Thalamocortical organoids reveal axonogenesis phenotypes of 22q11.2 microdeletion [scRNA-seq]

Dysfunction of the thalamocortical pathway has been implicated in multiple psychiatric disorders, but mechanisms by which these defects emerge remain poorly understood. We explored this question in the context of the 22q11.2 microdeletion, which represents a significant genetic risk for schizophrenia, leveraging emerging technologies of in vitro brain organogenesis using chimeric brain organoids derived from human induced pluripotent stem cells. Here we show that the 22q11.2 microdeletion leads to transcriptional dysregulation in thalamic organoids that is enriched for psychiatric disease risk genes, including elevated expression of FOXP2, which represents the most significantly dysregulated transcription factor in glutamatergic neurons and astroctyes. In a co-culture model fusing thalamic and cortical organoids, we demonstrate that the 22q11.2 deletion mediates an overgrowth of thalamic axons via overexpression of FOXP2, which then subsequently mediates the overgrowth of reciprocal corticothalamic axons. Dysregulation of FOXP2 leads to downregulation of ROBO2, an axon repulsive receptor important for thalamocortical axon pathfinding, and knockdown of ROBO2 in control organoids phenocopies excessive outgrowth of thalamic axons. Together, our study suggests that early steps in thalamocortical pathway development may be dysregulated in a model of genetic risk for schizophrenia, and contribute to neural phenotypes in 22q11.2 microdeletion syndrome. Thalamic and cortical organoids derived from iPS cells carrying the 22q11 deletion or karyotypically normal controls were cultured for 10 weeks and then dissociated to perform single cell RNA-sequencing (either 10X v2 or v3 platform)