Sperm Maturation Dynamics in Mammalian Systems

Sperm maturation in mammals encompasses a transformative journey from the completion of spermiogenesis in the testis to the acquisition of fertilisation competence during epididymal transit. Within the seminiferous epithelium, developing spermatids shed excess cytoplasm and remodel their acrosome, flagellum and mitochondrial sheath. Upon entry into the epididymis, sperm undergo progressive biochemical and structural refinement: residual cytoplasmic droplets are reorganised, metabolic enzymes are compartmentalised, centrioles are selectively degraded and membrane composition is tuned to prepare for capacitation. The epididymal environment supplies nutrients, signalling molecules and regional microenvironments that drive changes in motility, plasma‐membrane fluidity and the capacity to undergo the acrosome reaction. Interplay between vesicular trafficking, proteasomal activity and cytoskeletal remodelling ensures that sperm emerge from the cauda with optimised swimming velocity and fertilisation potential. These dynamic processes are essential for male fertility, underlie evolutionary adaptations across species and inform strategies for contraception, assisted reproduction and livestock breeding.

Research from Nature Portfolio

Recent studies have elucidated the molecular machinery governing cytoplasmic droplet formation and function. A key transmembrane protein was shown to direct vesicular delivery of Golgi‐derived saccules into the forming cytoplasmic droplet, ensuring segregation of metabolic enzymes that sustain late spermatid and epididymal sperm metabolism. In parallel, high‐resolution in vivo imaging has revealed that sperm centrioles, once thought to be inert vestiges, are actively dismantled during passage through the epididymal caput, preventing paternal centriole inheritance and reshaping microtubule organising capacity. Single‐cell analyses of boar semen have further demonstrated that an elevated incidence of retained cytoplasmic droplets can be offset by increasing sperm concentration in insemination doses, preserving motility and fertilisation outcomes despite incomplete epididymal maturation.

Sperm Maturation Dynamics in Mammalian Systems publication trend

The graph below shows the total number of articles in sperm maturation dynamics in mammalian systems across all publications each year (not limited to Nature Index journals).

Technical terms

Cytoplasmic droplet: A residual cytoplasmic structure at the sperm neck that serves in enzyme sequestration, osmoadaptation and energy supply during maturation.

Epididymis: The highly convoluted duct where sperm acquire motility, membrane remodelling and fertilisation competence after leaving the testis.

Capacitation: The final functional maturation process involving membrane fluidity changes and ion fluxes that render sperm capable of fertilising an oocyte.

Centriole: A microtubule‐based organelle initially present in sperm that is selectively degraded during epididymal transit to regulate zygotic microtubule organising activity.

Outer dense fibres: Accessory filamentous structures surrounding the axoneme that confer structural integrity and resilience to the sperm tail during motility.

References

1. SYPL1 defines a vesicular pathway essential for sperm cytoplasmic droplet formation and male fertility. Nature Communications (2023).
2. Comparative analysis of mammalian sperm ultrastructure reveals relationships between sperm morphology, mitochondrial functions and motility. Reproductive Biology and Endocrinology (2019).
3. Proteomic Analyses Reveal a Role of Cytoplasmic Droplets as an Energy Source during Epididymal Sperm Maturation. PLOS ONE (2013).
4. Compartmentalization of membrane trafficking, glucose transport, glycolysis, actin, tubulin and the proteasome in the cytoplasmic droplet/Hermes body of epididymal sperm. Open Biology (2015).
5. Post-Testicular Sperm Maturation: Centriole Pairs, Found in Upper Epididymis, are Destroyed Prior to Sperm’s Release at Ejaculation. Scientific Reports (2016).
6. Compensability of an enhanced incidence of spermatozoa with cytoplasmic droplets in boar semen for use in artificial insemination: a single cell approach. Scientific Reports (2022).