The translational oscillation in oocyte and early embryo development

Translation is critical for development as transcription in the oocyte and early embryo is silenced. To illustrate the translational changes during meiosis and consecutive two mitoses of the oocyte and early embryo, we performed a genome-wide translatome analysis. Acquired data showed significant and uniform activation of key translational initiation and elongation axes specific to M-phases. Although global protein synthesis decreases in M-phases, translation initiation and elongation activity increases in a uniformly fluctuating manner, leading to qualitative changes in translation regulation via the mTOR1/4F/eEF2 axis. Overall, we have uncovered a highly dynamic and oscillatory pattern of translational reprogramming that contributes to the translational regulation of specific mRNAs with different modes of polysomal occupancy/translation that are important for oocyte and embryo developmental competence. Our results provide new insights into the regulation of gene expression during oocyte meiosis as well as the first two embryonic mitoses and show, how temporal translation can be optimized. This study is the first step towards a comprehensive analysis of the molecular mechanisms that not only control translation during early development, but also regulate translation-related networks employed in the oocyte-to-embryo transition and embryonic genome activation. To decipher protein synthesis and its regulation, we conducted Scarce Sample Polysome Profiling (SSP-profiling) to analyse active translation of mRNA at a genome-wide level. The improved SSP-profiling protocol was followed by RNA sequencing (RNA-seq), which allowed us to analyze mRNA translational profiles of mouse oocytes at the GV, MII stages, zygote, zygote M phase, and 2-cell and 2-cell M-phase stages. A total of 10 fractions from mouse oocytes and embryos were separated by polysomal fractionation, from which first 5 fractions were pooled and labelled as non-polysome (NP) and heavier 5 fraction were pooled and labelled as a polysome (P), followed by RNA-sequencing analysis. This experiment was performed in biological triplicates. In addition, the oocytes or embryos collected from the same batch in each developmental stage were used to profile their transcriptomes by mRNA-seq. This experiment was performed in biological triplicates.