Figure 2.

(a) Converted human iNs display complex branching after six months in vivo; converted RFP-expressing human iNs keep their neuronal morphology and extend their branching from one to six months after transplantation. Scale bars, 20 μm. (b) Cells expressing the fibroblast markers, TE7 and RFP, are found both in the hippocampus and in the striatum at one month postgrafting. At 6 months, unconverted cells expressing TE7 can still be found. RFP-expressing cells, however, do not express TE7 at this time point. Scale bars: 20 μm. (c) Three electrophysiological profiles of iN cells are found six months after transplant. Representative traces of whole-cell recordings for the cells that do not fire any APs (nonspiking), the cells that fire one nonovershooting AP (not overshooting), and the cells that fire multiple APs (multiple APs). ((c), 1) Membrane potential changes induced by current injection steps with 20 pA increments at RMP. ((c), 2) Ramp depolarization from 0 to 50 pA. ((c), 3) 10 mV depolarization voltage steps from −70 mV induce small inward sodium current in the cells with single not overshooting AP and big inward sodium and outward potassium currents in the mature cells with multiple APs. Scale bars: (a) 20 mV/50 ms; (b) 10 mV/100 ms; and (c) 250 pA/5 ms. (d) A proportion of iN cells matures into GABAergic neurons expressing interneuron markers. Immunostaining for GABA and RFP revealed colocalisation in induced neurons, and staining for interneuron-specific marker parvalbumin (PV) showed presence of PV interneurons amongst directly converted neurons.