Tektin B1 demonstrates flagellar localization in human sperm

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.

Bringing proteomics to bear on male fertility: key lessons

INTRODUCTION

Male infertility is a major public health concern globally. Proteomics has revolutionized our comprehension of male fertility by identifying potential infertility biomarkers and reproductive defects. Studies comparing sperm proteome with other male reproductive tissues have the potential to refine fertility diagnostics and guide infertility treatment development.

AREAS COVERED

This review encapsulates literature using proteomic approaches to progress male reproductive biology. Our search methodology included systematic searches of databases such as PubMed, Scopus, and Web of Science for articles up to 2023. Keywords used included 'male fertility proteomics,' 'spermatozoa proteome,' 'testis proteomics,' 'epididymal proteomics,' and 'non-hormonal male contraception.' Inclusion criteria were robust experimental design, significant contributions to male fertility, and novel use of proteomic technologies.

EXPERT OPINION

Expert analysis shows a shift from traditional research to an integrative approach that clarifies male reproductive health's molecular intricacies. A gap exists between proteomic discoveries and clinical application. The expert opinions consolidated here not only navigate the current findings but also chart the future proteomic applications for scientific and clinical breakthroughs. We underscore the need for continued investment in proteomic research - both in the technological and collaborative arenas - to further unravel the secrets of male fertility, which will be central to resolving fertility issues in the coming era.

Identification of hub genes associated with spermatogenesis by bioinformatics analysis

Spermatogenesis is a complex process related to male infertility. Till now, the critical genes and specific mechanisms have not been elucidated clearly. Our objective was to determine the hub genes that play a crucial role in spermatogenesis by analyzing the differentially expressed genes (DEGs) present in non-obstructive azoospermia (NOA) compared to OA and normal samples using bioinformatics analysis. Four datasets, namely GSE45885, GSE45887, GSE9210 and GSE145467 were used. Functional enrichment analyses were performed on the DEGs. Hub genes were identified based on protein-protein interactions between DEGs. The expression of the hub genes was further examined in the testicular germ cell tumors from the TCGA by the GEPIA and validated by qRT-PCR in the testes of lipopolysaccharide-induced acute orchitis mice with impaired spermatogenesis. A total of 203 DEGs including 34 up-regulated and 169 down-regulated were identified. Functional enrichment analysis showed DEGs were mainly involved in microtubule motility, the process of cell growth and protein transport. PRM2, TEKT2, FSCN3, UBQLN3, SPATS1 and GTSF1L were identified and validated as hub genes for spermatogenesis. Three of them (PRM2, FSCN3 and TEKT2) were significantly down-regulated in the testicular germ cell tumors and their methylation levels were associated with the pathogenesis. In summary, the hub genes identified may be related to spermatogenesis and may act as potential therapeutic targets for NOA and testicular germ cell tumors.

Ovine fertility by artificial insemination in the breeding season could be affected by intraseasonal variations in ram sperm proteomic profile

It is important to note that seasonality could affect ram reproductive parameters, and therefore, fertility results after artificial insemination. In this work, 1) we assessed fertility rates after cervical artificial insemination of 11,805 ewes at the beginning (June 21st to July 20th) and at the end (November 20th to December 21st) of the reproductive season in the Assaf breed for the last four years, and 2) we aimed to identify male factors influencing the different reproductive success obtained depending on the time at the mating season in which ovine artificial insemination was performed. For this purpose, we evaluated certain ram reproductive and ultrasonographical parameters as well as we performed a multiparametric and proteomic sperm analysis of 6-19 rams at two very distant points in the mating season (July as Early Breeding Season -EBS- and November as Late Breeding Season -LBS-). Rutinary assessments carried out in the ovine reproduction centers (testicular volume, libido, sperm production and mass motility) showed non-significant differences (P ≥ 0.05) between both studied times, as well as the ram ultrasonographic evaluation (Resistive and Pulsatility Index as Doppler parameters; and pixels mean gray level, and hypoechoic areas percentage and density as echotexture parameters). However, at level of sperm functionality, although sperm quality appeared non-significantly lower (P ≥ 0.05) in the EBS, we identified a significantly different (P < 0.05) sperm proteomic profile between the seasonality points. The following proteins were identified with the lowest abundance in the EBS with a fold change > 4, a P = 2.40e-07, and a q = 2.23e-06: Fibrous Sheath-Interacting Protein 2, Disintegrin and Metalloproteinase Domain-Containing Protein 20-like, Phosphoinositide-Specific Phospholipase C, Tektin 5, Armadillo Repeat-Containing Protein 12 Isoform X3, Solute Carrier Family 9B1, Radial Spoke Head Protein 3 Homolog, Pro-Interleukin-16, NADH Dehydrogenase [Ubiquinone] 1 Alpha Subcomplex Subunit 8, Testis, Prostate and Placenta-Expressed Protein, and Acyl Carrier Protein Mitochondrial. In conclusion, while our basic analyses on male and sperm quality showed similar results between the beginning and the end of the breeding season, on a proteomic level we detected a lower expression of sperm proteins linked to the energy metabolism, sperm-oocyte interactions, and flagellum structure in the EBS. Probably, this different protein expression could be related to the lower fertility rate of Assaf ewes after cervical artificial insemination at this time. More importantly, sperm proteins can be used as highly effective molecular markers in predicting sperm fertilization ability related to intraseasonal variations.

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.

Downregulation of KIF2C and TEKT2 is associated with male infertility and testicular carcinoma

Background: Genetic factors are important in spermatogenesis and fertility maintenance, and are potentially significant biomarkers for the early detection of infertility. However, further understanding of these biological processes is required.

Methods: In the present study, we sought to identify associated genes by reanalyzing separate studies from Gene Expression Omnibus datasets (GSE45885, GSE45887 and GSE9210) and validation datasets (GSE4797, 145467, 108886, 6872). The differential genes were used the limma package in R language. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed by the clusterprofier package. The protein-protein interaction network was constructed by the STRING database. The interaction between mRNA and TF was predicted by miRWalk web. At last, The Cancer Genome Atlas data were used to identify hub gene expression levels in GEPIA web.

Results: The results showed that 27 shared genes associated with spermatogenesis. We effectively screen out two genes (KIF2C and TEKT2) and both validated by GSE4797, 145467, 108886 and 6872. Among 27 shared genes, KIF2C and TEKT2 both down-regulated in spermatogenesis. The network of TF-miRNA-target gene was established, we found KIF2C-miRNAs (has-miR-3154, 6075, 6760-5p, 1251-5p, 186-sp)-TFs (EP300, SP1) might work in spermatogenesis.

Conclusions: Our study might help to improve our understanding of the mechanisms in spermatogenesis and provide diagnostic biomarkers and therapeutics targets.

ZEB1 Represses Neural Differentiation and Cooperates with CTBP2 to Dynamically Regulate Cell Migration during Neocortex Development

Zinc-finger E-box binding homeobox 1 (Zeb1) is a key regulator of epithelial-mesenchymal transition and cancer metastasis. Mutation of ZEB1 is associated with human diseases and defective brain development. Here we show that downregulation of Zeb1 expression in embryonic cortical neural progenitor cells (NPCs) is necessary for proper neuronal differentiation and migration. Overexpression of Zeb1 during neuronal differentiation, when its expression normally declines, blocks NPC lineage progression and disrupts multipolar-to-bipolar transition of differentiating neurons, leading to severe migration defects and subcortical heterotopia bands at postnatal stages. ZEB1 regulates a cohort of genes involved in cell differentiation and migration, including Neurod1 and Pard6b. The interaction between ZEB1 and CTBP2 in the embryonic cerebral cortex is required for ZEB1 to elicit its effect on the multipolar-to-bipolar transition, but not its suppression of Neurod1. These findings provide insights into understanding the complexity of transcriptional regulation during neuronal differentiation.

Pericentric inversion in chromosome 1 and male infertility

Pericentric inversion in chromosome 1 was thought to cause male infertility through spermatogenic impairment, regardless of the breakpoint position. However, carriers of pericentric inversion in chromosome 1 have been reported with normal fertility and familial transmission. Here, we report two cases of pericentric inversion in chromosome 1. One case was detected in utero via amniocentesis, and the other case was detected after the wife of the carrier experienced two spontaneous abortions within 5 years of marriage. Here, the effect of the breakpoint position of the inversion in chromosome 1 on male infertility is examined and compared with the published cases. The association between the breakpoint of pericentric inversion in chromosome 1 and spermatogenesis is also discussed. Overall, the results suggest that the breakpoint position deserves attention from physicians in genetic counseling as inversion carriers can produce offspring.

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

•

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

•

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

•

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

•

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.

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.

Antisperm protein targets in azoospermia men

BACKGROUND:

The number of couples that meet the definition of infertility at reproductive ages is increasing worldwide. One of the most known conditions of infertility in males is azoospermia, defined as complete absence of spermatozoa in the semen. Azoospermia manifests in two forms, namely obstructive and non-obstructive azoospermia. Although the presence of antisperm antibody (ASA) has been reported in 88% of the patients with obstructive azoospermia (OA), interestingly, there is no data regarding ASA targets in OA individuals.

AIM:

The present study aimed to identify sperm antibody targets in a group of OA men.

SETTINGS AND DESIGN:

The present study was carried out on 27 OA infertile men and 27 healthy fertile age-matched males as cases and controls, respectively.

SUBJECTS AND METHODS:

The sperm proteome was separated using two-dimensional gel electrophoresis technique, transferred onto the polyvinylidene fluoride membrane, and blotted with the sera of a group of OA men. Then, it was compared with the membranes blotted with the sera of a group of healthy fertile men. Matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI TOF/TOF) mass spectrometry was used to identify the different blotted spots and finally the results of the mass analysis were confirmed using reverse transcriptase polymerase chain reaction method.

RESULTS:

The results indicated that OA patients might produce antibody against two sperm proteins, Tektin-2 and triose phosphate isomerase. Moreover, the expressions of the two targeted proteins were confirmed at RNA level.

CONCLUSIONS:

The findings of the present study revealed two functionally important sperm proteins as antibody targets in azoospermic men.

Association of polymorphisms in tektin-t gene with idiopathic asthenozoospermia in Sichuan, China

PURPOSE

The purpose of this research was to study the association between the single nucleotide polymorphisms (SNPs) of the tektin-t gene and idiopathic asthenozoospermia.

METHODS

We conducted sequence analyses of the tektin-t gene in 104 idiopathic asthenozoospermia and 102 fertile men with normospermic parameters in Sichuan, China.

RESULTS

In this study, we found that allele 136 T (odds ratio [OR] 1.745, 95 % confidence interval [CI] 1.146-2.655, P = 0.009) was significantly increased in idiopathic asthenozoospermic patients compared with fertile men. This mutation substitutes a highly conserved arginine at position 46 to cysteine. Moreover, PolyPhen-2 analysis predicted that this variant was "probably damaging". In addition, a novel heterozygous mutation, R207H (c.620G >A), was detected in five asthenozoospermic patients, while there was no detection of this genotype among the fertile candidates, indicating that the mutation was located within a conserved domain predicted by PolyPhen-2 analysis as "probably damaging" to the protein.

CONCLUSIONS

These results suggested that tektin-t variants (Arg/Cys + Cys/Cys) were probably one of the high risk genetic factors for idiopathic asthenozoospermia among males in Sichuan, China, while the R207H polymorphism may be associated with idiopathic asthenozoospermia risk.

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.

Identification of proteins involved in human sperm motility using high-throughput differential proteomics

Mammalian sperm motility is a prerequisite for in vivo fertilization, and alterations in this parameter are commonly observed in infertile males. However, we still do not have a complete understanding of the molecular mechanisms controlling it. The aim of this study was to identify proteins involved in human sperm motility deficiency by using TMT protein labeling and LC-MS/MS. Two complementary approaches were used: comparison between sperm samples differing in motility (asthenozoospermic versus normozoospermic) and comparison between sperm subpopulations of fractionated normozoospermic samples differing in motility (non-migrated versus migrated). LC-MS/MS resulted in the identification of 1157 and 887 proteins in the first and second approaches, respectively. Remarkably, similar proteomic alterations were detected in the two experiments, with 80 proteins differentially expressed in the two groups of samples and 93 differentially expressed in the two groups of subpopulations. The differential proteins were analyzed by GO, cellular pathways, and clustering analyses and resulted in the identification of core deregulated proteins and pathways associated with sperm motility dysfunction. These included proteins associated with energetic metabolism, protein folding/degradation, vesicle trafficking, and the cytoskeleton. Contrary to what is usually accepted, the outcomes support the hypothesis that several metabolic pathways (notably, mitochondrial-related ones) contribute toward regulating sperm motility.

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.

Serological identification of Tektin5 as a cancer/testis antigen and its immunogenicity

Background

Identification of new cancer antigens is necessary for the efficient diagnosis and immunotherapy. A variety of tumor antigens have been identified by several methodologies. Among those antigens, cancer/testis (CT) antigens have became promising targets.

Methods

The serological identification of antigens by the recombinant expression cloning (SEREX) methodology has been successfully used for the identification of cancer/testis (CT) antigens. We performed the SEREX analysis of colon cancer.

Results

We isolated a total of 60 positive cDNA clones comprising 38 different genes. They included 2 genes with testis-specific expression profiles in the UniGene database, such as TEKT5 and a CT-like gene, A kinase anchoring protein 3 (AKAP3). Quantitative real-time RT-PCR analysis showed that the expression of TEKT5 was restricted to the testis in normal adult tissues. In malignant tissues, TEKT5 was aberrantly expressed in a variety of cancers, including colon cancer. A serological survey of 101 cancer patients with different cancers by ELISA revealed antibodies to TEKT5 in 13 patients, including colon cancer. None of the 16 healthy donor serum samples were reactive in the same test.

Conclusion

We identified candidate new CT antigen of colon cancer, TEKT5. The findings indicate that TEKT5 is immunogenic in humans, and suggest its potential use as diagnostic as well as an immunotherapeutic reagent for cancer patients.

Transcription regulation of sex-biased genes during ontogeny in the malaria vector Anopheles gambiae

In Anopheles gambiae, sex-regulated genes are responsible for controlling gender dimorphism and are therefore crucial in determining the ability of female mosquitoes to transmit human malaria. The identification and functional characterization of these genes will shed light on the sexual development and maturation of mosquitoes and provide useful targets for genetic control measures aimed at reducing mosquito fertility and/or distorting the sex ratio.

We conducted a genome wide transcriptional analysis of sex-regulated genes from early developmental stages through adulthood combined with functional screening of novel gonadal genes. Our results demonstrate that the male-biased genes undergo a major transcription turnover starting from larval stages to adulthood. The male biased genes at the adult stage include a significant high number of unique sequences compared to the rest of the genome. This is in contrast to female-biased genes that are much more conserved and are mainly activated during late developmental stages.

The high frequency of unique sequences would indicate that male-biased genes evolve more rapidly than the rest of the genome. This finding is particularly intriguing because A. gambiae is a strictly female monogamous species suggesting that driving forces in addition to sperm competition must account for the rapid evolution of male-biased genes. We have also identified and functionally characterized a number of previously unknown A. gambiae testis- and ovary-specific genes. Two of these genes, zero population growth and a suppressor of defective silencing 3 domain of the histone deacetylase co-repressor complex, were shown to play a key role in gonad development.

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.

Proteomics-based study on asthenozoospermia: differential expression of proteasome alpha complex

With a view to understand the molecular basis of sperm motility, we have tried to establish the human sperm proteome by two-dimensional PAGE MALDI MS/MS analysis. We report identification of 75 different proteins in the human spermatozoa. Comparative proteome analysis was carried out for asthenozoospermic and normozoospermic patients to understand the molecular basis of sperm motility. Analysis revealed eight proteins (including one unidentified) with altered intensity between the groups. Differential proteins distributed into three functional groups: 'energy and metabolism' (triose-phosphate isomerase, glycerol kinase 2, testis specific isoform and succinyl-CoA:3-ketoacid co-enzyme A transferase 1, mitochondrial precursor); 'movement and organization' (tubulin beta 2C and tektin 1) and 'protein turnover, folding and stress response' (proteasome alpha 3 subunit and heat shock-related 70 kDa protein 2). It was interesting to note that although the proteins falling in the functional group of 'energy and metabolism' are higher in the asthenozoospermic patients, the other two functional groups contain proteins, which are higher in the normozoospermic samples. Validation of results carried out for proteasome alpha 3 subunit by immunoblotting and confocal microscopy, confirmed significant changes in intensity of proteasome alpha 3 subunit in asthenozoospermic samples when compared with normozoospermic controls. Significant positive correlation too was found between proteasome alpha 3 subunit levels and rapid, linear progressive motility of the spermatozoa. In our understanding, this data would contribute appreciably to the presently limited information available about the proteins implicated in human sperm motility.

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.

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.

Identification of novel immunodominant epididymal sperm proteins using combinatorial approach

Functionally immature spermatozoa leave the testis mature during epididymal transit. This process of maturation involves either addition of new proteins or modification of existing proteins onto the sperm domains that are responsible for domain-specific functions. Epididymal proteins are preferred targets for immunocontraception. In an attempt to identify epididymis-specific sperm proteins, we used a novel combinatorial approach comprising subtractive immunization (SI) followed by proteomics. Following SI, sera of mice were used for immunoproteomics, which led to the identification of 30 proteins, of which four proteins namely sperm head protein 1, sperm flagella protein 2 (SFP2), SFP3, and SFP4 are being reported for the first time on sperm. Another group of four proteins namely collagen α-2 (I) chain precursor, homeodomain-interacting protein kinase 1, GTP-binding protein Rab1, and ubiquinol cytochrome c reductase core protein II although reported earlier in testis are being reported for the first time in epididymal sperm. Furthermore, seven out of these eight novel proteins could be validated using peptide ELISA. These data are a useful repository, which could be exploited to develop targets for post-testicular immunocontraception or biomarkers for infertility diagnosis and management.

Analysis of flagellar phosphoproteins from Chlamydomonas reinhardtii

Cilia and flagella are cell organelles that are highly conserved throughout evolution. For many years, the green biflagellate alga Chlamydomonas reinhardtii has served as a model for examination of the structure and function of its flagella, which are similar to certain mammalian cilia. Proteome analysis revealed the presence of several kinases and protein phosphatases in these organelles. Reversible protein phosphorylation can control ciliary beating, motility, signaling, length, and assembly. Despite the importance of this posttranslational modification, the identities of many ciliary phosphoproteins and knowledge about their in vivo phosphorylation sites are still missing. Here we used immobilized metal affinity chromatography to enrich phosphopeptides from purified flagella and analyzed them by mass spectrometry. One hundred forty-one phosphorylated peptides were identified, belonging to 32 flagellar proteins. Thereby, 126 in vivo phosphorylation sites were determined. The flagellar phosphoproteome includes different structural and motor proteins, kinases, proteins with protein interaction domains, and many proteins whose functions are still unknown. In several cases, a dynamic phosphorylation pattern and clustering of phosphorylation sites were found, indicating a complex physiological status and specific control by reversible protein phosphorylation in the flagellum.

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.

A possible association of a human tektin-t gene mutation (A229V) with isolated non-syndromic asthenozoospermia: case report

Asthenozoospermia (AZS), characterized by grade A + B sperm motility (as in World Health Organization Guidelines) < or =50% or A <25% in fresh ejaculate, may exist as an isolated disorder, in combination with other sperm anomalies or as part of syndromic association. The majority of syndromic patients can be ascribed to mutations in dynein genes, while, to date, no genes have been described to be associated in humans with non-syndromic, isolated AZS. An interesting family of axonemal proteins, the tektins, has been recently identified in various mammals and they are thought to play a fundamental role in ciliary movement. Recently, the human tektin-t (or h-tekB1 or Tektin-2) gene has been cloned, showing specific expression in flagella of mature sperm. We report the screening of tektin-t gene in 90 isolated non-syndromic AZS patients. We found a heterozygous mutation (A229V) in one patient. Ultrastructural analysis showed anomalies in > or =80% of examined spermatozoa involving axoneme microtubules and mitochondria. Moreover, the viability and mitochondrial function of sperm were altered in the patient with the A229V mutation. This is the first description of human pathology linked to a tektin-family gene, since only murine models are available for these genes.

Equatorial segment protein (ESP) is a human alloantigen involved in sperm-egg binding and fusion

The equatorial segment of the sperm head is known to play a role in fertilization; however, the specific sperm molecules contributing to the integrity of the equatorial segment and in binding and fusion at the oolemma remain incomplete. Moreover, identification of molecular mediators of fertilization that are also immunogenic in humans is predicted to advance both the diagnosis and treatment of immune infertility. We previously reported the cloning of Equatorial Segment Protein (ESP), a protein localized to the equatorial segment of ejaculated human sperm. ESP is a biomarker for a subcompartment of the acrosomal matrix that can be traced through all stages of acrosome biogenesis (Wolkowicz et al, 2003). In the present study, ESP immunoreacted on Western blots with 4 (27%) of 15 antisperm antibody (ASA)-positive serum samples from infertile male patients and 2 (40%) of 5 ASA-positive female sera. Immunofluorescent studies revealed ESP in the equatorial segment of 89% of acrosome-reacted sperm. ESP persisted as a defined equatorial segment band on 100% of sperm tightly bound to the oolemma of hamster eggs. Antisera to recombinant human ESP inhibited both oolemmal binding and fusion of human sperm in the hamster egg penetration assay. The results indicate that ESP is a human alloantigen involved in sperm-egg binding and fusion. Defined recombinant sperm immunogens, such as ESP, may offer opportunities for differential diagnosis of immune infertility.

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.

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.

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

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

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

Tektins are composed of a family of filament-forming proteins associated with ciliary and flagellar microtubules. A new member of the TEKTIN gene family, which was designated as rat Tektin4, was obtained by PCR technique combined with yeast two-hybrid screening. Rat Tektin4 cDNA consists of 1,341 bp encoding a 52 kDa protein of 447 amino acids. Tektin4 protein contains a Tektin domain including a nonapeptide signature sequence (RPNVELCRD), which is a prominent feature of Tektins. Its amino acid sequence showed 29% approximately 58% identities to that of other Tektin family proteins registered in the public databases. Tektin4 gene, which was mapped to rat chromosome 10q12, is composed of six exons and spanning 5 kb. Reverse-transcriptional-PCR (RT-PCR) analysis indicated that Tektin4 was predominantly expressed in testis and its expression was upregulated during testis development. In situ hybridization analysis showed that Tektin4 mRNA was localized in round spermatids in the seminiferous tubules of the rat testis. Tektin4 protein was predominantly localized in the flagella of spermatozoa, suggesting that it might works as a flagellar component requisite for flagellar stability or sperm motility.

Mice deficient in the axonemal protein Tektin-t exhibit male infertility and immotile-cilium syndrome due to impaired inner arm dynein function

The haploid germ cell-specific Tektin-t protein is a member of the Tektin family of proteins that form filaments in flagellar, ciliary, and axonemal microtubules. To investigate the physiological role of Tektin-t, we generated mice with a mutation in the tektin-t gene. The homozygous mutant males were infertile, while the females were fully fertile. Sperm morphology and function were abnormal, with frequent bending of the sperm flagella and marked defects in motility. In vitro fertilization assays showed that the defective spermatozoa were able to fertilize eggs. Electron microscopic examination showed that the dynein inner arm structure was disrupted in the sperm flagella of tektin-t-deficient mice. Furthermore, homozygous mutant mice had functionally defective tracheal cilia, as evidenced by altered dynein arm morphology. These results indicate that Tektin-t participates in dynein inner arm formation or attachment and that the loss of Tektin-t results in impaired motility of both flagella and cilia. Therefore, the tektin-t gene is one of the causal genes for immotile-cilium syndrome/primary ciliary dyskinesia.

Tektin3 encodes an evolutionarily conserved putative testicular microtubules-related protein expressed preferentially in male germ cells

Tektins are microtubule-associated cytoskeletal proteins that are expressed primarily in the male germ cell-lineage in centrioles and basal bodies and within ciliary and flagellar doublet microtubules. They are proposed to be important for axonemal architecture and microtubule stability in the sperm tail and in other ciliated and flagellar structures. Using an in silico (electronic database) subtractive approach to identify germ cell-specific genes in vertebrates, we isolated a new member of the Tektin gene family from mice, Tektin3. Reverse transcriptase-polymerase chain reaction (RT-PCR) and Northern blot analyses confirm that Tektin3 encodes a 1.7 kb transcript detectable preferentially in the testes of adult mice. In situ hybridization analysis in the testes revealed Tektin3 mRNA expression exclusively in late pachytene spermatocytes and early round spermatids. The putative TEKTIN3 protein shares 83.5% overall sequence identity with the human ortholog and includes a fully conserved carboxy terminal nonapeptide signature sequence present in all TEKTIN family members. In addition, using database mining, highly conserved TEKTIN3 orthologs were identified in puffer fish (Fugu rubripes) and rats (Rattus norvegicus) which shared 60.9 and 91.4% identity, respectively, with mouse TEKTIN3. The Tekt3 gene maps to murine chromosome 11 in a region that is syntenic to the human 17p12 chromosomal region containing the human TEKTIN3 gene. Our studies demonstrate that TEKTIN3 is a novel evolutionarily conserved male germ cell-enriched protein and suggest that it might perform important roles in male reproductive development and physiology.

Equatorial segment protein defines a discrete acrosomal subcompartment persisting throughout acrosomal biogenesis

The equatorial segment of the acrosome underlies the domain of the sperm that fuses with the egg membrane during fertilization. Equatorial segment protein (ESP), a novel 349-amino acid concanavalin-A-binding protein encoded by a two-exon gene (SP-ESP) located on chromosome 15 at q22, has been localized to the equatorial segment of ejaculated human sperm. Light microscopic immunofluorescent observations revealed that during acrosome biogenesis ESP first appears in the nascent acrosomal vesicle in early round spermatids and subsequently segregates to the periphery of the expanding acrosomal vesicle, thereby defining a peripheral equatorial segment compartment within flattened acrosomal vesicles and in the acrosomes of early and late cap phase, elongating, and mature spermatids. Electron microscopic examination revealed that ESP segregates to an electron-lucent subdomain of the condensing acrosomal matrix in Golgi phase round spermatids and persists in a similar electron-lucent subdomain within cap phase spermatids. Subsequently, ESP was localized to electron-dense regions of the equatorial segment and the expanded equatorial bulb in elongating spermatids and mature sperm. ESP is the earliest known protein to be recognized as a marker for the specification of the equatorial segment, and it allows this region to be traced through all phases of acrosomal biogenesis. Based on these observations, we propose a new model of acrosome biogenesis in which the equatorial segment is defined as a discrete domain within the acrosomal vesicle as early as the Golgi phase of acrosome biogenesis.

SAMP14, a novel, acrosomal membrane-associated, glycosylphosphatidylinositol-anchored member of the Ly-6/urokinase-type plasminogen activator receptor superfamily with a role in sperm-egg interaction

We report a new member of the Ly-6/urokinase-type plasminogen activator receptor (uPAR) superfamily of receptors, SAMP14, which is retained on the inner acrosomal membrane of the human spermatozoan following the acrosome reaction and may play a role in fertilization. The SAMP14 sequence predicted a glycosylphosphatidylinositol (GPI)-anchored protein with a signal peptide, a transmembrane domain near the carboxyl terminus, and a putative transamidase cleavage site in the proprotein. Attachment of SAMP14 to the membrane by a lipid anchor was confirmed by its sensitivity to phosphatidylinositol phospholipase C. SAMP14 has a single functional domain similar to the Ly-6 and urokinase plasminogen activator receptor superfamily of proteins, and the gene mapped to 19q13.33, near the PLAUR locus for uPAR at 19q13.2. Northern and dot blotting showed that SAMP14 expression was testis-specific. Indirect immunofluorescence and immunoelectron microscopy with antisera to purified recombinant SAMP14 localized the protein to outer and inner acrosomal membranes as well as the acrosomal matrix of ejaculated human sperm. Acrosome-reacted sperm demonstrated SAMP14 immunofluorescence, indicating its retention on the inner acrosomal membrane following the acrosome reaction. However, SAMP14 localized to the entire sperm when unwashed swim-up sperm from the ejaculate were stained, indicating that some SAMP14 is loosely associated with the plasma membrane. Antibodies against recombinant SAMP14 inhibited both the binding and the fusion of human sperm to zona free hamster eggs, suggesting that SAMP14 may have a role in sperm-egg interaction. SAMP14 represents a GPI-anchored putative receptor in the Ly-6/uPAR family that is exposed on the inner acrosomal membrane after the acrosome reaction.

Cloning and characterization of testis-specific tektin in Bombyx mori

A testis-specific cDNA library of Bombyx mori was constructed by an mRNA subtraction technique. Several clones were randomly selected and determined for their nucleotide sequences. One of them, designated as BmTST, contained a 3'-part of an open reading frame homologous to tektin, the protein known to form filamentous polymers in the walls of ciliary and flagellar microtubules. Also isolated was a genomic fragment, which contains the 5'-part of the coding sequence of BmTST and its promoter region. As a whole, the complete open reading frame was found to encode 508 amino acid residues, whose sequence had 28, 28 and 30% identities with the Strongylocentrotus purpuratus tektins A1, B1 and C1, respectively. Expression analysis by reverse transcription polymerase chain reaction with the cDNA and Western blotting with a polyclonal antibody indicated that the BmTST gene was expressed specifically in the testis during sperm maturation. The protein was immunologically detected exclusively in the fraction expected to contain the 9 + 2 flagellar axonemes of sperms. We infer that the BmTst protein is possibly involved in the spermatogenesis of B. mori.