Translational control of intron splicing in eukaryotes

Area of Science:

• Molecular Biology
• Genetics
• Evolutionary Biology

Background:

• Eukaryotic gene expression involves removing non-coding introns from pre-mRNAs via splicing.
• Accurate splice site selection is crucial, yet poorly understood, especially with numerous potential sites.
• Alternative splicing and nonsense-mediated mRNA decay (NMD) further regulate mRNA variants.

Purpose of the Study:

• To investigate the role of intron characteristics and NMD in ensuring accurate gene expression.
• To determine if intron sequences are under selective pressure to trigger premature termination upon retention.
• To assess the impact of NMD on compensating for suboptimal splicing efficiency.

Main Methods:

• Comparative analysis of intron sequences across species, focusing on *Paramecium tetraurelia*.
• Gene knockdown experiments targeting UPF1, a key NMD protein, in *P. tetraurelia*.
• Quantification of spliced versus unspliced mRNA fractions under varying NMD activity.

Main Results:

• Tiny introns in *P. tetraurelia*, and short introns in plants, fungi, and animals, show a bias for causing premature translation termination if retained.
• Splicing efficiency varies significantly among different introns.
• NMD activity substantially decreases the proportion of unspliced mRNAs, demonstrating its role in quality control.

Conclusions:

• Intron sequences are under selective pressure to facilitate NMD, acting as a safeguard against aberrant splicing.
• Nonsense-mediated mRNA decay (NMD) is a universal mechanism compensating for imperfect splicing efficiency and accuracy, particularly in species with numerous introns.
• This NMD-mediated quality control operates independently of alternative splicing to ensure translatable mRNA production.