Our longstanding question is how neural stem cells are regulated to achieve precise cell division, cell migration, and cell fate specification during brain development. I use both in vivo mouse models and in vitro human cell cultures, combined with induced pluripotent stem cell (iPSC) technology, to model normal brain development and brain disorders. Especially, a recently developed protocol in the lab for 3D neural differentiation of brain organoids has provided a significant opportunity to study human brain development in vitro. Using these technologies, We have investigated neural stem cell behaviors under genetic mutations related to human brain disorders and pathogenic infection.