H2BC21 and glioblastoma: While the initial GFP label retention patterns appeared similar across culture conditions at day 7, by days 15 and 23, the GFP signals had largely disappeared in 2D G and 3D G condition; by contrast, we detected a significant amount of H2B‐GFPhigh signal (≈6–15% of GBM cells) in the 3D GAPE condition (Figure 6c,d).