The hiPSCs clones (provided by CAS, Dr Pei’s lab) were cultured in mTeSR™ 1 medium (STEMCELL Technologies) in a matrigel (BD Matrigel™, hESC-qualified Matrix, 354277) coated dish. When the confluence of iPSCs in a well of a 6-well plate reached 95%, the cells were detached with EDTA (5 × 10−4 mol/L) and replated into one well of a 12-well plate. When the cells reached full confluence after 1–2 days, the medium was switch to N2B27 + 2 inhibitors (Dorsomorphin and SB4315242, Selleck) so as to induce neuronal differentiation. Cells were mechanical divided into fragments after 8 days of neuronal differentiation induction. The fragments in one well of 12 well plate were replanted into 2 wells of a 6-well matrigel-coated plate, and cultured in neural proliferation system I (N2B27, Thermo Fisher Scientific) medium. On the 8th day of proliferation, cell clones form one well of the 6-well plate were mechanical scraped into floating fragments, and the floating fragments were plated into non-coated T25 flask for floating culture with neural proliferation system II (N2B27 + 20 ng/mL bFGF + 20 ng/mL EGF,
