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Direct view: dynamics of development.

For scientists intrigued by how nerve cells establish their highly regular pattern of connections, what could be better than just watching the cells project and perhaps rearrange their contacts?

Now scientists report they can do just that. Using a new long-lived flourescent dye, they can directly observe the development of connections between the eye and the brain in toad (Xenopus laevis) embryos. Their results indicate that at least some nerve fibers do not grow directly to their appropriate targets but, according to a "dynamic" mechanism, they establish a roughly ordered projection that is refined over time.

To view nerve cell projections in a live embryo, Nancy A. O'Rourke and Scott E. Fraser of the University of California at Irvine inject a fluorescent dextran dye into a single-celled embryo. As the embryo develops, the dye becomes distributed to all the cells. The scientists then take fluorescently labeled tissue destine to become an eye (or half of an eye) and graft it into the appropriate location on an embryo that was not injected with dye. Because the head of the developing larva becomes transparent, the scientists are able to follow for several weeks the growth of the labeled neurons.

Two phases of pattern development were revealed by this technique. On one axis across the retina, the dorsal-ventral nerve fibers form an ordered projection early in development, O'Rourke and Fraser report. In contrast, fibers from cells along the other axis, the nasal-temporal axis, initially overlap on the tectum, then sort out into the adult pattern over a period of days. This provides strong evidence for "dynamic behavior" of at least some nerve cell fibers in the patterning process.
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Title Annotation:fluorescent dye used to observe cell projections in a live embryo
Author:Miller, Julie Ann
Publication:Science News
Date:Nov 16, 1985
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