A CRISPR technique that removes the Y chromosome has allowed scientists to create female clones from male mice, a feat one researcher described as sci-fi. The approach could someday help conserve endangered species, but it also highlights cloning’s stranger possibilities, from pet cloning to the hypothetical human ‘organ sacks.’
Takashi Ishiuchi, a reproductive biologist at the University of Yamanashi who led the work with Shogo Matoba of the Riken BioResource Research Center, said the technique felt “a bit like sci-fi.” The team used CRISPR to cut out the Y chromosome from male mouse embryos, converting them into female clones. The resulting animals are genetically identical to the males except for the missing Y chromosome.
Cloning has traveled a long road since Dolly the sheep arrived in 1996 as the first mammal cloned from an adult cell. In that experiment, scientists transferred the nucleus of an adult mammary cell into an egg cell whose own nucleus had been removed. The embryo was implanted in a surrogate, and Dolly was born as a genetic copy of the DNA donor. The goal was to enable precise genetic modification of livestock, building on thousands of years of selective breeding with the ability to replicate prized traits exactly.
In recent years, cloning has expanded into the pet market. Barbra Streisand and Tom Brady are among those who have had deceased animals cloned. For a price that can reach tens of thousands of dollars, companies take cells from a pet and produce a living clone. But the practice requires egg cells from another animal and a surrogate pregnancy, and critics see little medical or environmental justification. Bioethicist Jessica Pierce has characterized dog cloning as “the exploitation of the canine underclass.”
Conservation presents a stronger case. Scientists have long preserved animal tissues, often cryopreserved in facilities called “frozen zoos.” The San Diego Zoo, for example, holds cells from over 1,300 species, some collected decades ago. Such material has already enabled the creation of clones for animals on the brink of extinction, including black-footed ferrets and Przewalski’s horses. It also raises the prospect of reviving species that have disappeared entirely.
One notable attempt occurred in 2009, when Spanish researchers reported cloning a Pyrenean ibex, a wild goat that had gone extinct. Using skin cells cryopreserved a decade earlier and egg cells from domestic goats, they produced 439 embryos. Only one, a female, was born, and she died minutes later from a lung defect. That makes the ibex the only animal known to have gone extinct twice.
More ambitious efforts to bring extinct species back are also underway. Colossal Biosciences is working to bring back species like the thylacine and woolly mammoth using old and potentially ancient genetic material. So far, the company’s efforts have centered on modifying the genomes of animals alive today.
Cloning humans is technically possible, though no one has done it as far as is known. Some have proposed it, including a biotech startup founder who pitched the idea of “brainless clones” engineered to lack brains but carry all the organs a person might need for future transplants. MIT Technology Review’s Antonio Regalado wrote about that proposal in March, and the author of this story had to pause lunch while reading it.
From Dolly to female clones of male mice, cloning has achieved remarkable feats over the past few decades. The author, for one, is both excited and slightly nervous about what the coming decades will bring.