# Effect of Nanoscale Active Zone Morphology on Synaptic Vesicle Release Probability

> **NIH NIH F31** · MASSACHUSETTS INSTITUTE OF TECHNOLOGY · 2020 · $45,520

## Abstract

Regulation of the release probability (Pr) of single synaptic vesicles (SVs) from active zones (AZs) determines
the presynaptic contribution to synaptic strength. Dynamic regulation of synaptic strength is thought to underlie
learning and memory, so fundamental knowledge of the molecular mechanisms governing Pr is critical to
understanding these vital neuronal processes. The Drosophila neuromuscular junction (NMJ) is a widely-used
model synapse for studying Pr due to its accessibility and genetic toolkit. In this system, two glutamatergic motor
neuron classes (termed 1b and 1s) with distinct excitability and synaptic properties each form hundreds of AZs
onto individual body wall muscles. At each AZ, structural proteins position SVs near voltage-gated calcium
channels. Calcium influx is detected by calcium-sensing proteins on SV membranes, triggering SV release.
However, calcium is also quickly buffered once inside the cell, making the distance between SVs and calcium
channels extremely important for determining Pr. Recent studies have shown that Pr is heterogeneous across
AZs formed by 1b and 1s and can vary as much as 50-fold between neighboring AZs. However, the sources of
this heterogeneity have not been fully identified. Accumulating evidence suggests that structural AZ proteins play
a large role in regulating Pr by regulating position of SVs relative to calcium channels. Super-resolution stimulated
emission depletion (STED) imaging reveals that AZ structural proteins vary widely in their nanoscale morphology
across individual AZs, suggesting that heterogeneity in AZ morphology could explain heterogeneity in Pr across
AZs. Additionally, recent data indicates that average AZ morphology and Pr are significantly different between
AZs formed by 1b and 1s, suggesting that a difference in gene expression between these neurons is likely to
control cell-wide AZ morphology. Single-cell RNA sequencing indicates that Toll-6 is one of the most differentially
expressed genes between 1b and 1s neurons, and preliminary data indicates that it is capable of affecting AZ
morphology and electrophysiology making it a likely candidate underlying difference in AZ properties between
these neuronal classes. To determine how AZ morphology correlates with Pr across 1b and 1s neurons, a novel
genetically encoded fluorescent release sensor and STED microscopy will be used on Drosophila NMJs to
compare nanoscale AZ morphology and Pr at single AZs. An exogenous calcium buffer will be used to investigate
importance of morphology in determining nanodomain distance coupling between SVs and calcium channels.
To determine how Toll-6 affects cell-wide AZ morphology and Pr, Toll-6 expression levels in 1b and 1s neurons
will be individually genetically manipulated. This project will be carried out in the lab of Dr. Troy Littleton in the
Picower Institute for Learning and Memory (PILM) at the Massachusetts Institute of Technology (MIT). All
necessary equipment is available through...

## Key facts

- **NIH application ID:** 10068206
- **Project number:** 1F31NS118948-01
- **Recipient organization:** MASSACHUSETTS INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** Andres Crane
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $45,520
- **Award type:** 1
- **Project period:** 2020-09-01 → 2023-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10068206

## Citation

> US National Institutes of Health, RePORTER application 10068206, Effect of Nanoscale Active Zone Morphology on Synaptic Vesicle Release Probability (1F31NS118948-01). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10068206. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*