Analysis of the gene expression pattern of bovine blastocysts at three stages of development.

Blastocyst formation is a primordial event of pre-implantation development since it is required for pregnancy establishment and progression. The blastocyst plays a pivotal role because it is the stage at which the embryo starts coordinated cross-talk with the mother. It is also the terminal step before transfer in bovine; it reflects all stresses the embryo may have faced during the process of in vitro treatment. Achieving the formation of a morphologically healthy blastocyst following normal kinetics is good, but remains a poor indicator of embryo quality. Considering the limitation of the invasive methods for competence assessment, the analysis of blastocysts' gene expression is a promising way to improve our understanding of blastocyst formation and to study the effects of different treatments on gene expression. To that end, early, expanded, and hatched blastocysts, derived from in vitro fertilization and culture, were collected for RNA extraction, amplification, and cDNA microarray hybridization. Gene candidates (IFNt, PLAC8, SSLP1, AKR1B1, HNRNPA2B1, ARGFX, NANOS, CCNB1) were selected and confirmed using real-time RT-PCR to validate the microarray data. Our analysis showed that hatched blastocysts are enriched in transcripts implicated in attachment, cell adhesion, and extracellular matrix digestion. Early blastocysts expressed genes mainly involved in cell cycle control, transcription, and translation. Real-time RT-PCR validated most microarray results (87.5%). Overall, our study provides new insights into the molecular regulation of blastocyst formation. In addition, it could help assess blastocyst staging and select better embryos based on the expression of quality markers.