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Charles E. Maier, Ph.D.
Regulation of Glia Cell Patterns in the Spinal
Cord During Development and Regeneration
Two types of
macroglial cells are found in the spinal cord –
oligodendrocytes and astrocytes.
Oligodendrocytes are the myelinating cells of
the vertebrate CNS while astrocytes perform a
variety of support functions. The notochord, a
transient structure present during development
in higher vertebrates, has been shown to produce
a protein encoded by the sonic hedgehog gene
that regulates motorneuron pattern in mouse,
chick and Xenopus. We have found that
elimination of the notochord prevents the
appearance of differentiated oligodendrocytes
while an ectopically implanted notochord is
associated with detection of oligodendrocytes in
the lateral and dorsal spinal cord at a stage
when they should only be found in the ventral
spinal cord. Current efforts are directed
towards determining whether the appearance and
distribution of oligodendrocytes and sonic
hedgehog are colocalized. If they do colocalize
it would suggest that sonic hedgehog also is the
mechanism that regulates oligodendrocyte
development. Radial glia, an early stage of
astrocyte development, extend from the central
canal to the pial surface of the developing
spinal cord and are believed to guide growing
axons to their targets. The ventrally located
notochord seems an unlikely candidate to
regulate the pattern of the evenly distributed
radial glia/astrocytes. Preliminary studies
indicate, however, that the radial glia/astrocyte
pattern is altered in the absence of the
notochord. Further, Xenopus are capable of
regenerating lesioned spinal cord axons until
metamorphosis when they lose this ability.
Preliminary studies have shown that after the
spinal cord is lesioned during development
oligodendrocyte and radial glia/astrocyte
patterns are perturbed. Studies are currently
underway to determine whether the changes in
glia cell patterns after spinal cord lesioning
may be a response which enables or facilitates
the regeneration process. Additional studies are
being undertaken to establish whether the
notochord, which disappears by metamorphosis, is
required for naturally occurring spinal cord
regeneration.
Selected References:
Maier C.E.,
and Miller R.H. Glial cell development and
regional specialization in Xenopus spinal cord.
Soc. Neurosci. Abstr. Vol. 17, Part 1, p. 733,
1991.
Maier C.E.,
and Miller R.H. Influence of notochord and
surrounding tissue on oligodendrocyte
differentiation in Xenopus spinal cord. Soc.
Neurosci. Abstr. Vol. 19 Part 2, p. 1712, 1993.
Maier C.E.,
and Miller R.H. Development of glial
cytoarchitecture in the frog spinal cord. Dev.
Neurosci. 17:149-159, 1995.
Maier C.E.,
and Miller R.H. Alteration of radial glia
pattern in spinal cords of notochordless Xenopus.
Soc. Neurosci. Abstr. Vol. 22, Part 2, p 900,
1996.
Maier C.E.,
and Miller, R.H. Notochord is essential for
oligodendrocyte development. J. Neurosci. Res.
47:361-371, 1997. |
