What are the molecular and cellular steps that govern presynaptic assembly and determine presynaptic function?
SYNAPSE DEVELOPMENT
MODELING PATIENT VARIANTS IN PRESYNAPTIC CALCIUM CHANNELS
WHAT IS THE ORDER OF ASSEMBLY AT NASCENT PRESYNAPTIC SPECIALIZATIONS?
We have found that the presynaptic scaffold protein SYD-1 coordinates presynaptic assembly through interactions with phospholipids in the membrane including PIP2. SYD-1 then subsequently recruits the cell-adhesion molecule neurexin, which serves to stabilize these nascent assemblies (Frankel et al., 2025).
Molecular dynamics simulation of SYD-1’s C2 domain interacting with PIP2 (green) in the plasma membrane.
We have found that a recently-identified, conserved short isoform of neurexin, called gamma-neurexin, which does not contain any of the canonical extracellular binding domains, can nonetheless mediate presynaptic assembly and maturation. Our current studies are focused on elucidating the role of this short but seemingly redundant isoform in synapse development.
Moreover, we have found that the intracellular domain of neurexin alone is sufficient for presynaptic assembly. To understand the contribution of neurexin’s intracellular domain to presynaptic organization, we are undertaking proximity labeling approaches to identify neurexin’s intracellular binding partners (Profes et al, 2024).
WHAT IS THE ROLE OF PRESYNAPTIC MRNAS IN SYNAPSE DEVELOPMENT?
Beta-actin mRNA labeled using the MS2 system allows for the visualization of both transcription sites in the nucleus (brightest spots) and RNA granules inside and outside of the nucleus.
SYNAPSE ASSEMBLY AT DISTINCT STAGES OF NEURONAL DEVELOPMENT
Detection of synaptic proteins at early stages of synapse formation in the embryonic nerve ring.
NON-CANONICAL ROLES FOR CELL ADHESION MOLECULES
We have identified non-canonical roles in synapse assembly for a pair of CAMs, SYG-1 and SYG-2. We have found that both SYG-1 and SYG-2 are expressed and function in the same presynaptic cell, suggesting they may interact in cis, contrary to their previously described role in the C. elegans HSN neuron. Furthermore, we have found that the intracellular domain of SYG-2 alone is sufficient for inducing presynaptic assembly, in contrast to the accepted idea that the extracellular domains of CAMs are required for their function. Using CRISPR transgenesis, we can identify the critical sub-domains of SYG-1 and SYG-2 required for their function in presynaptic assembly.
MODELING HUMAN PATIENT CALCIUM CHANNEL MUTATIONS IN C. ELEGANS
Secondary structure of UNC-2/CaV2α.
UNC-2 splice isoforms differ in the position of their I-II loop.
Behavioral changes, such as an increase in “reversals” (or, backwards/forwards movement switches), are characteristic of some gain-of-function mutants in these channels. We can leverage this both to understand the circuit-level effects of these mutations as well as to perform forward genetic screens for suppressors of this phenotype, in the hopes of identifying additional therapeutic targets for patients with these variants.