95 PRODUCTION OF GENE-EDITED PIGS, CATTLE, AND LAMBS BY EMBRYO INJECTION OF TALENS OR ZFNs

Abstract

Transcription activator-like effector nuclease (TALEN) and zinc finger nuclease (ZFN) DNA editing technology enables site-directed engineering of the genome. To date, all gene-edited large animals have been produced by treatment of somatic cells and cloning to produce gene-edited offspring. Although effective, it does not take advantage of the ‘leave-no-trace' aspect of site-specific nucleases, and the derivation of food animals by cloning is negatively perceived by the public. Thus, we have investigated production of gene-edited pigs, cattle and sheep by direct injection of TALEN or ZFN mRNAs to develop loss-of-function alleles for disease resistance (RELA) or enhanced meat production (GDF8). In vitro studies demonstrated activity of TALENs by cytoplasmic injection of mRNAs from dosages of 2 to 20 ng mL^–1 with an apparent increase in both editing frequency and toxicity at high dosage. Our first pregnancies were produced by transfer of pig embryos (in vivo produced) injected with 2 ng mL^–1 RELA TALEN mRNA. Pregnancy was confirmed in 5 of 7 recipients 4 of which went full term giving rise to 39 piglets, 8 of which carried editing events (21%). In parallel, we injected ZFN mRNA (2 ng mL^–1) targeted to a similar site of the RELA gene and 2 of 2 recipients became pregnant, resulting in the birth of 9 piglets, one of which was edited (11%). For cattle injections, we derived zygotes by ovum pickup from selected Nelore dams followed by in vitro maturation and fertilization with Nelore semen. Low (2 ng mL^–1) and medium (5 ng mL^–1) dosages of GDF8-targeted TALENs resulted in Day 7 development to morula/blastocyst stage in 40% (n = 18) and 10% (n = 66) of cultured embryos, respectively. A total of 20 morula/blastocysts were chosen for transfer to 11 recipients, resulting in two full-term pregnancies. One pregnancy produced two calves, both of which carried edited GDF8 alleles. Complications with parturition of the second pregnancy resulted in 2 stillborn calves, the genotypes of which are under investigation. Finally, 2 ng mL^–1 of TALEN mRNA targeted to ovine GDF8 was injected into in vivo-produced sheep zygotes and transferred into nine recipients, 3 blastocysts each. The pregnancy rate, number of live-born animals, and gene editing frequency is under investigation and will be reported.