Major contribution of epididymis to alpha-glucosidase content of ram seminal plasma

Acid alpha-glucosidase and L-carnitine (a well-known epididymal marker) were measured in rete testis and epididymal fluids of adult male rams. These fluids were collected by selective catheterization or by a micropuncture technique, respectively. Both parameters remained at a low and constant level in rete testis and all along caput and corpus epididymidis. Then they increased at equivalent rates in cauda epididymidis to much higher levels than those in seminal plasma (5 mU/mg protein and 10 mM, respectively). An optimum pH study of alpha-glucosidase activity in these fluids showed two well-separated peaks in rete testis and caput epididymal fluids around pH 4 and 7, respectively, but only a single peak at pH 4 in cauda epididymidis that was comparable to the one in seminal plasma. Sucrose density gradient fractions analyzed for their enzyme content in the absence or presence of sodium dodecyl sulfate (1% w/v), a selective inhibitor of acid alpha-glucosidase activity, allowed the demonstration of two enzyme forms at pH 6.8 in rete testis fluid sedimenting in the 7S and 4S regions of the gradient, while a unique 4S form was encountered in cauda epididymidis and in seminal plasma. Although the fate of the minor 7S component of the rete testis fluid in its epididymal transit is presently unknown, similarities between the enzyme in cauda epididymidis and seminal plasma are strong enough to support the hypothesis that epididymis contributes primarily to the acid alpha-glucosidase content of ram seminal plasma.     

Alpha-mannosidase activity in stallion epididymal fluid and spermatozoa

The expression of α-D-mannosidase activity was fluorometrically and electrophoretically assessed in spermatozoa, epididymal fluid and homogenates of stallion epididymal tissue. Enzyme activity had regional differences; it was higher (P < 0.05) in samples from the cauda epididymal region than in samples from the proximal caput region (largely composed of efferent ducts). Based on enzyme activity, as a function of pH of the assay substrate, electrophoretic analysis in native and native/SDS-PAGE conditions, and the effect of inhibitors or activators, we inferred the presence of at least two catalytically active forms of α-D-mannosidase. The neutral form of the enzyme (α-mannosidase II) was activated by Co²⁺, whereas the acid form (optimum pH 3.5 to 4.0) was sensitive to swainsonine (an inhibitor of α-mannosidase I), stabilized or stimulated by Zn²⁺, and not activated by Co²⁺ (activator of the neutral form). The activity of the acid form of the enzyme was highest in the epididymal fluid, where it seemed to be mainly in a secretory form. This form of the enzyme may have a role in plasma membrane remodeling associated with sperm maturation. In contrast, the activity of α-mannosidase II was higher in mature spermatozoa. It has been postulated that α-mannosidase II may act as a receptor in the recognition and binding of the complementary carbohydrate moieties present on the zona pellucida. With non-denaturing electrophoresis, α-D-mannosidase had an electrophoretic mobility of 0.35 and 0.24. When resolved by 1D and 2D SDS-PAGE (under denaturing conditions) the enzyme had a major protein band of molecular weight 154 kDa in spermatozoa and epididymal samples. Based on its properties under native conditions, we inferred that this enzyme might interact with other proteins and form transitory aggregates.     

Purification and properties of major alpha-D-mannosidase in the luminal fluid of porcine epididymis.

A lysosomal type alpha-D-mannosidase was successfully purified by DEAE-Sephacel, Red-Amicon and Superdex 200 column chromatographies from porcine cauda epididymal fluid. The purified enzyme consisted of 63 and 51 kDa subunits at equimolar amounts. It cleaved alpha1-2 linked mannosyl residues and less but significantly cleaved alpha1-3 and alpha1-6 linked mannosyl residues in the high-mannose oligosaccharides. The optimal pH to hydrolyze oligosaccharide was in the acidic pH range (pH 3.5 approximately 4.0).Total alpha-D-mannosidase activities in the porcine epididymal fluid increased from proximal to distal caput epididymis, which maintained to cauda epididymis. At least two kinds of alpha-D-mannosidase (lysosomal type enzyme and 135 kDa alpha-D-mannosidase (MAN2B2)) were contained in the porcine epididymal fluid. The activity of the lysosomal type enzyme is much higher than MAN2B2 at the physiological pH.These results suggest that the lysosomal type alpha-D-mannosidase is the predominantly active enzyme in the luminal fluid of porcine epididymis and that it participates in the glycoprotein modification on the sperm surface during epididymal transit.     

Expression and activity of gamma-glutamyl transpeptidase in the rat epididymis.

Following Northern analysis, GGT mRNA was found predominantly within the caput epididymides and kidney. The size of mRNAs for kidney, caput, corpus, and ductus deferens were 2.2, 2.3, 2.2, and 2.3 kb, respectively, whereas cauda showed a doublet of 2.2 and 2.3 kb. GGT transpeptidation and hydrolytic activity within epididymal luminal fluids collected by micropuncture showed caput = corpus greater than cauda and corpus greater than caput greater than cauda, respectively. Caput luminal GGT transpeptidation activity was significantly inhibited by serine-borate and was optimal at pH 8.0. The calculated Km and Vmax values for hydrolysis of GSH by caput luminal GGT were 0.06 microM and 2.19 nmoles/min/microliters luminal fluid at pH 8.5 compared to 0.49 microM and 0.49 nmoles/min/microliters luminal fluid, respectively, at the physiological pH 6.5 of caput fluid. These studies would suggest that the epididymis can control the activity of luminal GGT by pH. Lower Km (0.12 microM) and higher Vmax (1.13 nmoles/min/microliters luminal fluid) values were also calculated when GSSG was used compared to GSH. Results from Triton X-114 partitioning experiments suggest that luminal GGT probably exists in both membrane bound and nonmembrane bound forms. Western blot analysis of proteins within epididymal luminal fluids revealed both subunits of GGT in all epididymal regions studied. However, two lower molecular bands, approximately 22 kDa and 21 kDa, were also observed in cauda fluid. It is suggested that as GGT is transported along the epididymal duct it undergoes degradation, which accounts for its loss of activity in the distal epididymal regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

alpha-L-Fucosidase in the reproductive organs and seminal plasma of the bull

alpha-L-Fucosidase (EC 3.2.1.51) activity was studied in different reproductive organs, seminal plasma and spermatozoa of the bull. The highest specific activity of alpha-L-fucosidase was found in the epididymis. Gel filtration at pH 7.0 revealed two alpha-L-fucosidases (alpha-L-fucosidase I and alpha-L-fucosidase II) in most reproductive tissues, but seminal plasma, spermatozoa and epididymal cauda contained only form I. Fractionation at basic pH (pH 8.5) resulted in the elution of alpha-L-fucosidase as form II. Some differences were encountered in pH profiles and thermal stabilities of the two enzyme forms and they showed additional polymorphism after chromatofocusing. The comparison of enzyme profiles after fractionations suggests that cauda epididymidis is the main source of the seminal plasma activity in the bull.     

α-L-fucosidase in the reproductive organs and seminal plasma of the bull

α-L-Fucosidase (EC 3.2.1.51) activity was studied in different reproductive organs, seminal plasma and spermatozoa of the bull. The highest specific activity of α-L-fucosidase was found in the epididymis. Gel filtration at pH 7.0 revealed two α-L-fucosidases (α-L-fucosidase I and α-L-fucosidase II) in most reproductive tissues, but seminal plasma, spermatozoa and epididymal cauda contained only form I. Fractionation at basic pH (pH 8.5) resulted in the elution of α-L-fucosidase as form II. Some differences were encountered in pH profiles and thermal stabilities of the two enzyme forms and they showed additional polymorphism after chromatofocusing. The comparison of enzyme profiles after fractionations suggests that cauda epididymidis is the main source of the seminal plasma activity in the bull.     

Beta-galactosidase in the seminal plasma and reproductive organs of the bull

The distribution of beta-galactosidase activity was studied in different reproductive organs, seminal plasma and spermatozoa of the bull. The highest specific activity of beta-galactosidase was found in testis and in different parts of the epididymis, where the activity seemed to be partly in secretory (cauda secretion) and partly in non-secretory, bound form (caput to cauda epididymidis). Gel filtration on Sepharose 6B at pH 7.0 revealed two beta-galactosidase forms (GF-1, Mr approximately 500,000-600,000 and GF-2, Mr approximately 190,000-220,000) in reproductive organs and seminal plasma. The pH-optimum of both beta-galactosidase forms was about 3.75-4.75. Hg2+ and p-chloromercuribenzoate inhibited strongly these activities. Further, form GF-2 seemed to be slightly more sensitive to the thermal inactivation at 50-70 degrees C than form GF-1. In chromatofocusing beta-galactosidase activities in bull seminal plasma coeluted with those of the cauda epididymidis (pI-values 7.5-6.4). On the contrary, prostate, Cowper's gland, testis, ampulla and seminal vesicles had enzyme activities eluting at lower pI-values (6.3-4.2). Thus, the seminal plasma activity is mainly an indicator for the function of the epididymal cauda.     

A 105- to 94-kilodalton protein in the epididymal fluids of domestic mammals is angiotensin I-converting enzyme (ACE); evidence that sperm are the source of this ACE

SDS-PAGE analysis of luminal fluid from the ram testis and epididymis revealed a protein of about 105 kDa in the fluid in the caput epididymal region. The molecular mass of this fluid protein shifted from 105 kDa to 94 kDa in the distal caput epididymidis and remained at 94 kDa in the lower regions of the epididymis. The possible sperm origin of this protein was suggested by the decrease in intensity of a 105-kDa compound on the sperm plasma membrane extract and by its total disappearance from the fluid of animals with impaired sperm production caused by scrotal heating. The 94-kDa protein was purified from ram cauda epididymal fluid, and a rabbit polyclonal antiserum was obtained. This antiserum showed that membranes of testicular sperm and sperm from the initial caput were positive for the presence of an immunologically related antigen. The protein was immunolocalized mainly on the flagellar intermediate piece, whereas in some corpus and caudal sperm, only the apical ridge of the acrosomal vesicle was labeled. The purified protein was microsequenced: its N-terminal was not found in the sequence database, but its tryptic fragments matched the sequence of the angiotensin I-converting enzyme (ACE). Indeed, the purified 94-kDa protein exhibited a carboxypeptidase activity inhibited by specific blockers of ACE. All the soluble seminal plasma ACE activity in the ram was attributable to the 94-kDa epididymal fluid ACE. The polyclonal antiserum also showed that a soluble form of ACE appeared specifically in the caput epididymal fluid of the boar, stallion, and bull. This soluble form was responsible for all the ACE activity observed in the fluid from the distal caput to the cauda epididymidis in these species. Our results strongly suggest that the epididymal fluid ACE derives from the germinal form of ACE that is liberated from the testicular sperm in a specific epididymal area.     

Identification and expression of boar sperm proteins in the reproductive tract that interact with antibodies in serum from an infertile woman

Serum designated as IS obtained from a young healthy infertile woman induced a head-to-head agglutination of ejaculated boar sperm. The immunoglobulin G (IgG) prepared from IS localized to the acrosomal region of the sperm head obtained from the corpus and cauda epididymis as determined by an indirect immunofluorescent method. The IgG interacted with a boar sperm protein with an estimated molecular weight of 45-kDa, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoretic (SDS-PAGE) immunoblotting technique. However, the IgG did not interact with proteins extracted from sperm obtained from the testis and caput epididymis or from non-gonadal tissues including liver, kidney, spleen, muscle and serum. The IgG interacted with additional proteins of about 75- and 38-kDa present in the corpus and cauda epididymal fluids but not those in the caput epididymal fluid. The staining intensity of the 75-kDa band was reduced and that of the 38-kDa was nullified with ejaculated seminal plasma proteins. The interacting proteins were adsorbed when chromatographed on Concanavalin A Sepharose column, suggesting that they are glycoproteins.     

An epididymal form of cauxin, a carboxylesterase-like enzyme, is present and active in mammalian male reproductive fluids

Mass spectrometric analysis of a prion protein (PrP)-containing complex isolated from ram cauda epididymal fluid revealed a protein that showed homology to a carboxylesterase-like protein previously identified in cat urine (cauxin). Using anti-cauxin antibodies, immunoreactive bands were detected in corpus and cauda epididymal fluid from all mammals tested (ram, boar, mouse, and cat). In the ram, the protein was also present in seminal fluid but not found to be associated with sperm. The bands reacting with the anti-cauxin antibody coincided with those having esterase activity in a zymographic assay and its levels paralleled the esterase activity of native epididymal fluids. A partial nucleotide sequence of 1143 bp, corresponding to 380 amino acids, was obtained by RT-PCR amplification from total RNA from the corpus epididymis (zone 6). The deduced protein sequence shows a high degree of homology (up to 90%) with the different cauxin proteins found in databases but only up to 60% with other known carboxylesterases. By PCR, strong mRNA expression was found in the corpus and cauda epididymis, while the testis, kidney, and caput epididymis had low expression. No mRNA was detected in the lung, heart, or liver. These data demonstrate that an epididymal form of the cauxin enzyme is secreted into mammalian epididymal fluid. In the ram, it is associated with a high molecular-weight PrP-associated complex and may be responsible for the majority of the esterase activity in the cauda epididymal fluid of this species.     

beta-N-acetylglucosaminidase in the reproductive organs and seminal plasma of the bull

The highest specific activity of beta-N-acetylglucosaminidase (beta-NAG) was found in the different parts of the epididymis, where the activity seemed to be partly in secretory and partly in non-secretory, tissue-bound form. Epididymal spermatozoa also contained moderate beta-NAG activity. The beta-NAG was separated by chromatofocussing and anion exchange chromatography with HPLC into multiple forms with distinct pI values (8.0-4.0). The cauda epididymidis, ampulla and the seminal vesicles formed the major secretory sources of the high beta-NAG activity in bull seminal plasma. The major secretory forms of beta-NAG in caput and cauda epididymidis showed distinct elution profiles. In the fractionation with gel filtration on Sepharose 6B, the beta-NAG activities derived from bull testis and caput epididymidis had smaller molecular weights than did the secretory enzymes in seminal plasma, seminal vesicle secretion and cauda epididymidis. Maximum activity of all beta-NAG isoenzymes was observed at pH 5.0. They were almost totally inactivated at 60 degrees C and about 75-80% of the activity was lost at 55 degrees C. All the isoenzymes were strongly inhibited by thiol reagents but not with other metal ions and chelating agents. Histochemical studies showed a strong granular (lysosomal) reaction for beta-NAG in basal cells and basal parts of the principal cells in all but the initial segment of the epididymis. An apical (secretory) reaction was prominent in the distal caput and corpus as well as in distal cauda. After the distal caput the luminal sperm mass became increasingly mixed with a beta-NAG-positive material. The epithelial cells of the ampulla and seminal vesicle displayed a moderate apical (secretory) reaction.     

Tissue and cell specificity of immobilin biosynthesis

The mechanisms for the initiation of sperm motility have been poorly understood until recently. Immobilin is a novel mucin glycoprotein of high molecular weight found in the cauda epididymis of the rat that, at concentrations equivalent to those found in native cauda epididymal fluid, reversibly inhibits sperm motility. In this study, immobilin was purified from rat cauda epididymal fluid to apparent homogeneity and used to generate polyclonal antibody in rabbits. The antibody was characterized by immunoblotting, and immunofluorescence was used to localize immobilin in paraffin sections of components of the reproductive system of adult male rats. Immobilin was not detectable in the efferent duct and was first detectable in the apical portion of some epithelial cells of the initial segment of the caput epididymis. Immobilin was detectable intracellularly only in cells of the caput epididymis. In the corpus and cauda epididymis immobilin was detectable only in the lumen of the tubules. Immunoprecipitation of immobilin radiolabeled in vitro confirmed that immobilin biosynthesis in the adult rat is restricted to the caput epididymis. Principal cells in the caput epididymis synthesize immobilin and secrete it into the lumen of the tubules to travel with the sperm into the cauda.     

Sodium,potassium, and protein concentrations and 2D-SDS-page of epididymal luminal and ejaculated seminal fluids of the adult chimpanzee (Pan troglodytes)

The concentration of soluble protein and of sodium and potassium ions was estimated in chimpanzee caput epididymal luminal fluid, cauda epididymal luminal fluid, and ejaculated seminal fluid. Protein concentration was 48.5 ± 1.5 μg/μl in caput fluid, 26.8 ± 2.0 μg/μl in cauda fluid, and 53.0 ± 7.9 μg/μl in seminal fluid. Sodium concentration was 127.0 ± 7.0 mM in caput fluid, 34.5 ± 1.8 mM in cauda fluid, and 18.8 ± 1.8 mM in seminal fluid. Potassium concentration was 58.0 ± 0.0 mM in caput fluid, 56.8 ± 5.2 mM in cauda fluid, and 77.0 ± 1.7 mM in seminal fluid. Proteins in caput epididymal, cauda epididymal, and ejaculated seminal fluids, with approximate molecular weights (kDa) between <14.4 and 45.0 kDa and apparent isoelectric points (pIs) between 4.5 and 7.5, were resolved by two-dimensional SDS-polyacrylamide gel electrophoresis (2D-SDS-PAGE) and silver stained. In caput fluid, the most intensely stained polypeptides resolved between 14.4 and 21.5 kDa (pI 5.4–7.4). In cauda fluid, the number and intensity of stained components increased markedly, and the most intensely stained polypeptides resolved between 21.5 and 31.0 kDa (pI 5.7–7.3). In seminal fluid, polypeptides between <14.4 and 45.0 kDa (pI 5.7–7.4) appeared characteristically diffuse and distributed. These results demonstrate that the ions and the polypeptides in the luminal microenvironment change significantly along the epididymal duct of the male chimpanzee. © 1994 Wiley-Liss, Inc.     

Posttranslational processing of PH-20 during epididymal sperm maturation in the horse.

It is generally accepted that spermatozoa become functionally mature during epididymal transit. The objective of this study was to determine whether the cellular location of equine PH-20 is modified during epididymal transit and, if so, the mechanism for such modification. Sperm were isolated from caput and cauda epididymal regions from stallions undergoing castration (n = 7) and used as whole sperm cell or subjected to nitrogen cavitation for isolation of plasma membrane proteins. Both caput and cauda sperm and sperm protein extracts were subjected to N-deglycosylation, O-deglycosylation, or trypsinization. The SDS-PAGE and Western blot analysis using a polyclonal anti-equine PH-20 IgG were performed in sperm extracts, and indirect immunofluorescence on whole sperm was also performed to determine the cellular distribution of plasma membrane PH-20 following similar treatments (deglycosylation or trypsinization). Hyaluronan substrate gel electrophoresis was performed to detect hyaluronidase activity in SDS-PAGE proteins. Western blots revealed significant differences in electrophoretic migration of PH-20 proteins from caput and cauda epididymal sperm. No effect was seen from deglycosylation treatments on the Western blot pattern; caput protein extracts exposed to trypsin showed the same band pattern as extracts from the cauda epididymis. N-deglycosylation resulted in the loss of hyaluronidase activity of sperm from both epididymal regions, whereas O-deglycosylation or trypsinization did not affect hyaluronidase activity. In caput epididymal sperm, the PH-20 protein is distributed over the entire sperm head; in cauda epididymal sperm, it is restricted to the postacrosomal region. No effect from deglycosylation on the cellular distribution of PH-20 was observed; however, treatment with trypsin changed the cellular distribution of PH-20 in caput sperm similar to that of the distribution of cauda sperm. These results suggest that PH-20 distribution during epididymal maturation is dependent on proteolytic trypsin-like mechanisms and, possibly, on complementary membrane-associated factors.     

The effects of shRNA-mediated gene silencing of transcription factor SNAI1 on the biological phenotypes of breast cancer cell line MCF-7

Developing spermatozoa require a series of posttesticular modifications within the luminal environment of the epididymis to achieve maturation; this involves several surface modifications including changes in plasma membrane lipids, proteins, carbohydrates, and alterations in the outer acrosomal membrane. Epididymal maturation can therefore allow sperm to gain forward motility and fertilization capabilities. The objective of this study was to identify maturation-dependent protein(s) and to investigate their role with the production of functionally competent spermatozoa. Lectin blot analyses of caput and cauda sperm plasma membrane fractions identified a 17.5 kDa wheat germ agglutinin (WGA)-binding polypeptide present in the cauda sperm plasma membrane not in the caput sperm plasma membrane. Among the several WGA-stained bands, the presence of a 17.5 kDa WGA-binding polypeptide band was detected only in cauda epididymal fluid not in caput epididymal fluid suggesting that the 17.5 kDa WGA-binding polypeptide is secreted from the cauda epididymis and binds to the cauda sperm plasma membrane during epididymal transit. Proteomic identification of the 17.5 kDa polypeptide yielded 13 peptides that matched the sequence of peroxiredoxin-5 (PRDX5) protein (Bos Taurus). We propose that bovine cauda sperm PRDX5 acts as an antioxidant enzyme in the epididymal environment, which is crucial in protecting the viable sperm population against the damage caused by endogeneous or exogeneous peroxide.     

Identification of epididymal proteins associated with hamster sperm.

The electrophoretic analysis of the proteins that were extracted from immature caput and mature cauda sperm showed evidence of accumulation of several proteins during the epididymal transit of the sperm. An antiserum, raised against detergent-extracted proteins from mature spermatozoa, immunostained six epididymal proteins with apparent molecular masses of 16, 22.5, 26, 37, 60, and 80 kDa on Western blots of epididymal fluid. Of these proteins, only the 26 kDa protein was significantly immunodetected in proximal caput epididymal fluid. Its biosynthesis by caput epididymis was confirmed by immunoprecipitation of an in vitro translated product of caput poly (A) RNA. The homology of the 26 kDa epididymal protein with the 26 kDa sperm protein was verified by epitope mapping. The other epididymal proteins were found in the fluid of the more distal portions of the organ. Their presence in the epididymal fluid coincided with their detection on the sperm. These epididymal proteins were considered to be sperm-coating proteins.     

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.