Journal of Neuroscience, Vol 4, 1361-1369, Copyright © 1984 by Society for Neuroscience
Quantitative lineage analysis of the frog's nervous system. I. Lineages of Rohon-Beard neurons and primary motoneurons
M Jacobson and SA Moody
After injection of horseradish peroxidase into single blastomeres in
Xenopus embryos at 2- to 512-cell stages, all of the descendants could be
traced and counted at tailbud stages. Progenitors of Rohon-Beard neurons
and of primary spinal motoneurons were identified, and all neurons of each
type that originated from individual progenitors were counted. From these
data were derived the geometric mean of the number (N) of Rohon-Beard
neurons (or primary motoneurons) that descended from a single progenitor at
each generation from the first to ninth, the mean number of progenitors of
each generation, and the probability that, following mitosis, daughter
cells continue in the Rohon-Beard (or primary motoneuron) lineages (the
continuation probability). On a log- log plot a straight line fitted to the
N values intercepts the abscissa at the 13th generation for Rohon-Beard
progenitors and the 16th generation for primary motoneuron progenitors.
This indicates the number of generations before the entire set of each type
of neuron is finally produced. The Rohon-Beard neurons and primary
motoneurons each originated from a separate group of progenitors at the 9th
generation (512-cell stage), but those progenitors gave rise to mesodermal,
endodermal, and ectodermal cells in addition to neurons. Nevertheless, the
continuation probability significantly greater than 0.5 shows that there is
a bias toward recruitment of progenitors into lineages leading to
production of those two types of neurons.(ABSTRACT TRUNCATED AT 250 WORDS)