Transcription organizes euchromatin via microphase separation.

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Eukaryotic DNA is organized into chromatin within the nucleus, comprising DNA, histones, and RNA.
• Euchromatin, a transcriptionally active form of chromatin, is organized into domains with interspersed pockets of activity.
• The precise mechanisms by which transcription and RNA interplay to form and maintain these active transcription pockets remain incompletely understood.

Purpose of the Study:

• To investigate the dynamics of euchromatin organization during the exit from mitosis and the onset of transcription in pluripotent zebrafish cells.
• To elucidate the role of RNA accumulation and RNA-binding proteins in the formation of transcription pockets.
• To understand how RNA influences the spatial organization of transcriptionally active and inactive chromatin.

Main Methods:

• Combined theoretical modeling and experimental analysis.
• Studied pluripotent zebrafish cells as they transitioned from mitosis to active transcription.
• Utilized techniques to observe chromatin dynamics and RNA localization.

Main Results:

• Observed that accumulating RNA induces the formation of transcription pockets, displacing transcriptionally inactive chromatin.
• Proposed that accumulating RNA recruits RNA-binding proteins, promoting separation from inactive euchromatin.
• Demonstrated that RNA polymerase tethering prevents complete phase separation, leading to stable microphases characteristic of euchromatin organization.

Conclusions:

• RNA accumulation is a key driver in establishing transcription pockets within euchromatin.
• The interplay between RNA, RNA-binding proteins, and RNA polymerases governs the dynamic organization of the nucleus.
• This RNA-mediated phase separation mechanism establishes the characteristic spatial pattern of euchromatin organization.