Actin filaments form a size-dependent diffusion barrier around centrosomes.

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• Centrosomes are crucial non-membranous organelles that regulate cellular processes.
• The dense environment surrounding centrosomes suggests a potential diffusion barrier.
• Understanding molecular accessibility to centrosomes is key to deciphering their function.

Purpose of the Study:

• To investigate the presence and characteristics of a diffusion barrier at the centrosome.
• To determine the size-dependency of this barrier for soluble molecules.
• To elucidate the role of actin filaments in regulating centrosomal permeability.

Main Methods:

• Chemically inducible diffusion trapping assay to measure protein trapping kinetics.
• Quantitative analysis of soluble protein accessibility based on Stokes radius.
• Correlation of barrier permeability with actin filament dynamics and cell cycle stage.

Main Results:

• Centrosomes exhibit a size-dependent diffusion barrier, permeable to molecules <5.8 nm Stokes radius.
• Larger molecules are significantly restricted from accessing centrosomes.
• Barrier permeability is inversely correlated with branched actin filament density, decreasing during anaphase.
• The actin-based barrier interferes with gamma-tubulin ring complex recruitment, gating microtubule nucleation.

Conclusions:

• A size-selective diffusion barrier exists at the centrosome.
• Actin filaments dynamically regulate this barrier, influencing molecular access.
• The centrosomal diffusion barrier plays a role in controlling microtubule nucleation by modulating protein complex recruitment.