METTL4 catalyzes m6Am methylation in U2 snRNA to regulate pre-mRNA splicing

Area of Science:

• Molecular Biology
• RNA Biology
• Epigenetics

Background:

• N6,2"-O-dimethyladenosine (m6Am) is an RNA modification found in eukaryotic cells.
• While m6Am is common in mRNA, the enzyme responsible for internal m6Am, particularly in U2 small nuclear RNA (snRNA), was unknown.

Purpose of the Study:

• To identify the methyltransferase responsible for catalyzing internal m6Am formation in U2 snRNA.
• To investigate the function and targets of this methyltransferase in RNA processing and splicing.

Main Methods:

• Transcriptome-wide RNA methylation sequencing at single-base-resolution.
• Identification of human METTL4 as the m6Am writer enzyme.
• Analysis of METTL4 localization, catalytic activity, and in vivo target specificity.
• Assessment of splicing events in cells lacking METTL4.

Main Results:

• Human METTL4 was identified as the enzyme that directly methylates 2 -O-methyladenosine (Am) at U2 snRNA position 30 to form m6Am.
• METTL4 localizes to the nucleus, and its catalytic activity is essential for U2 snRNA methylation.
• METTL4-dependent m6Am modification in U2 snRNA influences splicing of specific pre-mRNAs, particularly those with weak 3 -splice sites.

Conclusions:

• METTL4 is the writer enzyme for internal m6Am in U2 snRNA.
• METTL4-mediated U2 snRNA methylation plays a regulatory role in specific pre-mRNA splicing events.
• This discovery advances understanding of RNA modification dynamics and their impact on gene expression.