# Molecular and Cellular Mechanisms Mediating Structural and Functional Active Zone Maturation

> **NIH NIH R01** · MASSACHUSETTS INSTITUTE OF TECHNOLOGY · 2021 · $384,313

## Abstract

The current proposal describes experimental approaches to determine how neurons regulate
structural and functional maturation of active zones (AZs), a key signaling hub where synaptic
communication occurs. Although membrane trafficking mechanisms are highly conserved
across cells, additional synapse-specific regulation has evolved to mediate rapid Ca2+-
dependent synaptic vesicle (SV) fusion at specialized presynaptic AZs that are precisely aligned
to postsynaptic receptors. Multiple evolutionarily conserved proteins are found at AZs, including
RIM, RIM binding protein, Syd-1, Liprin-α,
ELKS/CAST/Bruchpilot (BRP), Bassoon/Piccolo/Fife
and Unc13. Previous studies in our lab demonstrated that the hundreds of AZs formed by a
single glutamatergic motoneuron in Drosophila have a heterogeneous distribution of synaptic
strength, with neighboring AZs often showing >50-fold differences in the probability of release
(Pr) of SVs. We found that AZ maturation drives increased synaptic strength occur over a multi-
day developmental period, with newly formed AZs developing as weak Pr sites before maturing
into high Pr AZs through the coordinated accumulation of a core set of proteins. In the current
application, we will determine how neurons regulate structural and functional maturation of AZs,
and how variations in these processes drive synaptic diversity. The mechanisms regulating AZ
maturation fall into two broad categories: those that control cell-wide availability of key building
blocks to growing AZs (Aim 1) and those that affect capture and retention of new material at
individual AZs (Aim 2). We will determine whether specific AZ proteins are produced and
transported in excess of their incorporation into growing AZs, or whether their availability at the
synaptic terminal is rate-limiting for AZ maturation. In addition, we will characterize the efficiency
of material capture at individual AZs throughout the AZ maturation cycle. Finally, we will
examine how material availability and capture differ in tonic and phasic motoneurons that
innervate the same postsynaptic muscle, but display striking differences in their AZ organization
and SV release properties (Aim 3). These studies will provide new insights into how synaptic
strength develops across the cohort of AZs of a neuron, as well as how synaptic diversity can
be more broadly controlled across neuronal subclasses.

## Key facts

- **NIH application ID:** 10206877
- **Project number:** 1R01NS117588-01A1
- **Recipient organization:** MASSACHUSETTS INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** J. TROY LITTLETON
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $384,313
- **Award type:** 1
- **Project period:** 2021-02-15 → 2026-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10206877

## Citation

> US National Institutes of Health, RePORTER application 10206877, Molecular and Cellular Mechanisms Mediating Structural and Functional Active Zone Maturation (1R01NS117588-01A1). Retrieved via AI Analytics 2026-05-28 from https://api.ai-analytics.org/grant/nih/10206877. Licensed CC0.

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