Fig. 7. Myc may cause polyploidy in NPCs but it does not increase apoptosis. (A) Tetraploid Myc NPCs were found in one of the three transduced NPC progeny (Myc II) as shown by propidium iodide (PI) staining and flow cytometry. A higher rate of proliferation caused by Myc is seen as an increase in the percentages of cells in S and G2-M phases. The different amounts of debris shown can result from a number of factors: in addition to natural cell death, the mechanical dissociation of neurospheres into single cells causes debris and the amount varies somewhat between experiments. (B) Apoptosis is not changed by Myc overexpression in NPCs as analysed by Annexin staining and flow cytometry. Almost no apoptosis could be detected in NPCs (Contr 0.02%, n=5, s.d.=0.04 and Myc 0.18%, n=6, s.d.=0.35 Student's t-test P=0.31). Induced apoptosis in HU-VEC cells was used as a technical positive control for the Annexin staining.