Single-cell RNA-seq Analyses of Oocytes and Zygotes Reveal Earlier 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 confirm the existence of early gene expression in the mouse zygote while revealing a similar chain of events occurring in the rat zygote. We observe an increase in nascent transcription in both species. Moreover, we find subtle but pervasive signals of differential splicing of genes related to key early zygotic activities occurring in both species. Meanwhile, we find distinct profiles of alternative polyadenylation between zygotes and oocytes in both species, particularly, in genes related to major processes within the zygotes. 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 occurs earlier than originally thought.