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First published online 27 July 2004
doi: 10.1242/dev.01271
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1 Department of Biology, Rutgers, The State University of New Jersey, Camden, NJ
08102, USA
2 Department of Molecular and Cell Biology, 385 LSA, University of California,
Berkeley, CA 94720-3200, USA
* Author for correspondence (e-mail: dshain{at}camden.rutgers.edu)
Accepted 19 May 2004
The leech nervous system comprises a relatively simple network of
longitudinal (connective) and transverse (segmental) nerves. We have followed
the normal pattern of axon development in the glossiphoniid leech
Theromyzon rude by immunostaining embryonic preparations with
antibody to acetylated
-tubulin. The dependence of the normal pattern
of axon growth on cells in the mesodermal (M) and ectodermal (N, O, P and Q)
lineages was examined by selectively ablating subsets of these lineages in
developing embryos. We found that ablating mesoderm severely disrupted overall
axonogenesis, while various ectodermal ablations induced a range of more
specific phenotypes. In particular, formation of the posterior segmental nerve
(PP) was abnormal in embryos deficient in primary neuroectoderm (N lineage).
More specific ablations demonstrated that a subset of N-derived cells were
required for establishing the PP nerve root. Previous studies have shown that
the PP nerve root is normally pioneered by an O lineage-derived neuron
(PD). Our results suggest that the role of the N lineage-derived
cells is to induce the migration of neuron PD to its normal
position in the posterior compartment of the hemiganglion.
Key words: Theromyzon rude, Leech, Nervous system, Cell lineage, engrailed
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