Remodeling of donor nuclei, DNA-synthesis, and ploidy of bovine cumulus cell nuclear transfer embryos: Effect of activation protocol

The purpose of this study was to investigate the effects of two activation protocols on nuclear remodeling, DNA synthesis during the first cell cycle, chromosome segregation after first mitosis and development to blastocyst o f embryos produced by somatic nuclear transfer. Pronuclear formation was si gnificantly higher when activation lasted 5 hr compared to 3 hr for both et hanol-cycloheximide and ionomycin-bohemine treatment. However, the presence of a single nucleus was significantly higher in embryos activated for 3 hr in bohemine. Initiation of DNA synthesis was delayed in ethanol-cyclohexim ide group, however, after 12 hr labeling 100% of embryos synthesized DNA in both groups. Embryos activated with ethanol-cycloheximide developed to bla stocysts at a significantly higher rate than those activated with ionomycin -bohemine. Analysis of 2-cell embryos with DNA probes for chromosome 6, 7, and 15 by fluorescence in situ hybridization showed that at least 50% of NT embryos were of normal ploidy independent of the activation stimulus. The results presented in this study show differences between the protocols comp ared on the nuclear events during the first cell cycle and on the developme nt to blastocyst. (C) 2001 Wiley-Liss, Inc.