Schematic representation of Robo and Slit localization in the developing forebrain. Schematic drawings, based on in situ and immunohistochemical studies, illustrate robo and slit expression patterns during early (E13.5) (A) and mid (E15.5) (B) phases of cortical interneuron migration. Hatched patterns indicate regions of overlap in expression. Enlarged portions of the dorsal cortex at E13.5 (A′) and E15.5 (B′) show the localization of robo and slit and the regions of overlapping expression in greater detail. MZ, marginal zone; IZ, intermediate zone; VZ, ventricular zone; LGE, lateral ganglionic eminence; MGE, medial ganglionic eminence; Str, striatum; LV, lateral ventricle; CP, cortical plate; SP, subplate; LIZ/SVZ, lower intermediate zone/subventricular zone; POa, preoptic area.