Revisiting structure/functions of the human epididymis

The epididymis is the hallmark of all vertebrate species practicing internal fertilization. While the functions of the epididymis are well documented in laboratory rodents and some domestic animals, the structure and functions of the epididymis in humans remain poorly documented.

Using human tissues obtained with the collaboration of our local organ transplantation program, the histology, cell types, and three-dimensional organization of the excurrent duct were investigated. Microarrays were performed to determine the gene expression pattern along the human epididymis.

The histology of longitudinal sections of the proximal epididymis was described, and immunohistochemistry using specific antibodies was used to characterize cell types of the efferent duct and caput epididymis epithelia. The epididymis was divided into eight segments permitting gene profiling by microarray and gene ontology analysis.

The proximal region of the human epididymis is formed exclusively by efferent ducts. These ducts form a complex histological structure particularly at the junction of the efferent ducts and caput epididymis. The efferent ducts exhibit a specific cellular signature when compared with the adjacent epididymis tubule. Efferent duct gene expression is not segmented and is dedicated to cilium differentiation and movement. The gene expression pattern of the caput segment is homogeneous and specialized in defense and immune responses and fertilization.

In murine species, the epididymis is segmented into the initial segment, caput, corpus, and cauda regions, whereas in humans, the proximal region is formed by efferent ducts. The caput tubules have their own histological organization with a well-defined gene expression pattern. The distal corpus and cauda epididymis are distinct by a limited number of differentially expressed genes.

Knowledge of epididymis functions and structure obtained using laboratory species should be extrapolated to humans with caution.