The Postsynaptic Density Formation and Regulation via Phase Separation: From In Vitro Reconstitution to the Native System

Abstract

Phase separation has emerged as a key mechanism for organizing biomolecular assemblies in cells. In neurons, it is proposed to underlie the formation and plasticity of the postsynaptic density (PSD), a highly organized yet adaptable compartment critical for synaptic signaling. However, direct investigation of phase separation within synapses remains challenging due to their small sizes. In this study, we utilized native PSDs purified from mouse brain as a bridge between reconstituted systems and the synaptic environment in vivo. Unlike reconstituted PSDs that typically form liquid-like droplets, native PSDs display a gel-like morphology with well-defined molecular compositions. Despite their structural rigidity, native PSDs retain full molecular plasticity. They can selectively recruit or exclude synaptic proteins and undergo Ca²⁺-dependent structural reorganizations. Importantly, CaMKII within purified PSDs can be rapidly activated by Ca²⁺ signal, leading to sustained phosphorylation of GluA1 and other PSD components. Furthermore, actin polymerization enlarges PSD clusters, recapitulating the structural remodeling observed during synaptic potentiation. Together, these findings demonstrate that native PSDs behave as functional condensates formed and regulated via phase separation. Our work also stablishes purified native PSDs as an accessible and physiologically relevant platform for dissecting the molecular mechanisms governing synaptic signaling and plasticity.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Zhenguo WU (Supervisor) & Mingjie ZHANG (Supervisor)