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Control Culture Media
Antibody to Astrotactin
Control IgG
FIGURE 3.27 In vitro assay demonstrates the importance of
astrotactin in granule cell migration. When cerebellar glial cells are
co-cultured with granule cells, the glial cells adopt an elongate mor-
phology, and the neurons (red) crawl along the glial processes. When
astrotactin antiserum is added to these cultures, the neurons no
longer associate with the glial processes, and the long processes of
the glial cells retract. This in vitro assay has also been used to analyze
the effects of other molecules, like CAMs and extracellular matrix
molecules, on granule cell migration.
FIGURE 3.26 Neuronal migration along glial fibers can be
observed directly. In cerebellar neuron-glial co-cultures, the neurons
associate with the glial processes and slowly move along them.
Using time-lapse microscopy, this neuronal migration can be directly
observed and quantified. This has provided an excellent assay for
investigating the molecular basis for neuronal migration. (Courtesy
of M.E. Hatten)
they had raised against cerebellar cells to the cultures,
they found a significant inhibition of the granule cell
adhesion (Figure 3.27). They concluded that some type
of adhesion molecule was necessary for the migration
of these cells but that it was not one of the previously
known CAMs. To find this new CAM, they used a
clever approach: they absorbed the antigranule cell
antiserum with other types of neural cells and cell
lines, thus getting rid of those antibodies from the
serum that recognize common CAMs. What they were
left with was an antiserum that recognized a single
protein of approximately 100 kD, which they named
astrotactin. Subsequent studies showed that astro-
tactin is a protein that resembles other CAMs but is in
a distinct family. It is expressed in the migrating
granule cells, and antibodies raised against astrotactin
block the migration of the granule neurons along the
glial fibers.
class of cell surface proteins, known as cell adhesion
molecules, or CAMs, are known to mediate the adhe-
sion between cells and the migration of cells in many
tissues in the embryo. Are these proteins necessary for
the migration of granule cells along radial glial fibers?
Under control conditions, the granule cells migrate on
the radial glial cells in the cultures at about 33 mm/hr.
To test whether the most abundant CAMs in the
nervous system, NCAM, N-cadherin, and L1, are
important for granule cell migration, Hatten's group
added antibodies that specifically block the function of
these molecules to the cerebellar microcultures (Stitt
and Hatten, 1990). They found that none of these anti-
bodies interfered with the migration of the granule
cells. However, when they added an antiserum that
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