Complementary patterns of NRG expression and distribution of ErbB4-expressing INs at E13.5 in WT mice are degraded in ErbB4-deficient mice. (A-F) In situ hybridization on coronal sections at two different levels ((A-C) more posterior; (D-F) more anterior) as in Figure 1 but at E13.5; (C, F) are merged images shown in (A, B), and (D, E), respectively. In WT, migrating, ErbB4-expressing, MGE-derived INs (A, D) are distributed in the vTel, and a small number in the MZ and IZ in cortex. Nrg1-type III (B) and Nrg3 (E) are both expressed in the nascent cortical plate and in a largely complementary pattern in the vTel. Most ErbB4-expressing INs are found at locations with low or undetectable levels of expression of Nrg1-type III (C) and Nrg3 (F). Arrowheads in (A-C) and numbered arrows in (D-F) mark the positions of migrating streams of ErbB4-expressing INs at matching sites on adjacent sections. (G-I) In situ hybridization on coronal sections through forebrain of E13.5 ErbB4-/- HER4heart mice for expression of ErbB4, marking primarily INs generated in the MGE and migrating to the cortex, and Nrg3; (I) merged images shown in (G, H). Compared to their WT littermates (D-F), the distributions of the migrating ErbB4-expressing, MGE-derived INs in the ErbB4 mutants is broader and more diffuse, exhibiting abnormally extensive overlap with the expression domains of Nrg3 (I). Arrowheads mark matching sites on the pair of sections (G-I). CTX, cerebral cortex; LGE, lateral ganglionic eminence; MGE, medial ganglionic eminence. Scale bar: 500 μm.