Advances in genetic engineering of the avian genome

Even though the chicken genome was the first livestock genome to be completely sequenced, technologies to manipulate the avian genome were lagging behind other model and agricultural animal species. This is mainly due to a complex reproductive system and the lack of embryonic stem cell cultures contributing to the germline like in mice. With the availability of lentiviral gene transfer technologies, it became possible to generate transgenic chickens on a more routine basis but induction of specific knockouts and introduction of precise edits were still not possible. The possibility to cultivate and genetically manipulate primordial germ cells (PGCs) changed the field and allows now complex modifications of the chicken genome and the subsequent generation of genetically modified chickens. At the same time, the direct in ovo manipulation of migrating PGCs became possible. The availability of viral gene transfers, PGC culture, and different ways to directly manipulate the chicken genome in ovo paved the way to generate any given modification of the chicken genome.