Telomeric RNA and HP1α form interfacial clusters that stabilize HP1α-DNA condensates.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Phase separation of biomolecules is crucial for cellular processes, including nuclear chromatin organization and gene regulation.
• Heterochromatin formation involves DNA, repressive histone marks, and HP1α protein, but the mechanisms are not fully understood.
• Telomeric RNAs (TERRA) are implicated in heterochromatin formation, suggesting a role in nuclear organization.

Purpose of the Study:

• To investigate the interactions between telomeric RNA (TERRA), DNA, and HP1α protein.
• To elucidate the role of TERRA in the phase separation and organization of heterochromatin components.
• To understand how non-coding RNAs influence the material properties of protein-DNA condensates.

Main Methods:

• Investigated phase separation of HP1α with both TERRA and DNA using in vitro assays.
• Analyzed the formation of multiphase condensates when both nucleic acids were present.
• Characterized the localization and interactions within the multiphase condensates, focusing on TERRA-HP1α interactions.

Main Results:

• HP1α undergoes phase separation with both TERRA and DNA.
• In the presence of both nucleic acids, HP1α forms multiphase condensates with HP1α-TERRA clusters at the HP1α-DNA interface.
• Sequence-specific TERRA-HP1α interactions drive this multiphase architecture, with TERRA stabilizing DNA condensates and modulating their properties.

Conclusions:

• TERRA transcripts play a previously unrecognized role in regulating HP1α condensates.
• Structured non-coding RNAs like TERRA can significantly influence the material properties and organization of protein condensates.
• These findings provide insights into cooperative phase separation mechanisms governing nuclear compartmentalization and the regulatory roles of non-coding RNAs in chromatin organization.