Figure 1.

Neuronal migration from the upper rhombic lip in the transgenic gata1:GFP 781 strain. A–F, Lateral view of the developing cerebellum; pictures from individual time points of a time-lapse microscopy study of a transgenic 781 strain embryo are shown. For a schematic overview of the zebrafish cerebellum and migratory pathways, please refer to Figure 1f in Köster and Fraser (2001). A–C, GFP-expressing neuronal precursors appear ∼48 hpf in the URL from where they leave by migrating toward the MHB followed by a ventral migration along the MHB (blue arrowheads mark two individually traced cells) to settle in a cluster at the ventrolateral edge of rhombomere 1 (F, blue dashed circle). Around 60 hpf, the formation of an axon fascicle at the posterior border of the cerebellum can be observed (D–F, green arrowheads) that projects ventrally and subsequently caudally into posterior rhombomeres (supplemental movie 1, available at www.jneurosci.org as supplemental material). G–L, Dorsal view of the developing cerebellum, pictures from individual time points of a time-lapse microscopy study of a transgenic 781 strain embryo are shown. G–J, GFP-expressing neuronal precursors leave the URL migrating anteriorly toward the MHB (blue and orange arrowheads). Whereas cells originating close to the dorsal midline settle in a cluster closer to the midline (K, L, orange dashed circle), cells originating further laterally migrate along the MHB to form the ventrolateral cluster of neurons (K, L, blue dashed circle) observed in the lateral time-lapse study (F) (supplemental movie 2, available at www.jneurosci.org as supplemental material). K, L, The time-lapse analysis reveals that fascicle forming axons project toward the dorsal midline and cross the midline (K, yellow arrowheads) before projecting ventrally along the posterior border of the cerebellum and subsequently into the hindbrain (green arrow). cb, Cerebellar anlage; ot, optic tectum; rh, rhombencephalon.