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Methylation dynamics, epigenetic fidelity and X chromosome structure
1Biology Department, Beckman Research Institute of the City of Hope, Duarte, CA 91010-0269, USA.
Novartis Foundation Symposium
|May 27, 1998
Summary
This study investigates DNA methylation dynamics in mouse cells, revealing that epigenetic marks on the Igf2 gene region fluctuate after cell division but stabilize over time. Chromatin accessibility differences between active and inactive X chromosomes are also shown to be unstable.
Area of Science:
- Epigenetics
- Molecular Biology
- Genomics
Background:
- DNA methylation patterns are crucial for gene regulation and cellular identity.
- The X chromosome undergoes complex epigenetic modifications, including differential DNA methylation.
- Understanding epigenetic fidelity is key to comprehending cellular stability and development.
Purpose of the Study:
- To quantitatively measure DNA methylation at a specific CpG site (H3) in the mouse Igf2 upstream region during cell culture.
- To investigate the stability and dynamics of DNA methylation in subcloned cells.
- To assess chromatin accessibility differences between the active (Xa) and inactive (Xi) X chromosomes.
Main Methods:
- Quantitative measurement of DNA methylation at CpG site H3 in mouse Igf2 promoter region.
- Cell culture of subcloned cells over multiple generations.
- Measurement of chromatin accessibility using DNase I digestion.
Main Results:
- Initial DNA methylation levels at CpG site H3 were approximately 50% before subcloning.
- Post-subcloning, methylation levels showed high variability, with clones either gaining or losing methylation.
- Over approximately 25 generations, all clones returned to a stable 50% methylation level.
- Differences in DNase I accessibility between Xa and Xi were found to be labile and sensitive to DNA damage.
Conclusions:
- Epigenetic mechanisms governing DNA methylation exhibit stochasticity but maintain fidelity over time.
- Chromatin accessibility on the X chromosome is dynamic and can be rapidly altered.
- A model of stochastic methylation/demethylation influenced by chromatin structure explains the observed DNA methylation dynamics.