Transgenic poultry: derivation and areas of application (review)

Transgenic poultry is a powerful instrument for the biotechnologic research in agriculture and medicine as well as a useful biological model (H. Sang, 2004). The technologies of transgenesis can be also aimed at the improvement of qualitative and quantitative characteristics of poultry products (L.G. Korshunova, 2011); development of poultry crosses genetically resistible to infectious diseases (L.G. Korshunova et al., 2014); derivation of poultry that can produce recombinant proteins of different usage areas within the eggs (D. Cao et al., 2015). The most popular way to induce transgenicity is the microinjection of foreign DNA into the ovicell in the proper moment when the organism consists of a single cell (zygote). Certain peculiarities of avian reproduction, however, constrain the induction of the transgenesis. A hen produces daily a single fertilized ovicell which is large in size and extremely sensitive to any manipulation like those to be performed on the mammal ovicells at the injection of foreign DNA. Furthermore, normal embryonic development in avian eggs requires the integrity of tertiary coats - albumen, inner shell membrane, and eggshell itself. The cleavage of chicken ovicell starts as early as in the magnum while freshly laid egg contains ca. 50,000-60,000 cells. As a consequence, first transgenic bird was produced via retroviral vectors. Retroviruses were the first contenders for the role of vectors in the gene transfer since they normally can enter the genomic DNA of the host with subsequent replication. At present the induction of retroviral (D.W. Salter et al., 1986; D.W. et al. Salter, 1987; D.W. et al. Salter, 1989; R.A. Bosselman et al., 1989; L.B. Crittenden, 1991; L.B. Crittenden et al., 1992) and lentiviral (H.A. Kaleri et al., 2011; A.H. Seidl et al., 2013; N.A. Volkova et al., 2015) transgenesis in chicken and quails was reported. The technologies of genomic modification in chicken and quails are continuing their development: e.g. the methods with the use of zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) (T.S. Park et al., 2014), CRISPR/Cas9 (I. Oishi et al., 2016; Q. Zuo et al., 2016) were developed. The CRISPR/Cas9 technology allows for the further progress in the genetic manipulations to produce genome-edited lines of poultry (N. Veron et al., 2015). Avian embryos, primarily chicken ( Gallus gallus domesticus ) and quail ( Coturnix coturnix japonica ), served as a model for the embryologic studies in vertebrates for more than a century. Modern targeted genetic manipulations in chicken embryo as an in vivo model became possible via the CRISPR/Cas9 editing system (V. Morin et al., 2017). The alternative non-viral methods of the induction of transgenesis in avian species can be used; one of these methods involves the transfer of foreign embryonic cells (as foreign DNA vector) into the recipient embryo resulting in the chimeric birds (J.N. Petitte et al., 1990; J.Y. Han et al., 2017; N.A. Volkova et al., 2017). Another attractive technology for the transfer of foreign genetic material into avian embryos involves the use of spermatozoa as the vectors since artificial insemination is the traditional and common technique for poultry (E. Harel-Markowitz et al., 2009; A.V. Samoylov et al., 2013). The combination of spermatozoa vectors and CRISPR/Cas9 technology can result in transgenesis in the first generation and hence allows for the substantial savings in time and resources (C.A. Cooper et al., 2017). The microinjection of DNA into the zygote is still a classic technology of non-viral transgenesis. The method involves direct injection of gene construct into the cytoplasm of freshly fertilized ovicell and subsequent incubation of injected eggs. The ovicell for injection should be taken immediately after its fertilization which means that its movement down the oviduct should be interrupted; further development of the injected embryo require special cultivation system (C. Mather, 1994). Another microinjection technique for avian ovicells involves natural formation of tertiary coats in the oviduct. The method is based on the surgical operation to get the access to the ovicell, its microinjection with foreign DNA, and implantation of injected ovicell back to the maternal oviduct for the formation of normal egg suitable for incubation (R.V. Karapetyan, 1995). The populations of transgenic chicken and quails with different foreign gene constructs were produced with the use of this method (R.V. Karapetyan, 1996; L.G. Korshunova et al., 2013).