Outer dense fiber proteins are dominant postobstruction autoantigens in adult Lewis rats

Characterization of a spontaneously occurring self-reactive antibody against sperm in mice

We previously established a spontaneously occurring monoclonal antibody, namely Ts3, that was reactive to sperm from an aged male mouse. The present study investigated the characteristic properties and reproductive functions of Ts3. Immunofluorescent staining revealed that Ts3 reacted to epididymal sperm, and the corresponding antigen was located in the midpiece and principal piece. Immunohistochemistry revealed positive reactions in the germ cells and Sertoli cells in the testis, the epithelial cells in the epididymis and vas deferens. Through western blotting with two-dimensional electrophoresis, we demonstrated that Ts3 reacted with four spots, which were around Mr ∼25,000-60,000 and pI 5-6. MALDI-TOF/TOF mass spectrometry identified outer dense fiber 2 (ODF2) as a candidate for Ts3. ODF2 is a cytoskeletal structural component located in the midpiece and principal piece of the flagella of mammalian sperm. This was validated with the result of immunofluorescent staining, suggesting that ODF2 was the main target antigen for Ts3. Sperm immobilization test showed that Ts3 possessed sperm immobilizing activity. Furthermore, Ts3 impaired early embryo development but not in vitro fertilization. These results suggest that ODF2 plays an important role in both sperm function and early embryonic development.

The novel testicular enrichment protein Cfap58 is required for Notch-associated ciliogenesis

Cilia and flagella are critical organelles with conserved internal structures and diverse developmental and physiological processes according to cell type. Although the core components of structures are shared with thousands of associated proteins involved in cilia or flagella formation, we hypothesized that some unknown proteins, such as outer dense fiber 2 (Odf2/Cenexin) perform distinct functions in these organelles. In the present study, we identified several uncharacterized proteins through mass spectrometry interactome analysis of Odf2/Cenexin proteins. We further examined the expression patterns and functions of a protein named cilia and flagella associated protein 58 (Cfap58) in cultured astrocytes and sperm flagella. The results of a combination of biochemical analyses and drug administration studies reveal that Cfap58 is a testis-enrichment protein that exhibits similar localization to Odf2/Cenexin proteins and is required for the elongation of the primary cilium and sperm midpiece via modulation of the Notch signaling pathway. However, the cell cycle-related functions and localization of Odf2/Cenexin in the mother centriole were not altered in Cfap58 knockdown cells. These findings indicate that Cfap58 may be partially recruited by Odf2/Cenexin proteins and is indispensable for the cilia and flagellar assembly. These data provide us with a better understanding of ciliogenesis and flagellar elongation and may aid in identifying new targets for diseases caused by Notch-mediated ciliopathies and flagellar abnormalities.

Thiol based mechanism internalises interacting partners to outer dense fibers in sperm

The sperm tail outer dense fibres (ODFs) contribute passive structural role in sperm motility. The level of disulphide cross-linking of ODFs and their structural thickness determines flagellar bending curvature and motility. During epididymal maturation, proteins are internalized to modify ODF disulphide cross-linking and enable motility. Sperm thiol status is further altered during capacitation in female tract. This suggests that components in female reproductive tract acting on thiol/disulphides could be capable of modulating the tail stiffness to facilitate modulation of the sperm tail rigidity and waveform en route to fertilization. Understanding the biochemical properties and client proteins of ODFs in reproductive tract fluids will help bridge this gap. Using recombinant ODF2 (aka Testis Specific Antigen of 70 kDa) as bait, we identified client proteins in male and female reproductive fluids. A thiol-based interaction and internalization indicates sperm can harness reproductive tract fluids for proteins that interact with ODFs and likely modulate the tail stiffness en route to fertilization.

Inhibition of tyrosine phosphorylation of sperm flagellar proteins, outer dense fiber protein-2 and tektin-2, is associated with impaired motility during capacitation of hamster spermatozoa

In mammals, acquisition of fertilization competence of spermatozoa is dependent on the phenomenon of sperm capacitation. One of the critical molecular events of sperm capacitation is protein tyrosine phosphorylation. In a previous study, we demonstrated that a specific epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor, tyrphostin-A47, inhibited hamster sperm capacitation, accompanied by a reduced sperm protein tyrosine phosphorylation. Interestingly, a high percentage of tyrphostin-A47-treated spermatozoa exhibited circular motility, which was associated with a distinct hypo-tyrosine phosphorylation of flagellar proteins, predominantly of Mr 45,000-60,000. In this study, we provide evidence on the localization of capacitation-associated tyrosine-phosphorylated proteins to the nonmembranous, structural components of the sperm flagellum. Consistent with this, we show their ultrastructural localization in the outer dense fiber, axoneme, and fibrous sheath of spermatozoa. Among hypo-tyrosine phosphorylated major proteins of tyrphostin-A47-treated spermatozoa, we identified the 45 kDa protein as outer dense fiber protein-2 and the 51 kDa protein as tektin-2, components of the sperm outer dense fiber and axoneme, respectively. This study shows functional association of hypo-tyrosine-phosphorylation status of outer dense fiber protein-2 and tektin-2 with impaired flagellar bending of spermatozoa, following inhibition of EGFR-tyrosine kinase, thereby showing the critical importance of flagellar protein tyrosine phosphorylation during capacitation and hyperactivation of hamster spermatozoa.

Heat shock proteins on the human sperm surface

The sperm plasma membrane is known to be critical to fertilization and to be highly regionalized into domains of head, mid- and principal pieces. However, the molecular composition of the sperm plasma membrane and its alterations during genital tract passage, capacitation and the acrosome reaction remains to be fully dissected. A two-dimensional gel-based proteomic study previously identified 98 human sperm proteins which were accessible for surface labelling with both biotin and radioiodine. In this report twelve dually labelled protein spots were excised from stained gels or PDVF membranes and analysed by mass spectrometry (MS) and Edman degradation. Seven members from four different heat shock protein (HSP) families were identified including HYOU1 (ORP150), HSPC1 (HSP86), HSPA5 (Bip), HSPD1 (HSP60), and several isoforms of the two testis-specific HSP70 chaperones HSPA2 and HSPA1L. An antiserum raised against the testis-specific HSPA2 chaperone reacted with three 65kDa HSPA2 isoforms and three high molecular weight surface proteins (78-79kDa, 84kDa and 90-93kDa). These proteins, together with seven 65kDa HSP70 forms, reacted with human anti-sperm IgG antibodies that blocked in vitro fertilization in humans. Three of these surface biotinylated human sperm antigens were immunoprecipitated with a rabbit antiserum raised against a linear peptide epitope in Chlamydia trachomatis HSP70. The results indicate diverse HSP chaperones are accessible for surface labelling on human sperm. Some of these share epitopes with C. trachomatis HSP70, suggesting an association between genital tract infection, immunity to HSP70 and reproductive failure.

Studies on the Expression of 80-kDa Human Sperm Antigen in Rat Testis and Epididymis

The 80-kDa human sperm antigen (HSA) has demonstrated to be a promising candidate for development of an antifertility vaccine because it is a sperm-specific, conserved, and immunogenic protein. The present study demonstrates the androgen-regulated expression of 80-kDa HSA in testis and epididymis of rat by immunohistochemistry (IHC), using its specific antibodies. Developmental expression of 80-kDa HSA was investigated on days 10, 20, 40, 60, and 90 of age in the testis and epididymis by IHC, and relative staining intensity was estimated by image analysis using BIOVIS software. On days 10 and 20, no significant staining was observed in the testis and epididymis, whereas it gradually increased from day 40 onwards. The highest staining was seen on day 90 in both testis and epididymis. Gradual increase in expression of 80-kDa HSA after day 40 suggests that it is possibly regulated by androgen. To study the androgen-regulated expression of 80-kDa, adult male rats were treated with 75 mg/kg body weight of ethylene dimethane sulfonate (EDS), which selectively destroys Leydig cells and thus induces complete androgen withdrawal. It was observed that the staining intensity decreased following EDS treatment in rat testis as well as epididymis, and it was regained after supplementation with dihydrotestosterone. Increased expression during sexual maturation at the time of testosterone surge and its regulation by anti-androgen/androgen treatment suggest androgen-dependent expression of 80-kDa HSA in rat testis and epididymis.

A sperm cytoskeletal protein TSA70 is a novel phosphorylated member of cenexin/odf2 family

Using post-vasectomy monoclonal antibody we recently identified a testis specific sperm auto-antigen called TSA70 which is post-meiotically expressed and plays a role in sperm motility and capacitation-acrosome reaction. In the present study, we report its cytoskeletal nature based on its resistance to various high ionic salt solutions. TSA70 is developmentally regulated and appears postpubertally. The two protein spots identified by 2D WB namely TSA1-pI=5.821, MW=77.050 and TSA3-pI=6.173, MW=75.519 showed sequence homology to Cenexin/odf2 indicating that two are isoforms of the same protein. The immunoreactivity of TSA70 with anti-Cenexin antibody substantiates its homology with Cenexin/odf2. In silico analysis revealed the presence of two leucine zippers in TSA70 and also predicted potential phosphorylation sites at serine, threonine, and tyrosine residues. The phosphorylated status of TSA70 was further confirmed by immunoblot analysis. The differential cellular expression suggests that TSA70 is a novel member of Cenexin/odf2 family that exhibits functional divergence.

Identification of Evolutionary Conserved Mouse Sperm Surface Antigens by Human Antisperm Antibodies (ASA) from Infertile Patients

PROBLEM

The presence of antisperm antibodies (ASA) in semen may impair sperm function leading to immunological infertility. The aim of the study was to identify the evolutionary conserved antigens on mouse sperm surface that react with human ASA in order to study the mechanism of autoimmune infertility.

METHODS OF STUDY

The binding of human ASA to mouse sperm was investigated by means of indirect immunofluorescence. 2D-electrophoresis was applied to separate the biotin-labelled mouse membrane proteins using isoelectric focusing followed by polyacrylamide gel electrophoresis. Cognate antigens of ASA from seminal plasma of infertile patients were analysed by Western blotting. Performing avidin-blots it was detected which of the proteins recognized were sperm surface proteins. The spots of interest were analysed by means of mass spectrometry.

RESULTS

ASA bound most frequently (36%) to the post-acrosomal region and to the midpiece of mouse spermatozoa. About 30% of ASA recognized apo lactate dehydrogenase (LDHC4) as a cognate antigen, 30% voltage-dependent anion channel (VDAC2). ASA of 20% bound to outer dense fibre protein and 20% of samples recognized glutathione S-transferase mu5.

CONCLUSIONS

Human ASA bound to specific cognate antigens of mouse spermatozoa, offering the possibility to study their functional relevance in the mouse model.

Purification and characterization of an esterase isozyme involved in hydrolysis of organophosphorus compounds from an insecticide resistant pest, Helicoverpa armigera (Lepidoptera: Noctüidae)

An esterase isozyme was purified from the insecticide resistant pest, Helicoverpa armigera collected from field crops. Purification involved ammonium sulfate precipitation, hydrophobic interaction and ion exchange chromatography followed by gel filtration chromatography. The purification was 212-fold with 1% yield of the enzyme. The optimum pH of the isozyme was found to be 10.5 and 8.5 for p-nitrophenyl phosphate and paraoxon, respectively. The enzyme was unstable at temperature >50 degrees C. The molecular mass determined by SDS-PAGE was 66 kDa. Cations such as Hg(+2), Ag(+2), Cd(+2) inhibited the activity while Zn(+2) stimulated it. Kinetic studies indicated that the enzyme had low K(m) values of 0.238 and 0.348 mM for p-nitrophenyl phosphate and paraoxon, respectively. The enzyme had broad substrate specificity with high K(m) values for ATP, ADP and beta-glycerophosphate. This enzyme was partially sequenced and identified as an alkaline phosphatase.

Molecular identities of human sperm proteins reactive with antibodies in sera of immunoinfertile women

Antisperm antibodies (ASA) can cause infertility in both men and women. It is important to delineate the sperm antigens against which these ASA are directed. Sperm proteins were separated by 2D gel electrophoresis and transferred to nitrocellulose membrane and incubated with sera from fertile women or immunoinfertile women having ASA. The corresponding immunoreactive peptide spots were cored from the gel and analyzed by the two-dimensional (2D) gel electrophoresis/matrix-assisted laser desoprtion ionization-time of flight-mass spectrometry and liquid chromatography-mass spectrometry (MALDI-TOF-MS/LC-MS). A total of 68 spots belonging to 38 different proteins and their isomers were identified. Fourteen of these proteins and their isomers reacted with both the fertile and immunoinfertile sera. Twenty-four of these proteins reacted specifically only with the immunoinfertile sera and not with the fertile sera. Among them was a novel protein designated as a hypothetical protein FLJ32704 (accession # Q96MA6). An immunodominant sequence (amino acid 151-159) of this protein was identified and a nonamer peptide based upon this sequence (IQTLG1TPR) was synthesized and examined for its immunoreactivity. This synthetic peptide reacted with 90% (36/40) of immunoinfertile sera and not with any of the fertile sera (0/40) in the enzyme-linked immnosorbent assay (ELISA). In conclusion, using the 2D gel electrophoresis/MALDI-TOF-MS/LC-MS procedure, we have identified several known and at least one novel antigen against which the antibodies are present in sera of immunoinfertile but not fertile women. Some of these antigens may find applications in specific diagonsis and treatment of infertility/immunoinfertility, and in the development of new generation of contraceptive modalities including contraceptive vaccines.

Characterization of a novel human sperm-associated antigen 9 (SPAG9) having structural homology with c-Jun N-terminal kinase-interacting protein

We report a novel SPAG9 (sperm-associated antigen 9) protein having structural homology with JNK (c-Jun N-terminal kinase)-interacting protein 3. SPAG9, a single copy gene mapped to the human chromosome 17q21.33 syntenic with location of mouse chromosome 11, was earlier shown to be expressed exclusively in testis [Shankar, Mohapatra and Suri (1998) Biochem. Biophys. Res. Commun. 243, 561-565]. The SPAG9 amino acid sequence analysis revealed identity with the JNK-binding domain and predicted coiled-coil, leucine zipper and transmembrane domains. The secondary structure analysis predicted an alpha-helical structure for SPAG9 that was confirmed by CD spectra. Microsequencing of higher-order aggregates of recombinant SPAG9 by tandem MS confirmed the amino acid sequence and mono atomic mass of 83.9 kDa. Transient expression of SPAG9 and its deletion mutants revealed that both leucine zipper with extended coiled-coil domains and transmembrane domain of SPAG9 were essential for dimerization and proper localization. Studies of MAPK (mitogenactivated protein kinase) interactions demonstrated that SPAG9 interacted with higher binding affinity to JNK3 and JNK2 compared with JNK1. No interaction was observed with p38alpha or extracellular-signal-regulated kinase pathways. Polyclonal antibodies raised against recombinant SPAG9 recognized native protein in human sperm extracts and localized specifically on the acrosomal compartment of intact human spermatozoa. Acrosome-reacted spermatozoa demonstrated SPAG9 immunofluorescence, indicating its retention on the equatorial segment after the acrosome reaction. Further, anti-SPAG9 antibodies inhibited the binding of human spermatozoa to intact human oocytes as well as to matched hemizona. This is the first report of sperm-associated JNK-binding protein that may have a role in spermatozoa-egg interaction.

Identification of immunodominant autoantigens in rat autoimmune orchitis

Infection and inflammation of the genital tract are amongst the leading causes of male infertility. Experimental autoimmune orchitis (EAO) in the rat serves as a model for the investigation of inflammatory testicular impairment. In this study, experiments were conducted to identify the molecules that are responsible for eliciting the autoimmune attack on the testis. EAO was induced in in-bred Wistar rats by active immunization with testis homogenates (EAO group I). Development of disease was observed using histological techniques and a new non-invasive three-dimensional (3D) imaging technology for in vivo monitoring, termed flat-panel volumetric computed tomography (fpvCT). Examination of control and EAO testes demonstrated the superior image quality of high-resolution fpvCT. A proteomics approach using 2D SDS-PAGE and immunoblotting analysis with EAO sera identified 12 spots. Seven were subsequently identified by mass spectrometry as heat shock proteins 60 (Hsp60) and 70 (Hsp70), disulphide isomerase ER-60, alpha-1-anti-trypsin, heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1), sperm outer dense fibre major protein 2 (ODF-2), and phosphoglycerate kinase 1. Hsp70, ODF-2, hnRNP H1, and ER-60 were identified by all EAO sera studied. To test the capacity of the identified proteins to elicit testicular autoimmune disease, recombinant proteins were used either individually or in combination to immunize rats (EAO group II). In all groups, the incidence of EAO was 25%. Inflammatory-type (ED1+) and resident (ED2+) macrophages, lymphocytes (CD45RA+), and dendritic cells (Ox-62+) were strongly increased in EAO group II animals, comparable to the testes of EAO I rats. Pre-immunization with a low dose of recombinant Hsp 70, hnRNP H1 or ODF-2 before induction of EAO with testis homogenate significantly delayed the onset of EAO but could not prevent disease. The identification of testicular autoantigens will allow a better understanding of disease pathogenesis and could provide a basis for the development of novel therapies for inflammation-based male infertility.

Identification of a New, Testis-Specific Sperm Antigen Localized on the Principal Piece of the Spermatozoa Tail in the Fox (Vulpes vulpes)1

Fox (Vulpes vulpes) sperm antigens were identified to assess them as a potential target for a contraceptive vaccine. We report here the cloning and sequencing of fSP13, a fox sperm protein of 97 kDa. The fSP13 protein was both auto- and iso-antigenic in foxes; it was recognized by sera of foxes immunized with fox sperm proteins and vasectomized foxes. The NH2-terminal sequence of fSP13 was determined, and a piece of cDNA was amplified from testicular RNA by reverse transcription polymerase chain reaction. This piece was used to screen a cDNA library from fox testis by Southern blot. A sequence of 1662 base pairs was obtained, including a major open reading frame coding for 498 amino acid. Mass spectrometry analysis confirmed the position of the open reading frame and the presence of posttranscriptional modifications. Analysis of the predicted amino acid sequence revealed no apparent transmembrane regions. Comparison of the protein sequence with the Prosite database demonstrated the presence of four potential N-linked glycosylation sites. The fSP13 bears the closest amino acid similarity to two human sperm proteins: fibrousheathin 2 and testis-specific calcium binding protein 86-VII. The deduced 80 N-terminal amino acid sequence also presents similarity with the RIIalpha domain. By using a serum against fSP13, this antigen was localized on the principal piece of the fox spermatozoa. Northern blot analysis showed that fSP13 is specifically expressed in testis. The fSP13 is one of the first fox sperm antigens to be cloned and sequenced.

Spermatocyte/Spermatid-specific Thioredoxin-3, a Novel Golgi Apparatus-associated Thioredoxin, Is a Specific Marker of Aberrant Spermatogenesis

Mammalian germ cells are endowed with a complete set of thioredoxins (Trx), a class of redox proteins located in specific structures of the spermatid and sperm tail. We report here the characterization, under normal and pathological conditions, of a novel thioredoxin with a germ line-restricted expression pattern, named spermatocyte/spermatid-specific thioredoxin-3 (SPTRX-3). The human SPTRX-3 gene maps at 9q32, only 50 kb downstream from the TRX-1 gene from which it probably originated as genomic duplication. Therefore, human SPTRX-3 protein comprises a unique thioredoxin domain displaying high homology with the ubiquitously expressed TRX-1. Among the tissues investigated, Sptrx-3 mRNA is found exclusively in the male germ cells at pachytene spermatocyte and round spermatid stages. Light and electron microscopy show SPTRX-3 protein to be predominately located in the Golgi apparatus of pachytene spermatocytes and round and elongated spermatids, with a transient localization in the developing acrosome of round spermatids. In addition, increased levels of SPTRX-3, possibly caused by overexpression, are observed in morphologically abnormal human spermatozoa from infertile men. In addition, SPTRX-3 is identified as a novel postobstruction autoantigen. In this report, we propose that SPTRX-3 can be used as a specific marker for diverse sperm and testis pathologies. SPTRX-3 is the first thioredoxin specific to the Golgi apparatus, and its function within this organelle might be related to the post-translational modification of proteins required for germ cell-specific functions, such as acrosomal biogenesis.

Evidence that P36, a human sperm acrosomal antigen involved in the fertilization process is triosephosphate isomerase

P36 is one of the immunodominant sperm antigens identified by antibodies eluted from the spermatozoa of infertile men. In a previous study, we isolated and characterized this auto-antigen as a glycoprotein with several isoforms. Specific rabbit antibodies were produced to investigate sperm topography and the role of P36 in the fertilization process and we showed that P36 is present on the equatorial segment of acrosome-reacted spermatozoa and is involved in sperm-binding and the penetration of zona-free hamster oocytes. In the present study, we demonstrated, by means of immunofluorescence and electron microscopy, that P36 is present all over the acrosomal membranes of non-reacted spermatozoa. We also investigated the role of P36 in the acrosome reaction and sperm binding to the zona pellucida (ZP). The exposure of capacitated spermatozoa to rabbit anti-P36 antibodies had no effect on primary fixation to the ZP, but inhibited secondary binding to the ZP and the Ca2+ ionophore-induced acrosome reaction. These results suggest that P36, an acrosomal antigen, is involved in several steps of the fertilization process. On two-dimensional Western blots, human anti-sperm antibodies (ASA) and rabbit anti-P36 antibodies recognized five to six isoforms of P36, all 36/37 kDa in size, with a pI between 5.1 and 5.7. Two major spots were identified as human triosephosphate isomerase (TPI) by MALDI-TOF mass spectrometry. Anti-TPI antibodies were shown to react with the isoforms recognized by human and rabbit anti-P36 antibodies. We also demonstrated the presence of TPI in human sperm heads. Further studies are underway to establish whether there is a sperm-specific isoform of TPI and its role in sperm function.

The mammalian testis-specific thioredoxin system

Redox control of cell physiology is one of the most important regulatory mechanisms in all living organisms. The thioredoxin system, composed of thioredoxin and thioredoxin reductase, has emerged as a key player in cellular redox-mediated reactions. For many years, only one thioredoxin system had been described in higher organisms, ubiquitously expressed in the cytoplasm of eukaryotic cells. However, during the last decade, we and others have identified and characterized novel thioredoxin systems with unique properties, such as organelle-specific localization in mitochondria or endoplasmic reticulum, tissue-specific distribution mostly in the testis, and features novel for thioredoxins, such as microtubule-binding properties. In this review, we will focus on the mammalian testis-specific thioredoxin system that comprises three thioredoxins exclusively expressed in spermatids (named Sptrx-1, Sptrx-2, and Sptrx-3) and an additional thioredoxin highly expressed in testis, but also present in lung and other ciliated tissues (Txl-2). The implications of these findings in the context of male fertility and testicular cancer, as well as evolutionary aspects, will be discussed.

Cloning and developmental analysis of murid spermatid-specific thioredoxin-2 (SPTRX-2), a novel sperm fibrous sheath protein and autoantigen

Thioredoxins compose a growing family of proteins that participate in different cellular processes via redox-mediated reactions. We report here the cloning, developmental expression, and location of murid Sptrx-2. Mouse and rat SPTRX-2 proteins display a high homology to their human ortholog in the thioredoxin and NDP kinase domains, and the coding genes are located at syntenic positions. Northern blotting and in situ hybridization confirmed the testis-specific expression of murine Sptrx-2 mRNA, mostly in round spermatids. Immunohistochemical analysis of the 19 steps of rat spermiogenesis showed that SPTRX-2 expression becomes prominent in the cytoplasmic lobe of step 15-18 spermatids and diminishes in step 19 just before spermiation. However, in the spermatid tail, SPTRX-2 immunoreactivity increased from step 15 to 19 and was confined to the principal piece. By immunogold electron microscopy, SPTRX-2 was first detected scattered throughout the cytoplasm of the axoneme in step 14-15 spermatids, but began to be incorporated by step 16 into the fibrous sheath (FS). During steps 17-18, the labeling increased over the ribs and columns of the assembled FS. It peaked in step 19 and remained in the FS of epididymal spermatozoa. Immunoblots of isolated FS obtained from spermatozoa confirmed that SPTRX-2 is an integral component of the FS and a post-obstruction autoantigen in vasectomized rats. Our data indicate that SPTRX-2 incorporation into the FS lags well behind FS assembly, suggesting it is required during the final stages of sperm tail maturation in the testis and/or epididymis, where extensive disulfide bonding of FS proteins occurs.

Cloning and characterization of a novel sperm-associated isoantigen (E-3) with defensin- and lectin-like motifs expressed in rat epididymis

In the present study we report the identification of a novel epididymis-specific secretory glycoprotein, E-3, which is a sperm-associated isoantigen containing defensin- and lectin-like motifs. E-3 was detected in rat epididymal fluid and in sperm extracts by two-dimensional (2-D) Western blotting using rat hyperimmune sera raised against rat sperm. The immunoreactive spot of approximately 28 kDa with an isoelectric point (pI) of 3.5 was cored from silver-stained gels. Microsequencing by tandem mass spectrometry and database searches revealed several peptides to be novel sequences. Degenerate deoxyinosine-containing primers corresponding to the novel peptides were used in rapid amplification of cDNA ends and polymerase chain reaction to clone E-3 from a rat epididymal cDNA library. A 449-base pair nucleotide sequence was subsequently obtained consisting of a complete open reading frame (ORF) of 111 amino acids, which showed similarity to the defensin and lectin families. The first 21 amino acids constituted a putative signal peptide, suggesting that E-3 is a secretory protein. Mature E-3 protein corresponding to amino acids 22-111 was expressed in E. coli, and chickens were immunized with recombinant E-3 (rE-3). The resulting anti-rE-3 antisera recognized the recombinant immunogen as well as a "native" protein of 28 kDa, pI 2.5-3.5 in both epididymal fluid and in sperm extracts on 2-D Western blots. Northern hybridization indicated that E-3 mRNA was present in the epididymis but not in testis or other tissues, and that E-3 mRNA was predominantly expressed in the corpus and cauda of the epididymis, but not in the initial segment or caput. Similarly, Western blots detected the E-3 protein only in the epididymal fluid and sperm from the corpus and caudal regions. Finally, indirect immunofluorescence localized E-3 on the entire tail, and with less intensity on the head of the sperm. These observations indicate that E-3 is a secreted epididymal protein that becomes associated with the sperm as it transits through the corpus and cauda. The presence of a defensin-like motif suggests that E-3 may play a role in protecting the sperm from microbial infections in the epididymis and in the female reproductive tract.

A novel asparaginase-like protein is a sperm autoantigen in rats

A novel asparaginase-like protein (ALP) of spermatozoa was cloned from rat and human testis cDNA libraries on the basis of reactivity with antibodies produced after vasectomy. Although obstruction of the male reproductive tract is known to cause an immunologic response, few of the sperm antigens responsible for the generation of autoantibodies have been characterized. We are identifying proteins of interest by coring autoantigenic protein spots from two-dimensional (2-D) gels of rat sperm extracts and microsequencing them by mass spectrometry. The peptide sequences from ALP, a 28 kDa, pI 5.7 protein, matched to a single partial length rat EST. These peptide sequences were used to clone a cDNA encoding a novel 333 amino acid open reading frame. The new protein had a similarity to portions of L-asparaginases of plants (43%) and to glycosylasparaginases in animal cells (32%). Human ALP cDNA was subsequently cloned. It showed 77% identity to the rat ALP sequence and the gene, ASRGL1 (asparaginase-like 1), mapped to chromosome locus 11q12.3. Purified recombinant rat ALP (rALP), expressed in E. coli, was used to raise polyclonal antiserum in guinea pigs. Two observations verified that the correct protein had been cloned: 1) the anti-rALP antibody reacted with both rALP and rat sperm; and 2) post-vasectomy sera bound rALP. Anti-rALP antibody stained the midpiece of rat and human sperm coincident with staining by MitoTracker Green FM, suggesting that ALP is associated with the mitochondria. Northern analysis revealed that rat ALP message was abundantly expressed in the testis but was also present in heart, brain, liver, skeletal muscle, and kidney.