Understanding the impact of early microexon misregulation on zebrafish sleep/wake behaviour

The developing nervous system requires a well-orchestrated and diverse set of proteins, setting the foundation of how an animal perceives the world. Disruptions may result in neurodevelopmental disorders, including autism spectrum disorders (ASD), with patients displaying altered sensitivity to their environment. A highly-conserved program of neuron-specific microexons (3-27 nucleotides) is frequently disrupted in ASD and known to shape protein-protein interactions during late neurogenesis, fine-tuning neuronal processes such as synapse formation. Little is known as to how misregulation of this program affects signalling cascades in the developing brain, shaping behaviour. Using zebrafish larvae, we set out to investigate this using a mutant of the microexon splicing master regulator srrm3. Performing single-cell and bulk RNA-sequencing experiments we found that microexon-harbouring genes are more frequently differentially expressed. Phenotypically, using zebrafish tracking and calcium imaging, we described ASD-like phenotypes including sensory hypersensitivity, hyperlocomotion and sleep loss accompanied by altered neuronal firing in srrm3 mutants. Coupling of behavioural and pharmacological assays allowed us to identify in mutants aberrant cAMP signalling, likely resulting in a downregulation of synaptic plasticity genes that could be rescued pharmacologically. Our research sheds new light onto the dynamics of the developing zebrafish nervous system in the context of microexon misregulation, with wider implications on the connection between brain state and behaviour.