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Evidence for gene silencing by DNA methylation in normal human diploid fibroblasts
1CSIRO Division of Biomolecular Engineering, Sydney Laboratory, North Ryde, NSW, Australia.
Abstract:
Human diploid fibroblasts, strain MRC-5, were permeabilized by electroporation and treated with 5-methyl deoxycytidine triphosphate (5-methyl dCTP) in the S phase of the cell cycle. The frequency of TGR HPRT- cells was increased up to 20-fold in comparison to control untreated cultures. Representative TGR clones were unable to grow in HAT, and these were treated with 5-azacytidine (5-aza-CR). In many cases subsequent growth in HAT medium was observed, but in others it is likely that the cells had run out of growth potential. The results provide the first evidence of the silencing and reactivation of a gene in normal diploid mammalian cells.
Insights
Researchers demonstrated gene silencing and reactivation in normal diploid mammalian cells. Treatment with 5-methyl deoxycytidine triphosphate (5-methyl dCTP) and 5-azacytidine (5-aza-CR) induced and reversed gene silencing, respectively.
Area of Science:
- Molecular Biology
- Cell Biology
- Epigenetics
Background:
- Gene silencing is crucial for cellular differentiation and development.
- Understanding gene reactivation mechanisms is vital for therapeutic applications.
Purpose of the Study:
- To investigate gene silencing and reactivation in normal diploid mammalian cells.
- To explore the role of epigenetic modifications in gene regulation.
Main Methods:
- Human diploid fibroblasts (MRC-5) were treated with 5-methyl deoxycytidine triphosphate (5-methyl dCTP) during the S phase.
- Electroporation was used for cell permeabilization.
- Cells were subsequently treated with 5-azacytidine (5-aza-CR) to assess gene reactivation.
Main Results:
- A significant increase (up to 20-fold) in TGR HPRT- cells was observed after 5-methyl dCTP treatment.
- Some TGR clones, initially unable to grow in HAT medium, regained growth after 5-aza-CR treatment, indicating gene reactivation.
- Not all clones showed reactivation, suggesting potential limitations or alternative cellular fates.
Conclusions:
- This study provides the first evidence of reversible gene silencing and reactivation in normal diploid mammalian cells.
- Epigenetic modifications, induced by 5-methyl dCTP and reversed by 5-aza-CR, play a key role in regulating gene expression.
- These findings have implications for understanding gene regulation and developing novel epigenetic therapies.