Developmental kinetics of the first cell cycles of bovine in vitro produced embryos in relation to their in vitro viability and sex

摘要

The development of in vitro-produced cattle embryos was observed in a time-lapse culture system to determine cell-cycle lengths of (1) embryos that developed into compact morulae (CM) or blastocysts within 174 h of insemination (viable), (2) embryosthat became arrested during earlier stages (non-viable) and (3) male and female embryos. In 4 replicates, inseminated oocytes were cultured on a microscope stage in 3-4 groups on a granulosa cell monolayer in supplemented TCM-199. Images were sequentially recorded and stored at 30-min intervals. All embryos that could be identified throughout the culture period were included (n = 392), and the times of cleavage events were noted. After culture, 100 CM + blastocysts were randomly selected for sexing bythe PCR. Blastocysts developed equally well in the time-lapse and control culture systems (36 vs. 38%). The lengths of the first 4 cell cycles of viable embryos were 32.0±3.9, 8.8±1.6, 10.8±4. 7 and 47.7±11.8 h respectively. The intervals between the 9-to 16-cell, early morula, CM and blastocyst stages lasted 16.2-18.2 h. Blastomeres of 2-, 4- and 8-cell embryos cleaved asynchronously at <1, 2.6±2.5 and 9.2±4.5 h intervals respectively. The interval from insemination to tight compaction and formation ofa blastocoel was 128.4±10.7 and 145.8±12.5 h respectively. Compared with values for non-viable embryos, the first 3 cell cycles of viable embryos were approximately 3 h shorter and the fourth cycle was 5 h shorter. Using these cycle lengths, it was possible to define time windows in which the proportions of viable 2-, 3- to 4-, 5- to 8- and 9- to 16-cell embryos were maximal. Male and female embryos did not differ in cleavage interval.