Influence of Apoptosis in Bovine Embryo's Development

The correlation between apoptosis and early bovine embryonic loss is still not fully elucidated. In the present study, the relationship between the arrest of bovine embryos at the different stages of development and apoptosis was evaluated. We used embryos 7 days after in vitro maturation and fertilization, and morphologic and biochemical apoptotic analyses were performed by using a phase contrast microscope and by the terminal transferase dUTP nick end-labelling respectively. For the statistic, the apoptotic cell ratio (ACR) was determined as the percentage of apoptotic cells per embryo. To evaluate the relation between ACR and fragmentation pattern, embryos were divided into five groups, groups I-V. To assess the relation between ACR and cytoplasmatic fragmentation, embryos were divided into three groups, according to the fragmentation percentage (< 5%; 5-15% and >15%). Of the total 139 embryos included, 65 arrested at 2-8 cells; 14 arrested at 9-16 cells; 18 compacted morula and 42 were non-arrested blastocysts. The average number of embryonic fragmentation at different stages of the development, 2-8 cells, 9-16 cells, compacted morula and blastocyst, was 16.0 +/- 1.5, 28.7 +/- 4.4, 4.4 +/- 2.4 and 1 +/- 0.3 respectively. The embryos at the stage of arrested 9-16 cells and compacted morula had higher ACR than those at the blastocyst stage, excluding the stage of 2-8 cells (the genome is not yet active). The correlation detected between embryonic development and ACR was 0.92 (p < 0.01). It was observed that embryos possessing high fragmentation showed the higher ACR value (r = 0.98, p < 0.05). Comparing the results between fragmentation percentage and ACR, it was observed that the embryos with higher percentage of fragmentation corresponded to higher ACR (r = 0.97, p < 0.01). These results clearly demonstrated that bovine embryonic arrest at different stages of development is correlated with the apoptotic mechanisms.