Early-born (E12.5) interneurons in Dab1 mutant brains show layer inversion. A, Double-labeling for GABA (green) and BrdU (red) reveals that the vast majority of double-labeled cells (yellow) in wild-type cortex are in the lower layers at P16. B, Higher magnification of boxed area in A indicating that the majority of double-labeled interneurons (arrows) are in the lower layers of the cortex. C, Histogram depicting the layer positions of GABA–BrdU interneurons (n = 3 animals, 147 cells; mean ± SEM percentage) indicating that majority of early-born interneurons in wild-type cortices are distributed in the lower layers. D, In Dab1 mutants, double-labeled interneurons (yellow) born at E12.5 are found in the upper layers. E, Higher magnification of boxed area in D indicating that the majority of double-labeled interneurons (arrows) are in the upper layers of the cortex. F, Histogram depicting the layer positions of GABA–BrdU interneurons (n = 3 animals, 246 cells; mean ± SEM percentage) indicating that the majority of early-born interneurons in Dab1 mutant cortices are distributed in the upper layers. Scale bar: A, D, 160 μm; B, E, 80 μm. WM, White matter.