Cortical interneurons include a diverse set of neuron types with distinct roles in cortical development and function (Batista-Brito and Fishell, 2009). The relatively rapid pace of maturation in our mouse cortical feeder system allowed us to assess co-expression of more mature interneuron markers and to define neurotransmitter phenotypes beyond GABA and ChAT. In the day 2-18 group we observed a large percentage of GFP+ cells expressing TH (Figure 6A), consistent with the dopaminergic nature of NKX2.1-lineage hypothalamic neurons (Yee et al., 2009). Immunohistochemistry showed high percentages of nNOS cells in GFP+ cells from the day 2-18 and Calbindin in those from the day 10-18 group (Figure 6B,C). We also observed expression of markers characteristic of differentiated cortical interneurons, including SST and PV (Figures 6D,E), again mainly in the day 10-18 group. Representative images for each subgroup marker, co-expressed together with NKX2.1::GFP, are presented in Figure 6F–J. No VIP or calretinin expressing neurons were observed suggesting the lack of cells exhibiting features of the caudal ganglionic eminence (Xu et al., 2004). The derivation of NKX2.1+/PV+ was particularly remarkable given the late
