Mapping and engineering RNA-controlled architecture of the multiphase nucleolus

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Biomolecular condensates drive intracellular compartmentalization.
• The nucleolus, a nuclear condensate, is vital for ribosome biogenesis and rRNA processing.
• Understanding rRNA processing's link to nucleolar structure is limited by current tools.

Purpose of the Study:

• To develop methods for spatiotemporal mapping of rRNA processing.
• To engineer synthetic nucleoli to study structure-function relationships.
• To elucidate how rRNA maturation dictates nucleolar organization.

Main Methods:

• Development of complementary approaches for rRNA processing analysis.
• Spatiotemporal mapping using sequencing and imaging.
• Engineering of synthetic nucleoli via an rDNA plasmid system.

Main Results:

• rRNA processing steps are spatially segregated within the nucleolus.
• Sequential rRNA maturation drives its movement through nucleolar phases.
• SSU processing defects alter nucleolar phase order, leading to 'inside-out' nucleoli.
• LSU precursors are essential for the outermost nucleolar layer.

Conclusions:

• rRNA acts as both a scaffold and substrate in nucleolar assembly.
• rRNA sequence dictates the multiphase architecture of the nucleolus.
• This architecture facilitates the assembly of essential molecular machines like ribosomes.