Jmjd2b antagonizes H3K9 trimethylation at pericentric heterochromatin in mammalian cells

Area of Science:

• Epigenetics and chromatin biology.
• Enzymology and protein function.
• Molecular and cellular biology.

Background:

• Histone lysine trimethylation, particularly H3K9me3, is a key epigenetic mark in eukaryotic chromatin.
• The Jmj2 (or JMJD2) family of proteins are demethylases involved in epigenetic regulation.
• Understanding the dynamic regulation of histone marks is crucial for comprehending gene expression and cellular processes.

Purpose of the Study:

• To identify specific Jmjd2 proteins that antagonize H3K9me3.
• To investigate the mechanism and timing of Jmjd2b's effect on H3K9me3.
• To explore the role of Jmjd2b in active demethylation of histone trimethyl states.

Main Methods:

• Candidate gene approach to identify Jmjd2 proteins targeting H3K9me3.
• Analysis of H3K27me3 and H4K20me3 marks in Jmjd2b-GFP cell lines.
• Metabolic labeling with heavy methyl groups to track H3K9me3 dynamics.
• Assessment of Jmjd2b activity on chromosomal H3K9me3 before replication.

Main Results:

• Murine Jmjd2 proteins were identified as antagonists of H3K9me3 at pericentric heterochromatin.
• Jmjd2b was found to reduce H3K9me3 and H3K36 methylation, but not H3K27me3 or H4K20me3.
• Metabolic labeling demonstrated that Jmjd2b actively removes chromosomal H3K9me3 prior to DNA replication.
• Recombinant Jmjd2b showed poor enzymatic activity, suggesting a complex regulatory mechanism.

Conclusions:

• Specific Jmjd2 proteins, including Jmjd2b, actively antagonize the H3K9me3 epigenetic mark.
• The removal of H3K9me3 by Jmjd2b is an active process occurring before chromatin replication.
• These findings highlight a pathway involving jmjC hydroxylases that actively reverses histone lysine trimethylation states.