Fig. 4. Aberrant migration of facial visceral motoneurons in reeler mutants. Facial branchial (VII) and visceral motoneurons (FVM) were retrogradely labeled with DiI by injection from the VIIth nerve root at E11.5 and E12.5. Embryos were flat mounted at E11.5 (A,B) and E12.5 (C,D). (A,B) At E11.5, characteristic axon fasciculation and caudal migration of facial motoneurons were observed at the r4 level. White arrow indicates caudally migrating facial motoneurons. In r5, FVMs were migrating from the ventricular zone to a lateral position both in control embryos and in reeler mutants. (C,D) At E12.5, FVMs are organized in a compact group caudal to the axon exit point in control and reeler embryos. (E,F) Transverse vibratome sections of embryos in C and D indicated that FVMs have migrated ventrally toward the pial surface in controls (dashed circle in E). In reeler mutants, FVM neurons remained in a more mediolateral position (circled in F). C-F are confocal images. fp, floor plate.