Use of cross-species in-situ hybridization (ZOO-FISH) to assess chromosome abnormalities in day-6 in-vivo- or in-vitro-produced sheep embryos

Causes of chromosomal differences such as mosaicism between embryos developed in vivo and in vitro may be resolved using animal models to compare embryos generated in vivo with those generated by different production systems. The aims of this study were: (1) to test a ZOO-FISH approach (using bovine painting probes) to detect abnormal chromosome make-up in the sheep embryo model, and (2) to examine the extent of chromosome deviation in sheep embryos derived in vivo and in vitro. Cytogenetic analysis was performed on day 6 in-vivo and in-vitro derived sheep embryos using commercially available bovine chromosome painting probes for sex chromosomes X-Y and autosomes 1-29. A total of 8631 interphase and metaphase nuclei were analyzed from 49 in-vitro-derived and 51 in-vivo-derived embryos. The extent of deviation from normal ovine chromosome make-up was higher (p < 0.05) in in-vitro-produced embryos relative to in-vivo-derived embryos (65.3% vs. 19.6% respectively) mainly due to diploid-polyploid mosaicism. Polyploid cells ranged from 3n to 8n with tetraploids most predominant among non-diploid cells. The proportions of polyploid cells per mixoploid embryo in in-vitro-produced embryos ranged from 1.4% to 30.3%, in contrast to less than 10% among the in-vivo-derived embryos. It was concluded that in-vitro-derived embryos are vulnerable to ploidy change compared to their in-vivo counterparts. The application of ZOO-FISH to domestic animal embryos is an effective approach to study the chromosome complement of species for which DNA probes are unavailable.