91色情片

STEM cells from the brain can be transformed into muscle, researchers in
Italy have found. Such cells could provide an inexhaustible supply of material
for treating muscle-wasting disorders such as muscular dystrophy. The
researchers have also found clues to what triggers the stem cells to change.

Angelo Vescovi and his colleagues at the National Neurological Institute in
Milan, Italy, have shown that adult stem cells from mouse brains become muscle
cells when implanted in the muscles of live mice. And when human adult stem
cells extracted from the brains of miscarried fetuses are implanted in mouse
muscle, they too turn into muscle cells. The team had already demonstrated that
mouse brain cells could turn into blood cells
(This Week, 19 August, p 16).

Scientists used to think that 鈥渁dult鈥� stem cells鈥攖hose produced after
the embryo becomes a fetus and the organs start to develop鈥攃an only turn
into tissue from which they were derived, such as brain, blood or muscle.
Vescovi hopes his new results will help to convince sceptics that adult stem
cells can also turn into other types of cell. 鈥淚 hope people consider that this,
if not the final proof, is at least a further indication that it鈥檚 possible,鈥� he
says.

Martin Raff, who works on neural stem cells at University College London
points to a flood of similar results. So many interconversions of tissue are now
being reported, he says, that Vescovi鈥檚 results are hardly surprising.
鈥淓veryone鈥檚 finding this enormous plasticity of cells,鈥� he says.

In his latest research, Vescovi found that brain cells only changed role if
they touched muscle cells. 鈥淭hey wouldn鈥檛 do it even when a few micrometres
away,鈥� he says. He is now looking for the chemical cues from muscle which
trigger the change.

His finding implies that brain cells must be isolated from each other before
they will change. Otherwise neighbouring brain cells would continue to exert
more influence over each other鈥檚 fate than competing signals from muscle
cells.

He suggests that stem cells may be pre-programmed in the embryo to become
specific types of cell. But this 鈥渄efault鈥� may be overridden if competing
signals such as those from muscle are strong enough, he says.

Campaigners opposed to abortion are claiming that Vescovi鈥檚 successes with
cells from adult mice reinforce their case for banning research on embryos and
fetuses. But Vescovi points out that it is practically impossible to extract and
multiply brain stem cells from people. The only alternative is to use stem cells
from fetuses. And he says he could never have established colonies of mouse
adult stem cells without experimenting for years on mouse embryonic stem
cells.