Meet Cosmo, a bull calf designed to produce more male offspring
Scientists use CRISPR technology to insert sex-determining gene

Date:
July 23, 2020
Source:
University of California - Davis
Summary:
Scientists have successfully produced a bull calf, named Cosmo,
who was genome-edited as an embryo so that he'll produce more
male offspring.



FULL STORY ========================================================================== Scientists at the University of California, Davis, have successfully
produced a bull calf, named Cosmo, who was genome-edited as an embryo so
that he'll produce more male offspring. The research was presented in a
poster today (July 23) at the American Society of Animal Science meeting.


========================================================================== Using the genome-editing technology CRISPR, researchers can make targeted
cuts to the genome or insert useful genes, which is called a gene
knock-in. In this case, scientists successfully inserted or knocked-in
the cattle SRY gene, the gene that is responsible for initiating male development, into a bovine embryo.

It's the first demonstration of a targeted gene knock-in for large
sequences of DNA via embryo-mediated genome editing in cattle.

"We anticipate Cosmo's offspring that inherit this SRY gene will grow
and look like males, regardless of whether they inherit a Y chromosome,"
said Alison Van Eenennaam, animal geneticist with the UC Davis Department
of Animal Science.

MORE MALES, MORE BEEF Van Eenennaam says part of the motivation to produce
more male cattle is that male cattle are about 15 percent more efficient
at converting feed into weight gain. They are more fuel-efficient than
females. Additionally, they tend to be processed at a heavier weight.

It could also be a win for the environment, with fewer cattle needed to
produce the same amount of beef. "Ranchers could produce some females as replacements and direct a higher proportion of male cattle for 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 genomic safe harbor site. That ensures the genetic elements
function predictably and don't disrupt the expression or regulation of
adjacent genes. Chromosome 17 was chosen after unsuccessful attempts to knock-in the gene on the X chromosome, which would have resulted in a
bull that produced only male offspring. Cosmo is expected to produce 75
percent male offspring -- the normal 50 percent XY animals, and another 25percent XX animals that inherit the SRY gene.

"It took two and a half years to develop the method to insert a gene into
the developing embryo and another two years to successfully establish
a pregnancy," said Owen. But in April of 2020, a healthy 110-pound male
calf was born.

"This has been a real labor of love," said Van Eenennaam.

She said this is just the beginning of the research. Cosmo will reach
sexual maturity in a year, and he will be bred to study if inheriting the
SRY gene on chromosome 17 is sufficient to trigger the male developmental pathway in XX embryos, and result in offspring that will grow and look
like males. As the Food and Drug Administration regulates gene-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 with 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 Biotechnology Risk Assessment Grant Program
from the U.S. Department of Agriculture, the California Agricultural
Experiment Station at UC Davis and the USDA NIFA National Needs Graduate
and Postgraduate Fellowship.


========================================================================== Story Source: Materials provided by
University_of_California_-_Davis. Original written by Amy Quinton. Note: Content may be edited for style and length.


==========================================================================


Link to news story: https://www.sciencedaily.com/releases/2020/07/200723115855.htm

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