The Paf1 complex represses small-RNA-mediated epigenetic gene silencing

Area of Science:

• Epigenetics
• Molecular Biology
• Gene Regulation

Background:

• RNA interference (RNAi) silences gene expression via small interfering RNAs (siRNAs).
• Endogenous small RNAs are vital for chromatin regulation, but inducing chromatin changes using siRNAs in trans has been challenging.
• The RNA polymerase-associated factor 1 complex (Paf1C) is a conserved regulator of transcription.

Purpose of the Study:

• To investigate the role of Paf1C in RNAi-directed heterochromatin formation.
• To uncover mechanisms controlling epigenetic gene silencing initiated by trans-acting siRNAs.
• To understand how epigenetic memory is established and maintained.

Main Methods:

• Utilized fission yeast as a model system.
• Introduced synthetic hairpin RNA to trigger RNAi.
• Generated and analyzed Paf1C mutants.
• Assessed heterochromatin formation and gene silencing.
• Investigated transcription termination and nascent transcript release.

Main Results:

• Paf1C negatively controls RNAi-directed heterochromatin formation.
• Paf1C mutants allow synthetic siRNAs to induce stable, trans-acting heterochromatin and gene silencing.
• This silenced state is propagated across generations via secondary siRNAs.
• Paf1C promotes transcription termination and nascent transcript release, preventing siRNA targeting.
• Impaired transcription termination and nascent transcript release are crucial for stable epigenetic silencing.

Conclusions:

• Paf1C acts as a barrier to siRNA-mediated epigenetic gene silencing.
• Disrupting Paf1C function enables the establishment of stable heterochromatin and epigenetic memory via RNAi.
• This study reveals a novel mechanism for small RNA-guided epigenome regulation and highlights Paf1C's role in epigenetic inheritance.