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Scientists created a ‘woolly mouse’ with mammoth traits. Is it a step toward
bringing back the extinct giant?
Katie Hunt
By Katie Hunt, CNN
5 minute read
Updated 10:22 AM EST, Tue March 4, 2025
89 comments
The genetically modified woolly mice embody several woolly mammoth-like traits,
according to Dallas-based Colossal Biosciences.
The genetically modified woolly mice embody several woolly mammoth-like traits,
according to Dallas-based Colossal Biosciences. Colossal Biosciences
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—
It’s tiny, but this lab mouse could have a mammoth impact.
With curly whiskers and wavy, light hair that grows three times longer than that of
an ordinary lab mouse, the genetically modified rodent embodies several woolly
mammoth-like traits, according to Colossal Biosciences. The private Dallas company
is behind efforts to resurrect the mammoth and other extinct animals.
Colossal said its woolly mouse would enable its scientists to test hypotheses about
the link between specific DNA sequences and physical traits that enabled the
mammoth, which went extinct around 4,000 years ago, to adapt to life in cold
climates.
“It is an important step toward validating our approach to resurrecting traits that
have been lost to extinction and that our goal is to restore,” said Dr. Beth
Shapiro, chief science officer at Colossal, in a news release Tuesday. Shapiro is
currently on a leave of absence from her role as professor of ecology and
evolutionary biology at the University of California, Santa Cruz.
The genetically engineered mice are lighter in color than ordinary lab mice.
The genetically engineered mice are lighter in color than ordinary lab mice.
Colossal Biosciences
How to make a woolly mouse
To create the woolly mouse, Colossal said it had identified genetic variants in
which mammoths differed from their closest living relative: the Asian elephant.
The company’s scientists then pinpointed 10 variants related to hair length,
thickness, texture, color and body fat that corresponded to similar, known DNA
variants in a lab mouse.
For example, scientists targeted a gene known as FGF5 (fibroblast growth factor 5),
which targets the cycle of hair growth, creating longer, shaggy hair. They also
altered the function of three genes related to hair follicle development and
structure to create woolly hair texture, wavy coats and curled whiskers, the
company said in a news release.
Other target genes included MC1R (melanocortin 1 receptor), which regulates melanin
production, in order to produce mice with golden hair rather than the usual dark
fur and a variant associated with changes in body weight.
In total, the team made eight edits simultaneously, using three cutting-edge
techniques, to seven mice genes.
Colossal shared an unpublished, or preprint, scientific paper describing the
research, which has not undergone peer review.
“I think that the ability to edit multiple genes at the same time in mice, and to
do so and obtain the expected woolly appearance, is a very important step,” said
Love Dalén, a professor of evolutionary genomics at Stockholm University. Dalén is
an advisor to Colossal and was a coauthor on the paper.
“It is a proof-of-principle that Colossal has the know-how to do this kind of gene
editing, including to insert mammoth gene variants into a different species.”
Colossal Biosciences
Just ‘cute, hairy-looking mice’?
The research outlined in the unpublished paper was technically impressive and the
genetic changes precise and efficient, said Robin Lovell-Badge, head of the Stem
Cell Biology and Developmental Genetics Laboratory at The Francis Crick Institute
in London.
“My biggest problem with the paper is that there is nothing addressing whether the
modified mice are cold-tolerant — through introducing traits that are apparent in
mammoths — which is the justification given for carrying out the work,” Lovell-
Badge said via email.
“As it is, we have some cute looking hairy mice, with no understanding of their
physiology, behaviour, etc. It doesn’t get them any closer to know if they would
eventually be able to give an elephant useful mammoth-like traits and we have
learned little biology.”
4th March 1938: A Dodo skeleton opposite a reconstructed model of the extinct bird
in the National Museum of Wales, Cardiff.
Related article
Scientists say they are close to resurrecting a lost species. Is the age of de-
extinction upon us?
Colossal has raised $435 million since it was founded in 2021 by entrepreneur Ben
Lamm and Harvard University geneticist George Church.
The company plans to recreate the mammoth, dodo, and Tasmanian tiger, or thylacine,
by editing the genome of each species’ closest living relative to make a hybrid
animal that would be visually indistinguishable from its extinct forerunner.
Ultimately, the company wants to restore the fauna to their natural habitat.
In the case of mammoths, the company argues that having mammoth-like creatures
lumbering through the Arctic would compress the snow and grass that insulates the
ground, slowing the rate of permafrost thaw and the release of carbon contained in
this fragile ecosystem. Colossal has previously said it’s on track to introduce the
first woolly mammoth calves in 2028.
Skeptics argue that the huge sums of money invested in the project could be better
spent elsewhere. Raising and breeding the hybrid animals, they say, could imperil
living animals used as surrogates.
“While we know a lot about mouse genetics, we know much less about mammoths and
elephants. It isn’t yet known which sections of the genome are vital for achieving
the characters (needed) to make an elephant fit for life in the Arctic circle,”
said Tori Herridge, Senior Lecturer, School of Biosciences, University of
Sheffield, in a statement shared by the Science Media Centre. “Genes that are
linked to fur and fat in well-studied animals like mice are obvious targets, but
the devil is in the detail.”
What do you think?
Join 89 others in the comments
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“Unless you decide to make EVERY edit necessary … in the genome, you are only ever
going to create a crude approximation of any extinct creature, based on an
incomplete idea of what it should look like. You are never going to ‘bring back’ a
mammoth,” she added.
Critics say it will only ever be possible to bring back an incomplete approximation
of a mammoth.
Critics say it will only ever be possible to bring back an incomplete approximation
of a mammoth. Colossal Biosciences
Lab mice are commonly genetically engineered to have certain traits, including
human ones, in order to conduct research on disease and drug development.
Rob Taft, a principal scientist at The Jackson Laboratory, a biomedical research
institution that helped pioneer humanized lab mice, said via email that the woolly
mouse was an “innovative extension of the use of the mouse as a model system and an
innovative approach to understanding the physiology of animals that are now
extinct.”
His biggest question was how Colossal would translate this research back to
elephants.
“Working with mice or even cattle is relatively easy,” Taft said. “We know a lot
about reproduction in these species and assisted reproductive technologies are well
developed and used routinely in these species but there’s a lot about elephant
reproduction that is not known and assisted reproductive technologies are not well
developed for use in elephants.”
89 comments
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