Autism-misregulated eIF4G microexons control synaptic translation and higher-order cognitive functions [iCLIP-seq]

Microexons represent the most highly conserved class of alternative splicing, yet their functions are poorly understood. Here, we focus on closely related neuronal microexons overlapping prion-like domains in the translation initiation factors, eIF4G1 and eIF4G3, the splicing of which is activity-dependent and frequently disrupted in autism. CRISPR-Cas9 deletion of these microexons selectively up-regulates synaptic proteins that control neuronal activity and plasticity and further triggers a gene expression program mirroring that of activated neurons. Mice lacking the Eif4g1 microexon display social behavior, learning and memory deficits, as well as alterations in hippocampal synaptic plasticity. The eIF4G microexons appear to reduce synaptic protein synthesis by causing ribosome stalling, through a mechanism whereby they promote the coalescence of cytoplasmic granule components associated with translation repression, including the Fragile X mental retardation protein, FMRP. The results thus reveal an autism-disrupted mechanism by which alternative splicing specializes translation to control higher-order cognitive functioning. Overall design: iCLIP-seq of Srrm3 and Srrm4 in in-vitro differentiated mouse neurons