The fact that such a complex procedure works at all is amazing and is the result of decades of pioneering research.
In this review, the historical work in domestic species leading up to the development of somatic cell nuclear transfer (SCNT), along with the practical applications of this technology, will be discussed.
Domestic animals can be cloned using techniques such as embryo splitting and nuclear transfer to produce genetically identical individuals.
Although embryo splitting is limited to the production of only a few identical individuals, nuclear transfer of donor nuclei into recipient oocytes, whose own nuclear DNA has been removed, can result in large numbers of identical individuals.
Subsequently, controversial studies in the 1970s suggested that nuclei from cells that had undergone the first lineage differentiation (that is, cells that had formed the inner cell mass) could direct normal development if substituted for the zygotic nucleus (15).
However, failure of other research groups to replicate these studies led some scientist to state that mammalian nuclei after embryonic gene activation were unable to direct development due to irreversible programming changes (16).
In addition to providing a means of rescuing and propagating valuable genetics, somatic cell nuclear transfer (SCNT) research has contributed knowledge that has led to the direct reprogramming of cells (e.g., to induce pluripotent stem cells) and a better understanding of epigenetic regulation during embryonic development.
In this review, I provide a broad overview of the historical development of cloning in domestic animals, of its application to the propagation of livestock and transgenic animal production, and of its scientific promise for advancing basic research.
Although the fact that an adult nucleus could indeed direct normal development (resulting in a live offspring) was revolutionary for developmental biology, it followed a series of discoveries that suggested such a possibility (Fig. The initial attempts to artificially clone domestic animals involved embryo splitting.
Steen Willadsen demonstrated that twins could be produced in sheep (17) and cattle (18) after splitting of cleavage-staged embryos and transfer of the demi-embryos into recipients.