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Volume 16, Number 21,
Issue of November 1, 1996
pp. 6853-6863
Copyright ©1996 Society for Neuroscience
Restricted Expression of the Actin-Regulatory Protein,
Tropomyosin, Defines Distinct Boundaries, Evaginating Neuroepithelium,
and Choroid Plexus Forerunners during Early CNS Development
Received June 17, 1996; revised Aug. 13, 1996; accepted Aug. 16, 1996.
Kelley Nicholson-Flynn,
Sarah E. Hitchcock-DeGregori, and
Pat Levitt
Department of Neuroscience and Cell Biology, Robert Wood Johnson
Medical School, University of Medicine and Dentistry of New Jersey,
Piscataway, New Jersey 08854
In the hindbrain, rhombomeres represent morphological units that
develop characteristic, segment-specific structures. Similar segments,
known as prosomeres, have been proposed to exist in the forebrain. The
neuroepithelial cells of the sharp boundary regions that form the
borders between many segments often exhibit distinct shapes, reflecting
unique cytoskeletal organization. The present investigation examined
the expression of one family of actin-binding, regulatory proteins, the
tropomyosins (TM), in boundaries. We found that high molecular weight
TMs selectively concentrate in boundary cells and other neuroepithelial
zones that exhibit unique cell shapes and movements. Specific TM
expression is found at hindbrain boundaries as early as embryonic day
10 in the rat, whereas rhombomeres themselves were TM-negative. Highly
restricted TM localization also defined some prosomere boundaries in
the early forebrain, particularly those exhibiting unique cell shapes.
Furthermore, several regions of the neuroepithelium that evaginate are
TM-immunoreactive, including tuberal and preoptic neuroepithelium. Most
striking, a subpopulation of neuroepithelial cells in the medial
telencephalic wall expresses TM, apparently marking the neuroepithelial
region that gives rise to the choroid plexus at least 2 d before
its formation. This suggests that the medial cerebral wall is not
entirely dedicated to generating cells that comprise allocortex. TM
expression in the choroid plexus is maintained through initial
evagination and appearance in all ventricles. The spatially restricted
expression of TMs implicates that this actin-binding protein is
involved in the dynamic regulation of cell shape or motility associated
with boundary formation and morphogenesis of the neuroepithelium during
critical stages of brain development.
Key words:
tropomyosin;
rhombomere;
prosomere;
choroid plexus;
segmentation;
cytoskeleton;
cell shape;
cell fate
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