Immunohistochemical and Western blot analysis of Cbx1^−/− brains. (A–D) Hematoxylin and eosin–stained sagittal sections of E17 (A and B) and E19 (C and D) neocortices correspond to the antibody-stained cortices in E–H. Genotypes of the embryos are marked above the photographs. (E–H) α-NeuN–stained E17 and E19 neocortices. The staining of the wild-type E17 cortex with the α-NeuN antibody (E) detects a layer of SP cells that separates the CP from the intermediate zone (IZ). These cells are very weakly stained in the Cbx1^−/− neocortex (F). Similarly, CP cells are strongly stained with the α-NeuN antibody in the E19 neocortex (G), but such staining of CP cells is reduced to background levels in the E19 Cbx1^−/− neocortex (H). MZ, marginal zone. (I) HP1-β protein is not detected in extracts from Cbx1^−/− brains using an antibody to the C terminus of HP1-β; an N-terminal antibody also fails to detect HP1-β in the same way (Fig. S1, available). The levels of HP1-α, HP1-γ, Me(3)K9H3, Me(3)K20H4, and NeuN are not significantly changed in Cbx1^−/− compared with wild-type brain extracts. The bottom panel is the actin-loading control. Identical results were obtained using whole embryo extracts (not depicted). (J) Me(3)K9H3 heterochromatic distribution is not affected by the Cbx1^−/− mutation. Cbx1^−/− and Cbx1^+/+ CP neurons show identical Me(3)K9H3 staining patterns. (K) Me(3)K20H4 heterochromatic distribution is not affected by the Cbx1^−/− mutation. Cbx1^−/− and Cbx1^+/+ CP neurons show identical Me(3)K20H4 staining patterns. Bars: (A–H) 100 μm; (J and K) 10 μm.