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Visualization of transcription sites at the electron microscope
A Trentani1, P S Testillano, M C Risueño
1Dipartimento di Biologia Animale, Laboratorio di Biologia Cellulare, and Istituto di Genetica Molecolare, University of Pavia, Italy.
European Journal of Histochemistry : EJH
|September 30, 2003
Summary
This study identifies pre-messenger RNA (mRNA) and pre-ribosomal RNA (rRNA) transcription sites using bromo-uridine incorporation and specific antibodies. Perichromatin fibrils are confirmed as pre-mRNA sites, while the nucleolus
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Localizing transcription sites at the electron microscopy (EM) level is crucial for understanding gene expression dynamics.
- Distinguishing between pre-messenger RNA (pre-mRNA) and pre-ribosomal RNA (pre-rRNA) transcription sites requires specific molecular markers.
- Previous studies have suggested various nuclear structures as potential transcription sites, but definitive localization remains challenging.
Purpose of the Study:
- To precisely localize the sites of pre-mRNA and pre-rRNA transcription within the cell nucleus at the EM level.
- To investigate the role of perichromatin fibrils and interchromatin granules in mRNA synthesis.
- To identify the specific sub-compartment within the nucleolus responsible for rRNA transcription.
Main Methods:
- Short incorporation of bromo-uridine (BrU) to label newly synthesized RNA.
- Immunodetection of DNA/RNA hybrid molecules and m3G-capped structures using specific antibodies.
- Electron microscopy (EM) combined with terbium citrate staining for RNA visualization.
Main Results:
- Perichromatin fibrils incorporated BrU and were labeled by anti-hybrid probes, identifying them as pre-mRNA transcription sites.
- Interchromatin granules did not incorporate BrU and were not labeled, suggesting they are not active pre-mRNA synthesis sites.
- In the nucleolus, anti-hybrid and anti-BrdU antibodies colocalized on the dense fibrillar component, indicating it as the rRNA transcription site.
Conclusions:
- Perichromatin fibrils represent the primary sites of pre-mRNA transcription.
- The dense fibrillar component of the nucleolus is the site of rRNA transcription.
- Structural similarities between the dense fibrillar and granular components suggest a common fibrogranular RNA structure involved in rRNA processing.