Is the Epididymis a Series of Organs Placed Side By Side?

Abstract

The mammalian epididymis is more than a highly convoluted tube divided into four regions: initial segment, caput, corpus and cauda. It is a highly segmented structure with each segment expressing its own and overlapping genes, proteins, and signal transduction pathways. Therefore, the epididymis may be viewed as a series of organs placed side by side. In this review we discuss the contributions of septa that divide the epididymis into segments and present hypotheses as to the mechanism by which septa form. The mechanisms of Wolffian duct segmentation are likened to the mechanisms of segmentation of the renal nephron and somites. The renal nephron may provide valuable clues as to how the Wolffian duct is patterned during development, whereas somitogenesis may provide clues as to the timing of the development of each segment. Emphasis is also placed upon how segments are differentially regulated, in support of the idea that the epididymis can be considered a series of multiple organs placed side by side. One region in particular, the initial segment, which consists of 2 or 4 segments in mice and rats, respectively, is unique with respect to its regulation and vascularity compared to other segments; loss of development of these segments leads to male infertility. Different ways of thinking about how the epididymis functions may provide new directions and ideas as to how sperm maturation takes place.

An atlas of cell types in the mammalian epididymis and vas deferens

“…For example, within the caput epididymis, principal cells from segments 1-2 ( Lcn2 , Cst11 ) could be distinguished from cells from segments 3-4 ( Defb15 ), while corpus principal cells were similarly separated into Lcn5 / Rnase9 -positive cells corresponding to segments 5-6, and Npy -positive cells corresponding to segment 7 ( Figures 3D-E ). This is consistent with prior functional and molecular studies of epididymal segmentation, and supports the notion that the anatomical segmentation of the epididymis generates multiple discrete microenvironments experienced by sperm during post-testicular maturation (Domeniconi et al, 2016).…”

“…The organ responsible for this ever-expanding diversity of functions is a long tube on the order of 1-10 meters long when extended, depending on the species – of pseudo-stratified epithelium. The functions of the epididymis differ extensively along its length (Domeniconi et al, 2016; Turner et al, 2003), as for example many genes such as Rnase10 and Lcn8 are expressed almost exclusively in the proximal epididymis, most notably including the testis-adjacent section of the caput epididymis known as the “initial segment” (Hsia and Cornwall, 2004; Jelinsky et al, 2007; Jervis and Robaire, 2001; Johnston et al, 2005; Turner et al, 2003). Connective tissue septa separate the mouse epididymis into ten anatomically-defined segments (this number varies in other mammals) (Turner et al, 2003), with early microarray studies revealing a wide variety of gene expression profiles across these ten segments, and defining roughly six distinct gene expression domains across the epididymis (Johnston et al, 2005).…”

Spatiotemporal expression patterns of natriuretic peptides in rat testis and epididymis during postnatal development

“…The epididymis is a highly convoluted duct composed of structurally four different regions: initial segment, caput epididymis, corpus epididymis and cauda epididymis (Domeniconi, Souza, Xu, Washington, & Hinton, ). The epididymis supports male fertility by ensuring spermatozoa maturation (Cornwall, ).…”

“…Nielsen et al () reported that NPPC is expressed in the epididymal epithelium. Since region‐specific differences exist in the cellular activities of the epididymal epithelium, each segment seems to harbour unique and common regulators that are involved in gene and protein expression and signalling events (Domeniconi et al, ). In this respect, the expression of NPPA, NPPB and NPPC in the epididymis has not been studied in a region‐dependent manner.…”

Cell-lineage specificity of primary cilia during epididymis post-natal development

“…The epididymis is a highly segmented tubule with each segment displaying distinct features in terms of cell populations, cell composition and cell functions [51]. We investigated the properties of basal cell primary cilia throughout the different segments of the epididymis from Arl13b-Cetn2 tg mice ( i.e.…”