Cell allocation and chromosomal complement of parthenogenetic and IVF bovine embryos

Considerable concerns exist regarding the quality of parthenogenetically ac tivated embryos in terms of sufficient numbers of cells comprising the inne r cell mass (ICM) and trophectoderm (TE) and the ploidy. Therefore, these t wo parameters were used to assess the quality of embryos derived from parth enogenetic activation by using calcium ionophore A23187 (Cal) followed by e ither 6-dimethylaminopurine (6-DMAP, 3.5 hr or 6.5 hr) or cycloheximide (CH X) plus cytochalasin D (CD). The conventional in vitro (IVF) produced embry os served as a control. Double staining of the parthenogenetic blastocysts showed that the total cell number (TC) of embryos from the 6-DMAP 3.5 hr (8 7.0 +/- 5.3) and CHX + CD (79.0 +/- 6.1) groups was not different (P > 0.05 ), but was lower than that of control embryos (116.0 +/- 5.8, P < 0.001). T he mean ratios of inner cell mass (ICM) and trophectoderm (TE) cells in the 6-DMAP 3.5 hr group (0.57 +/- 0.04) and the control IVF group (0.50 +/- 0. 02) did not differ significantly. Both were higher than those of the CHX CD group (0.36 +/- 0.02; P < 0.05). Further analysis of chromosomal composi tions of developing stage embryos at day four after IVF or parthenogenetic activation demonstrated that prolonged treatment with 6-DMAP for 6.5 hr res ulted in a significantly lower percentage of diploid embryos and a signific antly higher percentage of abnormal ploidy embryos compared to treatment wi th 6-DMAP for 3.5 hr or with CHX and IVF. In conclusion, parthenogenetic ac tivation of bovine oocytes with Cal followed by 6-DMAP for 3.5 hr could pro duce better quality embryos in terms of total cell numbers, the number of c ells allocated to the ICM, and the ploidy of embryos. (C) 1999 Wiley-Liss, Inc.