Low survival rate and deformities arising from the NT procedure is presumed to be a result of inappropriate reprogramming. In addition, highly abnormal methylation patterns in various genomic regions of cloned embryos was found and similar developmental abnormalities of cloned animals could be due to incomplete epigenetic reprogramming of donor DNA.
The number of nuclei in these NT-derived embryos appears to be low. In a recent paper of ours, an average nuclear number of 39 was reported from cells that resulted in term development, whereas here, the same cell line resulted in a nuclear number of 33. In addition, a nuclear number of 30 from embryos cultured in vitro can make fetuses.
In this study, we showed that expression of an eGFP transgene is not uniform between or within embryos, and that transgenic pigs can be duplicated by NT technology without a change in the transgene. The rates of term development and subsequent survival are still low. The efficiency can likely be improved by further studies into the epigenetic factors that affect embryo development.