16 | New Scientist | 1 February 2020
SOME mice have sequences in
their genome from a virus that
infected their fathers. We know
that events like this must have
happened many times in the
ancient past, but this is the first
time it has been observed in
action. And it involved a virus
that we thought couldn’t do this.
The finding means that even
more of the DNA of animals
derives from viruses than we
thought, says Eiichi Hondo at
Nagoya University in Japan. It also
suggests that viral pandemics can
alter the characteristics of animals
by changing their genes, he says.
“We believe that future
pandemics of viral diseases could
alter mammalian morphology or
functions very quickly in their
descendants,” say Hondo.
The researchers studied the
(EMCV), which circulates in
rodents but can infect a wide range
of animals, including humans.
They first showed that EMCV can
integrate into the genome of testes
cells of mice growing in a dish.
Next, Hondo and his colleagues
infected male mice with EMCV,
then allowed those that survived
to mate. They found signs of viral
genetic sequences in the earlobes
of the offspring, but not in those
of the fathers. They are now
sequencing the whole genome
of the offspring to find out which
viral sequences became integrated
and where (bioRxiv, doi.org/dkhp).
Viral genes passing down to
offspring in the genome in this
way was thought to happen only
every few hundred thousand
years. But this isn’t the only reason
the team’s findings are surprising.
The EMCV virus shouldn’t
readily integrate into the genome
at all, says John Coffin at Tufts
University School of Medicine in
Massachusetts. This is because
animal genomes consist of DNA,
so only sequences that are also
made of DNA can be added to it.
However, the genomes of many
viruses are made of RNA.
One group, called retroviruses,
gets around this by making
enzymes that turn their RNA into
DNA so the virus can add its genes
to the genome of a cell it infects, in
order to hide for years. This is why
HIV, which is a retrovirus, is so
hard to eliminate from the body.
It was thought that non-
retroviral RNA viruses, including
EMCV, couldn’t get into animals’
genomes. Then in 2010, Coffin and
other researchers showed that
genes from a non-retroviral RNA
virus called a bornavirus were
present in some mammals, such
as people, rodents and elephants.
But bornavirus replicates in the
nucleus of cells, says Coffin, where
there is a chance of its RNA being
turned into DNA and splicing into
a host genome. EMCV, by contrast,
replicates outside the nucleus,
so shouldn’t be integrated.
Hondo says bits of DNA in
mammals often resemble viral
sequences. This is often dismissed
as coincidence if those sequences
are in viruses we didn’t think
could invade genomes. His team
plans to see what other non-
retroviral RNA viruses – including
Ebola and Zika – have genetic
sequences that have been or could
be passed to animals in this way. ❚
Michael Le Page
Computer-made image of
RNA, the genetic material
in many viral genomes
Giant dinosaurs may
have crossed water
using just front feet
SAUROPODS may have sometimes
walked on just their two forelimbs,
if their fossil footprints are to be
believed. These dinosaurs were
so huge they needed four pillar-like
legs to support their bodies, but a
set of three tracks appears to show
only sauropod forefeet.
James Farlow at Purdue
University Fort Wayne, Indiana, and
his colleagues have now analysed
60 of these sauropod footprints in
a quarry near Austin, Texas, in
rocks roughly 110 million years
old (Ichnos, doi.org/dkdg). We know
that three types of sauropods lived
there at the time: Sauroposeidon,
Astrophocaudia and Cedarosaurus.
In theory, one of these species
could have made the tracks.
Some of the footprints are
70 centimetres wide. It is hard
to judge a dinosaur’s size from its
footprints, but estimates suggest
these sauropods may have been
25 metres or more in length and
weighed 15 to 78 tonnes.
It is inconceivable that beasts
of this size and weight could
walk on two legs, says Farlow.
He says the dinosaurs may
instead have had a centre of mass
that lay closer to the front than
the rear of their body. Walking over
relatively firm ground, their forefeet
might have left an impression in the
surface while their hindfeet didn’t.
But in other sauropod trackways,
the hindfeet leave prints as deep or
deeper than the forefeet, he says.
There is also a strangely wide
separation between a set of left and
right prints, as if the sauropod’s legs
splayed outwards. It is possible the
“bipedal” tracks were left when the
dinosaurs waded in shoulder-deep
water, using their front legs to punt
along the bottom, says Farlow.
But Paul Barrett at the Natural
History Museum in London says
sauropods may have avoided
deep water as they may have
been prone to tipping over.
“These animals would have been
surprisingly light for their size, due
to their large lungs and the many
air sacs [in their] bones,” he says. ❚
Virus genes seen invading animal
genome and then being inherited
“ Sauropods may have
avoided deep water
as they may have been
prone to tipping over”