55 Morphokinetics of in vitro-derived bovine embryo is associated with the transcriptomic profile of the developed blastocyst
S. Yaacobi-Artzi A , D. Kalo A and Z. Roth AA Department of Animal Sciences, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
Reproduction, Fertility and Development 34(2) 263-263 https://doi.org/10.1071/RDv34n2Ab55
Published: 7 December 2021
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
Bovine embryos are transferred to synchronised recipients when they reach the blastocyst stage. This promising process has still not been perfected and, among other methods, embryo selection for transfer needs to be optimised. We examined a noninvasive selection approach based on the embryo’s morphokinetics. Use of a time-lapse system enabled continuous imaging of individual embryos with the aim of (1) characterising the embryo’s morphokinetics, i.e. cell divisions and morphology; (2) associating the morphokinetics with the embryo’s developmental competence, and (3) examining the transcriptomic profile of the developed blastocyst. In vitro-derived bovine oocytes were fertilised and putative zygotes were individually cultured in a Miri®TL incubator (Esco Medical) equipped with a time-lapse system. Embryo morphokinetics and blastocyst transcriptome profile were examined. Statistical analysis was performed using JMP-Pro 15 software (SAS Institute Inc.). Cleavage to 2- to 4-cell-stage embryos, blastocyst formation rate, and embryo kinetics were analysed by one-way ANOVA followed by Tukey-Kramer test. Proportion of synchronously and asynchronously embryos that developed to the blastocyst stage was analysed by chi-squared followed by Pearson test. The proportion of oocytes that cleaved and developed to blastocysts was 85.4 ± 2.7 and 26.4 ± 4.1%, respectively. Embryos were categorised as normal (68.9%) or abnormal (31.1%) according to the pattern of their first cleavage. Of the normally cleaved embryos, 61.6% underwent synchronous cleavage and 38.3% asynchronous cleavage. The proportion of blastocysts that developed from synchronously cleaved embryos was lower than that from asynchronously cleaved embryos (42.2% vs. 57.7%, respectively; P < 0.01). For the synchronously cleaved embryos, the median cleavage time to firstt, second, third, morula, early blastocyst, blastocyst, and expanded blastocyst stages was 29.0, 38.7, 51.0, 113.0, 130.5, 159.5, and 166.5 h post-fertilisation, respectively. Embryos that cleaved earlier and showed good morphology score following first divisions had high potential of developing to blastocysts. Cleavage of the abnormally cleaved embryos was categorised as direct (18.6%), unequal (30.3%), or reverse (9.6%). These embryos expressed very low to no blastocyst formation relative to normally cleaved embryos (P < 0.001). Microarray analysis revealed 67 differentially expressed genes in blastocysts from synchronously vs. asynchronously cleaved embryos (P < 0.05). About 310 genes were differentially expressed in blastocysts from synchronously vs. directly cleaved embryos (P < 0.05) and 270 genes were differentially expressed in blastocysts from asynchronously vs. directly cleaved embryos (P < 0.05). The differentially expressed genes were involved in various biological pathways, such as cell cycle, cytoskeleton regulation, apoptosis and metabolism. In summary, morphokinetics of first cleavages was associated with embryonic developmental competence and further expressed in the blastocyst’s transcriptomic profile. Selecting embryos based on their morphokinetics might serve as a practical tool to improve embryo transfer programs.
