Tails grow back
with dash of salt
Sodium needed to stimulate
limb regeneration in tadpoles
By Laura Sanders
Researchers have hit on a winning recipe
for regrowing limbs: Add a pinch of salt
to a tailless tadpole; let sit for one hour.
Yield: one perfectly formed tail, complete with nerves, muscles, blood vessels
and other tissues.
It’s not quite that simple, but results
published in the Sept. 29 Journal of
Neuroscience extend the time that tadpoles can regrow a tail, raising the possibility that salt’s surprise role in amphibian
regeneration may ultimately lead to ways
to coax human tissue into regrowing severed limbs and damaged organs.
Tadpoles can completely regrow
appendages after an injury. Humans
retain some of this ability: Until about
age 11, children can regrow fingertips
under the right conditions.
In the new study, researchers led by
Michael Levin of Tufts University in
Medford, Mass., found that tadpoles
engineered so that they couldn’t shuttle salt into their cells couldn’t regrow
a tail, while normal tadpoles were
perfectly able to.
Tadpole tails don’t usually grow back
more than about 18 hours after an injury,
when scarlike tissue has formed around
the amputated limb. But salt imported
into cells near the wound can stimulate
regeneration even after this scarlike tissue is established, Levin’s team reports.
A salty environment alone isn’t enough
to cause the tail to regrow. The salt has to
be ushered into the cells near the wound.
One particular salt-importing channel, called NaV1.2, was required for tail
regrowth, the team found. Such channels are well-known for their roles in
brain cell communication and heart cell
beating, but scientists had no idea one
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might be important for regeneration.
The NaV1.2 channel is just one of salt’s
avenues into a cell. There are other ways
in, Levin says, raising the possibility of
simpler treatments. “It really doesn’t matter how the sodium gets in there,” he says.
One way to salt cells is with a small
molecule called monensin that shuttles
sodium into cells. A one-hour treatment
with monensin induced tail regeneration in tadpoles with wounds that had
already formed scarlike tissue. “This
simple signal kick-starts a remarkably
complex process,” Levin says.
The hope is that one day a simple salt
signal might turn out to be useful in
coaxing human appendages to regrow.
Normally, tadpoles can regrow their tails
after an injury (top). Keeping sodium out
of cells blocks this process (bottom).
“All studies up until now had to treat
animals before wounding,” Levin says.
“You can’t go to a doctor and get treated
before you have your accident.”
Heaps of genes have hand in height
Study finds hundreds of genetic variants influencing stature
By Tina Hesman Saey
Geneticists are getting to the long and
short of the genes that control how tall a
person will grow. The short answer is that
at least 180 common genetic variants are
involved; the long, that up to a thousand
variants may control human height.
Scanning the genetic blueprints of
more than 100,000 people, scientists have
turned up at least 180 different genetic
variants involved in determining human
height, the researchers report online
September 29 in Nature. That may sound
impressive, but each of the genes involved
has a small effect, and researchers are still
able to account for only about 10 percent
of the genetic contributions that give rise
to the wide diversity seen in height.
“It’s a lot more complicated than we
originally thought, and there may be thou-
sands of variants with subtle effects,” says
Michael Weedon, a geneticist at Peninsula
College of Medicine & Dentistry in Exeter,
England. Weedon is one of 293 coauthors
of the new study, which reanalyzed data
from more than 50 previous genome-
wide association studies to find genes
that affect growth in people.