Summary: A new study found that altered neuronal microexons cause hyperarousal and insomnia in zebrafish. The researchers discovered that abnormal alternative splicing spikes cAMP signaling, which acts as an internal neuronal thermostat, leaving the brain permanently overexcited.
Because this pathway is evolutionarily conserved and linked to human microexon mutations, the findings offer vital insights into the sleep disturbances and sensory hypersensitivity seen in autism and schizophrenia, while proving that chemical inhibitors targeting cAMP can completely normalize hyperactivity.
Key Facts
- Microexon-Driven Hyperarousal: Disrupted alternative splicing of tiny neuronal microexons directly causes sensory hypersensitivity, hyperarousal, and severe sleep deprivation.
- The Cellular Thermostat: The genetic alteration causes a spike in cAMP signaling within the forebrain, permanently overexciting neurons and driving daytime hyperactivity.
- Reversible Behavioral Deficits: Scientists successfully normalized the hyperactive swimming and insomnia in mutated zebrafish by introducing a chemical inhibitor that lowers cAMP levels.
- Evolutionary Conservation: This sleep-deprivation mechanism is identical to patterns previously identified by the same team in fruit flies, indicating the pathway is likely conserved in mammals and humans.
- Clinical Relevance to ASD & Schizophrenia: While not the sole cause of these complex conditions, microexon mis-regulation offers a clear biological explanation for the severe sleep disturbances and anxiety found in neurodevelopmental disorders.
Source: UPF Barcelona
The altered presence of tiny fragments of neuronal genes, called microexons, causes hyperarousal in zebrafish. This is the main conclusion of an international study led by the Pompeu Fabra University (UPF) and the Centre for Genomic Regulation (CRG).
An abnormal pattern of neural microexon presence leads to a hyperarousal state characterized by heightened neural activity and insomnia, commonly associated with stress but also in neurodevelopmental disorders. Arousal regulation is highly conserved in evolution.
Therefore, this finding could help understand the mechanism underlying some human neurodevelopmental disorders, such as autism and schizophrenia, conditions associated with microexon mutations.
To survive, animals need to be ready to react to external and internal stimuli. This activation of the central nervous system, arousal, is highly conserved throughout the animal kingdom. Proper regulation of arousal ensures that neural and thus behavioural responses maintain a balance between drowsiness or reduced responsiveness and insomnia and sensory hypersensitivity. Two states associated with stress and neurodevelopmental disorders.
To properly regulate arousal during development and adulthood, organisms require a broad range of diverse proteins that are achieved via alternative splicing. This is a process that can produce two functionally distinct proteins with similar but not identical amino acid sequence, in response to the presence or absence of one or more microexons.
The study published in Science Advances shows that, in zebrafish, an alteration in the presence of neural microexons leads to a state of hyperarousal. Abnormal fish larvae have an altered swim pattern and reduced sleep. “They sleep less frequently, for shorter durations and take longer to fall asleep” explains Tahnee Mackensen, first author of the study. Who adds, “It is fascinating to see how, by analysing the movement of this transparent larvae, you can recall fish internal states.”.
In addition to the behavioural alterations, researchers found that mis-splicing alters cAMP levels –a signal produced within cells that regulates neuronal activity– making them more or less excitable. “Abnormal fish are permanently overexcited”, clarifies Mackensen. They have increased activity in the forebrain and elevated cAMP signalling, responsible for the hyperactivity during the day. However, this hyperactivity can be normalized by manipulating cAMP pharmacologically.
According to the study, reducing cAMP with a chemical inhibitor lowers the activity of the mutated fish to a normal level, whereas maintaining elevated cAMP levels in normal fish using drugs—either by inducing its synthesis or reducing its degradation—imitates highly aroused behaviour, confirming that cAMP is key to driving arousal behaviour. Or in the words of the scientist, ‘in neurons, cAMP acts as a thermostat for its activity’.
Study in zebrafish with a human angle
The constellation of behavioural and neuronal shifts observed in abnormal zebrafish had also been reported in flies in a previous study of the same group. “We do know that the alteration of these microexons causes sleep deprivation in fish and flies”, explains Manuel Irimia, who has led the research. And adds, “this mechanism is likely to be conserved in mammals, including humans, but maybe not in the exactly very same way”.
In humans, sleep disturbances and sensory hypersensitivity are frequent in neurological disorders like autism and schizophrenia, two disorders that are reported to have an altered microexon regulation.
“Despite not being causative of the disease, we know that changes in protein production, can contribute to symptoms of the disorder”, acknowledges Irimia, leader of the Transcriptomics of Development and Evolution lab at UPF and CRG. Who concludes, “in this sense, it is plausible to study whether the treatment to restore the arousal state in fish also corrects or alleviates the symptoms in other species”.
This cAMP-regulated arousal pathway is also implicated in anxiety and depression. That is why Mackensen believes it is worth continuing to investigate because “this could be just the tip of the iceberg”.
Key Questions Answered:
A: Microexons are tiny fragments of genes within neurons. Through a process called alternative splicing, the brain includes or excludes these fragments to build a vast, diverse range of proteins. When microexon patterns are disrupted, the brain can no longer properly regulate arousal, causing a state of hyperarousal where individuals sleep less frequently, stay asleep for shorter periods, and take much longer to fall asleep.
A: Cyclic adenosine monophosphate (cAMP) functions as an internal “thermostat” for neuronal activity. The study discovered that mis-spliced microexons cause a significant spike in cAMP levels, leaving the brain permanently overexcited. However, this is a two-way street: raising cAMP in normal fish instantly mimics hyperactive behavior, while chemically lowering cAMP in the mutated fish successfully cools down the thermostat and restores normal activity.
A: Arousal regulation is a deeply ancient, evolutionary mechanism shared across the animal kingdom. Because identical sleep deprivation patterns were found in both flies and zebrafish, it is highly likely that mammals and humans share this exact pathway. Since people with autism and schizophrenia frequently carry microexon mutations alongside severe insomnia and sensory overload, this research points to a concrete biological pathway that could be targeted to alleviate those specific symptoms.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neuroscience research news
Author: Marta Vila Cejudo
Source: UPF Barcelona
Contact: Marta Vila Cejudo – UPF Barcelona
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Neuronal microexons modulate arousal via the cAMP-PKA-CREB pathway in zebrafish” by Mackensen T, Iñiguez LP, Mullen TS, Rodriguez-Marin C, Kroll F, Zuccarini G, Fernandez-Albert J, Sancho-Vila L, Permanyer J, Bianco IH, Orger M, Rihel J, Irimia M. Science Advances
DOI:10.1126/sciadv.ady8291
Abstract
Neuronal microexons modulate arousal via the cAMP-PKA-CREB pathway in zebrafish
Proper regulation of arousal maintains the balance of rest and activity and enables appropriate responses to stimuli; its disruption is a hallmark of many neurodevelopmental disorders. Although transcriptional mechanisms of arousal control are well defined, the contribution of posttranscriptional processes such as alternative splicing remains unclear.
Here, we identify a critical role for the microexon splicing regulator srrm3 in maintaining arousal homeostasis in zebrafish. srrm3 mutants exhibit persistent hyperarousal characterized by sleep loss, sensory hypersensitivity, and elevated behavioral and neuronal activity.
We identify the cyclic adenosine monophosphate (cAMP)–cAMP-dependent protein kinase (PKA)–cAMP response element–binding protein (CREB) signaling axis as a central driver of mutant hyperarousal. Specifically, pharmacological inhibition of cAMP signaling rescues mutant hyperactivity and associated transcriptional changes whereas wild-type cAMP activation phenocopies the mutant.
Down-regulation of immediate early genes and reduced CREB phosphorylation further suggest adaptation to sustained neuronal activation. These findings establish srrm3-dependent microexon splicing as a key molecular layer of arousal regulation linking RNA-processing defects to neuromodulatory imbalance.
