@article {70420, title = {In situ molecular architecture of the mammalian sperm nuclear vacuole}, journal = {bioRxiv}, year = {2026}, month = {2026 May 20}, abstract = {

Direct identification of macromolecular complexes in their native context remains a major barrier to unbiased biological discovery. This challenge is particularly acute in mammalian sperm nuclei, in which condensed chromatin is interspersed with poorly understood phase-separated compartments termed nuclear vacuoles. Vacuoles are associated with reduced fertilization efficiency, yet their composition remains unclear. Here we combine high-resolution\ in situ\ cryo-electron tomography (cryo-ET) with AlphaFold docking to identify vacuole components as proteasomes, the proteasome activator PA200, and ferritin.\ In situ\ structures at resolutions up to 3.8 {\r A} reveal distinct proteasome-PA200 associations and gating states, consistent with a stepwise activation mechanism. Ferritin assemblies exhibit heterogeneous mineralization states and directly contact chromatin. Together, these findings establish the molecular organization of sperm nuclear vacuoles and implicate protein turnover and metal homeostasis in shaping the nuclear landscape, while demonstrating the power of\ in situ\ cryo-ET to resolve protein identity and conformational dynamics in native cellular environments.

}, doi = {10.64898/2026.05.18.725999}, url = {https://www.biorxiv.org/content/early/2026/05/20/2026.05.18.725999}, author = {Braxton, Julian R. and Qu, Songrong and Skinner, Will M. and Shiozaki, Momoko and Jean, Nikki and Yan, Rui and Zhao, Xiaowei and Yu, Zhiheng and Lishko, Polina V. and Chen, Zhen} } @article {68562, title = {In situ cryo-electron tomography reveals the asymmetric architecture of mammalian sperm axonemes.}, journal = {Nature Structural \& Molecular Biology}, volume = {30}, year = {2023}, month = {2023 Mar 01}, pages = {360-9}, abstract = {

The flagella of mammalian sperm display non-planar, asymmetric beating, in contrast to the planar, symmetric beating of flagella from sea urchin sperm and unicellular organisms. The molecular basis of this difference is unclear. Here, we perform in situ cryo-electron tomography of mouse and human sperm, providing the highest-resolution structural information to date. Our subtomogram averages reveal mammalian sperm-specific protein complexes within the microtubules, the radial spokes and nexin-dynein regulatory complexes. The locations and structures of these complexes suggest potential roles in enhancing the mechanical strength of mammalian sperm axonemes and regulating dynein-based axonemal bending. Intriguingly, we find that each of the nine outer microtubule doublets is decorated with a distinct combination of sperm-specific complexes. We propose that this asymmetric distribution of proteins differentially regulates the sliding of each microtubule doublet and may underlie the asymmetric beating of mammalian sperm.

}, issn = {1545-9985}, doi = {10.1038/s41594-022-00861-0}, author = {Chen, Zhen and Greenan, Garrett A and Shiozaki, Momoko and Liu, Yanxin and Skinner, Will M and Zhao, Xiaowei and Zhao, Shumei and Yan, Rui and Yu, Zhiheng and Lishko, Polina V and Agard, David A and Vale, Ronald D} }