Researchers at VIB, VUB and the Medical Research Council Laboratory of Molecular Biology in the UK have identified a previously hidden feature inside human sperm cells that could help reshape understanding of male fertility. The team used advanced imaging to reveal specialized compartments within the sperm nucleus that are packed with proteasomes, the molecular machines responsible for breaking down and recycling proteins.
The findings, reported in Nature Structural & Molecular Biology, suggest that the sperm nucleus is more structurally organized than scientists had assumed. Rather than being uniformly dense, it contains small DNA-free cavities that appear to function as dedicated hubs for proteasomes. These structures, first observed years ago and known as lacunae, had remained largely unexplained until now.
A closer look inside the sperm nucleus
Using cryo-electron tomography, the researchers were able to study sperm cells in their native state at extremely high resolution. That approach showed that the cavities are not empty spaces, but clusters containing large numbers of proteasomes arranged in distinct patterns. The team also identified a previously unknown variant of a sperm-specific proteasome component, adding another layer to the discovery.
According to Prof. Tom Dendooven of the VIB-VUB Center for Structural Biology, the work revealed an unexpected level of organization inside the sperm head and points to an important biological role for these compartments. The study also examined human testis tissue to understand when the structures appear during development.
Why the timing matters for fertility
The proteasome-rich compartments were found to emerge during the final stages of sperm development, when genetic material is being reorganized and tightly compacted. That timing suggests the proteasomes may help coordinate key steps in sperm maturation. The researchers said the discovery offers a foundation for future work on male reproductive health and early embryonic development.
The study also raises the possibility that these proteasomes remain active after sperm enters the egg, where they may help remodel the paternal genome during the earliest stages of embryonic development. While much remains to be learned, the findings give scientists a new framework for studying what happens in the moments before and after fertilization.
For UK-led fertility research, the work is notable because it combines structural biology with human tissue analysis to map a process that had not been clearly understood before. By showing how protein recycling machinery is organized inside sperm cells, the study may help guide future investigations into infertility and reproductive medicine.
More details about the research can be found in the original report from News Medical and the linked journal publication in Nature Structural & Molecular Biology: News Medical report and Nature Structural & Molecular Biology study.
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