Figure 1. Slit/Robo expression in the developing forebrain. Coronal sections of the middle forebrain at E12.5 (A–H) and E14.5 (I–P) showing localization by in situ hybridization (A–D, I–L) expression of Slit1 (A, I), Slit2 (B, J), Robo1 (C, K), and Robo2 (D, L). A, I, In the dorsal forebrain, strong Slit1 mRNA expression can be seen along the PPL at E12.5 and in the CP at E14.5, while considerably weaker expression is present in the VZ at both ages. In the ventral forebrain, strong expression is predominantly localized in the MGE, LGE, POA, and Sp. B, J, Slit2 mRNA is restricted mainly in the POA and ChP at E12.5, whereas at E14.5 is strongly expressed in the CH and weakly in the VZ of the cortex, MGE, and LGE. C, K, At E12.5, Robo1 mRNA is expressed strongly in the PPL and weakly in the VZ of the dorsal telencephalon. In the ventral telencephalon, it is localized predominantly in the MGE and LGE. This pattern is maintained at E14.5, with additional strong expression in the CP. D, L, Robo2 mRNA is abundantly expressed in the PPL, but absent from the proliferative zones of the cortex. E, F, M, N, Immunohistochemistry for TauGFP-labeling in Slit1+/− (E, M) and Slit2+/− (F, N) mice show GFP protein expression in the forebrain, in a pattern similar to that of Slit1 and Slit2 mRNA. I, M (arrows) and J, N (insets) point to Slit-expressing cortical vasculature. Protein expression patterns for Robo1 (G, O) and Robo2 (H, P) mirror mRNA expression. ChP, Choroid plexus; LV, lateral ventricle; Sp, septum; Str, striatum.