Abstract
In this study, for the first time, we demonstrated the presence of microRNAs and extracellular vesicles in human blastocoel fluid. The bioinformatic and comparative analyses identified the biological function of blastocoel fluid microRNAs and suggested a potential role inside the human blastocyst. 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. 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. Their characterization is important to better understand the earliest stages of embryogenesis and the complex circuits regulating pluripotency. Moreover, blastocoel fluid microRNA profiles could be influenced by blastocyst quality, therefore, microRNAs might be used to assess embryo potential in IVF cycles.
Highlights
During 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
In 2013, for the first time, genomic DNA was identified inside Blastocoel Fluid (BF) and the authors proposed that BF could represent a good option for preimplantation genetic diagnosis (PGD) avoiding the potential risk associated with embryo biopsy[10]
MiR-17, miR-519d and miR-372 absolute quantification, by droplet digital PCR, demonstrated that BF miRNAs were effectively detectable in the 3 analyzed samples
Summary
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. 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] 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[4,5,6]. Two recent papers have shown that extracellular vesicles secreted by blastocysts in culture medium are taken up by endometrial epithelial cells and these papers did not characterize the molecule cargo, they certainly demonstrated that embryonic cells use microvesicles and exosomes to communicate with maternal tissues[18,19]. BF miRNA profiles could be influenced by blastocyst quality; these miRNAs might be used to assess embryo potential in IVF cycles
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