Nucleolar RNA polymerase II drives ribosome biogenesis

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Ribosomes, essential for protein synthesis, are assembled in the nucleoli.
• Ribosomal RNA (rRNA) expression is primarily attributed to RNA polymerases I and III (Pol I and Pol III).

Purpose of the Study:

• To investigate the role of RNA polymerase II (Pol II) in nucleolar function and rRNA gene expression.
• To elucidate the mechanism by which Pol II influences nucleolar organization and ribosome biogenesis.

Main Methods:

• Utilized an experimental system involving RNaseH1, eGFP, and dCas9 ('red laser') to modulate R-loop formation.
• Investigated the impact of Pol II inhibition, senataxin loss, and Ewing sarcoma on nucleolar function.

Main Results:

• Demonstrated that Pol II operates within human nucleoli to drive rRNA expression.
• Showed Pol II, with senataxin, forms R-loops that shield rRNA genes from Pol I-driven disruptive noncoding RNAs (sincRNAs).
• Identified that loss of Pol II activity or senataxin leads to nucleolar disruption via sincRNAs.

Conclusions:

• Revised understanding of RNA polymerase roles in rRNA synthesis and ribosome biogenesis.
• Highlighted a Pol II-dependent mechanism critical for nucleolar organization and protein synthesis.
• Established R-loop modulation as a target for understanding and potentially treating diseases linked to nucleolar dysfunction.