BTG2 and infection: The infection of the dentate gyrus of Tis21-null adult mice (at P60) with a retrovirus expressing Tis21 and GFP (pCAG-IRES-GFP-Tis21; Figures 5A–E) occurred only in proliferating progenitors; however, the analysis of infected cells (GFP+) was performed 5 days after infection, hence cells were detected that either continued to proliferate or had differentiated.