Foxp1 regulates the development of glutamatergic synaptic input onto spiny projection neurons expressing Drd2 [snRNA-seq]

Long-range glutamatergic inputs from the cortex and thalamus provide important motor and cognitive information to the striatum where they are integrated for learning and action planning. Genetic programs and transcription factors that orchestrate the development of these inputs are relatively unknown. The transcription factor, FOXP1, is crucial for the development of spiny projection neurons (SPNs) in the striatum. We investigated the cell-specific role of Foxp1 in the formation of glutamatergic inputs – including corticostriatal inputs. Embryonic Foxp1 deletion in dopamine receptor 2-expressing SPNs (D2 Foxp1cKO) leads to reduced transmission of corticostriatal excitatory inputs and decreased synaptically driven excitability. Postnatal deletion of Foxp1 also resulted in decreased glutamatergic inputs onto D2 SPNs. Single nuclei RNA sequencing of D2 Foxp1cKO striatum identified downregulated postsynaptic genes, consistent with the synaptic phenotype. Reinstating Foxp1 postnatally rescued electrophysiological deficits and expression of a subset of genes that were altered by embryonic deletion in D2 SPNs. Postnatal Foxp1 reinstatement could also rescue behavioral phenotypes. In summary, we demonstrate that FOXP1 regulates the development of corticostriatal circuitry. Further, changes at multiple levels of brain function resulting from loss of Foxp1 are rescued with postnatal Foxp1 reinstatement, indicating a therapeutic approach for individuals with FOXP1 syndrome. We used single nuclei RNA sequencing (snRNA-Seq) in juvenile (P18) mouse striatum to test the effects of loss of Foxp1 in D2 SPNs and study gene expression changes with postnatal reinstatment of Foxp1 in striatum.