To assemble the forebrain spheroids, hCS and hSS (~60 to 90 days of in vitro differentiation), which were virally labeled 8–10 days before, were transferred to a 1.5 ml microcentrifudge Eppendorf tube for three days and placed in an incubator. During this time, more than 95% of hCS and hSS fused. These hSS-hCS cultures were carefully transferred into 24 well ultralow attachment plates (Corning) using a cut P-1000 pipette tip and medium changes were performed very gently every two to three days.
