A big surprise: Young nerve cells can rewind their developmen...( The cerebral cortex is mass...)

The cerebral cortex is massively folded gray matter incorporating billions of neurons. Despite its complexity, the cortex comprises six orderly layers of cortical cells that are laid down during development at a precise time and in a precise sequence. In the study, the researchers asked which cortical cell types embryonic mice lacking Foxg1 can generate. Carina Hanashima, Ph.D., a postdoctoral fellow in Dr. Fishell's laboratory who had previously worked with Dr. Lai, conducted a series of experiments that made the analysis possible.

The progenitor cells for the cortex are born in a zone deep in the brain, and migrate to their assigned layer, depending on the time they are born. So a cortical cell's identity is based on the date of its birth. The first cortical cells to be born populate layer 1, the most superficial layer, which is made up of special Cajal-Retzius (CR) cells. The next cells born migrate to the innermost layer, layer 6. Subsequent layers pile up above layer 6 (between layers 6 and 1), and in descending numerical order from 5 to 2. Each layer has a specific type of neuron associated with it.

The researchers looked at the cortical layers in embryonic mice at a time in their development when layers 1, 6, and 5, would normally have already been formed. In mice lacking the Foxg1 gene, the researchers found that only layer 1, which is made up of CR cells, was present, and these cells were abundant. The absence of other cell types implicated the gene in producing later-born cortical cell types.

One of the ways the scientists were able to identify CR cells was by the expression of a protein called reelin, which plays a vital role in building the developing brain and is only present in CR cells. Mice lacking the protein stumble around so much that they were named "reelers." The cortical layers in these mice are scrambled. In recent years, reelin deficiencies have been linked to such human disorders as sc
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Contact: Pamela McDonnell
Pamela.Mcdonnell@med.nyu.edu
212-404-3555
New York University Medical Center and School of Medicine
1-Jan-2004