Genome Editing by Programmable Nucleases and Their Applications in Livestock Species

Genetic modification in livestock species is almost 30 years old but many technical issues limited its use. The earlier methods - pronuclear injection and viral integration had several problems including random integration, silencing, low efficiency, inefficient gene expression regulation etc. With the advent of programmable nucleases such as Zinc Finger Nucleases (ZFNs), Transcription Activator-Like Effector Nucleases (TALENs) and Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 (CRISPR/Cas9), precision genome editing has now become possible. Genome editing by these nucleases is an efficient and powerful technique to alter the genome of organisms for site-specific modification and integration of endogenous and exogenous genes respectively. These techniques have already been used in species like Drosophila, zebrafish, mice, rats, monkeys, humans, pigs, cattle, sheep, goats and others. Generation of genome edited livestock has been proved feasible and valuable and they are useful for the understanding of complex physiology, generation of animals with improved traits and disease resistance, producing transgenic animals for the therapeutic proteins and large animal models for human diseases. Given the high efficiency of these techniques, it is expected that a large number of genome edited livestock will be produced in the future. In this review, we provide an overview of the programmable nucleases, their underlying mechanism, and usefulness of genome editing in livestock species.