High frequency of DNA ploidy abnormalities in preimplantation embryos of the rabbit

The DNA ploidy of Feulgen-stained cell nuclei of in vivo preimplantation rabbit embryos was assayed by cytophotometry. DNA ploidy abnormalities were detected in single-cell nuclei readings by the criterion of > or = 5C DNA. These hypermodal DNA contents are referred as to DNA aneuploidy. Two, 4 and 6 days old rabbit embryos, all of normal gross morphology, were investigated. The incidence of embryos with DNA ploidy abnormalities increased from 17% in 2-day-old cleavage stages to 51% in 6-day-old expanded blastocysts. All these embryos were mosaics and the percentage of DNA aneuploid nuclei per embryo did not usually exceed 9%. Fifteen percent of the expanded blastocysts, however, contained up to 23% abnormal nuclei. Throughout the embryonic stages studied, the DNA content of abnormal nuclei was remarkably constant and averaged 5.8C. DNA aneuploid and euploid blastocysts did not differ in size. A maternal FSH treatment did not influence the DNA ploidy. This is the first report on the DNA ploidy pattern in preimplantation rabbit embryos. Our results indicate that DNA aneuploidy of single blastomeres is common in this species and occurs more often than generally assumed. The embryonic viability does not seem to be affected by the presence of DNA aneuploid blastomeres supporting earlier findings that a limited number of abnormal blastomeres is compatible with normal preimplantation development.