Summary: New research clarifies the molecular and genetic mechanisms that allow the brain to form long-term memories. A single stimulation of hippocampal synapses triggered repeated cycles in which the memory-related gene Arc produced mRNA that was locally translated into Arc protein, strengthening synapses. The team identified a novel feedback loop that helps explain how short-lived mRNA and proteins sustain long-lasting memories.
Source: Albert Einstein College of Medicine
How do we keep vivid memories of childhood moments — helping your mother make pancakes at age three, learning to ride a bike without training wheels, or your first romantic kiss?
A new study published online on April 25 in Neuron by researchers at Albert Einstein College of Medicine sheds light on that question.
“The ability to learn new information and retain it over long periods is one of the brain’s most remarkable features,” said Robert H. Singer, Ph.D., co-corresponding author of the study.
“In mice, we uncovered surprising molecular behavior that helps explain how those long-term memories are built and maintained.” Dr. Singer is a professor of cell biology in the Dominick P. Purpura Department of Neuroscience, chair emeritus of anatomy & structural biology, and director of the Program in RNA Biology at Einstein.
Researchers already knew that memories are formed and stored in neurons within the hippocampus, and that repeated neural activity strengthens synapses — the connections between nerve cells. Forming long-term memories requires the stabilization of those strengthened synapses, a process that depends on new proteins. Those proteins are produced from messenger RNA (mRNA) transcribed from memory-associated genes.
“Here is the paradox: long-term memory formation takes hours, but many of the mRNAs and proteins involved are short-lived, disappearing within an hour,” said Sulagna Das, Ph.D., first and co-corresponding author and research assistant professor of cell biology at Einstein. “How can short-lived molecules support a process that unfolds over much longer times?”
To investigate, the team engineered a knockin mouse model in which every mRNA molecule transcribed from the Arc gene — a gene essential for converting experience into long-term memory — was fluorescently tagged. Arc is known as an immediate early gene (IEG) that plays a key role in synaptic plasticity and memory consolidation.
Using high-resolution imaging techniques developed in their lab, the researchers stimulated hippocampal synapses and tracked Arc mRNA dynamics and local protein synthesis in individual neurons in real time, both in cultured cells and in brain tissue slices.
They found that a single, brief synaptic stimulus was enough to trigger multiple rounds of Arc transcription and local translation within the same neuron. New Arc protein produced after the initial stimulus returned to the Arc gene locus and reactivated transcription, creating a positive feedback loop that produced repeated cycles of mRNA production and translation.
“We observed that some protein molecules produced from the initial synaptic event feed back to reinduce Arc transcription, setting off another round of mRNA synthesis and protein production,” said Dr. Singer. “This cycle repeated several times.”
With each cycle, more Arc protein accumulated at specific synaptic locations, forming translational “hotspots.” These hotspots concentrated Arc at the synapse and consolidated protein into dendritic hubs where memories are stabilized. “This feedback loop explains how short-lived mRNAs and proteins can collectively produce long-lived synaptic changes required for persistent memory,” said Dr. Das.
Dr. Singer offered a real-world analogy: memorizing a poem requires repeated readings; each reading acts like a discrete stimulus that adds memory-building protein to the synapse, progressively strengthening and stabilizing the memory trace.
Because incorrect Arc expression has been linked to human memory disorders and neurological conditions such as autism spectrum disorder and Alzheimer’s disease, understanding Arc’s dynamics in response to neural activity may illuminate underlying causes and suggest new directions for research into these conditions, Dr. Das added.
The paper is titled “Maintenance of a short-lived protein required for long-term memory involves cycles of transcription and local translation.” Additional Einstein co-authors include Pablo Lituma, Ph.D., and Pablo Castillo, M.D., Ph.D., in the Dominick P. Purpura Department of Neuroscience.
About this memory research news
Author: Elaine Iandoli
Source: Albert Einstein College of Medicine
Contact: Elaine Iandoli – Albert Einstein College of Medicine
Image: The image is in the public domain
Original Research: Closed access. “Maintenance of a short-lived protein required for long-term memory involves cycles of transcription and local translation” by Robert H. Singer et al., published in Neuron.
Abstract
Maintenance of a short-lived protein required for long-term memory involves cycles of transcription and local translation
Highlights
- Reactivation of transcription drives repeated cycles of Arc gene expression in individual neurons
- New Arc proteins provide positive feedback that reinduces Arc transcription in subsequent cycles
- Arc mRNAs produced in later cycles preferentially localize to sites already marked by prior Arc protein
- Repeated local translation in hotspots consolidates Arc protein into selective dendritic hubs
Summary
Activity-dependent expression of immediate early genes (IEGs) is essential for long-term synaptic remodeling and memory consolidation. A major unresolved question has been how IEG-driven protein expression sustains memory when both transcripts and proteins turn over rapidly. To address this, the authors focused on Arc, an IEG critical for memory formation.
Using a knockin mouse in which endogenous Arc alleles were fluorescently tagged, the team performed real-time imaging of Arc mRNA and protein dynamics in single neurons in culture and in brain tissue. They discovered that a single burst of activity can trigger cycles of transcriptional reactivation in the same neuron. These subsequent transcription cycles depend on translation: newly synthesized Arc proteins participate in an autoregulatory positive feedback loop that reinduces transcription.
Arc mRNAs from later cycles localize to sites marked by earlier Arc protein, creating translation hotspots and consolidating protein into dendritic hubs. These cycles of transcription–translation coupling sustain Arc protein expression over time and provide a plausible molecular mechanism by which brief events can produce durable changes in synaptic strength underlying long-term memory.