In order to promote the GABAergic cell fate, we cloned six transcription factors known to play important roles during the formation of inhibitory neurons and expressed each of the factors together with Ngn2, Neurod1 or Ascl1 + Myt1l (collectively termed AM) in human ES cells using doxycycline-inducible lentiviral vectors. We cultured the transduced cells with mouse glia and performed patch–clamp recordings 28 d later to assess the formation of functional inhibitory synapses (Supplementary Fig. 1). The iN cells generated by various transcription factor combinations displayed three different patterns of spontaneous synaptic currents—exclusively excitatory postsynaptic currents (EPSCs), exclusively inhibitory postsynaptic currents (IPSCs), or both EPSCs and IPSCs (mixed currents). Of note, the combination of AM factors together with Dlx2 (AMD pool) produced cells with only IPSCs, which suggested that the cultures consisted of largely homogenous GABAergic neurons (Fig. 1a and Supplementary Fig. 1). We therefore decided to further characterize the iN cells generated by AMD.
