Pax3 promotes proliferation in vitro and brainstem gliomagenesis in vivo in the absence of p53. a-d Brainstem progenitor cells from P3 Ntv-a;p53fl/fl mice were cultured in vitro, infected with the indicated RCAS viruses, and assayed for (a) Caspase 3/7 activity at 72 hours after plating, normalized to Cre + RCAS-Y, (b) BrdU incorporation at 72 hours after plating, normalized to Cre + RCAS-Y, p = 0.0007 paired t-test, and (c-d) cell number at the indicated time points after plating. c One representative experiment conducted in one progenitor line. d The fold change in Cre + Pax3 cells over Cre + RCAS-Y cells at each time point compiled from multiple progenitor lines, p = 0.03 (day 4), p = 0.005 (day 5), p < 0.0001 (day 6), paired t-test. e Kaplan-Meier survival curve of Ntv-a;p53fl/fl mice (Control) and Ntv-a;p53fl/fl;Pax3fl/fl mice (Pax3-KO) injected with RCAS-PDGF-B + RCAS-Cre into the brainstem at P2-4.