Bovine parthenogenesis is characterized by abnormal chromosomal complements: implications for maternal and paternal co-dependence during early bovine development.
The present study was conducted to examine the karyotypes of parthenogenetic bovine embryos arising from the application of standard oocyte activation and diploidization methods. Bovine cumulusoocyte complexes were collected and matured in vitro for 24 hr prior to oocyte activation with either 5 microM ionomycin or 7% ethanol for 5 min. Groups of activated oocytes were further treated with 5 micrograms/ml cytochalasin D or 1.9 mM 6-dimethylaminopurine (DMAP) for 6 hr. Cleavage varied significantly (P < .05) among the treatment groups with 68.0% of the ethanol- and DMAP-treated oocytes dividing. Blastocyst development did not vary with 18.4 +/- 2.5% of all treated oocytes progressing to this stage. Blastocyst development did not occur in groups subjected to oocyte activation alone. Blastocysts displayed haploid (2.3%), diploid (11.4%), tetraploid (40.9%), octaploid (4.5%), and mixoploid chromosomal complements (40.9%). Two-cell stage parthenogenotes resulting from ethanol or ionomycin treatment alone displayed haploid (66.7%), diploid (16.7%), tetraploid (4.2%), and mixoploid (12.5%) complements. Our results demonstrate that diploid bovine parthenogenotes arising from these procedures are a minority, with the majority of parthenogenotes displaying polyploid and mixoploid chromosomal complements. The events contributing to these abnormal chromosomal complements occur as early as completion of the first cell cycle, possibly linking these events with the absence of a paternally supplied centrosome.