Single-cell RNA-seq Reveals Early Transcriptional Programs of the Maternal to Zygote Transition in Mice and Rats

The maternal to zygote transition in mammals has been an area of intensive research over the past few decades, with an ever-changing landscape of understanding that has accompanied the rapid development of cell-profiling technology. Utilizing a full-length single cell RNA-seq protocol, we profiled mature oocytes and zygotes of mice and rats to uncover elusive transcriptomic dynamics during the maternal to zygote transition. We note the existence of early gene expression of crucial zygotic development pathways in the mouse zygote while revealing a similar chain of events occurring in the rat zygote. We further observe an increase in nascent and intergenic transcription in both species. Moreover, we find subtle but pervasive signals of differential transcript usage in genes related to epigenetic regulation occurring in both species. In terms of post-transcriptional modifications, we find distinct profiles of alternative polyadenylation between zygotes and oocytes in both species, particularly, in genes related to cell cycle processes within the zygotes of mice. Finally, although a more dynamic transcriptomic landscape exists in the mouse zygote, the rat zygote also displays similar transcriptomic features, suggesting that minor zygotic activation in rat may occur earlier than originally thought.