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Our
experiments draw on a number of techniques, including time-lapse
videomicroscopy of retinal axon growth in living embryonic tissues;
identification of cell surface and matrix molecules along the retinal
pathways; and analysis of mice with targeted disruptions of genes
encoding specific proteins in the developing visual system.
In recent laboratory studies, we found that during development,
retinal axons encounter a protein called netrin-1, located at the
optic disc (the exit point from the eye into the optic nerve), which
is highly effective in promoting retinal axon outgrowth. Analysis
of embryonic mice with abnormally low amounts of this protein revealed
that retinal axons from these animals could not exit the eye, and
the optic nerves were severely reduced in size. Conditions characterized
by small optic nerves, known as optic nerve hypoplasia, are also
found in human patients and are a significant cause of congenital
blindness. Our results indicate that the normal exit of axons from
the retina into the optic nerve is critically dependent on interactions
with a specific guidance molecule at the developing optic disc.
Studies of retinal axon guidance will further our understanding
of how long-distance axon projections are formed in the brain. They
may be important for future efforts to promote CNS (central nervous
system) function after disease or injury.
Timelapse
Movies of Retinal Axon Pathfinding
"Retinal
Neurites Respond to EphB Extracellular Domains"
The following
QuickTime movies show retinal axon growth cones growing on laminin
and responding to gradients of soluble EphB receptor extracellular
domain (ECD) fusion proteins (EphB·ECD-Fc) presented by a
micropipette.
Videos presented at 420 times normal axon growth rate.
Please be aware that, due to their large files sizes, each movie
may take 1-2 minutes or more to load, depending on the speed of
your connection.
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(Figure
4A; 9MB file)
Time-lapse
of retinal growth cones responding to Fc control protein.
Note continued growth and elongation during protein expulsion
from micropipette.
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(Figure
4B; 7MB file)
Example
of retinal growth cones collapsing and retracting after
exposure to EphB1-ECDs from micropipette.
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(Figure
4C; 14 MB file)
Example
of several growth cones in field that are growing well before
reagent application, but after release of EphB2-ECDs from
micropipette, the growth cones cease motile activity (freeze).
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The videos are
the supplementary materials for Birgbauer, et al (2001) in the journal
Development (see Figure 4).
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