Genome Editing and Transgenes in Pigs

Disruption of specific target genes is a first step to uncover the gene function. Large-sized animals are difficult to be targeted in embryo level, causing damages in early embryo developments. The recent development of genome editing techniques is being evolved to the easier ZFN, TALEN, and CRISPR/Cas9 technologies than the conventional laborious one in various animals, giving generation of gene knock-out pigs. The pig genome is about 2.7 Gb size in length, which is packaged in 18 autosomes with sex chromosomes X and Y [1, 2]. Genetic manipulation in pigs was conventionally performed by breeding selection to keep specific segments of the genome. The first genetic modification in the pig was the transgenic case [3]. Then, homologous recombination-based gene knocking out [4, 5] and knocking in were made in pigs and knock-ins [6], respectively. Gene KO disrupts specific genetic sequence to inactivate the genes that encode proteins, while knock-in gene is reversed with the gene’s encoded protein.