Developmental expression of spermatid-specific thioredoxin-1 protein: transient association to the longitudinal columns of the fibrous sheath during sperm tail formation

Structure and Composition of Spermatozoa Fibrous Sheath in Diverse Groups of Metazoa

The proper functioning and assembly of the sperm flagella structures contribute significantly to spermatozoa motility and overall male fertility. However, the fine mechanisms of assembly steps are poorly studied due to the high diversity of cell types, low solubility of the corresponding protein structures, and high tissue and cell specificity. One of the open questions for investigation is the attachment of longitudinal columns to the doublets 3 and 8 of axonemal microtubules through the outer dense fibers. A number of mutations affecting the assembly of flagella in model organisms are known. Additionally, evolutionary genomics data and comparative analysis of flagella morphology are available for a set of non-model species. This review is devoted to the analysis of diverse ultrastructures of sperm flagellum of Metazoa combined with an overview of the evolutionary distribution and function of the mammalian fibrous sheath proteins.

Sperm Motility Annotated Genes: Are They Associated with Impaired Fecundity?

Sperm motility is a prerequisite for achieving pregnancy, and alterations in sperm motility, along with sperm count and morphology, are commonly observed in subfertile men. The aim of the study was to determine whether the expression level of genes annotated with the Gene Ontology (GO) term 'sperm motility' differed in sperm collected from healthy men and men diagnosed with oligoasthenozoospermia. Reverse transcription quantitative real-time PCR (RT-qPCR), quantitative mass spectrometry (LC-MS/MS), and enrichment analyses were used to validate a set of 132 genes in 198 men present at an infertility clinic. Out of the 132 studied sperm-motility-associated genes, 114 showed differentially expressed levels in oligoasthenozoospermic men compared to those of normozoospermic controls using an RT-qPCR analysis. Of these, 94 genes showed a significantly lower expression level, and 20 genes showed a significantly higher expression level. An MS analysis of sperm from an independent cohort of healthy and subfertile men identified 692 differentially expressed proteins, of which 512 were significantly lower and 180 were significantly higher in oligoasthenozoospermic men compared to those of the normozoospermic controls. Of the 58 gene products quantified with both techniques, 48 (82.75%) showed concordant regulation. Besides the sperm-motility-associated proteins, the unbiased proteomics approach uncovered several novel proteins whose expression levels were specifically altered in abnormal sperm samples. Among these deregulated proteins, there was a clear overrepresentation of annotation terms related to sperm integrity, the cytoskeleton, and energy-related metabolism, as well as human phenotypes related to spermatogenesis and sperm-related abnormalities. These findings suggest that many of these proteins may serve as diagnostic markers of male infertility. Our study reveals an extended number of sperm-motility-associated genes with altered expression levels in the sperm of men with oligoasthenozoospermia. These genes and/or proteins can be used in the future for better assessments of male factor infertility.

Loss of CEP70 function affects acrosome biogenesis and flagella formation during spermiogenesis

The spermatogenesis process is complex and delicate, and any error in a step may cause spermatogenesis arrest and even male infertility. According to our previous transcriptomic data, CEP70 is highly expressed throughout various stages of human spermatogenesis, especially during the meiosis and deformation stages. CEP70 is present in sperm tails and that it exists in centrosomes as revealed by human centrosome proteomics. However, the specific mechanism of this protein in spermatogenesis is still unknown. In this study, we found a heterozygous site of the same mutation on CEP70 through mutation screening of patients with clinical azoospermia. To further verify, we deleted CEP70 in mice and found that it caused abnormal spermatogenesis, leading to male sterility. We found that the knockout of CEP70 did not affect the prophase of meiosis I, but led to male germ-cell apoptosis and abnormal spermiogenesis. By transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis, we found that the deletion of CEP70 resulted in the abnormal formation of flagella and acrosomes during spermiogenesis. Tandem mass tag (TMT)-labeled quantitative proteomic analysis revealed that the absence of CEP70 led to a significant decrease in the proteins associated with the formation of the flagella, head, and acrosome of sperm, and the microtubule cytoskeleton. Taken together, our results show that CEP70 is essential for acrosome biogenesis and flagella formation during spermiogenesis.

Testis-Specific Thioredoxins TXNDC2, TXNDC3, and TXNDC6 Are Expressed in Both Testicular and Systemic DLBCL and Correlate with Clinical Disease Presentation

DLBCL is the most common type of non-Hodgkin lymphoma with a substantial group of patients suffering a poor prognosis. Therefore more specific markers are required for better understanding of disease biology and treatment. This study demonstrates that testis-specific antioxidant enzymes TXNDC2, TXNDC3, and TXNDC6 alongside oxidative stress marker 8-OHdG are expressed in both testicular and systemic DLBCL, and their presence or absence has correlations with clinical risk factors such as the number of extranodal effusion, the appearance of B-symptoms, and treatment response. Biopsy samples were collected from 28 systemic and 21 testicular male DLBCL patients. The samples were histostained with TXNDC2, TXNDC3, TXNDC6, and 8-OHdG, then graded by a hematopathologist blinded to clinical data. Immunoelectron microscopy was used as a second method to confirm the reliability of the acquired immunohistochemistry data. The absence of nuclear TXNDC2 expression in testicular DLBCL cells correlated with worse primary treatment response, cytoplasmic TXNDC3 expression in testicular and systemic DLBCL associated with lower frequency of B-symptoms, and TXNDC6 expression in cytoplasm in systemic DLBCL had a clinical significance with higher LD levels suggesting a role in the biological nature of these lymphomas. Overall, TXNDC3 cytoplasmic expression is correlated with a more positive outcome in both testicular and systemic DLBCL, while TXNDC6 cytoplasmic expression is associated with a negative outcome in systemic DLBCL.

Proteomic analysis reveals dysregulated cell signaling in ejaculated spermatozoa from infertile men

Dysfunctional sperm maturation is the primary reason for the poor sperm motility and morphology in infertile men. Spermatozoa from infertile men were fractioned on three-layer density gradient (80%, 60%, and 40%). Fraction 1 (F1) refers to the least mature stage having the lowest density, whereas the fraction 4 (F4) includes the most dense and morphologically mature motile spermatozoa. Fraction 2 (F2) and fraction 3 (F3) represent the intermediate stages. Proteins were extracted and separated by 1-dimensional gel. Bands were digested with trypsin and analyzed on a LTQ-Orbitrap Elite hybrid mass spectrometer system. Functional annotations of proteins were obtained using bioinformatics tools and pathway databases. A total of 1585 proteins were detected in the four fractions of spermatozoa. A dysregulated protein turnover and protein folding may lead to accumulation of defective proteins or proteins that otherwise would have been eliminated during the process of maturation, resulting in the impairment of sperm function. Aberrant chaperone expression may be a major contributing factor to the defective sperm function. Androgen receptor was predicted as a transcription regulator in one of the networks and the affected pathways were chaperone-mediated stress response, proteosomal pathway, and sperm function. The downregulation of key pathways and proteins which compromises the fertilizing potential of spermatozoa may provide insight into the mechanisms that lead to male infertility.

Redox Regulation and Oxidative Stress: The Particular Case of the Stallion Spermatozoa

Redox regulation and oxidative stress have become areas of major interest in spermatology. Alteration of redox homeostasis is recognized as a significant cause of male factor infertility and is behind the damage that spermatozoa experience after freezing and thawing or conservation in a liquid state. While for a long time, oxidative stress was just considered an overproduction of reactive oxygen species, nowadays it is considered as a consequence of redox deregulation. Many essential aspects of spermatozoa functionality are redox regulated, with reversible oxidation of thiols in cysteine residues of key proteins acting as an “on–off” switch controlling sperm function. However, if deregulation occurs, these residues may experience irreversible oxidation and oxidative stress, leading to malfunction and ultimately death of the spermatozoa. Stallion spermatozoa are “professional producers” of reactive oxygen species due to their intense mitochondrial activity, and thus sophisticated systems to control redox homeostasis are also characteristic of the spermatozoa in the horse. As a result, and combined with the fact that embryos can easily be collected in this species, horses are a good model for the study of redox biology in the spermatozoa and its impact on the embryo.

Dynamic redox balance directs the oocyte-to-embryo transition via developmentally controlled reactive cysteine changes

The metabolic and redox state changes during the transition from an arrested oocyte to a totipotent embryo remain uncharacterized. Here, we applied state-of-the-art, integrated methodologies to dissect these changes in Drosophila We demonstrate that early embryos have a more oxidized state than mature oocytes. We identified specific alterations in reactive cysteines at a proteome-wide scale as a result of this metabolic and developmental transition. Consistent with a requirement for redox change, we demonstrate a role for the ovary-specific thioredoxin Deadhead (DHD). dhd-mutant oocytes are prematurely oxidized and exhibit meiotic defects. Epistatic analyses with redox regulators link dhd function to the distinctive redox-state balance set at the oocyte-to-embryo transition. Crucially, global thiol-redox profiling identified proteins whose cysteines became differentially modified in the absence of DHD. We validated these potential DHD substrates by recovering DHD-interaction partners using multiple approaches. One such target, NO66, is a conserved protein that genetically interacts with DHD, revealing parallel functions. As redox changes also have been observed in mammalian oocytes, we hypothesize a link between developmental control of this cell-cycle transition and regulation by metabolic cues. This link likely operates both by general redox state and by changes in the redox state of specific proteins. The redox proteome defined here is a valuable resource for future investigation of the mechanisms of redox-modulated control at the oocyte-to-embryo transition.

Evaluation of the p53 and Thioredoxin reductase in sperm from asthenozoospermic males in comparison to normozoospermic males

Thioredoxin (Trx) system has a defensive role against the harmful effect of oxidative stress in sperm. p53 is an important regulator of apoptosis and normal process of spermatogenesis. Regulation of p53 by redox state of the cell and Thioredoxin system has been reported. The aim of this study was to evaluate the ROS level, Thioredoxin reductase (TrxR) activity and p53 protein levels in sperm of asthenozoospermic and normozoospermic males. Semen samples from 80 donors were divided into asthenozoospermic (n = 40) and normozoospermic (n = 40) groups using the WHO criteria. DNA fragmentation (TUNEL assay) of spermatozoa was identified·H₂O₂ and O₂•- were determined by flow cytometry. p53 protein levels and TrxR activity were measured in sperm cell lysate by appropriate kit. Total antioxidant capacity (TAC) and thiol groups in seminal plasma were measured spectrophotometery. MDA content in seminal plasma was determined fluorometrically.

RESULTS

The percentage of cells with H₂O₂, O₂•- and DNA fragmentation was higher in asthenozoospermic compared to normozoospermic groups (p < 0.05). The p53 protein level was significantly higher in asthenozoospermic group (P < 0.001). TrxR activity in normozoospermic was significantly higher than asthenozoospermic group (P < 0.001). Total thiol groups and TAC levels were significantly higher in normozoospermic samples (P < 0.05). A significantly high negative correlation was seen between p53 protein levels with TrxR activity (r = - 0.49, P < 0.001), total motility (r = - 0.65, P < 0.001). p53 and ROS levels were increased in asthenozoospermic males while the TrxR activity was decreased. These changes lead to an increase in apoptotic, immotile and immature spermatozoa in the ejaculatory semen.

Negative biomarker based male fertility evaluation: Sperm phenotypes associated with molecular-level anomalies

Biomarker-based sperm analysis elevates the treatment of human infertility and ameliorates reproductive performance in livestock. The negative biomarker-based approach focuses on proteins and ligands unique to defective spermatozoa, regardless of their morphological phenotype, lending itself to analysis by flow cytometry (FC). A prime example is the spermatid specific thioredoxin SPTRX3/TXNDC8, retained in the nuclear vacuoles and superfluous cytoplasm of defective human spermatozoa. Infertile couples with high semen SPTRX3 are less likely to conceive by assisted reproductive therapies (ART) and more prone to recurrent miscarriage while low SPTRX3 has been associated with multiple ART births. Ubiquitin, a small, proteolysis-promoting covalent posttranslational protein modifier is found on the surface of defective posttesticular spermatozoa and in the damaged protein aggregates, the aggresomes of spermiogenic origin. Semen ubiquitin content correlates negatively with fertility and conventional semen parameters, and with sperm binding of lectins LCA (Lens culinaris agglutinin; reveals altered sperm surface) and PNA (Arachis hypogaea/peanut agglutinin; reveals acrosomal malformation or damage). The Postacrosomal Sheath WWI Domain Binding Protein (PAWP), implicated in oocyte activation during fertilization, is ectopic or absent from defective human and animal spermatozoa. Consequently, FC-parameters of PAWP correlate with ART outcomes in infertile couples and with fertility in bulls. Assays based on the above biomarkers have been combined into multiplex FC semen screening protocols, and the surface expression of lectins and ubiquitin has been utilized to develop nanoparticle-based bull semen purification method validated by field artificial insemination trials. These advances go hand-in-hand with the innovation of FC-technology and genomics/proteomics-based biomarker discovery.

ROS, thiols and thiol-regulating systems in male gametogenesis

BACKGROUND

During maturation and storage, spermatozoa generate substantial amounts of reactive oxygen species (ROS) and are thus forced to cope with an increasingly oxidative environment that is both needed and detrimental to their biology. Such a janus-faceted intermediate needs to be tightly controlled and this is done by a wide array of redox enzymes. These enzymes not only have to prevent unspecific modifications of essential cellular biomolecules by quenching undesired ROS, but they are also required and often directly involved in critical protein modifications.

SCOPE OF REVIEW

The present review is conceived to present an update on what is known about critical roles of redox enzymes, whereby special emphasis is put on the family of glutathione peroxidases, which for the time being presents the best characterized tasks during gametogenesis.

MAJOR CONCLUSIONS

We therefore demonstrate that understanding the function of (seleno)thiol-based oxidases/reductases is not a trivial task and relevant knowledge will be mainly gained by using robust systems, as exemplified by several (conditional) knockout studies. We thus stress the importance of using such models for providing unequivocal evidence in the molecular understanding of redox regulatory mechanisms in sperm maturation.

GENERAL SIGNIFICANCE

ROS are not merely detrimental by-products of metabolism and their proper generation and usage by specific enzymes is essential for vital functions as beautifully exemplified during male gametogenesis. As such, lessons learnt from thiol-based oxidases/reductases in male gametogenesis could be used as a general principle for other organs as it is most likely not only restricted to this developmental phase. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

The Enzymatic Antioxidant System of Human Spermatozoa

The ejaculated spermatozoon, as an aerobic cell, must fight against toxic levels of reactive oxygen species (ROS) generated by its own metabolism but also by other sources such as abnormal spermatozoa, chemicals and toxicants, or the presence of leukocytes in semen. Mammalian spermatozoa are extremely sensitive to oxidative stress, a condition occurring when there is a net increase in ROS levels within the cell. Opportunely, this specialized cell has a battery of antioxidant enzymes (superoxide dismutase, peroxiredoxins, thioredoxins, thioredoxins reductases, and glutathione s-transferases) working in concert to assure normal sperm function. Any impairment of the antioxidant enzymatic activities will promote severe oxidative damage which is observed as plasma membrane lipid peroxidation, oxidation of structural proteins and enzymes, and oxidation of DNA bases that lead to abnormal sperm function. Altogether, these damages occurring in spermatozoa are associated with male infertility. The present review contains a description of the enzymatic antioxidant system of the human spermatozoon and a reevaluation of the role of its different components and highlights the necessity of sufficient supply of reducing agents (NADPH and reduced glutathione) to guarantee normal sperm function.

Peroxiredoxins: hidden players in the antioxidant defence of human spermatozoa

Spermatozoon is a cell with a precious message to deliver: the paternal DNA. Its motility machinery must be working perfectly and it should be able to acquire fertilizing ability in order to accomplish this mission. Infertility touches 1 in 6 couples worldwide and in half of the cases the causes can be traced to men. A variety of conditions such as infections of the male genital tract, varicocele, drugs, environmental factors, diseases, smoking, etc., are associated with male infertility and a common feature among them is the oxidative stress in semen that occurs when reactive oxygen species (ROS) are produced at high levels and/or when the antioxidant systems are decreased in the seminal plasma and/or spermatozoa. ROS-dependent damage targets proteins, lipids, and DNA, thus compromising sperm function and survival. Elevated ROS in spermatozoa are associated with DNA damage and decreased motility. Paradoxically, ROS, at very low levels, regulate sperm activation for fertilization. Therefore, the regulation of redox signaling in the male reproductive tract is essential for fertility. Peroxiredoxins (PRDXs) play a central role in redox signaling being both antioxidant enzymes and modulators of ROS action and are essential for pathological and physiological events. Recent studies from our lab emphasize the importance of PRDXs in the protection of spermatozoa as infertile men have significant low levels of PRDXs in semen and with little enzymatic activity available for ROS scavenging. The relationships between sperm DNA damage, motility and lipid peroxidation and high levels of thiol-oxidized PRDXs suggest the enhanced susceptibility of spermatozoa to oxidative stress and further support the importance of PRDXs in human sperm physiology. This review aims to characterize PRDXs, hidden players of the sperm antioxidant system and highlight the central role of PRDXs isoforms in the protection against oxidative stress to assure a proper function and DNA integrity of human spermatozoa.

Is thioredoxin reductase involved in the defense against DNA fragmentation in varicocele?

We aimed to investigate the role of thioredoxin reductase (TR) and inducible heat shock protein 70 (iHsp70) and their relationship with sperm quality in varicocele (VAR) patients. Semen samples were obtained from 16 subfertile men diagnosed as VAR and 10 fertile men who applied to the Andrology Laboratory of Istanbul Medical Faculty of Istanbul University. The sperm TR and iHsp 70 expression levels were determined using Western blot analysis. The TR activity of the sperm was assayed spectrophometrically. The sperm quality was evaluated both by conventional sperm analysis and by a terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) technique that assayed DNA-fragmented spermatozoa in semen samples. The percentage of TUNEL-positive spermatozoa in the VAR group (16.3%± 5.6%) was higher than that in the fertile group (5.5%± 1.9%). Significant inverse correlations were detected between the percentage of TUNEL-positive cells and both the concentration (r=-0.609; P=0.001) and motility (r=-0.550; P=0.004) of spermatozoa. Both the TR expression and activity were increased significantly in the VAR group (U=22.0; P=0.001 and U=33.5; P=0.012, respectively) as analyzed using the Mann-Whitney U Wilcoxon rank sum W test. Furthermore, significant positive correlations were found between TR expression and activity (r=0.406; P=0.040) and between TR expression and the percentage of TUNEL-positive cells (r=0.665; P=0.001). Sperm iHsp70 expression did not differ between the VAR and fertile groups. In conclusion, increased sperm TR expression might be a defense mechanism against apoptosis in the spermatozoa of men with VAR.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Focus on mammalian thioredoxin reductases--important selenoproteins with versatile functions

Thioredoxin systems, involving redox active thioredoxins and thioredoxin reductases, sustain a number of important thioredoxin-dependent pathways. These redox active proteins support several processes crucial for cell function, cell proliferation, antioxidant defense and redox-regulated signaling cascades. Mammalian thioredoxin reductases are selenium-containing flavoprotein oxidoreductases, dependent upon a selenocysteine residue for reduction of the active site disulfide in thioredoxins. Their activity is required for normal thioredoxin function. The mammalian thioredoxin reductases also display surprisingly multifaceted properties and functions beyond thioredoxin reduction. Expressed from three separate genes (in human named TXNRD1, TXNRD2 and TXNRD3), the thioredoxin reductases can each reduce a number of different types of substrates in different cellular compartments. Their expression patterns involve intriguingly complex transcriptional mechanisms resulting in several splice variants, encoding a number of protein variants likely to have specialized functions in a cell- and tissue-type restricted manner. The thioredoxin reductases are also targeted by a number of drugs and compounds having an impact on cell function and promoting oxidative stress, some of which are used in treatment of rheumatoid arthritis, cancer or other diseases. However, potential specific or essential roles for different forms of human or mouse thioredoxin reductases in health or disease are still rather unclear, although it is known that at least the murine Txnrd1 and Txnrd2 genes are essential for normal development during embryogenesis. This review is a survey of current knowledge of mammalian thioredoxin reductase function and expression, with a focus on human and mouse and a discussion of the striking complexity of these proteins. Several yet open questions regarding their regulation and roles in different cells or tissues are emphasized. It is concluded that the intriguingly complex regulation and function of mammalian thioredoxin reductases within the cellular context and in intact mammals strongly suggests that their functions are highly fi ne-tuned with the many pathways involving thioredoxins and thioredoxin-related proteins. These selenoproteins furthermore propagate many functions beyond a reduction of thioredoxins. Aberrant regulation of thioredoxin reductases, or a particular dependence upon these enzymes in diseased cells, may underlie their presumed therapeutic importance as enzymatic targets using electrophilic drugs. These reductases are also likely to mediate several of the effects on health and disease that are linked to different levels of nutritional selenium intake. The thioredoxin reductases and their splice variants may be pivotal components of diverse cellular signaling pathways, having importance in several redox-related aspects of health and disease. Clearly, a detailed understanding of mammalian thioredoxin reductases is necessary for a full comprehension of the thioredoxin system and of selenium dependent processes in mammals.

Biofluid mechanics of the human reproductive process: modelling of the complex interaction and pathway to the oocytes

Recent revelations in the human reproductive process have fuelled much interest in this field of study. In particular, the once prevailing view of large numbers of ejaculated sperms racing towards the egg has been refuted recently. This is opposed to the current views derived from numerous clinical findings that state that only a very small number of sperms will ever enter the oviduct. It is believed that these few sperms must have been guided to make the long, tedious and obstructed journey to the egg. For a mature spermatozoon, its hyperactivated swimming motility upon capacitation plays an important role in the fertilization of a mature egg. Likewise, the female genital tract also provides guiding mechanisms to complement the survival of normal hydrodynamic profile sperms and thus promotes an eventual sperm–egg interaction. Understanding these mechanisms can be essential for the derivation of assisted conception techniques especially those in vitro. With the aid of computational models and simulation, suitability and effectiveness of novel assisted conception methodology can be assessed, particularly for those yet to be ready for clinical trials. This review discusses the possible bioengineering models and the mechanisms by which human spermatozoa are guided to the egg.

Rat Spag5 associates in somatic cells with endoplasmic reticulum and microtubules but in spermatozoa with outer dense fibers

The leucine zipper motif has been identified as an important and specific interaction motif used by various sperm tail proteins that localize to the outer dense fibers. We had found that rat Odf1, a major integral ODF protein, utilizes its leucine zipper to associate with Odf2, another major ODF protein, Spag4 which localizes to the interface between ODF and axonemal microtubule doublets, and Spag5. The rat Spag5 sequence indicated a close relationship with human Astrin, a microtubule-binding spindle protein suggesting that Spag5, like Spag4, may associate with the sperm tail axoneme. RT PCR assays indicated expression of Spag5 in various tissues and in somatic cells Spag5 localizes to endoplasmic reticulum and microtubules, as expected for an Astrin orthologue. MT binding was confirmed both in vivo and in in vitro MT-binding assays: somatic cells contain a 58 kDa MT-associated Spag5 protein. Western blotting assays of rat somatic cells and male germ cells at different stages of development using anti-Spag5 antibodies demonstrated that the protein expression pattern changes during spermatogenesis and that sperm tails contain a 58 kDa Spag5 protein. Use of affinity-purified anti-Spag5 antibodies in immuno electron microscopy shows that in rat elongated spermatids and epididymal sperm the Spag5 protein associates with ODF, but not with the axonemal MTs. This observation is in contrast to that for the other Odf1-binding, MT-binding protein Spag4, which is present between ODF and axoneme. Our data demonstrate that Spag5 has different localization in somatic versus male germ cells suggesting the possibility of different function.

Structure of mammalian spermatozoa in respect to viability, fertility and cryopreservation

Morphological assessment of spermatozoa has a long history and it is generally accepted that specific morphologic structural deviations correlate with male sub- and infertility. Although many different and also new methods are used in semen analysis, light microscopy is still used for routine morphological evaluation. This paper gives an overview about the detailed structure of physiological mammalian spermatozoa as well as the most common morphological deviations in correlation to fertility. This should be the basis for explanation of problems resulting from semen cryopreservation. General aspects of semen cryopreservation should be regarded before to facilitate the understanding of methods and mechanisms.

Cloning and characterization of rat spermatid protein SSP411: a thioredoxin-like protein

In an attempt to identify new sperm-specific genes that are involved in sperm maturation, fertilization, and embryo development, such as the mammalian ortholog of the sperm-supplied protein gene, spe-11, in Caenorhabditis elegans, we cloned and characterized a new spermatid-specific protein gene, ssp411, from adult rat testes. The ssp411 cDNA shared >85% sequence identity with an unnamed human protein, FLJ21347, and an uncharacterized mouse testicular protein called transcript increased in spermiogenesis 78 (TISP78). A 2.8-kb ssp411 mRNA was expressed in a testis-specific and age-dependent manner; the mRNA was evident at 28 days and remained at high levels throughout adulthood. An SSP411 protein of molecular weight 88 000 was detected in testicular extracts by Western blot analysis. Ssp411 mRNA and SSP411 protein, as analyzed by in situ hybridization and immunohistochemistry, were both expressed in a stage-dependent fashion during the cycle of the seminiferous epithelium. The ssp411 mRNA was predominantly localized to round and elongated spermatids, with maximal expression at stages VII-XII. The SSP411 protein was mainly observed in elongated spermatids and reached its highest levels during stages V-VI. A conserved thioredoxin-like domain was detected in the N-terminal region of SSP411 and its orthologs. An analysis of the predicted 3-dimensional structural modeling and folding pattern further suggested that SSP411 is identifiable as a member of thioredoxin family. In summary, we have identified a new rat spermatid protein gene, ssp411, and its orthologs in human and mouse and demonstrated that SSP411 might belong to a testis-specific thioredoxin family. This suggests that SSP411 may play a role in sperm maturation, fertilization, and/or embryo development, as has been shown in thioredoxin family.

Evidence for intriguingly complex transcription of human thioredoxin reductase 1

Human thioredoxin reductase 1 (TrxR1, the TXNRD1 gene product) is a ubiquitously expressed selenoprotein with many important redox regulatory functions. In this study, we have further characterized the recently identified core promoter region of TXNRD1. One critical Sp1/Sp3 site was found to be important in A549 and HeLa cells, whereas another Sp1/Sp3 site and one Oct1 site bound transcription factors but were, nonetheless, dispensable for transcription. We also experimentally identified several 5'-region TXNRD1 transcript variants using 5'-RACE with cDNA derived from different tissues, and we analyzed all available TXNRD1-derived EST sequences. The results show that the core promoter governs transcription of the clear majority of TXNRD1 transcripts but also that alternative promoters may be activated under rare conditions or in specific cell types. Furthermore, extensive alternative splicing occured in the 5' region of TXNRD1. In total, 21 different transcripts were identified, potentially encoding five isoforms of TrxR1 carrying alternative N-terminal domains. One isoform encompassed a glutaredoxin domain, whereas another encoded a predicted mitochondrial localization signal. These results reveal that the human thioredoxin system is intriguingly complex. Cell-specific transcription of the TXNRD1 gene encoding different isoforms of TrxR1 must be taken into account to fully understand the functions of the human thioredoxin system.

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.

Transcription in haploid male germ cells

Major modifications in chromatin organization occur in spermatid nuclei, resulting in a high degree of DNA packaging within the spermatozoon head. However, before arrest of transcription during midspermiogenesis, high levels of mRNA are found in round spermatids. Some transcripts are the product of genes expressed ubiquitously, whereas some are generated from male germ cell-specific gene homologs of somatic cell genes. Others are transcript variants derived from genes with expression regulated in a testis-specific fashion. The haploid genome of spermatids also initiates the transcription of testis-specific genes. Various general transcription factors, distinct promoter elements, and specific transcription factors are involved in transcriptional regulation. After meiosis, spermatids are genetically but not phenotypically different, because of transcript and protein sharing through cytoplasmic bridges connecting spermatids of the same generation. Interestingly, different types of mRNAs accumulate in the sperm cell nucleus, raising the question of their origin and of a possible role after fertilization.

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.

Tsga10 encodes a 65-kilodalton protein that is processed to the 27-kilodalton fibrous sheath protein

We had previously reported the isolation of the testis-specific human gene Tsga10, which is not expressed in testes from two infertile patients. To study its role and function, we cloned the mouse homologue Mtsga10. Mtsga10 localizes to mouse chromosome 1, band B. This region is syntenic with human chromosome 2q11.2, where Tsga10 is located. We demonstrate that Mtsga10 mRNA is expressed in testis, but not in other adult tissues, and in several human fetal tissues and primary tumors. We uncovered that different species use different first exons and, consequently, different promoters. Using several antibodies, we discovered that, in mouse testis, Mtsga10 encodes a 65-kDa spermatid protein that appears to be processed to a 27-kDa protein of the fibrous sheath, a major sperm tail structure, in mature spermatozoa. Mtsga10 protein contains a putative myosin/Ezrin/radixin/moesin (ERM) domain. Transfection of fibroblasts with GFP-Mtsga10 fusion protein results in formation of short, thick filaments and deletion of the myosin/ERM domain abolished filament formation. Our results suggest the possibility that Tsga10 plays a role in the sperm tail fibrous sheath.

New insights into the assembly of the periaxonemal structures in mammalian spermatozoa

Disruption of Ube2b in the mouse has revealed that the regular and symmetric organization of the fibrous sheath of the sperm flagella is dependent on expression of the ubiquitin-conjugating enzyme UBE2B. These data could cast light on how a component of the ubiquitin-proteasome pathway participates in the assembly of flagellar periaxonemal structures. Data in the literature support the notion of involvement of ubiquitin-proteasome pathways in the assembly of cytoskeletal components in somatic cells. This review attempts to integrate recent knowledge regarding flagellar components that could be related to proteasome components and, therefore, could be targets of UBE2B in the spermatid. An attempt is made to characterize the human flagellar anomalies of infertile patients, which are the closest to those of Ube2b-deficient mice. These new insights regarding the assembly of mammalian sperm flagella provide a basis for studying the ontogenesis of flagellar accessory structures and suggest leads for medical and genetic investigations.

The thioredoxin system?From science to clinic

The thioredoxin system-formed by thioredoxin reductase and its characteristic substrate thioredoxin-is an important constituent of the intracellular redox milieu. Interactions with many different metabolic pathways such as DNA-synthesis, selenium metabolism, and the antioxidative network as well as significant species differences render this system an attractive target for chemotherapeutic approaches in many fields of medicine-ranging from infectious diseases to cancer therapy. In this review we will present and evaluate the preclinical and clinical results available today. Current trends in drug development are emphasized.