Figure 1.

Methods to generate genome-edited pigs and chickens. (A–C) Editing in pigs. (A) Somatic cell nuclear transfer or more commonly known as cloning. Genome editing is performed in fibroblast cells, which are cultivated in vitro. A specific edit can be selected for before transfer of the nucleus into an enucleated oocyte before transfer to a recipient gilt or sow. (B) Ex vivo ovary (often slaughterhouse-derived) derived oocytes are fertilized in vitro to yield zygotes for editing or zygotes harvested from donor gilts or sows. Genome editing reagents are microinjected into the zygotes and transferred to a recipient. (C) Spermatogonial stem cells are isolated, cultivated, and edited in vitro prior to transfer to a surrogate sire. Heterozygous offspring often need to be mated before yielding a resistant pig. (D–F) Editing in chickens. (D) Electroporation in ovo. Genome editing reagents are electroporated into the embryo in ovo. Resulting chickens are often mosaic and breeding of resistant chickens is only possible if the germ cells are edited. (E) Editing of sperm by lipofection or electroporation can generate heterozygous offspring following artificial insemination. They often have to be mated to yield, homozygous chickens. (F) Primordial germ cells are isolated from embryos, cultivated, and edited in vitro. Selected edited cells are transferred to the blood stream of an embryo where they migrate to the gonad and develop into germ cells. Breeding with the resulting offspring is required to generate homozygous chickens.