Circular RNA biogenesis can proceed through an exon-containing lariat precursor

Area of Science:

• Molecular Biology
• Genetics
• RNA Biology

Background:

• Circular RNAs (circRNAs) are widespread in eukaryotes, but their biogenesis mechanisms are not fully understood.
• Current models suggest backsplicing, often mediated by flanking inverted repeats, but this is not universal.
• Mammalian-centric models are insufficient for explaining circRNA formation in organisms like lower eukaryotes where repeats are rare.

Purpose of the Study:

• To investigate the mechanism of circular RNA biogenesis in the lower eukaryote Schizosaccharomyces pombe.
• To identify sequence and structural elements governing circRNA formation.
• To explore alternative pathways for circRNA generation independent of flanking secondary structures.

Main Methods:

• Systematic splice site mutagenesis of specific genes.
• Identification and analysis of splicing intermediates.
• High-throughput and comprehensive mutagenesis of a circle-forming exon.
• Investigation of exon length effects on RNA circularization.

Main Results:

• Demonstrated that circRNA in Schizosaccharomyces pombe is generated via an exon-containing lariat precursor.
• Identified a significant, systematic effect of exon length on the efficiency of RNA circularization.
• Uncovered a novel circRNA biogenesis mechanism that does not rely on flanking intronic secondary structures.

Conclusions:

• The lariat precursor pathway provides a mechanism for circRNA formation in genes lacking canonical flanking repeats.
• Exon length is a critical determinant of circRNA biogenesis efficiency.
• This study expands our understanding of the diversity of circRNA formation pathways across eukaryotes.