Scientists at the University of California, Davis, have successfully produced a calf, named Cosmo, which was genetically edited as an embryo to produce more male offspring. The research was featured in a poster today (July 23) at the meeting of the American Society for Animal Science.
Using CRISPR genome editing technology, researchers can make specific cuts in the genome or insert useful genes, called a knock-in gene. In this case, the scientists successfully inserted or inserted the SRY gene from cattle, the gene responsible for initiating male development, into a bovine embryo. It is the first demonstration of a targeted gene gene for large DNA sequences through embryo-mediated genome editing in cattle.
“We anticipate that Cosmo pups that inherit this SRY gene will grow and look male, regardless of whether they inherit a Y chromosome,” said Alison Van Eenennaam, an animal geneticist in the UC Davis Department of Animal Science.
More males, more beef
Van Eenennaam says that part of the motivation for producing more male cattle is that male cattle are approximately 15 percent more efficient at converting feed to weight gain. They are more fuel efficient than women. Also, they tend to be processed with a heavier weight.
It could also be a victory for the environment, since fewer livestock are needed to produce the same amount of meat. “Ranchers could produce some females as replacements and direct a higher proportion of male cattle to the market,” said Joey Owen, a postdoctoral researcher in animal science who is leading the project with Van Eenennaam.
An arduous journey
The SRY gene was inserted into bovine chromosome 17, which is a safe genomic protection site. This ensures that genetic elements function predictably and do not disrupt the expression or regulation of adjacent genes. Chromosome 17 was chosen after unsuccessful attempts to activate the gene on the X chromosome, which would have resulted in a bull that produced only male offspring. Cosmo is expected to produce 75% male offspring: 50% normal XY animals and another 25% XX animals that inherit the SRY gene.
“It took two and a half years to develop the method of inserting a gene into the developing embryo and another two years to successfully establish a pregnancy,” Owen said. But in April 2020, a healthy 110-pound calf was born.
“This has been a true labor of love,” said Van Eenennaam.
She said this is only the beginning of the investigation. Cosmo will reach sexual maturity in a year, and will be raised to study whether the inheritance of the SRY gene on chromosome 17 is sufficient to trigger the male development pathway in XX embryos and result in offspring that will grow and look like males. . Because the Food and Drug Administration regulates the genetic editing of animals as if they were drugs, Cosmo and his offspring will not enter the food supply.
Other researchers on the team include James Murray, Pablo Ross, Sadie Hennig and Jason Lin of the UC Davis Department of Animal Science, and Bret McNabb and Tamer Mansour of the UC Davis School of Veterinary Medicine.
This project was supported by the U.S. Department of Agriculture’s Biotechnology Risk Assessment Grant Program, The California Agricultural Experiment Station at UC Davis, and the USDA NIFA Graduate and National Needs Scholarship.
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