Cosmo, the bull calf designed to produce more male offspring

CRISPR technology´s applications are endless and it will be a long time before we stop being surprised by what we can do with the help of this technique. In this article, we´ll discuss the implications of the use of CRISPR technology in farm animals and what that means in terms of sustainability. 

What is CRISPR?

For those who are not so familiar with the subject, CRISPR is a technique that can be used to edit a genome. 

Although it seems quite complicated, CRISPR is a natural defense mechanism of bacteria against invaders. When a foreign organism invades this bacteria, they use CRISPR-derived RNA and various Cas proteins, including Cas9, to prevent the attack. The system will then destroy the DNA of the invader by chopping it up. Scientists discovered that this system could be transferred into more complex organisms and used to edit their genes. 

CRISPR technology has many applications. Here are some examples: 

• Diagnostics of infectious and non-infectious diseases. E.g. coronavirus.

• Treatment of genetic diseases like cancer and sickle cell anemia.

• Producing biofuels

• Crop improvement 

• Animal breeding

One intriguing application of CRISPR technology is the genome editing of farm animals which allow the introduction of useful alleles into cattle breeds to improve their productivity. 

Using CRISPR technology to insert sex-determining genes

CRISPR allows researchers to make targeted cuts to the genome, or insert useful genes (knock-in). Recently, scientists at the University of California, Davis, used this technique to produce a bull calf named Cosmo. When Cosmo was just an embryo, his genome was edited so he´ll produce more male offspring when he grows up. 

Cosmo, a 110-pound bull calf was born in April of 2020 at UC Davis. Scientists successfully genome-edited him as an embryo to produce more male offspring. (Alison Van Eenennaam/UC Davis)

To make this possible they inserted a gene into Cosmo´s genome, the cattle SRY gene. This gene is responsible for initiating male development into a bovine embryo. It was the first time that a targeted gene knock-in for large sequences of DNA via embryo-mediated genome editing in cattle was done. 

The researchers expect that Cosmo´s offspring which inherit the SRY gene will develop into males regardless of whether they inherited the Y chromosome or not. The SRY gene was inserted into chromosome 17 which is a safe harbor site. This ensures that the genetic elements will function correctly and prevents the disruption of the expression and regulation of adjacent genes. In one year, Cosmo will reach its sexual maturity. By then, he is expected to generate at least 75% of male offspring. The researchers will continue to investigate it´s breeding to study if the SRY gene alone will be able to trigger male development in XX embryos. 

At least for now, Cosmo and his offspring won´t be considered as food supply due to federal regulations regarding gene-editing technology. 

More males, more beef. 

It seems that male cattle are 15% more efficient at converting food into weight gain. They also tend to be processed at a higher weight when compared to females. Thus, we would need fewer cattle to produce the same amount of meat. 

"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 Alison Van Eenennaam.

Ethical implications 

Genome-edited products are likely to be ready for commercialization in the coming years. However, public acceptance and the bureaucracy required to approve these products can become a barrier. 

One of the major concerns of those against GM (genetic modified) products is the introduction of transgenes. With CRISPR, that wouldn't be a problem. 

However, there are still concerns about the possibility of generating off-target mutations that could potentially alter the animal´s proteins and lead to food allergies, for example. 

All of this will have to be addressed by the scientific community and regulatory agencies. On the other hand, the public should be properly educated regarding the benefits and safety issues of eating genetically altered meat. 

In summary

Gene editing technology using CRISPR has a multitude of applications ranging from the medical and pharmaceutical fields to the food industry.

At the same time that the technique starts to be explored and develops more and more, important ethical questions arise.

References

University of California - Davis. "Meet Cosmo, a bull calf designed to produce more male offspring: Scientists use CRISPR technology to insert the sex-determining gene." ScienceDaily. ScienceDaily, 23 July 2020.

Yum, Soo-Young, et al. "Development of genome engineering technologies in cattle: from random to specific." Journal of animal science and biotechnology 9.1 (2018): 1-9.

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