Figure 1. Characterization of neuronal conversion and maturation in human induced-neuronal cells.

(a) Schematic of long-term iN reprogramming to functional neurons. (b) After 12 days of conversion, iN cells express βIII-tubulin and MAP2. (c) Further differentiation on glial cells for 28 days allows specification of several neuronal subtypes, including vesicular GABA transporter-expressing GABAergic neurons and tyrosine hydroxylase-expressing dopaminergic neurons, in addition to the predominantly glutamate vescular transporter-expressing glutamatergic neurons. (d) Day 28 iN cells also extensively express mature neuronal makers such as the synaptic vesicle protein synaptophysin. (e) Whole-cell current recordings demonstrate that iN cells after 14 days culture in the absence of glia are predominantly electrically active with functional voltage-dependent Na⁺ channels, as well as voltage-dependent K⁺ channels, and (f) fire repetitive induced-action potentials (n=27/27). Scale bar, 50 μm. Inset: Scale bar, 10 μm.