Successful production of high quality blastocysts in vitro depends on the use of a culture system that ensures the acquisition of developmental competence by the maturing oocyte. It is now clear that the in vitro maturation environment has a major influence on the oocyte's ability to acquire the potential to develop into blastocysts. In this work we examine the impact of oocyte culture media on the quality of blastocysts by comparing developmental rates, cell number and their allocation to embryonic cell lineages, apoptosis, and expression of developmentally important genes. Higher total cell count and ICM:TCN ratio, which are indicative of embryo viability, were observed in embryos derived from oocyte maturation in TCM-199 supplemented with serum when compared to blastocysts derived from oocyte maturation in SOF BSA. Moreover, oocyte maturation in TCM-199 supplemented with serum-generated embryos of higher morphological quality and producing higher levels of Interferon Tau transcripts when compared to embryos derived from oocyte maturation in SOF BSA. In conclusion, the oocyte maturation regimen affected the morphological feature of blastocysts, including total cell count and allocation of cells to trophectoderm (TE) and inner cell mass (ICM) lineages and the expression profiles of genes involved in various embryo functions such as early embryonic growth, regulation of gene transcription, trophoblast differentiation and function, embryo-maternal communication, and stress response. Our results show that the oocyte culture media have strong impact on the quality of embryos produced in vitro and emphasize the need for more in depth evaluation of oocyte maturation protocols.

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Environment is crucial for in vitro development of gametes and embryos. The recent progression of culture media towards defined conditions brought to surface the impact of different medium supplements on oocyte and embryo development. In this work we evaluate the effect of various oocyte culture media on bovine oocyte maturation and subsequent embryo development. Bovine cumulus-oocyte complexes were recovered from slaughterhouse ovaries and matured in vitro in either TCM-199 (Gibco) or SOF (Synthetic Oviduct Fluid) media supplemented with BSA (fatty acid-free) or serum (fetal bovine serum). Oocytes from each treatment group were denuded and fixed at 18, 20, 22, 24, 26 and 28h post-maturation (p.m.). Oocyte meiotic progression was monitored in each of the groups (n=28–40 oocytes/group) by immunofluorescence microscopy of chromatin. Oocytes matured in SOF showed a slower rate of meiotic progression when compared to the other groups, with the highest percentage of oocytes reaching the MII stage by 28h p.m. (60.71% SOF-BSA, 71.43% SOF-Serum). The fastest developmental rate was observed in oocytes matured in TCM-serum (77.15% at 24h p.m.) followed by oocytes matured in TCM-BSA (74.29% at 26h p.m.). In order to evaluate the effect of nuclear maturation on chromosome segregation, chromosomal organization of MII oocytes was evaluated by immunofluorescence microscopy within each media group (n=26–31 oocytes/group) at 18, 22 and 26h p.m.. No chromosomal abnormalities were found at 18h p.m.. Both media supplemented with BSA induced lower frequencies of chromosomal abnormalities (0 to 3.23%) and (3.57 to 7.69%) for SOF and TCM, respectively, when compared to their serum-supplemented counterparts (7.14 to 11.54%) and (10 to 10.71%) for SOF and TCM, respectively at 22 and 26h p.m.. Remarkably, the maturation medium and its supplements influenced the speed of blastocyst development. For this experiment, oocytes were matured in TCM-BSA, TCM-Serum, SOF-BSA or SOF-serum, fertilized in vitro in a TALP-base media supplemented with BSA and cultured in SOF-BSA. Blastocyst development was assessed at 7, 8 and 9 days of culture. Cleavage rates were similar between the groups (84–90%), whereas development rates to blastocyst stage varied among treatment groups. Maturation in SOF-BSA induced a delay in blastocyst formation that reached its highest percentage only on day 9 of culture (30.8%); moreover, blastocyst development was carried over until Day 12. When oocytes were matured in the presence of serum, the number of blastocysts did not increase after Day 8 of culture (26.6%, TCM-serum). These results provide evidence of a severe impact of oocyte culture media on the nuclear maturation of oocytes and their subsequent embryonic development after IVF. Moreover, the difference in the rate of oocyte maturation and blastocyst formation emphasizes the necessity for reviewing and adapting current protocols to new systems such as SOF-BSA. [Research funded by NSERC and OMAF of Canada.]