PROGRESSIVE PRODUCER
GENE EDITING:
HOW CAN IT BE INCORPORATED IN BEEF CATTLE BREEDING PROGRAMS? by Maci Mueller, Ph.D. Candidate, University of California, Davis Leaders in all segments of the beef industry, from researchers to producers to allied industry partners, gathered this June to discuss and guide the improvement of the beef industry at the 2021 Beef Improvement Federation (BIF) Research Symposium and Convention. The symposium, held in Des Moines, Iowa, featured two and a half days of educational programming and a full day of tours. Thanks to the support of the California Beef Cattle Improvement Association (CBCIA), as a University of California, Davis (UC Davis), graduate student I was able to attend the symposium and gain valuable insight and understanding of the current status of beef cattle genetics and related technologies, in order to be better prepared for my future career as an animal geneticist. The theme for General Session 2 was “Precision Livestock Technology,” which Alison Van Eenennaam, Ph.D., explained was very fitting for her topic of “Gene Editing Today and in the Future” because gene editing is a form of precision animal breeding. Van Eenennaam, a Cooperative Extension Specialist in Animal Genomics and Biotechnology at the UC Davis first presented about the emerging technology of gene editing at the 2017 BIF during a technical breakout. Over the past five years gene editing has become an increasingly popular topic in animal breeding and recently the Red Angus Association of America announced, “they will provide herdbook registry of Red Angus animals carrying gene-edited traits for heat tolerance and coat color” (https://www.beefmagazine.com/ beef/beef-breed-approves-gene-edited-traitsanimal-registration). Van Eenennaam updated the BIF audience on the latest gene editing research advancements and also discussed how this precision breeding technology could be incorporated into current beef cattle breeding programs. Before diving into gene editing, Van Eenennaam first described the current state of cattle breeding practices to set the stage for understanding how gene editing could fit in. The bovine genome (~3 billion base pairs) was first sequenced in 2009 and since then thousands of cattle have been sequenced. The ‘1000 Bull Genomes Project’ actually sequenced 2,703 bulls from all over the world and found over 86.5 million genomic variations, including SNPs (single nucleotide polymorphisms) and indels (small insertions/ deletions) between breeds. Van Eenennaam explained that this amazing genetic diversity, 14 California Cattleman November 2021
“is actually the engine that drives genetic improvement." That is what you are selecting on, this genetic variation that spontaneously occurs and that is the result of why different breeds of cattle exist and why different cattle are adapted to different environments.” Sequencing the bovine genome opened the door to genomics by enabling the development of high-density SNP chips, which were rapidly adopted by the global cattle breeding community. At first, there was some antagonism between genomics and quantitative genetics (i.e., expected progeny difference or EPD), but eventually it all came together to form an integrated system where genomics is incorporated as an additional data source to get a more accurate EPD. Van Eenennaam sees parallels of this genomics pathway with the future incorporation of gene editing to animal breeding. She explained that gene editing is a method to introduce a double strand break at a targeted location in the genome. The revolutionary part of gene editing is that an animal breeder can tell the gene editors (e.g., Zinc finger nuclease, TALENS, CRISPR/Cas9), which can be thought of as molecular scissors, exactly where in the genome to make the cut. The cell doesn’t like breaks in the DNA so it will try to repair the break. Sometimes the cell repairs the break incorrectly by adding or subtracting extra base pairs which can lead to the gene being inactivated, otherwise known as a “knockout.” Animal breeders may want to knockout ...CONTINUED ON PAGE 16
