowly expressed in classic HH CSC–derived tumors, whereas it is very highly expressed in LC/A tumors derived from a subset of HH (CSC line L84) and from Myc^T58A CSC lines (CSC line ML9). All scale bars: 50 μm. (D) Tumors from HN CSCs (CSC lines L83 and L66) show LC/A traits, such as increased nuclear pleomorphism, presence of large cells, and high level of cellular atypia. pS6 is hyperactivated in tumor cells (cytoplasmic staining, brown), as demonstrated by the absence of colabeling of pS6⁺ cells (cytoplasmic staining, blue) with IRF8 (nuclear staining, brown). c-Myc expression is found in medium-to-high number of cells. All scale bars: 50 μm. (E) Quantification of the level of marker expression is shown in the graphs. Quantitative data are presented as floating bars from minimum to maximum values, line at mean. One-way ANOVA followed by Tukey’s multiple comparison test. See Supplemental Table 5 for detailed statistical analysis.