DALLAS– In an extraordinary achievement of advanced multiplexed genome engineering, Colossal Biosciences announces the birth of the Colossal Woolly Mouse—mice engineered to express multiple key mammoth-like traits that provide adaptations to life in cold climates. By successfully modifying seven genes simultaneously, Colossal’s team created mice with dramatically altered coat color, texture, and thickness reminiscent of the woolly mammoth’s core phenotypes. This achievement demonstrates the feasibility of expressing traits using information learned from the computational analysis of 59 woolly, Columbian, and steppe mammoth genomes ranging from 3,500 to over 1,200,000 years old confirming these pathways as the crucial targets for mammoth de-extinction.
“The Colossal Woolly Mouse marks a watershed moment in our de-extinction mission,” said Ben Lamm, Co-Founder and CEO of Colossal Biosciences. “By engineering multiple cold-tolerant traits from mammoth evolutionary pathways into a living model species, we’ve proven our ability to recreate complex genetic combinations that took nature millions of years to create. This success brings us a step closer to our goal of bringing back the woolly mammoth.”
Colossal’s mammoth team explored a data set of 121 mammoth and elephant genomes, including Colossal-created high quality reference genomes for Asian and African elephants, to identify significant genes that impact hair and other cold-adaptation traits. The team focused on a suite of genes in which mammoths had evolved fixed differences compared to their closely related Asian elephant cousins. The Colossal scientists refined the list to include ten genes related to hair length, thickness, texture, and color as well as lipid metabolism that were compatible with expression in a mouse.
The team then edited the mouse genome using a streamlined strategy that combined three editing technologies: RNP-mediated knockout, multiplex precision genome editing, and precision homology directed repair (HDR) and made eight edits simultaneously, some with editing efficiencies as high as 100%, to modify seven genes.
The gene editing resulted in mice with the predicted traits from the team’s computational analysis and design for specific phenotypic changes. Colossal woolly mice all have an edit that causes loss of function in the gene Fibroblast growth factor 5, or FGF5, which alters hair growth cycles, leading to hair that can grow as much as three times longer than wild type. Similarly, loss of function of FAM83G, FZD6, or TGM3 leads to Colossal woolly mice demonstrating hair phenotypes with a woolly hair texture, wavy coats, and curled whiskers through changes to hair follicle development and structure.
The Colossal woolly mouse is a powerful system for testing hypotheses about the link between specific DNA sequences and physical traits. Mammoths have a nonfunctional version of the gene Transforming growth factor alpha, or TGFA, as well as a mutation of the keratin gene KRT27 that encodes a valine at position 191 rather than the usual methionine. Both genes are predicted to contribute to the woolly mammoth coat. Colossal woolly mice have been engineered with both a non-functional TGFA and a valine at position 191 of KRT27, just like the woolly mammoth, and display a wavy coat phenotype.
Colossal woolly mice also express several engineered traits other than hair length and texture. To re-create the lighter coat colors observed in woolly mammoth mummies, Colossal woolly mice have a modified version of the gene MC1R, which regulates melanin production, that produces mice with golden hair rather than the black/agouti wild type coat color. Colossal woolly mice also express a truncated version of fatty acid binding protein 2, or FABP2, reflecting a similar change in mammoths. FABP2 is associated with lipid metabolism and fatty acid absorption. In mice, truncated versions of this gene that are similar to that which evolved in mammoths leads to changes in body weight.
“The Colossal Woolly Mouse showcases our ability to use the latest genome editing tools and approaches to drive predictable phenotypes,” said Dr. Beth Shapiro, Chief Science Officer at Colossal. “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.”
“I’m incredibly proud of what our team has accomplished here in the lab in such a short period of time,” said Dr. Michael Abrams, who co-leads Colossal’s Mammoth Team. “We’ve pushed the boundaries of genetic engineering by coordinating multiple complex trait modifications in living animals with exceptionally high efficiency. This achievement showcases both the technical expertise of our scientists and the power of our genetic engineering platform to deliver predictable phenotypes.”
The implications of this breakthrough extend beyond the laboratory. Not only is the Colossal Woolly Mouse the first living animal engineered to express multiple cold-adapted traits using mammoth gene orthologs, but it is also a living model for studying cold-climate adaptations in mammals. Additional future analyses of the Colossal Woolly mice will also improve our understanding of how multiple genes work together to manifest physical traits.
“The Colossal Woolly Mouse demonstrates remarkable progress we’ve made in precise genome engineering, including optimized delivery methods, innovative multiplexing and combinations of gene targeting strategies.” said George Church, Professor of Genetics at the Wyss Institute and Harvard Medical School and Co-founder of Colossal. “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.”
