Measuring Mobility in Chromatin by Intensity-Sorted FCS.

Area of Science:

• Molecular Biology
• Biophysics
• Cell Biology

Background:

• Chromatin organization influences genome regulation by affecting molecular mobility.
• Fluorescence Correlation Spectroscopy (FCS) analyzes fluorescence fluctuations to study molecular diffusion.
• Current FCS methods struggle to detect subtle mobility differences across distinct chromatin regions.

Purpose of the Study:

• To develop an advanced FCS method for probing molecular mobility in various nuclear chromatin environments.
• To overcome limitations of existing FCS techniques in resolving intranuclear mobility variations.
• To investigate the impact of chromatin density and compaction on molecular diffusion.

Main Methods:

• A novel FCS approach involving slow scanning of the observation volume across the nucleus.
• Analyzing data in short time segments to maintain high temporal resolution.
• Sorting FCS data based on probe intensity to differentiate chromatin regions and averaging for statistical robustness.

Main Results:

• Quantified reduced diffusion of monomeric Green Fluorescent Protein (GFP) in heterochromatin compared to less dense regions.
• Observed significantly lower GFP mobility within perinucleolar heterochromatin.
• Demonstrated differential effects of chromatin compaction modulation (via ATP depletion or osmolarity changes) on diffusion ratios between regions.

Conclusions:

• The developed scanning FCS method effectively resolves intranuclear variations in molecular mobility.
• Chromatin density and compaction significantly impact molecular diffusion, with heterochromatin restricting movement.
• The method provides a robust tool for studying molecular dynamics within specific nuclear substructures and can be combined with super-resolution techniques.