The epididymis is a single convoluted tubule lined by a pseudostratified epithelium. Specialized epididymal epithelial cells, the so-called principal, basal, narrow, and clear cells, establish a unique luminal environment for the maturation and storage of spermatozoa. The epididymis is functionally and structurally divided into several segments and sub-segments that create regionally distinct luminal environments. This organ is immature at birth, and epithelial cells acquire their fully differentiated phenotype during an extended postnatal period, but the factors involved in this complex process remain incompletely characterized. In the adult epididymis, the establishment of an acidic luminal pH and low bicarbonate concentration in the epididymis contributes to preventing premature activation of spermatozoa during their maturation and storage. Clear cells are proton-secreting cells throughout the epididymis, but principal cells have distinct acid/base transport properties, depending on their localization within the epididymis. Basal cells are located in all epididymal segments, but they have a distinct morphology depending on the segment and species examined. How this structural plasticity of basal cells is regulated is discussed here. Also, the role of luminal factors and androgens in the regulation of epithelial cells is reviewed in relation to their respective localization in the proximal versus distal regions of the epididymis. Finally, we describe a novel role for CFTR in tubulogenesis and epithelial cell differentiation.

Mutations in CFTR lead to dysfunction of tubular organs, which is currently attributed to impairment of its conductive properties. We now show that CFTR regulates tight junction assembly and epithelial cell differentiation through modulation of the ZO-1–ZONAB pathway. CFTR colocalizes with ZO-1 at the tight junctions of trachea and epididymis, and is expressed before ZO-1 in Wolffian ducts. CFTR interacts with ZO-1 through the CTFR PDZ-binding domain. In a three-dimensional (3D) epithelial cell culture model, CFTR regulates tight junction assembly and is required for tubulogenesis. CFTR inhibition or knockdown reduces ZO-1 expression and induces the translocation of the transcription factor ZONAB (also known as YBX3) from tight junctions to the nucleus, followed by upregulation of the transcription of CCND1 and downregulation of ErbB2 transcription. The epididymal tubules of cftr^−/− and cftr^ΔF508 mice have reduced ZO-1 levels, increased ZONAB nuclear expression, and decreased epithelial cell differentiation, illustrated by the reduced expression of apical AQP9 and V-ATPase. This study provides a new paradigm for the etiology of diseases associated with CFTR mutations, including cystic fibrosis.

The initial segment (IS) in rodents is functionally and structurally distinct from other epididymal segments and plays an important role in sperm mat

Summary Sentence. This study shows the equal contribution of clear and principal cells to proton secretion, and the dual role of principal cells in bicarbonate

A subset of basal cells (BCs) in the initial segment (IS) of the mouse epididymis has a slender body projection between adjacent epithelial cells. We