Transgenesis in farm animals

Abstract

The production of transgenic animals has many biotechnological applications; however, available techniques still remain inefficient. This review summarizes the contributions of our group to transgenesis in domestic animal. One of the most traditional transgenesis techniques in farm animals is somatic cell nuclear transfer using genetically modified somatic cells. Using this technique, we produced transgenic cloned cows capable of producing human growth hormone in the milk, and viable offspring was obtained after recloning of these transgenic animals. Another technique available to produce transgenic animals is intracytoplasmic sperm injection (ICSI). With this technique, we could obtain transgenic embryos in five different domestic species (bovine, ovine, feline, porcine and equine). To improve transgenic ICSI (ICSI-Tg) efficiency in cattle, different chemical activation treatments were evaluated, including ionomycin followed by 6-Dimethylaminopurine (6-DMAP), strontium chloride and ethanol. In addition, in the latest years, our group has developed several alternative methods to produce transgenic animals involving injection of ooplasmic vesicles, liposomes or cells previously incubated with the transgene, into zygotes or enucleated oocytes respectively. All of these treatments proved to be efficient to induce the expression of exogenous DNA into pre-implantatory embryos. However, high levels of transgene expression mosaicism were detected. For that reason, different approaches were also tested to reverse mosaicism, including a novel cloning gamete technique. We conclude this review with a brief description of novel molecular tools for transgenesis, including enzymes such as transposases, Zinc finger and Talem nucleases, which could help to increase transgenesis efficiency in domestic species. The new transgenesis variants described in this review aim to turn animal transgenesis accessible to a greater number of research groups.