hiPSCs were differentiated into MGE progenitors as previously reported with modifications26–28. On day 1 through day 8 of differentiation, MGE spheres were grown in suspension in KSR medium supplemented with Rock Inhibitor (RI, Tocris Bioscience), the TGF-ß receptor inhibitor SB431542 (SB, Stemgent), the Wnt pathway inhibitor Wnt Antagonist II (IWP-II, Millipore), the Hedgehog pathway activator Smoothened Agonist (SAG, Millipore), and the bone morphogenetic protein receptor inhibitor LDN-193189 (LDN, Stemgent). On day 8, MGE spheres were transferred to KSR media supplemented with FGF-8 (PeproTech), IWP-II, SAG, and LDN. On day 21, MGE-progenitors were dissociated with Accutase and plated on culture plates coated with PLL overnight at 37°C and Laminin for ≥ 1hour at 37°C in neural induction medium containing DMEM/F12 and Neurobasal Medium (1:1, Thermo Fisher), N2 Supplement, B27 Supplement (Life Technologies), NEAA, Glutamax, and penicillin/streptomycin supplemented with Brain-Derived Neurotrophic Factor (BDNF, PeproTech), Glial-Derived Neurotrophic Factor (GDNF, PeproTech), the γ secretase inhibitor DAPT (Tocris), the MEK/ERK pathway inhibitory SU5402 (STEMCELL Technologies), and the MEK inhibitor PD0325901 (Tocris). From day 28 on, maturing GABAergic inhibitory interneurons were cultured in neural induction medium containing BDNF and GDNF for up to 5 weeks.
