Self-organizing cortex generated from human iPSCs with combination of FGF2 and ambient oxygen.

Human brain development has generally been studied through the analysis of postmortem tissues because of limited access to fetal brain tissues. This approach, however, only provides information from the perspective of long-term development. To investigate the pathophysiology of neurodevelopmental disorders, it is necessary to understand the detailed mechanisms of human brain development. Recent advances in pluripotent stem cell (PSC) technologies enable us to establish in vitro brain models from human induced PSCs (hiPSCs), which can be used to examine the pathophysiological mechanisms of neurodevelopmental disorders. We previously demonstrated that self-organized cerebral tissues can be generated from human PSCs in a three-dimensional (3D) culture system. Here, we describe the cerebral tissues differentiated from hiPSCs in a further-optimized 3D culture. We found that treatment with FGF2 is helpful to form iPSC aggregates with efficiency. Neuroepithelial structures spontaneously formed with apico-basal polarity in the aggregates expressing forebrain marker FOXG1. The neuroepithelium self-forms a multilayered structure including progenitor zones (ventricular and subventricular zones) and neuronal zone (cortical plate). Furthermore, with the same level of oxygen (O) as in ambient air (20% O), we found that self-formation of cortical structures lasted for 70 days in culture. Thus, our optimized 3D culture for the generation of cortical structure from hiPSCs is a simple yet effective method.