18 | NewScientist | 3 November 2018For new stories every day, visit newscientist.com/newsA day in the shade
builds up a tanSKIN seems to tan most when you
spend every other day out of the
sun. This also reduces DNA damage.
Sunlight contains ultraviolet
rays that can harm DNA and lead
to premature ageing and skin
cancer. To protect against this, skin
produces melanin, a dark pigment
that acts like a natural sunscreen.
The pigment starts to form within
hours of sunlight exposure and
gives the skin a tanned look.
Carmit Levy at Tel Aviv University
in Israel and her colleagues
measured how much melanin
mice produced when they were
exposed to UV light every day,
every second day or every third day.
To their surprise, the mice
that tanned the most were those
exposed to UV every second day.
The extra pigmentation the mice
produced meant their skin also
experienced the least DNA damage.
The same result was seen for
human skin samples (Molecular
Cell, doi.org/cwbb). Together,
the findings suggest that skin
cells need 48 hours between sun
exposure periods to build up their
maximum defences, says Levy.
Her team is now trying to work
out the evolutionary reason behind
the two-day melanin cycle. “It’s
strange because ancient humans
would have been exposed to sun
most days, so we don’t know why
it takes 48 hours to work,” she says.Fish evolution soared in the shallows
BACKBONES helped vertebrate
animals conquer the oceans, then
the land and the skies. Until now, the
early history of the group has been
a bit of a mystery, but an analysis
suggests shallow waters were key.
Vertebrates are thought to have
begun to diversify about 480 million
years ago, splitting into groups
that would become jawless fish,
cartilaginous fish and a lineage
including bony fish. This last group
ultimately gave rise to amphibians,
reptiles, birds and mammals.
But our grasp of this split is
hampered by the fact that most ofour well-preserved fish fossils are
no more than 360 million years old.
Now Lauren Sallan at the
University of Pennsylvania and her
colleagues have collated records of
fish fossils from before this time.
“We found that all vertebrates, from
the first jawless forms to sharks
and bony fishes, originated in very
restricted shallow waters hugging
the coastline,” says Sallan.
This suggests that the
evolutionary events that helped
fill the seas with fishes occurred
in tidal areas and lagoons (Science,
DOI: 10.1126/science.aar3689).A HORMONE released by bone
during exercise boosts memory
storage and retrieval in older
mice. The protein it uses has now
been identified, and could form
the basis of a treatment for age-
related memory loss.
As we get older, the gearwheels
that keep our body functioning,
such as hormone secretion and
cell regeneration, turn at a slower
rate. For instance, we make less of
a bone-building hormone called
osteocalcin as we age.
In previous research, Eric
Kandel and his colleagues atColumbia University in New York
found that mice with osteocalcin
deficiency showed symptoms of
memory loss. They have also tied
this memory loss to a gene called
RbAp48, whose activity increases
in mice injected with osteocalcin.
Now Kandel’s team has
injected 16-month-old mice with
osteocalcin. Within 48 hours,
the expression of RbAp48 in the
brains of these old mice had risen
by 15 per cent.
In tests, old mice given the
injection appeared to have fewer
memory problems than old micethat had not received the shot.
Digging deeper, the researchers
found that RbAp48 controls the
expression of a protein called
GPR158, to which osteocalcin
must bind to pass on its memory-
boosting impact (Cell Reports,
doi. org/cwbt).
“It’s the first time we have
shown the detailed pathway
between RbAp48 and osteocalcin,”
says Kandel. “In the future, it may
be possible to develop a form of
GPR158 that can be administered
to help reverse age-related
memory loss.”Exercise hormone may lead to drug to prevent memory loss
Liquid metal puts
wheels in motionA SMALL drop of liquid metal
pushed along by an electric
current is enough to propel a
wheeled robot. Larger, soft-bodied
robots that can change their shape
could use the technique to roll like
tumbleweed through unfriendly
terrain on rescue missions.
First, Shi-Yang Tang at the
University of Wollongong in
Australia and his colleagues put a
drop of liquid metal made mostly
of gallium in a small, plastic
wheel. They added two electrodes,
one either side of the drop, on a
platform that slides around the
wheel as it turns.
While the electrodes are
switched on, the resulting voltage
pushes the metal droplet towards
one electrode. Like a hamster
running in a wheel, the metal
drop keeps moving forward as
the tiny tyre turns. Because the
drop changes the robot’s centre
of gravity, it continues to roll
(Advanced Materials, doi.org/
gff6ds).
The system takes less than
0.4 seconds to reach a maximum
speed of 5.5 centimetres a second.
This rolling motion takes less
power and can generate higher
speeds than other methods of
robot motion, says Tang.PLAINPICTURE/TROMP L’OEIL
NOBUMICHI TAMURAIN BRIEF