Gene editing could help save the planet — if scientists can avoid the typos

For the last few years,
writers
and scientists have

marveled
at the
potential
for gene
editing
to allow farmers to grow more food
on less land
and allow more of the earth to grow
carbon-sucking
forests and savannas.

The main advantage of gene editing is precision. It’s right
there in the name: Instead of dealing with the randomness of
breeding, or the rough power-tool work implied by the term
“genetic engineering,” the “editing” suggests that
scientists could now change the letters of genetic code with the
same ease that a writer corrects typos.

But in late July, FDA
scientists found a chunk of bacterial DNA
in gene-edited
calves, prompting people to wonder if this precision tool wasn’t
as precise as advertised. That hopeful vision of a gene-edited
future — verdant with pesticide-free, carbon-sequestering crops
— flickered.

On Monday, the scientists studying these gene-edited cattle
published a
paper in the journal Nature Biotechnology
explaining what
happened. Essentially, this new paper tells us that gene editing
precisely tweaked specific letters of DNA, exactly what it was
supposed to do. But scientists also used older, cruder tools, and
one of those caused the genetic typo. Even so, the end result might
be that gene-editing slides into the muck of controversy over
GMOs.

To be clear, the cows at the center of this study have nothing
to do with creating more productive, pest-resistant foods. The
scientists had edited their genes in stem cells, which grew into
calves without horns. Farmers usually remove the horns to prevent
cattle from injuring each other — goring is a real danger.

When I visited the University of California Davis in 2015, I saw
a pair of these black-and-white bull calves standing and chewing in
an outdoor pen, like ordinary but adorable bovines. Unlike other
calves, however, they wouldn’t have to suffer through a painful
dehorning operation, in which a veterinarian burns out their horn
buds.

Some cows are naturally hornless: Angus and Hereford breeds, for
instance. But those are beef cattle. For dairy you want Holsteins
or Jerseys, and these champion milk producers are more carefully
bred than the winners of the Westminster dog show. If you started
crossing muscled Herefords with black-and-white Holsteins, it would
take decades of breeding to move the hornless trait into the dairy
line then weed out all the beefy traits.

What if you just plucked a single gene and moved it into dairy
cows? With gene editing, you could tweak dairy cows without messing
up their finely tuned milk-producing DNA so that they would no
longer have to endure dehorning. The Minnesota-based company
Recombinetics tried this using a technique called TALENS (you might
have heard of CRISPR — this is just a different version of the
same thing).

To run with the editing metaphor, Recombinetics basically took
out the DNA that laid out instructions for “HORN” and replaced
it with 202 letters of DNA that said “HORNLESS.” But first,
they attached it to a bacterial plasmid — think of it as a
sub-cellular copy machine — that would reproduce this strand over
and over again (HORNLESS, HORNLESS, HORNLESS!). Then they injected
all those copies into a cow cell — that gave one of those copies
a much better chance of bumping into the one spot in the DNA that
read HORN. This is where things went wrong. Instead of just
replacing HORN with HORNLESS, the plasmid also folded into the
cell’s DNA so that it read something like
HORNLESS-COPYMACHINE-HORNLESS. That genetic information went into
an egg, which went into a cow’s uterus, and, in 2015, grew into a
hornless calf. No one noticed until years later.

The calves I saw at Davis were there to be studied by Alison Van
Eenennaam, an animal geneticist. Funded by a U.S. Department of
Agriculture program to assess the risks of biotech, her team first
verified that the hornless trait was being passed down through
generations of cattle. “Basically, we found that Mendel knew his
shit,” said Van Eenennaam (that’s Gregor Mendel, the scientist
from the 1800s who described how traits are inherited).

With this new paper, Van Eenennaam’s team showed that the
bacterial plasmid had also been passed down to some of the calves,
again following the rules of genetics 101. It doesn’t seem to be
causing a problem — it’s fairly normal for DNA from germs and
viruses to work its way into genomes (the human genome is about

8 percent virus DNA
), and critters can usually just roll with
it. But because these cattle had DNA from a bacteria, it meant they
were genetically modified organisms, or GMOs in the eyes of
government regulators. That, in turn, meant they would have to
undergo years of testing. A giant corporation like Bayer could
afford that, but not a small startup like Recombinetics. The FDA is
now treating gene-edited animals like new drugs, requiring multiple
rounds of safety testing, which effectively puts an end to the
quest to make hornless dairy cows. Longtime opponents of
biotechnology think that would be a good thing. Friends of the
Earth recently released a
report
with Janet Cotter, who runs the consultancy Logos
Environmental, condemning gene edited animals.

“The scientific evidence shows that gene editing, particularly
in animals, is far from precise.” Cotter said in a statement.
“Instead, it can produce unintended changes to genetic material
and disrupt genetic processes. Such effects could have far reaching
consequences for food safety, so these applications will require a
rigorous assessment if they are to be used in agriculture.”

It would be easy enough to screen out plasmids before putting
gene-edited eggs into a cow’s womb. That’s a routine procedure,
said Van Eenennaam. But she worries that won’t quell fears that
gene editing is sloppier than expected. Treating gene-edited
animals like drugs is not proportionate with the risk, Van
Eenennaam said, and would prevent breakthroughs that might help us
meet the challenge of climate change,
whether it’s cows that don’t belch methane, or corals that can
survive heat.
, Van Eenennaam said.

“The debate has pretty much blocked the technology in animals
through my whole career. I was hoping gene-editing would be
different,” she said. “I have students who are excited about
gene editing for disease-resistance — but now I feel like it’s
Ground Hog Day. Here we go again.”

This story was originally published by Grist with the headline
Gene editing could help save the planet — if scientists can avoid
the typos
on Oct 7, 2019.

Source: FS – All – Science – News
Gene editing could help save the planet — if scientists can avoid the typos