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Scanning electron microscopic detection of nuclear structures involved in DNA replication
1Institute of Human Anatomy, Bologna University Faculty of Medicine, Italy.
Archives of Histology and Cytology
|December 22, 1999
Summary
This study reveals the 3D chromatin structure using electron microscopy and BrdU labeling. The 10 nm fiber forms a network crucial for DNA synthesis during the S phase.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Understanding the three-dimensional (3D) chromatin arrangement is crucial for comprehending nuclear organization and function.
- Interphase and S phase chromatin structure are key to DNA replication and gene regulation.
Purpose of the Study:
- To investigate the 3D chromatin organization at the ultrastructural level during interphase and S phase.
- To identify the role of specific chromatin fibers in DNA synthesis.
Main Methods:
- Immunogold detection of Bromodeoxyuridine (BrdU) as a marker for DNA synthesis.
- Field emission in-lens scanning electron microscopy (FEISEM) of ultrathin cryosections.
- DNase treatment to analyze fiber composition.
Main Results:
- A regular 3D network of 10 nm fibers organized in loops (80-100 nm) was observed in dispersed chromatin.
- Thicker structures (approx. 30 nm) were identified as nodal points and overlapping coils.
- DNase treatment removed 10 nm fibers, and BrdU labeling showed newly synthesized DNA within this regular arrangement.
Conclusions:
- The 10 nm chromatin fiber is likely the fundamental unit for DNA condensation at the start of DNA replication.
- This fiber network forms the primary structure of the interphase nucleus.
- The observed 3D chromatin organization is consistent across different human and murine cell lines.