Use of gene-editing technology to introduce targeted modifications in pigs

Pigs are an important resource in agriculture and serve as a model for human diseases. Due to their physiological and anatomical similarities with humans, pigs can recapitulate symptoms of human diseases, making them a useful model in biomedicine. However, in the past pig models have not been widely used partially because of the difficulty in genetic modification. The lack of true embryonic stem cells in pigs forced researchers to utilize genetic modification in somatic cells and somatic cell nuclear transfer(SCNT) to generate genetically engineered(GE) pigs carrying site-specific modifications. Although possible, this approach is extremely inefficient and GE pigs born through this method often presented developmental defects associated with the cloning process. Advancement in the gene-editing systems such as Zinc-Finger Nucleases(ZFNs), Transcription activator-like effector nucleases(TALENs), and the Clustered regularly interspaced short palindromic repeat(CRISPR)/CRISPR-associated 9(Cas9) system have dramatically increased the efficiency of producing GE pigs. These gene-editing systems, specifically engineered endonucleases, are based on inducing double-stranded breaks(DSBs) at a specific location, and then site-specific modifications can be introduced through one of the two DNA repair pathways: non-homologous end joining(NHEJ) or homology direct repair(HDR).Random insertions or deletions(indels) can be introduced through NHEJ and specific nucleotide sequences can be introduced through HDR, if donor DNA is provided. Use of these engineered endonucleases provides a higher success in genetic modifications, multiallelic modification of the genome, and an opportunity to introduce site-specific modifications during embryogenesis, thus bypassing the need of SCNT in GE pig production. This review will provide a historical prospective of GE pig production and examples of how the gene-editing system, led by engineered endonucleases, have improved GE pig production. We wil also present some of our current progress related to the optimal use of CRISPR/Cas9 system during embryogenesis.

A novel pig model capturing clinical symptoms of harlequin ichthyosis

The application of proper animal models is essential for developing effective treatments in biomedicine. Due to practicality, rodent models have been dominantly used as a model to identify potential treatments for patients. However, differences in physiology and anatomy between rodents and humans have been an obstacle when translating the data generated from rodents to clinics. Large animal models such as pigs can recapitulate symptoms of human diseases, making pigs an ideal model for preclinical assessment of new treatments (Prather et al., 2013). For instance, symptoms of primary immunodeficiency are more accurately represented in pigs compared to mice (Suzuki et al., 2012), demonstrating their suitability as an animal model in biomedicine. Unfortunately, the number of available pig models is low, in part, because of challenges in establishing pig models through current genetic engineering technology.