Dynamic organization of DNA replication in mammalian cell nuclei: spatially and temporally defined replication of chromosome-specific alpha-satellite DNA sequences.
Five distinct patterns of DNA replication have been identified during S-phase in asynchronous and synchronous cultures of mammalian cells by conventional fluorescence microscopy, confocal laser scanning microscopy, and immunoelectron microscopy. During early S-phase, replicating DNA (as identified by 5-bromodeoxyuridine incorporation) appears to be distributed at sites throughout the nucleoplasm, excluding the nucleolus. In CHO cells, this pattern of replication peaks at 30 min into S-phase and is consistent with the localization of euchromatin. As S-phase continues, replication of euchromatin decreases and the peripheral regions of heterochromatin begin to replicate. This pattern of replication peaks at 2 h into S-phase. At 5 h, perinucleolar chromatin as well as peripheral areas of heterochromatin peak in replication. 7 h into S-phase interconnecting patches of electron-dense chromatin replicate. At the end of S-phase (9 h), replication occurs at a few large regions of electron-dense chromatin. Similar or identical patterns have been identified in a variety of mammalian cell types. The replication of specific chromosomal regions within the context of the BrdU-labeling patterns has been examined on an hourly basis in synchronized HeLa cells. Double labeling of DNA replication sites and chromosome-specific alpha-satellite DNA sequences indicates that the alpha-satellite DNA replicates during mid S-phase (characterized by the third pattern of replication) in a variety of human cell types. Our data demonstrates that specific DNA sequences replicate at spatially and temporally defined points during the cell cycle and supports a spatially dynamic model of DNA replication.
O'Keefe
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Cold Spring Harbor Laboratory, New York 11724-2217.
Henderson
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Spector
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D000818:Animals; D001973:Bromodeoxyuridine; D016466:CHO Cells; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000378:metabolism*; D002503:Centromere / Q000378:metabolism*; D006224:Cricetinae; D004261:DNA Replication; D004276:DNA, Satellite / Q000032:analysis*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008297:Male; D016196:S Phase; D014407:Tumor Cells, Cultured
D004276:DNA, Satellite; D001973:Bromodeoxyuridine