The internal loops in the lower stem of primary microRNA transcripts facilitate single cleavage of human...

Area of Science:

• Molecular Biology
• Gene Regulation
• RNA Processing

Background:

• The Microprocessor complex, comprising DROSHA and DGCR8, is essential for initiating microRNA (miRNA) synthesis by processing primary miRNA (pri-miRNA) transcripts.
• DROSHA possesses two RNase III domains (RIIIDa and RIIIDb) responsible for cleaving the 3p- and 5p-strands of pri-miRNAs, respectively.

Purpose of the Study:

• To investigate the role of internal loops in the lower stem of pri-miRNAs in regulating Microprocessor complex activity.
• To explore how manipulating these internal loops affects miRNA production and expression levels.

Main Methods:

• Analysis of pri-miRNA structures, focusing on internal loops within the lower stem.
• In vitro pri-miRNA processing assays using the Microprocessor complex.
• Experiments involving manipulation of internal loop size in pri-miRNAs within human cells.

Main Results:

• An internal loop in the lower stem of pri-miRNAs selectively inhibits Microprocessor cleavage of the 3p-strand.
• This selective inhibition leads to single-strand cleavage on the 5p-strand, which downregulates miRNA expression rather than producing mature miRNA.
• Modulating the size of the internal loop alters the ratio of single-cut to double-cut products, thereby influencing miRNA production.

Conclusions:

• The internal loop in pri-miRNAs acts as a regulatory element controlling Microprocessor complex activity.
• Single-strand cleavage, mediated by internal loops, represents a novel mechanism for downregulating miRNA expression.
• This finding offers a new strategy for miRNA knockdown and understanding gene regulation.