07 Dec 2000

Undifferentiated cells from the adult spinal cord can generate neurons when transplanted to the adult hippocampus, reveal Fred Gage, California, and his coworkers at the Salk Institute in the current issue of the Journal of Neuroscience. Because these cells would not have become neurons in the spinal cord, the results reinforce the importance of the cellular environment in determining the ultimate fate of immature cells.

In recent years, there has been a rapid retreat from the dogma that there are no new neurons or glia in the adult mammalian brain. Actively dividing cells have been found in many species, particularly near the ventricles where cells arise during embryogenesis, but also in the dentate gyrus of the hippocampus. Some of these immature, or "progenitor," cells can be induced to become either neurons or glia (i.e., they are "stem" cells). It is thought that they could ultimately replace dead neurons or glia in neurodegenerative diseases.

In the spinal cord, as Gage's group showed earlier this year (J Neurosci 2000;20:2218-28), progenitor cells (isolated by their responsiveness to basic fibroblast growth factor [FGF-2]) are found primarily away from the central canal in adult rats and will only develop into glia. In the current experiment, the researchers first used clonal cultures to demonstrate that these cells are true stem cells, in that they can differentiate into neurons, astroglia, or oligodendrocytes. In the second part of the experiment, the cells were removed from the "non-neurogenic" spinal cord environment to the hippocampus, where some gave rise to neuron-like cells in the granular layer of the dentate gyrus, a neurogenic zone. Transplanted cells found in nonneurogenic hippocampal areas, on the other hand, had matured only into astroglia or oligodendroglia-type cells.

These results add support to the possibility of delivering signals such as growth factors to the spinal cord and inducing neurogenesis from cells that would otherwise differentiate into glia, conclude the authors.—Hakon Heimer