Figure 4.

Fusion of chromocenters occurs throughout interphase. C2C12 myoblasts were double transfected with MeCP2-YFP and DsRed-Ligase I to track cell cycle progression. Schematic diagrams of the fusion proteins are depicted in A. (B) Maximum intensity projections generated from confocal image stacks of four time points of an MeCP2-YFP–transfected myoblast are shown (full time-lapse in Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200502062/DC1). MeCP2-YFP is shown in green, phase-contrast images are in red. (C) As apparent from the DsRed-Ligase I replication pattern, this cell was in late S-phase and moved into G2 after 3 h. In B, the last 180 min from the time series are shown. Three fusion events are highlighted in different colors (yellow, white, and black). The time points where the actual fusions take place are marked by an asterisk and were analyzed in all three dimensions. Most observed fusions included very close chromocenters, but as in the case highlighted in yellow it could also affect chromocenters located >2 μm apart. Bar (B and C), 5 μm. The table in D summarizes the analysis from 14 time series. In 9 of these cells chromocenter fusions occurred.