Epididymal secreted protein Crisp-1 and sperm function

Crisp-1 is a member of the cysteine-rich secretory protein family. This family of proteins is characterized by the presence of 16 conserved cysteine residues, the characteristic from which the family name is derived. Members of the Crisp protein family are found in the secretions of the reproductive tract and salivary glands, including venom toxins from several species of snakes and lizards. The Crisp proteins are modular, each containing an amino terminal pathogenesis-related (PR)-like domain and a carboxyl terminal cysteine-rich domain (CRD) connected by a hinge region. Sequence and structural similarities to proteins with known functions suggest that the Crisp family of proteins may act by regulating cellular ion channels. Rat Crisp-1 is synthesized as two distinct isoforms (referred to as Proteins D and E) by the epididymal epithelium and both are secreted into the luminal fluid where they interact with spermatozoa. Our laboratory has correlated Crisp-1 binding to sperm with inhibiting the signaling cascades that initiate capacitation while others have shown that blocking Crisp-1 binding sites on oocytes interferes with sperm-egg fusion. We hypothesize that the D and E populations of rat Crisp-1 have different interactions with sperm that modulate these distinct biological activities. Through tandem mass spectrometry (MS/MS) and monosaccharide composition analyses, we have identified at least one difference between the D and E forms as an additional single O-linked N-acetyl galactosamine on an amino terminal threonine residue in Protein E. This post-translational modification appears to account for the unique 'E' epitope bound by monoclonal antibody 4E9 developed in our laboratory, and may also lead to differential processing and localization of Protein E on sperm, when compared to Protein D. These findings are the first step in distinguishing the molecular basis of the biological activities of the D and E forms of rat Crisp-1. The epididymal-specific expression of Crisp-1, combined with its role in regulation of sperm capacitation and oocyte interaction, make it an attractive target for post-testicular contraceptive development.

Electron microscopic immunolocalization of the 18 and 29 kilodalton secretory proteins in the mouse epididymis: evidence for differential uptake by clear cells

In previous studies we reported the synthesis, secretion, and immunolocalization at the light microscopic level of two mouse epididymal proteins, MEP 7 and MEP 10 [Rankin et al. (1992b), Biol. Reprod., 46:747-766]. MEP 7 is the mouse homologue of the rat metalloproteins, AEG/D and E, and MEP 10 is the mouse homologue of the rat retinoic acid binding proteins, B and C. We now describe the immunolocalization of MEP 7 and MEP 10 in the mouse epididymis at the electron microscopic level. MEP 7 was localized in the Golgi apparatus, in small electron-lucent secretory vesicles, and on microvilli of the principal cells from the distal caput epididymidis to the cauda. The luminal contents were also immunoreactive in these regions of the epididymis. Although some gold particles were associated with the sperm surface, there was no selective concentration of these particles. In addition, MEP 7 was localized in large (600 nm) supranuclear endocytic vesicles and in infranuclear lysosomes. MEP 10 immunoreactivity was also seen on the microvilli of the principal cells of the distal caput and corpus and the luminal contents from the distal caput to the cauda epididymidis. There was no association of gold particles with the sperm surface. In contrast to MEP 7, there was no detectable MEP 10 immunoreactivity on the organelles of the principal cells involved in protein secretion or endocytosis. Clear cells also demonstrated immunoreactivity to MEP 7 and MEP 10. However, the intensity of immunolabeling, and the number of clear cells labeled, was greater with MEP 10 than MEP 7. In the case of MEP 7, the gold particles were located on the large supranuclear endocytic vesicles and on some infranuclear lysosomes, from the proximal corpus to the middle cauda, while in the case of MEP 10, gold particles were predominantly present in infranuclear lysosomes from the distal caput to the middle cauda. These results suggest that the principal cells are involved in both the secretion and endocytosis of MEP 7. The MEP 10 and MEP 7 proteins present in the lumen of the mouse epididymis are endocytosed from the lumen and degraded in the clear cells. However, the process of endocytosis by the clear cells of these two proteins appears to be different.

Rat epididymis-specific sperm maturation antigens. I. Evidence that the 26 kD 4E9 antigen found on rat caudal epididymal sperm tail is derived from a protein secreted by the epididymis

Monoclonal antibody 4E9, which was raised against a partially purified detergent extract of rat caudal epididymal sperm, recognizes the tail of sperm from the cauda, but not from caput epididymidis, as well as epithelial cells in a restricted region of the distal caput/corpus epididymidis and proteins in epididymal fluid from corpus and cauda epididymidis. The antigen is apparently a glycoprotein, since it is retained on a Ricinus communis agglutinin I lectin column. Epididymal fluid antigens have apparent M(rs) of 38-26 kD, whereas the membrane-associated form of the molecule has an M(r) of 26 kD. Immunocytochemical data and Western immunoblot data suggest that the membrane antigen is derived from the fluid antigen, which, in turn, is secreted by the epididymal epithelium. Characterization of the membrane antigen indicates that it is tightly associated with the sperm surface, behaving as though it is an integral membrane protein. The antigen persists on ejaculated sperm.

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.

Plasma membrane alterations of maturing goat (Capra indicus) spermatozoa: lectin-binding and freeze-fracture study

A qualitative and quantitative analysis of lectin-binding sites has been undertaken on spermatozoa recovered from different regions of the epididymis of the goat (Capra indicus) using fluorescein isothiocyanate-linked lectins (Bauhinia purpurea BPA, Concanavalin A Con A, Dolichos biflorus DBA, Maclura pomifera MPA, Arachis hypogaea or peanut agglutinin PNA, Glycine max or soyabean agglutinin SBA, Ulex europaeus UEA, and Triticum vulgaris or wheat-germ agglutinin WGA), in conjunction with scanning and transmission electron microscopy, and freeze-fracture techniques. Flow cytometric analysis has also been used to quantitize binding affinity. Spermatozoa from caput to cauda epididymidis show no significant variation in lectin-binding ability, but the samples removed from the corpus epididymidis contain a greater number of binding sites. The passage of spermatozoa through the epididymidis is accompanied by a redistribution of the plasma membrane lectin-receptors covering the sperm head and tail. Receptors for BPA, DBA, PNA and SBA are specifically restricted to the anterior region of the acrosome in caudal spermatozoa. Freeze-fracture replicas, examined to study changes in organisation of intramembranous particles of the plasma membrane during sperm maturation, reveal distinct changes in their distribution in the acrosome, post-acrosome and spermatozoon tail, especially in the corpus and cauda epididymidis.

In vivo secretion and association of clusterin (SGP-2) in luminal fluid with spermatozoa in the rat testis and epididymis

Clusterin (sulfated glycoprotein-2) is a heterodimeric glycoprotein synthesized and secreted by rat Sertoli cells. An antigenically similar form is synthesized and secreted by the epididymis. The goal of this study was to define the epididymal regions in which clusterin is present and the regions in which clusterin is secreted and interacts with developing spermatozoa. Seminiferous tubule (STF), caput, corpus, and cauda fluids were collected by micropuncture and/or microperfusion and two-dimensional Western blot analysis was performed with a polyclonal antibody directed against Sertoli cell clusterin. Clusterin was found in both STF and epididymal fluid. STF contained predominantly the clusterin heavy chain (45 kd); however, a 70 Kd heterodimer was present under nonreducing conditions. Two subunits of clusterin with lower molecular weights (41 kd, heavy chain; 32 kd, light chain) and higher isoelectric points were present in the luminal fluid of all epididymal regions. The intraluminal levels of the heavy and light chains decreased from caput to cauda. Analysis by two-dimensional gel electrophoresis of proteins secreted directly into the epididymal luminal fluid revealed that clusterin was secreted by caput epithelium and not by the corpus and cauda epithelium. Western blots of membrane extracts from testicular, caput, and cauda spermatozoa revealed that testicular clusterin was associated with testicular sperm and epididymal clusterin with predominantly caput sperm. Our findings suggest that clusterin is secreted into the caput epididymal lumen, where it binds to sperm and then dissociates from sperm to be endocytosed by cells of the distal epididymal epithelium.

The major maturation glycoprotein found on rat cauda epididymal sperm surface is linked to the membrane via phosphatidylinositol

The experiments reported here further characterize a approximately 26[3H] kD cell surface glycoprotein that can be detected on rat cauda epididymal sperm using the galactose oxidase/NaB[3H]4 technique (1). When labeled sperm are treated with PI-PLC the 26[3H] kD is completely released from the cell. The released molecule can be recovered undegraded from incubation supernatant. Release by PI-PLC converts the hydrophobic, membrane-anchored form into a hydrophilic molecule as assessed by partition studies using Triton X114. Isoelectric focusing studies using both untreated (control) and PI-PLC treated samples shows that there is charge heterogeneity with two major peaks at pls of approximately 5.0 and approximately 4.5. We also show for the first time that the molecule persists on ejaculated cells.

Immunocytochemistry of male reproductive organs

Immunological techniques have enabled us to see that mammalian sperm undergo complex surface changes during maturation in the male reproductive tract. Binding affinity and sperm surface binding domains have been demonstrated using immunocytochemical technique. Recent studies using monoclonal antibodies suggest that these highly specific probes are useful for detecting changes in the sperm surface during epididymal transit and in defining the role of these complex changes in sperm maturation and the process of fertilization. Studies involving immunological mapping of the sperm surface, in parallel with immunohistological and functional inhibition test, have provided important information concerning the role of individual sperm antigens in fertility. A better understanding of local antibody production and cell-mediated immune responses in the male reproductive tract has also led to the understanding of immunological infertility. Sperm membrane is comprised of multiple domains each of which is sharply demarcated, with a unique composition and physiological role.

Masking of sperm maturation antigen by sialic acid in the epididymis of the mouse. An immunohistochemical study

Sperm antigen expression during epididymal transit was examined in 4- to 16-week-old intact and castrated ICR mice, using the avidin-biotin complex (ABC) immunohistochemical method with monoclonal antibody T21 against a flagellar surface antigen. On untreated sections, the antigen was first expressed weakly on sperm in the proximal part of the corpus epididymis, and intraluminal components were stained in 4-week-old mice. Epididymal epithelial cells and their stereocilia, and cells in other reproductive organs were not stained. In contrast, on sections treated with neuraminidase, (1) the initial site of antigen appearance is a more proximal position in treated than in untreated sections, (2) stereocilia stained strongly, (3) the staining intensity of sperm and intraluminal components increased, and (4) some clear cells in the epithelium from the distal position of the caput to the corpus epididymis were stained. These results indicate that the antigen is produced by clear cells of the epididymal epithelium, that the antigenic determinant is masked initially by sialic acid residues, and that expression of the antigenic determinant on the sperm surface during epididymal maturation apparently involves desialylation.

Androgen-regulated epididymal secretory proteins associated with post-testicular sperm development

A considerable body of information has now been assembled with regard to the major androgen-dependent secretory proteins of the rat epididymis. The proteins have been purified, specific antibodies have been developed against them, and their primary structure has been determined from cDNA clones. The antibody and cDNA probes have, in turn, been used to study the androgenic regulation of the synthesis and secretion of the proteins, the distribution of the proteins in various tissues and animal species, and the association of the proteins with the sperm surface during epididymal maturation. Despite this intensive effort, the precise physiological functions of the proteins still remain obscure, although circumstantial evidence indicates that glycoproteins D and E may be associated with surface receptors responsible for gamete recognition. Elucidation of the physiological roles of the proteins is clearly the area that warrants the greatest attention in future work.

Changes in binding of a 27-kilodalton chimpanzee cauda epididymal protein glycoprotein component to chimpanzee sperm

Motility patterns of caput epididymal chimpanzee sperm, caput epididymal chimpanzee sperm incubated in vitro with chimpanzee cauda epididymal fluid, and cauda epididymal chimpanzee sperm were assessed quantitatively. Sperm recovered from the caput epididymis showed no motility, whereas sperm recovered from cauda epididymis showed progressive forward motility. After incubation in cauda fluid, approximately 25% of caput epididymal sperm showed some motile activity. Electrophoretic analysis of 125I-labeled sperm plasma membrane preparations revealed that the surface of caput epididymal sperm, incubated in cauda fluid, was modified by the appearance of a major protein-glycoprotein surface component with an apparent molecular weight of 27 kilodaltons (kD). THis 27-kD component was not detected on caput epididymal sperm incubated in buffer or in caput fluid. However, it was present in cauda fluid and on cauda epididymal sperm. Binding to caput epididymal sperm was cell specific in that chimpanzee erythrocytes incubated in cauda fluid did not bind this 27-kD cauda fluid component. Motility patterns of ejaculated chimpanzee sperm and of ejaculated chimpanzee sperm incubated in the uterus of adult female chimpanzees also were assessed quantitatively. Ejaculated sperm showed progressive forward motility, whereas in utero incubated ejaculated sperm showed hyperactivated motility typical of capacitated sperm. Electrophoretic analysis of 125I-labeled sperm plasma membrane preparations revealed the loss of a 27-kD component from the surface of ejaculated sperm after in utero incubation. No significant change in the 125I-distribution pattern was detectable when ejaculated sperm were incubated in buffer. These results suggest that the lumenal fluid component, which becomes adsorbed to the surface of chimpanzee sperm during maturation in the epididymis and which is removed from the surface of mature chimpanzee sperm in the female reproductive tract, affects sperm motility.

Modification of the rat sperm flagellar plasma membrane during maturation in the epididymis

Previously, we demonstrated that surface radiolabeling of rat epididymal spermatozoa by lactoperoxidase-catalyzed iodination reveals a major component with an apparent molecular weight of 26,000 to 28,000 daltons (26 kDa) on spermatozoa from the cauda but not the caput epididymidis. To characterize this surface component further, sperm surface constituents radiolabeled by lactoperoxidase-catalyzed iodination were separated by 2-D PAGE. The 26 kDa component was localized by autoradiography and appeared as the major labeled acidic spot on cauda spermatozoa, but neither a radiolabeled spot nor a corresponding stained spot was present on caput spermatozoa. The 26 kDa spot was excised from 2-D gels of plasma membranes from cauda spermatozoa and utilized for immunization. The monospecific antiserum stained a single band of 26 kDa on Western blots of SDS-PAGE-separated plasma membranes from cauda spermatozoa and in a 100,000 X g supernatant fluid of the luminal contents of the cauda epididymidis. Immunohistochemical staining of cauda spermatozoa revealed antigen exclusively on the flagellar domain; the antigen was not seen on caput spermatozoa but first appeared in spermatozoa from the proximal corpus epididymidis. Immunoelectron microscopy confirmed the 26 kDa component was localized to the external face of the flagellar plasma membrane. Immunohistochemical staining of caput spermatozoa incubated in vitro with cauda epididymal luminal fluid revealed the 26 kDa component specifically bound the flagellar domain of immature spermatozoa.

Antibody and complement-binding activity of viable and nonviable human spermatozoa

Antibody and complement fixation by viable and nonviable spermatozoa were studied by means of immunofluorescence and a hemolytic assay (CH-50). Spermatozoa were incubated in sera from fertile male and female donors and in peritoneal fluid from fertile women undergoing laparoscopy. Nonviable spermatozoa were able to bind antibody or complement from sera and peritoneal fluid. There was no evidence of antibody or complement fixation by viable spermatozoa. The antibodies present in the serum that bind to spermatozoa belong to the IgG and IgM class; in peritoneal fluid, only IgG could be found. Complement fixation occurred via the classical (antibody-mediated) and alternative pathway. Viable spermatozoa possess antigenic properties different from nonviable spermatozoa. The lack of immunological reaction of women to viable spermatozoa and a possible mechanism for immunological infertility is considered.

Immunodissection of sperm surface modifications during epididymal maturation

Mammalian spermatozoa undergo changes in morphology, composition, and function during transit through the epididymis. These changes correlate with acquisition by sperm of the ability to fertilize ova. It has been found that sperm from the cauda epididymidis, but not those from the caput epididymidis, are able to bind to the zona pellucida. This would imply a modification in sperm surface characteristics. Biochemical and immunological studies have demonstrated changes in sperm surface composition during epididymal maturation. These changes involve addition of epididymal secretory products to the sperm surface, loss or alteration of existing sperm surface molecules, and possibly the unmasking of preexisting molecules or epitopes. Several laboratories have studied the epididymal secretory proteins in the rat, but a consensus has not been reached on the identification, characterization, source, and sperm surface association of these proteins. Monoclonal antibodies are beginning to be used to characterize sperm surface components and sperm maturation antigens. They are proving to be valuable tools for the dissection of epididymal maturation when used in conjunction with biochemical and physiological approaches.