Journal of Neuroscience, Vol 6, 2736-2746, Copyright © 1986 by Society for Neuroscience
Gangliogenesis in leech embryos: migration of neural precursor cells
SA Torrence and DK Stuart
In the metameric CNS of leeches, identified neurons occupy highly
stereotyped positions in each segmental ganglion. Although many of the
neural precursor cells arise near their definitive positions, some arise
outside the prospective domain of the segmental ganglia and thus must
migrate into the CNS. Here, we report the results of an analysis of the
role of cell migration in gangliogenesis in the leech Theromyzon rude.
Segmental ganglia of the ventral nerve cord arise as laterally thickened
sheets of tissue lying astride the ventral midline. Particular identified
circular and longitudinal muscle fibers, visualized by indirect
immunofluorescence using a monoclonal antibody against leech muscle,
outline the presumptive ganglionic territories even before the ganglionic
rudiments become morphologically distinct and serve as anatomical landmarks
to which the cell movements are related. Cell lineage tracers microinjected
into precursor blastomeres are used to visualize migratory cells. Small
groups of neural precursor cells that arise outside the prospective
ganglionic territories migrate with stereotyped timing along stereotyped
pathways to reach their definitive positions, and each group of migratory
cells gives rise to a stereotyped subset of the cells in a ganglion. No
segmental or regional differences are observed in any aspect of cell
migration studied here, supporting the view that segmental differences in
the architecture of the leech CNS arise only after the initial condensation
of the ganglionic rudiments.
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