FIG 1.

SV40 TAg does not require activator E2Fs to induce proliferation in MEFs. (A) Western blot analysis showing SV40 TAg expression in wt and DKO backgrounds. (B) Growth curve comparison between wt and DKO MEFs in the presence or absence of TAg. Equal numbers of cells were plated for all cell types, and cells were counted periodically in duplicate to obtain the growth curves (n = 2). (C) Comparison of morphology and cell growth characteristics after removal of E2F3 by cre-recombinase. Images were taken after infection of cells with retroviruses containing either empty vector (DKO and DKO;TAg cells) or cre-recombinase (TKO and TKO;TAg cells). All images were taken at the same time point and with the same magnification. (D) Beta-galactosidase staining to determine senescence in DKO MEFs treated with E2F3-specific or control shRNAs. Four E2F3-specific shRNA treatments were used and yielded the same results. An image representative of one of the shRNA-generated cells is shown. Blue-violet positive staining and enlarged morphology were observed only in E2F3 shRNA-treated DKO MEFs and not in control shRNA-treated cells.