In spite of their importance, stem cells are hard to spot among the multitude of cells in complex tissue. Several years ago, neuroscientist Grigori Enikolopov, Ph.D., an associate professor at Cold Spring Harbor Laboratory (CSHL), and his colleagues developed a tool to look for stem cells that give rise to new adult brain cells. Researchers had known that a gene called Nestin was active in these neural stem cells. The CSHL team genetically engineered mice so that the same conditions that activate Nestin in a particular cell also make it glow green under ultraviolet light.
Using these mice gives researchers an important pointer to cells that may be adult stem cells. Almost 100 research teams around the world have now used these special mice to help find adult stem cells in hair follicles, liver, muscle, and other tissues.
Looking at the pituitary
One place where stem cells had been suspected — but never found — is the pituitary gland. This organ, which in people is about the size of a pea, sits at the base of the brain, where it secretes hormones that regulate various processes throughout the body. In mice, the gland develops in the embryo, but then has a second growth spurt.
“A few weeks after they are born the pituitary undergoes massive expansion” says Dr. Enikolopov, which suggests a role for adult stem cells.
Anatoli Gleiberman, Ph.D., a researcher in the lab of pituitary expert M. Geoff Rosenfeld at the University of California, San Diego, initiated collaboration between the two labs to look for pituitary stem cells. The researchers used the Nestin-tracking mice to identify candidate cells in the anterior pituitary, the section of the organ that secretes hormones. They then used other techniques to show that these are true stem cells.
“There are six main lineages in the adult pituitary and we can demonstrate that one adult stem cell can generate all six lineages...” with each cell type secreting a different hormone, says Dr. Enikolopov.
A distinct kind of stem cell
These cells differ from most adult stem cells, however.
“In most cases that we know, cells that become stem cells of the adult have been also contributing to embryonic development and continue to serve as stem cells in the adult,” says Dr. Enikolopov. The research team demonstrated that adult stem cells in the pituitary did not help construct the embryonic organ.
Their research, the scientists suggest, indicates that the adult mouse pituitary includes two similar — but not identical — types of hormone-producing cells: some that grew in the developing embryo, and some that appeared later. They speculate that having two sets of cells may let the organ respond differently to changing body conditions.
Dr. Enikolopov notes that hormones strongly influence human neuropsychiatric phenomena, including stress and depression that are his main research focus.
“All are mediated through the pituitary,” he said, so changes that happen during the later growth of the gland could have lasting effects.
Reference:
Genetic approaches identify adult pituitary stem cells
Anatoli S. Gleiberman , Tatyana Michurina, Juan M. Encinas, Jose L. Roig, Peter Krasnov, Francesca Balordi, Gord Fishell, Michael G. Rosenfeld,, and Grigori Enikolopov
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0801644105
About CSHL:
Cold Spring Harbor Laboratory is a private, non-profit research and education institution dedicated to exploring molecular biology and genetics in order to advance the understanding and ability to diagnose and treat cancers, neurological diseases and other causes of human suffering.
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For more on stem cells and cloning, go to CellNEWS at http://www.geocities.com/giantfideli/index.html
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