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Embryo's nerve-inducing messenger found.

Leave it to an embryologist with a wry British wit to name his chemical messenger "noggin." Technically a quarter of a pint, noggin is also slang for head and, more recently, the name of a protein that seems to induce brain development in amphibian embryos.

Richard M. Harland of the University of California, Berkley, coined this name for the substance because without it, "you can make an animal that will make no head," he says. And if one exposes a developing embryo to too much noggin, "it will turn the whole animal into a head," Harland jokes. He reported noggin's existence in 1992, having found it in the part of a developing embryo that becomes nervous tissue. Then last February, he and his colleagues demonstrated that noggin could cause ventral mesodermal tissue -- the stuff of blood and bone -- to become dorsal mesoderm, the precursor of muscle.

Now, they show that noggin probably plays a key role in brain development.

The finding, reported in the Oct. 29 SCIENCE, is part of a renaissance in research about how embryos develop nervous tissue, says Harland. Almost 70 years ago, biochemists realized that certain chemicals play a key role in this conversion, but thier studies of newt and salamander tissues yielded no decisive answers to those chemicals' identity. Indeed, some laboratory reagents seemed to induce nerve-cell development.

However, Harland and others now use the South African clawed frog, Xenopus, and know more exactly the timing of this induction. By looking for substances that appear at that time, they are better able to pinpoint putative neural inducers, he explains.

Harland and his colleagues conducted a series of experiments. In some they transferred into embryonic frog tissue the messenger RNA that translates the genetic code for noggin; in others, they applied noggin directly to embryos at different stages of development. The researchers used embryos altered to a lack of natural supply of this protein.

The experiments showed -- for the first time, Harland notes -- that noggin causes cells to become neural tissue, even when added at inappropriate points in development. Its presence activates certain genes and leads to the production of molecules associated with newly created nervous tissue, his group reports.

However, Harland cautions that his team's experiments used much more noggin than they would expect to find in a normal embryo. Thus, noggin probably works in conjunction with other substances. It may actually perform some function other than neural induction in normal embryos.

Indeed, other neural inducers must exist, since noggin causes forebrain and midbrain to form but not spinal cord or hindbrain, Harland and his colleagues report. Moreovedr, "the [induced] cells don't differentiate into neurons," he adds.
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Title Annotation:chemical messenger called 'noggin' crucial to brain development
Author:Pennisi, Elizabeth
Publication:Science News
Article Type:Brief Article
Date:Oct 30, 1993
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