Profiling and functional characterization of maternal mRNA translation in mouse maternal-to-zygotic transition

Translational regulation plays an important role in gene expression and function. Although the transcriptional dynamics of mouse pre-implantation embryos has been well characterized, the global mRNA translation landscape and the master regulators of zygotic genome activation (ZGA) remain unknown. Here, by developing and applying a low-input ribosome profiling (LiRibo-seq) technique, we profiled the mRNA translation landscape in mouse pre-implantation embryos and revealed the translational dynamics during mouse pre-implantation development. We identified a dramatic translational transition from MII oocytes to zygotes, and demonstrated that active translation of maternal mRNAs is essential for maternal-to-zygotic transition (MZT). We further showed that two maternal factors, Smarcd2 and Cyclin T2, whose translation is activated in zygotes, are required for chromatin reprogramming and ZGA, respectively. Our study thus not only filled in a knowledge gap on translational regulation during mammalian pre-implantation development, but also revealed new insights into the critical function of maternal mRNA translation in MZT. Overall design: In this study, we modified RiboLace sequencing method to achieve mRNA translation profiling using as few as 100-250 oocytes or embryos. Using this low-input ribosome sequencing (LiRibo-seq) method, we have generated mRNA translation profiling of mouse MII oocytes and preimplantation embryos from 1-cell to blastocyst stage, revealing the dynamics of mRNA translation during the natural developmental process. We constructed a total of 14 LiRibo-seq datasets, including: two 5k ESC libraries, two MII oocyte libraries, two 1-cell embryo libraries, two 2-cell embryo libraries, two 4-cell embryo libraries, two morula libraries, two blastocyst embryo libraries. 12 total RNA-seq datasets were generated including two MII oocyte libraries, two 1-cell embryo libraries, two 2-cell embryo libraries, two 4-cell embryo libraries, two morula libraries, two blastocyst embryo libraries. 16 polyA RNA-seq datasets were generated including two MII oocyte libraries, two 1-cell embryo libraries, two DMSO and CHX treated zygote libraries, two DMSO and AMA treated zygote libraries, two siRNA control and Ccnt2 KD 2-cell embryo libraries. 8 ATAC-seq datasets were generated including two DMSO and CHX zygotes libraries, two siRNA control and Smarcd2 KD 1-cell embryo libraries.