GE-PRLR-SLICK cattle were generated using CRISPR/Cas9 gene editing. Embryos were in vitro fertilised and subsequently injected with genome editing reagents. These embryos were transferred into surrogates.
In GE-PRLR-SLICK cattle, the prolactin receptor gene (prlr) has been disrupted in exon 9 using CRISPR/Cas9 resulting in a truncation of the encoded protein due to introduction of a premature stop codon. The truncated protein retains its lactogenic function, but causes the animal to have a short-hair coat. The mutation is equivalent to naturally occurring mutations in conventionally raised cattle. Animals with this so-called ‘slick phenotype’ have been reported to be heat tolerant, allowing to raise them successfully under conditions with greater heat stress.
Overall three calves (founder animals) were born containing the intended alteration in the prlr gene and showed the expected slick phenotype. One of these animals died due to a heart defect which seemingly was not related to the genomic alteration. Due to the specific process to generate the founder animals, the two remaining GE-PRLR-SLICK cattle were mosaic and might contain 2 or more genetically different sets of cells.
Whole genome sequencing revealed unintended mutations in the genomic sequence of the founder calves. These included a duplication located in a repetitive intergenic region and short insertions and deletions ranging from 1 to 11 base pairs in intronic or intergenic regions (no detailed information available).
In 2022 the FDA determined the intentional genetic alteration (IGA) in GE-PRLR-SLICK cattle to be low-risk and had no objections against the marketing of products (e.g. live animals, semen, embryos, meat) derived from the two-genome edited beef cattle and their progeny.
Sources:
FDA document
Patent US10716298
