Mackensen, T. | bioRxiv Science

bioRxiv2025

Neural microexons modulate arousal states via cAMP signalling in zebrafish

Arousal states, often dysregulated in neurodevelopmental disorders, shape how organisms perceive and respond to their environment. Here, we show that srrm3, a master regulator of neural microexons, is essential for normal arousal in zebrafish larvae. srrm3 mutants exhibit persistent hyperarousal, including sleep loss, sensory hypersensitivity, anxiety-like behaviour, and heightened neural and behavioural activity. Elevated cAMP signalling likely drives this hyperarousal, as pharmacologically reducing cAMP rescues mutant behaviour, while increasing cAMP in wild-type larvae phenocopies the mutant hyperaroused state. Pharmacological cAMP modulation also mimics and reverses srrm3-dependent transcriptional changes. These include immediate early gene downregulation, which, together with altered activity-dependent transcription factor motif occupancy, suggest adaptation to sustained neuronal hyperactivity. Additionally, srrm3 mutants show upregulation of microexon- containing genes, likely compensating for microexon loss. Together, these findings reveal a role for neural microexons in shaping arousal via cAMP signalling, providing insight into how splicing defects may underlie sensory and sleep disturbances.

neuroscience↗

bioRxiv2024

Phenotypic impact of individual conserved neuronal microexons and their master regulators in zebrafish

Microexons exhibit striking evolutionary conservation and are subject to precise, switch-like regulation in neurons, orchestrated by the splicing factors Srrm3 and Srrm4. Disruption of these regulators in mice leads to severe neurological phenotypes, and their misregulation is linked to human disease. However, the specific microexons involved in these phenotypes and the effects of individual microexon deletions on neurodevelopment, physiology, and behavior remain poorly understood. To explore this, we generated zebrafish lines with deletions of 18 individual microexons, alongside srrm3 and srrm4 mutant lines, and conducted comprehensive phenotypic analyses. We discovered that while loss of srrm3, alone or together with srrm4, resulted in significant alterations in neuritogenesis, locomotion, and social behavior, individual microexon deletions typically produced mild or no noticeable effects. Nonetheless, we identified specific microexons associated with defects in neuritogenesis (evi5b, vav2, itsn1, src) and social behavior (vti1a, kif1b). Additionally, most microexon deletions triggered coordinated transcriptomic changes in neural pathways, suggesting the presence of molecular compensatory mechanisms. Our findings suggest that the severe phenotypes caused by Srrm3/4 depletion arise from the combined effects of multiple subtle disruptions across various cellular pathways, which are individually well-tolerated.

molecular biology↗