Dynamics of process formation during differentiation of tectal neurons in embryonic zebrafish

dendritic tree (phase 2). The dendritic tree develops inABSTRACT: Neurons acquire their distinct shapes the tectal neuropil through emission and retraction ofafter passing through many transitional stages in early many branches during a period of 20 h (our longestdevelopment. To reveal the dynamics and spatiotempo-continuous time-lapse movie). The tectal territory ‘‘ex-ral sequence of process formation in situ, the growth of plored’ ’ in this way is larger than the area finally cov-neurons in the optic tectum of live zebrafish embryos ered by the tree resulting from growth and loss of(54 to 100 h old) was monitored using time-lapse vid-branches. The dynamics observed here directly areeorecordings. Neurons were labeled by injecting the flu-probably characteristic for dendrite formation in verte-orescent vital dye DiO into the cell-rich layer of the brates. Moreover, consistent with the sequence of neu-developing tectum in 50- to 70-h-old embryos. In phase ronal differentiation observed in vitro, the growth of1, tectal neurons possess an apical ‘‘primary process’’ the axon precedes that of the dendrites, although bothwhich reaches to the ventral aspect of the tectal neuropil. emerge from a common primary process in this type ofThe primary process produces at its tip short transitory tectal neuron. q 1997 John Wiley & Sons, Inc. J Neurobiol 32:branches, some with growth cones, over a period of 627–639, 1997roughly 6 h. One of the growth cones then elongates Keywords: tectal neurons; in vivo development; zebra-rapidly and grows toward the caudal tectum via a rout