Satou, C., Kimura, Y., and Higashijima, S. (2012) Generation of multiple classes of v0 neurons in zebrafish spinal cord: progenitor heterogeneity and temporal control of neuronal diversity. The Journal of neuroscience : the official journal of the Society for Neuroscience. 32(5):1771-1783.
The developing spinal cord is subdivided into distinct progenitor domains, each of which gives rise to different types of
neurons. However, the developmental mechanisms responsible for generating neuronal diversity within a domain are not well
understood. Here, we have studied zebrafish V0 neurons, those that derive from the p0 progenitor domain, to address this question.
We find that all V0 neurons have commissural axons, but they can be divided into excitatory and inhibitory classes. V0 excitatory
neurons (V0-e) can be further categorized into three groups based on their axonal trajectories; V0-eA (ascending), V0-eB (bifurcating),
and V0-eD (descending) neurons. By using time-lapse imaging of p0 progenitors and their progeny, we show that inhibitory and
excitatory neurons are produced from different progenitors. We also demonstrate that V0-eA neurons are produced from distinct
progenitors, while V0-eB and V0-eD neurons are produced from common progenitors. We then use birth-date analysis to reveal
that V0-eA, V0-eB, and V0-eD neurons arise in this order. By perturbing Notch signaling and accelerating neuronal differentiation,
we predictably alter the generation of early born V0-e neurons at the expense of later born ones. These results suggest that
multiple types of V0 neurons are produced by two distinct mechanisms; from heterogeneous p0 progenitors and from the same
p0 progenitor, but in a time-dependent manner.