Pax6 is required cell autonomously for Tbr2 expression and repression of lateral ganglionic eminence markers in cortical cells. (A, B) Sections of cortex of Pax6−/−↔Pax6+/+ chimera double-labeled for Tbr2 protein (green) and Pax6−/− cells (red dots resulting from DNA–DNA in situ hybridization to a reiterated β-globin transgene, β-glb). Most Pax6−/− cells do not express Tbr2 (Panel A, rostral section; Panel B, central section). (C, D) Sections of cortex (C) and lateral ganglionic eminence (D) of Pax6−/−↔Pax6+/+ chimera double-labeled for Mash1 protein (grey) and Pax6−/− cells (brown dots). In cortex, Mash1 expression is in Pax6−/− cells but not in wild-type cells. In the lateral ganglionic eminence, Mash1 is expressed in both wild-type and Pax6−/− cells. (E, F) Sections of rostral (E) and caudal (F) cortex of Pax6−/−↔Pax6+/+ chimera double-labeled for Gsh2 protein (grey) and Pax6−/− cells (brown dots). Gsh2 expression coincides with the Pax6−/− cells. (G) Dlx2-positive cells in the cortex of a Pax6−/−↔Pax6+/+ chimera. (H) Dlx2-positive cells in the lateral ganglionic eminence (lge), medial ganglionic eminence (mge) and cortex (ctx) of a Pax6−/−↔Pax6+/+ chimera; (I) Dlx2-positive cells in the cortex are Pax6−/− (i.e., Tg-positive). (J) Nkx2.1-positive cells in the medial ganglionic eminence (mge) and around the internal capsule (ic) of a Pax6−/−↔Pax6+/+ chimera; (K) Pax6−/− (Tg+) cortical cells are Nkx2.1-negative. Scale bars: (A, B, G, K) = 40 μm; (C–F, I) = 20 μm; (H, J) = 60 μm.