We then sought to characterize the neurotransmitter phenotype of iN cells. After 21 days of culture in minimal neuronal media, we detected vGLUT1-positive puncta outlining MAP2-positive neurites of some cells, indicating the presence of excitatory, glutamatergic neurons (Fig. 1o). In addition, we found iN cells labeled with antibodies against GABA, the major inhibitory neurotransmitter in brain (Fig. 1p). Some iN cells (9 out of ~500) contained the Ca2+-binding protein calretinin, a marker for cortical interneurons and other neuronal subtypes (Supplementary Fig. 3c). No expression of tyrosine hydroxylase (TH), choline acetyltransferase (ChAT) or serotonin (5HT) was detected. The vast majority of iN cells were negative for peripherin, an intermediate filament characteristic of peripheral neurons (data not shown)27.
