Investigation of the Developmental Potential and Developmental Kinetics of Bovine Parthenogenetic and Somatic Cell Nuclear Transfer Embryos Using a Time-Lapse Monitoring System.

Abstract

A time-lapse monitoring system has predictive value for selecting good-quality embryos with the highest implantation potential. Using this new tool, we investigated the developmental potential and developmental kinetics of bovine parthenogenetic (PA) and two types of somatic cell nuclear transfer (NT) embryos. Bovine non-transgenic ear cells (bECs) or transgenic cells (bTGCs) were used as donor cells. The cleavage and blastocyst development rates did not significantly differ among the PA, NT-bEC, and NT-bTGC groups, and first cleavage occurred an average of 19.3 hours (n = 70), 21.6 hours (n = 60), and 21.3 hours (n = 62) after activation, respectively (20.4 hours [n = 192] for all embryos). When embryos were classified into early cleaving (≤20 hours) and late cleaving (>20 hours) groups, the blastocyst formation rate was much higher in the early cleaving groups (PA, 46%; NT-bEC, 50%; NT-bTGC, 39%) than in the late cleaving groups (PA, 18%; NT-bEC, 23%; NT-bTGC, 28%), while the percentage of embryos whose development was blocked between the two- and eight-cell stages was increased in the late cleaving groups. The percentage of embryos classified as early cleaving with a normal morphology was twofold higher in the PA group (20.0%, n = 14) than in the NT-bTGC group (9.7%, n = 6). The timing of each developmental stage varied widely; the timing of first cleavage varied from 7.6 hours in the PA group to 34.5 hours in the NT-bEC group and the timing of expanded/hatching blastocyst appearance varied from 141.6 hours in the PA group to 196.3 hours in the NT-bTGC group, differences of 26.9 and 54.7 hours, respectively (PA>NT-bEC>NT-bTGC). These results demonstrate that time-lapse monitoring provides novel data regarding individual embryo developmental kinetics and helps to predict developmental potential for improved bovine NT embryo selection based on early cleavage (≤20 hours) and normal morphology.