Fig. 3

The guidance cues Slit1 and 2, and receptors Robo1 and 2, are in position to prevent oculomotor migration across the floor plate on E10.5. Coronal sections were taken through the posterior midbrain on E10.5 to determine Slit and Robo expression. Following protein (Robos) or mRNA (Slits) labeling, the same or adjacent section was labeled for Islet1/2 to co-localize expression to oculomotor neurons (A’-B’, A”, B”). A, B Robo1 and 2 protein was found in the ventral midbrain and in the oculomotor nerve fibers (nIII). Expression was co-localized with Islet1/2 indicating Robo1 and Robo2 expression in oculomotor neurons (A”,B”). Robo1 antibody also strongly labels the adjacent medial longitudinal fasciculus (mlf). C-E In situ hybridization for Slit1, 2, and 3 mRNA. Slit 1, 2 and 3 expression was localized to the floor plate. Expression of Slit2 and 3 co-localized to Islet 1/2+ neurons (D’, E’). Scale bars: B”, 50 μm, applies to Robo antibody labels; C’, 100 μm, applies to Slit in situs