Developmental expression and androgenic regulation of the mRNA for major secretory proteins of the rat epididymis

Distinct actions of testicular endocrine and lumicrine signaling on the proximal epididymal transcriptome

The epididymal function and gene expression in mammals are under the control of the testis. Sex steroids are secreted from the testis and act on the epididymis in an endocrine manner. There is another, non-sex steroidal secreted signaling, named lumicrine signaling, in which testis-derived secreted proteins go through the male reproductive tract and act on the epididymis. The effects of such multiple regulations on the epididymis by the testis have been investigated for many genes. The recent development of high-throughput next-generation sequencing now enables us a further comparative survey of endocrine and lumicrine action-dependent gene expression. In the present study, testis-derived endocrine and lumicrine actions on epididymal gene expression were comparatively investigated by RNA-seq transcriptomic analyses. This investigation utilized experimental animal models in which testis-derived endocrine and/or lumicrine actions were interfered with, such as unilateral or bilateral orchidectomy. By bilateral orchidectomy, which interferes with both endocrine and lumicrine actions, 431 genes were downregulated. By unilateral orchidectomy, which also interferes with endocrine and lumicrine actions by the unilateral testis, but the endocrine action was compensated by the contralateral testis, 283 genes were downregulated. The content of such genes downregulated by unilateral orchidectomy was like those of lumicrine action-interfered efferent duct-ligation, W/Wv, and Nell2-/- mice. When genes affected by unilateral and bilateral orchidectomy were compared, 154 genes were commonly downregulated, whereas 217 genes were specifically downregulated only by bilateral orchidectomy, indicating the distinction between endocrine and lumicrine actions on the proximal epididymal transcriptome. Comparative transcriptome analyses also showed that the expressions of genes emerging since Amniota were notably impacted by bilateral orchidectomy, unilateral orchidectomy, and lumicrine action-interfering treatments; the degree of influence from these treatments varied based on the evolutionary stage beyond Amniota. These findings unveil an evolutional transition of regulated gene expression in the proximal epididymis by two different testis-derived signaling mechanisms.

Busulfan administration replicated the characteristics of the epididymal initial segment observed in mice lacking testis-epididymis lumicrine signaling

The physiological functions of the mammalian epididymis are typically regulated by the testes. In addition to sex steroids secreted by testicular Leydig cells, which act on the epididymis in an endocrine manner, there is a non-sex-steroidal signaling pathway known as the lumicrine pathway. This lumicrine signaling pathway involves ligand proteins secreted from germ cells within the testicular seminiferous tubules traversing the male reproductive tract, which induce epithelial differentiation in the epididymis. These findings prompted an inquiry into whether treatments influencing testis physiology can disrupt epididymal function by interfering with testis-epididymis communication. Busulfan, an alkylating agent commonly used to deplete testicular germ cells in reproductive biology, has not been sufficiently explored because of its effects on the epididymis. This study investigated the effects of busulfan administration on the proximal epididymis using histological and transcriptomic analyses. Notably, busulfan, as opposed to the vehicle dimethyl sulfoxide (DMSO), altered the morphology of the initial segment of the epididymis, leading to a reduction in the cell height of the luminal epithelium. RNA sequencing identified 185 significantly downregulated genes in the proximal epididymis of busulfan-administered mice compared to DMSO-administered mice. Comparative transcriptome analyses revealed similarities between the epididymal transcriptome of busulfan-administered mice and lumicrine-deficient mice, such as efferent-duct-ligated W/Wv and Nell2-/- mice. However, this differed from that of bilaterally orchidectomized mice, in which both the endocrine and lumicrine signaling pathways were simultaneously ablated. Collectively, these results suggested that the harmful effects of busulfan on the proximal epididymis are secondary consequences of the ablation of testis-epididymis lumicrine signaling.

Epididymal contribution to male infertility: An overlooked problem

The diagnosis and treatment of male infertility, excluding assisted conception, are limited because of, but not limited to, poor understanding of sperm post-testicular development and storage. Many may think that sperm dysfunction is only self-contained in the sperm cell itself as a result of defective spermatogenesis. However, it can also be a consequence of inadequate epididymal maturation following disorders of the epididymis. Improper epididymal functions can disturb semen parameters and sperm DNA integrity, result in high leucocyte concentrations and high numbers of immature germ cells and debris or even cause idiopathic infertility. To date, the data are limited regarding critical markers of sperm maturation and studies that can identify such markers for diagnosis and managing epididymal dysfunction are scarce. Therefore, this article aims to draw attention to recognise a disturbed epididymal environment as a potential cause of male infertility.

Abdominal temperature induces region-specific p53-independent apoptosis in the cauda epididymidis of the mouse

It is widely accepted that temperature regulates gene expression and function in the epididymis. However, the significance of reduced temperature of the scrotum in cell survival had not often been examined. Our hypothesis was that the experimental increase of the temperature could induce apoptosis. Using a surgical method that consists of surgically reflecting the cauda epididymidis in the abdomen, we have been able to show that this is the case. Apoptosis was examined by histologic procedures and by visualization of DNA fragmentation in agarose gels. We determined that the apoptosis is region-specific and affects only the principal cells of the proximal region of the cauda. It starts 12 h after surgery and ends by the third day. The apoptotic cells are eliminated by extrusion into the lumen and phagocytosis by adjacent cells. The complete molecular mechanism of apoptosis in this case remains unknown, but we have used the techniques of immunocytochemistry, Western blot, and reverse transcription-polymerase chain reaction to determine the role of some molecules. We have seen no significant role of androgens, the tumor suppressor p53, nor two heat shock proteins, hsp-25 and hsp-70. Nevertheless, we have detected a strong induction of bax and bcl-2 gene products. While the former should be responsible for the apoptosis observed, the latter would promote the survival of most of the cells of the cauda epididymis.

Prostaglandin D2 synthase secreted in the caput epididymidis displays spatial and temporal delay between messenger RNA and protein expression during postnatal development

Highly regionalized protein secretory activity is established progressively throughout the epididymal tubule during postnatal development. Prostaglandin D(2) synthase (PGDS) is a major protein in the ovine epididymis, the secretion of which is restricted to the proximal part of the epididymis. We investigated the mRNA and protein expression of PGDS during ontogenesis. PGDS mRNA was present in the testis and epididymis in the 50-day-old sheep fetus and persisted until 4 mo of age (2 mo before puberty) without mRNA translation in the epididymis. At 4.5 mo, mRNA was present in all of the epididymis, but translation occurred in only the proximal caput. The secreted protein present in the lumen from the caput to the cauda had the same molecular mass and isoelectric point (pI) characteristics as the testicular form. At 5.5 mo, both mRNA and protein expression were restricted to the proximal caput. The protein secreted accumulated in the cauda but was not processed after secretion as it is in the adult animal; no changes in molecular mass or pI were observed. Our results show that for at least one gene (PGDS), transcriptional and posttranscriptional regulation during postnatal development is linked to the presence of unidentified translation factors present in testicular fluid.

Castration induces apoptosis in the mouse epididymis during postnatal development

The effect of castration on apoptosis in the mouse epididymis during postnatal development was examined. The weight of the epididymis slowly increased from day 0 (day of birth) to day 20 after birth, followed by a rapid increase thereafter. Castration on days 0, 5, 10, 20, 30, 40 and 60 increased apoptotic indices (percentages of apoptotic cells) of epithelia of the caput (head), corpus (body), and cauda (tail) epididymis, their apoptotic indices reaching maximal levels on day 2 after castration with the exception of a maximal apoptotic index on day 4 in the tail after castration on day 60. The maximal levels of apoptotic indices of the head, body and tail after castration on days 0, 5, 10 and 20 were significantly lower than those after castration on days 40 and 60. DNAs extracted from the epididymides 2 days after castration on days 0, 5, 10 and 60 showed a ladder pattern on agarose gel electrophoresis, which is a characteristic of apoptosis. When testosterone propionate (10 microg/g body weight) was injected twice a day into mice which had been castrated on day 10, 30 or 60, the increases in apoptotic indices of the head, body and tail of the epididymis were completely inhibited. The weights of the paired epididymides 6 days after castration on days 0, 5, 10, 20, 30, 40 and 60 were significantly lower than those of sham-operated mice, indicating the secretion of androgen by the testes from birth to adulthood. The present results indicated that androgen deprivation caused by castration induces apoptosis in the epithelium of the epididymis of mice from birth to adulthood, and suggested that a proportion of epithelial cells, the survival of which is dependent on the testes, is smaller in the epididymides during a slow growth stage than in the epididymides after this stage.

Expression, immunolocalization and sperm-association of a protein derived from 24p3 gene in mouse epididymis

The cDNA sequence for 24p3 protein in ICR mouse epididymal tissue was determined by PCR using primers designed according to the cDNA sequence derived from 24p3 protein in mouse uterine tissue. In the present study, 24p3 protein was immunolocalized in the epithelial cells and lumen of mouse epididymis. Both immunoblot analysis for protein and northern blot analysis for mRNA level showed a declining gradient of 24p3 expression from the caput to caudal region of the epididymis. The 24p3 protein was undetectable in the testis. These findings suggest that the 24p3 protein is a caput-initiated secretory protein in the mouse epididymis. A postnatal study revealed that 24p3 gene expression occurred in mice at the age of 14 days, before the completion of epididymal differentiation. This expression remained at a constant level until epididymal differentiation was completed. We also found that the secreted 24p3 protein interacted predominantly with the acrosome of caudal spermatozoa. Our findings suggest that the epididymal 24p3 protein is a caput-initiated and sperm-associated gene product and may be important in the reproductive system.

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.

Histochemical studies on sialic acids in the epididymis during post-natal development of the rat

A variety of sialic acids contained in the rat epididymis during post-natal development were examined by means of lectin and carbohydrate histochemistry. Epididymides from male Sprague-Dawley rats on post-natal days 14, 21, 30, 39, 49, 56 and 70 were fixed in Bouin's fluid and embedded routinely in paraffin wax. Hydrated sections were subjected either to the lectin methods using biotinylated Sambucus sieboldiana lectin or Maackia amurensis lectin or to the selective periodate oxidation-phenylhydrazine-thiocarbohydrazide-silver protein-physical development technique with or without saponification. The results revealed that sialic acids appeared in the epididymal epithelium at day 14, followed by particular distribution patterns corresponding to cell differentiation during days 21-39. High-level O-acetylation of sialic acids was observed in the principal cells of the initial segment and proximal caput after day 39. These results suggest that sialic acids with different linkages and O-acetylation become adult in distribution at the 'differentiation' period under the influence of androgen, before spermatozoa reach the epididymal lumen. Such carbohydrates may be correlated, at least in part, with sperm-binding sialoproteins, which increase dramatically during the window between days 21 and 39.

Genomic organization and chromosomal localization of the murine epididymal retinoic acid-binding protein (mE-RABP) gene

The murine epididymal retinoic acid-binding protein (mE-RABP) is specifically synthesized in the mouse mid/distal caput epididymidis and secreted in the lumen. In this report, we have demonstrated by Southern blot analysis of genomic DNA that mE-RABP is encoded by a single-copy gene. A mouse 129/SvJ genomic bacterial artificial chromosome (BAC) library was screened using a cDNA encoding the minor form of mE-RABP. One positive BAC clone was characterized and sequenced to determine the nucleotide sequence of the entire mE-RABP gene. The molecular cloning of the mE-RABP gene completes the characterization of the 20.5-kDa-predicted preprotein leading to the minor and major forms of mE-RABP. Comparison of the DNA sequence of the promoter and coding regions with that of the rat epididymal secretory protein I (ESP I) gene showed that the mE-RABP gene is the orthologue of the ESP I gene that encodes a rat epididymal retinoic acid-binding protein. Several regulatory elements, including a putative androgen receptor binding site, "CACCC-boxes," NF-1, Oct-1, and SP-1 recognition sites, are conserved in the proximal promoter. Analysis of the nucleotide sequence of the mE-RABP gene revealed the presence of seven exons and showed that the genomic organization is highly related to other genes encoding lipocalins. The mE-RABP gene was mapped by fluorescent in situ hybridization to the [A3-B] region of the murine chromosome 2. Our data, combined with that of others, suggest that the proximal segment of the mouse chromosome 2 may be a rich region for genes encoding lipocalins with a genomic organization highly related to the mE-RABP gene.

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.

Regionalized expression of CD52 in rat epididymis is related to mRNA poly(A) tail length

The regional pattern of CD52 expression in the rat epididymis was followed by Northern analyses and carbohydrate-labelling of glycoconjugates on Western blots. CD52 mRNA showed a novel aspect of regionalization, namely region-dependent length differences in its poly(A) tail. 'Short' CD52 mRNA molecules were present in all parts of this organ and also in the seminal vesicles. Additionally, the cauda epididymidis contained mRNA molecules with an extended poly(A) tail. Their appearance coincided with the occurrence of the principal M(r) approximately 26 kDa glycopeptide in the cauda region, representing the CD52 product. CD52 expression seemed to be regulated or modulated synergistically by androgens, temperature, and (an) unknown testicular factor(s), depending on the poly(A) tail length of its mRNA. Androgens alone exerted an effect only on molecules with 'short' poly(A) tails. They were down-regulated in castrated animals, and restored to normal levels upon testosterone supplementation. However, 'long' CD52 mRNA molecules were not affected. Only if combined with the exposure of the epididymis to the elevated temperature of the abdomen, castration of animals resulted in a complete loss of the CD52 mRNA, including the 'long' cauda species. Loss of 'long' CD52 mRNA molecules was also observed when the abdominal location was combined with efferent duct ligation. This combination of treatments, however, did not affect 'short' CD52 mRNA levels. Loss of the 'long' CD52 mRNA molecules by any treatment coincided with a loss of the principal M(r) approximately 26 kDa glycopeptide from caudal protein extracts.

The molecular biology of the sperm surface. Post-testicular membrane remodelling

The membrane of testicular spermatozoa undergoes extensive changes in the epididymis, including rearrangement, modification and loss of pre-existing components, addition of new glycoproteins from epididymal secretions, and exchange of lipid constituents. As a result, the membrane of cauda epididymidal spermatozoa has a different composition and different properties, which collectively contribute to male fertility. Special significance has been attributed to sperm surface structures that only appear post-testicularly in the epididymis, the so-called "maturation antigens". Therefore, human post-testicular proteins have been cloned by substractive screening of epididymal cDNA libraries, employing testis as the primary negative control. To date, there is scanty information on their function and mechanism of deposition on the sperm surface. However, the major maturation antigen CD52 seems to bind firmly to the sperm membrane via its GPI anchor. Its synthesis is carefully regulated by the cells of the epididymal epithelium, with temperature and androgens acting synergistically on CD52 mRNA levels.

Molecules involved in mammalian sperm-egg interaction

To achieve fertilization, sperm and egg are equipped with specific molecules which mediate the steps of gamete interaction. In mammals, the first interaction between sperm and egg occurs at an egg-specific extracellular matrix, the zona pellucida (zp). The three glycoproteins, ZP1, ZP2, and ZP3, that comprise the zp have been characterized from many species and assigned different roles in gamete interaction. A large number of candidate-binding partners for the zp proteins have been described; a subset of these have been characterized structurally and functionally. Galactosyltransferase, sp56, zona receptor kinase, and spermadhesins are thought to participate in the primary binding between sperm and zp and may initiate the exocytotic release of hydrolytic enzymes in the sperm head, the acrosome reaction. Digestion of the zp by these enzymes enables sperm to traverse the zp, at which time the proteins PH20, proacrosin, sp38, and Sp17 are thought to participate in secondary binding between the acrosome-reacted sperm and zp. Once through the zp, sperm and egg plasma membranes meet and fuse in a process reported to involve the egg integrin alpha 6 beta 1 and the sperm proteins DE and fertilin. These molecules and the processes involved in gamete interaction are reviewed in this chapter within a physiological context.

Tissue and developmental distribution, dependence upon testicular factors and attachment to spermatozoa of GPX5, a murine epididymis-specific glutathione peroxidase

Using immunohistochemistry and Western blotting analyses, we present a detailed study of the distribution of the glutathione peroxidase protein (GPX5) within the mouse epididymis. We have shown that the expression of the epididymis-specific protein is restricted to the caput and essentially localized to the apical cell border of the caput epithelium. Secretion of the protein was detected as early as the proximal segment of the caput and GPX5 was subsequently found in the lumen of corpus and cauda epididymis duct. Within the caput, Western blot analyses have shown that equivalent quantities of GPX5 protein were found in segments I, II, and III. During ontogenesis, GPX5 appeared at 20 days postnatal, before the completion of the morphological differentiation of the caput and concomitantly with the appearance of spermatozoa within the epididymis, in agreement with what was reported earlier regarding the transcription of its corresponding gene during epididymal ontogenesis (Faure et al., 1991). Hormonal privation by castration abolished the accumulation of the GPX5 protein confirming previous data obtained on GPX5 mRNA levels. Treatments such as testosterone replacement or hemicastration led to the restriction of the protein to the caput epithelium, suggesting that protein secretion partly depends both on the presence of testicular factors and on spermatozoa. Using electron microscopy, we have shown that the secreted protein binds to spermatozoa and is found predominantly on the sperm acrosomic region. Finally, we report here that the GPX5 protein can be detected in fluids recovered from the uterine horns of freshly mated female mice. These results suggest that GPX5 might play an important role in sperm maturation from the early events up to the onset of fertilization and therefore could potentially be used as a tool to monitor sperm quality.

Mouse androgen-dependent epididymal glycoprotein CRISP-1 (DE/AEG): isolation, biochemical characterization, and expression in recombinant form

In the rat, the secretory glycoprotein DE/AEG is one of the main constituents of the epididymal fluid. We have recently reported the cloning of the cDNA for the related cysteine-rich secretory protein-1 (CRISP-1) from murine epididymis (Haendler et al., 1993; Endocrinology 133:192-198). The protein has now been isolated from the same organ and its N-terminal amino acid sequence has been determined. CRISP-1 exhibited an isoelectric point of approximately 6.8. High levels of CRISP-1 antigen were detected in the corpus and cauda of the epididymis, vas deferens, seminal vesicle, prostate, and in the salivary gland by immunohistochemistry. A quantitative analysis of the cauda epididymal fluid by sandwich ELISA revealed that CRISP-1 represented approximately 15% of the total protein. For heterologous expression, the CRISP-1 coding sequence was introduced into the pMPSV/CMV vector before transfection of baby hamster kidney (BHK) cells and selection with puromycin and neomycin. Expression in insect cells was achieved by co-transfection of Sf9 cells with a transfer vector and baculovirus DNA. Recombinant CRISP-1 was isolated in quantities sufficient for structural analysis. Ethyl maleimide treatment showed that all 16 cysteines were engaged in disulfide bonds. Proteolytic digestion demonstrated that the six cysteines localized in the N-terminal moiety formed three bonds with each other, suggesting the existence of two discrete domains in the protein.

Developmental expression of sulfated glycoprotein-2 in the epididymis of the rat

BACKGROUND

Sulfated glycoprotein-2 (SGP-2), also designated as clusterin, is a protein secreted by the epididymis and which binds to spermatozoa. In adult rats it is secreted at high levels by principal cells of the distal initial segment, intermediate zone and caput epididymidis, and at relatively lower levels by principal cells of the corpus and cauda epididymidis. The objective of this study was to correlate the developmental events in the maturation of the epididymis with the timing of SGP-2 expression in order to evaluate the testicular or epididymal factors which may regulate it.

METHODS

Our approach was to follow and compare the developmental expression of SGP-2 by immunocytochemistry in normal untreated control rats and rats whose efferent ducts were ligated on day 15 and examined at different postnatal ages thereafter.

RESULTS

In control animals, SGP-2 expression in principal cells of the distal initial segment, intermediate zone, and caput and distal cauda epididymidis, as characterized in normal 90-day-old adult animals, was attained between postnatal days 39 and 49. However, only by postnatal day 56 did SGP-2 display in the corpus and proximal cauda the characteristic secretory pattern found in adult rats. In contrast, in efferent duct ligated rats examined at postnatal day 64, SGP-2 was absent in principal cells of the corpus and proximal cauda epididymidis but continued to be secreted by the distal initial segment, intermediate zone, and caput and distal cauda epididymidis. Furthermore, unlike the case in control rats, SGP-2 was secreted at high levels by the principal cells of the proximal initial segment. Thus during normal postnatal development, in the proximal initial segment, the production of SGP-2 is suppressed by luminal factors originating from the testis, while in the distal initial segment, intermediate zone, and caput epididymidis, it is unaffected by these factors. On the other hand, the production of SGP-2 in the corpus and proximal region of the cauda epididymidis is normally stimulated by luminal factors originating from the testis, while in the distal cauda, it is unaffected by these factors.

CONCLUSIONS

Our results thus show a differential regulation of SGP-2 expression in principal cells of the proximal versus distal regions of the epididymis and even within subdivisions of each region. In some regions of the epididymis, SGP-2 production appears to be unaffected by luminal factors originating from the testis, while in other regions it is either inhibited or stimulated by these factors.

Developmental expression of immobilin in the rat epididymis

BACKGROUND

Immobilin is a protein secreted by principal cells of the distal initial segment, intermediate zone and caput epididymidis of adult rats, which serves to immobilize spermatozoa. In the distal cauda, epithelial clear cells are involved in its endocytosis. The objective of this study was to correlate the developmental events in the maturation of the epididymis with the timing of immobilin secretion and endocytosis in order to evaluate the testicular or epididymal factors which may influence or regulate immobilin expression.

METHODS

Our approach was to follow and compare the developmental expression of immobilin by light microscope immunocytochemistry in control and efferent duct ligated rats of different postnatal ages.

RESULTS

Coincident with the morphological maturation of the principal cells by postnatal day 39, immobilin displayed the characteristic secretory immunostaining pattern found in adults. This adult-like expression occurred despite the absence of spermatozoa in the lumen but was coincident with high levels of circulating and luminal androgens. In contrast, immobilin secretion in rats whose efferent ducts were ligated at day 15 was weak to non-existent in the principal cells of the caput epididymidis at day 28 and remained so into adulthood, indicating that principal cells of this region of the epididymis are dependent either directly or indirectly upon testicular factors present in the lumen for immobilin expression. However, secretion of immobilin in the principal cells of the distal initial segment was unaffected by ligation and unlike the case in control rats high levels of immobilin also continued to be secreted into adulthood by the principal cells of the proximal initial segment. Thus in the distal initial segment immobilin secretion is not regulated by luminal factors originating from the testis, while in the proximal initial segment the normal suppression of immobilin that occurs by postnatal day 39 is. Despite ligation, endocytosis of immobilin by clear cells of the distal cauda epididymidis occurred by day 49, indicating that luminal testicular factors are not essential for stimulating the uptake of immobilin by these cells.

CONCLUSIONS

The results taken together suggest that there are stimulatory and inhibitory luminal testicular factors involved in the regional development of immobilin secretion in the epididymis. There are also immobilin secreting regions in the epididymis, whose secretory development is independent of luminal testicular factors.

Developmental expression and androgen regulation of 24 kDa secretory proteins by the murine epididymis

Two peptides with a molecular weight of 24 kDa and a P(i) of 8.4-8.8 were found to be synthesized and secreted specifically by the caput epididymis of adult male mice under androgen control. The peptides can interact with spermatozoa. In the present study, the developmental pattern of [35S]-methionine-labelled proteins synthesized by the murine caput epididymis at 10, 20, 30 and 40 days of age were studied using two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and autoradiography. Active synthesis of the 24 kDa proteins was detected in the epididymis from 20 days of age, but secretion of the two peptides was only observed from 30 days of age onwards. To determine whether androgens influenced the active expression of 24 kDa proteins in the developing epididymis, their effect on [35S]-methionine incorporation into proteins was assessed using 2D PAGE. Mice were either castrated, castrated then testosterone injected or simply testosterone injected at 10, 20, 30 or 40 days of age. Androgen control of 24 kDa protein expression was also studies in vitro in epididymal organ culture over a 10-day period, with or without testosterone. Androgens were not involved in the initiation of synthesis of the 24 kDa proteins from days 10 to 20, as shown by in-vivo and in-vivo experiments. However, androgens appeared to be essential for maintaining synthesis and secretion of the proteins from 20 days of age onwards. Administration of excessive testosterone was only able to increase secretion of the 24 kDa proteins in intact male mice aged 40 days.

Regulation of the epididymal glutathione peroxidase-like protein in the mouse: dependence upon androgens and testicular factors

The protein MEP24 was previously described as a glutathione peroxidase-like molecule specifically secreted by the mouse caput epididymidis. Recently, its binding to the head of spermatozoa was demonstrated. Here, the regulation of MEP24 expression was studied by analyzing transcriptional and translational activities in the epididymis (1) of adult mice castrated on day 60 and given various substitutive testosterone (T) treatments from day 90 and (2) of hemicastrated adult animals. In castrated mice, T treatment induced a significant rise in plasma T and 5 alpha-dihydrotestosterone (DHT) concentrations that greatly exceeded the control values. Owing to efficient regulation, however, the epididymal T and DHT levels were never higher than those of the controls. The restoration of MEP24 mRNA accumulation was complete when the epididymal DHT content returned to its normal value. However, when estimated in a cell-free system, the in vitro translatable MEP24 mRNA level never exceeded 70% of control values, even though the DHT and accumulated mRNAs were restored by 100% or more. In hemicastrates, the T content was normal on the castrated side, while the DHT content exhibited a significant decrease (47%). In this case, the MEP24 mRNA accumulation reached 88% of the normal value, but the translation rate, both in vitro and in vivo, was only about 50%. Ultrastructural studies showed that the normal rough endoplasmic reticulum organization in segment I cells is dependent upon the presence of testicular fluid in the epididymal duct lumen. Thus, this report shows that the MEP24 mRNA steady-state level is completely recovered in the presence of a normal epididymal DHT content, while restoration of the regulation of translation is just partial. This could be related to the cell organization but seems mainly dependent upon the presence of specific mRNA-associated factors which are probably under the control of androgens and/or molecules carried by the testicular fluid.

Structural differentiation of the epithelial cells of the testicular excurrent duct system of rats during postnatal development

The light and electron microscopic appearance of the various epithelial cells lining the efferent ducts and different regions of the epididymis were examined in rats on postnatal days 21, 39, 49, 56, and 90 to determine the role of androgens and/or spermatozoa, as well as other possible factors, on the structural differentiation of these cells. Five conclusions may be drawn from the observations made. First, on day 21 epithelial cells of all regions are structurally undifferentiated. Second, it was not until day 49 that nonciliated cells of the efferent ducts resembled those of adult animals, suggesting that more than one factor, such as androgens, testicular products, and/or spermatozoa, is needed for their full structural differentiation. Third, principal cells of the epididymis become structurally differentiated by day 39, i.e., these cells contained an elaborate Golgi apparatus, endoplasmic reticulum cisternae, and numerous 200-400 nm electron lucent secretory vesicles, as well as a full complement of endocytic organelles; this occurred in spite of the absence of spermatozoa in the epididymal lumen. The differentiation of these epididymal cells may be under the influence of androgens, which are known to be high at this time, but may also be due to specific secretions from Sertoli cells secreted directly into the efferent ducts. Fourth, clear cells of the cauda epididymidis are fully differentiated by day 39. The presence of degenerating germ cells in the lumen of the cauda epididymidis and various cellular debris, as well as high androgen levels, may be factors causing the differentiation of the cells of this region. Finally, clear cells of the corpus and cauda epididymidis only become fully differentiated by day 49, at a time when spermatozoa appear in the lumen, despite high levels of androgens at day 39; this observation indicates that the presence of spermatozoa in the lumen may be a necessary factor in causing their differentiation. Overall, these results suggest that a combination of different factors are necessary for the structural differentiation of the various epithelial cell types of the different regions of the epididymis.

Protein D is differentially expressed and regulated in the rat epididymis

We report the use of a sensitive and specific enyzme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) to study the expression of protein D, a major androgen-regulated sperm-binding glycoprotein at the protein and mRNA level in different anatomical regions of the rat epididymis. The concentration of protein D in the caput, corpus and cauda region of the epididymis was 10.2 +/- 0.67, 7.3 +/- 0.61 and 22.8 +/- 1.34 ng/micrograms total protein, respectively. The total RNA extracted from the caput, corpus and cauda regions of the rat epididymis was amplified by PCR with oligonucleotide primers specific for the 5' and 3' portion of protein D cDNA. Compared to the caput and cauda region, a significant reduction (greater than 82 +/- 3%) in the expression of protein D mRNA levels was observed for corpus epididymal RNA. This data demonstrates regional differences in the concentration of protein D and suggests that protein D expression may be regulated at the level of mRNA within the corpus epididymidis.

Structure and expression of the rat epididymal secretory protein I gene. An androgen-regulated member of the lipocalin superfamily with a rare splice donor site

The complete rat epididymal secretory protein I (ESP I) gene was isolated from a genomic library constructed in bacteriophage lambda Charon 4A. The complete nucleotide sequence of the gene and its immediate 5' and 3' flanking sequences were determined. Interesting features include the presence of a rare, but functional, splice donor site (...GC) and the presence of a putative androgen-receptor-binding element. A detailed analysis of ESP I regulation was carried out after castration and subsequent testosterone treatment, demonstrating the requirement for androgens. Efferent-duct ligation and cryptorchism, on the other hand, had no effect on the steady-state concentrations of ESP I transcripts. Comparison of the exon/intron organization of the ESP I gene with those of members of the lipocalin superfamily provides strong support for a common ancestral origin.

Differential patterns of regulated gene expression in the adult rat epididymis

Specialization among the principal epithelial cells of the epididymal tubule is documented following the analysis of transcriptional activity of four distinct species of mRNA. In situ histochemical analysis revealed a unique pattern of expression for each transcript. This observation supports the concept that region-specific patterns of transcriptional expression along the epididymal tubule serve as the major molecular basis underlying region-specific patterns of luminal proteins within the tubule. Additionally, multiple testicular factors appear to regulate expression of these mRNAs. The transcript encoding peptidyl-prolyl cis-trans isomerase is constitutively expressed. Those encoding the major secretory proteins, protein B/C and protein D/E, are directly regulated by testicular androgen. That encoding the opioid peptide precursor, proenkephalin, is regulated by a non-androgen testicular factor(s), specifically, spermatozoa or a spermatozoa-related factor. Thus, a complex array of nuclear events and signals received by the principal cells serve to determine the transcriptional status of genes expressed within this epididymal cell type.

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

The epididymal tubule is a dynamic structure, in which spermatozoa undergo distinct physiological and morphological changes. The epithelial cells lining the ductuli vary dramatically in their histochemical and cytological properties according to the region of the tubule in which they are located. Additionally, regional variation is observed regarding the biosynthetic, secretory, and absorptive properties of the epithelial cells. Using in situ histochemical analysis, we document here the region-specific expression of a variety of genes that are transcriptionally active in the adult rat epididymis. Radiolabeled antisense riboprobes were used to localize, within the efferent duct/caput epididymis, transcripts encoding protein B/C, protein D/E (acidic epididymal glycoprotein), sulphated glycoprotein 1, sulphated glycoprotein 2, cellular retinol-binding protein, and the neuroendocrine peptide precursor proenkephalin. Each species of mRNA exhibits a unique pattern of hybridization, revealing that gene transcription within the efferent duct/caput epididymis is also highly region specific. This observation may partially elucidate the molecular basis underlying the phenomenon of regional alterations in the composition of protein factors within the tubule lumen.

Androgen dependence during development of the mouse vas deferens protein mRNA

The mRNA encoding a major protein of the mouse vas deferens (MVDP) was first detected in 10-day-old males and its concentration increased sharply between 10 and 20 days, reaching adult levels at 40 days. This increase was not associated with an increase in tissular androgen concentrations. In 30-day-old mice castrated at birth or treated with cyproterone acetate over 29 days, MVDP mRNA levels were not abolished and were similar to those measured in 10- and 20-day-old controls. These results suggest that the neonatal expression of MVDP gene is independent of androgens. In addition, precocious accumulation of MVDP mRNA could be induced by injection of excess amounts of androgens in 20- but not in 10-day-old animals. The prepubertal increase in MVDP mRNA levels is androgen-dependent but other factors may be necessary for MVDP expression.

Analysis of major androgen-regulated cDNA clones from the rat epididymis

Four abundant cDNA clones have been isolated from a rat epididymal cDNA library. Northern blot analysis has shown that these clones partially encode 4.5 kb, 2.8 kb, 1.2 kb and 0.85 kb mRNAs and that their expression is not detectable in total RNA preparations from heart, kidney, liver or testis. Fourteen days after castration the levels of the 2.8 kb, 1.2 kb and 0.85 kb transcripts were greatly reduced whereas the 4.5 kb mRNA was undetectable. Subsequent treatment of castrated rats with testosterone for 1 day resulted in a complete restoration of the pre-castration steady-state levels of the 2.8 kb and 0.85 kb mRNAs, restoration of the 4.5 kb mRNA to 70% of pre-castration levels, and a slight over-induction of the 1.2 kb mRNA. Analyses of separate regions of the epididymal tract showed that expression of the 2.8 kb and 1.2 kb mRNAs increased towards the distal end of the epididymis, while the 4.5 kb and 0.85 kb transcripts were primarily synthesised in the caput region.

Androgen regulation of the mRNA encoding a major protein of the mouse vas deferens

A cDNA encoding the major mouse vas deferens protein (MVDP) has been cloned and characterized. Using in situ hybridization we have identified the epithelial cells of the vas deferens as the site of synthesis of MVDP mRNA. Northern blot analysis suggests that a high level of an mRNA corresponding to the MVDP gene is present in the mouse vas deferens whereas the amount of MVDP mRNA in vas deferens of other species studied, or in other mouse tissues, even if present, is undetectable. Steady-state levels of MVDP mRNA are decreased by approximately 42% 3 days after castration but a significant hybridization signal is still observed even 50 days after castration. Testosterone treatment for 2 weeks is necessary to completely reverse the effect of castration. In vitro transcription assays on isolated nuclei showed that the hormonal induction of the MVDP gene is achieved mainly at transcriptional level.

Multiple effects of ethane dimethanesulfonate on the epididymis of adult rats

Ethane dimethanesulfonate (EDS), a Leydig cell toxicant which results in transient infertility, was used in a 4 day postexposure experimental protocol designed to identify any effects this compound might exert on the epididymis. The techniques of efferent duct ligation and testosterone (T) implantation were used to negate the role of testicular effects on the epididymal parameters. Numerous evaluations were performed including light and electron microscopy, computer assisted sperm motion analyses, and electrophoresis of sperm membrane proteins. EDS was shown to affect the epididymis in a dose-dependent fashion. The action of EDS on the epididymis is in part due to Leydig cell cytotoxicity and the resulting decrease in circulating androgen since T implantation prevented some of the changes in sperm proteins and motility. However, neither efferent duct ligation nor T implantation prevented the formation of sperm granulomas in the caput epididymidis, the distinct morphological alterations of the corpus epididymidis, the modification of certain sperm membrane proteins, or the decrease in the progressive motility and velocity of sperm following EDS treatment. Although we cannot prove these effects of EDS are due to a direct action on the epididymis, it is now clear that EDS has a distinct action on the epididymis which is unrelated to circulating T or testicular fluid.