To determine the extent of interneuron precursor maturation in vivo, we assessed morphological appearance and the expression of interneuron-related markers in the grafted cells from the day 10-18 group (Figure S3). At 1–2 months after grafting into the neonatal cortex most human cells retained undifferentiated bipolar or unipolar morphologies and NKX2.1 expression. Furthermore, essentially all grafted cells expressed the neuronal precursor marker DCX, including those with multipolar morphologies (Figure S3). As it occurs in rodents, the large majority of human interneuron precursors expressed GABA (46/51 GFP+ cells located at the section surface; Figure S3). In contrast, there was no co-labeling for parvalbumin (PV) or somatostatin (SST), two proteins marking the major subclasses of Nkx2.1-lineage interneurons. These data suggest that even by six or 8 weeks post-transplant, the Nkx2.1-GFP+ cells had not yet differentiated into mature interneurons (Figure S3).
