Researchers in China have reported creating tuberculosis-resistant cattle using
CRISPR/Cas9 genome editing.
Led by senior author Yong Zhang of Northwest Agricultural & Forestry
University, the team used a single Cas9 nickase - a single-strand cutting Cas9
variant - to induce genome editing using the homology-directed repair pathway,
inserting a gene for natural resistance-associated macrophage protein-1
(NRAMP1) into bovine fetal fibroblasts. As the researchers reported today in
Genome Biology, they used somatic nuclear transfer to get the edit into an egg
cell, creating 11 cows in vitro with NRAMP1 (nine using Cas9 nickase) and
demonstrating that the gene provided increased resistance to tuberculosis.
Moreover, they said that while the Cas9 nickase did not completely eliminate
off-target edits, it did reduce them, especially when compared to standard Cas9
which creates double-strand breaks and is much more likely to create indel
mutations via the non-homologous end-joining DNA repair pathway.
While the team said that this was the first instance of gene insertion into
cattle using a single nicking Cas9, it was far from the first application of
genome editing to livestock, or even cows. In May 2016, researchers led by
Minnesota-based gene editing firm Recombinetics reported substituting an allele
in dairy cattle to eliminate horns, using transcription activator-like effector
nucleases (TALENs) to induce HDR. And last fall, another team of scientists
from Northwest A&F University reported editing cashmere goats using CRISPR
to produce more of the fine hairs used in wool production.