@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} }