Interphase cell cycle dynamics of a late-replicating, heterochromatic homogeneously staining region: precise choreography of condensation/decondensation and nuclear positioning.
Recently we described a new method for in situ localization of specific DNA sequences, based on lac operator/repressor recognition (Robinett, C.C., A. Straight, G. Li, C. Willhelm, G. Sudlow, A. Murray, and A.S. Belmont. 1996. J. Cell Biol. 135:1685-1700). We have applied this methodology to visualize the cell cycle dynamics of an approximately 90 Mbp, late-replicating, heterochromatic homogeneously staining region (HSR) in CHO cells, combining immunostaining with direct in vivo observations. Between anaphase and early G1, the HSR extends approximately twofold to a linear, approximately 0.3-mum-diam chromatid, and then recondenses to a compact mass adjacent to the nuclear envelope. No further changes in HSR conformation or position are seen through mid-S phase. However, HSR DNA replication is preceded by a decondensation and movement of the HSR into the nuclear interior 4-6 h into S phase. During DNA replication the HSR resolves into linear chromatids and then recondenses into a compact mass; this is followed by a third extension of the HSR during G2/ prophase. Surprisingly, compaction of the HSR is extremely high at all stages of interphase. Preliminary ultrastructural analysis of the HSR suggests at least three levels of large-scale chromatin organization above the 30-nm fiber.
Li
G
G
Department of Cell and Structural Biology, University of Illinois, Urbana-Champaign, Urbana, Illinois 61801, USA.
Sudlow
G
G
Belmont
A S
AS
D000818:Animals; D016466:CHO Cells; D002467:Cell Nucleus / Q000378:metabolism; D006224:Cricetinae; D004261:DNA Replication; D016193:G1 Phase; D006570:Heterochromatin; D007150:Immunohistochemistry; D007399:Interphase; D008938:Mitosis; D016196:S Phase; D013194:Staining and Labeling / Q000379:methods; D013692:Telophase; D013997:Time Factors
D006570:Heterochromatin