Summary: Researchers detail how individual neurons achieve distinct communication patterns through RNA editing of a key presynaptic protein.
Using Drosophila fruit fly motor neurons as a model, scientists identify the protein Complexin as a key regulator that limits spontaneous neurotransmitter release. Their work shows that RNA editing can generate up to eight different versions of the Complexin 7A protein, and these variants change how effectively Complexin suppresses glutamate release at synapses.
This molecular flexibility appears to provide neurons with a precise, cell-by-cell way to tune synaptic output and shape neural circuit function.
Key Facts:
- Complexin is a presynaptic protein in fruit fly neurons that controls the release of the neurotransmitter glutamate.
- RNA editing of the Complexin 7A transcript produces multiple protein variants with different clamping abilities, altering spontaneous neurotransmitter release.
- Heterogeneous RNA editing across neurons — and combinations of edited forms within the same neuron — can fine-tune synaptic signaling and potentially neural development.
Source: Picower Institute for Learning and Memory
Neurons communicate by releasing chemical signals called neurotransmitters at synapses, producing behaviors from movement to mood. Even cells of the same neuronal type can differ in how and when they release these signals.
A study published in Cell Reports from researchers at The Picower Institute for Learning and Memory reveals a molecular mechanism that helps explain this intra-type diversity. Focusing on motor neurons that control muscle in Drosophila, the team probed how RNA editing of Complexin 7A influences synaptic glutamate release.
Complexin is known to clamp spontaneous fusion of glutamate-filled vesicles at the presynaptic membrane, preserving neurotransmitter for action potential–triggered release. In flies, two Complexin isoforms were previously identified; mammals have more. Earlier work from Troy Littleton’s lab showed that the less common 7B splice form is regulated by phosphorylation. How the abundant 7A form is tuned, however, remained unclear.
Previous observations indicated that the RNA encoding Complexin 7A can be modified by the ADAR enzyme, which edits adenosine to inosine in RNA. In the current study, led by former graduate student Elizabeth Brija, the researchers examined whether such editing changes Complexin function and whether editing varies between individual neurons.
Their findings reveal substantial and stochastic diversity. By sequencing RNA from the nuclei and cell bodies of 200 identified motor neurons, the team found that three adjacent adenosine nucleotides in the Complexin C-terminus can be edited in various combinations, producing eight distinct protein variants. Although one form tended to dominate, 96 percent of the neurons showed at least some editing, and the relative abundance of the edited forms varied widely between cells.
Functional tests confirmed that these molecular differences matter. The researchers removed Complexin genetically and then “rescued” flies by supplying either the unedited 7A form or specific edited versions. One edited variant acted as a weak clamp: it failed to prevent much spontaneous glutamate release and allowed increased synaptic currents. Another edited version proved to be a stronger clamp than the unedited protein, tightly suppressing spontaneous release and limiting synaptic output.
These differences extended to synaptic structure. While both edited forms displayed altered subcellular localization, drifting away from synapses into axons, only the strong-clamping edition prevented excessive synaptic growth. The weak-clamping edition permitted greater synapse overgrowth, indicating that editing not only modulates acute neurotransmitter release but can influence synaptic development.
Because individual neurons commonly express multiple Complexin editions simultaneously, the team also tested mixed rescues. Combining the unedited form with a weak-clamping edition produced intermediate effects, reducing spontaneous release compared with the weak form alone. This combinatorial behavior implies that neurons can tune synaptic output in graded ways by varying the mixture of edited Complexin variants.
Further analysis showed that other presynaptic proteins implicated in glutamate release, including Synapsin and Syx1A, also undergo RNA editing with differing levels across the same neuron population. This pattern suggests a broader strategy: RNA editing might act in parallel across several synaptic components to produce nuanced, cell-specific control of neurotransmission.
“By editing RNA transcripts differently across cells, a single transcriptome can give rise to diverse neuronal behaviors,” said Littleton. The authors emphasize that stochastic RNA editing offers a flexible and robust mechanism to alter multiple features of neuronal output without changing underlying DNA sequences.
In addition to Elizabeth Brija and Troy Littleton, co-authors include Zhuo Guan and Suresh Jetti.
Funding: The research was supported by the National Institutes of Health, The JPB Foundation and The Picower Institute for Learning and Memory.
About this neuroscience research news
Author: David Orenstein
Source: Picower Institute for Learning and Memory
Contact: David Orenstein – Picower Institute for Learning and Memory
Image: The image is credited to Neuroscience News
Original Research: Open access. “Stochastic RNA editing of the Complexin C-terminus within single neurons regulates neurotransmitter release” by Troy Littleton et al., Cell Reports