Subcellular compartmentalization by local differentiation of cytoplasmic structure

Area of Science:

• Cell Biology
• Biophysics

Background:

• Eukaryotic cells utilize internal membranes for compartmentalization.
• Subcellular localization of macromolecules is typically mediated by specific binding mechanisms.

Purpose of the Study:

• To investigate potential compartmentalization of the cytoplasmic ground substance based on particle size.
• To explore the use of ratio imaging and FRAP to identify and characterize these cytoplasmic domains.

Main Methods:

• Utilized size-fractionated fluorescent tracer particles in living cells.
• Employed ratio imaging to visualize particle distribution.
• Applied fluorescence recovery after photobleaching (FRAP) to assess particle dynamics.

Main Results:

• Large and small fluorescent particles exhibited distinct subcellular distributions, indicating size-based sorting.
• Spatial variations in diffusion coefficients and mobile fractions were observed for large particles but not small ones.
• FRAP data suggested heterogeneity in the cytoplasmic ground substance.

Conclusions:

• The cytoplasmic ground substance exhibits structural differentiations that compartmentalize particles by size.
• Ratio imaging and FRAP serve as empirical tools for identifying and studying cytoplasmic compartments.
• A model was developed, enabling FRAP to detect sol-gel transitions in the cytoplasm.