Promoter-proximal pausing mediated by the exon junction complex regulates splicing.

Area of Science:

• Molecular Biology
• Gene Regulation
• Developmental Biology

Background:

• Promoter-proximal pausing of RNA polymerase II (Pol II) is a key regulatory mechanism in gene expression across metazoans.
• The precise molecular players and mechanisms governing this pausing remain incompletely understood.
• The nuclear exon junction complex (pre-EJC) is primarily known for its role in mRNA processing.

Purpose of the Study:

• To investigate the role of the nuclear exon junction complex (pre-EJC) in regulating promoter-proximal Pol II pausing.
• To elucidate the mechanism by which pre-EJC influences transcriptional elongation.
• To determine if pre-EJC-mediated regulation of pausing is functionally relevant for cellular differentiation.

Main Methods:

• Depletion of pre-EJC subunits using molecular biology techniques.
• Analysis of Pol II pausing dynamics genome-wide.
• Assessment of positive transcription elongation factor b (P-TEFb) binding at promoters.
• In vivo studies of photoreceptor differentiation and exon skipping.

Main Results:

• Depletion of pre-EJC subunits globally decreased Pol II pausing and led to premature transcriptional elongation.
• Pre-EJC components were non-canonically recruited to promoters, influencing Pol II release.
• Failure to recruit pre-EJC resulted in increased P-TEFb binding and enhanced Pol II release.
• Restoring Pol II pausing rescued exon skipping and photoreceptor differentiation defects.

Conclusions:

• The pre-EJC functions as a critical and conserved regulator of promoter-proximal Pol II pausing.
• Pre-EJC acts as an early transcriptional checkpoint, preventing premature elongation and ensuring proper RNA processing.
• This mechanism is essential for accurate exon definition and cellular differentiation, as demonstrated in photoreceptor development.