Journal of Neuroscience, Vol 3, 1019-1038, Copyright © 1983 by Society for Neuroscience
Clonal organization of the central nervous system of the frog. III. Clones stemming from individual blastomeres of the 128-, 256-, and 512- cell stages
M Jacobson
Horseradish peroxidase injected into individual blastomeres of 128-, 256-,
and 512-cell embyros of Xenopus laevis was identified in cells of the
central nervous system (CNS) at early to middle larval stages. Labeled
cells were dispersed, mingled with unlabeled cells. Four boundaries in the
CNS could be defined by the behavior of clones of labeled cells: in the
transverse plane at the level of the isthmus; in the horizontal plane
between dorsal and ventral regions extending the entire length of the CNS;
in the dorsal midline extending the entire length; and in the ventral
midline of rhombencephalon and spinal cord but absent more rostrally. Cells
injected with HRP at the 512-cell stage produced clones that, with rare
exceptions, did not cross any boundary, whereas labeled clones initiated at
earlier stages frequently crossed boundaries. Axons and dendrites were not
restricted by these boundaries. These boundaries subdivided the CNS into
seven compartments, each of which was occupied exclusively by the
descendants of a group of 14 to 26 blastomeres in the 512-cell embryo.
These groups of blastomeres formed a bilaterally symmetrical pattern
composed of a single anterior median group straddling the dorsal midline
near the animal pole and three groups on each side. Because cells mingled
in each compartment but not across compartmental boundaries, there was a
one-to-one relationship between individual blastomeres and CNS compartments
but one-many and many-one relationships between individual blastomeres and
neuroanatomical subdivisions smaller than a compartment. There was no
constant relationship between phenotypes of nerve cells and their ancestry
from individual blastomeres of the 512- cell or earlier stages.
Previous Article | Next Article
