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. 2004 Jan;24(2):595–607. doi: 10.1128/MCB.24.2.595-607.2004

FIG. 7.

FIG. 7.

Redistribution of histone gene loci to perinucleolar replication foci during S phase in high-density cells. (A) Localization of histone gene loci relative to the nucleolus in asynchronous low- and high-density WI-38 cells. An antibody to NPAT (α-NPAT) is used to mark the histone gene clusters. At high cell density there is a significant redistribution of NPAT foci to perinucleolar regions in S-phase cells. NPAT foci associated with chromosome 6 are more intense than those associated with chromosome 1, and therefore they are distinguishable. (B) Comparison of histone gene loci to perinucleolar replication foci in early-S-phase low-density cells and asynchronous high-density cells. Whereas overlap between NPAT and the perinucleolar foci is minimal at low cell density, there is a significant increase in overlap at high cell density, with up to two NPAT foci coinciding with perinucleolar sites of replication. (C) Representative volume view images displaying the relative lack of colocalization between NPAT and perinucleolar replication foci at low cell density (left) and an increase in overlap at high cell density (right). Colocalization of NPAT (red) and BrdU (green) appears yellow. DAPI, 4′,6′-diamidino-2-phenylindole. (D) Slices of 0.25 μm through the nucleus of the high-density cell shown in panel C, demonstrating that the overlap between NPAT and BrdU occurs in the same plane and is not a result of volume averaging.