Cryo-EM structure of native mouse oocyte cytoplasmic lattices reveals a hierarchical assembly of 14 protein components—including PADI6 tubular scaffolds, two SCMC subtypes, and sequestered ubiquitination machinery—that organize into periodic filaments and higher-order helical bundles, functioning as multifunctional storage depots that preserve maternal factors including assembly-competent tubulin dimers and autoinhibited protein degradation modules in functionally inactive states for timely deployment during early embryonic development.

Oocytes depend on maternal factors for maturation and early embryogenesis. Cytoplasmic lattices (CPLs) are distinctive fibrillar structures in mammalian oocyte cytoplasm implicated in maternal factor storage and developmental competence, yet their molecular composition and architecture remain elusive. Here, we use cryo-electron microscopy to resolve the high-resolution structure of native mouse oocyte CPLs. We identify 14 intrinsic components of multiple copies that assemble into filaments in which PADI6-mediated self-assembly and two subtypes of subcortical maternal complexes (SCMCs) form the core scaffold. Unexpectedly, we discover that α/β-tubulin dimers and two autoinhibited ubiquitination modules (UHRF1-UBE2D3, SKP1-FBXW18) are internal components of CPLs. We also uncover multivalent interactions that organize adjacent CPL filaments into higher-order helical bundles. By integrating CPL structure with biochemical and proteomic data, we propose a hierarchical assembly mechanism of CPLs, from subcomplexes to filaments to supramolecular lattices. Our study offers mechanistic insights into how maternal proteins are spatially organized to ensure successful early embryonic development and provides a structural foundation for understanding female infertility related to CPL-associated gene mutations.