Cohesion promotes nucleolar structure and function.

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• The cohesin complex plays a role in ribosome function, but the mechanisms are not fully understood.
• Cohesinopathies, such as Roberts syndrome (RBS), arise from compromised cohesin function, particularly reduced Smc3 subunit acetylation.
• Defects in cohesin acetylation impact rRNA production, ribosome biogenesis, and protein synthesis.

Purpose of the Study:

• To investigate the role of cohesin in organizing ribosomal DNA (rDNA) and its impact on ribosome biogenesis.
• To elucidate the molecular mechanisms linking cohesin function to nucleolar integrity and ribosome production.

Main Methods:

• Utilized yeast models with specific cohesin mutations (eco1-W216G) mimicking Roberts syndrome.
• Analyzed nucleolar structure, rDNA looping, and RNA polymerase I occupancy.
• Assessed rRNA production rates and rRNA cleavage kinetics.

Main Results:

• The RBS mutation in yeast led to a disorganized nucleolus and reduced rDNA looping, without affecting RNA polymerase I recruitment.
• Impaired rRNA production in RBS mutants was linked to slower rRNA cleavage.
• Disrupting cohesin function, through mutation or depletion, caused loss of nucleolar integrity and defects in ribosome biogenesis.

Conclusions:

• Cohesin-mediated organization of rDNA is essential for proper nucleolus formation and function.
• Cohesin defects directly impair ribosome biogenesis and protein synthesis.
• Understanding cohesin's role in rDNA organization is critical for addressing cohesinopathies.