Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Kenneth L White


Kenneth L White


Gregory J. Podgorski


Abby D. Benninghoff


S. Clay Isom


Thomas D. Bunch


Dirk K. Vanderwall


The cloning of domestic species has tremendous potential, as the technology can be used in selective breeding, conservation, and the production of transgenic animals. The technique of cloning involves the transplant of DNA from a cell to a recipient gamete. Following transfer to a surrogate, the cloned embryo may successfully complete development to a live offspring. Despite intensive research, the success rate of cloning remains prohibitively low, and the potential benefits of cloning have not yet been realized. Embryos produced from cloning suffer from high rates of embryo degradation, implantation failure, and abortion. The goal of this dissertation research project was to determine the mechanisms that cause the high rates of embryo failure in clones.

In order for embryo development to occur properly following cloning, the donor cell genome must undergo epigenetic reprogramming, a process that resets the donor nuclei to an embryonic state. Epigenetic markings alter the expression of genes within a cell, and are one factor that prevents cells from reverting back to a primordial state. As part of this research, we measured methylation of DNA, a type of epigenetic mark, to determine the level of reprogramming that occurs in cloned embryos. Our results demonstrate that cloned embryos have abnormalities in reprogramming following cloning for some important genes. This observation provides further support for the notion that the inefficiency of the cloning process may be a result of the inability of donor cells to readily reactivate genes that have been epigenetically silenced.

A second area of research into the causes of cloning failure was to examine the role of programmed cell death within cloned embryos. Every cell contains an innate defense system that triggers programmed cell death when the cell is under severe stress or has undergone irreparable DNA damage. We observed increased incidence of programmed cell death in cloned embryos that contributes to the high rates of developmental failure. These findings may potentially allow therapeutics targeted at preventing cell death, and thereby increase the success of cloning.