Spatiotemporal dynamics of epididymal epithelial cells uncover a novel KRT5⁺ATP6V1A⁺ subpopulation of basal cell in postnatal mouse development

Epididymal epithelial cells are critical for sperm maturation. Although previous studies have determined the development of epididymal epithelial cells in rat epididymis, the postnatal developmental trajectories of distinct epithelial cell types in the mouse epididymis remain elusive. Here, we examined the developmental timeline of mouse epididymal epithelium differed from that of the rat by confocal immunostaining and single-cell RNA sequencing (scRNA-seq). In mice, principal and basal cells appeared as early as postnatal day 7 (PD7) across all segments, labeled by AQP9 and KRT5, in contrast to the later emergence in rats (e.g., basal cells at PD14 in rat cauda). ATP6V1A-positive clear cells were detected at PD28 in caput, corpus, and cauda but not in the initial segment, while narrow cells were observed in all segments beginning at PD14. These contrasted with the rat, in which clear cells appeared at PD14. Notably, scRNA-seq and immunostaining identified a previously unrecognized KRT5⁺/ATP6V1A⁺ narrow-like basal cell subpopulation, enriched in lysosomes and mainly localized to the caput and corpus. These findings revealed an earlier epithelial maturation in mice compared to rats, underscoring the importance of choosing animal models. The newly identified basal subpopulation may contribute to luminal acidification and homeostasis, offering new insights into epididymal physiology and reproductive biology.