Moreover, to prevent the transmission of single gene disorders such as cystic fibrosis and β-thalassemia, different methods of preimplantation genetic diagnosis (PGD) have been developed 8. In addition to these conventional methods of embryo evaluation, preimplantation genetic screening (PGS) in IVF cycles has been introduced as a valuable tool aimed at choosing euploid embryos to improve pregnancy rates 7. For this purpose, several morphological scoring systems, mainly based on the expansion of the blastocoel cavity, as well as on the appearance of the ICM and TE cells, have been proposed 4– 6. In spite of numerous papers suggesting time-lapse microscopy, as well as biochemical and molecular analyses to detect the most suitable embryo, to date, in clinical applications, morphological evaluation is the most accepted method to assess embryo quality 3. Of course, the assessment of blastocyst quality represents the basic step to achieve a successful pregnancy. In assisted reproductive cycles, over the last few years, extended embryo culture up to the blastocyst stage is widely practiced to improve pregnancy rates and reduce the probability of multiple pregnancies 2. As the embryo further divides, the blastocoel expands and the ICM becomes positioned on one side of the trophoblast cells forming the mammalian blastula, called blastocyst, ready for implantation 1. Moreover, blastocoel fluid microRNA profiles could be influenced by blastocyst quality, therefore, microRNAs might be used to assess embryo potential in IVF cycles.ĭuring cavitation, at day 4 of human preimplantation development, embryo cells begin to differentiate into the Inner Cell Mass (ICM) and Trophectoderm (TE) lineages and secrete fluid into the morula to create a fluid-filled cavity, the blastocoel. Their characterization is important to better understand the earliest stages of embryogenesis and the complex circuits regulating pluripotency. Blastocoel fluid microRNAs reflect the miRNome of embryonic cells and their presence, associated with the discovery of extracellular vesicles, inside blastocoel fluid, strongly suggests their important role in mediating cell communication among blastocyst cells. We found 89 microRNAs, expressed at different levels, able to regulate critical signaling pathways controlling embryo development, such as pluripotency, cell reprogramming, epigenetic modifications, intercellular communication, cell adhesion and cell fate. The bioinformatic and comparative analyses identified the biological function of blastocoel fluid microRNAs and suggested a potential role inside the human blastocyst. In this study, for the first time, we demonstrated the presence of microRNAs and extracellular vesicles in human blastocoel fluid.
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