RNA G-quadruplexes regulate mammalian mirtron biogenesis

Area of Science:

• Molecular Biology
• RNA Biology
• Genetics

Background:

• Mirtrons are noncanonical microRNAs processed via splicing, independent of Drosha.
• The precise mechanisms governing mirtron biogenesis are not fully understood.
• Potential interference of mirtron splicing with canonical microRNA pathways exists.

Purpose of the Study:

• To elucidate the regulatory mechanisms of mirtron biogenesis.
• To investigate sequence and structural features differentiating plant, invertebrate, and vertebrate mirtrons.
• To determine the role of RNA G-quadruplexes (rG4s) in mammalian mirtron formation.

Main Methods:

• Comparative sequence analysis of mirtrons across different species.
• In silico prediction and in vitro structural analysis of RNA G-quadruplexes (rG4s).
• Mutagenesis studies to assess the impact of rG4 disruption on splicing and maturation.

Main Results:

• Vertebrate, particularly mammalian, mirtrons show a distinct enrichment of guanines in their 5' arm compared to uracil-enriched plant/invertebrate mirtrons.
• Most mammalian mirtrons contain RNA G-quadruplexes (rG4s), predominantly located in the 5' arm.
• In vitro experiments confirmed rG4 formation in human mirtrons, and disruption of these rG4s significantly inhibited splicing and maturation, while other mutations had no effect.

Conclusions:

• RNA G-quadruplexes (rG4s) in the 5' arm are critical regulatory elements for mammalian mirtron biogenesis.
• rG4 formation facilitates the splicing-dependent maturation pathway of mammalian mirtrons.
• This study highlights a novel role for rG4s in small RNA biology and mirtron evolution.