Live-cell imaging reveals a stable cohesin-chromatin interaction after but not before DNA replication.
Cohesin is a multisubunit protein complex that links sister chromatids from replication until segregation. The lack of obvious cohesin-targeting-specific sequences on DNA, as well as cohesin's molecular arrangement as a large ring, has led to the working hypothesis that cohesin acts as a direct topological linker. To preserve the identity of sister chromatids, such a linkage would need to stably persist throughout the entire S and G2 phases of the cell cycle. Unexpectedly, cohesin binds chromatin already in telophase, and a large fraction dissociates from chromosomes during prophase in a phosphorylation-dependent manner, whereas initiation of anaphase requires proteolytic cleavage of only a small fraction of cohesin. These observations raised the question of how and when cohesin interacts with chromatin during the cell cycle. Here, we report a cell-cycle dependence in the stability of cohesin binding to chromatin. Using photobleaching and quantitative live-cell imaging, we identified several cohesin pools with different chromatin binding stabilities. Although all chromatin bound cohesin dissociated after a mean residence time of less than 25 min before replication, about one-third of cohesin was bound much more stably after S phase and persisted until metaphase, consistent with long-lived links mediating cohesion between sister chromatids.
Gerlich
Daniel
D
Gene Expression Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.
Koch
Birgit
B
Dupeux
Florine
F
Peters
Jan-Michael
JM
Ellenberg
Jan
J
D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D004261:DNA Replication / Q000502:physiology*; D036681:Fluorescence Recovery After Photobleaching; D006801:Humans; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D000097722:Cohesins
D018797:Cell Cycle Proteins; D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D009687:Nuclear Proteins; D000097722:Cohesins