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bioRxiv · 10.64898/2025.12.01.691703

Sperm-specific fertility factors SMZ-1/2 promote FB-MO biogenesis and MSP filament assembly in C. elegans

Peng, H.-F.·Liu, C.-L.·Jane, W.-N.·Chen, C.-S.·Wang, C.-W.·Wu, J.-c.
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Abstract

In nematode sperm, motility is powered by polymerization of major sperm protein (MSP) into filaments assembled from a specialized organelle (FB-MO), but how filament formation begins is unclear. We identify two sperm-specific PDZ proteins, SMZ-1 and SMZ-2 (SMZ-1/2), that initiate MSP loading into pre-formed membranous organelles in Caenorhabditis elegans. SMZ-1/2 were expressed specifically in spermatogenic germ cells, colocalized with developing FB-MOs from diplotene through spermatid formation, and were redundant for fertility. Loss of SMZ-1/2 abolished MSP filaments, left MOs MSP-negative and morphologically immature, and caused primary spermatocyte arrest. Electron microscopy showed fewer, smaller FB-MOs lacking crystalline FBs, consistent with a defect in assembly initiation rather than late polymerization. SMZ-1/2 cytoplasmic structures were absent in spe-6 casein kinase mutants, placing SMZ-1/2 within a SPE-6-dependent initiation module. These findings identify SMZ-1/2 as PDZ scaffold proteins that initiate MSP assembly and couple kinase signaling to FB-MO biogenesis during nematode spermatogenesis.

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Peng, H.-F., Liu, C.-L., Jane, W.-N., Chen, C.-S., Wang, C.-W., Wu, J.-c.. 2025-12-03. Sperm-specific fertility factors SMZ-1/2 promote FB-MO biogenesis and MSP filament assembly in C. elegans. https://doi.org/10.64898/2025.12.01.691703

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