Fig. 5. Co-cultures reveal migration cues within r1. (A) Cell migration can be induced from rhombic lip fragments cultured directly on the pialward surface of flatmounted explants. Cells from E4 rhombic lip fragments (green) align themselves along the same axis as endogenous migratory cells labelled with DiI (red) in the underlying E4 explant. The full bilateral dorsoventral axis is shown in the confocal montage with the ventral midline (vml) at its centre. (B) E4 fragment on E6 cerebellum. (C) E6 fragment on E6 cerebellum. (D) E4 fragment on E6 hindbrain. (E) E6 fragment on E6 hindbrain. (F) Radial plots compare the orientation of the leading process of 1683 clearly identified cells from E4 or E6 rhombic lip fragments (n=110) with respect to an axis perpendicular to the ventral midline. For each plot, orientations were scored in 15° bins and plotted as a percentage of the mode. The orientation on E6 cerebellar substrates (top) is contrasted with that on E6 hindbrain (bottom), as indicated in the accompanying schematic diagrams (left). In light grey (middle), the orientation on cerebellar territory is re-plotted with respect to an axis perpendicular to the closest segment of rhombic lip. (G) Cells only exit a fragment of rhombic lip where it contacts the explant substrate (the boundary of the explanted hindbrain is denoted by a broken line). (H) An isolated rhombic lip fragment will produce processes but few cells emerge. As no migrating cells were observed, these fragments were excluded from analysis. Scale bars: in A, 100 µm for A; in H, 100 µm for B-E,G,H.