Mammalian oocytes store proteins in cytoplasmic lattices

Oocytes must accumulate and store maternal factors such as proteins during growth to sustain the first stages of embryonic development. How mammalian oocytes store maternal proteins is not understood. Here, we show that mouse and human oocytes store proteins on cytoplasmic lattices. With super-resolution light microscopy and electron tomography, we demonstrate that cytoplasmic lattices are twisted filament bundles formed by proteins of the subcortical maternal complex, filling the entire ooplasm. The lattices were associated with many proteins that have crucial functions during early embryo development, including proteins controlling genome methylation. Loss of cytoplasmic lattices prevented the accumulation of these proteins and resulted in early embryonic arrest. Thus, cytoplasmic lattices are important for storage of essential maternal proteins and the developmental success of early mammalian embryos.