Effects of METTL3-METTL14 on primary microRNA processing by Drosha-DGCR8

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Regulation

Background:

• MicroRNAs (miRNAs) are crucial regulators of gene expression, with their maturation involving the Microprocessor complex (Drosha-DGCR8).
• Chemical modifications, such as N6-methyladenosine (m6A), on primary miRNA transcripts (pri-miRNAs) are proposed to influence Microprocessor processing efficiency.
• The methyltransferase complex METTL3-METTL14 is known to produce m6A modifications on RNA molecules.

Purpose of the Study:

• To investigate whether METTL3-METTL14 or m6A modification directly impacts the function of Drosha-DGCR8 in pri-miRNA processing.
• To elucidate the molecular mechanism by which METTL3-METTL14 might affect pri-miRNA maturation.

Main Methods:

• Reconstitution assays using purified METTL3-METTL14 methyltransferase complex and Drosha-DGCR8 Microprocessor complex.
• Biochemical assays to assess the processing efficiency of pri-miRNAs with and without m6A modification.
• Analysis of potential complex formation between METTL3-METTL14 and DGCR8.

Main Results:

• The presence of METTL3-METTL14 complexes did not alter the processing efficiency of Drosha-DGCR8 on pri-miRNAs.
• pri-miRNAs modified with m6A showed similar processing rates compared to unmodified transcripts.
• Stable complex formation between recombinant METTL3-METTL14 and DGCR8 was not observed, contradicting models of enhanced DGCR8 recruitment.

Conclusions:

• METTL3-METTL14 and m6A modification do not generally promote Microprocessor-mediated pri-miRNA processing.
• The findings challenge the existing model suggesting a direct role for METTL3-METTL14 in enhancing Drosha-DGCR8 activity.
• While not a general mechanism, specific roles in certain pri-miRNA processing events cannot be excluded.