Fig. 1. (A) The recombinant targeting construct used to generate a mutant mouse with a disrupted Id4 locus, and a Southern blot and PCR analysis demonstrating the successful targeting event. (B) E15.5 Id4 mutant brain (right) and a littermate wild-type control brain (left). (C,C') Cresyl violet-stained coronal sections through E12.5 wild-type and mutant telencephalon. Measurements of neocortex and hippocampal primordium shown in Fig. 2 were made between the arrows shown. Also, the thickening of the neocortex in the mutant (C') is indicated by a comparison of the length of the black bar (wild-type thickness) to the yellow bar (mutant thickness). Basal ganglia (LGE and MGE) of the mutant appear normal in size. (D,D') E18.5 saggital sections of control (D) and Id4^-/- (D') telencephalon stained with cresyl violet. (E-H) Quantitation of the cortical VZ surface areas at E11.5, E12.5 and E15.5, in control and Id4^-/- littermates at matched levels on coronal sections (E,F) and saggital sections (G,H), normalized to littermate controls. Yellow bar, Id4^+/–; blue bar, Id4^-/-; wt, wild type; mt, mutant; LGE, lateral ganglionic eminence; MGE, medial ganglionic eminence; hp, hippocampus; ctx, neocortex; OB, olfactory bulb; st, striatum; LV, lateral ventricle.