Multiple targeting motifs direct NRAMP1 into lysosomes

Livestock 2.0 - genome editing for fitter, healthier, and more productive farmed animals

The human population is growing, and as a result we need to produce more food whilst reducing the impact of farming on the environment. Selective breeding and genomic selection have had a transformational impact on livestock productivity, and now transgenic and genome-editing technologies offer exciting opportunities for the production of fitter, healthier and more-productive livestock. Here, we review recent progress in the application of genome editing to farmed animal species and discuss the potential impact on our ability to produce food.

Genome editing for disease resistance in livestock

One of the major burdens on the livestock industry is loss of animals and decrease in production efficiency due to disease. Advances in sequencing technology and genome-editing techniques provide the unique opportunity to generate animals with improved traits. In this review we discuss the techniques currently applied to genetic manipulation of livestock species and the efforts in making animals disease resistant or resilient.

Single Cas9 nickase induced generation of NRAMP1 knockin cattle with reduced off-target effects

BACKGROUND

The CRISPR-Cas9 system is a widely utilized platform for transgenic animal production in various species, although its off-target effects should be addressed. Several applications of this tool have been proposed in model animals but remain insufficient for transgenic livestock production.

RESULTS

Here, we report the first application of single Cas9 nickase (Cas9n) to induce gene insertion at a selected locus in cattle. We identify the main binding sites of a catalytically inactive Cas9 (dCas9) protein in bovine fetal fibroblast cells (BFFs) with chromatin immunoprecipitation sequencing (ChIP-seq). Subsequently, we demonstrate that a single Cas9n-induced single-strand break can stimulate the insertion of the natural resistance-associated macrophage protein-1 (NRAMP1) gene with reduced, but still considerable, off-target effects. Through somatic cell nuclear transfer, we finally obtain transgenic cattle with increased resistance to tuberculosis.

CONCLUSIONS

Our results contribute to the development of CRISPR-Cas9 system for agriculture applications.

Functional analysis of bovine Nramp1 and production of transgenic cloned embryos in vitro

Natural resistance-associated macrophage protein 1 (Nramp1) plays an important role in restraining the growth of intracellular pathogens within macrophages. In this study, Nramp1 cDNA was cloned from Qinchuan cattle and its anti-bacterial activity was demonstrated as being able to significantly inhibit the growth of Salmonella abortusovis and Brucella abortus in macrophages. Calf fibroblasts stably transfected with pSP-NRAMP1-HA vector were used to reconstruct bovine embryos by somatic cell nuclear transfer (SCNT). Reconstructed embryos were maturated in vitro and the blastocyst formation rate (14.0%) was similar to that of control embryos (14.5%). Transgenic blastocysts were transplanted into 43 recipient cattle, of which 14 recipients became pregnant as evidenced by non-return estrus and by rectal palpation. One fetus was aborted after 6½ months of pregnancy and transgene integration was confirmed by semi-quantitative polymerase chain reaction. Together, this study showed that bovine Nramp1 retains biological function against the growth of intracellular bacteria and can be used to reconstruct embryos and produce Nramp1 transgenic cattle, which may benefit the animal and enhance their ability to prevent attack by intracellular pathogens.