The development of the brain proceeds a little like the European settlement of North America. The earliest pioneers settled on the east coast with subsequent waves of settlers forming communities further and further westward. In cortical regions of the developing brain, generations of young neurons undergo a staged migration as well, with the earliest-born cells staying relatively close to their birthplace and subsequent generations traveling further, ultimately stratifying into six neuronal layers in the mature brain. Now, for the first time, imaging studies have identified the "motors" that propel a unique form of cell migration that creates these layers that
"The complexity of the cell types is so much greater in the brain than in other parts of the body, nothing else compares," says Mary E. Hatten, head of the Laboratory of Developmental Neurobiology at The Rockefeller University. "Since different classes of neurons are born at different times in the brain's development, neuronal migration is responsible for patterning specific types of cells into particular layers. The normal development of the brain depends critically on this specialized form of motility, which places the neurons in the right layer."
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| Migrant neuron. Using high-resolution imaging techniques, scientists have identified the molecular motors (green) that pull neurons forward as they migrate during the development of the brain. The motors assemble close to the neurons nucleus (red) to control the process. |
Hatten and former postdoctoral associate David Solecki, now at St. Jude Children's Research Hospital, focused on the mechanism of neuronal migration in cortical regions of the brain, including the cerebellum, hippocampus and cerebral cortex. With colleagues, they developed techniques to fluorescently label the motor proteins inside the tiny neurons and watch their dynamics as the cells migrate along what Hatten calls a monorail system - glial fibers - toward their destinations. The researchers used a spinning-disk, confocal microscope, equipped with a CCD camera to image the migration in real time at extremely high resolution, allowing them to examine the motor proteins in great detail.