CaMKII Drives Synaptic Maturation by Coordinating Spine Remodeling and Receptor Segregation via Liquid-Liquid Phase...

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• Mature excitatory synapses feature dendritic spines and organized nanoarchitecture, with trans-synaptic nanocolumns aligning receptors and release sites.
• The mechanisms underlying synaptic maturation, including spine development and receptor organization, remain unclear.
• Calcium-calmodulin-dependent protein kinase II (CaMKII) is implicated in synaptic transmission and can undergo liquid-liquid phase separation (LLPS), influencing receptor organization.

Purpose of the Study:

• To investigate the role of CaMKII-mediated LLPS in driving the maturation of excitatory synapses.
• To determine if CaMKII acts as a structural element in shaping synaptic architecture during neuronal development.

Main Methods:

• Super-resolution microscopy was employed on primary hippocampal cultures from embryonic rats.
• CaMKII levels were manipulated (overexpression and mutation) to assess its impact on synaptic structure.
• Analysis focused on dendritic spine density, size, and the segregation of AMPA-type glutamate receptors (AMPAR) and NMDA-type glutamate receptors (NMDAR) nanodomains.

Main Results:

• Immature neurons with low CaMKII showed reduced spine density/size and poor receptor nanodomain segregation compared to mature neurons.
• Overexpressing CaMKII in immature neurons recapitulated mature synaptic features, increasing spine density, size, and receptor segregation.
• A CaMKII mutation preventing LLPS abolished these maturation effects.

Conclusions:

• CaMKII-mediated LLPS is a key mechanism driving synaptic maturation.
• CaMKII acts as a structural component, organizing dendritic spines and receptor nanodomains.
• This study reveals a link between CaMKII function, LLPS, spine formation, and receptor organization in mature synapses.