Current applications of SCNT in advanced breeding and genome editing in livestock

Abstract

SCNT (Somatic Cell Nuclear Transfer) has complemented the toolbox of ARTs offering yet another technique to reproduce animals in an unprecedented way. Despite remarkable achievements, SCNT suffers of low efficiency, high pregnancy losses and higher than normal stillbirth rates that makes it an expensive technique to reproduce animals. Moreover, due to welfare issues associated with gestation and the newborn offspring, it is banned in some countries. It has become evident that these problems are of epigenetic nature associated with incomplete genome reprogramming, observed more frequently in ruminants and less often and of minor degree in pigs and horses. Genome editing is enormously benefiting from SCNT to turn genome edited cells into animals, even if zygote microinjection of CRISPR/Cas9 will become an alternative route in some occasions. SCNT will also be a route to reprogram somatic cell to pluripotency since bona fide iPSC in livestock are missing while embryonic stem cells have been now established. This opens the way to other technologies like the development of artificial gametes or interspecies nuclear transfer. To strengthen its commercial applications, SCNT will face three major challenges, i.e. intellectual property (extremely unclear in genome editing), regulatory approval by the relevant authorities of the potential products resulting and finally acceptance by the public who will eventually decide with its behavior the life or the death of the technology.

Synergistic power of genomic selection, assisted reproductive technologies, and gene editing to drive genetic improvement of cattle

“…Alternatively, adult somatic cell NT (SCNT) cloning can be used to multiply unique genotypes (Oback and Wells 2003;Wilmut et al 1997). Unfortunately, due to faulty or incomplete epigenetic reprogramming of the donor cell genome, SCNT cloning often results in high rates of pregnancy loss and can also negatively affect the viability of live-born calves (Akagi et al 2013;Galli and Lazzari 2021;Keefer 2015). Therefore, SCNT cloning is primarily used for research or to produce "back-ups" of individual animals with unique genetic features (Bousquet and Blondin 2004;Loi et al 2016).…”

Reproduction of Sheep through Nuclear Transfer of Somatic Cells: A Bibliometric Approach

“…However, SCNT is an inefficient biotechnology, for example, for newborns lambs, have been reported an efficiency range from 5.7 to 15% per transferred blastocyst and from 7.1% to 19.5% per segmented embryo [57]. Although sheep are easy to handle and have a relatively short gestation period compared with that of the other species of zootechnical interest [58], their small value and limited potential, do not make them attractive for agriculture use like other livestock species [59]. If we also take into account that the infrastructure used for SCNT is basically the same for all species, nowadays the SCNT applied to sheep reproduction is not profitable.…”

State of the art of nuclear transfer technologies for assisting mammalian reproduction

“…SCNT remains challenging, and its inefficiency in producing live offspring limits its application for animal production. Despite this, SCNT is required to preserve valued animal genetics (particularly by the horse breeding industry, Gambini & Maserati, 2017), for conservation of endangered species (briefly described later in this review), for pets genetic preservation (private companies such as ViaGen pets; https://viagenpets.com and Sinogene; https://www.sinogene.org), and to produce genetically modified animals (Galli & Lazzari, 2021). Several modifications to the initial cloning procedure were emerging, as assisted chemical enucleation, new fusion methods, donor cell and recipient oocyte cycle synchronization, new artificial activation methods, use of epigenetic modulating agents, antioxidants, novel culture systems, among others, leading to differences in SCNT protocols among laboratories (Loi et al, 2021).…”

“…ViaGen pets; https://viagenpets.com and Sinogene; https://www. sinogene.org), and to produce genetically modified animals (Galli & Lazzari, 2021). Several modifications to the initial cloning procedure were emerging, as assisted chemical enucleation, new fusion methods, donor cell and recipient oocyte cycle synchronization, new artificial activation methods, use of epigenetic modulating agents, antioxidants, novel culture systems, among others, leading to differences in SCNT protocols among laboratories (Loi et al, 2021).…”