A rat sperm flagellar surface antigen that originates in the testis and is expressed on the flagellar surface during epididymal transit

The involvement of immunoglobulin superfamily proteins in spermatogenesis and sperm-egg interaction

The immunoglobulin superfamily (IgSF) proteins are expressed on the plasma membrane between Sertoli cells and germ cells in the testis. IgSF proteins are specifically present at the apical Sertoli-germ cell junction, that is, ectoplasmic specialization and are involved in germ cell differentiation. Some IgSF proteins are present on the surface of germ cells and undergo further biochemical modifications during sperm maturation. These IgSF proteins undergo final modifications during capacitation and/or the acrosome reaction. The function and expression of IgSF proteins in the testis and spermatozoa, as they relate to spermatogenesis and sperm-egg interaction, are discussed. (Reprod Med Biol 2006; 5: 87-93).

The involvement of immunoglobulin superfamily proteins in spermatogenesis and sperm-egg interaction

The immunoglobulin superfamily (IgSF) proteins are expressed on the plasma membrane between Sertoli cells and germ cells in the testis. IgSF proteins are specifically present at the apical Sertoli-germ cell junction, that is, ectoplasmic specialization and are involved in germ cell differentiation. Some IgSF proteins are present on the surface of germ cells and undergo further biochemical modifications during sperm maturation. These IgSF proteins undergo final modifications during capacitation and/or the acrosome reaction. The function and expression of IgSF proteins in the testis and spermatozoa, as they relate to spermatogenesis and sperm-egg interaction, are discussed. (Reprod Med Biol 2006; 5: 87-93).

Molecular modifications of MC31/CE9, a sperm surface molecule, during sperm capacitation and the acrosome reaction in the rat: is MC31/CE9 required for fertilization?

We examined the modification of the MC31 molecule during capacitation, the acrosome reaction, and studied its role in fertilization. These studies revealed that the molecular mass of MC31 in cauda spermatozoa was approximately 28,000-26,000 Dalton (28-26 kDa). A limited change in molecular mass was seen in capacitated spermatozoa. Treatment of sperm extracts with peptide-N-glycosidase (PN glycosidase) reduced the molecular mass of MC31 in both cauda and capacitated spermatozoa from 28-26 kDa to 23-20 kDa, suggesting that MC31 from both cauda and capacitated spermatozoa is glycosylated, and indicating that capacitation induces minor posttranslational modifications in the structure of the MC31 antigen. The MC31 antigen was redistributed from the midpiece of cauda epididymal spermatozoa to the head and equatorial segment after capacitation and acrosome reaction, respectively, when traced by indirect immunofluorescence under in vitro fertilization (IVF) conditions. Some spermatozoa did not stain for the MC31 antigen and might represent spermatozoa that have shed the antigen. IVF experiments conducted to assess the effect of an anti-MC31 monoclonal antibody (mMC31) revealed that this antibody significantly (P < 0.01) inhibited fertilization of cumulus-invested zona pellucida-intact and the zona pellucida-free oocytes in a dose-dependent manner. However, sperm-oolemma binding was not affected. These findings suggest the MC31 antigen facilitates sperm-oocyte interactions.

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 expression and cellular localization of the sperm flagellar protein MC31/CE9 in the rat testis: possible posttranscriptional regulation during rat spermiogenesis

We isolated the MC31 cDNA clone coding the antigen specifically recognized by the monoclonal antibody mMC31, and found that MC31 was identical to rat CE9. Therefore, this molecule is called MC31/CE9. MC31/CE9, a member of the immunoglobulin superfamily molecules, was localized on the rat sperm flagellar plasma membrane. We analyzed the expression and cellular localization of MC31/CE9 mRNA and protein in the adult rat testis by use of Northern hybridization, in situ hybridization, and immunohistochemical analyses. In the course of spermatogenesis, MC31/CE9 mRNA first appeared in type B spermatogonia. The mRNA signal intensity increased progressively to pachytene spermatocytes and remained constantly at a considerable level throughout the subsequent phases of spermatocytes and round spermatids, and then decreased gradually from step-11 spermatids to disappear in step-15 spermatids. On the other hand, MC31/CE9 protein expression showed a bimodal pattern. Immunohistochemical analysis for the MC31/CE9 protein revealed its most intense immunoreactivity on the flagella of step-8 to step-19 elongated spermatids. The cytoplasmic immunoreactivity of the MC31/CE9 protein also appeared in preleptotene to early pachytene spermatocytes and elongated spermatids, with particularly intense immunoreactivity in the Golgi complexes of zygotene and early pachytene spermatocytes (stage XIII to III) as well as step-8 to step-13 spermatids. Between these two phases, the MC31/CE9 protein proved undetectable in the cytoplasm of any spermatogenic cells. Sertoli cells and Leydig cells were devoid of MC31/CE9 mRNA and its protein. Therefore, the production of MC31/CE9 is thought to be posttranscriptionally regulated during spermiogenesis.

An MN9 antigenic molecule, equatorin, is required for successful sperm-oocyte fusion in mice

The acrosome plays an important role in fertilization. This study was designed to examine the role and behavior of a molecule, equatorin (the antigenic molecule of the monoclonal antibody mMN9), localized at the equatorial segment of the acrosome. In vitro fertilization (IVF) investigation was conducted to examine the role of this molecule, by assessing the effect of mMN9 in TYH medium (a modified Krebs Ringer bicarbonate solution) containing mMN9 at 0 (control), 25, 50, and 100 microg/ml. Under these conditions, the IVF investigation was divided into two experiments: 1) the zona pellucida (zona)-intact experiment, in which capacitated sperm inseminated cumulus- and zona-intact oocytes; and 2) the zona-free experiment, in which acrosome-reacted sperm inseminated zona-free oocytes. It was found that mMN9 did not affect sperm motility, zona binding, or zona penetration, but it significantly inhibited fertilization, reducing the rates of pronucleus and two-cell embryo formation in both the zona-intact and zona-free oocyte experiments. In addition, when judged at 5 h after insemination in the zona-intact experiment, nearly half of the unfertilized oocytes had accumulated sperm in the perivitelline space (perivitelline sperm), and concurrently we confirmed by electron microscopy the presence of many unreleased cortical granules preserved beneath the oolemma, indicating no occurrence of sperm-oocyte fusion. Confocal laser scanning light microscopy with indirect immunofluorescence demonstrated that equatorin was localized at the equatorial segment in both capacitated and perivitelline sperm (acrosome-reacted sperm). These results suggest that equatorin that is preserved at the equatorial segment is involved in the process of sperm-oocyte fusion in mice.

Analysis of the process of localization of fertilin to the sperm posterior head plasma membrane domain during sperm maturation in the epididymis

Fertilin is a heterodimeric (subunits alpha and beta) sperm plasma membrane protein. Both subunits belong to the ADAM protein family of surface proteins that contain a disintegrin and a metalloprotease domain. Fertilin functions in sperm-egg fusion by binding the sperm to the egg plasma membrane via a binding site in the disintegrin domain of fertilin beta. On testicular sperm of guinea pig, fertilin is distributed on the plasma membrane over the entire sperm head, but is found only on the posterior head once sperm have passed through the epididymis. This redistribution of fertilin to the posterior head can be partially mimicked in vitro if testicular sperm are briefly treated with trypsin. In this study we used immunofluorescence and digital image analysis to analyze how fertilin becomes restricted to the posterior head. We found that fertilin became restricted to the posterior head by migration of anterior head fertilin molecules into the posterior head domain. Comparison of immunofluorescence patterns and immunoblots of fertilin from seven regions of the epididymis showed a temporal correlation between the beginning of fertilin's migration to the posterior head and the proteolytic processing of the full-length fertilin beta precursor (the 85-kDa pro-beta form) to a 75-kDa intermediate, pro-beta*. Completion of the migration coincided with the further cleavage of pro-beta* to the 25- to 28-kDa mature form. Our data suggest that the cleavage of fertilin pro-beta to pro-beta* may initiate fertilin's migration into the posterior head domain and, after localization to that membrane domain, pro-beta* is cleaved to mature beta. We also report evidence that a common mechanism may be used to change the localization pattern of other sperm surface molecules. Other surface proteins were shown to become localized to either the posterior or the anterior head membrane domains on sperm at the same time fertilin became localized to the posterior head. These restrictions of surface protein localizations were also shown to immediately precede the development of the sperm's ability to swim and undergo the acrosome reaction, and thus redistribution of surface proteins may be necessary before sperm become functional.

Intra-acrosomal 155,000 dalton protein increases the antigenicity during mouse sperm maturation in the epididymis: a study using a monoclonal antibody MC101

We found an intra-acrosomal antigen of about 155,000 daltons (155 kDa) in a survey using the monoclonal antibody MC101 raised against mouse cauda epididymal spermatozoa. Morphological studies by means of indirect immunofluorescence and immunogold electron microscopy localized the antigen to the cortex region of the anterior acrosome. Avidin biotin complex immunocytochemistry initially demonstrated a faint signal at the anterior acrosome in the testis spermatozoa that increased in intensity as the sperm moved toward the distal epididymis. This incremental immunoreactivity was also confirmed by immunoblotting following one-dimensional SDS-PAGE. The 155 kDa protein band was immunostained, and it was much more intense in the cauda epididymal than in the caput and corpus epididymal spermatozoa. Only a trace or no immunostain was evident in the caput or testis spermatozoa. The antigen localization did not change during passage through the epididymis, being confined at the cortex region of the anterior acrosome. The epididymal epithelial cells were not immunostained. These findings suggested that the 155 kDa protein is biochemically modified, further implying that the biochemical alteration of intra-acrosomal material is involved in sperm maturation in the epididymis.

Olfactory receptors are displayed on dog mature sperm cells

Olfactory receptors constitute a huge family of structurally related G protein-coupled receptors, with up to a thousand members expected. We have shown previously that genes belonging to this family were expressed in the male germ line from both dog and human. The functional significance of this unexpected site of expression was further investigated in the present study. We demonstrate that a few dog genes representative of various subfamilies of olfactory receptors are expressed essentially in testis, with little or no expression in olfactory mucosa. Other randomly selected members of the family show the expected site of expression, restricted to the olfactory system. Antibodies were generated against the deduced amino acid sequence of the most abundantly expressed olfactory receptor gene in dog testis. The purified serum was able to detect the gene product (DTMT receptor) in late round and elongated spermatids, as well as in the cytoplasmic droplet that characterizes the maturation of dog sperm cells, and on the tail midpiece of mature spermatozoa. Western blotting further confirmed the presence of a 40-kD immunoreactive protein in the membrane of mature sperm cells. Altogether , these results demonstrate that the main expression site of a subset of the large olfactory receptor gene family is not olfactory mucosa but testis. This expression correlates with the presence of the corresponding protein during sperm cell maturation, and on mature sperm cells. The pattern of expression is consistent with a role as sensor for unidentified chemicals possibly involved in the control of mammalian sperm maturation, migration, and/or fertilization.

Characterization of the antigen recognized by a monoclonal antibody MN9: unique transport pathway to the equatorial segment of sperm head during spermiogenesis

MN9, a monoclonal antibody raised against mouse spermatozoa, specifically recognizes the equatorial segment of sperm head in several mammalian species, including humans. Colloidal gold-immuno-electron microscopy of mouse spermatozoa has shown that the antigen is localized in the space between the outer and inner acrosome membranes and on the acrosome membranes at the equatorial segment. Immunoblotting after electrophoresis of spermatozoa from the cauda epididymidis has identified two immunoreactive bands: 38 kDa and 48 kDa in mouse, and 48 kDa in rat. During spermiogenesis in rat, this antigen is transported to the equatorial segment via a unique pathway, first appearing in some cisternae of the endoplasmic reticulum and in the Golgi apparatus of spermatids at around step 3. The antigen can further be found on the vesicles at the trans-side of the Golgi apparatus, in the matrix of the head cap, and on the head cap membrane in step-4 to step-7 spermatids. The antigen appears to be concentrated at the equatorial segment during late spermiogenesis. Neither the (pro-)acrosomic granule nor the surrounding membrane are required in this pathway. This pathway can be termed the 'Golgi-head cap tract'.