Evaluation of the site of synthesis of rabbit sperm acrosome stabilizing factor using immunocytochemical and metabolic labeling techniques

Distinct segment-specific functions of calyculin A-sensitive protein phosphatases in the regulation of cAMP-triggered events in ejaculated bull spermatozoa

Livestock spermatozoa possess more tenacious suppressors of cAMP-triggered events-including capacitation-associated changes-than laboratory animal spermatozoa, leading to flagellar hyperactivation. In order to identify the suppressors, we examined effects of an inhibitor of serine/threonine protein phosphatases (calyculin A) on cAMP-triggered changes in the protein phosphorylation state, and subsequent occurrence of hyperactivation and acrosome reaction in ejaculated bull spermatozoa. Ejaculated spermatozoa were incubated in cAMP-supplemented medium, then assessed for motility, acrosome morphology, and phosphorylated protein localization. The addition of calyculin A greatly enhanced cAMP-triggered protein phosphorylation at serine/threonine and tyrosine residues in the connecting piece and induction of flagellar hyperactivation. Most hyperactivated spermatozoa exhibited extremely asymmetrical bends at the middle piece, which produced intensive twisting or figure-eight movements. In the sperm head, however, cAMP-triggered dephosphorylation of serine/threonine-phosphorylated proteins and subsequent acrosome reaction were abolished by the addition of calyculin A. Based on these results, we suggest that calyculin A-sensitive protein phosphatases in the connecting piece are suppressors of cAMP-triggered events leading to hyperactivation. By contrast, similar protein phosphatases in the sperm head accelerate cAMP-triggered events leading to the acrosome reaction. These findings are consistent with the indication that calyculin A-sensitive protein phosphatases have distinct functions in the regulation of cAMP-triggered events in different regions of ejaculated bull spermatozoa.

Singular features of fertilization and their impact on the male reproductive system in eutherian mammals

Therian (marsupial and eutherian) mammals have evolved a suite of novel reproductive features – seen variously in their gametes, the steps of fertilization and the male reproductive tract – whose adaptive significance remains unclear. Present evidence for the better-understood eutherian mammals suggests that the ‘prime mover’ in their evolution has been the character of the egg coat, with other such features being adaptations to the consequences of this. Its elastic thickness allows the zona pellucida to stretch to a variable degree and yet remain around the blastocyst during much or all of its expansion before implantation, but its character represents an unusual challenge for spermatozoa. Novel aspects of the acrosome related to this challenge enable it to maintain a relatively prolonged binding after the onset of the acrosome reaction, and the structure, shape and behaviour of the sperm head point to physical thrust as a major element of zona penetration – with the unique configuration of gamete fusion as a sequela of this strategy. In the male, such adaptations are reflected in sperm head formation in the testis and in sperm maturation in the epididymis involving at least the sperm head's structure, plasmalemma and acrosome. This complexity allied to a slow epididymal sperm transport, a relatively modest sperm production and the brief life span of mature spermatozoa kept above the cauda epididymidis could account for the evolution of the sperm storage function – a development seemingly linked, in turn, to the need for sperm capacitation and scrotal evolution.

Secretory proteins from the epididymis and their clinical relevance

The literature pertaining to epididymal proteins and their functions in fertilization is reviewed. Animal studies have indicated that specific epididymal proteins may be involved in aspects of sperm motility, sperm-zona binding and the acrosome reaction. If analogous proteins in the human exist, use could be made of them in the andrology clinic. Currently, only one specific epididymal protein (alpha-glucosidase) is routinely measured for semen analysis. Glucosidase secretion, in addition to reflecting inflammation of the organ, is used in conjunction with other markers of human fertility to identify patients with ductal occlusion for whom bypass operations may be useful therapy. Glucosidase inhibitors have been used to improve the assay, by establishing true semen blank values, and to quantify histochemical activity in frozen tissue sections. From its localization in the human corpus and cauda epididymidis, neutral glucosidase can not be used to identify occlusion in the proximal regions of the duct. Other proteins may be valuable markers of these regions. In the future, other specific proteins of epididymal origin found in seminal fluid could well illuminate dysfunction of the organ in cases of infertility or be end-points of the disruptive action of drugs aimed at the epididymis.

Testicular descent, sperm maturation and capacitation. Lessons from our most distant relatives, the monotremes

The present review examines whether monotremes may help to resolve three questions relating to sperm production in mammals: why the testes descend into a scrotum in most mammals, why spermatozoa are infertile when they leave the testes and require a period of maturation in the specific milieu provided by the epididymides, and why ejaculated spermatozoa cannot immediately fertilise an ovum until they undergo capacitation within the female reproductive tract. Comparisons of monotremes with other mammals indicate that there is a need for considerable work on monotremes. It is hypothesised that testicular descent should be related to epididymal differentiation. Spermatozoa and ova from both groups share many of the proteins that are thought to be involved in gamete interaction, and although epididymal sperm maturation is significant it is probably less complex in monotremes than in other mammals. However, the monotreme epididymis is unique in forming spermatozoa into bundles of 100 with greatly enhanced motility compared with individual spermatozoa. Bundle formation involves a highly organised interaction with epididymal proteins, and the bundles persist during incubation in vitro, except in specialised medium, in which spermatozoa separate after 2–3 h incubation. It is suggested that this represents an early form of capacitation.

Enigmas of mammalian gamete form and function

The gametes of man and some other Eutheria have been manipulated successfully for practical reasons, but many gaps remain in our basic understanding of the way that they function. This situation stems not least from a failure to recognize the extent to which eutherian spermatozoa and eggs, and elements related to their operation, have come to differ from those of other groups. Novel features in the male that reflect this include a radical design of the sperm head with the acrosome seeming to function primarily in egg-coat binding rather than its lysis, a multifaceted post-testicular sperm maturation and an androgen/low-temperature-regulated system of sperm storage--both tied to the epididymis, a variable male accessory sex gland complex, and descent of the testis and epididymis to a scrotum. In the female, such novelties are represented in a need for sperm capacitation, in an unusual regulation of sperm transport within the oviduct, in the cumulus oophorus and character of the zona pellucida around the small egg, and in a unique configuration of gamete fusion. The collective evidence now suggests that many of these features reflect a new fertilisation strategy or its consequences, with most being causally linked. One initial 'domino' in this regard appears to be the small yolkless state of the egg and its intolerance for polyspermy, as determinants of the unusual mode of oviductal sperm transport and possibly the existence and form of the cumulus oophorus. However, a particularly influential first 'domino' appears to be the physical character of the eutherian zona pellucida. This differs from the egg coats of other animal groups by virtue of a resilient elasticity and thickness. These qualities allow this primary and often only coat to stretch and so persist during later expansion of the blastocyst, usually until close to implantation. At the same time, the dimensions, physical character, and particularly the relative protease-insensitivity of the zona appear to have had profound effects on sperm form and function and, more indirectly, on sperm-related events in the male and the female tract. Marsupials display some similarities and also some strikingly different features, against which the enigmas of the eutherian situation can be evaluated.

Rabbit epididymal secretory proteins. II. Immunolocalization and sperm association of REP38

Polyclonal antibody was used to partially characterize REP38, a major rabbit epididymal secretory protein. Western blot analyses and immunohistochemistry indicated that REP38 is only expressed in regions 5 and 6 of the epididymis (corpus epididy-midis) and is localized in the supranuclear region and microvilli of the principal cells in these regions. It was not expressed in other tissues of the body. In region 8 (cauda epididymidis), REP38 was detected in the luminal border and cytoplasm of scattered principal cells, indicating that it may be reabsorbed in this region. This protein accumulated on the sperm plasma membrane downstream of region 5 and was localized predominantly over the acrosomal and postacrosomal regions of the head and the middle piece. Although tightly bound to epididymal sperm, REP38 migrated to the equatorial segment under conditions in vivo that would promote capacitation. When tested in vitro, anti-REP38 IgG reduced the percentage of ova fertilized in a concentration-dependent manner, apparently by blocking sperm-egg fusion.

Autoradiographic distribution and physiological regulation of 2-[125I]iodomelatonin binding in rat epididymis

Autoradiographic study was conducted to localize 2-[125I]iodomelatonin binding in the rat epididymis. In the peripubertal (6 weeks old), postpubertal (8 weeks old) and adult (3 months old) rats, intense specific 2-[125I]iodomelatonin labelling of the corpus epididymidis was observed. The intensity of 2-[125I]iodomelatonin binding in the distal epididymal segment was significantly decreased in orchidectomized rats but the effect could be reversed with testosterone replacement. The intensity of 2-[125I]iodomelatonin binding in the distal rat epididymal segment did not show any diurnal rhythmicity when mid-light period and mid-dark period levels were compared, and was unaffected by constant lighting. Our data suggest androgen-dependent expression of 2-[125I]iodomelatonin binding sites, independent of light-induced changes in circulating melatonin, in the rat corpus epididymidis. A novel role of melatonin and its receptor in the regulation of the functions of rat corpus epididymidis is strongly implicated.

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.

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.

Glycoprotein changes in the rat sperm plasma membrane during maturation in the epididymis

To investigate surface glycoprotein changes during post-testicular maturation, plasma membranes were isolated from proximal caput, distal caput, and cauda epididymal rat spermatozoa. Membrane glycoproteins were identified on Western blots of SDS-PAGE fractionated samples using biotinylated lectins and Vecta-stain reagents; these were compared to glycoproteins present in cauda epididymal luminal fluid. Lens culinaris agglutinin, Pisum sativum agglutinin, peanut agglutinin, wheat germ agglutinin, Ricinus communis agglutinin, Ulaex europaeus agglutinin, and Dolichol biflorus agglutinin each bound a specific subset of the polypeptides present. Several types of glycoprotein changes were noted including their appearance, loss, alteration of staining intensity, and alteration of electrophoretic mobility. Some maturation-dependent sperm surface glycoproteins co-migrated with glycoproteins present in epididymal fluid. This approach of direct analysis of the glycoproteins in purified plasma membranes identifies a broader spectrum of maturation-related surface changes occurring within the epididymis than are noted with surface labeling procedures.

Regional differences in the morphology of the goat epididymis: a light microscopic and ultrastructural study

The goat epididymis, based on morphological differences, was divided into five regions; regions I and II, and the proximal part of region III constituted the head; the distal part of region III and region IV, the body; and region V, the tail. The epithelium of all regions contained principal and basal epithelial cells and intraepithelial lymphocytes and macrophages. In addition, regions II to IV also contained a few apical cells. Clear cells were absent. The epithelium varied in height from the tallest in region I (88 +/- 33 microns) to the shortest in region V (38 +/- 5 microns). Conversely, the luminal diameter, thickness of smooth muscle wall, and luminal sperm concentration were highest in region V. The irregular epithelial height of regions I and IV accounted for a stellate lumen in contrast to the oval lumen of the other regions. Whereas the lumen of region I contained only a few sperm, those of regions II, III, and IV were filled with sperm. Principal cells were the only cell type that showed striking cytological differences between regions. While they contained absorptive features (canaliculi, pinocytotic and coated vesicles, and subapical vacuoles) in all regions, the principal cells of region II were filled with large, heterogeneous vacuoles (up to 5 microns in diameter), suggesting that they may be preferentially involved in transporting and digesting particulate material. Besides absorptive features, principal cells of all regions contained morphological correlates of protein synthesis such as highly developed Golgi complexes in the supranuclear area and numerous cisternae of RER near the Golgi body and in the infranuclear cytoplasm. The cisternae of RER were more developed in region IV, and in some instances, they were distended with flocculent material resembling newly synthesized protein. Unlike the protein synthesizing organelles, principal cells of all regions lacked morphological correlates of steroid hormone synthesis. These results are compared with previously published data on the regional differences in the epididymis of other species, especially with those of the rat and the bull, in an effort to understand the significance of the epididymis in sperm maturation.

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.

Protein synthesis and secretion in the human epididymis and immunoreactivity with sperm antibodies

The synthesis and secretion of proteins in the different regions of the human epididymis were studied in vitro. Epididymal tissues obtained from patients undergoing castration for prostatic carcinoma or from cadavers were incubated in the presence of [35S]methionine, and the resulting radiolabeled proteins were analysed on SDS-PAGE. The corpus region was found to be the most active segment in total protein synthesis. Significant qualitative and quantitative changes were observed in the pattern of proteins secreted from the different epididymal regions. To establish those epididymal proteins that interact with maturing sperm, the secreted products were immunoreacted with antibodies raised against a Triton X-100 extract of ejaculated human sperm heads. The antibodies react mainly with the head region of ejaculated spermatozoa as judged by indirect immunofluorescence. Protein A-gold labeling of freeze-fracture images showed gold particle distribution on the sperm plasma membrane. Western blot analysis of the secreted proteins revealed four bands (66, 37, 32, and 29 kDa) in the proximal regions and six additional bands (80, 76, 48, 27, 22, and 17 kDa) in the distal part of the epididymis. Immunoprecipitation of the secreted proteins with these antibodies revealed six radioactive bands of 170, 80, 76, 60, 48, and 37 kDa, which indicates that certain proteins of epididymal origin bind to the sperm plasma membrane.

In vitro biosynthesis and secretion of rabbit epididymal secretory proteins: regulation by androgens

The biosynthesis and secretion of epididymal proteins were studied in an in vitro system using explants from rabbit epididymis cultured in a defined medium. Epididymal explants actively incorporated [35S]methionine into cellular proteins, about 7% of them being secreted into the medium. SDS-PAGE of the labeled proteins secreted to the medium showed regional differences in their synthesis and secretion along the epididymal tract. Castration resulted in the inhibition of the synthesis and secretion of at least two polypeptides of Mr 150,000 and 21,000, but at the same time induced the appearance of other polypeptides. Immunoprecipitations with a specific antibody indicated that the variations in the amounts of the secreted 21 kDa component were associated with differences in its rate of synthesis. Epididymis from immature rabbits synthesized some polypeptides that are repressed in the adult state. The results suggest a dual effect of testosterone on rabbit epididymal secretory proteins.

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.

Immunocytochemical localization of the major glycoprotein of epididymal fluid from the cauda in the epithelium of the mouse epididymis

The most abundant protein in fluid from the mouse cauda epididymidis, designated CP 27, is a glycoprotein that migrates at approximately 27000 daltons on SDS-polyacrylamide gels. Samples of CP 27 were isolated by preparative gel electrophoresis and were used to raise a guinea-pig polyclonal antiserum, which reacted with a single band on western blots of caudal epididymal fluid. This antiserum was used for immunocytochemical localization of CP 27 in histological sections of mouse epididymis using the peroxidase-antiperoxidase and protein A-gold methods. The most proximal staining with anti-CP 27 was in segment 6 of the distal caput epididymidis, where the lumen and a portion of the supranuclear cytoplasm of principal cells were stained. In contrast, in the distal corpus and cauda epididymidis (segments 8-11), there was pronounced staining of the luminal contents, sterocilia, and scattered cells identified as the "light" cells of the epididymal epithelium. Although CP 27 was found in the epididymal lumen of all segments distal to segment 6, the intensity of staining appeared to decline distally in the cauda epididymidis. Control sections exposed to pre-immune serum instead of anti-CP 27 showed no reaction. The results suggest that CP 27, the major glycoprotein of cauda epididymal fluid, is synthesized by principal cells of segment 6 of the distal caput epididymidis. CP 27 may be among the substances absorbed from the lumen by the light cells of the distal epididymis.

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.

Secretion of proteins and glycoproteins by perifused rabbit corpus epididymal tubules: effect of castration

Protein synthesis in epididymal tissue of intact and castrated rabbits was studied after incubation of epididymal minces with [35S]-cysteine or [35S]-methionine and protein separation by two-dimensional gel electrophoresis. Regional differences in the pattern of protein synthesized were observed. Castration did not change overall protein synthesis, but it reduced these regional differences. The presence of 5 alpha-DHT in the culture medium of the proximal corpus epididymidis perfused for 24 hr did not increase overall protein synthesis in tubules from intact or castrated rabbits and did not reinitiate synthesis of the proteins that had disappeared after castration. The kinetics of glycoprotein synthesis and secretion were studied by light and electron microscopy autoradiography at 0.5, 2, 6, and 24 hr after exposure to [3H]-mannose, [3H]-fucose, and [3H]-glucosamine. Changes in the distribution of mannose- and glucosamine-labeled material indicated that the decline in grain density over the epithelium from 30 min to 24 hr coincided with an increasing reaction over the stereocilia border from 30 min to 2 hr and in the lumen from 2 to 24 hr. The distribution of fucose-labeled material indicated that the grain reaction over the epithelium declined more rapidly than with the mannose label. When the glucosamine-labeled sperm mass was released from the tubules, the labeled material was lost after the first washing, indicating that the glucosamine-labeled glycoproteins did not bind firmly to corpus spermatozoa within 24 hr. After castration, both mannose- and fucose-labeled materials migrated to the cell apex more rapidly than in the intact animal, but they were not released as readily into the lumen. The culture of epididymal tubules from castrated males with 5 alpha-DHT for 24 hr did not promote the release of either mannose- or fucose-labeled material into the lumen. However, testosterone given in vivo for 2 weeks restored secretion of mannose-labeled material into the lumen.

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.

Maturation antigen of the mouse sperm flagellum: II. Origin from holocrine cells of the distal caput epididymis

During epididymal transit, the mouse sperm flagellum acquires a surface glycoprotein (SMA4) from epididymal fluid that functions as a sperm antiagglutinin. To determine the origin of this molecule, testes and epididymides of male mice were sectioned for light microscopy and stained with wheat germ agglutinin (WGA)-peroxidase, a probe that has been used previously to examine the biology of SMA4. WGA reactivity was localized to the cytoplasm in a small population of cells in the distal caput epididymis. Testis cells and principle cells of the caput were nonreactive with WGA, while stereocilia were stained on principle cells in the corpus and cauda. The WGA-positive cells in the distal caput were identified as holocrine cells on the basis of morphology, distribution, and PAS + reaction. At high magnification, intense WGA reactivity was due to the presence of numerous apical granules in the cytoplasm. The location of the cells in distal caput coincided exactly with the region of tubule in which sperm first acquired SMA4 on their flagellae. These data suggest that holocrine cells near the junction of caput and corpus epididymis are the source of the sperm antiagglutinin SMA4.

Histochemical evaluation of glycoconjugates in the male reproductive tract with lectin-horseradish peroxidase conjugates: I. Staining of principal cells and spermatozoa in the mouse

Several glycoconjugates are thought to bind spermatozoa as they pass through reproductive ducts. Paraffin sections of testis, ductuli efferentes, epididymis, and vas deferens of male mice were stained with ten different lectin-horseradish peroxidase conjugates to localize possible sites of synthesis and secretion of such glycoconjugates, based on the carbohydrate moieties in their constituent oligosaccharide side chains. Principal (columnar) cells lining the efferent ducts, germinal epithelium, and developing and maturing spermatozoa were examined with light microscopy. Staining of the Golgi and apical zones of cells was interpreted as evidence for synthesis and secretion of glycoconjugates. Principal cells synthesized and secreted glycoconjugates with sugar moieties as follows: sialic acid, all regions of the efferent ducts examined; the terminal disaccharide D-galactose- (beta 1----3) -N-acetyl-D-galactosamine, all regions of ducts except epididymis I; terminal alpha-D-galactosamine, some cells in epididymis III-V; N-acetyl-D-galactosamine, ductuli efferentes, epididymis I, II, and some cells in epididymis III-V; alpha-L-fucose, ductuli efferentes, vas deferens, and all regions of the epididymis except IV; N-glycosidic side chains, ductuli efferentes, vas deferens, and epididymis I, IV, and V. All of these sugar residues as well as N-acetyl-D-glucosamine were associated with the acrosomes and tails of spermatozoa throughout the ducts except for alpha-N-acetyl-D-galactosamine in epididymis I, and all occurred during one or more stages of spermiogenesis. The synthesis and secretion of glycoconjugates that bind to spermatozoa appear to involve more regions of the primary reproductive structures than was believed previously.

Identification and isolation of epididymal luminal proteins of the mouse

Proteins of mouse cauda epididymal fluid were analyzed by polyacrylamide gel electrophoresis. Fluid expressed from the cauda epididymidis and samples obtained by micropuncture of the epididymal lumen showed very similar patterns with respect to the major proteins they contained, with the exception of a small amount of serum albumin found in expressed caudal fluid. Eight prominent peptides present in both micropuncture fluid and expressed caudal epididymal fluid were selected for further study, and were designated CP 47, 42, 35, 29, 27, 25, 18, and 13 according to their mobility. Six of these were never detected in serum. Periodic acid-Schiff staining indicated that at least three were glycoproteins. The epididymal proteins were purified by preparative polyacrylamide gel electrophoresis and electroelution. Upon re-electrophoresis, the individual purified peptides comigrated with the corresponding bands in whole epididymal fluid, and no additional bands were detected, indicating that the proteins were purified to a high degree of homogeneity. Several of the mouse epididymal peptides resemble in their mobility proteins identified previously in other species, most notably the widely studied 33 Kd and 16 to 18 Kd proteins detected in the rat.

Sperm surface components involved in the control of the acrosome reaction

Several lines of evidence suggest that decapacitation of sperm occurs normally in the male reproductive tract, and as a result the acrosome is stabilized and the acrosome reaction is controlled. Since the defining experiments in 1951, where decapacitation was reversed in the female reproductive tract by capacitation, investigations have pursued the molecular events of this process. This review attempts to examine critically the older literature and compare that perspective with the current theories. The theories for decapacitation of sperm include the possible role of a peptide decapacitation factor, a glycoprotein-mediated steroid transfer to the sperm, masking of a galactosyl transferase by some macromolecule-containing carbohydrate, preclusion of calcium influx by a binding protein, and sperm interaction with the acrosome stabilizing factor. Although these theories are diverse, there are some unifying aspects. However, there remain some major unanswered questions. For example, although we point to some circumstantial evidence that infers a single decapacitation factor, this needs to be further substantiated. It is concluded that with the purification of a macromolecule involved in capacitation, specific proposals on the mechanism of capacitation, and new tools to evaluate the capacitation process, it is likely that another decade will not pass without emergence of a unifying molecular theory of sperm capacitation.

Surface of the rooster spermatozoon changes in passing through the Wolffian duct

Fluid secreted by the rooster Wolffian duct contains several proteins separable on polyacrylamide gel electrophoresis (PAGE) and isoelectric focusing (IEF) gels. Antibodies against these fluid components were obtained by immunizing rabbits, and the IgG fraction was then purified. As judged by indirect immunofluorescence, purified IgG against rooster duct fluid did not bind to any testicular spermatozoa. However, it bound distinctly to the whole surface of spermatozoa from the initial (epididymal) region and more intensely to all spermatozoa from the mid- and terminal regions of the Wolffian duct of the rooster, though not at all to mature duck or pigeon spermatozoa. Thus, in the rooster, as in therian mammals, the surface of the spermatozoon clearly acquires specific components secreted by the Wolffian duct. It should not be assumed that such surface change in rooster spermatozoa is entirely comparable, in a functional sense, to that undergone by mammalian spermatozoa, in which this seems directly related to fertilizing ability. Unlike those of mammals, rooster spermatozoa do not seem to require capacitation, and some spermatozoa in the testis already are competent to fertilize. Components acquired in the Wolffian duct by the rooster spermatozoon may bear on other aspects, perhaps sperm transport and/or survival in the female.

Characterization of maturation-dependent extrinsic proteins of the rat sperm surface

Mammalian spermatozoa must mature in the epididymis before they can fertilize an egg. It is known that modification of the protein composition of the sperm surface is an important part of the maturation process. In this paper, we present data on two related glycoproteins that can be extracted from mature but not immature spermatozoa. Cell surface radioiodination has shown that these proteins are on the sperm surface, and immunofluorescence microscopy, by use of monospecific antibodies to the proteins, has indicated that their localization is restricted to the periacrosomal region of the sperm head. We have also shown that in vitro, these proteins will bind to the identical region of immature sperm. Immunohistochemical localization of the proteins in the epididymis shows that they are produced and secreted by the cauda region. The significance of the addition of these proteins to the sperm surface in both maturation and fertilization is discussed.

Maturation of spermatozoa in the epididymis of the Chinese hamster

Chinese hamster spermatozoa gain their ability to move when they descend from the testis to the distal part of the caput epididymis, but it is not until they enter the corpus epididymis that they become capable of fertilizing eggs. The maturation of the spermatozoa proceeds as they further descend the tract and perhaps continues even in the vas deferens. During transit between the distal caput and proximal cauda epididymides, small membrane-limited vesicles (and tubules) appear on the plasma membrane over the acrosomes of the spermatozoa. The number of vesicles appearing on the sperm brane reaches a maximum when the spermatozoa are in the proximal cauda epididymis. It declines sharply in the distal cauda epididymis. Spermatozoa in the vas deferens are free of the vesicles. The origin, chemical nature, and functional role of the vesicles that appear on the sperm surface during epididymal transit must be the subject of further investigation.

Regional differences in luminal fluid polypeptides of the rat testis and epididymis revealed by two-dimensional gel electrophoresis

Luminal fluid samples were collected by micropuncture of the seminiferous tubule, rete testis, and defined levels of the epididymal tubule. After removal of spermatozoa by centrifugation, the supernatant fluids were analyzed by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and an ultrasensitive silver staining procedure to define the sequential change in protein composition along the excurrent duct system. Fluid from each segment displayed a characteristic 2-D PAGE map composed of numerous polypeptides. Seminiferous tubule fluid contained a wide array of polypeptides, with most concentrated in the 45 Kd to 90 Kd range, but, in contrast, rete testis fluid lacked most of these polypeptides. The major complex of rete testis fluid comigrated with serum albumin and was present in all distal segments. Other major rete testis components were not noted distally. Fluid from the caput was characterized by new major components of 30 to 37 Kd, 28 to 30 Kd, 24 Kd, and 23 Kd, each of which consisted of multiple spots of apparent isoelectric variants; all except the 30 to 37 Kd complex were present in the fluid from more distal segments. Proceeding distally, there was a temporal appearance of new polypeptides, especially in the molecular weight range below 30 Kd. Two-dimensional PAGE analysis of detergent extracts of washed spermatozoa indicate that a specific subset of these fluid polypeptides are sperm associated.

The secretory pathway in the mouse epididymis as shown by electron microscope radioautography of principal cells exposed to monensin

The secretory pathway in principal cells of the mouse epididymis was studied using in vitro labeling and electron microscope radioautography of tissue exposed to the ionophore monensin. After a 5-minute pulse of 3H-leucine, control samples of caput epididymidis were incubated in a modified Krebs-Ringer solution (MKRH medium), while experimental specimens were placed in the same medium, to which 1 microM monensin had been added. At intervals between 5 minutes and 4 hours, samples were fixed and prepared for electron microscope radioautography. Analysis of control specimens revealed heaviest labeling of the rough and the sparsely granulated endoplasmic reticulum early in the experiment followed by a fall in radioactivity, maximal labeling of the Golgi apparatus at 30 minutes, and a pronounced rise in the percentage of grains associated with the apical cell surface and the epididymal lumen beginning 1 hour after administration of precursor. In monensin-treated epididymides, radioactive material accumulated in the Golgi region while the normal increase in labeling of the apical surface and the lumen was completely inhibited for at least 2 hours. The percentage of grains attributed to coated vesicles was also reduced in samples exposed to monensin. In contrast, labeling patterns of the abundant, sparsely granulated, endoplasmic reticulum and the rough endoplasmic reticulum were very similar in monensin-treated and control specimens. The concomitant alterations in labeling of the Golgi apparatus and the lumen demonstrate that the Golgi apparatus participates in intracellular transport of secretory proteins in epididymal principal cells, and is not bypassed as previously suggested. The percentage of grains associated with the sparsely granulated endoplasmic reticulum suggests that much of the synthesis of secretory protein in the principal cells occurs in this organelle, and the lack of alteration of its labeling in the presence of a monensin-induced block at the level of the Golgi apparatus indicates that the sparsely granulated endoplasmic reticulum lies before the Golgi apparatus in the secretory pathway. It is speculated that vesicles play a role in transport of secretory protein from the Golgi apparatus to the lumen.