We observed that the percentage of dividing progenitors observed in Tis21-null mice was not affected by the infection with the GFP-shId3 retrovirus, as compared to a control retrovirus expressing an shRNA targeting luciferase (GFP-shLUC, Farioli-Vecchioli et al., 2014a; GFP-shId3+Ki67+/total GFP-shId3+ vs. GFP-shLUC+Ki67+/total GFP-shLUC+p = 0.35; Figures 6A,C). Here, BTG2 is linked to infection.