Fig. 7. Relationship between reelin pathway elements and hindbrain neuron ventral migration. Whole-mount ISH for reelin expression revealed an increase in reelin expression between E11.5 and E12.5 (compare A with B). (C-K) Combined reelin ISH followed by islet 1 immunohistochemistry (C,F,I) were performed concomitantly with reelin (D,G,J) and Dab1 (E,F,K) ISH in adjacent vibratome sections at E12.5. (C,D) At r4 level, islet 1-positive OC cells are observed at the pial surface, in close association with a highly reelin-positive area. The circle represents an equivalent position on adjacent sections. (F) At r5 level, islet 1-positive VII motoneurons undergoing caudal migration can be seen near the midline. (G) Reelin-expressing cells are found in several areas with a strong expression near the pial surface. Islet 1-positive FVM cells are observed in a position close to this reelin-positive region (F). (I) At r6 level, VII motoneurons are in the final migratory step toward the pial surface. This shows that the final position of the neurons is a reelin-positive area (J), whereas longitudinal migrating VII motoneurons are reelin negative (F,G). Dab1 is strongly expressed in a region that includes the OC cells in r4 (E), the FVM in r5 (H), and the migrating branchial motoneurons in r6 (K).