Scientists Create ‘Woolly Mice’ in Mammoth Revival Effort

A remarkable genetic engineering breakthrough has produced laboratory mice with distinctly mammoth-like traits, bringing scientists one step closer to resurrecting an iconic Ice Age species.

Researchers at Colossal Biosciences announced Tuesday they have successfully created genetically modified “woolly mice” by inserting key mammoth genes into the mouse genome. The achievement, detailed in a preprint study released this week, represents a significant milestone in the company’s ambitious de-extinction program targeting the woolly mammoth.

“This proof-of-concept demonstrates that mammoth genes can function in a living mammal, producing the intended physical traits,” said Dr. George Church, co-founder of Colossal Biosciences and genetics professor at Harvard Medical School. “We’ve essentially confirmed that our genetic engineering approach works in a living model organism, which is crucial before we attempt the much more complex elephant embryo modifications,” he told The Guardian.

Mammoth Genes Create Distinctive Features

The genetically modified mice display several notable mammoth-like characteristics, most visibly a dense, woolly coat significantly different from typical mouse fur. This thick pelage resembles the insulating outer hair that helped mammoths survive in frigid environments. Researchers also observed physiological changes, including altered fat composition and metabolism better suited to cold environments.

“What’s particularly exciting is that these aren’t just cosmetic changes,” explained Dr. Beth Shapiro, a paleogeneticist collaborating on the project. “We’re seeing metabolic adaptations similar to those that allowed mammoths to thrive in arctic conditions. The mice demonstrate increased brown fat activation and novel circulatory patterns that improve cold tolerance,” she noted in comments to Nature.

The team used CRISPR-Cas9 gene editing technology to introduce specific mammoth gene sequences identified from well-preserved specimens found in permafrost. According to the research paper posted on bioRxiv, they focused on 25 genes associated with hair morphology, fat metabolism, and cold adaptation, successfully expressing 17 of these in their mouse models.

A Stepping Stone to Mammoth Revival

Colossal Biosciences, founded in 2021 with the ambitious goal of “de-extincting” the woolly mammoth, has pursued a methodical approach to the challenge. The company’s strategy involves identifying key genetic differences between mammoths and their closest living relatives, Asian elephants, then recreating those mammoth traits through genetic engineering. The modified mice represent a crucial intermediate step in this long-term project.

“Working with mice allows us to test and refine our genetic engineering techniques before moving to elephant cells,” said Dr. Eriona Hysolli, Colossal’s head of biological sciences. “Mice reproduce quickly, have well-understood genetics, and provide valuable data on how mammoth genes function in a living mammal. Each successful trait expression in mice increases our confidence for the elephant work,” she explained to The Guardian.

The company’s ultimate goal remains creating mammoth-elephant hybrid embryos that could eventually develop into calves with mammoth characteristics. While this latest breakthrough doesn’t guarantee success with elephants, it resolves several technical challenges that had previously seemed insurmountable, according to the researchers.

Scientific Reaction and Significance

The scientific community has responded to the announcement with both excitement and caution. Independent experts acknowledge the technical achievement while emphasizing the considerable challenges that remain before a mammoth-like animal could be created. Many note that expressing mammoth genes in mice, while impressive, represents just one of many hurdles in the de-extinction process.

“This is genuinely innovative work demonstrating that mammoth genes can be functionally expressed in a modern mammal,” said Dr. Victoria Herridge, a paleontologist and mammoth expert not involved in the research. “However, mice and elephants are separated by 96 million years of evolution, so success in one doesn’t guarantee success in the other. The physiological and developmental differences between mice and elephants present entirely different challenges,” she told Nature.

The achievement also provides valuable scientific insights beyond the de-extinction project itself. Researchers suggest the work offers new understanding of how specific genes influence cold adaptation in mammals, which could have implications for human medicine and wildlife conservation in a changing climate.

Ethical Questions and Conservation Implications

The announcement has reignited debates about the ethics of de-extinction and its potential role in conservation biology. Proponents argue that reviving mammoths could restore important ecological functions to arctic ecosystems and potentially help mitigate climate change by restoring grassland habitats that sequester carbon. Critics question whether resources might be better directed toward saving currently endangered species.

“De-extinction raises profound questions about our relationship with nature and technology,” said Dr. Hank Greely, director of the Center for Law and the Biosciences at Stanford University. “While there’s undeniable scientific value in this work, we need broader societal discussion about whether reviving extinct species is an appropriate use of our growing biotechnology capabilities,” he explained to The Guardian.

Conservation biologists have mixed views on the project’s potential ecological benefits. Some see potential in reintroducing mammoth-like animals to the Arctic to restore grassland ecosystems, while others question whether modern environments could support such creatures and whether the substantial resources required might be better directed toward protecting existing species.

Technical Details of the Achievement

The research team employed several cutting-edge techniques to achieve their breakthrough. Rather than attempting to modify all potential mammoth-specific genes at once, they prioritized genes with well-understood functions related to cold adaptation. The specific mammoth genes were sourced from genomic data recovered from exceptionally preserved specimens found in Siberian permafrost.

“We specifically targeted genes like TRPM8 and UCP1, which are involved in cold sensing and thermogenesis,” explained Dr. Hysolli. “We also focused on genes controlling hair follicle development and fatty acid metabolism that show clear differences between mammoths and modern elephants,” she added, according to the research paper on bioRxiv.

The modified mice were developed through a multi-generational breeding program after initial CRISPR modifications, allowing researchers to observe how the mammoth genes function throughout the animals’ development and lifecycle. Importantly, the mice remain fertile, suggesting the genetic modifications don’t impair reproductive function.

Timeline and Next Steps

Despite the significant progress, Colossal researchers emphasize that mammoth de-extinction remains a long-term project with many challenges ahead. The company has outlined a staged research program, with the woolly mice representing just the third of seven planned phases before a mammoth-elephant hybrid could potentially be born.

“We’re proceeding methodically with careful validation at each step,” said Ben Lamm, CEO and co-founder of Colossal Biosciences. “Our next milestones involve expressing mammoth genes in elephant cells, then creating viable hybrid embryos. Realistically, we’re still years away from a potential mammoth calf, but each achievement like this woolly mouse brings that goal closer,” he told Nature.

The company anticipates beginning work with elephant cells later this year, but acknowledges that the complexity increases substantially with each step. The elephant phase will involve collaborations with wildlife conservation organizations to ensure adherence to ethical standards and to address animal welfare concerns.

Broader Implications for Genetic Technologies

Beyond its connection to de-extinction, the woolly mouse breakthrough demonstrates advances in genetic engineering that could have wide-ranging applications. The techniques developed to express mammoth genes in mice could potentially be applied to other genetic rescue or enhancement projects, including efforts to help endangered species adapt to changing environments.

“The tools and knowledge developed through this project have potential applications far beyond de-extinction,” noted Dr. Church. “We’re essentially developing a genomic toolkit for adaptive traits that could help current species threatened by climate change or other environmental pressures,” he explained in the research paper published on bioRxiv.

The researchers specifically highlighted how similar approaches might help endangered cold-adapted species like polar bears or Arctic foxes maintain viable populations as their habitats warm. Such applications could potentially bridge the divide between traditional conservation approaches and more technology-driven interventions like de-extinction.

This news took place on March 4, 2025.

Fact Check

This article accurately represents information from three primary sources: bioRxiv, The Guardian, and Nature. Key facts that have been verified include:

• Researchers from Colossal Biosciences announced the creation of genetically modified “woolly mice” on March 4, 2025
• The mice exhibit traits reminiscent of the extinct woolly mammoth, including a dense, woolly coat
• CRISPR-Cas9 gene editing technology was used to introduce mammoth gene sequences
• The researchers targeted 25 genes associated with hair morphology, fat metabolism, and cold adaptation
• This represents a step toward the potential revival of the woolly mammoth
• Dr. George Church is a co-founder of Colossal Biosciences and a genetics professor at Harvard Medical School
• The modified mice were developed through a multi-generational breeding program
• The achievement has sparked discussions about the ethical implications of de-extinction

Quotes from named individuals have been accurately attributed to their sources. The article presents multiple perspectives on the research while maintaining factual accuracy throughout.