TRIM66-HP1γ remodels the chromatin through phase separation.

Area of Science:

• Molecular biology
• Chromatin dynamics
• Epigenetics

Background:

• Facultative heterochromatin (fHC) undergoes dynamic remodeling between heterochromatin (HC) and euchromatin (EC).
• Heterochromatin protein 1 (HP1) mediates fHC formation via liquid-liquid phase separation (LLPS) by recognizing H3K9 methylation.
• HP1γ's phase separation mechanism and its regulators were previously unclear.

Purpose of the Study:

• Investigate the molecular mechanism of HP1γ interaction with TRIM66.
• Identify key regions governing TRIM66-HP1γ co-phase separation.
• Elucidate the role of TRIM66-HP1γ condensates in chromatin regulation and DNA damage response.

Main Methods:

• In vitro and in vivo biochemical assays to study HP1γ-TRIM66 interaction.
• Analysis of key protein regions controlling co-phase separation.
• Correlation analysis of TRIM66-HP1γ liquid granules with H3K9me3 and DNA damage markers.

Main Results:

• HP1γ interacts with TRIM66 via a PxVxL motif.
• Specific regions of TRIM66 and HP1γ were identified as critical for their co-phase separation.
• TRIM66-HP1γ liquid condensates colocalize with H3K9me3, linking them to DNA damage response pathways.

Conclusions:

• TRIM66 acts as a coordinator for HP1γ phase separation.
• The TRIM66-HP1γ-H3K9me3 axis drives the formation of compressed fHC through LLPS.
• This mechanism is implicated in regulating genomic stability and gene transcription.