YBX1 mediates alternative splicing and maternal mRNA decay during pre-implantation development

In mammals, maternal gene products decay and zygotic genome activation (ZGA) during maternal to zygotic transition (MZT) is critical for the early embryogenesis. Y-box binding protein YBX1 plays vital roles in RNA stabilization and transcriptional regulation, but its roles remain to be elucidated during pre-implantation development.

In the present study, we re-analyzed transcriptional level of YBX1 in mice, human, bovine, and goat embryos using public RNA-seq datasets. We further performed siRNA microinjection to knock down the expression of YBX1, and RNA sequencing of the 8-cell stage embryos in the control and YBX1 knockdown group. To reveal the regulation mechanisms of YBX1, we conducted differentially expression analysis, alternative splicing (AS) analysis, enrichment analysis, and 5-EU staining using DESeq2, rMATs, clusterProfiler, and immunofluorescence technique, respectively.

The expression of YBX1 was increased during MZT in goat, bovine, human, and mice, but significantly decreased in YBX1 knockdown embryos compared with the controls, suggesting successfully knockdown of YBX1. The percentage of blastocyst was decreased, while embryos blocked at the 2- and 4-cell stage were increased in YBX1 knockdown embryos compared to the controls. Using RNA-seq, we identified 1623 up-regulated and 3531 down-regulated genes in the 8-cell stage YBX1 knockdown embryos. Of note, the down-regulated genes were enriched in regulation of RNA/mRNA stability and spliceosome, suggesting that YBX1 might medicate RNA stability and AS. To this end, we identified 3284 differential AS events and 1322 differentially expressed maternal mRNAs at the 8-cell stage YBX1 knockdown embryos. Meanwhile, the splicing factors and mRNA decay-related genes showed aberrant expression, and the transcriptional activity during ZGA in goat and mice was compromised when YBX1 was knocked down.

YBX1 serves an important role in maternal mRNA decay, alternative splicing, and the transcriptional activity required for early embryogenesis, which will broaden the current understanding of YBX1 functions during the stochastic reprogramming events.