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Brake on Nerve Repair Identified

Unlike skin cells, neurons in the brain and spinal cord don't grow back after they've been injured. This intransigence seems to crop up as soon as developing neurons grow their insulating sheath made of myelin. Last year, scientists found the gene for a protein in myelin that shut down nerve growth. But they had no idea how this protein signal, called Nogo, gets picked up.

To find out, a team led by Stephen Strittmatter of Yale University sampled genes expressed in mouse brain to look for ones that would allow nonneuronal cells to bind Nogo (which they normally wouldn't do). They found their needle in a haystack: a gene they named NgR. Another experiment bolstered the idea that NgR is a Nogo receptor: When young neurons were manipulated to produce the NgR protein, they stopped growing in the presence of Nogo, the team reports in the 18 January issue of Nature.

The finding gives researchers "a very strong handle" on how Nogo stops nerve growth, says Marie Filbin of Hunter College of the City University of New York. Buoyed by this understanding, Strittmatter hopes that injured neurons could be encouraged to regrow, perhaps with a small molecule or peptide to disrupt the partnering of Nogo with its receptor. Such a treatment may eventually help people with spinal cord injuries. But just blocking only NgR may not be enough, cautions Filbin, who thinks that other signals besides Nogo may block regrowth.

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