Comprehensive analysis of soluble RNAs in human embryo culture media

Spent culture media was collected on day 5 after in vitro fertilization from 5 human blastocysts that were subsequently transferred or frozen. Corresponding blank culture media from the same lot were cultured alongside the embryos and used as negative controls along with PBS. The samples were prepared for total RNA sequencing using SMARTer® Stranded Total RNA-Seq Kit v2 - Pico Input Mammalian (Takara) and for small RNA sequencing using the QIAseq RNA Library Prep kit (Qiagen). Prepared libraries were sequenced as 100 bp paired end on an Illumina HiSeq 4000 sequencer for total RNA and Illumina NextSeq500 sequencer for small RNA. We found that total RNA mapped only 3% of the reads to gene regions in spent culture media and control and only 2% in PBS samples mapped to gene regions. For the small RNA analysis, human annotated miRNAs constituted from 0.1% to 1.4% of the mapped reads and 40% of small RNA reads mapped to the human genome. tiRNAs derived from 5 different mature tiRNA were differentially expressed when comparing conditioned to unconditioned media. We conclude, that in spite of applying state-of-the-art sensitive detection methods no miRNAs were found to be reliably present in the spent culture medium. In contrast, tiRNA fragments appear to be overexpressed in cultured IVF media samples. examination of total RNA and small RNA in spent culture medium from human in vitro fertilized blastocysts