Extinct Mammoth Genes Engineered Into “Woolly Mouse”

Colossal Biosciences has announced the birth of the world’s first “woolly mouse”.

The mouse has been genetically engineered to possess genes associated with hair morphology and lipid metabolism in woolly mammoths. 

The multiplexed genome editing feat brings the de-extinction company, which was co-founded in 2021 by Professor George Church and serial entrepreneur Ben Lamm, one step closer to its goal of resurrecting the woolly mammoth.   

The company has shared the work in a pre-print.^*

Validating insights from ancient gene variants

Colossal has three ongoing de-extinction projects: the woolly mammoth, the thylacine and the dodo.

These projects aim to resurrect the phenotypes of extinct organisms by engineering the genes behind such traits into its closest living relative. In the case of the woolly mammoth project, this is the Asian elephant, Elephas maximus.

Advances in DNA extraction and sequencing have made it possible for scientists to access and read the genome of extinct organisms, including the woolly mammoth. But identifying which gene variants underlie specific traits requires – in an ideal world – experimental validation.

“One of the hardest challenges in biology is to understand the link between a DNA sequence variant and the way the animal with that variant looks and acts – but this is exactly the challenge that we need to solve in order to edit an elephant cell that can become a functional woolly mammoth,” Dr. Beth Shapiro, chief science officer at Colossal, told Technology Networks.

The company has been engineering mammoth edits into elephant cells for the last few years, Shapiro said. Using elephant models for validation studies is neither practical (they have a 22-month gestation period) nor ethical, as they are an endangered species.

The woolly mouse represents Colossal’s first success in engineering multiple traits into a living model.

Why start with genes relating to hair? “The woolly hair phenotype is one of the key traits of mammoths that we need to engineer into an elephant genome, and also one that is readily visible in a living animal model,” Shapiro explained.

Woolly mice have long hair and a wavy coat

Colossal conducted a computational analysis of 59 woolly, Columbian and steppe mammoth genes, which ranged from 3,500 to over 1.2 million years old. Genomes were compared with Asian elephants to identify genes that had evolved fixed differences in mammoths.

“We identified genes linked to cold adaptation and woolly phenotype through comparative genomic analysis of mammoths and elephants and then looked for variation in the mouse version of those genes that leads to mice with long or curly hair, or different coat colors, or, in the case of FABP2, variation in the way they metabolize fats,” Shapiro explained. “We then combined these edits (all of which had been observed individually in healthy mice) to create our woolly mouse.”

Three editing technologies – RNP-mediated knockout, multiplex precision genome editing and precision homology-directed repair – were used to achieve multiplex editing. A total of eight edits were made simultaneously to modify seven genes.

Colossal’s woolly mice have distinctly long hair, caused by an edit that causes loss of function in the FGF5 gene. This impacts hair growth cycles and leads to hair that grows ~three times longer than wild-type mice.

Other features of their hair phenotype, including the animal’s wavy coat and curled whiskers, are attributed to the loss of function of genes including FAM83G, FZD6 and TGM3, which affect hair follicle development.

“For some genes, we turned the gene off so that it does not express a protein. For others, we altered the protein,” Shapiro said. “For example, for the gene FABP2, all mammoths have a protein that is truncated compared to their elephant cousins. Mice that have a similarly shortened protein show differences in how they metabolize fat.”

Colossal’s woolly mice also express a truncated version of the FABP2 protein. “We will explore how this impacts their metabolism of fat under different diets,” Shapiro explained.

Choosing the edits has been an ongoing process since Colossal was founded. “We have been fortunate to have academic collaborators including Dr Love Dalén, who have been collecting mammoth ancient DNA for decades, as partners,” Shapiro said.

“Together, our teams have assembled more than 50 ancient mammoth genomes that our computational biologists have been using to identify potential gene targets. Our genome engineering team, led by Dr. Michael Abrams, optimized the guides and put everything in place for successful generation of the woolly mice in a remarkably short time.”

Understanding how woolly mice tolerate cold

Colossal isn’t going to be commercializing the mice as laboratory models. “We do not plan to sell our woolly mice, despite their remarkable cuteness – although this is a question that we are asked by nearly everyone!” Shapiro said.

Rather, the team will be conducting behavioral analysis over the next few months to explore the extent to which the edits affect the cold tolerance of woolly mice.

“Over the next 6–12 months, we will be working with these mice to better understand how their edited genes impact their tolerance to cold under different diets, using experimental approaches that are standard in mouse research that are currently under review by our external ethics board,” Shapiro said. These data will be used to update the preprint before it is submitted to a scientific journal.

Shapiro is “super happy” with the whole team at Colossal and how this project has progressed. “Once we began to edit the mouse cells, the project moved quickly. Our first woolly mice were born in under two months from the initiation of editing,” she said.

“This is validation that our approach to de-extinction of key traits – from identifying target edits from ancient DNA, to designing and optimizing guides, to editing cells, to turning those cells into animals that display precisely the predicted phenotype – is going to be a success!” she continued.

Though mice are incredibly useful laboratory models, it is always possible that the functional consequences of genetic modifications will differ in a model compared to the actual organism. It’s a limitation acknowledged by Colossal in the pre-print. Regardless, the company is confident that the approach for multiplexed editing provides a foundation for “evaluating complex combinations of genetic modifications leading to the mammoth phenotype.”

"The Colossal woolly mouse demonstrates the remarkable progress we've made in precise genome engineering, including optimized delivery methods, innovative multiplexing and combinations of gene targeting strategies," Church said. "We are showing that we can now rationally design and construct complex genetic adaptations, with profound implications for the future of multi-gene de-extinction and engineering."

Shapiro told Technology Networks that the three de-extinction projects are all making progress and developing tools that can be applied to biodiversity conservation.

“We’re close to a breakthrough from the aviation team,” she hinted, “which may be the next thing we tell the world about. Watch this space!”

This article is based on research findings that are yet to be peer-reviewed. Results are therefore regarded as preliminary and should be interpreted as such. Find out about the role of the peer review process in research here. For further information, please contact the cited source.

About the interviewee: 

Beth Shapiro, PhD is an evolutionary biologist and CSO at Colossal Biosciences. A pioneer in the scientific field “ancient DNA,” Beth travels extensively in the Arctic collecting bones and other remains of long-dead creatures including mammoths, giant bears, and extinct camels and horses. She uses DNA extracted from these remains to better understand how communities responded to past climate changes, with a goal to help develop strategies to conserve endangered species and ecosystems today. A MacArthur Fellow, National Geographic Explorer and Fellow of the American Academy of Arts & Sciences, Beth is highly acclaimed for both her research and her popular science communication. Her books “How to Clone a Mammoth: The Science of De-extinction” (Princeton University Press 2015, 2020) and “Life As We Made It” (Basic Books 2021) explore how humans have been manipulating life on Earth for as long as we have existed and the potential of using our biotechnologies to bring extinct species back to life. 

Dr. Beth Shapiro. Credit: John Davidson.