Spatial and temporal regulation of synapse formation through phase separation - Synapses are the basic unit of neuronal communication, and consequently their location, number, and properties govern the function of neural circuits and nervous systems. How synapses form remains a fundamental question in contemporary neuroscience. A wide variety of synaptic cell adhesion molecules (syCAMs) are capable of initiating synapse formation. Downstream of these diverse connections, however, common pre- and post-synaptic specializations are formed. On the presynaptic side, an “active zone” structure is formed comprised of large multi-valent scaffolding proteins. The active zone coordinates the central functions of the presynapse by tethering and priming synaptic vesicles, clustering calcium channels, and aligning with the postsynapse through transmembrane connections. Recently the candidate showed conserved C. elegans active zone scaffolds SYD-2/Liprin-α and ELKS form liquid-liquid phase separated condensates at developing synapses, and this activity was required for active zone assembly. This work positioned active zone phase separation as a central assembly hub in the presynapse. The overall goal of the proposed studies is to determine molecular mechanisms and novel components that drive active zone phase separation, and thus presynapse formation. In Aim 1, phosphorylation will be investigated as a mechanism that controls active zone phase separation. Preliminary data suggest SAD-1 kinase phosphorylation of SYD-2 controls its activity. This phosphoregulation will be investigated with live animal in vivo imaging at single-synapse resolution in combination with in vitro phase separation assays. In Aim 2, the connection between synaptogenic syCAMs and active zone phase separation will be investigated. Multiple syCAMs have been identified to build local F- actin networks, which may link these upstream molecules to active zone phase separation. The requirement and sufficiency of F-actin networks in active zone formation and phase separation will be determined with optogenetic methods in vivo, and reconstitution of syCAM signaling and active zone phase separation in vitro. Finally, automated forward genetic screens will be performed to identify novel regulators of active zone formation. As all synapses across the diversity of neurons build a conserved core active zone, these studies have the potential to uncover common synapse assembly pathways. A fundamental understanding of synapse assembly will yield insight into synapse regeneration and future treatment of synaptopathies and is of primary relevance to the NINDS mission. The candidate will perform the K99 phase at Stanford University under the mentorship of Dr. Kang Shen, an expert in molecular and developmental neuroscience. This award will support the candidate’s career development with personalized training in research methods (genetic screening, phosphoregulation, and in vitro reconstitution) and career development (scientific writing, teaching, and management). This training will enable the candidate to successfully complete the proposed research and transition to an independent position investigating synapse formation.
