Fig. 7. Morphogenetic movements in the dorsal neural tube at the MHB junction, based on observations in chick and mouse. Midbrain-derived cells, blue; isthmus-derived, pink; cerebellum, green (darker for the vermis). Double-headed arrows indicate AP orientation. (Top) The two drawings on the left depict the formation of the cerebellum (purple) and caudal midbrain (gray) roof plate structures derived from a restricted midline region in chick HH10. The cerebellum then fuses (third drawing, chick HH24 and mouse E15) over an isthmus-derived territory. The fourth drawing illustrates the medial retraction of the cerebellar cortex in perinatal mice and the growth of the velum medullaris. Pink circles represent isthmic nuclei. The white area derives from the hindbrain. (Bottom) Seesaw motion of the cerebellar cortex over the isthmic-derived territory. Schematic sagittal sections through the isthmo-cerebellar region close to the midline. The choroid plexus (black coil) marks the posterior pole of the region. Red arrows indicate the direction of cerebellar cortex displacement. Global tissue displacements are illustrated in the upper panels 1 and 2, and in 3. The orientation of radial glia (thin pink and green lines) in the same sections is illustrated in the lower panels 1 and 2. In 2, the radial glia become bent by the sliding cerebellum; pink dots in 2 and 3 represent isthmus-derived interneurons.

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