Ultrastructural localization of a nuclear autoantigenic sperm protein in spermatogenic cells and spermatozoa

Vertebrate nucleoplasmin and NASP: egg histone storage proteins with multiple chaperone activities

Recent reviews have focused on the structure and function of histone chaperones involved in different aspects of somatic cell chromatin metabolism. One of the most dramatic chromatin remodeling processes takes place immediately after fertilization and is mediated by egg histone storage chaperones. These include members of the nucleoplasmin (NPM2/NPM3), which are preferentially associated with histones H2A-H2B in the egg and the nuclear autoantigenic sperm protein (NASP) families. Interestingly, in addition to binding and providing storage to H3/H4 in the egg and in somatic cells, NASP has been shown to be a unique genuine chaperone for histone H1. This review revolves around the structural and functional roles of these two families of chaperones whose activity is modulated by their own post-translational modifications (PTMs), particularly phosphorylation. Beyond their important role in the remodeling of paternal chromatin in the early stages of embryogenesis, NPM and NASP members can interact with a plethora of proteins in addition to histones in somatic cells and play a critical role in processes of functional cell alteration, such as in cancer. Despite their common presence in the egg, these two histone chaperones appear to be evolutionarily unrelated. In contrast to members of the NPM family, which share a common monophyletic evolutionary origin, the different types of NASP appear to have evolved recurrently within different taxa.

The antibody against a nuclear autoantigenic sperm protein can result in reproductive failure

To study whether the antibody against the testis form of the nuclear autoantigenic sperm protein (tNASP) could result in reproductive failure, we successfully cloned and expressed a 339-bp cDNA fragment of mouse tNASP (mtNASP). Using mouse as a model, recombinant mtNASP (rmtNASP) and a synthetic peptide, human tNASP(393-408) (htNASP(393-408)), were investigated for their antifertility effect. Active immunization with rmtNASP or the synthesized peptide raised high antibody titers in the immunized mice. Sperm-egg binding and fusion assay were carried out in 8-10-week-old BALB/c mice. Sperm-egg binding and in vitro fertilization of mouse oocytes were inhibited by co-incubation of zona-free mouse oocytes with capacitated mouse spermatozoa in the presence of varying concentrations of the antisera against rmtNASP. There was a significant antifertility effect in animals immunized with rmtNASP or the synthesized peptide. The effect on fertility in the mice immunized with the synthesized peptide was reversible. Our data indicate that active immunization with rmtNASP antigen may induce a strong antibody response that causes an inhibition of fertility.

sNASP, a histone H1-specific eukaryotic chaperone dimer that facilitates chromatin assembly

NASP has been described as a histone H1 chaperone in mammals. However, the molecular mechanisms involved have not yet been characterized. Here, we show that this protein is not only present in mammals but is widely distributed throughout eukaryotes both in its somatic and testicular forms. The secondary structure of the human somatic version consists mainly of clusters of alpha-helices and exists as a homodimer in solution. The protein binds nonspecifically to core histone H2A-H2B dimers and H3-H4 tetramers but only forms specific complexes with histone H1. The formation of the NASP-H1 complexes is mediated by the N- and C-terminal domains of histone H1 and does not involve the winged helix domain that is characteristic of linker histones. In vitro chromatin reconstitution experiments show that this protein facilitates the incorporation of linker histones onto nucleosome arrays and hence is a bona fide linker histone chaperone.

Screening of an antigen target for immunocontraceptives from cross-reactive antigens between human sperm and Ureaplasma urealyticum

Epidemiologic studies indicated that some infertile men who were infected with Ureaplasma urealyticum displayed positive antisperm antibodies in their serum and/or semen. The purpose of this study was to investigate the possible mechanism of antisperm antibodies production after infection with U. urealyticum and to analyze the relationship between U. urealyticum and infertility. The existence of cross-reactive antigens (61, 50, and 25 kDa) between U. urealyticum and human sperm membrane proteins was confirmed. Among the cross-reactive antigens, the urease complex component UreG of U. urealyticum was determined. By searching the Swiss-Prot protein database, a pentapeptide identity (IERLT) between UreG and human nuclear autoantigenic sperm protein (NASP) was found. Furthermore, using Western blot analysis and enzyme-linked immunosorbent assay, the cross-reaction between the NASP and UreG was verified. Both anti-rUreG antibody and the antiserum against the synthetic peptide NASP393-408 containing the pentapeptide inhibited mouse sperm egg binding and fusion. After immunization by rUreG or the synthetic peptide, 81.2 and 75% female mice became sterile, respectively. The effect on fertility in mice immunized with the synthetic peptide was reversible. These findings proved for the first time that it was feasible to screen antigens for immunocontraceptives from cross-reactive antigens between sperm and microorganisms which induce infertility.

The rat Tspy is preferentially expressed in elongated spermatids and interacts with the core histones

The testis specific protein Y encoded (TSPY) gene is a tandemly repeated gene on the mammalian Y chromosome. It encodes several slightly variant proteins that harbor a conserved domain of approximately 170 amino acids, termed TSPY/SET/NAP1 domain, capable of binding to cyclin B. The human TSPY is preferentially expressed in spermatogonia and to lesser extent in the spermatids. Although rat harbors a single functional Tspy gene on its Y chromosome, the human and rat genes differ in their expression patterns, suggesting that they might serve different or variant functions in the testis. Transcripts of rTspy were first detected in the testis of 28-day-old rats, at which time the first wave of meiotic division was occurring. The rTspy protein was initially detected in stage-9 elongating spermatids and peaked at stage-13 spermatids in adult testis, but not in spermatogonia, unlike the expression pattern of the human TSPY gene. Using a GST pull-down assay, we demonstrated that rTspy could bind to the core histones H2A, H2B, H3, and H4. Rat Tspy co-localized with the histones in the cytoplasm of selected elongated spermatids. Our results suggest that the rTspy may play critical roles as a histone chaperone during maturation of the elongating spermatids in the rat testis.

Transcriptional Profiling of Pig Embryogenesis by Using a 15-K Member Unigene Set Specific for Pig Reproductive Tissues and Embryos1

Differential mRNA expression patterns were evaluated between germinal vesicle oocytes (pgvo), four-cell (p4civv), blastocyst (pblivv), and in vitro-produced four-cell (p4civp) and in vitro-produced blastocyst (pblivp) stage embryos to determine key transcripts responsible for early embryonic development in the pig. Five comparisons were made: pgvo to p4civv, p4civv to pblivv, pgvo to pblivv, p4civv to p4civp, and pblivv to pblivp. ANOVA (P < 0.05) was performed with the Benjamini and Hochberg false-discovery-rate multiple correction test on each comparison. A comparison of pgvo to p4civv, p4civv to pblivv, and pgvo to pblivv resulted in 3214, 1989, and 4528 differentially detected cDNAs, respectively. Real-time PCR analysis on seven transcripts showed an identical pattern of changes in expression as observed on the microarrays, while one transcript deviated at a single cell stage. There were 1409 and 1696 differentially detected cDNAs between the in vitro- and in vivo-produced embryos at the four-cell and blastocyst stages, respectively, without the Benjamini and Hochberg false-discovery-rate multiple correction test. Real-time polymerase chain reaction (PCR) analysis on four genes at the four-cell stage showed an identical pattern of gene expression as found on the microarrays. Real-time PCR analysis on four of five genes at the blastocyst stage showed an identical pattern of gene expression as found on the microarrays. Thus, only 1 of the 39 comparisons of the pattern of gene expression exhibited a major deviation between the microarray and the real-time PCR. These results illustrate the complex mechanisms involved in pig early embryonic development.

The role of histones in chromatin remodelling during mammalian spermiogenesis

One of the most dramatic chromatin remodelling processes takes place during mammalian spermatogenesis. Indeed, during the postmeiotic maturation of male haploid germ cells, or spermiogenesis, histones are replaced by small basic proteins, which in mammals are transition proteins and protamines. However, nothing is known of the mechanisms controlling the process of histone replacement. Two hints from the literature could help to shed light on the underlying molecular events: one is the massive synthesis of histone variants, including testis-specific members, and the second is a stage specific post-translational modification of histones. A new testis-specific 'histone code' can therefore be generated combining both histone variants and histone post-translational modifications. This review will detail these two phenomena and discuss possible functional significance of the global chromatin alterations occurring prior to histone replacement during spermiogenesis.

Analysis of the autoimmune epitopes on human testicular NASP using recombinant and synthetic peptides

The human nuclear autoantigenic sperm protein, NASP, is a testicular histone-binding protein of 787 amino acids to which most vasectomized men develop autoantibodies. In this study to define the boundaries of antigenic regions and epitope recognition pattern, recombinant deletion mutants spanning the entire protein coding sequence and a human NASP cDNA sublibrary were screened with vasectomy patients' sera. Employing panel sera from 21 vasectomy patients with anti-sperm antibodies, a heterogeneous pattern of autoantibody binding to the recombinant polypeptides was detected in ELISA and immunoblotting. The majority of sera (20/21) had antibodies to one or more of the NASP fusion proteins. Antigenic sites preferentially recognized by the individual patients' sera were located within aa 32-352 and aa 572-787. Using a patient's serum selected for its reactivity to the whole recombinant protein in Western blots, cDNA clones positive for the C-terminal domain of the molecule were identified. The number and location of linear epitopes in this region were determined by synthetic peptide mapping and inhibition studies. The epitope-containing segment was delimited to the sequence aa 619-692 and analysis of a series of 74 concurrent overlapping 9mer synthetic peptides encompassing this region revealed four linear epitopes: amino acid residues IREKIEDAK (aa 648-656), KESQRSGNV (aa 656-664), AELALKATL (aa 665-673) and GFTPGGGGS (aa 680-688). All individual patients' sera reacted with epitopes within the sequence IREellipsis.GGS (aa 648-688). The strongest reactivity was displayed by peptides corresponding to the sequence AELALKATL (aa 665-673). Thus, multiple continuous autoimmune epitopes in NASP involving sequences in the conserved C-terminal domain as well as in the less conserved testis-specific N-terminal region comprising the histone-binding sites, as predicted for an antigen-driven immune response, may be a target of autoantibodies in vasectomized men and may provide a relevant laboratory variable to describe more accurately the spectrum of autoantibody specificities associated with the clinical manifestation of vasectomy.

The nuclear status of human sperm cells

In the last decade, and in particular since the development of in vitro fertilization techniques, the nuclear status of human sperm cells has shown to be a key parameter in the assessment of male fertility. The shape and condensed state of the mature sperm nucleus are determined by structural and functional events that occur during spermiogenesis. This paper reviews essential findings on re-organization of the nucleus during sperm differentiation and maturation, and reports recent data on the architecture, biochemical composition and stability of the nucleus in human ejaculated spermatozoa. Different methods used to evaluate nuclear maturity in relation to male fertility are critically appraised.

Primate testicular histone H1t genes are highly conserved and the human H1t gene is located on chromosome 6

The testis-specific histone H1t gene is known to be transcribed only in pachytene primary spermatocytes during spermatogenesis. Previous studies of the rat histone H1t gene revealed a unique promoter sequence element between the H1/GC box and the H1/CCAAT box. Proteins in crude nuclear extracts of rat testis bind specifically to this sequence element and a temporal correlation exists between the appearance of these DNA binding proteins and the onset of transcription. These discoveries led to a search for histone H1t genes in other mammalian species. The human and monkey histone H1t genes were amplified from genomic DNA using the polymerase chain reaction (PCR). The amplified genes were cloned and the genomic derived inserts were sequenced using linear PCR. Both proximal promoters contained the highly conserved H1/AC box, H1/CCAAT box, and H1/TATA box found in nongerminal H1 genes. Both promoters also contained the H1/GC box and the H1t/CCTAGG sequence element between the H1/GC box and H1/CCAAT box previously seen only in the H1t promoter. Specific amplification of the human H1t gene using template DNA samples from a NIGMS human/rodent somatic cell hybrid mapping panel has shown that the human histone H1t gene is located on chromosome 6.