![]() Though the induction of the KO was successful, it had the disadvantage of low efficiency ( Thomas and Capecchi, 1987). The generation of knockout (KO) animals was achieved for the first time by gene targeting in embryonic stem cells (ES) ( Evans and Kaufman, 1981 Thomas and Capecchi, 1987). Although this method was used for a long time, it did not allow the induction of targeted gene modifications and had the disadvantage of generating random integrations ( Perleberg et al., 2018). While mice were the first animals to be genetically modified ( Costantini and Lacy, 1981 Gordon and Ruddle, 1981), pronuclear DNA microinjections allowed the introduction of foreign DNA leading to genetic modifications in livestock including rabbits, sheep and pigs ( Hammer et al., 1985). Genetically modified animals have significantly contributed to our understanding of different aspects related to immunity, infectious diseases, neurology, behavior, and developmental biology ( Yeh et al., 2002 Lyall et al., 2011 Lalonde et al., 2012 Pinkert, 2014 Park et al., 2017b). This review focuses on the advances made in gene editing in chickens and the future perspectives including the generation of specific-pathogen-resistant birds. In addition, there is an increasing interest to generate genetically modified chickens resistant to specific pathogens, benefiting from the availability of gene manipulation techniques. More recently, using genetically modified chickens as a model for various research areas like developmental biology, immunology, physiology and neurology is gaining importance in the avian research community ( Mozdziak and Petitte, 2004 Stern, 2004, 2005). ![]() Furthermore, bacterial agents such as Campylobacter jejuni and Salmonella enteritidis cause food borne illnesses in humans associated with digestive symptoms ( Bryan and Doyle, 1995). Viral pathogens such as influenza A viruses can be transmitted to humans leading to death ( Gao et al., 2013). Chickens are constantly exposed to a plethora of pathogens threatening animal welfare as well as human health ( Perdue and Swayne, 2005 Humphrey, 2006). The chicken represents an important source of protein worldwide and a valuable model for the study of developmental biology in vertebrates ( Yasugi and Nakamura, 2000 Speedy, 2003). Herein we review the current and future prospects of gene editing and how it possibly contributes to the development of resistant chickens against infectious diseases. This was previously demonstrated by targeting the Trp38 region which was shown to be effective in the control of avian leukosis virus in chicken DF-1 cells. Thus, it may provide a powerful tool for the generation of genetically modified chickens carrying resistance for certain pathogens. Furthermore, the latest advances in the field of genome editing including the CRISPR/Cas9 system allowed the introduction of site specific gene modifications in various animal species. ![]() Subsequent studies using immunoglobulin knockout birds helped to understand different aspects related to B cell development and antibody production. Recently, homologous recombination was used to knockout the chicken immunoglobulin genes. Although it was the first livestock species to have its genome sequenced, there was no reverse genetic technology available to help understanding specific gene functions. The chicken represents a valuable model for research in the area of immunology, infectious diseases as well as developmental biology. Department of Animal Sciences, Reproductive Biotechnology, School of Life Sciences Weihenstephan, Technical University Munich, Freising, Germany.
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