MicroRNAs activate gene transcription epigenetically as an enhancer trigger

Area of Science:

• Molecular Biology
• Epigenetics
• Gene Regulation

Background:

• MicroRNAs (miRNAs) are typically known as cytoplasmic gene silencers.
• Emerging research indicates miRNAs also reside in the nucleus, but their functions there are unclear.
• The role of nuclear miRNAs in gene regulation, particularly in gene activation, is largely undetermined.

Purpose of the Study:

• To investigate the functional significance of nuclear miRNAs.
• To identify miRNAs that can regulate gene enhancers.
• To elucidate the mechanism by which miR-24-1 activates gene transcription via enhancers.

Main Methods:

• Screening of miRNA databases to identify potential enhancer-regulating miRNAs.
• Experimental validation of gene activation by specific miRNAs, focusing on miR-24-1.
• Utilizing TALEN to delete enhancer sequences and assess the impact on miR-24-1's function.
• Analysis of enhancer RNA (eRNA) expression, histone modifications, and recruitment of p300 and RNA Polymerase II (Pol II).

Main Results:

• A subset of miRNAs was identified with gene-activating functions, contrary to their known repressive roles.
• miR-24-1 was found to activate gene transcription by targeting enhancer elements.
• Deletion of the enhancer sequence abolished miR-24-1-mediated activation.
• miR-24-1 promotes eRNA expression, alters histone modifications, and enhances the enrichment of p300 and RNA Pol II at target enhancers.

Conclusions:

• MicroRNAs can function as gene transcriptional activators by targeting enhancers.
• miR-24-1 acts as an enhancer trigger, demonstrating a novel mechanism of gene activation.
• These findings expand the known functions of miRNAs beyond cytoplasmic gene silencing.