Fig. 3. ApoER2 controls late stages of cortical layer formation. (A,F) BrdU-labeling at E12.5 and staining of sagittal brain sections through the cerebral cortex at P0 showed the strongest signal close to the ventricle in wild-type mice (A, arrowhead). By contrast, in ApoER2 mutants (F), many heavily BrdU-labeled cells were also found in superficial portions of the cortex. (B,G) Labeling at E13.5 revealed many BrdU-stained cells in the inner to middle portion of the cortex in wild-type animals (B, arrowhead), whereas in ApoER2 mutants (G) an altered pattern was observed (arrowhead), and the formation of two separate bands became apparent. When labeling for BrdU was carried out at E14.5 (C,H) and E15.5 (D,I), the separation of these two layers was more clearly visible (H,I, arrowheads), whereas in wild-type (C,D) mice, only the upper cortical layers were strongly labeled (arrowheads). (E,J) Labeling at E16.5, a late stage of corticogenesis, resulted in a heavily stained band in the outermost portion of the cortex in wild-type animals (E, arrowhead), whereas in ApoER2 mutants (J) strongly labeled cells were located close to the ventricle (arrowhead). Scale bar: 200 µm.