The size and shape of brain structures can be controlled by a signaling molecule known as Sonic Hedgehog, University of Chicago researchers show in a paper published in the March 16, 2001 issue of Science and previously published in Science Online.
During development, the brain becomes organized into highly specialized groups of neurons, called brain nuclei, each expressing its own set of genes and participating in very specific neural functions. Little is known, however, about how brain nuclei of the appropriate size, shape and location are generated. The researchers show that this process can be coordinated by the secretion of a single molecule, Sonic Hedgehog, that operates as a 'positional signal'.
"A positional signal is a neat mechanism for creating patterns of different types of cells," said Cliff Ragsdale, Ph.D., assistant professor in neurobiology, pharmacology and physiology at the University of Chicago, and principal investigator in the study. "Target cells respond differently to a signaling molecule according to their distance from the source of the signal."
Ragsdale's group studies this process in the midbrain, a major division of the central nervous system, of embryo chicks. The midbrain was an attractive model for studying the formation of the organization of brain, or morphogenesis, because it is very simply organized during development into a set of cell columns, called arcs, each with distinct molecular identities.
The group found that Sonic Hedgehog is normally expressed along the midline during midbrain development, suggesting that Sonic Hedgehog might be the morphogen setting up the midbrain pattern.
This signal is called a morphogen because it is a "form-producing substance." Though the idea of morphogens has been around since 1952 when the British mathematician Alan Turing coined the term, it is only in the last ten years that true morphogens used in animal development ha
Contact: Jeanne Galatzer-Levy
University of Chicago Medical Center