Chronological Appearance of Apoptosis in Bovine Embryos Reconstructed by Somatic Cell Nuclear Transfer from Quiescent Granulosa Cells

Contents Efficiency of cloning has remained low and in spite of attempts to improve this technology, many reconstructed embryos do not implant or are lost during early pregnancy. Chromosomal aberrations, deviant gene expression patterns and abnormal regulation of cell death may be involved in this increased early embryonic loss. Here, we investigate the chronological onset of both apoptotic changes in nuclear morphology and DNA degradation [detected by transferase‐mediated dUTP nick‐end labelling (TUNEL) reaction] in bovine two‐cell‐ to blastocyst‐stage embryos. Such embryos were generated either by reconstruction with nuclear transfer from quiescent granulosa cells or by regular in vitro embryo production. Nuclear condensation was observed from the two‐cell stage and TUNEL labelling was observed from the six‐cell stage in reconstructed embryos, whereas nuclear condensation was evident from the eight‐cell stage and TUNEL labelling from the 13‐cell stage in embryos derived in vitro . Furthermore, reconstructed embryos displayed elevated ratios of embryos containing apoptotic nuclei at pre‐compaction stages and higher indices of apoptotic nuclei in morula and blastocyst stages when compared with in vitro ‐produced embryos.