16 | New Scientist | 6 February 2021
News
THE human placenta is riddled
with cancer-like patterns of
mutations. But the discovery
is better news than it might
appear: it is helping scientists
open a new window on the
mysterious world of early
human development.
In some ways, the placenta
is a forgotten organ. It begins to
form shortly after fertilisation
from the embryo’s cells and
then helps to support the future
fetus as it develops before being
discarded at birth.
But it is difficult to study how
embryos “decide” which cells
are destined for the placenta
and which for the fetus.
“So far, we’ve been blind to
the first split,” says Tim Coorens
at the Wellcome Sanger Institute
near Cambridge, UK.
Coorens and his colleagues,
including his PhD supervisor
Sam Behjati, decided to retrace
the lineages of cells in full-term
placentas to see where they
came from.
Their approach relies on
the fact that cells naturally
accumulate mutations in their
DNA and then pass these on
when they divide. By comparing
patterns of mutations between
samples, it is possible to trace
cells’ family trees back in time.
The team studied 42 human
placentas, taking several small
biopsies from each and
sequencing the whole genomes
of the cells within them.
A key discovery was just how
mutated placental tissue can be.
Some body cells, such as certain
cells lining the colon, are known
to have a naturally high rate of
mutation, but the placental cells
had about five times as many
mutations to a single DNA
“letter” as even these cells.
The placental tissue also
had large numbers of changesinvolving the addition or loss
of chunks of DNA – a form of
mutation that is vanishingly
rare in most human tissues,
but common in certain
childhood cancers.
Why such a vital organ
should be so cavalier about its
genome remains unclear. Its
disposability might provide
a clue: as it only “lives” for
nine months, it doesn’t need toinvest precious resources into
repairing itself, says Coorens.
The placenta may even
benefit the embryo by acting
as a sort of dumping ground for
potentially problematic cells.
By comparing placental
samples with samples of
umbilical cord, which grows
from future fetal cells, Coorens
and his colleagues found that
a cell’s “decision” to join the
placental or fetal lineages
happens at the earliest stages
of development, even as soonas the first division that turns
a fertilised egg into two cells.
The team found evidence in
favour of this idea in one of the
placentas. It contained cells with
three copies of chromosome 10,
but the associated umbilical
cord had the usual two.
Cell family tree tracing
showed that the cells with three
copies of the chromosome were
directed towards the placenta
during some of the first cell
divisions following fertilisation
(bioRxiv, doi.org/ghv9sk).
The work adds to evidence
that mammalian embryos push
their cells towards particular
destinies at a much earlier
stage of development than
previously thought, says
Magdalena Zernicka-Goetz
at the California Institute of
Technology, whose research in
mice first suggested this idea.
“It is incredible for me to
see that the same now is found
to be the case in the human
embryo,” she says. ❚SOFT robots with translucent
“skin” can detect human touch and
differentiate a prod, a stroke or a
hug. The technology could lead to
better non-verbal communication
between people and robots.
Guy Hoffman and his team
at Cornell University in Ithaca,
New York, made a prototype robot
with a nylon skin stretched over a
1.2-metre tall cylindrical scaffold
atop a platform on wheels. Inside
sits a commercial USB camera,
which can interpret different
types of touch on the nylon.
The team built a database from
camera images of people making
one of six interactions with the skin
of the robot, such as a point, a punch
or a palm touch. These were used to
train a neural network, a type of AI,
that let the robot detect and identify
interactions with an accuracy of up
to 92 per cent (Proceedings of
the ACM on Interactive, Mobile,
Wearable and Ubiquitous
Technologies, doi.org/fsf9).
The researchers assigned simple
commands to various touches. They
could poke it to make it turn around,
pat it on the back to order it from
the room or even stroke it forwards
or backwards to make it roll in that
direction. The hug wasn’t assigned
a command, but shows the robot
can identify touch all over its skin.
The system uses the shadow that
is made on the skin to work out what
type of touch a person is making, so
it had a hard time identifying a hug
at night. It also confused a punch
with a poke during daylight.
The team used a projector
to display a touchscreen interface
on the robot’s skin. Incorporating
touch sensitivity in robots currently
requires heavy and expensive
sensors and electronics. The new
approach is low-tech and low-cost.
It means soft robots, which offer
safety benefits and can fit into tight
spaces, can detect touch without
rigid electronics on their surfaces. ❚Pregnancy RoboticsClaire Ainsworth Matthew SparkesLE
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/SCIENCE^PH
OTO^ LIBRARYPlacenta is full of mutated
cells dumped by embryo
Soft-skin robot
can tell a hug from
a poke or punchA magnified image
showing blood flow
in a human placenta“The human placenta
had five times as many
mutations to single DNA
‘letters’ as other tissues”