In vivo imaging of axonogenesis. Lateral view of the cerebellar anlage of a 36-hpf Tg(atoh1a:Gal4TA4)^hzm2 transgenic zebrafish embryo coinjected with Janus vector J8 (marking nucleus in blue and centrosome in red, red arrows) and 5xUAS:Kif5c-YFP (emerging axons labeled with yellow fluorescence, here shown in green). (A) Due to coinjection of two vectors, only the more anteriorly located cell expresses the Kif5c-YFP fusion protein. Kif5c-YFP is initially distributed throughout the soma of the cell (green arrow), while the centrosomes of both cells are localized at the apical side (red arrows). (B–D) Kif5c-YFP localizes to a protrusion, the later axon, in the front of the cell, at the time when the centrosome is homing toward the soma. (E and F) Kif5c-YFP localizes to a growth cone–like structure of the emerging axon, while the centrosome has not reached the soma. This temporal sequence of axonogenesis and centrosome dynamics reveals that a proximal position of the centrosome is not required for selecting the site of axon formation in THN neurons in vivo. Images are taken from Video 10. MHB, midbrain-hindbrain boundary; URL, upper rhombic lip.