I-12: Nuclear Reprogramming in Bovin Somatic Cell Nuclear Transfer

Somatic cell nuclear transfer (SCNT or cloning) returns a differentiated cell to a totipotent status; a process termed nuclear reprogramming. Reproductive cloning has potential applications in both agriculture and biomedicine, but is limited by low efficiency. To understand the deficiencies of nuclear reprogramming, our research has focused on both candidate genes and global gene expression patterns in cloned bovine embryos/offspring as compared to those generated by conventional reproduction. We also studied the telomere restoration, growth patterns, behavior, reproduction, and milk and meat compositions of cloned animals. Cloned animals that survived beyond the first month of life are generally normal and healthy. We found aberrant expression patterns in both imprinted as well as X-linked genes in term cloned calves. The expression profiles of cloned blastocysts, however, closely resembled those of the naturally fertilized embryos but were considerably different from those of their nuclear donor cells. Our findings suggest that cloned embryos have undergone significant nuclear reprogramming by the blastocyst stage. However, it is possible that during re-differentiation in later development gene expression aberrancies occur. Additionally, small initial nuclear reprogramming errors may be manifested during subsequent development.