Solid phase transitions as a solution to the genome folding paradox

Area of Science:

• Molecular Biology
• Genomics
• Cell Biology

Background:

• Ultra-long-range genomic contacts are crucial for neuronal genome architecture but biochemically enigmatic.
• Regulatory DNA elements selectively contact distant sequences over proximal ones in processes like olfactory receptor gene regulation.

Purpose of the Study:

• To investigate the biochemical mechanisms underlying the formation of selective, long-range genomic contacts.
• To understand how olfactory receptor (OR) enhancer hubs assemble and maintain their structure.

Main Methods:

• In vitro assembly of OR enhancer hubs using recombinant proteins and DNA.
• Cell-free reconstitution assays to analyze condensate properties.
• Single-molecule tracking and pulse-chase experiments in olfactory sensory neuron (OSN) nuclei.

Main Results:

• OR enhancers form nucleoprotein condensates with solid-like characteristics in vitro.
• Specific DNA motifs within OR enhancers orchestrate condensate assembly.
• LHX2 and EBF1 proteins form transcription-competent condensates with solid properties in OSN nuclei.

Conclusions:

• Homophilic nucleoprotein interactions, influenced by DNA sequence, generate novel biomolecular condensates.
• These solid condensates provide a potential explanation for the stability and specificity of long-range genomic contacts.
• The findings offer a generalizable model for genomic organization across different cell types.