Assessment of chromosomal abnormalities in bovine nuclear transfer embryos and in their donor cells

Chromosomal anomalies were assessed in nuclear transfer (NT) embryos (n = 148) at 1-4-cell stage (n = 88), and morula (n = 60), as well as in donor cells (n = 97) derived from two different cell lines. Two different cytogenetic approaches were used: conventional karyotyping and fluorescent in situ hybridization (FISH) with painting probes, specific for bovine X and Y chromosomes. The total rate of NT embryos with abnormal nuclei was 43%. These anomalies were mainly nuclear fragmentation (30%), hypoploidy/hypoploidy-mixoploidy (9%, n = 14) and hyperploidy/hyperploidy-mixoploidy (3%, n = 5). The incidence at which these anomalies occurred in NT embryos varied according to the donor cell culture and paralleled the frequency of anomalies in donor cells. A higher frequency of total anomalies was observed in NT embryos (55%) derived from the donor cell cultures with the highest incidence of anomalies (23%). An increase in the rate of total anomalies of the cell, after transfer to recipient cytoplasm, was also observed. These results suggest that proper screening of donor cells for chromosomal anomalies must be performed prior to NT procedure. They also suggest that the NT procedure itself might have a detrimental effect on some mechanism of chromosome segregation and distribution during cell division.