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Keeping stem cells alive by insulin signal

Biologists of the University of California, Berkeley have found a
signal that keeps stem cells alive in the adult brain. It gives a
focus for scientists looking for ways to regrow or reseed stem cells
in the brain to allow injured areas to repair themselves.

The researchers discovered in fruit flies that keeping the insulin
receptor revved up in the brain prevents the die-off of neural stem
cells. It occurs when most regions of the brain mature into their
adult forms. Whether the same technique will work in humans is
unknown, but the UC Berkeley team hopes to find out.

New finding shows that it is also necessary to provide an insulin-like
signal. It is known that other researchers have gotten neural stem
cells to persist by blocking genes that cause them to die. Yet this
alone does not produce healthy, normal-looking neural stem cells that
can make mature neurons.

Most areas of the adult mammalian brain and fruit fly brain are devoid
of neural stem cells, the only cells able to generate full-fledged
neurons. A scientist Hariharan noted that because of the lack of
neural stem cells the injured brain is unable to replace dead neurons.

In subsequent experiments, she attempted to prevent the death of
neural stem cells in fruit flies by genetically blocking a process
called programmed cell death (apoptosis). This allowed the stem cells
to survive longer. The cells showed signs of impaired growth,
suggestive of insulin withdrawal.

Then various genetic manipulations were made to mimic an insulin-type
signal, using mutant fruit flies with their blocked apoptosis genes.
The result was amazing - neural stem cells persisted for at least a
month and generated many mature normal nerve cells.

The biologists plan to continue their study through mutant fruit flies
to find other genes that improve survival in the mushroom body and
allow stem cells in other areas of the fly brain to persist.