Journal of Neuroscience, Vol 15, 4157-4172, Copyright © 1995 by Society for Neuroscience
R-cadherin expression during nucleus formation in chicken forebrain neuromeres
SI Ganzler and C Redies
Department of Biochemistry, Max Planck Institute for Developmental Biology, Tubingen, Germany.
The primordial neuroepithelium of the vertebrate forebrain consists of
transverse and longitudinal morphogenetic compartments ("neuromeres").
During development, neurons born in the ventricular zone of each neuromere
migrate outward to the mantle zone. Here, neuroblasts gradually accumulate
and aggregate either into sheets ("laminae") or into roundish structures
("nuclei"). As brain architecture matures, sets of nuclei and laminae
derived from several neuromeres become connected by fiber tracts to form
functional circuits. We show by immunostaining and in situ hybridization
techniques that, in the E3-E5 chicken embryo, the cell adhesion molecule
R-cadherin is expressed in several stripes and patches in the forebrain
neuroepithelium. This expression pattern reflects, at least in part, the
neuromeric organization of the forebrain. For example, in both the ventral
and dorsal thalamus, R-cadherin expression has a sharp border at the
respective caudal neuromere boundary. Moreover, focusing on the mid-
hypothalamic region, we demonstrate that a subset of postmitotic
neuroblasts in the ventricular zone express R-cadherin during their
migration to the mantle zone, where they aggregate into particular nuclei.
In the mantle zone, R-cadherin-expressing neuroblasts accumulate in
parallel with neuroblasts expressing another cadherin, N- cadherin. The two
types of cells segregate from each other to form adjacent nuclei. Some of
the R- and the N-cadherin-positive nuclei form parts of particular
functional circuits in the mature brain. In conclusion, our results suggest
that cadherins play a role in the formation of brain nuclei and in the
developmental transformation from neuromeric to functional organization in
the vertebrate forebrain.
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