ARTICLE: Stem Cell Self-Renewal Gene Identified

[Murray Charters <mcharters@xxxxxxxxxxxxxx>]

Stem Cell Self-Renewal Gene Identified
By Nancy Touchette
Posted: October 30, 2003

One of the most perplexing questions in stem cell biology is ?What makes a stem 
cell a stem cell?? Researchers studying
adult stem cells would like to know what distinguishes a stem cell, which can 
replenish itself indefinitely, from a
progenitor cell, which can proliferate only a limited number of times. Now, 
researchers are one step closer to
understanding the difference.

Researchers at the University of Michigan in Ann Arbor have identified a gene 
that is required for the proliferation of
three types of adult stem cells from mice. Stem cells from the central nervous 
system, the peripheral nervous system
and the blood all rely on a gene called Bmi-1 to renew themselves. However, the 
gene is not required for the
proliferation of progenitor cells from the same tissues.

?This is the first gene identified that is consistently required by stem cells 
to proliferate, but it's not required by
at least some types of progenitor cells,? says Sean J. Morrison, who led the 
research. ?We expected that there would be
genes like this, but it was really exciting to finally find one.?

Researchers would like to identify the genes that distinguish stem cells from 
progenitor cells because the two are
often confused. Stem cells are more difficult to isolate because there are far 
fewer of them in the body, but they are
considered more useful because they proliferate in culture and can replace most 
of the cell types of a given tissue.

Previous studies by Morrison and Michigan colleague Michael F. Clarke showed 
that the Bmi-1 gene is needed to maintain
stem cells from the blood. The new study, reported in Nature, shows that the 
gene is also required by nerve stem cells
from the brain and gut. The new study further shows that the gene affects the 
process of proliferation, but has no
effect on how long a cell survives.

Maarten van Lohuizen of the Netherlands Cancer Center in Amsterdam discovered 
the Bmi-1 gene in cancer cells in 1991
and found that it blocks two proteins that normally inhibit cell proliferation.

Van Lohuizen also finds that the gene is needed for the renewal of stem cells. 
His studies also suggest that the gene
is active in some cells in the cerebellum that do not appear to be stem cells.

Interestingly, many cancer cells also over express the gene. Because the gene 
makes cells immortal, it may play a key
role in cancer development. Researchers studying both cancer and stem cells are 
keen on figuring out which genes are
regulated by Bmi-1.

. . .

Molofsky, A.V. et al. Bmi-1 dependence distinguishes neural stem cell 
self-renewal from progenitor proliferation.
Nature, published online October 22, 2003.


PubMed Abstract: Bmi-1 dependence distinguishes neural stem cell self-renewal 
from progenitor proliferation.


Reference:

The Scientist - October 23, 2003
Bmi-1 promotes neural stem cell proliferation
Neural stem cell self-renewal is distinct from proliferation of progenitor cells


Nature (May 2003)


SOURCE: Genome News Network


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