Forebrain assembloids support the development of fast-spiking human PVALB+ cortical interneurons and uncover schizophrenia-associated defects.
Disruption of parvalbumin positive (PVALB+) cortical interneurons is implicated in the pathogenesis of schizophrenia. However, how these defects emerge during development is not well understood. The protracted maturation of these cells during postnatal development has made their derivation from human pluripotent stem cells (hPSCs) extremely difficult, precluding  hPSC-based disease modeling of their role in neuropsychiatric diseases. Here we present a cortical assembloid system that supports the development of PVALB+ cortical interneurons which match the molecular profiles of primary PVALB+ interneurons and display their distinctive electrophysiological features. Further, we characterized cortical interneuron development in a series of CRISPR-generated isogenic structural variants associated with schizophrenia and identified variant-specific phenotypes in cortical interneuron migration and the molecular profile of PVALB+ cortical interneurons. These findings reveal plausible mechanisms on how disruption of cortical interneuron development may impact schizophrenia risk and provide an exciting human experimental platform to facilitate the study of PVALB+ cortical interneurons. Overall design: Cortical assembloids were generated by seperately patterning dorsal and ventral forebrain organoids using dual SMAD and WNT inhibition followed by Sonic activation for the ventral forebrain. Organoids were fused at day 30 to make assembloids and collected for scRNA seq at days 60, 75 or 125 via a papain dissociation.