Salk scientists identify key nerve navigati...( LA JOLLA CA Newly launched nerve ce...)

LA JOLLA, CA Newly launched nerve cells in a growing embryo must chart their course to distant destinations, and many of the means they use to navigate have yet to surface. In a study published in the current issue of the journal Neuron, scientists at the Salk Institute for Biological Studies have recovered a key signal that guides motor neurons the nascent cells that extend from the spinal cord and must find their way down the length of limbs such as arms, wings and legs.

The Salk study, led by Samuel Pfaff, Ph.D, a professor in the Gene Expression Laboratory, identifies a mutation they christened Magellan, after the Portuguese mariner whose ship Victoria was first to circumnavigate the globe. The Magellan mutation occurs in a gene that normally pilots motor neurons on the correct course employing a newly discovered mechanism, their results demonstrate.

In the mutants, growing neurons can be seen leaving the spinal cord normally but then appear to lose direction. The elongating cells develop kinks and sometimes fold back on themselves or become entwined in a spiral, forming coils outside the spinal cord. They appear to become lost in a traffic roundabout, described Pfaff, who observed the growing neurons with fluorescent technology.

Understanding how motor neurons reach the appropriate targets is necessary for the implementation of novel therapies, including embryonic stem cell replacement for the treatment of presently incurable disorders such as Lou Gehrigs disease, in which motor neurons undergo irreversible decay.

Embryonic studies provide useful insights on how to replicate the system in an adult, said Pfaff. And, as he also pointed out, the mechanisms used by motor neurons are likely to be similar to those used in other parts of the central nervous system, such as the brain. The Magellan mutation discovered by Pfaffs group was found in mice, but the affected gene, called Phr1, has also been identified in other m
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