(a, b) By Nissl staining, both mutant mouse lines had reduced thickness of layer 2–4, but not layer 5–6 (n = 3–5, scale bar = 100 μm). (c, d) Immunofluorescent staining of the cortex from 5-week old control and mutant animals. The number of CTIP2+ cells in layer 5–6 did not change, but the numbers of SATB2+ and CUX1+ cells were reduced in the mutant cortex (n = 4–5, scale bar = 100 μm). (d, inset) Mutant mice showed fewer layer 2–4 SATB2+ cells coexpressing CUX1. (Arrowhead: SATB2 single positive cells.) Data are represented as mean ± s.e.m. *: P < 0.05; **: P < 0.01; ***: P < 0.001; ****: P < 0.0001