Journal of Neuroscience, Vol 9, 2919-2930, Copyright © 1989 by Society for Neuroscience
Quantitative lineage analysis of the origin of frog primary motor and sensory neurons from cleavage stage blastomeres
SA Moody
Department of Anatomy, University of Virginia School of Medicine, Charlottesville 22908.
The average number of primary motoneurons and Rohon-Beard neurons that
descend from each "identified" blastomere of the 16- and 32-cell stages of
the frog Xenopus laevis was determined. The dorsal, animal blastomeres are
the major motoneuron progenitors, and the ventral, animal blastomeres are
the major Rohon-Beard progenitors. Cells along the midline primarily give
rise to only one of these phenotypes, whereas cells along the frontal
plane, which separates dorsal from ventral, give rise to both phenotypes.
Each blastomere produces a characteristic number of each type of neuron,
with only small variations between embryos. The mean values were used to
construct quantitative retrospective lineage diagrams for the first 5 cell
cycles after fertilization. These diagrams illustrate that the fate to
become a major neuronal progenitor is segregated as early as the 4-cell
stage. The lineage patterns of which sister cell makes the majority of
primary neurons at each cleavage after the 4-cell stage are quite similar
for both neurons in the D lineage but only moderately similar for both
neurons in the V lineage. The pattern of predominant Rohon-Beard neuron
fate is very similar in the D and V lineages. Analysis of the axial
distribution of the primary motoneurons and Rohon-Beard neurons that
descend from each blastomere indicates that the major progenitors
contribute neuronal descendants periodically, to nearly every segmental
bin, but the minor progenitors distribute neuronal descendants randomly
along the axis. These data demonstrate that primary neuronal phenotype,
cell number, predominant lineal pattern, and in some cases segmental
distribution are highly regular across a large population of embryos. This
population consistency suggests that several features of neuronal fate may
be influenced either by cell position or lineage.