Figure 3. p53 and p21 Prevent Progression into Mitosis in the Presence of Uncapped Telomeres in MEFs.
(A) MEFs established from wild-type, p53−/−, p21−/−, or Terc−/− p53sh embryos were arrested in mitosis with colcemid, and mitotic chromosomes were spread via the cytospin method. Preparations were fixed and stained with anti-γH2AX monoclonal antibody (green). Telomeres were visualized with a Cy3-conjugated (CCCTAA)6-PNA probe (red). DNA was counter-stained with DAPI (blue). Insets show enlarged images of the areas marked with yellow rectangles.
(B) TIF frequency was determined by counting the number of foci in 100–150 metaphases. Error bars represent SD of three independent experiments.
(C) Metaphase chromosomes from p53+/+ and p53−/− MEFs were stained with DAPI and telomeres were visualized by FISH. Examples of end-to-end fusions with telomeric sequences at the fusion site and DNA breaks are shown.
(D) End-to-end fusions with or without telomeric repeats at the fusion site were quantified in at least 142 metaphases from each genotype. Error bars represent SD of values obtained for three different embryos of each genotype. The p value was calculated with an unpaired two-tailed t test. *p < 0.05.
This figure is related to Figure S3.