Cell type-specific disruption of cortico-striatal circuitry drives repetitive patterns of behaviour in fragile X syndrome model mice

Individuals with fragile X syndrome (FXS) are frequently diagnosed with autism spectrum disorder (ASD), including increased risk for restricted and repetitive behaviours (RRBs). Consistent with observations in humans, FXS model mice display distinct RRBs and hyperactivity that are consistent with dysfunctional cortico-striatal circuits, an area relatively unexplored in FXS. Using a multidisciplinary approach, we dissected the contribution of two populations of striatal medium spiny neurons (SPNs) in the expression of RRBs in FXS model mice. We found that dysregulated protein synthesis at cortico-striatal synapses is a molecular culprit of the synaptic and ASD-associated motor phenotypes displayed by FXS model mice. Cell-type-specific translational profiling of the FXS mouse striatum revealed differentially translated mRNAs, providing critical information concerning potential therapeutic targets. Our findings represent the first evidence of a cell-type specific impact of the loss of FMRP on translation and the sequence of neuronal events in the striatum that drive RRBs in FXS. Highlights Dysregulated striatal protein synthesis underlies altered synaptic plasticity and RRBs displayed by FXS model mice FXS model mice exhibit cell type-specific molecular, morphological, and synaptic changes in the dorsolateral striatum Selective deletion of Fmr1 from dSNPs in mice alters translation and causes repetitive behavior TRAP-Seq indicates that there is altered binding of >120 mRNAs to ribosomes in dSNPs of Fmr1 KO mice G-protein signaling (RGS) 4 translation is significantly reduced in dSPNs in FXS model mice Treatment of FXS model mice with VU0152100, a positive allosteric modulator of the M4 muscarinic receptor that is upstream of RGS4, can reverse RRBs