Phase separation-mediated actin bundling by the postsynaptic density condensates.

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Synaptic strength correlates with postsynaptic density (PSD) size.
• The PSD interacts with the actin cytoskeleton for spine structure and volume.
• Molecular mechanisms linking PSDs and actin are not well understood.

Purpose of the Study:

• Investigate the molecular mechanism of PSD-actin cytoskeleton communication.
• Determine how PSDs influence actin polymerization and spine morphology.

Main Methods:

• In vitro reconstitution of PSD condensates.
• Biochemical assays for actin polymerization and bundling.
• Neuronal imaging to observe spine growth.

Main Results:

• Reconstituted PSD condensates promote actin polymerization and F-actin bundling independently of other regulatory proteins.
• Homer proteins within PSDs are essential for this actin bundling and spine growth.
• Homer-induced actin bundling requires Homer to form condensates with Shank and SAPAP.
• PSD-induced actin bundling is regulated by CaMKII and Homer1a, suggesting modulation via phase separation.

Conclusions:

• Homer proteins in PSD condensates directly drive actin polymerization and bundling.
• PSD phase separation is a key regulator of synaptic actin dynamics and spine structure.
• This provides a novel mechanism for activity-dependent synaptic plasticity.