The rete testis in man: ultrastructural aspects

ARL13B controls male reproductive tract physiology through primary and Motile Cilia

ARL13B is a small regulatory GTPase that controls ciliary membrane composition in both motile cilia and non-motile primary cilia. In this study, we investigated the role of ARL13B in the efferent ductules, tubules of the male reproductive tract essential to male fertility in which primary and motile cilia co-exist. We used a genetically engineered mouse model to delete Arl13b in efferent ductule epithelial cells, resulting in compromised primary and motile cilia architecture and functions. This deletion led to disturbances in reabsorptive/secretory processes and triggered an inflammatory response. The observed male reproductive phenotype showed significant variability linked to partial infertility, highlighting the importance of ARL13B in maintaining a proper physiological balance in these small ducts. These results emphasize the dual role of both motile and primary cilia functions in regulating efferent duct homeostasis, offering deeper insights into how cilia related diseases affect the male reproductive system.

Anatomy, Endocrine Regulation, and Embryonic Development of the Rete Testis

Reproduction in males requires the transfer of spermatozoa from testis tubules via the rete system to the efferent ductules, epididymis, and vas deferens. The rete therefore forms an essential bridging system between the testis and excurrent ducts. Yet the embryonic origin and molecular regulation of rete testis development is poorly understood. This review examines the anatomy, endocrine control, and development of the mammalian rete testis, focusing on recent findings on its molecular regulation, identifying gaps in our knowledge, and identifying areas for future research. The rete testis develops in close association with Sertoli cells of the seminiferous cords, although unique molecular markers are sparce. Most recently, modern molecular approaches such as global RNA-seq have revealed the transcriptional signature of rete cell precursors, pointing to at least a partial common origin with Sertoli cells. In the mouse, genes involved in Sertoli cell development or maintenance, such as Sox9, Wt1, Sf1, and Dmrt1, are also expressed in cells of the rete system. Rete progenitor cells also express unique markers, such as Pax8, E-cadherin, and keratin 8. These must directly or indirectly regulate the physical joining of testis tubules to the efferent duct system and confer other physiological functions of the rete. The application of technologies such as single-cell RNA-seq will clarify the origin and developmental trajectory of this essential component of the male reproductive tract.

Primary cilia: biosensors of the male reproductive tract

BACKGROUND

The primary cilium is a microtubule-based organelle that extends transiently from the apical cell surface to act as a sensory antenna. Initially viewed as a cellular appendage of obscure significance, the primary cilium is now acknowledged as a key coordinator of signaling pathways during development and in tissue homeostasis.

OBJECTIVES

The aim of this review was to present the structure and function of this overlooked organelle,with an emphasis on its epididymal context and contribution to male infertility issues.

MATERIALS AND METHODS

A systematic review has been performed in order to include main references relevant to the aforementioned topic.

RESULTS

Increasing evidence demonstrates that primary cilia dysfunctions are associated with impaired male reproductive system development and male infertility issues.

DISCUSSION

While a large amount of data exists regarding the role of primary cilia in most organs and tissues, few studies investigated the contribution of these organelles to male reproductive tract development and homeostasis.

CONCLUSION

Functional studies of primary cilia constitute an emergent and exciting new area in reproductive biology research.

Morphology and Innervation Pattern of the Feline Urogenital Junction

The feline urogenital junction is situated between the extratesticular rete and the spacious initial segments of the efferent ductules. The rete epithelium is cuboidal to low columnar. The rete cells forming the junction rest on a wavy basal lamina, display deep mutual invaginations, possess central nuclei with several infoldings and form a distinct border with the columnar epithelial cells of the initial segments of the ductuli efferentes. The epithelium of the initial segments is composed of ciliated cells and non-ciliated principal cells. The latter are the dominating type and characterized by an apical brush-border and a supranuclear endocytotic apparatus. The stroma of the extratesticular rete contains an abundance of collagen whereas contractile cells are here generally absent. In contrast, the initial segments of the efferent ductules are surrounded by elastic fibres and a layer of contractile cells. All nerves for the feline urogenital junction come from the nervus spermaticus superior. In the epididymal head, small nerve bundles deviate into the septa between the ductules. Single fibres establish a dense network within the muscular coat of the ductuli. At the transition to the extratesticular rete, this network ends abruptly. Nerve fibres in the confines of the rete are associated with blood vessels or proceed to the testicular interior, but establish no relationships with the rete epithelium or the myofibroblasts of the mediastinum. The nervous network in the walls of the efferent ductules and their initial segments is not only composed of sympathetic but also parasympathetic, non-myelinated fibres. Particularly noteworthy is the abundance of calcitonin gene-related peptide (CGRP)- and substance P (SP)-containing axons around the initial segments. Both neuroproteins are consistent markers for sensory neurones. Taken together, it can be assumed that the entry of seminal fluid and spermatozoa into the efferent ductules is controlled by a regulatory nervous chain provided with afferent and efferent components.

Rete testis mucinous adenocarcinoma in a dog

A bilateral testicular neoplasm from an 11-year-old mixed-breed male dog was removed surgically and examined histologically. The neoplasm was nonencapsulated and composed of acinar and tubular structures lined by one or more layers of neoplastic polyhedral epithelial cells with an abundant mucinous secretion. On histochemistry, all neoplastic cells and associated secretions were periodic acid-Schiff positive. Some neoplastic cells and all associated secretions were positive on mucicarmine stain, and some neoplastic cells, all the stroma, and associated secretions were positive on alcian blue stain. On immunohistochemistry, the neoplastic cells had strong diffuse cytoplasmic immunoreactivity for cytokeratin and vimentin, weak scattered cytoplasmic immunoreactivity for carcinoembryonic antigen and neuron-specific enolase, and no immunoreactivity for S-100. On the basis of histopathology, histochemistry, and immunohistochemical findings, a diagnosis of mucinous adenocarcinoma of rete testis was made. Rete testis adenocarcinoma is a well known but very rare neoplasm in humans. To our knowledge, this is the first report of the mucinous variant of adenocarcinoma of the rete testis in a dog.

Pictorial review: ultrasound appearances of the rete testis

The rete testis is formed in the fifth week of intra-uterine life. The epithelium along the medial side of the mesonephric ridge thickens to form a genital ridge; cellular gonadal cords at the periphery of the ridge unite with a tubular network from the mesonephric mesenchyme forming the testicular rete. On ultrasound, a range of normal appearances of the rete testis is recognised from ill-defined areas of decreased reflectivity to a coarse tubular appearance (often with finger like projections). In the present review the embryological development of the rete testis is briefly outlined. In addition, the important anatomical variations, pertinent to ultrasound imaging, will be presented.

Sertoli-stromal cell tumor of the ovary: immunohistochemical, ultrastructural, and genetic studies

The Sertoli-stromal cell tumor (SSCT) of the ovary shows a histologic resemblance to developing or adult testes and is often associated with virilization caused by tumor-produced androgenic hormone. In spite of the unique manifestation of SSCT, detailed characteristics of this tumor are still obscure. The mechanism by which SSCT occurs has not yet been determined. Six SSCTs were studied immunohistochemically, ultrastructurally, and by polymerase chain reaction (PCR) for the presence of sex-determining region Y (SRY) gene and the X chromosome activation state. Immunohistochemically, Sertoli-like cells of SSCT were positive not only for alpha-inhibin but also low-molecular-weight cytokeratin. In control testes, the expression of alpha-inhibin and cytokeratin was limited to a Sertoli cell component and rete testis, respectively. Ultrastructurally, tumor cells composing hollow tubules had an elongated nucleus with deep indentation and annulate lamellae, which are characteristic structures of mature Sertoli cells. In addition, they had studded microvilli on the apical surface and frequent desmosomes, which are structures noted in the cells of rete testis. Histologically, tumor cells of hollow tubules sometimes pouted into the lumen, as did the cells of tubulae rete, entrance into rete testis from seminiferous tubules. All of these findings indicate that some tumor cells of a SSCT show simultaneous differentiation into both Sertoli cells and cells of rete testis. SRY gene was not detected in any cases, and the X chromosome activation pattern was the same as that of the female control.

Overview of male reproductive pathology

An understanding of form and function is important for examination of the male reproductive tract. A basic understanding of spermatogenesis and hormonal function in the reproductive tract is essential for the pathologists in this evaluation. Gross and histologic reproductive changes need to be distinguished from normal variation and correlated with the reproductive status of the animal. This is especially important when correlating histologic changes with organ weight and other reproductive parameters, such as seminal analysis data. Sexual maturity of animals and tissue handing can impact interpretation. Sexual immaturity of preclinical safety animals can present challenges for accurate identification of compound-related changes. Likewise, proper handling of unfixed reproductive tissues and appropriate selection of a fixation protocol are important in avoiding artifacts that may interfere with the microscopic evaluation. The histopathology technician needs to recognize testicular landmarks that allow for correct orientation at trimming so the pathologist can assess not only the morphology of seminiferous tubules but also the outflow tract. For the most effective evaluation of the male reproductive tract, the testes and epididymides should be examined concurrently. Although the term "staging" is often used inappropriately, the pathologist should review testicular tissues in a "stage-aware" manner. This article reviews gross and histologic changes of the male reproductive tract as well as tissue orientation and fixation to assist in accurate interpretation of potential treatment-related changes in male reproduction.

Distribution of keratins, vimentin, and actin in the testis of two South American camelids: vicuna (Vicugna vicugna) and llama (Lama glama). An immunohistochemical study

The purpose of the present study was to investigate the pattern of distribution of cytokeratins, vimentin and muscular actin in the testis of vicuna (Vicugna vicugna) and llama (Lama glama) two species of camelids native of the Andean high plateau of South America. Testicular biopsies of four vicunas and five llamas were used. Animals were healthy breeders. The tissues were processed by standard immunohistochemistry with antipancytokeratinAE1/AE3, antikeratin 18 (K 18), CAM 5.2 (antikeratin 5, 18, and 19), antivimentin, and smooth-muscle-specific antiactin antibodies to track the cytoskeletal pattern of testicular cells. Using AE1/AE3 antibody the immunostaining was found in the epithelial lining of tubuli recti and rete testis. The reaction was relatively stronger in the apical cytoplasm of epithelial cells. The testicular cells of the two species showed no reaction to K 18 and CAM 5.2 antibodies. Antivimentin antibody stained the basal cytoplasm of the Sertoli cells, the Leydig cells, and the epithelial lining of tubuli recti and rete testis. In the last two structures the immunostain was relatively more intense in the basal cytoplasm of epithelial cells. Antiactin antibody stained the peritubular cells and the muscle cells of the lamina propria oftubuli recti and rete testis. The presence in these species of only some keratins found in man, its coexpression with vimentin in epithelial lining of tubuli recti and rete testis and the peritubule organization, so different from other ungulates may reflect a differential adaptation of the cytoskeleton to particular reproductive strategies.

Adenocarcinoma of the rete testis

To date, no studies have evaluated adenocarcinoma of the rete testis statistically, because reports have been limited to single cases or series of 2 cases only. Univariate and multivariate analyses on disease-free survival have been performed after combining all data available in the literature with our own. Information about disease-free survival has been collected in 38 patients. As many as 40% of them died within the first year of diagnosis. Three and 5-year disease-free survival was 49% and 13%, respectively. We have not detected any difference in survival between age groups or side of the lesion. Similarly, statistical difference cannot be proved between survival of tumors with nodular infiltrating or cystic growth pattern, although it has been suggested that these two varieties represent different tumor types from a gross and microscopic morphologic point of view. Univariate analysis reveals that tumor stage, tumor size, and therapy may have an influence on survival. Tumors that are organ-confined and small lesions (testicular mass < 5 cm in maximum diameter) behave definitely better than those disseminated at diagnosis or of a bigger size. Surprisingly, tumor size is not associated with tumor stage or histologic growth pattern (nodular infiltrating versus predominantly cystic). With regard to therapy, cases in which RPLND has been performed as part of the therapy behave better in univariate analysis, while patients who receive radiation do worse. Most probably these facts reflect that patients with clearly advanced disease where local control cannot be achieved by surgery tend to undergo palliative treatment by radiation. On the other hand, RPLND tends to be performed in patients in whom there is no evidence of distant spread. Therefore, it would really be the primary stage that would set the prognosis rather than the consequent treatment, and neither radiation therapy nor RPLND would be true independent variables. Similarly, no significant difference is observed when patients receive chemotherapy. Cox's regression analysis reveals size of the testicular tumor as the only independent predictor of survival. Stage at diagnosis does not have an influence by itself and neither does any form of therapy. In this sense, the negative effect of radiotherapy is eliminated. We are aware that the results drawn from a literature review are far from ideal, but there is not enough evidence to suggest an optimal sequence of treatment for this rare malignancy. To date, no effective chemotherapy has been found. Whenever the tumor is resectable, there appears to be merit in an RPLND.(ABSTRACT TRUNCATED AT 400 WORDS)

Pathology of osseous and genitourinary lesions of Proteus syndrome

A male patient followed from the age of 3 to 25 years was eventually diagnosed as having Proteus syndrome. He was born with linear epidermal nevi of the neck and forearm and presented with macrodactyly of the right hand and progressive hemihypertrophy of the right lower limb recurring after multiple reduction operations. The bone ends showed disorderly overgrowth of hyaline and fibrocartilage mixed with collagen and bone, and early differential diagnoses included Ollier's disease. The child also had vertebral anomalies, scoliosis, a bony protrusion of the cranial vertex, and strabismus. In the second decade he developed gyriform swelling of the soles, retinopathy, bilateral papillary cysts of the epididymis, and a giant cyst of the left kidney with complex glandular foci. At 22 years a 3-cm meningioma containing adipose tissue was resected, and at 24 years a 3-cm cellular nodule of the rete testis with hyperchromatic foci, probably an adenoma, was removed. The features of Proteus syndrome were those of hyperplasia and neoplasia of mostly mesodermal tissues. Unlike other reported cases, overgrowth of a finger recurred at 25 years.

Ultrastructure of the rete testis in the cat (Felis domestica, L.)

The rete testis (RT) in the cat comprises three distinct and sequential parts: septal or adlobular; mediastinal and tunical parts. This last part is followed by the small extratesticular rete testis. The whole of the RT tubules and/or channels is lined by single low columnar and/or cuboidal epithelium with ultrastructural peculiarities of secretory and absorptive functions. The Golgi apparatus polarity (cis-trans surfaces), its relation with the long profiles of the ER, mainly with the rough ER, and presence of apical uncoated electrodense granules are suggestive of active release of macromolecules, probably glycoproteins. The absorptive function is proposed through the observation of a conspicuous microvacuolar-vesicular apical complex in epithelial cells. Moreover spermatozoa phagocytosis is also noticed, mainly in the septal part of the RT.

Composition of fluids obtained from human epididymal cysts

The fluid composition of five epididymal spermatocoeles, one epididymal cyst and a hydrocoele was examined. The fluid obtained from the spermatocoeles was a dilute suspension of mainly immotile spermatozoa. The sperm-free fluid contained less protein, phosphate, glucose, triglyceride and cholesterol than serum but more testosterone and chloride than peripheral blood. It contained no epididymal secretion products. Proteins in the fluid differed from those in serum. From the fluid composition these cysts appeared to be continuous with the rete testis, either dilatations of efferent ducts or Haller's superior aberrant duct (vas aberrans of the rete testis). Fluid from an epididymal cyst containing no spermatozoa was mainly of similar composition. In contrast, hydrocoele fluid resembles blood serum.

Reexamination of the morphology of the extratesticular rete and ductuli efferentes in the goat

The morphology of the extratesticular rete and ductuli efferentes was reexamined in serial cross sections collected from the entire mass of the efferent ductules and in longitudinal sections collected from the partially unraveled efferent ductules. The extratesticular rete forms a 3-4-mm-long sac-like dilatation, which, within the head of the epididymis, has a wide lumen (up to 4 mm) and gives off along its length numerous evaginations, which, in turn, make connections with the ductuli efferentes. The latter is a mass of 16-18 ductules lined by three types of nonciliated cells: type II cells are characterized by dense, periodic acid-Schiff (PAS)-positive granules; type III cells are characterized by empty-appearing, PAS-negative vacuoles; and type I cells lack both granules and vacuoles. The distribution of the three types of nonciliated cells varies along the length. Whereas only type I cells are present in the beginning portion of the efferent ductule, type II cells predominate in the middle portion and type III cells in the distal portion (near the epididymis). The transition from one cell type to the other type is gradual; thus there are short segments along the length that share characteristics first for type I and type II cells and then for type II and type III cells. These results demonstrate that different nonciliated cell types are not randomly distributed in the epithelium of the ductuli efferentes but, instead, gradually differentiate from type I to type II to type III cells along the length of each efferent ductule. Factors controlling this differentiation remain to be studied.

Acquired cystic transformation of the rete testis secondary to renal failure

The histologic study of testicular specimens from 218 consecutive autopsies revealed a cystic transformation of the rete testis in 26 men. Serial sections of the testes, epididymides, and spermatic cords of these men were studied by light microscopy. In 15 cases, the rete testis dilation was caused by obstruction of the epididymis. In five cases, the dilation was due to obstruction of the intratesticular excretory ducts caused by varicocele. In the remaining six men, no evidence of obstructive processes was found. These six patients had been diagnosed with renal failure and underwent hemodialysis. The rete testis in these men showed dilated channels lined by a high columnar or pseudostratified epithelium. They contained spermatozoa, with a proteinaceous material and calcium oxalate crystals. The ductuli efferents showed eosinophilic granules in their epithelial cells and their lumen contained spermatids, spermatozoa, cell remnants, calcium oxalate crystals, and multinucleate giant cells. These rete testis lesions are similar to those previously reported in the kidney of hemodialyzed patients.

Adenocarcinoma of the rete testis with a spindle cell component. A possible metaplastic carcinoma

A case of adenocarcinoma of the rete testis was encountered in a 36-year-old white man. The tumor fulfilled established criteria for determining origin in the rete and showed an unusual biphasic morphology with papillary adenocarcinoma mixed with a prominent component of cytologically malignant spindle cells. Immunohistochemical study demonstrated a positive reaction in the epithelium for cytokeratin and epithelial membrane antigen, and the cytoplasm of a few of the spindle cells also reacted with these antibodies. Electron microscopic study confirmed the biphasic pattern, showing epithelial gland formation and mesenchymal cells. The results indicate that this tumor is a metaplastic carcinoma of the rete testis. Recognition of this pattern of rete carcinoma may further enhance our knowledge of primary tumors at this unusual site.

Nodular proliferation of calcifying connective tissue in the rete testis: a study of three cases

We report the first description of a bilateral rete testis lesion. The lesion was found in three adult men with histories of myocardium infarct or hemorrhage. The histologic study of the rete testis in these men revealed nodular sessile or pediculate formations which protruded into the rete testis channels. These polypoid formations consisted of an axis of connective tissue covered by a flattened epithelium. The axis contained a variable number of fibroblasts, areas with fibrin-like material, and small to large calcium deposits. Inflammatory infiltrates were neither observed in the rete testis nor in the testicular parenchyma. The testicular pattern varied from seminiferous tubules with complete spermatogenesis (two cases) to tubules with Sertoli cells and a few spermatogonia, surrounded by a thickened tunica propia. The term "nodular proliferation of calcifying connective tissue in the rete testis" is proposed to designate this lesion.

Spatial topography of the excurrent duct system in the bovine testis

The rete testis of the bull is situated within an axial mediastinum and consists of approximately 30 longitudinally arranged, anastomosing rete channels. At the cranial testicular pole all rete channels empty into a common space, the area confluens retis, which is subdivided by small septa and narrow chordae retis. The area confluens always contains numerous spermatozoa and is connected with the bulbous initial portions of the efferent ductules by short, often tortuous rete tubules. Since the connection between rete and efferent ductules is situated within the tunica albuginea, the bovine excurrent duct system is not provided with an extratesticular rete as in many other mammals. Straight testicular tubules merge from all directions to connect with superficial rete channels, but the inlets are not evenly distributed. In the periphery each straight tubule begins with a cup-like structure followed by a narrow stalk region and a heavily folded portion opening either immediately into a rete channel or into a tube-like lateral rete extension. In close contiguity to the rete testis lie extremely coiled arterial portions connecting the centripetal and the centrifugal branches of the testicular artery. Since intrinsic musculature is scarcely developed in the mediastinum, and transport of rete content relies primarily on massage due to external pressure changes, the pulsatile blood flow through these coiled arteries may influence conveyance processes within the rete testis. An intimate spatial association between area confluens retis and adjacent large, thin-walled lymph vessels may facilitate a transfer of androgens into the fluid of the rete testis.

Testicular and epididymal involvement in Fabry's disease

Autopsy specimens of the testes and epididymis of a 32-year-old male with Fabry's disease were studied by light and electron microscopy. The characteristic ceramide deposits (lamellar inclusions, myeloid-bodies, zebra-bodies) were found in the Leydig cells as well as in the epithelial lining of both the ductuli efferentes and the ductus of the epididymis. Similar myeloid-bodies were observed in the blood vessels, connective tissue cells and muscle cells of the testicular interstitium, tunica albuginea and epididymis. In contrast, myeloid-bodies were absent or scarce in both the seminiferous epithelium and the mediastinum testis. However, the seminiferous tubules were severely affected showing reduced diameter, thickening of the tunica propria, and a few degenerated spermatogonia and primary spermatocytes. The different degrees of involvement of the testicular structures might be related to their different functions, the absorptive and permeable structures being the most severely affected. The development of testicular alterations seems to have been slow, since the patient fathered three children.

Gynandroblastoma: its ultrastructure

Gynandroblastoma is a rare, sex-cord stromal tumor of the ovary that shows morphologic evidence of female and male differentiation. Such a tumor produced masculinization in a 24-year-old woman, whose symptoms disappeared following removal of the tumor. By electron microscopy, the granulosa cell nests displayed Call-Exner (CE) bodies of the hyaline type composed of multiple layers of basal lamina resembling CE bodies of the normal graafian follicle. In contrast, CE bodies of a classic granulosa theca cell tumor were of the spongiform type, consisting of a space limited by a single basal lamina containing altered granulosa cells and cell processes. Both types of CE bodies are believed to arise following secretion by and/or degeneration of granulosa cells, the variation in morphology between the two resulting from differences in amounts of basal lamina deposited. The tubular components of the tumor resembled more closely the rete ovarii than did Sertoli cells, and its proposed that such structures be called by the alternate and less specific term "androblastoma." The identity of Leydig cells was established by demonstrated of intracytoplasmic Reinke crystals. Despite a difference in architectural pattern, there was a close ultrastructural resemblance between the different sex-cord components of the gynandroblastoma.

Ultrastructural study of a female adnexal tumor of probable wolffian origin

A broad-ligament tumor, of probable wolffian origin, is presented. The ultrastructural features of this histologically benign tumor have not been previously described. The fine structure of this tumor is compared with normal structures and tumors derived from wolffian and müllerian anlage. The findings are consistent with derivation from wolffian duct.

The mammalian tubuli recti: ultrastructural study

The ultrastructure of the tubuli recti was studied in the testes of sexually mature bulls, boars, rams, goats, rabbits and rats fixed by vascular perfusion. The tubuli recti are lined with a simple epithelium that varies in height, from squamous to tall columnar according to the species and the region. The cells are characterized by extensive lateral and tortuous basal plasma membranes and a luminal border with microvilli. Tight junctions and desmosomes are found in the upper half of the lateral borders. The Golgi apparatus is sizable and associated with it are coated vesicles and many smooth vesicles concentrated towards the luminal border. A distal segment of the tubuli recti is found in bulls only and is characterized by a high epithelium which is thrown into folds giving the lumen a festooned appearance. It is suggested that the epithelial cells of the tubuli recti are involved in fluid exchange and in the removal of unwanted spermatozoa.

Spermatophagy in the seminiferous tubules and excurrent ducts of the testis in Rhesus monkey and in man

The fine structure of cells capable of phagocytosing spermatozoa in the testes and epididymes of monkeys and men was studied by means of transmission and scanning electron microscopy. Both resident cells, such as Sertoli cells and epithelia of the rete testis, and free cells, such as macrophages (spermatophages) were found to phagocytose spermatozoa or fragments of spermatozoa in the seminiferous tubules and excurrent ducts. The spermatophages develop from precursor cells which invade the seminiferous tubules. After phagocytosis of spermatozoa they increase in size and sometimes possess more than one nucleus. Large spherically shaped spermatophages are found in the epididymis. In the rete spaces of Macaca fascicularis spermatophages are able to penetrate the rete epithelia and reside in the subepithelial connective tissue layers. Spermatophagy is frequently seen in the gonads of older men and in certain cases of oligozoospermia. In Macaca an increased number of spermatophages occurs at the end of the spermatogenetic season.