Proliferation-dependent and cell cycle–regulated transcription of mouse pericentric heterochromatin

(D) Six spatial patterns of DNA synthesis can be distinguished in mouse fibroblasts representing different stages of S phase, as previously described in detail (Wu et al., 2005). DNA is stained with DAPI, and sites of DNA synthesis are visualized by indirect immunofluorescence with an antibody specific to BrdU-substituted DNA. Images have been deconvolved and a merge of the BrdU and DAPI staining patterns is shown to illustrate the two stages during which cells are engaged in the replication of chromocenters, used to score γ satellite replication in C and Fig. 3. A schematic of the length of time that C127 cells spend in each stage of S phase is given at the bottom (adapted from Wu et al., 2006a). Experiments were repeated for three independent synchronizations. At least 150 cells were counted for each time point. Bars, 5 μm.