We investigated the neurodevelopmental stages of cells in each zone by immunostaining for proliferating NPCs with the nuclear Ki67 antigen46, doublecortin (DCX) expressed by neuroblasts, and βIII-tubulin expressed by young, immature neurons (NCCs)45. These stainings revealed cellular organization consistent with the inside-out pattern of human neocortex development15 (Fig. 1, b3, b4 and b5). Proliferative Ki67+ cells (Fig. 1, b5, Supplementary Fig. 1b3) and GFAP-expressing radial glia (Supplementary Fig. 1b2) were mostly present in the VZ, similar to the developing brain in the ventricular and sub-VZs, where generation of new cells by the brain stem and progenitor cells takes place. Few Ki67+ cells were found in the IZ and proliferating cells were not detected in the CZ (Fig. 1, b5, Supplementary Fig. 1b3). The doublecortin+ neuroblasts were present in the IZ and the CZ, and the βIII-tubulin+ NCCs were found predominantly in the CZ.
