Differential Regulation of Calcium Dependent Phase Separation and Modular Assembly of Sap97/Hdlg Enriched Molecular Complexes

Abstract

Recent studies over a few decades have changed the perspective of the molecular architecture of functional zones within synapses and other cell junctions. Observations in the last decade confirm Post Synaptic Density as an assembly of segregated nanomachines than a single micromachinery. Multi-domain scaffolding molecules in the family of SAP97/hDLG form the skeleton of most of the cell-cell junctions. SAP97/hDLG, a synaptic scaffolding protein, is known for its diversity of isoforms and coordinates heterogeneity in organizing near membrane molecular complexes and differential sensitivity to second messengers like Calcium. To understand the heterogeneity in an isoform-specific organization, we used a combination of super-resolution microscopy, classical nucleation theory, pharmacology and Rank-order analysis to understand the molecular organization of SAP97/hDLG in heterologous cells and in young and matured hippocampal pyramidal neurons. In our study, we observed that SAP97/hDLG shows distinct isoform-specific nanoscale phase transitions in heterologous cells and age-specific differences in hippocampal pyramidal neurons. It opens a broader perspective to understand the molecular insights that modulate the calcium-dependent realtime-nanoscale heterogeneities in synaptic transmission and other cell-cell interfaces