Histone H3K4 trimethylation: dynamic interplay with pre-mRNA splicing

Area of Science:

• Epigenetics
• Molecular Biology
• Gene Regulation

Background:

• Histone H3 lysine 4 trimethylation (H3K4me3) is traditionally considered a marker of active gene promoters.
• Recent observations indicate H3K4me3 is predominantly located downstream of the first exon, at 5' splice sites and CpG islands in mammals.

Purpose of the Study:

• To investigate the precise genomic localization of H3K4me3.
• To explore the functional relationship between H3K4me3 and pre-mRNA splicing.

Main Methods:

• Chromatin immunoprecipitation-based assays to determine H3K4me3 positioning.
• Analysis of enzyme complexes involved in H3K4me3 deposition (writers) and removal (erasers).
• Investigation of H3K4me3-binding proteins (readers) and their roles in splicing.

Main Results:

• H3K4me3 is primarily localized at the 5' splice site, overlapping with CpG islands.
• Enzymes like SETD1A, SETD1B, and MLL1 (writers) deposit H3K4me3, with CXXC1 targeting them to CpG islands.
• KDM5 family members (erasers) remove the H3K4me3 mark.
• Proteins recognizing H3K4me3, including those involved in splicing, are identified.
• Experimental evidence shows that altering H3K4me3 levels affects pre-mRNA splicing, and vice versa.

Conclusions:

• The localization of H3K4me3 extends beyond active promoters to critical pre-mRNA splicing sites.
• H3K4me3 is intricately linked with the pre-mRNA splicing machinery, suggesting a dual role in gene regulation.
• This finding redefines the functional landscape of H3K4me3 in mammalian cells.