Curating fertility-proteomic remodelling of sperm during epididymal transit

The epididymis is a highly specialized organ essential for promoting the post-testicular functional maturation of spermatozoa, a process underpinning male fertility. This review examines the latest proteomics advances that have been used to unravel the complex molecular landscape of the epididymis, revealing the dynamic protein networks that shape sperm function beyond their genomic and transcriptomic blueprints. Here, we highlight how high-resolution mass spectrometry has helped to map the proteomic signatures of epididymal tissue, luminal extracellular vesicles (epididymosomes), and spermatozoa at different maturation stages, pinpointing key regulators of motility, capacitation, fertilization competence, and immune regulation. However, critical knowledge gaps remain, including deep protein characterization of the cytoplasmic droplet, epididymal fluid, and relatively underexplored anatomical tissue segments such as the corpus and cauda epididymis. We discuss how integrating global proteomic insights with complementary omics, single-cell proteomics, and advanced imaging is poised to reveal the spatial and temporal refinement of the sperm proteome, providing insights into how its disruption may contribute to idiopathic infertility. To promote data accessibility and accelerate discovery in epididymal biology, we introduce ShinyEpididymis (https://reproproteomics.shinyapps.io/ShinyEpididymis/), an interactive, web-based resource integrating publicly available proteomic datasets from spermatozoa, epididymosomes, and epididymal tissue. This platform enables researchers to rapidly query proteins of interest, explore spatial patterns of expression, and identify potential biomarkers or therapeutic targets. By consolidating current knowledge and defining future priorities, this review positions proteomics at the forefront of understanding epididymal biology, emphasising its clinical relevance and untapped potential for diagnosing and treating male infertility.