SON protects nascent transcripts from unproductive degradation by counteracting DIP1

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Regulation

Background:

• Gene expression requires precise transcription and splicing, including intron removal.
• Disco-interacting protein 1 (DIP1) degrades intronic sequences (INE-1 sisRNAs) post-splicing in Drosophila.
• Mechanisms protecting nascent transcripts containing intronic sequences from premature degradation are unclear.

Purpose of the Study:

• To investigate how nascent transcripts containing intronic sequences are protected from degradation.
• To elucidate the role of the Drosophila SON homolog (Dsn) in this process.
• To understand the regulatory relationship between Dsn and DIP1.

Main Methods:

• Observation of DIP1 binding to nascent transcripts.
• Localization studies of Dsn in ovaries.
• Analysis of DIP1 posttranslational modifications (sumoylation).
• Genetic analysis using DIP1 and Sumo heterozygous mutants.

Main Results:

• Nascent transcripts are bound by DIP1 but protected from degradation by Dsn in ovaries.
• Dsn localizes to sites of INE-1 sisRNA decay mediated by DIP1.
• Dsn acts as a repressor of DIP1 sumoylation, inhibiting DIP1 activity.
• Dsn depletion-induced pre-mRNA destabilization is rescued by mutations in DIP1 or Sumo.

Conclusions:

• Dsn protects nascent transcripts containing intronic sequences from premature DIP1-mediated degradation until intron excision.
• Dsn functions as a negative regulator of DIP1 activity.
• This regulation ensures proper intron removal and gene expression.