Figure 6.
N-myc overexpression increases the tumorigenic potential of PNCs. PNCs were isolated from 5- to 6-wk-old ptc+/− mice and infected with either control GFP virus or N-myc-IRES-GFP virus. After 24 h, 5 × 105 cells were implanted into the cerebellum of SCID-beige hosts. (A) Whole-mount imaging of a host brain transplanted with GFP-infected PNCs showed normal morphology 4 mo after transplantation. (B) Section from the animal shown in A, stained with anti-βgal (red) and anti-Ki67 (blue) antibodies. Transplanted PNCs could be located by βgal staining, but were not proliferating. (The faint blue staining is not nuclear and is also seen with isotype-control antibodies, and is therefore nonspecific.) (C) Whole-mount imaging of a host brain transplanted with N-myc-infected PNCs, showing the large GFP+ tumors that result from such transplants. Tumors from N-myc-infected PNCs, unlike those from control PNCs, frequently invade the forebrain (arrow). (D) Section from the animal shown in C, stained with antibodies specific for N-myc (red) and GFP (green). Magnification in B and D is 20×. (E) Survival of mice receiving GFP-infected and N-myc-infected PNCs, showing the increased incidence and decreased latency of tumors arising from N-myc-infected PNCs.