Cellular and genomic reprogramming of donor nuclei in bovine nuclear transfer embryos

Cloning of animals using somatic cell nuclei has been achieved in several mammalian species. However, this process is inefficient and the majority of cloned fetuses are lost due to several developmental abnormalities. Increased birth weight, increased gestation length, placental abnormalities and endocrine system failures are common among cattle clones.; Insufficient reprogramming of donor nucleus at the cellular, genomic and epigenetic levels is thought to be responsible for such a low efficiency. Several factors could affect the outcome of cloning experiments such as origin of donor cell, the quality of oocyte, cell cycle coordination between the recipient and the donor cell and a number of technical factors. Incomplete reprogramming could manifest itself as aberrations in DNA methylation and gene expression patterns at the molecular level. Since these developmental events are vitally important for embryogenesis to occur faithfully, abnormal phenotypes associated with cloned animals could be related to disorders in these processes.; In the present study, the effect of donor cell origin on developmental potential of cloned bovine embryos was investigated using four different somatic cell types, fetal and adult fibroblasts, chondrocytes, and cumulus cells. Lamin A/C protein expression in preimplantation embryos was also monitored as a marker for nuclear remodeling. Furthermore the expression patterns of five developmentally important genes in cloned bovine preimplantation embryos were analyzed.; Frequency of blastocyst development was not affected by donor cell type while individual cell lines displayed marked differences. Lamin A/C protein expression was faithfully reprogrammed in nuclear transfer embryos. When cell lines with different efficiencies in supporting development to term were used as donor nuclei, expression patterns of histone deacetylase-1, -2, -3 ( HDAC-1, -2 -3), DNA methyl transferase-3A (DNMT3A) and octamer binding protein gene (POU5F1) were somewhat altered compared to in vitro produced control embryos. The expression patterns of these genes in the embryos derived from cell lines with high efficiency tend to resemble in vitro produced embryos compared to those derived from inefficient cell lines. The results of this study indicate that transcriptional regulation, genomic imprinting and cell lineage differentiation in early cloned embryos might be disrupted as judged by the gene expression patterns.