TSSK5, a novel member of the testis-specific serine/threonine kinase family, phosphorylates CREB at Ser-133, and stimulates the CRE/CREB responsive pathway

Novel Aspects of cAMP-Response Element Modulator (CREM) Role in Spermatogenesis and Male Fertility

Spermatogenesis is a very complex process with an intricate transcriptional regulation. The transition from the diploid to the haploid state requires the involvement of specialized genes in meiosis, among other specific functions for the formation of the spermatozoon. The transcription factor cAMP-response element modulator (CREM) is a key modulator that triggers the differentiation of the germ cell into the spermatozoon through the modification of gene expression. CREM has multiple repressor and activator isoforms whose expression is tissue-cell-type specific and tightly regulated by various factors at the transcriptional, post-transcriptional and post-translational level. The activator isoform CREMτ controls the expression of several relevant genes in post-meiotic stages of spermatogenesis. In addition, exposure to xenobiotics negatively affects CREMτ expression, which is linked to male infertility. On the other hand, antioxidants could have a positive effect on CREMτ expression and improve sperm parameters in idiopathically infertile men. Therefore, CREM expression could be used as a biomarker to detect and even counteract male infertility. This review examines the importance of CREM as a transcription factor for sperm production and its relevance in male fertility, infertility and the response to environmental xenobiotics that may affect CREMτ expression and the downstream regulation that alters male fertility. Also, some health disorders in which CREM expression is altered are discussed.

Broad phosphorylation mediated by testis-specific serine/threonine kinases contributes to spermiogenesis and male fertility

Genetic studies elucidate a link between testis-specific serine/threonine kinases (TSSKs) and male infertility in mammals, but the underlying mechanisms are unclear. Here, we identify a TSSK homolog in Drosophila, CG14305 (termed dTSSK), whose mutation impairs the histone-to-protamine transition during spermiogenesis and causes multiple phenotypic defects in nuclear shaping, DNA condensation, and flagellar organization in spermatids. Genetic analysis demonstrates that kinase catalytic activity of dTSSK, which is functionally conserved with human TSSKs, is essential for male fertility. Phosphoproteomics identify 828 phosphopeptides/449 proteins as potential substrates of dTSSK enriched primarily in microtubule-based processes, flagellar organization and mobility, and spermatid differentiation and development, suggesting that dTSSK phosphorylates various proteins to orchestrate postmeiotic spermiogenesis. Among them, the two substrates, protamine-like protein Mst77F/Ser⁹ and transition protein Mst33A/Ser²³⁷, are biochemically validated to be phosphorylated by dTSSK in vitro, and are genetically demonstrated to be involved in spermiogenesis in vivo. Collectively, our findings demonstrate that broad phosphorylation mediated by TSSKs plays an indispensable role in spermiogenesis.

Association of Intrauterine Microbes with Endometrial Factors in Intrauterine Adhesion Formation and after Medicine Treatment

Intrauterine adhesions (IUAs) have caused serious harm to women’s reproductive health. Although emerging evidence has linked intrauterine microbiome to gynecological diseases, the association of intrauterine microbiome with IUA, remains unknown. We performed metagenome-wide association, metabolomics, and transcriptomics studies on IUA and non-IUA uteri of adult rats to identify IUA-associated microbial species, which affected uterine metabolites and endometrial transcriptions. A rat model was used with one side of the duplex uterus undergoing IUA and the other remaining as a non-IUA control. Both 16S rRNA sequencing and metagenome-wide association analysis revealed that instead of Mycoplasmopsis specie in genital tract, murine lung pathogen Mycoplasmopsispulmonis markedly increased in IUA samples and displayed a distinct positive interaction with the host immune system. Moreover, most of the IUA-enriched 58 metabolites positively correlate with M.pulmonis, which inversely correlates with a mitotic progression inhibitor named 3-hydroxycapric acid. A comparison of metabolic profiles of intrauterine flushing fluids from human patients with IUA, endometritis, and fallopian tube obstruction suggested that rat IUA shared much similarity to human IUA. The endometrial gene Tenascin-N, which is responsible for extracellular matrix of wounds, was highly up-regulated, while the key genes encoding parvalbumin, trophectoderm Dkkl1 and telomerase involved in leydig cells, trophectoderm cells, activated T cells and monocytes were dramatically down-regulated in rat IUA endometria. Treatment for rat IUA with estrogen (E2), oxytetracycline (OTC), and a traditional Chinese patent medicine GongXueNing (GXN) did not reduce the incidence of IUA, though inflammatory factor IL-6 was dramatically down-regulated (96–86%) with all three. Instead, in both the E2 and OTC treated groups, IUA became worse with a highly up-regulated B cell receptor signaling pathway, which may be associated with the significantly increased proportions of Ulvibacter or Staphylococcus. Our results suggest an association between intrauterine microbiota alterations, certain uterine metabolites, characteristic changes in endometrial transcription, and IUA and the possibility to intervene in IUA formation by targeting the causal factors, microbial infection, and Tenascin-like proteins.

Identification of the TSSK4 Alternative Spliceosomes and Analysis of the Function of the TSSK4 Protein in Yak (Bos grunniens)

In mammals, the testis-specific serine/threonine kinase (TSSK) is essential for spermatogenesis and male fertility. TSSK4 belongs to the family of the testis-specific serine/threonine-protein kinase (TSSK), with a crucial role in spermatogenesis. This study aimed to analyze the variable spliceosome of the TSSK4 gene in the yak for understanding the regulatory function of the TSSK4 spliceosome in yak testis development using PCR amplification and cloning techniques. The GST pull-down was used for pulling down the protein interacting with TSSK4, and then the protein interacting with TSSK4 was identified using LC–MS/MS. The results of the PCR amplification demonstrated multiple bands of the TSSK4 gene in the yak. The cloning and sequencing yielded a total of six alternative spliceosomes, which included only two alternative spliceosomes before sexual maturity and four alternative spliceosomes after sexual maturity. The sub-cells of the alternative spliceosomes were found to localize in the nucleus before sexual maturity and in the cytoplasm after sexual maturity. The LC–MS/MS analysis of the alternative spliceosome with the highest expression after sexual maturity yielded a total of 223 interacting proteins. The enrichment analysis of the 223 interacting proteins revealed these proteins participate in biological processes, cell composition, and molecular functions. The KEGG analysis indicated that the TSSK4-interacting protein participates in the estrogen signaling pathways, tight junctions, endoplasmic reticulum protein processing, and other signaling pathways. This study cloned the six alternative spliceosomes of the TSSK4 gene laying the foundation for studying the function of each spliceosome in the future.

ATF6 deficiency damages the development of spermatogenesis in male Atf6 knockout mice

Activating transcription factor 6 (ATF6), also known as ACHM7, ATF6A, encodes a transcription factor that activates target genes for the unfolded protein response (UPR) during endoplasmic reticulum (ER) stress. It functions as nuclear transcription factor via a cis-acting ER stress response element (ERSE) that is presented in the promoters of genes encoding ER chaperones. Studies have shown that endoplasmic reticulum stress (ERS) can cause damage to spermatozoa and testes, leading to male sterility. And we find that the expression of ATF6 in spermatozoa of some infertile patients is significantly reduced. Then, we construct the Atf6 knockout mice model and interestingly find a decline in male fertility. The downstream gene testis-specific serine/threonine-protein kinase 4 (Tssk4) is screened based on transcriptome sequencing. We use Western blot and real-time PCR to confirm this result in both 293T cells and Atf6 knockout mice. TSSK4 is essential in male germ cell genesis and sperm maturation. Our results suggest that the expression of TSSK4 may be regulated by ATF6. The effect of Atf6 knockout on the reproductive development of male mice may be related to the low expression of TSSK4, which further verify that there may be some relationship between ERS and male reproduction.

Testis-specific serine kinase protein family in male fertility and as targets for non-hormonal male contraception†

Male contraception is a very active area of research. Several hormonal agents have entered clinical trials, while potential non-hormonal targets have been brought to light more recently and are at earlier stages of development. The general strategy is to target genes along the molecular pathways of sperm production, maturation, or function, and it is predicted that these novel approaches will hopefully lead to more selective male contraceptive compounds with a decreased side effect burden. Protein kinases are known to play a major role in signaling events associated with sperm differentiation and function. In this review, we focus our analysis on the testis-specific serine kinase (TSSK) protein family. We have previously shown that members of the family of TSSKs are postmeiotically expressed in male germ cells and in mature mammalian sperm. The restricted postmeiotic expression of TSSKs as well as the importance of phosphorylation in signaling processes strongly suggests that TSSKs have an important role in germ cell differentiation and/or sperm function. This prediction has been supported by the reported sterile phenotype of the Tssk6 knockout (KO) mice and of the double Tssk1 and Tssk2 KO mice and by the male subfertile phenotype observed in a Tssk4 KO mouse model.

RNAi-Mediated Knockdown of Tssk1 and Tektin1 Genes Impair Male Fertility in Bactrocera dorsalis

The genetic-based sterile insect technique (SIT) is an effective and environmentally safe strategy to diminish populations of agricultural and horticultural insect pests. Functional characterization of genes related to male fertility can enhance the genetic-based SIT. Tssk1 has been involved to control male fertility in both mammals and insects. Moreover, Tektin1 has also been revealed to influence male fertility in both human and mammals. These findings suggested that Tssk1 and Tektin1 identified from Bactrocera dorsalis could be required for male fertility in B. dorsalis. In this study, expression profiles of these two genes were studied at different developmental stages and in various tissues of adult males. Remarkably, it was found that Tssk1 and Tektin1 were highly expressed in the testis of mature adult males of B. dorsalis. Furthermore, Tssk1 and Tektin1 genes were downregulated by using the RNA interference (RNAi) method. Fertility assays including egg laying, hatching, and spermatozoa count were also performed to investigate male fertility of B. dorsalis. Results showed that knockdown of Tssk1 and Tektin1 caused male sterility up to 58.99% and 64.49%, respectively. As expected, the total numbers of spermatozoa were also significantly reduced by 65.83% and 73.9%, respectively. These results suggested that male sterility was happened wing to the low number of spermatozoa. In conclusion, we demonstrate that Tssk1 and Tektin1 are the novel agents that could be used to enhance the genetic-based SIT, or their double-stranded RNA (dsRNA) can be used as biopesticides to control the population of B. dorsalis.

Recombinant production of enzymatically active male contraceptive drug target hTSSK2 - Localization of the TSKS domain phosphorylated by TSSK2

The testis-specific serine/threonine kinase 2 (TSSK2) has been proposed as a candidate male contraceptive target. Development of a selective inhibitor for this kinase first necessitates the production of highly purified, soluble human TSSK2 and its substrate, TSKS, with high yields and retention of biological activity for crystallography and compound screening. Strategies to produce full-length, soluble, biologically active hTSSK2 in baculovirus expression systems were tested and refined. Soluble preparations of TSSK2 were purified by immobilized-metal affinity chromatography (IMAC) followed by gel filtration chromatography. The biological activities of rec.hTSSK2 were verified by in vitro kinase and mobility shift assays using bacterially produced hTSKS (isoform 2), casein, glycogen synthase peptide (GS peptide) and various TSKS peptides as target substrates. Purified recombinant hTSSK2 showed robust kinase activity in the in vitro kinase assay by phosphorylating hTSKS isoform 2 and casein. The ATP Km values were similar for highly and partially purified fractions of hTSSK2 (2.2 and 2.7 μM, respectively). The broad spectrum kinase inhibitor staurosporine was a potent inhibitor of rec.hTSSK2 (IC50 = 20 nM). In vitro phosphorylation experiments carried out with TSKS (isoform 1) fragments revealed particularly strong phosphorylation of a recombinant N-terminal region representing aa 1-150 of TSKS, indicating that the N-terminus of human TSKS is phosphorylated by human TSSK2. Production of full-length enzymatically active recombinant TSSK2 kinase represents the achievement of a key benchmark for future discovery of TSSK inhibitors as male contraceptive agents.

Phosphorylated testis-specific serine/threonine kinase 4 may phosphorylate Crem at Ser-117

We aimed to investigate the internal existence status of testis-specific serine/threonine kinase 4 (Tssk4) and the interaction of Tssk4 and Cre-responsive element modulator (Crem). The internal existence status of Tssk4 in testis of mice was detected using western blotting and dephosphorylation method. The interaction of Tssk4 and Crem was analyzed by western blotting, immunohistochemistry, immunofluorescence, in vitro co-immunoprecipitation assays, and in vitro kinase assay. The results revealed that Tssk4 existed in testis both in phosphorylation and unphosphorylation status by a temporal manner with the development of testis. Immunofluorescence results showed that Tssk4 had identical distribution pattern with Crem in testis, which was utterly different to the localization of Cre-responsive element binding (Creb). In conclusion, our study demonstrated that phosphorylated Tssk4 might participate in testis genes expressions by phosphorylating Crem at Ser-117.

Testis specific serine/threonine protein kinase 4 (TSSK4) leads to cell apoptosis relying on its kinase activity

Testis specific serine/threonine protein kinase 4 (TSSK4) belongs to the TSSK family, and its members play an important role in spermatogenesis and/or spermiogenesis. Mouse TSSK4 has been reported to be expressed exclusively in the testis and can maintain its kinase activity through autophosphorylation at Thr-197. However, its biological function remains poorly understood. Here we found that GFP-TSSK4-overexpressed HeLa cells showed apoptotic bodies, indicating TSSK4 can lead to apoptosis in vitro. Furthermore, TSSK4 induced apoptosis in different cell lines including HeLa, Cos-7 and H1299 tested by flow cytometry but not its kinase-dead mutant TSSK4-K54M. TSSK4 knockout mice showed increased testes weight and decreased apoptotic spermatogonia and spermatocytes at 21st day after birth tested by TUNEL technology. So TSSK4 was able to induce cell apoptosis in vitro depending on its kinase activity, which leads to abnormal testes weight and apoptosis, shedding light on its function in the process of spermatogenesis and/or spermiogenesis.

Tssk4 is essential for maintaining the structural integrity of sperm flagellum

Tssk4 belongs to the Testis Specific Serine/threonine protein Kinase (TSSK) family, members of which play an important role in spermatogenesis and/or spermiogenesis. Several Tssk family proteins have extensively been studied. However, the exact function of Tssk4 remains unclear. A Tssk4 knockout mouse model was generated and the males were subfertile due to seriously decreased sperm motility. The ultrastructure of the Tssk4(-/-)sperm tail is disorganized at the midpiece-principal piece junction, leading to a severe bend in the sperm flagellum. One or more axonemal microtubule doublets are absent and the midpiece is fused with the principal piece. Furthermore, we identified the association between Tssk4 and Odf2, a prominent cytoskeletal protein of the outer dense fiber (ODF) in sperm flagellum. Tssk4 can change the phosphorylation state of Odf2 and conversely Odf2 potentiates the autophosphorylation activity of Tssk4. These findings reveal that Tssk4 is required for maintaining the structural integrity of sperm flagellum and male fertility.

Testis specific serine/threonine kinase 4 (Tssk4) maintains its kinase activity by phosphorylating itself at Thr-197

The testis specific serine/threonine protein kinase family (Tssk) members play important roles in spermatogenesis and/or spermiogenesis. Similar to other Tssk family members, Tssk4 protein shows exclusive expression in testis, but its biochemical and biological functions are still largely unknown. In present work, we generate a polyclonal antibody which specifically recognizes Tssk4 but not the other three Tssk family members (Tssk1, Tssk2 and Tssk3). By using the qualified antibody, we show that Tssk4 protein is constantly expressed in testis from haploid round spermatids to morphological mature spermatozoa. Further experiments reveal that Tssk4 has autophosphorylation activity and self-association character in vitro. Importantly, we find that autophosphorylation of Tssk4 at Thr-197 in the T-loop region is essential to its kinase activity. Taken together, these findings suggest that autophosphorylation at Thr-197 plays a critical role in maintaining Tssk4 kinase activity, which might be involved in spermiogenesis.

Expression and localization of five members of the testis-specific serine kinase (Tssk) family in mouse and human sperm and testis

Members of the testis-specific serine/threonine kinases (Tssk) family may have a role in sperm differentiation in the testis and/or fertilization. To gain insight into the functional relevance of these kinases, their expression was examined both at the mRNA and protein levels. Quantitative PCR analysis confirmed that all five Tssk mRNAs are almost exclusively expressed postmeiotically in the testis. Recombinant mouse and human Tssks were cloned and used for validation of an array of commercial and custom-made antibodies against Tssks. Immunolocalization in mouse testis, and in mouse and human sperm, showed that Tssk1, Tssk2, Tssk4 and Tssk6, but not Tssk3, were present in mouse sperm and in germ cells from mouse testis. TSSK1, TSSK2 and TSSK6 were also detected in human sperm, while TSSK3 was absent. In both mouse and human sperm, Tssk1 was partially soluble, while Tssk2, Tssk4 and Tssk6 were insoluble in non-ionic detergents. In vitro recombinant TSSK2 activity assays showed maximum enzymatic activity at 5 mM Mg(2+) and a Km for ATP of ∼10 µM. These, observations together with findings that the Tssk1/Tssk2 double knock-out as well as the Tssk6 null mice are sterile without presenting other detectable defects, suggest that these kinases could be used as targets for male contraception.

Functional transformation of the chromatoid body in mouse spermatids requires testis-specific serine/threonine kinases

The cytoplasmic chromatoid body (CB) organizes mRNA metabolism and small regulatory RNA pathways, in relation to haploid gene expression, in mammalian round spermatids. However, little is known about functions and fate of the CB at later steps of spermatogenesis, when elongating spermatids undergo chromatin compaction and transcriptional silencing. In mouse elongating spermatids, we detected accumulation of the testis-specific serine/threonine kinases TSSK1 and TSSK2, and the substrate TSKS, in a ring-shaped structure around the base of the flagellum and in a cytoplasmic satellite, both corresponding to structures described to originate from the CB. At later steps of spermatid differentiation, the ring is found at the caudal end of the newly formed mitochondrial sheath. Targeted deletion of the tandemly arranged genes Tssk1 and Tssk2 in mouse resulted in male infertility, with loss of the CB-derived ring structure, and with elongating spermatids possessing a collapsed mitochondrial sheath. These results reveal TSSK1- and TSSK2-dependent functions of a transformed CB in post-meiotic cytodifferentiation of spermatids.

c.822+126T>G/C: a novel triallelic polymorphism of the TSSK6 gene associated with spermatogenic impairment in a Chinese population

TSSK6 is a member of the testis-specific serine/threonine kinase family. Male Tssk6 knockout mice are infertile owing to spermatogenic impairment, including sperm count reduction, a decrease in motile sperm number and motility rates, and an increase in the number of sperms with abnormal morphology. We investigated the possible association between variations of the TSSK6 gene and spermatogenic impairment in humans. Mutation screening of TSSK6 was carried out in 519 patients with azoospermia (n = 273) or severe oligozoospermia (n = 246) and in 359 controls with normozoospermia by denaturing high-performance liquid chromatography and DNA sequencing. The frequencies of alleles and genotypes of gene polymorphism were compared between patients and controls. A novel triallelic polymorphism in TSSK6, c.822+126T>G/C, was identified. The frequencies of genotype TT and allele T were increased dramatically in infertile patients compared with controls, whereas genotype TG, allele G and allele C frequencies were significantly higher in controls than in patients. Further study revealed that the allele C frequency of controls was remarkably higher than that of patients with oligospermia. Our findings, for the first time, suggested an association of c.822+126T>G/C in TSSK6 with spermatogenic impairment in humans in which allele T may be a risk factor for male infertility, while alleles C and G may decrease susceptibility to male infertility.

Identification of peptide substrate and small molecule inhibitors of testis-specific serine/threonine kinase1 (TSSK1) by the developed assays

In this paper, a peptide substrate (Pep8) of TSSK1 is identified. Using Pep8 as a substrate, two homogeneous and efficient assays for TSSK1 inhibitors screening have been developed, including luminescent kinase assay and LC-MS-based high-throughput assay. Two classes of compounds were identified that are able to efficiently inhibit phosphorylation catalyzed by TSSK1.

DAZL binds to the transcripts of several Tssk genes in germ cells

The Dazl gene encodes a germ-cell-specific RNA-binding protein which is essential for spermatogenesis. It has been proposed that this protein (DAZL) binds to RNA in the cytoplasm of germ cells and controls spermatogenesis. Using the specific nucleic acids associated with proteins (SNAAP) technique, we identified 17 target mRNAs bound by mDAZL. Among these transcripts, we focused on TSSK2, which encodes a testis-specific serine/threonine kinase. To date, five TSSK family members have been cloned, and all are exclusively expressed in the testis. We demonstrated that in addition to the TSSK1 3'UTR , the 3'UTRs of TSSKs 2 and 4 were bound by human and mouse DAZL, and that human DAZL (hDAZL) bound to the 3'UTR of human TSSK5 (hTSSK5). Our results suggest that the Dazl gene may play different roles in human and mouse spermatogenesis by regulating different members of the downstream gene family.

Targeted deletion of Tssk1 and 2 causes male infertility due to haploinsufficiency

Targeted deletion of Tssk1 and 2 resulted in male chimeras which produced sperm/spermatogenic cells bearing the mutant allele, however this allele was never transmitted to offspring, indicating infertility due to haploinsufficiency. Morphological defects in chimeras included failure to form elongated spermatids, apoptosis of spermatocytes and spermatids, and the appearance of numerous round cells in the epididymal lumen. Characterization of TSSK2 and its interactions with the substrate, TSKS, were further investigated in human and mouse. The presence of both kinase and substrate in the testis was confirmed, while persistence of both proteins in spermatozoa was revealed for the first time. In vivo binding interactions between TSSK2 and TSKS were established through co-immunoprecipitation of TSSK2/TSKS complexes from both human sperm and mouse testis extracts. A role for the human TSKS N-terminus in enzyme binding was defined by deletion mapping. TSKS immunoprecipitated from both mouse testis and human sperm extracts was actively phosphorylated. Ser281 was identified as a phosphorylation site in mouse TSKS. These results confirm both TSSK 2 and TSKS persist in sperm, define the critical role of TSKS' N-terminus in enzyme interaction, identify Ser 281 as a TSKS phosphorylation site and indicate an indispensable role for TSSK 1 and 2 in spermiogenesis.

Phosphorylation of mouse sperm axoneme central apparatus protein SPAG16L by a testis-specific kinase, TSSK2

The mammalian protein SPAG16L, the ortholog of Chlamydomonas Pf20, is an axoneme central apparatus protein necessary for flagellar motility. The SPAG16L protein sequence contains multiple potential phosphorylation sites, and the protein was confirmed to be phosphorylated in vivo. A yeast two-hybrid screen identified the testis-specific kinase, TSSK2, to be a potential SPAG16L binding partner. SPAG16L and TSSK2 interactions were confirmed by coimmunoprecipitation of both proteins from testis extracts and cell lysates expressing these proteins, and their colocalization was also noted by confocal microscopy in Chinese hamster ovary cells, where they were coexpressed. TSSK2 associates with SPAG16L via its C-terminal domain bearing WD repeats. The N-terminal domain containing a coiled coil motif does not associate with TSSK2. SPAG16L can be phosphorylated by TSSK2 in vitro. Finally, TSSK2 is absent or markedly reduced from the testes in most of the SPAG16L-null mice. These data support the conclusion that SPAG16L is a TSSK2 substrate.

The expression of the testis-specific Dyrk4 kinase is highly restricted to step 8 spermatids but is not required for male fertility in mice

Members of the dual specificity tyrosine phosphorylated and regulated kinase family (Dyrk) were shown to have a highly testis-abundant or testis-restricted expression pattern. Furthermore, for some members of the family an involvement in gene expression regulation by phosphorylating transcription factors has been shown. Since little is known about the complex regulation of germ cell differentiation in spermatogenesis, we analysed the possible involvement of Dyrk kinases in this process. ISH experiments showed specific distribution of Dyrk kinases mainly in postmeiotic germ cell. We identified Dyrk4 as a testis-specific kinase with a very restricted expression to stage VIII postmeiotic spermatids. In vitro and in vivo experiments proved the enzymatic activity and suggested the cytoplasmatic localisation of Dyrk4. Finally, analysis of a Dyrk4 deficient mouse line showed that Dyrk4 is dispensable for male fertility, hence suggesting a functional redundancy of some Dyrk isoforms during spermiogenesis.