Winter 1996 Volume 5, Number 1

Matching Molecules

Researchers have long sought Nature's ways and means of wiring up the developing nervous system. Duplication of key processes involved could help in repairing brain and spinal cord injuries. Now John Flanagan and Hwai-Jong Cheng of Harvard Medical School have found two molecules thought critical to one of these processes, the "topographic mapping" of the developing visual system.

Topographic mapping --topos means "place" in Greek --is the way in which nerve-cell connections set up neighbor relations once they reach a target region in the developing brain. The result is a one-to-one correspondence between two sets of neurons --those sending and those receiving the neural signals. This mapping sets the system at "go."

Flanagan and Cheng found that in the embryo two molecules together appear to act as a matchmaker for neurons growing from the retina. Once guided to the right neighborhood in the tectum of the chick midbrain, nerve fibers from the retina recognize their connective sites by the binding of the two molecules.

According to Flanagan, the molecules can now help as a tool to decipher further how Nature wires up the visual system. Both molecules -- a receptor protein in the retina called Mek4 and a "ligand," ELF-1 in the tectum --have many close relatives that may act in similar ways throughout the brain, says Flanagan, so that the wiring up of the visual system could serve as a model for other brain systems.

Molecules

Mek4 receptor protein from retina, introduced in brain of chick embryo during period of mapping, binds to ELF-1 in tectum (darkest area). A = anterior; P = posterior. (Courtesy of Dr. Flanagan.)

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