211 IN VITRO CULTURE CONDITIONS AFFECT GENE EXPRESSION PATTERN OF BOVINE BLASTOCYST IN A STAGE-SPECIFIC MANNER

Abstract

The aim of this study was to examine the effect of in vitro culture conditions at specific phases of early embryonic development on the transcriptome profile of bovine blastocysts. Simmental heifers were superovulated and artificially inseminated 2 times with the same frozen–thawed commercial bull semen. Using nonsurgical endoscopic oviductal flushing technology (Besenfelder et al. 2001 Theriogenology 55, 837–845), 6 different blastocyst groups were flushed out at different time points (2-, 4-, 8-, 16-, 32-cell and morula). After flushing, embryos cultured under in vitro conditions until the blastocyst stage. Blastocysts from each group were collected and pooled in groups of 10. Complete in vivo blastocysts were produced and used as control. A unique custom microarray (Agilent) containing 42 242 oligo probes (60-mers) was used over 6 replicates of each group v. the in vivo control group to examine the transcriptome profile of blastocysts. A clear difference in terms of the number of differentially expressed genes (DEG, fold change ≥2, false discovery rate ≤0.05) has been found between groups flushed out at 2-, 4-, and 8-cell (1714, 1918, 1292 DEG, respectively) and those flushed out at 16-, 32-cell and morula stages and cultured in vitro until blastocyst stage (311, 437, 773 DEG, respectively) compared with the complete vivo group. Ontological classification of DEG showed cell death to be the most significant function in all groups. However, the longer time embryos spent under in vitro conditions, the more the percentage of DEG involved in cell death and apoptosis processes are represented in those groups. In addition, genes related to post-translational modification and gene expression processes were significantly dysregulated in all groups. Pathway analysis revealed that protein ubiquitination pathway was the dominant pathway in the groups flushed out at 2-, 4-, and 8-cells but not in the other groups flushed at later stages compared with the in vivo control group. Moreover, retinoic acid receptor activation and apoptosis signalling pathways followed the same pattern. Embryos flushed out before the time of embryonic genome activation and subsequently cultured in vitro were highly affected by culture conditions. Overall, the results of the present study showed that despite the fact that embryos originated from the same source, in vitro culture condition affected embryo quality, measured in terms of gene expression, in a stage-specific manner.