Cell death reduces Mpp5 het CKO progenitor pools. (A–L) Mice injected with BrdU at E13.5 analyzed at E14.5 with double immunostaining for BrdU and additional markers. The proportion of radial glia progenitors (Sox9+, A–C, −50%, P = 0.00002), intermediate progenitors (Tbr2+, D–F, −29%, P = 0.0001) and post-mitotic cortical cells (p27+, G–H, −11%, P = 0.02) among total BrdU+ cells is compared in WT and Mpp5 het CKO. The proportion of cells undergoing apoptotic cell death marked by CC3 among total BrdU+ cells is also assessed (J–L, 442%, P = 0.00016). Data are presented as mean ± SEM. E14: WT, n = 4; Mpp5 het cKO, n = 4.