day 25 (Fig. 1c) but was distributed more broadly at later stages (Fig. 1d). At day 60, we observed strong expression of GABA and the GABA-synthesizing enzyme GAD67 in neurons (Fig. 1e, f). Of the known markers that identify GABAergic subtypes, somatostatin (SST), calretinin (CR) and calbindin (CB) were the most strongly expressed; at later stages (> 200 days), and consistent its expression later in development in vivo12, parvalbumin (PV) was also present (Fig. 1g, h; Extended Data Fig. 1).
