In situ histochemical analysis of region-specific gene expression in the adult rat epididymis

A New Gene SCY3 Homologous to Scygonadin Showing Antibacterial Activity and a Potential Role in the Sperm Acrosome Reaction of Scylla paramamosain

In the study, a new gene homologous to the known antimicrobial peptide Scygonadin was identified in mud crab Scylla paramamosain and named SCY3. The full-length sequences of cDNA and genomic DNA were determined. Similar to Scygonadin, SCY3 was dominantly expressed in the ejaculatory ducts of male crab and the spermatheca of post-mating females at mating. The mRNA expression was significantly up-regulated after stimulation by Vibrio alginolyticus, but not by Staphylococcus aureus. The recombinant protein rSCY3 had a killing effect on Micrococcus luteus and could improve the survival rate of mud crabs infected with V. alginolyticus. Further analysis showed that rSCY3 interacted with rSCY1 or rSCY2 using Surface Plasmon Resonance (SPR, a technology for detecting interactions between biomolecules using biosensor chips) and Mammalian Two-Hybrid (M2H, a way of detecting interactions between proteins in vivo). Moreover, the rSCY3 could significantly improve the sperm acrosome reaction (AR) of S. paramamosain and the results demonstrated that the binding of rSCY3, rSCY4, and rSCY5 to progesterone was a potential factor affecting the sperm AR by SCYs on. This study lays the foundation for further investigation on the molecular mechanism of SCYs involved in both immunity and physiological effects of S. paramamosain.

Analysis of Epididymal Protein Synthesis and Secretion

The mammalian epididymis generates one of the most complex intraluminal fluids of any endocrine gland in order to support the post-testicular maturation and storage of spermatozoa. Such complexity arises due to the combined secretory and absorptive activity of the lining epithelial cells. Here, we describe the techniques for the analysis of epididymal protein synthesis and secretion by focusing on the model protein family of dynamin (DNM) mechanoenzymes; large GTPases that have the potential to regulate bi-directional membrane trafficking events. For the study of protein expression in epididymal tissue, we describe robust methodology for immunofluorescence labeling of target proteins in paraffin-embedded sections and the subsequent detection of the spatial distribution of these proteins via immunofluorescence microscopy. We also describe optimized methodology for the isolation and characterization of exosome like vesicles, known as epididymosomes, which are secreted into the epididymal lumen to participate in intercellular communication with maturing sperm cells. As a complementary approach, we also describe the immunofluorescence detection of target proteins in an SV40-immortalized mouse caput epididymal epithelial (mECap18) cell line. Moreover, we discuss the utility of the mECap18 cell line as a suitable in vitro model with which to explore the regulation of epididymal secretory activity. For this purpose, we describe the culturing requirements for the maintenance of the mECap18 cell line and the use of selective pharmacological inhibition regimens that are capable of influencing their secretory protein profile. The latter are readily assessed via harvesting of conditioned culture medium, concentration of secreted proteins via trichloroacetic acid/acetone precipitation and their subsequent analysis via SDS-PAGE and immunoblotting. We contend that these combined methods are suitable for the analysis of alternative epididymal protein targets as a prelude to determining their functional role in sperm maturation and/or storage.

Characteristics of the Epididymal Luminal Environment Responsible for Sperm Maturation and Storage

The testicular spermatozoa of all mammalian species are considered functionally immature owing to their inability to swim in a progressive manner and engage in productive interactions with the cumulus-oocyte complex. The ability to express these key functional attributes develops progressively during the cells' descent through the epididymis, a highly specialized ductal system that forms an integral part of the male reproductive tract. The functional maturation of the spermatozoon is achieved via continuous interactions with the epididymal luminal microenvironment and remarkably, occurs in the complete absence of de novo gene transcription or protein translation. Compositional analysis of the luminal fluids collected from the epididymis of a variety of species has revealed the complexity of this milieu, with a diversity of inorganic ions, proteins, and small non-coding RNA transcripts having been identified to date. Notably, both the quantitative and qualitative profile of each of these different luminal elements display substantial segment-to-segment variation, which in turn contribute to the regionalized functionality of this long tubule. Thus, spermatozoa acquire functional maturity in the proximal segments before being stored in a quiescent state in the distal segment in preparation for ejaculation. Such marked division of labor is achieved via the combined secretory and absorptive activity of the epithelial cells lining each segment. Here, we review our current understanding of the molecular mechanisms that exert influence over the unique intraluminal environment of the epididymis, with a particular focus on vesicle-dependent mechanisms that facilitate intercellular communication between the epididymal soma and maturing sperm cell population.

Estrogen receptors and function in the male reproductive system

A substantial advance in our understanding on the estrogen signaling occurred in the last decade. Estrogens interact with two receptors, ESR1 and ESR2, also known as ERα and ERβ, respectively. ESR1 and ESR2 belong to the nuclear receptor family of transcription factors. In addition to the well established transcriptional effects, estrogens can mediate rapid signaling, triggered within seconds or minutes. These rapid effects can be mediated by ESRs or the G protein-coupled estrogen receptor GPER, also known as GPR30. The effects of estrogen on cell proliferation, differentiation and apoptosis are often mediated by growth factors. The understanding of the cross-talk between androgen, estrogen and growth factors signaling pathways is therefore essential to understand the physiopathological mechanisms of estrogen action. In this review we focused on recent discoveries about the nature of the estrogen receptors, and on the signaling and function of estrogen in the male reproductive system.

The CAP superfamily: cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins--roles in reproduction, cancer, and immune defense

The cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins (CAP) superfamily members are found in a remarkable range of organisms spanning each of the animal kingdoms. Within humans and mice, there are 31 and 33 individual family members, respectively, and although many are poorly characterized, the majority show a notable expression bias to the reproductive tract and immune tissues or are deregulated in cancers. CAP superfamily proteins are most often secreted and have an extracellular endocrine or paracrine function and are involved in processes including the regulation of extracellular matrix and branching morphogenesis, potentially as either proteases or protease inhibitors; in ion channel regulation in fertility; as tumor suppressor or prooncogenic genes in tissues including the prostate; and in cell-cell adhesion during fertilization. This review describes mammalian CAP superfamily gene expression profiles, phylogenetic relationships, protein structural properties, and biological functions, and it draws into focus their potential role in health and disease. The nine subfamilies of the mammalian CAP superfamily include: the human glioma pathogenesis-related 1 (GLIPR1), Golgi associated pathogenesis related-1 (GAPR1) proteins, peptidase inhibitor 15 (PI15), peptidase inhibitor 16 (PI16), cysteine-rich secretory proteins (CRISPs), CRISP LCCL domain containing 1 (CRISPLD1), CRISP LCCL domain containing 2 (CRISPLD2), mannose receptor like and the R3H domain containing like proteins. We conclude that overall protein structural conservation within the CAP superfamily results in fundamentally similar functions for the CAP domain in all members, yet the diversity outside of this core region dramatically alters target specificity and, therefore, the biological consequences.

The Rat Epididymal Transcriptome: Comparison of Segmental Gene Expression in the Rat and Mouse Epididymides1

Regional differences along the epididymis are essential for the establishment of the luminal environment required for sperm maturation. In the current study, 19 morphologically distinct segments of the rat epididymis were identified by microdissection. Total RNA was isolated from each segment and subjected to microarray analysis. Segmental analysis of epididymal gene expression identified more than 16,000 expressed qualifiers, whereas profiling of RNA from whole rat epididymis identified approximately 12,000 expressed qualifiers. Screening a panel of normal rat tissues identified both epididymal-selective and epididymal-specific transcripts. In addition, more than 3500 qualifiers were shown to be present and differentially upregulated or downregulated by more than fourfold between any two segments. The present study complements our previous segment-dependent analysis of gene expression in the mouse epididymis and allows for comparative analyses between datasets. A total of 492 genes was shown to be present on both the MOE430 (mouse) and RAE230_2 (rat) microarrays, expressed in the epididymis of both species, and differentially expressed by more than fourfold in between segments in each species. Moreover, in-depth quantitative RT-PCR analysis of 36 members of the beta defensin gene family showed highly conserved patterns of expression along the lengths of the mouse and rat epididymides. These analyses elucidate global gene expression patterns along the length of the rat epididymis and provide a novel evaluation of conserved and nonconserved gene expression patterns in the epididymides of the two species. Furthermore, these data provide a powerful resource for the research community for future studies of biological factors that mediate sperm maturation and storage.

Molecular evolution of epididymal lipocalin genes localized on mouse chromosome 2

We previously identified two murine secretory proteins, mE-RABP(Lcn5) and mEP17(Lcn8), belonging to the lipocalin family and specifically expressed in the epididymis. The genes are contiguous and localized on mouse chromosome 2. We now show that five other related lipocalin genes, Lcn9, Lcn10, Lcn11, Lcn12, and Lcn13, that evolved by in situ tandem duplication are present on the same locus. Lcn9, Lcn10, Lcn12, and Lcn13 genes, like Lcn5 and Lcn8 genes, are specifically expressed in the mouse epididymis. However, each gene has a distinct spatial expression within the epididymis and different regulation. Analysis of the human genome sequence shows the presence of genes encoding lipocalins with genomic organization, chromosomal arrangement, and orientation similar to that of the corresponding murine genes, indicating that the epididymal cluster is evolutionary conserved. A phylogenetic analysis of the new epididymal proteins reveals their spread position in the lipocalin protein family tree. This suggests the preservation of the regulatory sequences, while protein sequences have greatly diverged, reflecting functional diversity and possibly multifunctionality. In terms of the cluster ancestry, epididymal expression possibly appeared in a PGDS-like lipocalin in amniotes, and the duplications generating the cluster occurred at least in the common ancestor of rodents and primates. The presence and conservation of a cluster of five genes encoding epididymal lipocalins, differently regulated and regionalized in the epididymis, strongly suggests that these proteins may play an important role for male fertility.

Postnatal development and regulation of beta-hexosaminidase in epithelial cells of the rat epididymis

beta-Hexosaminidase (Hex) catalyzes the hydrolysis of terminal sugar residues from a number of substrates such as GM2 gangliosides, glycoproteins, glycolipids, and glycosaminoglycans. As an enzyme present in lysosomes of epithelial cells of the adult rat epididymis, it serves to degrade substances endocytosed from the epididymal lumen. In this way, it modifies and creates a luminal environment where sperm can undergo their maturational modifications. In this study, the postnatal developmental pattern of expression of Hex was examined in animals from days 7-56. In addition, the role of testicular factors on Hex expression in the different cell types and regions of the epididymis of adult rats was examined in orchidectomized and efferent duct-ligated rats. Both parameters were examined on Bouin-fixed epididymides in conjunction with light microscope immunocytochemistry. At postnatal day 7, the epithelium of the entire epididymis was unreactive for anti-Hex antibody. By day 21, narrow and clear cells of their respective regions became reactive, whereas basal cells became reactive only by day 29. Principal cells displayed only an occasional reactive lysosome at day 21, several by day 29, and numerous reactive lysosomes by day 39, comparable to the region-specific distribution noted for 90-day-old animals, and at an age when high androgen levels are attained. Thus, postnatal onset of Hex expression varies according to the different cell types of the epididymis, suggesting different regulatory factors. This finding was confirmed from studies employing adult orchidectomized and efferent duct-ligated adult rats. Indeed, in all experimental animals, Hex immunostaining in narrow, clear, and basal cells was intense and comparable to control animals. In contrast, there was a notable absence of lysosomal staining in principal cells at all time points after orchidectomy, which was restored, however, following testosterone replacement. No effect on Hex expression was observed in efferent duct-ligated animals. Taken together, the data suggest that Hex expression in lysosomes of principal cells is regulated by testosterone or one of its metabolites. However, the expression of Hex being independent of testicular factors in narrow, clear, and basal cells of adult animals, but occurring at different time points during postnatal development, suggests that different regulatory factors are responsible for onset of Hex expression in these cell types during development.

LCN6, a novel human epididymal lipocalin

BACKGROUND

The lipocalin (LCN) family of structurally conserved hydrophobic ligand binding proteins is represented in all major taxonomic groups from prokaryotes to primates. The importance of lipocalins in reproduction and the similarity to known epididymal lipocalins prompted us to characterize the novel human epididymal LCN6.

METHODS AND RESULTS

LCN6 cDNA was identified by database analysis in a comprehensive human library sequencing program. Macaca mulatta (rhesus monkey) cDNA was obtained from an epididymis cDNA library and is 93% homologous to the human. The gene is located on chromosome 9q34 adjacent LCN8 and LCN5. LCN6 amino acid sequence is most closely related to LCN5, but the LCN6 beta-barrel structure is best modeled on mouse major urinary protein 1, a pheromone binding protein. Northern blot analysis of RNAs isolated from 25 human tissues revealed predominant expression of a 1.0 kb mRNA in the epididymis. No other transcript was detected except for weak expression of a larger hybridizing mRNA in urinary bladder. Northern hybridization analysis of LCN6 mRNA expression in sham-operated, castrated and testosterone replaced rhesus monkeys suggests mRNA levels are little affected 6 days after castration. Immunohistochemical staining revealed that LCN6 protein is abundant in the caput epithelium and lumen. Immunofluorescent staining of human spermatozoa shows LCN6 located on the head and tail of spermatozoa with the highest concentration of LCN6 on the post-acrosomal region of the head, where it appeared aggregated into large patches.

CONCLUSIONS

LCN6 is a novel lipocalin closely related to Lcn5 and Lcn8 and these three genes are likely products of gene duplication events that predate rodent-primate divergence. Predominant expression in the epididymis and location on sperm surface are consistent with a role for LCN6 in male fertility.

Immunolocalization of the Yb1 subunit of glutathione S-transferase in the adult rat epididymis following orchidectomy and efferent duct ligation

In addition to the maturation of sperm, the epididymis also serves to protect sperm from harmful reactive oxygen species. To this end, various antioxidant enzymes are produced by the epididymis, such as glutathione S-transferases (GSTs), a family of dimeric proteins that catalyze the conjugation of glutathione to various electrophilic compounds, thus providing cellular detoxification. In the present study, the regulation of the Yb(1) subunit of GST was examined in Bouin-fixed epididymides of adult control, orchidectomized (O) rats with or without testosterone (T) supplementation and efferent duct-ligated (EDL) rats using light microscope immunocytochemistry with an anti-Yb(1)-GST antibody. The intensely reactive ciliated cells of the efferent ducts and principal cells of the epididymis showing a checkerboard staining pattern were unaltered in their expression of Yb(1)-GST after all experimental procedures, suggesting their regulation by factors other than of testicular origin. On the other hand, the intense reaction of narrow/apical cells and moderate reaction of basal cells of the proximal initial segment of control animals became negligible in O rats and was not restored with T supplementation. As staining was also absent after EDL, the data suggest that a luminal testicular factor(s), other than androgens, regulates expression of Yb(1)-GST in narrow/apical and basal cells of the proximal initial segment. Although basal cells of the caput and cauda epididymidis were unreactive after all experimental protocols, as also noted in controls, the intensely reactive basal cells of the corpus epididymidis of control animals became unreactive in O animals. However, Yb(1)-GST expression was restored to these cells with T supplementation, and as there was no effect on Yb(1)-GST expression after EDL, the data suggest that circulating testosterone or one of its metabolites regulates expression of Yb(1)-GST in basal cells of the corpus region. Taken together, these data indicate a differential regulation with respect to the expression of Yb(1)-GST in the various cell types and regions of the epididymis.

Regulation of sulfated glycoprotein-1 and cathepsin D expression in adult rat epididymis

Endocytosis, whereby proteins are internalized from the epididymal lumen to be eventually degraded in lysosomes, is one of the major functions of the epididymal epithelial cells in maintaining a proper luminal milieu conducive for sperm maturation. In the present study, using light microscope immunocytochemical methods, we examined the regulation of 2 lysosomal enzymes, sulfated glycoprotein-1 (SGP-1) and cathepsin D, in adult rat epididymides fixed in Bouin fixative and embedded in paraffin. After orchidectomy (O) with or without testosterone (T) supplementation, efferent duct ligation (EDL), or hypophysectomy (H), lysosomes of principal cells were intensely reactive with the anti-SGP-1 antibody, as were narrow, clear, and basal cells, with staining patterns similar to that of control animals. These experimental procedures also had no effect on cathepsin D expression in all cell types, except for clear cells of the corpus and cauda epididymidis, which after orchiedectomy and hypophysectomy, became intensely reactive, unlike their completely unreactive state in control animals. In O+T animals, as well as in EDL animals, clear cells remained unreactive. These data taken together suggest that expression of SGP-1 is not under the control of testicular or pituitary factors, as is also the case for cathepsin D expression by principal, narrow, and basal cells. However, specific inhibition of cathepsin D expression by testosterone or one of its metabolites appears to occur in clear cells of the corpus and cauda epididymidis. Furthermore, in addition to small, typical lysosomes, principal cells also revealed large supranuclear and infranuclear spherical structures that were immunoreactive with both anti-SGP-1 and anti-cathepsin D antibodies, suggesting their lysosomal nature. With electron microscopy, these structures appeared electron-lucent and contained membranous profiles embedded in an electron-dense, granular background. Such images suggest that the various experimental procedures adversely affect the expression of several other lysosomal enzymes in principal cells, leading to a lysosomal phenotype similar to that observed in various lysosomal storage diseases.

Cloning and characterization of the rat Crisp-1 gene

Rat androgen-regulated acidic epididymal glycoprotein (AEG), also known as Protein DE, is a product of the Crisp-1 gene. Protein DE is secreted into the epididymal lumen and binds to sperm heads during their transit through the epididymis. In experiments reported here, the rat Crisp-1 gene has been cloned and its structure determined. The rat Crisp-1 gene spans 38kb and contains nine exons encoding an 1120bp epididymal Protein DE mRNA. The boundaries of the protein-coding exons are structurally organized similar to the mouse Crisp-1 gene, except for the 5' untranslated sequence, which is encoded by one exon in the mouse Crisp-1 gene and two exons in the rat gene. All the introns are flanked by AG/GT consensus splice sequences. Crisp-1 is a single-copy gene as shown by the presence of single bands by Southern blot analysis and PCR using rat genomic DNA as template. Recognition sites for steroid hormone receptors are present in the 5' flanking region and in intron 1, consistent with the known regulation of Protein DE expression by androgens. RT-PCR experiments demonstrate three splice variant mRNAs involving the non-coding exon 2. The Crisp-1 gene also produces an mRNA without an exon 1 sequence by utilizing a transcription start site in intron 1, 5' of the start of exon 2. All forms of the Crisp-1 mRNA are predicted to encode Protein DE.

p53 independent, region-specific epithelial apoptosis is induced in the rat epididymis by deprivation of luminal factors

Luminal testicular factors are known to be important for the regulation of the epididymal epithelium. The present study was undertaken to test the hypothesis that complete deprivation of luminal factors by efferent duct ligation (EDL) would induce apoptosis in the epididymal epithelium, as does removal of trophic factors from other cell types. Additionally, experiments were performed to determine whether the apoptosis detected was p53 dependent or independent. Apoptosis detection was by terminal deoxynucleotidyl-mediated deoxyuridine triphosphate-biotin nick-end labeling and by DNA fragmentation studies. EDL caused loss of testicular luminal contribution in zone 1A of the rat epididymis (proximal initial segment) within 6 hr and induced epithelial apoptosis within 12 hr of the efferent duct obstruction. The wave of apoptosis in zone 1A was completed by three days after EDL and was followed by a much smaller wave in zone 1B which peaked three days after EDL. Significant apoptosis was not detected in any epididymal region distal to the initial segment for periods as long as 15 days after EDL. p53, a key apoptotic-pathway molecule in many tissues and conditions was tested by immunohistochemical and Western blot techniques and was not upregulated in the initial segment epithelium within the time cells were undergoing apoptosis and well before the wave of apoptosis was complete. It was concluded that epithelial apoptosis in the initial segment of the rat epididymis is induced by deprivation of luminal testicular factors, is localized to the proximal and middle initial segment, and is p53 independent.

Gene expression in the epididymis

The epididymis is a tubular organ exhibiting vectorial functions of sperm concentration, maturation, transport, and storage. The molecular basis for these functions is poorly understood. However, it has become increasingly clear that regional differences along the length of the duct play a role in epididymal physiology and that region-specific gene expression is involved in the formation of these differences. Although not an overtly segmented organ, the epididymis consists of a series of highly coiled "zones," separated by connective tissue septulae and distinct by cell morphology and their pattern of gene expression. Thus, it constitutes an interesting mammalian model to study how pattern formation is achieved by differential gene activity. A large number of epididymis-expressed genes have been cloned and analyzed at the molecular level, most of them have been characterized by a distinct temporal and spatial expression pattern within the organ. Only recently have theories been developed about how and when during ontogenesis this pattern formation takes place and what its significance might be. This review summarizes the current knowledge on regionalized gene expression in the epididymis and presents hypotheses concerning its ontogenetic origin and regulation in the adult.

Molecular cloning and hormonal regulation of a murine epididymal retinoic acid-binding protein messenger ribonucleic acid

A complementary DNA encoding the mouse epididymal secretory protein MEP 10 (mouse epididymal protein 10) was cloned and is now renamed murine epididymal retinoic acid binding protein (mE-RABP). The analysis of the predicted primary amino acid sequence showed that mE-RABP has a 75% identity with rat ESP I (epididymal secretory protein I), another epididymal retinoic acid-binding protein. The homology strongly suggests that mE-RABP is the mouse orthologue of rat ESP I. A computer analysis of the predicted three-dimensional structure confirmed that mE-RABP can accommodate retinoic acid as ligand. In the rat, ESP I messenger RNA (mRNA) is expressed in the efferent ducts and in the entire caput epididymidis. However, in the mouse, the expression of a 950-bp mE-RABP mRNA was detected only in principal cells of the mid/distal caput epididymidis, suggesting that the regulation of region-specific expression is different in rat and mouse. Northern blot analyses showed that mE-RABP gene expression is no longer detected 10 days after castration but progressively rebounds between days 15 and 60. However, mE-RABP protein could not be detected by Western blot 30 days after castration. Androgen replacement, begun 5 days after castration and continued for 4 days restored significant expression of mE-RABP mRNA. Efferent duct ligation for 10 days did not affect gene expression. Taken together, these results indicate that mE-RABP mRNA expression is regulated by androgens but not by testicular factors. The overall similarity in the primary amino acid sequence of mE-RABP with ESP I and other members of the lipocalin superfamily suggests that they are evolutionarily related.

Isolation and culture of epithelial cells from rat ductuli efferentes and initial segment epididymidis

To improve the study of epithelial function in rat ductuli efferentes (efferent ductules) and initial segment epididymis, we developed a primary cell culture system with modification of the Klinefelter method (1992). The cultured efferent ductal epithelium was grown to confluence and the cells maintained many of the organelles characteristic of these cells in vivo, including dense-staining granules, indented nuclei and apical cilia. Ciliary beat was observed for up to 10 days in culture, Cultured initial segment epithelial cells were elongated and characterized by apical branched microvilli. Electron microscopy revealed intact cell junctions, and endocytotic apparatus and lysosomal granules. Ultrastructurally, the initial segment epithelium contained a well developed Golgi apparatus. For both epithelia, cell characteristics were also confirmed by indirect immunofluorescent staining for cytokeratins 8, 18. Endocytotic activity was detected by the uptake of cationic ferritin at the apical surface and within vesicles. Estrogen receptor and clusterin mRNAs were expressed in the cultured epithelia and no difference was found in their expressions when cultured with or without 10(-9)M 17-beta estradiol. Indirect immunofluorescent staining for clusterin further indicated that this protein was present in the cultures. In conclusion, these in vitro methods will be useful for the investigation of epithelial function in the head of the epididymis.

Role of the epididymis in mediating changes in the male gamete during maturation

This article reviews recent knowledge about events occurring in the epididymis that are important for sperm to fertilise eggs. Well established concepts are stated without references (see Cooper, 1986 for older literature) but recent references are included where they throw light on mechanisms of epididymal function. During their sojourn in the epididymis spermatozoa acquire the capacity to move and to fertilise eggs; they are then stored in a quiescent state prior to ejaculation. The ability of sperm to undergo the events of fertilisation are developed as a result of interactions with certain epididymal secretions. Increases in our knowledge about the genes coding for epididymal secretions has not yet been matched by similar insight into the role that these secretions play in the maturation process. However, information about the changes that occur to the sperm cells during maturation permit certain scenarios to be sketched that may reflect reality. This review is one such attempt to bring the epididymal sperm-epithelial secretion into focus.

Epididymal epithelium: its contribution to the formation of a luminal fluid microenvironment

To understand the process of sperm maturation, an understanding of interactions between the spermatozoa with the luminal fluid microenvironment and with the epididymal epithelium is necessary. The composition of epididymal luminal fluid of several species is well documented but the manner by which the epididymis contributes to the formation of this specialized milieu is not so well understood. A major role played by the epididymis is to finely regulate the movement of molecules into and out of the lumen. This ensures that as spermatozoa progress along the duct they are exposed to a continually changing, but optimal environment necessary for their maturation and survival. This review focusses on our current understanding of the contributions of the epididymal epithelium to the formation of a specialized luminal fluid microenvironment. The role of the blood-epididymis barrier, the composition of the epididymal luminal fluid, the permeability properties of the epididymal epithelium, and recent studies on a number of luminal fluid proteins and expression of the genes which encode these proteins are discussed.

Regional variation of specific gene expression in the dog epididymis as revealed by in-situ transcript hybridization

In-situ transcript hybridization was used to characterize the regional distribution of three marker gene transcripts which are expressed abundantly in the canine epididymis. The gene products CE1, CE4 and CE5, which are the canine equivalents of the human homologues HE1, HE4 and HE5, are shown to be expressed in a tissue-specific and regionally characteristic pattern in the epididymal epithelium. CE1 mRNA was expressed very weakly in the efferent ducts but was expressed at a high level throughout the caput and corpus regions of the epididymis, decreasing somewhat in the distal cauda region. CE4 mRNA was not detectable in the efferent ducts and was only expressed moderately in the remainder of the epididymis, with greatest levels in the caput and proximal cauda regions, and decreasing in the distal cauda. CE5 mRNA showed the most marked regional variation in levels with little or no mRNA detectable in the caput and proximal corpus regions, but increasing dramatically in the distal corpus and cauda. In the transition region of the central corpus, the CE5 mRNA appeared to be expressed intermittently, giving a mottled signal appearance over the epididymal epithelium. The patterns of mRNA distribution for the three marker genes in the dog epididymis were, therefore, essentially similar to those for the equivalent human homologues, providing further support for the suitability of the dog epididymis as a model for the human.

Members of the raf gene family exhibit segment-specific patterns of expression in mouse epididymis

The proto-oncogene c-raf-1 and the related genes A-raf and B-raf encode serine/threonine protein kinases thought to be involved in regulating gene expression by acting as part of second-messenger signaling pathways within the cell. Among the tissues in which A-raf and c-raf-1 have been shown to be expressed was mouse epididymis. The present studies were undertaken to determine if the raf family genes exhibited specificity in their pattern of expression that might be indicative of specific function in the epididymis. Northern and in situ hybridization analyses demonstrated that c-raf-1 mRNA was expressed as a 3.1 kb transcript at uniform levels throughout the length of the epididymis in all types of epididymal epithelial cells. Neither the germ cell-specific testicular transcripts nor the somatic transcripts of B-raf were detected by either Northern or in situ hybridization analysis in any region of the epididymis. A-raf, expressed as two transcripts of 2.6 and 4.3 kb, was the only gene examined which exhibited a segment-specific pattern of expression, being highest in the principal epithelial cells of the proximal caput epididymis and decreasing progressively in more distal regions of the tubule. These studies indicate that each raf gene exhibits a characteristic pattern of expression in the epididymis; A-raf in particular may play a unique regulatory role in the regionalized functions of the epididymis.

Region-specific variation of gene expression in the human epididymis as revealed by in situ hybridization with tissue-specific cDNAs

Three tissue-specific gene probes that had been isolated by differential screening from a human epididymal cDNA library--HE1, HE2, and HE5--were employed to investigate regional specializations in the human epididymis. All 3 cDNAs were derived from major transcripts of the epithelial cells lining the epididymal duct. Each mRNA species, however, exhibited a discrete longitudinal pattern of hybridization with maxima in different regions of this organ, suggesting regional specializations of gene expression. The HE5 mRNA, which was recently shown to encode the peptide backbone of the human leukocyte differentiation antigen CDw52, showed maximum levels in the distal corpus epididymidis and in the vas deferens, whereas the HE2 mRNA was found predominantly in the caput and proximal corpus sections of the epididymis. HE1 mRNA was found in high amounts in all parts of the epididymis, displaying a 2-peak expression pattern with maxima in the distal caput and distal corpus of the epididymal duct.

Human sperm proteins from testicular and epididymal origin that participate in fertilization: modulation of sperm binding to zona-free hamster oocytes, using monoclonal antibodies

In order to identify human sperm surface proteins involved in the gamete recognition process, mouse monoclonal antibodies were directed against human spermatozoa and screened with live spermatozoa by enzyme-linked immunosorbent assay (ELISA). Immunoperoxidase staining of human testis showed the early presence of four corresponding proteins on germinal cells, while six were detected primarily in testis fluid. The presence of 17 proteins was evidenced in the epididymis. Eight were detected with a decreasing gradient from the beginning to the end of the organ, including vasa efferentia for three of them. The other nine were observed in only one defined segment, usually the caput epididymis, which was found to be the most active region. Comparison of spermatozoa patterns from testis, vasa efferentia, and the three regions of epididymis pointed out a progressive coating. By contrast, three antibodies displayed a migration of spermatozoa surface domains in the course of epididymal transit. Six antibodies were found to inhibit human spermatozoa adherence to zona-free hamster oocytes, while nine promoted it. Molecular weights of antigens corresponding to nine of the antibodies ranged from 11 to 215 kDa. No correlation could be established with previously described human proteins. These observations emphasize the role of epididymis in human sperm maturation.