An important observation made repeatedly during this study was that the cellular structures and zones of the organoid rosettes and their development were consistently reproducible among hESC H9, HUES8, and the four control iPSC line organoids, but were noticeably disturbed in all schizophrenia iPSC organoids and after pharmacological inhibition of FGFR1. In the organoids developed from either hESCs or control iPSCs, the proliferating cells were restricted to 2–3 layers surrounding the lumen of the VZ rosettes. Relatively few cells that migrated to the IZ remained in a proliferative state, but essentially, no such cells were found in the CZ. One of the most striking features of the schizophrenia iPSC organoids was the disruption of the developmental strata. Specifically, we observed significantly increased proliferation and movement of Ki67+ NPCs into the IZ, and development of atypically placed deep subcortical neurons. These changes were accompanied by significant loss of the TBR1 pioneer neurons from the top cortical layers, while they remained abundant deep in the IZ. Together, these findings illuminated an abnormal subcortical neuronogenesis in schizophrenia tissue and were consistent with the increased, premature neuronal generation, predicted from the transcriptome studies of the NPCs derived from schizophrenia iPSCs29.
