Related Experiment Videos
Fundamental study on the mechanism of DNA degradation in tissues fixed in formaldehyde
Y Tokuda1, T Nakamura, K Satonaka
1Department of Pathology, Kobe University School of Medicine, Japan.
Abstract:
The mechanism of DNA degradation and its clinical applications were examined. When purified lambda phage and extracted liver DNA were fixed in phosphate buffered formaldehyde, the DNA did not degrade, but there was incomplete digestion with endonuclease. Rat liver tissues were fixed under various conditions and DNA extracted. Immediate fixation with buffered formaldehyde at low temperature, or the addition of EDTA to buffered formaldehyde blocked the DNA degradation. Analysis of pulsed field gel electrophoresis also showed that DNA was degraded before extraction. These results suggest that tissue nuclease has an important role in DNA degradation in tissue. Furthermore, formaldehyde fixation at low temperature, which may take time and which decreases slightly the staining capacity, is useful for the extraction of intact DNA. For clinical application, the detection of provirus was examined. Genomic DNA was extracted from a necropsy sample of adult T cell leukaemia fixed in formaldehyde; human T cell leukaemia virus type-I (HTLV-I) provirus was successfully detected by Southern blotting.
Insights
Tissue nucleases degrade DNA, but low-temperature formaldehyde fixation preserves intact DNA for clinical applications like detecting human T-cell leukaemia virus type-I (HTLV-I) provirus.
Area of Science:
- Molecular Biology
- Biochemistry
- Clinical Diagnostics
Background:
- DNA degradation in tissues poses challenges for molecular analysis.
- Understanding DNA degradation mechanisms is crucial for preserving genetic material.
- Formaldehyde fixation is commonly used but can affect DNA integrity.
Purpose of the Study:
- To investigate the mechanisms of DNA degradation in fixed tissues.
- To identify methods for preserving intact DNA for clinical applications.
- To evaluate the efficacy of formaldehyde fixation in preserving DNA for provirus detection.
Main Methods:
- Experimentation with purified lambda phage and rat liver DNA.
- Formaldehyde fixation under various conditions (temperature, EDTA).
- Pulsed field gel electrophoresis for DNA integrity analysis.
- Southern blotting for human T-cell leukaemia virus type-I (HTLV-I) provirus detection.
Main Results:
- Tissue nucleases play a significant role in DNA degradation.
- Immediate fixation with buffered formaldehyde at low temperatures, or addition of EDTA, inhibited DNA degradation.
- Low-temperature formaldehyde fixation yielded intact DNA suitable for analysis.
- HTLV-I provirus was successfully detected in a formaldehyde-fixed necropsy sample.
Conclusions:
- Tissue nuclease activity is a primary driver of DNA degradation.
- Low-temperature formaldehyde fixation is a viable method for preserving DNA integrity.
- This method facilitates the clinical detection of viral DNA, such as HTLV-I provirus.