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Nuclear matrix-bound replicational sites detected in situ by 5-bromodeoxyuridine
L M Neri1, G Mazzotti, S Capitani
1Istituto di Anatomia Umana Normale, Universitá di Ferrara, Italy.
Abstract:
The nuclear matrix was prepared in situ from Swiss 3T3 cells, which were synchronized by contact inhibition and serum starvation and pulse-labelled for very short periods of time with 5-bromodeoxyuridine (5-BrdU). For the first time 5-BrdU has been employed to demonstrate the association of newly synthesized DNA with a nucleoskeleton. Immunofluorescence analysis using a monoclonal antibody to 5-BrdU revealed five different intranuclear staining patterns at different stages of the S phase. These patterns were observed also in intact cells and did not change during the matrix preparation steps which involve extraction with 2 M NaCl and DNase I digestion. Such an observation was also confirmed by spatial confocal microscopy studies. The intensity of fluorescence, which was evaluated by cytofluorometry, increased to reach a maximum during mid-S phase and then decreased. Because no significant difference was found in the time to label residual DNA of different 5-BrdU staining patterns, this strongly suggests that a different number of replicons is activated at different stages of the S phase. These results strengthen the hypothesis that eukaryotic DNA replication occurs in close association with an insoluble protein nuclear skeleton, which determines the three-dimensional spatial organization of chromosome duplication.
Insights
Newly synthesized DNA associates with the nuclear matrix during the S phase of the cell cycle. This study used 5-bromodeoxyuridine (5-BrdU) to visualize DNA replication sites within the nuclear skeleton.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- The nuclear matrix is an insoluble scaffold within the cell nucleus.
- Understanding DNA replication's spatial organization is crucial for cell cycle regulation.
Purpose of the Study:
- To investigate the association of newly synthesized DNA with the nuclear matrix during S phase.
- To visualize DNA replication sites using 5-bromodeoxyuridine (5-BrdU) and immunofluorescence.
Main Methods:
- Preparation of nuclear matrix in situ from synchronized Swiss 3T3 cells.
- Pulse-labeling with 5-bromodeoxyuridine (5-BrdU) and immunofluorescence staining.
- Confocal microscopy and cytofluorometry for quantitative analysis.
Main Results:
- Five distinct intranuclear 5-BrdU staining patterns were observed during S phase.
- These patterns remained consistent after nuclear matrix preparation.
- Fluorescence intensity peaked in mid-S phase, suggesting stage-specific replicon activation.
Conclusions:
- Eukaryotic DNA replication is closely associated with the nuclear skeleton.
- The nuclear skeleton likely dictates the spatial organization of chromosome duplication.
- Differential replicon activation occurs throughout S phase.