Molecular cloning of a new member of TEKTIN family, Tektin4, located to the flagella of rat spermatozoa

Proteomic profiling of TBC1 domain family member 21-null sperms reveals the critical roles of TEKT 1 in their tail defects

BACKGROUND

Approximately 7% of the males exhibit reduced fertility; however, the regulatory genes and pathways involved remain largely unknown. TBC1 domain family member 21 (TBC1D21) contains a conserved RabGAP catalytic domain that induces GDP/GTP exchange to inactivate Rabs by interacting with microtubules. We previously reported that Tbc1d21-null mice exhibit severe sperm tail defects with a disrupted axoneme, and that TBC1D21 interacts with RAB10. However, the pathological mechanisms underlying the Tbc1d21 loss-induced sperm tail defects remain unknown.

RESULTS

Murine sperm from wild-type and Tbc1d21-null mice were comparatively analyzed using proteomic assays. Over 1600 proteins were identified, of which 15 were significantly up-regulated in Tbc1d21-null sperm. Notably, several tektin (TEKT) family proteins, belonging to a type of intermediate filament critical for stabilizing the microtubular structure of cilia and flagella, were significantly up-regulated in Tbc1d21-/- sperm. We also found that TBC1D21 interacts with TEKT1. In addition, TEKT1 co-localized with RAB10 during sperm tail formation. Finally, we found Tbc1d21-null sperm exhibited abnormal accumulation of TEKT1 in the midpiece region, accompanied by disrupted axonemal structures.

CONCLUSIONS

These results reveal that TBC1D21 modulates TEKTs protein localization in the axonemal transport system during sperm tail formation.

Hdh-Tektin-4 Regulates Motility of Fresh and Cryopreserved Sperm in Pacific Abalone, Haliotis discus hannai

As structural components of sperm, tektins are thought to play a fundamental role in sperm flagellar motility. In this study, Tektin-4 (Hdh-TEKT4) gene was successfully cloned and characterized from the testis tissue in Pacific abalone, Haliotis discus hannai. The full-length cDNA of Hdh-TEKT4 was 1,983 bp, with a coding region of 1,350 bp encoding 51.83 kDa putative protein of 449 deduced amino acids. Hdh-TEKT4 contains a tektin domain including a nonapeptide signature motif (RPGVDLCRD). Fluorescence in situ hybridization revealed that Hdh-TEKT4 localized in the spermatids of Pacific abalone testis. qRT-PCR analysis showed that Hdh-TEKT4 was predominantly expressed in testis tissues. Hdh-TEKT4 mRNA expression was upregulated during the fully mature testicular developmental stage in both seasonal development and EAT exposed abalone. Furthermore, mRNA expression of Hdh-TEKT4 was significantly higher in sperm with higher motility than in sperm with lower motility during peak breeding season, induced spawning activity stages, and after cryopreservation in different cryoprotectants. Taken together, these results indicate that the expression of Hdh-TEKT4 in Pacific abalone sperm might have a positive correlation with sperm motility.

Influence of cryopreservation on the CATSPER2 and TEKT2 expression levels and protein levels in human spermatozoa

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The cryopreservation process could lead to a reduction in the expression levels of the CATSPER2 and TEKT2 gene in human spermatozoa.

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The cryopreservation process could lead to a down-regulation in the expression of CATSPER2 and TEKT2 gene in human spermatozoa.

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The cryopreservation process could lead to a reduction in the level of CatSper 2 and Tektin 2 protein in human spermatozoa.

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The CatSper 2 and Tektin 2 may be used as markers to explain the causes of motility loss in the spermatozoa after the cryopreservation process.

This study designed to assess the expression level of CATSPER2 and TEKT2 and to evaluate the levels of CatSper2 and Tektin2 proteins in human spermatozoa before and after cryopreservation. One hundred and twenty semen samples were included in this study. All the samples were subjected to qPCR and Western blot analysis. The results showed a significant reduction in the expression levels of CATSPER2 and TEKT2 in the cryopreserved compared to the fresh samples (P = 0.0039 and P = 0.0166, respectively), and the results showed down-regulation in the expression level of CATSPER2 and TEKT2 genes between the study groups. Moreover, the protein levels of the CatSper2 and Tektin2 were lower in cryopreserved samples compared to fresh samples (P = 0.0001). In conclusion, the reduction in the proteins level and expression level of the CATSPER2 and TEKT2 in cryopreserved samples could be used as an indicator of sperm motility loss.

Comparative proteomic analysis of Tibetan pig spermatozoa at high and low altitudes

Background

To illuminate the mechanisms underlying the high-altitude tolerance of Tibetan pig spermatozoa, proteomes of spermatozoa from Tibetan pigs raised in high and low altitudes were compared using a tandem mass tag (TMT)-labeled quantitative proteomics approach.

Results

A total of 77 differentially expressed proteins (DEPs) were identified. Gene Ontology (GO) analysis revealed DEPs that were predominantly associated with the actin cytoskeleton, the tricarboxylic acid (TCA) cycle, and adenosine triphosphate (ATP) metabolism, and were from 12 enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Three subnetworks were significantly enriched and 10 centric proteins were identified by protein-protein interaction (PPI) network analysis. Relative expression levels of the proteins (ATP5H, CYCS, MYH9 and FN1) were confirmed using Western blotting.

Conclusions

Our study is the first to use a tandem mass tag (TMT) approach to analyze Tibetan pig spermatozoa, and provides a foundation to understand the mechanisms underlying the reproductive adaptations of Tibetan pigs to high-altitude environments.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5873-0) contains supplementary material, which is available to authorized users.

Production of recombinant human tektin 1, 2, and 4 and in vitro assembly of human tektin 1

Proteins predicted to be composed of large stretches of coiled-coil structure have often proven difficult to crystallize for structural determination. We have successfully applied EPR spectroscopic techniques to the study of the structure and assembly of full-length human vimentin assembled into native 11 nm filaments, in physiologic solution, circumventing the limitations of crystallizing shorter peptide sequences. Tektins are a small family of highly alpha helical filamentous proteins found in the doublet microtubules of cilia and related structures. Tektins exhibit several similarities to intermediate filaments (IFs): moderate molecular weight, highly alpha helical, hypothesized to be coiled-coil, and homo- and heteromeric assembly into long smooth filaments. In this report, we show the application of IF research methodologies to the study of tektin structure and assembly. To begin in vitro studies, expression constructs for human tektins 1, 2, and 4 were synthesized. Recombinant tektins were produced in E. coli and purified by chromatography. Preparations of tektin 1 successfully formed filaments. The recombinant human tektin 1 was used to produce antibodies which recognized an antigen in mouse testes, most likely present in sperm flagella. Finally, we report the creation of seven mutants to analyze predictions of coiled-coil structure in the rod 1A domain of tektin 1. Although this region is predicted to be coiled-coil, our EPR analysis does not reflect the parallel, in register, coiled-coil structure as demonstrated in vimentin and kinesin. These results document that tektin can be successfully expressed and assembled in vitro, and that SDSL EPR techniques can be used for structural analysis.

Translocation of Tektin 3 to the equatorial segment of heads in bull spermatozoa exposed to dibutyryl cAMP and calyculin A

Tektins (TEKTs) are filamentous proteins associated with microtubules in cilia, flagella, basal bodies, and centrioles. Five TEKTs (TEKT1, -2, -3, -4, and -5) have been identified as components of mammalian sperm flagella. We previously reported that TKET1 and -3 are also present in the heads of rodent spermatozoa. The present study clearly demonstrates that TEKT2 is present at the acrosome cap whereas TEKT3 resides just beneath the plasma membrane of the post-acrosomal region of sperm heads in unactivated bull spermatozoa, and builds on the distributional differences of TEKT1, -2, and -3 on sperm heads. We also discovered that hyperactivation of bull spermatozoa by cell-permeable cAMP and calyculin A, a protein phosphatase inhibitor, promoted translocation of TEKT3 from the post-acrosomal region to the equatorial segment in sperm heads, and that TEKT3 accumulated at the equatorial segment is lost upon acrosome reaction. Thus, translocation of TEKT3 to the equatorial segment may be a capacitation- or hyperactivation-associated phenomenon in bull spermatozoa. Mol. Reprod. Dev. 84: 30-43, 2017. © 2016 Wiley Periodicals, Inc.

Molecular Cloning of Spergen-4, Encoding a Spermatogenic Cell-Specific Protein Associated with Sperm Flagella and the Acrosome Region in Rat Spermatozoa

We used a differential display in combination with complementary DNA (cDNA) cloning approach to isolate a novel rat gene LOC690919 with an open reading frame of 1227-length nucleotides encoding a protein of 409 amino acids. This gene was designated as Spergen-4 (a spermatogenic cell-specific gene-4). Spergen-4 mRNA was highly expressed in testis, and its expression was detected in rat testis starting at three weeks of postnatal development and persisting up to adulthood. Mouse and human orthologs, which lack N-terminal 77 amino acid residues of rat Spegen-4, were found in the database. Immunofluorescence microscopy and immunoblot analysis demonstrated that Spergen-4 was not expressed in spermatogonia, spermatocytes, and round spermatids, but was restrictedly detected at sperm head, cytoplasm, and developing flagella of elongated spermatids in rat testis. In mature spermatozoa, Spergen-4 was detected at the acrosome region as well as the principal piece of flagella. Spergen-4 immunosignal disappeared from sperm heads on acrosome reaction induced by progesterone. These data suggest that Spergen-4 integrated into elongated spermatids during spermiogenesis serves as a constituent for acrosome region and flagella of rat spermatozoa.

Identification and characterization of a bovine sperm acrosomal matrix protein and its mechanism of interaction with acrosomal hydrolases

Fertilization, the union of male and female gametes to create offspring, is an intricate biological process dependent upon several biochemical and physiological events. Our understanding of the functions of protein constituents of the outer acrosomal membrane-associated matrix complex (OMC) is limited. A highly purified OMC fraction isolated from bovine cauda sperm heads comprised 54, 50, 45, and 38-19 kDa polypeptides. The objective of this study is to identify and characterize the 45 kDa (OMC45) polypeptide, to define its role in binding acrosomal hydrolases, and to examine the fate of OMC45 polypeptide during the acrosome reaction. We isolated OMC45 polypeptide from the high-pH insoluble fraction of OMC. Proteomic analysis of OMC45 by MALDI-TOF-TOF yielded eight peptides that matched the NCBI database sequence of Tektin 3 (TEKT3). Triton X-100-permeabilized cauda sperm exhibited intense staining of the acrosomal segment with anti-OMC45 and anti-TEKT3. The OMC45 polypeptide was solubilized by radio-immunoprecipitation assay buffer extraction. The solubilized fraction was subjected to immunoprecipitation analysis. The OMC45 polypeptide was recovered in the anti-OMC45 immunoprecipitation pellet. An identical blot stained with anti-TEKT3 exhibited the presence of TEKT3 polypeptide in the anti-OMC45 pellet. Our immunofluorescence and biochemical studies confirm the proteomics identification of OMC45 polypeptide and that it exhibits a sequence similarity to TEKT3. OMC45 glycoprotein possesses both N-linked and O-linked oligosaccharides. Deglycosylated OMC45 revealed a significant reduction in both acrosin and N-acetylglucosaminidase (NAGA) binding in comparison with acrosin and NAGA binding to a native OMC45 polypeptide, demonstrating the important role of oligosaccharides in hydrolase binding. OMC45 polypeptide is not released during the acrosome reaction but remains in the particulate cell subfraction, associated with the hybrid membrane complex.

Molecular cloning and subcellular localization of Tektin2-binding protein 1 (Ccdc 172) in rat spermatozoa

Tektins (TEKTs) are composed of a family of filament-forming proteins localized in cilia and flagella. Five types of mammalian TEKTs have been reported, all of which have been verified to be present in sperm flagella. TEKT2, which is indispensable for sperm structure, mobility, and fertilization, was present at the periphery of the outer dense fiber (ODF) in the sperm flagella. By yeast two-hybrid screening, we intended to isolate flagellar proteins that could interact with TEKT2, which resulted in the isolation of novel two genes from the mouse testis library, referred as a TEKT2-binding protein 1 (TEKT2BP1) and -protein 2 (TEKT2BP2). In this study, we characterized TEKT2BP1, which is registered as a coiled-coil domain-containing protein 172 (Ccdc172) in the latest database. RT-PCR analysis indicated that TEKT2BP1 was predominantly expressed in rat testis and that its expression was increased after 3 weeks of postnatal development. Immunocytochemical studies discovered that TEKT2BP1 localized in the middle piece of rat spermatozoa, predominantly concentrated at the mitochondria sheath of the flagella. We hypothesize that the TEKT2-TEKT2BP1 complex might be involved in the structural linkage between the ODF and mitochondria in the middle piece of the sperm flagella.

Levels of Tektin 2 and CatSper 2 in normozoospermic and oligoasthenozoospermic men and its association with motility, fertilization rate, embryo quality and pregnancy rate

PURPOSE

To compare the expression profiles of Tektin 2 and CatSper 2 motility proteins in the spermatozoa of normozoospermic and oligoasthenozoospermic men and determine its correlation with sperm motility, fertilization rate, embryo quality and pregnancy rate.

METHODS

Tektin 2 and CatSper 2 protein expression was studied using Western Blotting and immunofluorescence. Tektin 2 and CatSper 2 protein levels were quantified by ELISA.

RESULTS

Oligoasthenozoospermic men were found to have lower fertilization rates, poor embryo quality and lower pregnancy rates as compared to normozoospermic men. The levels of Tektin 2 and CatSper 2 are significantly lower in spermatozoa of oligoasthenozoospermic men as compared to normozoospermic controls; the levels were also lower in immotile fraction as compared to motile fraction of spermatozoa obtained from normozoospermic individuals. The levels of Tektin 2 and CatSper 2 were higher in individuals demonstrating sperm motility >60 % as compared to sperm motility <30 %. Tektin 2 but not CatSper 2 levels were positively associated with fertilization rate, embryo quality and pregnancy rate.

CONCLUSION

Levels of Tektin 2 and CatSper 2 proteins are positively associated with sperm motility parameters. Measurements of Tektin 2 levels can be correlated with the clinical outcome of ICSI.

Molecular cloning and localization of a CEACAM2 isoform, CEACAM2-L, expressed in spermatids in mouse testis

Carcinoembryonic antigen (CEA) family, a subgroup of the immunoglobulin (Ig) superfamily, is divided into two sub-families: the CEA-related cell adhesion molecules (CEACAM) and the pregnancy-specific glycoproteins. The isoform CEACAM2 is expressed in mouse testis; in this study, we identified a novel isoform of Ceacam2, Ceacam2-Long (Ceacam2-L). CEACAM2-L is different from CEACAM2 in that it has much longer cytoplasmic tail region. Ceacam2-L starts to appear faintly in mouse testis after 3 weeks of postnatal development, and its expression level increased after 5 weeks. Immunoblot analysis confirmed the expression of CEACAM2-L in the seminiferous epithelium of mouse testis. Immunohistochemical data showed that CEACAM2-L was not observed on spermatogonia, spermatocytes, round spermatids, or Sertoli cells, but was seen at the plasma membrane of elongating spermatids in contact with extended cytoplasmic processes of Sertoli cells. CEACAM2-L was not detected at the head region of elongating spermatids, where the apical ectoplasmic specialization is constructed. These data suggest that CEACAM2-L might be a novel adhesion molecule contributing to cell-to-cell adhesion between elongating spermatids and Sertoli cells within the seminiferous epithelium.

Immunolocalization of spetex-1 at the connecting piece in spermatozoa of the musk shrew (Suncus murinus)

Spetex-1, which has been isolated by differential display and rat cDNA library screening as a haploid spermatid-specific gene, encodes a protein with two coiled-coil motifs that locates at both the segmented column in the connecting piece and outer dense fibers-affiliated satellite fibrils in rat sperm flagella. Orthologs of Spetex-1 are identified in many animal species, including human, chimpanzee, macaque, cow, dog, African clawed frog, green spotted puffer, and zebrafish. In this study, we used RT-PCR in combination with 5' and 3' RACE (Rapid Amplification of cDNA End) technique to isolate Spetex-1 ortholog of the musk shrew (Suneus murinus), which yielded a full-length Suncus Spetex-1 gene containing an open reading frame of 1,908 base pairs encoding a protein of 636 amino acids with the predicted molecular mass of 72,348 Da. Suncus Spetex-1 has two coiled-coil motifs at 118-184 and 242-276 amino acid residues, which is a characteristic shared by mammalian Spetex-1 proteins. To examine the subcellular localization of Spetex-1 in Suncus spermatozoa, we produced the anti-Suncus Spetex-1 antibody and carried out immunocytochemistry. In spite of that the primary structure of Suncus Spetex-1 is basically similar to that of rat and mouse Spetex-1, confocal laser scanning microscopy and immunoelectron microscopy revealed that Spetex-1 was restricted to the segmented column and capitulum in the connecting piece of Suncus spermatozoa and was not detected in other parts of flagella, suggesting a diversity of Spetex-1 localization in mammalian spermatozoa.

Subcellular localization of Tektin2 in rat sperm flagellum

Tektins are evolutionarily conserved filament-forming proteins localized in flagella and cilia, and have been reported to be involved in the stability and structural complexity of axonemal microtubules. Five mammalian Tektins (Tektin1-5) have been reported. Of these, Tektin2 (TEKT2) has been found to be required for normal flagellum structure and function. Tekt2-null sperm display flagellum bending and reduced motility, probably due to disruption of the dynein inner arm. However, the subcellular localization of TEKT2 in spermatozoa has not been clarified at the ultrastructural level. To elucidate the molecular localization of TEKT2 in flagella of rat spermatozoa, we performed confocal laser scanning microscopy, extraction of flagella followed by immunoblot analysis, and immunogold electron microscopy. Extraction of sperm flagella by SDS-EDTA resulted in complete extraction of axonemal tubulins, while TEKT2 was only partially released from flagella, suggesting that TEKT2 might be present in the peri-axonemal component, not directly associated with axonemal tubulins. Confocal laser scanning microscopy and pre-embedding immunoelectron microscopy revealed that TEKT2 is associated with the surface of outer dense fibers (ODFs). TEKT2 may function as an ODF-affiliated molecule required for flagellum stability and sperm motility.

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.

Characterization of Spetex-1, a new component of satellite fibrils associated with outer dense fibers in the middle piece of rodent sperm flagella

Spetex-1, which has been isolated by differential display as a haploid spermatid-specific gene, encodes a protein with two coiled-coil motifs located in the middle piece of flagella in rodent spermatozoa. The middle piece of flagella is composed of axoneme and peri-axonemal elements including outer dense fibers (ODFs) and satellite fibrils. Pre-embedding immunoelectron microscopy clearly demonstrated that Spetex-1 is located at satellite fibrils associated with ODFs in the middle piece of flagella of rat spermatozoa. Extraction of Spetex-1 from spermatozoa by SDS or urea required dithiothreitol, suggesting crosslinking by disulfide bond is involved in the assembly of satellite fibrils containing Spetex-1. We identified putative Spetex-1 orthologs in many animal species, and both cysteine residues and coiled-coil motifs were well conserved in mammalian orthologs of Spetex-1. When Spetex-1 was co-transfected into COS-7 cells with myc-tagged Tektin4, another filamentous protein associated with ODFs, the two molecules were co-localized in various sizes of aggregates in the cells. These data suggested that Spetex-1, a new component of satellite fibrils, might be involved in the structural stability of the sperm flagellar middle piece and functions in co-operation with Tektin4.

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.

Tektin 3 is required for progressive sperm motility in mice

Tektins are evolutionarily conserved flagellar (and ciliary) filamentous proteins present in the axoneme and peri-axonemal structures in diverse metazoan species. We have previously shown that tektin 3 (TEKT3) and tektin 4 (TEKT4) are male germ cell-enriched proteins, and that TEKT4 is essential for coordinated and progressive sperm motility in mice. Here we report that male mice null for TEKT3 produce sperm with reduced motility (47.2% motility) and forward progression, and increased flagellar structural bending defects. Male TEKT3-null mice however maintain normal fertility in two different genetic backgrounds tested, in contrast to TEKT4-null mice. Furthermore, male mice null for both TEKT3 and TEKT4 show subfertility on a mixed B6;129 genetic background, significantly different from either single knockouts, suggesting partial nonredundant roles for these two proteins in sperm physiology. Our results suggest that tektins are potential candidate genes for nonsyndromic asthenozoospermia in humans.

Male infertility caused by spermiogenic defects: lessons from gene knockouts

Spermiogenesis refers to the process by which postmeiotic spermatids differentiate into elongated spermatids and eventually spermatozoa. During spermiogenesis, round spermatids undergo dynamic morphologic changes, which include nuclear condensation and elongation, formation of flagella and acrosome, reorganization of organelles and elimination of cytoplasm upon spermiation. This cellular differentiation process is unique to male haploid germ cells, which may explain why approximately half of the testis-specific genes are exclusively expressed in spermiogenesis. The spermiogenesis-specific expression implies that these genes contribute to either structural or functional aspects of future sperm. Many such genes have been inactivated in mice and some of these gene knockout mice display male infertility due to nonfunctional sperm which display no or various degrees of structural abnormalities. Since the majority of these spermiogenesis-specific genes are highly conserved between mice and humans, findings from knockout mouse studies may be applicable to human infertility. Here, I briefly review some of these spermatid-specific gene knockouts. The mouse studies strongly suggest that sperm quality rather than quantity is a better indicator of male fertility and novel assays should be developed to determine sperm functionality.

The tektin family of microtubule-stabilizing proteins

Tektins are insoluble a-helical proteins essential for the construction of cilia and flagella and are found throughout the eukaryotes apart from higher plants.

Germ cell-less like-2 protein is a new component of outer dense fibers in rat sperm flagella

We have analyzed the expression profiles of ten genes in terms of testis development and organ specificity in rat, which were selected from 215 round spermatid-specific transcripts listed in a database. Out of the ten genes, we directed our attention to one gene, a germ cell-less like-2 gene (gcl-2), a homolog ofDrosophilagcl gene (gcl), which is a component of the germ plasma and required for primordial germ cell formation. Rat genome contains duplicate rat gcl-2 (rgcl-2) genes,rgcl-2Aandrgcl-2B, both of which are located at Xq13. RT-PCR analysis showed that the expression of the two genes was up-regulated during testis development and that they were predominantly expressed in the testis. Bothrgcl-2Aandrgcl-2Bencode a protein of 498 amino acid residues, showing 90.56% identity at the amino acid level. Confocal laser scanning microscopy revealed that rgcl-2 protein was synthesized in the cytoplasm of elongating spermatids and at least a part of it was integrated into the middle piece of spermatozoa during spermiogenesis. Immunogold electron microscopy uncovered that rgcl-2 was localized at the abaxial (convex) surface of outer dense fibers (ODF) of rat sperm flagella. Therefore, we concluded that rgcl-2 is a new component of ODF in sperm flagella.

Integrative characterization of germ cell-specific genes from mouse spermatocyte UniGene library

Background

The primary regulator of spermatogenesis, a highly ordered and tightly regulated developmental process, is an intrinsic genetic program involving male germ cell-specific genes.

Results

We analyzed the mouse spermatocyte UniGene library containing 2155 gene-oriented transcript clusters. We predict that 11% of these genes are testis-specific and systematically identified 24 authentic genes specifically and abundantly expressed in the testis via in silico and in vitro approaches. Northern blot analysis disclosed various transcript characteristics, such as expression level, size and the presence of isoform. Expression analysis revealed developmentally regulated and stage-specific expression patterns in all of the genes. We further analyzed the genes at the protein and cellular levels. Transfection assays performed using GC-2 cells provided information on the cellular characteristics of the gene products. In addition, antibodies were generated against proteins encoded by some of the genes to facilitate their identification and characterization in spermatogenic cells and sperm. Our data suggest that a number of the gene products are implicated in transcriptional regulation, nuclear integrity, sperm structure and motility, and fertilization. In particular, we found for the first time that Mm.333010, predicted to contain a trypsin-like serine protease domain, is a sperm acrosomal protein.

Conclusion

We identify 24 authentic genes with spermatogenic cell-specific expression, and provide comprehensive information about the genes. Our findings establish a new basis for future investigation into molecular mechanisms underlying male reproduction.

Absence of tektin 4 causes asthenozoospermia and subfertility in male mice

Sperm flagellar motion is the outcome of a dynamic interplay between the axonemal cytoskeleton, the peri-axonemal accessory structures, and multiple regulatory networks that coordinate to produce flagellar beat and waveform. Tektins are conserved components of the flagellar proteome in evolutionarily diverse species and are believed to play essential roles in the mechanics of sperm motility. Using database mining, we identified multiple new paralogs of previously annotated tektins, including tektin 4 (TEKT4), which shares 77.1% identity with its nearest human homologue. Mouse Tekt4 is a germ cell-enriched gene, most abundantly expressed in haploid round spermatids in the testis, and the protein is localized to the sperm flagella. Male mice lacking TEKT4 on a 129S5/SvEvBrd inbred background are subfertile. Tekt4-null sperm exhibit drastically reduced forward progressive velocity and uncoordinated waveform propagation along the flagellum. In Tekt4-null sperm, flagellar ultrastructure is grossly unaltered as revealed by transmission electron microscopy. However, the ineffective flagellar strokes lead to approximately 10-fold higher consumption of intracellular ATP in Tekt4-null sperm as compared to wild-type, and null spermatozoa rapidly lose progressive motility when incubated for > or = 1.5 h. Our studies demonstrate that TEKT4 is necessary for the proper coordinated beating of the sperm flagellum and male reproductive physiology.

Proteomic Profiling of Accessory Structures from the Mouse Sperm Flagellum

The flagellum of a mammalian spermatozoon consists of an axoneme surrounded in distinct regions by accessory structures known as the fibrous sheath, outer dense fibers, and the mitochondrial sheath. Although the characterization of individual proteins has provided clues about the roles of these accessory structures, a more complete understanding of flagellar function requires the identification of all the polypeptides in these assemblies. Epididymal mouse sperm were treated with SDS to dislodge sperm heads and to extract the axoneme and membranous elements. The remaining flagellar accessory structures were purified by sucrose gradient centrifugation. Analysis of proteins from these structures by two-dimensional gel electrophoresis and colloidal Coomassie Blue staining showed a highly reproducible pattern of >200 spots. Individual spots were picked, digested with trypsin, and identified by mass spectrometry and peptide microsequencing. Approximately 50 individual proteins were identified that could be assigned to five general categories: 1) proteins previously reported to localize to the accessory structures, e.g. ODF2 in the outer dense fibers, the sperm-specific glyceraldehyde-3-phosphate dehydrogenase in the fibrous sheath, and glutathione peroxidase in the mitochondrial sheath, validating this proteomic approach; 2) proteins that had not been shown to localize to any accessory structure but would be predicted to be present, e.g. glycolytic enzymes; 3) proteins known to be part of the flagellum but not localized to a specific site, e.g. adenylate kinase; 4) proteins not expected to be part of the accessory structures based on their previously reported locations, e.g. tektins; and 5) unknown proteins for which no information is available to make a determination as to location. The unexpected presence of the tektins in the accessory structures of the flagellum was confirmed by both immunoblot and immunofluorescence analysis. This proteomic analysis identified a number of unexpected and novel proteins in the accessory structures of the mammalian flagellum.

Spetex-1: a new component in the middle piece of flagellum in rodent spermatozoa

Spetex-1 has recently been isolated by differential display and screening of cDNA library. It encodes a protein of 556 amino acid residues possessing coiled-coil motifs. In the rat seminiferous tubules (ST), Spetex-1 was expressed in the cytoplasm of elongating spermatids. To examine the subcellular distribution of Spetex-1 in mature spermatozoa, we performed biochemical and immunocytochemical approaches. We found that Spetex-1 that was synthesized in the cytoplasm of elongating spermatids was subsequently integrated as a middle piece component into spermatozoa during spermiogenesis. After integration, the majority of Spetex-1 in spermatozoa could be extracted by 6M urea under reduced condition but not released by the treatment of 1% Triton X-100. Immunoelectron microscopy demonstrated that Spetex-1 seemed to locate at the inner side of outer dense fibers (ODFs) in the middle piece or the narrow space between ODFs and axoneme. Spetex-1 might be involved in the stability of the structural complexity comprising axoneme and ODFs in the middle piece of sperm flagellum.

Tektin 4 is located on outer dense fibers, not associated with axonemal tubulins of flagella in rodent spermatozoa

Tektins, which are thought to be the constitutive proteins of microtubules in cilia, flagella, basal bodies, and centrioles, have been reported to be involved in the stability and structural complexity of axonemal microtubules. Four types of mammalian Tektins have been reported, and at least two types of Tektins, Tektin 2 and Tektin 4, have been verified to be present in sperm flagella. To elucidate the molecular localization of Tektin 4 in flagella of rodent spermatozoa, we performed immunocytochemistry, fractionation study followed by immunoblot analysis, and immunogold electron microscopy. Confocal laser scanning microscopy and immunogold electron microscopy indicated that Tektin 4 was associated with outer dense fibers (ODFs) in both the middle and principal piece of flagella in rat and mouse spermatozoa. Tektin 4 in rat spermatozoa is completely released by 6 M urea treatment, but not extracted by 1% Triton X-100 and 0.6 M potassium thiocyanate. Pre-embedding immunoelectron microscopy demonstrated that Tektin 4 located on the abaxial (convex) surface of ODFs in flagella, not associate with axonemal microtubules. Our data strongly suggested that Tektin 4 is not associated with axonemal tubulins but an ODFs-affiliated molecule in rodent spermatozoa.