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#chromatin modification

2 public questions tagged with this topic.

Stem Cell -ll

Which type of chromatin modification is associated with stem cell differentiation?

Stem cell differentiation is accompanied by dramatic widespread chromatin reorganization from open to restrictive configuration. Pluripotent cells exhibit globally open euchromatin enriched in activating H3K9 acetylation and H3K4 trimethylation marks, maintaining accessibility of self-renewal genes like Nanog. Upon lineage commitment, histone deacetylases remove acetyl groups, H3K27 methyltransferase EZH2 component of PRC2 deposits repressive marks, DNA methyltransferases methylate CpG islands of Oct4 and Nanog promoters, and heterochromatin protein 1 consolidates constitutive heterochromatin foci at repeats. These coordinated modifications collectively silence pluripotency program and permanently lock lineage-specific expression patterns essential for stability.

Ref: Bernstein et al., Cell 2006; Spivakov & Fisher, Nat Rev Genet 2007: Chromatin modifications differentiation bivalency.

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Regulation of chromatin structure

Which residue is commonly acetylated in histones?

Lysine residues in histone tails are primary targets for acetylation because their ε-amino group carries positive charge at physiological pH and can accept acetyl from acetyl-CoA via HAT enzymes such as p300/CBP and Gcn5. Acetylation neutralizes charge, disrupts salt bridges with DNA phosphate, increases tail flexibility and creates docking sites for bromodomains. Arginine undergoes methylation, serine and threonine undergo phosphorylation, while lysine uniquely combines charge modulation with reader recruitment. Frequent sites include H3K9, K14, K27 and H4K5, K8, K12, K16, linking metabolic acetyl-CoA availability to gene activation status.

Ref: Berg et al., Biochemistry, 9th ed., Chapter 30: Histone Acetylation at Lysine Residues

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