Role for PADI6 and the cytoplasmic lattices in ribosomal storage in oocytes and translational control in the early mouse embryo

The mechanisms that mediate the establishment of totipotency during the egg-to-embryo transition in mammals remain poorly understood. However, it is clear that unique factors stored in the oocyte cytoplasm are crucial for orchestrating this complex cellular transition. The oocyte cytoplasmic lattices (CPLs) have long been predicted to function as a storage form for the maternal contribution of ribosomes to the early embryo. We recently demonstrated that the CPLs cannot be visualized in Padi6^-/- oocytes and that Padi6^-/- embryos arrest at the two-cell stage. Here, we present evidence further supporting the association of ribosomes with the CPLs by demonstrating that the sedimentation properties of the small ribosomal subunit protein, S6, are dramatically altered in Padi6^-/- oocytes. We also show that the abundance and localization of ribosomal components is dramatically affected in Padi6^-/- two-cell embryos and that de novo protein synthesis is also dysregulated in these embryos. Finally, we demonstrate that embryonic genome activation (EGA) is defective in Padi6^-/- two-cell embryos. These results suggest that, in mammals, ribosomal components are stored in the oocyte CPLs and are required for protein translation during early development.