While several recent studies discovered molecules that repel motor neuron axons from incorrect targets in the limb, scientists at the Salk Institute for Biological Studies have identified a molecule, known as FGF, that actively lures growing axons closer to the right destination. Their findings appear in the June 15 issue of Neuron.
"The most important aspect of our finding is not necessarily that we finally nailed the growth factor FGF as the molecule that guides a specific subgroup of motor neurons to connect to the muscles that line our spine and neck," says senior author Samuel Pfaff, Ph.D., a professor in the Gene Expression Laboratory, "but that piece by piece, we are uncovering general principles that ensure that the developing nervous system establishes proper neuronal connections."
Understanding how axons find their destinations may help restore movement in people following spinal cord injury, or those with motor neuron diseases such as Lou Gehrig's disease, spinal muscle atrophy, and post-polio syndrome. Failure to establish proper connectivity in the brain may also underlie autism spectrum disorders and mental retardation.
The multitasking members of the FGF growth factor family regulate blood vessel formation, wound repair, lung maturation, and development of skeletal muscle, blood and bone marrow cells. The Salk study adds on more job to an already long list.
"Our study emphasizes that the nervous system does not necessarily rely on an entirely new set of molecules to govern axon navigation, but instead uses growth factors already involved in embryonic development in clever and novel ways," Pfaff says.
Skeletal muscle consists of thousands of muscle fibers, each controlled by one motor neuron