Characterization of the testis-specific gene 'calmegin' promoter sequence and its activity defined by transgenic mouse experiments

CATSPERε extracellular domains are essential for sperm calcium channel assembly and activity modulation

The sperm flagellar-specific CatSper Ca2+ channel is a multiprotein complex critical for successful fertilization. The four ancillary subunits, CATSPERβ, γ, δ, and ε, form a unique canopy structure over the pore-forming channel. However, how the canopy is formed and what it does in the assembled channel complex remains unknown. Here, we report that extracellular domains (ECDs) of CATSPERε are essential for canopy and holo-complex assembly and modulate channel activity during sperm capacitation. CATSPERε-deficient males are sterile due to the absence of the entire channel and defective sperm hyperactivation. Expressing ECDs-truncated CATSPERε during spermatogenesis does not rescue the knockout because it fails to incorporate into the native complex. In contrast, addition of a CATSPERε ECD fragment during sperm capacitation significantly reduces channel activity. These findings provide insight into the underlying molecular and developmental mechanisms of CatSper assembly and how the channel can be modulated in physiological settings and by therapeutic intervention.

MYCBPAP is a central apparatus protein required for centrosome-nuclear envelope docking and sperm tail biogenesis in mice

The structure of the sperm flagellar axoneme is highly conserved across species and serves the essential function of generating motility to facilitate the meeting of spermatozoa with the egg. During spermiogenesis, the axoneme elongates from the centrosome, and subsequently the centrosome docks onto the nuclear envelope to continue tail biogenesis. Mycbpap is expressed predominantly in mouse and human testes and conserved in Chlamydomonas as FAP147. A previous cryo-electron microscopy analysis has revealed the localization of FAP147 to the central apparatus of the axoneme. Here, we generated Mycbpap-knockout mice and demonstrated the essential role of Mycbpap in male fertility. Deletion of Mycbpap led to disrupted centrosome-nuclear envelope docking and abnormal flagellar biogenesis. Furthermore, we generated transgenic mice with tagged MYCBPAP, which restored the fertility of Mycbpap-knockout males. Interactome analyses of MYCBPAP using Mycbpap transgenic mice unveiled binding partners of MYCBPAP including central apparatus proteins, such as CFAP65 and CFAP70, which constitute the C2a projection, and centrosome-associated proteins, such as CCP110. These findings provide insights into a MYCBPAP-dependent regulation of the centrosome-nuclear envelope docking and sperm tail biogenesis.

A small secreted protein NICOL regulates lumicrine-mediated sperm maturation and male fertility

The mammalian spermatozoa produced in the testis require functional maturation in the epididymis for their full competence. Epididymal sperm maturation is regulated by lumicrine signalling pathways in which testis-derived secreted signals relocate to the epididymis lumen and promote functional differentiation. However, the detailed mechanisms of lumicrine regulation are unclear. Herein, we demonstrate that a small secreted protein, NELL2-interacting cofactor for lumicrine signalling (NICOL), plays a crucial role in lumicrine signalling in mice. NICOL is expressed in male reproductive organs, including the testis, and forms a complex with the testis-secreted protein NELL2, which is transported transluminally from the testis to the epididymis. Males lacking Nicol are sterile due to impaired NELL2-mediated lumicrine signalling, leading to defective epididymal differentiation and deficient sperm maturation but can be restored by NICOL expression in testicular germ cells. Our results demonstrate how lumicrine signalling regulates epididymal function for successful sperm maturation and male fertility.

The association of ODF4 with AK1 and AK2 in mice is essential for fertility through its contribution to flagellar shape

Normal sperm flagellar shape and movement are essential for fertilization. The integral protein outer dense fiber 4 (ODF4) localizes to ODFs, but its function remains unclear. Adenylate kinase (AK) is a phosphotransferase that catalyzes the interconversion and controls the concentration equilibrium of adenine nucleotides. AK shuttles ATP to energy-consuming sites. Here, we report on the relationship of flagellar shape and movement with ODF4, AK1 and AK2 by using Odf4-deletion (Odf4^-/-) mice. Soluble ODF4 is coimmunoprecipitated with AK1 and AK2 in Odf4^+/+ spermatozoa. ODF4, AK1 and AK2 localize to whole flagella (plasmalemma, mitochondria, ODFs, and residual cytoplasmic droplets (CDs)), principal pieces, and midpieces, respectively. Odf4^-/- sperm flagella lose ODF4 and reduce AK1 and AK2 but produce ATP. The flagellum is bent (hairpin flagellum) with a large CD in the midpiece. There is no motility in the midpiece, but the principal piece is motile. Odf4^-/- spermatozoa progress backward and fail to ascend in the uterus. Thus, Odf4^-/- males are infertile owing to abnormal flagellar shape and movement caused mainly by the loss of ODF4 with AK1 and AK2. This study is supported by the rescue experiment; the abnormalities and male infertility caused by Odf4 deletion were reversed by Odf4 restoration.

Proximity-dependent biotin labeling in testicular germ cells identified TESMIN-associated proteins

Characterization of protein-protein interactions (PPI) is a key to understanding the functions of proteins of interest. Recently developed proximity-dependent biotin identification (BioID) has been actively investigated as an alternative PPI mapping method because of its usefulness in uncovering transient PPI. Here, as an example of proximity labeling proteomics application in the testis, we generated two transgenic mouse lines expressing two biotin ligases (BioID2 or TurboID) fused with TESMIN, which translocates from the cytosol to the nucleus during meiotic progression and is required for reproduction. The BioID2 transgene, albeit not the TurboID transgene, rescued fertility defects of the Tesmin KO male mice, indicating that the TESMIN-BioID2 fusion can physiologically replace TESMIN. Furthermore, biotinylated protein pull-down and affinity-purification followed by mass spectrometry using the TESMIN-BioID2 transgenic mice captured components of the MYBL1-MuvB complex that regulate cell-cycle gene expression. Thus, our study shows that proximity labeling proteomics can be applied in male germ cells, although the choice of biotin ligase needs to be carefully tested.

Trim41 is required to regulate chromosome axis protein dynamics and meiosis in male mice

Meiosis is a hallmark event in germ cell development that accompanies sequential events executed by numerous molecules. Therefore, characterization of these factors is one of the best strategies to clarify the mechanism of meiosis. Here, we report tripartite motif-containing 41 (TRIM41), a ubiquitin ligase E3, as an essential factor for proper meiotic progression and fertility in male mice. Trim41 knockout (KO) spermatocytes exhibited synaptonemal complex protein 3 (SYCP3) overloading, especially on the X chromosome. Furthermore, mutant mice lacking the RING domain of TRIM41, required for the ubiquitin ligase E3 activity, phenocopied Trim41 KO mice. We then examined the behavior of mutant TRIM41 (ΔRING-TRIM41) and found that ΔRING-TRIM41 accumulated on the chromosome axes with overloaded SYCP3. This result suggested that TRIM41 exerts its function on the chromosome axes. Our study revealed that Trim41 is essential for preventing SYCP3 overloading, suggesting a TRIM41-mediated mechanism for regulating chromosome axis protein dynamics during male meiotic progression.

FAM71F1 binds to RAB2A and RAB2B and is essential for acrosome formation and male fertility in mice

The acrosome is a cap-shaped, Golgi-derived membranous organelle that is located over the anterior of the sperm nucleus and highly conserved throughout evolution. Although morphological changes during acrosome biogenesis in spermatogenesis have been well described, the molecular mechanism underlying this process is still largely unknown. Family with sequence similarity 71, member F1 and F2 (FAM71F1 and FAM71F2) are testis-enriched proteins that contain a RAB2B-binding domain, a small GTPase involved in vesicle transport and membrane trafficking. Here, by generating mutant mice for each gene, we found that Fam71f1 is essential for male fertility. In Fam71f1-mutant mice, the acrosome was abnormally expanded at the round spermatid stage, likely because of enhanced vesicle trafficking. Mass spectrometry analysis after immunoprecipitation indicated that, in testes, FAM71F1 binds not only RAB2B, but also RAB2A. Further study suggested that FAM71F1 binds to the GTP-bound active form of RAB2A/B, but not the inactive form. These results indicate that a complex of FAM71F1 and active RAB2A/B suppresses excessive vesicle trafficking during acrosome formation.

SPATA33 localizes calcineurin to the mitochondria and regulates sperm motility in mice

Calcineurin is a target of immunosuppressive drugs such as cyclosporine A and tacrolimus. In the immune system, calcineurin interacts with NFAT via the PxIxIT motif to activate T cells. In contrast, little is known about the proteins that interact with a testis-enriched calcineurin that is essential for sperm motility and male fertility. Here, we discovered that calcineurin interacts with SPATA33 via a PQIIIT sequence in the testis. Further analyses reveal that SPATA33 plays critical roles in sperm motility and male fertility. Our finding sheds new light on the molecular mechanisms of sperm motility regulation and the etiology of human male fertility. Furthermore, it may help us not only understand reproductive toxicities but also develop nonhormonal male contraceptives.

Calcineurin is a calcium-dependent phosphatase that plays roles in a variety of biological processes including immune responses. In spermatozoa, there is a testis-enriched calcineurin composed of PPP3CC and PPP3R2 (sperm calcineurin) that is essential for sperm motility and male fertility. Because sperm calcineurin has been proposed as a target for reversible male contraceptives, identifying proteins that interact with sperm calcineurin widens the choice for developing specific inhibitors. Here, by screening the calcineurin-interacting PxIxIT consensus motif in silico and analyzing the function of candidate proteins through the generation of gene-modified mice, we discovered that SPATA33 interacts with sperm calcineurin via a PQIIIT sequence. Spata33 knockout mice exhibit reduced sperm motility because of an inflexible midpiece, leading to impaired male fertility, which phenocopies Ppp3cc and Ppp3r2 knockout mice. Further analysis reveals that sperm calcineurin disappears from the mitochondria in the Spata33 knockout testis. In addition, immunoprecipitation analysis indicates that sperm calcineurin interacts with not only SPATA33 but also the mitochondrial protein VDAC2. These results indicate that SPATA33 localizes calcineurin to the mitochondria and regulates sperm motility.

KCTD19 and its associated protein ZFP541 are independently essential for meiosis in male mice

Meiosis is a cell division process with complex chromosome events where various molecules must work in tandem. To find meiosis-related genes, we screened evolutionarily conserved and reproductive tract-enriched genes using the CRISPR/Cas9 system and identified potassium channel tetramerization domain containing 19 (Kctd19) as an essential factor for meiosis. In prophase I, Kctd19 deficiency did not affect synapsis or the DNA damage response, and chiasma structures were also observed in metaphase I spermatocytes of Kctd19 KO mice. However, spermatocytes underwent apoptotic elimination during the metaphase-anaphase transition. We were able to rescue the Kctd19 KO phenotype with an epitope-tagged Kctd19 transgene. By immunoprecipitation-mass spectrometry, we confirmed the association of KCTD19 with zinc finger protein 541 (ZFP541) and histone deacetylase 1 (HDAC1). Phenotyping of Zfp541 KO spermatocytes demonstrated XY chromosome asynapsis and recurrent DNA damage in the late pachytene stage, leading to apoptosis. In summary, our study reveals that KCTD19 associates with ZFP541 and HDAC1, and that both KCTD19 and ZFP541 are essential for meiosis in male mice.

Meiosis is a fundamental process that consists of one round of genomic DNA replication and two rounds of chromosome segregation, producing four haploid cells. To properly distribute their genetic material, cells need to undergo complex chromosome events such as a physical linkage of homologous chromosomes (termed synapsis) and meiotic recombination. The molecules involved in these events have not been fully characterized yet, especially in mammals. Using a CRISPR/Cas9-screening system, we identified the potassium channel tetramerization domain containing 19 (Kctd19) as an essential factor for meiosis in male mice. Further, we confirmed the association of KCTD19 with zinc finger protein 541 (ZFP541) and histone deacetylase 1 (HDAC1). By observing meiosis of Zfp541 knockout germ cells, we found that Zfp541 was also essential for meiosis. These results show that the KCTD19/ZFP541 complex plays a critical role and is indispensable for male meiosis and fertility.

NELL2-mediated lumicrine signaling through OVCH2 is required for male fertility

The lumicrine system is a postulated signaling system in which testis-derived (upstream) secreted factors enter the male reproductive tract to regulate epididymal (downstream) pathways required for sperm maturation. Until now, no lumicrine factors have been identified. We demonstrate that a testicular germ-cell-secreted epidermal growth factor-like protein, neural epidermal growth factor-like-like 2 (NELL2), specifically binds to an orphan receptor tyrosine kinase, c-ros oncogene 1 (ROS1), and mediates the differentiation of the initial segment (IS) of the caput epididymis. Male mice in which Nell2 had been knocked out were infertile. The IS-specific secreted proteases, ovochymase 2 (OVCH2) and A disintegrin and metallopeptidase 28 (ADAM28), were expressed upon IS maturation, and OVCH2 was required for processing of the sperm surface protein ADAM3, which is required for sperm fertilizing ability. This work identifies a lumicrine system essential for testis-epididymis-spermatozoa (NELL2-ROS1-OVCH2-ADAM3) signaling and male fertility.

Proteasomal and lysosomal clearance of faulty secretory proteins: ER-associated degradation (ERAD) and ER-to-lysosome-associated degradation (ERLAD) pathways

About 40% of the eukaryotic cell's proteins are inserted co- or post-translationally in the endoplasmic reticulum (ER), where they attain the native structure under the assistance of resident molecular chaperones and folding enzymes. Subsequently, these proteins are secreted from cells or are transported to their sites of function at the plasma membrane or in organelles of the secretory and endocytic compartments. Polypeptides that are not delivered within the ER (mis-localized proteins, MLPs) are rapidly destroyed by cytosolic proteasomes, with intervention of the membrane protease ZMPSTE24 if they remained trapped in the SEC61 translocation machinery. Proteins that enter the ER, but fail to attain the native structure are rapidly degraded to prevent toxic accumulation of aberrant gene products. The ER does not contain degradative devices and the majority of misfolded proteins generated in this biosynthetic compartment are dislocated across the membrane for degradation by cytosolic 26S proteasomes by mechanisms and pathways collectively defined as ER-associated degradation (ERAD). Proteins that do not engage ERAD factors, that enter aggregates or polymers, are too large, display chimico/physical features that prevent dislocation across the ER membrane (ERAD-resistant misfolded proteins) are delivered to endo-lysosome for clearance, by mechanisms and pathways collectively defined as ER-to-lysosomes-associated degradation (ERLAD). Emerging evidences lead us to propose ERLAD as an umbrella term that includes the autophagic and non-autophagic pathways activated and engaged by ERAD-resistant misfolded proteins generated in the ER for delivery to degradative endo-lysosomes.

Heritable methylation marks associated with breast and prostate cancer risk

BACKGROUND

DNA methylation can mimic the effects of germline mutations in cancer predisposition genes. Recently, we identified twenty-four heritable methylation marks associated with breast cancer risk. As breast and prostate cancer share genetic risk factors, including rare, high-risk mutations (eg, in BRCA2), we hypothesized that some of these heritable methylation marks might also be associated with the risk of prostate cancer.

METHODS

We studied 869 incident prostate cancers (430 aggressive and 439 non-aggressive) and 869 matched controls nested within a prospective cohort study. DNA methylation was measured in pre-diagnostic blood samples using the Illumina Infinium HM450K BeadChip. Conditional logistic regression models, adjusted for prostate cancer risk factors and blood cell composition, were used to estimate odds ratios and 95% confidence intervals for the association between the 24 methylation marks and the risk of prostate cancer.

RESULTS

Five methylation marks within the VTRNA2-1 promoter region (cg06536614, cg00124993, cg26328633, cg25340688, and cg26896946), and one in the body of CLGN (cg22901919) were associated with the risk of prostate cancer. In stratified analyses, the five VTRNA2-1 marks were associated with the risk of aggressive prostate cancer.

CONCLUSIONS

This work highlights a potentially important new area of investigation for prostate cancer susceptibility and adds to our knowledge about shared risk factors for breast and prostate cancer.

Influence of high-mannose glycan whose glucose moiety is substituted with 5-thioglucose on calnexin/calreticulin cycle

Our study first revealed that UDP-5-thioglucose functions as a glycosyl donor of UDP-glucose: glycoprotein glucosyltransferase to produce 5-thio-glucosylated Man9 (5S-G1M9).

Integration of the mouse sperm fertilization-related protein equatorin into the acrosome during spermatogenesis as revealed by super-resolution and immunoelectron microscopy

Spermatids must precisely integrate specific molecules into structurally supported domains that develop during spermatogenesis. Once established, the architecture of the acrosome contributes to the acrosome reaction, which occurs prior to gamete interaction in mammals. The present study aims to clarify the morphology associated with the integration of the mouse fertilization-related acrosomal protein equatorin (mEQT) into the developing acrosome. EQT mRNA was first detected by in situ hybridization in round spermatids but disappeared in early elongating spermatids. The molecular size of mEQT was approximately 65 kDa in the testis. Developmentally, EQT protein was first detected on the nascent acrosomal membrane in round spermatids at approximately step 3, was actively integrated into the acrosomal membranes of round spermatids in the following step and then participated in acrosome remodeling in elongating spermatids. This process was clearly visualized by high-resolution fluorescence microscopy and super-resolution stimulated emission depletion nanoscopy by using newly generated C-terminally green-fluorescent-protein-tagged mEQT transgenic mice. Immunogold electron microscopy revealed that mEQT was anchored to the acrosomal membrane, with the epitope region observed as lying 5-70 nm away from the membrane and was associated with the electron-dense acrosomal matrix. This new information about the process of mEQT integration into the acrosome during spermatogenesis should provide a better understanding of the mechanisms underlying not only acrosome biogenesis but also fertilization and male infertility.

Visualization of the moment of mouse sperm-egg fusion and dynamic localization of IZUMO1

Gene disruption experiments have proven that the acrosomal protein IZUMO1 is essential for sperm-egg fusion in the mouse. However, despite its predicted function, it is not expressed on the surface of ejaculated spermatozoa. Here, we report the dynamics of diffusion of IZUMO1 from the acrosomal membrane to the sperm surface at the time of the acrosome reaction, visualized using a fluorescent protein tag. IZUMO1 showed a tendency to localize in the equatorial segment of the sperm surface after the acrosome reaction. This region is considered to initiate fusion with the oolemma. The moment of sperm-egg fusion and the dynamic movements of proteins during fusion were also imaged live. Translocation of IZUMO1 during the fertilization process was clarified, and a fundamental mechanism in mammalian fertilization is postulated.

A-MYB (MYBL1) stimulates murine testis-specific Ldhc expression via the cAMP-responsive element (CRE) site

Generally, knowledge of the mechanism regulating gene expression in primary spermatocytes is incomplete. We have used the lactate dehydrogenase gene (Ldhc) as a model to explore these mechanisms during spermatogenesis. Its 100-bp core promoter contained two essential elements common to many genes, a GC box and a CRE site. Here we report results that support a model in which transcription factor MYBL1 acts as a coactivator directing tissue-specific expression via the CRE cis element. We hypothesize that this is a common mechanism involving activation of multiple genes in the primary spermatocyte. MYBL1 is expressed predominantly as a tissue-specific transcription factor in spermatocytes and breast epithelial cells. Our finding that LDHC expression is lost in 21-day testes of MYBL1 mutant mice supports our hypothesis. In the GC1-spg germ cell line exogenous MYBL1 induces activity 4- to 8-fold, although extracts from these cells do not show MYBL1 binding activity for the Myb consensus sequences in the Ldhc promoter by EMSA. Rather, MYBL1 stimulates expression from a synthetic promoter containing only CRE elements, suggesting MYBL1 activates the promoter by interacting with protein that binds to a CRE element. Mutation of three Myb sites does not affect Ldhc promoter activity significantly (P > 0.05). CREB-binding protein (CBP) is a coactivator that interacts with CRE-binding protein CREB. We show that the transactivation domain (TAD) in MYBL1 interacts with the KIX domain in CBP, and the TAD domain and DNA binding domain in MYBL1 each interact with the CREB N-terminal domain. MYBL1 also stimulated expression from testis-specific genes Pgk2 (phosphoglycerate kinase 2) and Pdha2 (pyruvate dehydrogenase alpha 2) promoters, each of which contains CRE promoter elements and is expressed in primary spermatocytes. We propose that MYBL1 directs germ cell-specific activation via the CRE site of certain genes that are activated specifically in the primary spermatocyte, although other, more indirect effects of MYBL1 remain a possible explanation for our results.

Calsperin is a testis-specific chaperone required for sperm fertility

Calnexin (CANX) and calreticulin (CALR) are homologous lectin chaperones located in the endoplasmic reticulum and cooperate to mediate nascent glycoprotein folding. In the testis, calmegin (CLGN) and calsperin (CALR3) are expressed as germ cell-specific counterparts of CANX and CALR, respectively. Here, we show that Calr3(-/-) males produced apparently normal sperm but were infertile because of defective sperm migration from the uterus into the oviduct and defective binding to the zona pellucida. Whereas CLGN was required for ADAM1A/ADAM2 dimerization and subsequent maturation of ADAM3, a sperm membrane protein required for fertilization, we show that CALR3 is a lectin-deficient chaperone directly required for ADAM3 maturation. Our results establish the client specificity of CALR3 and demonstrate that the germ cell-specific CALR-like endoplasmic reticulum chaperones have contrasting functions in the development of male fertility. The identification and understanding of the maturation mechanisms of key sperm proteins will pave the way toward novel approaches for both contraception and treatment of unexplained male infertility.

Regulation of murine lactate dehydrogenase C (Ldhc) gene expression

Expression of Ldhc begins with the onset of meiosis in male germ cells and continues throughout spermatogenesis. Transcriptional regulatory mechanisms, especially in primary spermatocytes, are poorly described because of the lack of a reliable cell culture system. We constructed mouse transgenics and transfected germ cells in situ to study expression of the testis-specific isozyme of lactate dehydrogenase (LDH). From previous work, we determined that a 100-bp Ldhc core promoter contained potential cis regulatory elements, including a palindrome (-21 to +10), GC box (-70 to -65), and cAMP-responsive element (CRE) sites (-53 to -49, -39 to -35). We provide here the demonstration of a functional role for these sequences by expression of mutated transgenes in vivo. Our results reveal for the first time that mutation of the GC box does not abolish promoter activity, which remains testis-specific. Mutation of GC box or CRE sites resulted in a 73% and 74% reduction in promoter activity, respectively, in a transient transfection of germ cells in vivo by electroporation; the combination of GC box and CRE site mutations eliminates promoter activity. Therefore, we conclude that simultaneous occupancy of the GC box and CRE sites in the core promoter is necessary for full expression of Ldhc in the testis.

Characterization of a human TSPY promoter

Human TSPY is a candidate oncogene and is supposed to function as a proliferation factor during spermatogenesis. It is the only mammalian protein-coding gene known to be organized as a tandem repeat gene family. It is expressed at highest level in spermatogonia and to a lower amount in primary spermatocytes. To characterize the human TSPY promoter we used the luciferase reporter system in a mouse spermatogonia derived cell line (GC-1 spg) and in a GC-4 spc cell line, that harbour prophase spermatocytes of the preleptotene and early pachytene stage. We isolated a 1303 bp fragment of the 5'-flanking region of exon 1 that shows significant promoter activity in GC-1 spg and reduced activity in GC-4 spc cells. In order to gain further insight into the organization of the TSPY-promoter, stepwise truncations of the putative promoter sequence were performed. The resulting fragments were cloned into the pGL 3-vector and analysed for reporter gene activity in the murine germ cell lines GC-1 spg and GC-4 spc, leading to the characterization of a core promoter (--159 to--1), an enhancing region (--673 to--364) and a silencing region (--1262 to--669). Database research for cis-active elements yielded two putative SOX-like binding sites in the enhancing region and reporter gene activity was drastically reduced when three nucleotides of the AACAAT SOX core sequence were mutated. Our findings strongly suggest that testis-specific expression of human TSPY is mediated by Sox proteins.

Basic helix-loop-helix transcription factor Tcfl5 interacts with the Calmegin gene promoter in mouse spermatogenesis

In mouse spermatogenesis, differentiating germ line cells initiate expression of specific genes at subsequent developmental steps. The Calmegin (Clgn) gene is first expressed in meiotic prophase, in primary spermatocytes, and encodes a protein that acts as a chaperone. To identify testis-specific transcription factors that control expression of the Clgn gene in spermatogenesis, we performed a yeast one-hybrid screening with a Clgn promoter sequence as bait DNA. This screening resulted in the identification of mouse Tcfl5 as a candidate Clgn promoter-binding protein. Tcfl5 is a member of the basic helix-loop-helix (bHLH) family of transcription factors, and mouse Tcfl5 shows 83% amino acid sequence identity with human TCFL5. Gel-shift and yeast one-hybrid experiments showed that Tcfl5 interacts with a non-canonical CACGCG site that is present in the Clgn promoter. By using northern blot, RT-PCR and in situ hybridization, mouse Tcfl5 mRNA was detected only in testis, with the highest expression level in primary spermatocytes and round spermatids. The highest level of Tcfl5 protein was found in primary spermatocytes at the diplotene stage of meiotic prophase, where the protein colocalizes with transcriptionally active chromatin.

A Short Core Promoter Drives Expression of the ALF Transcription Factor in Reproductive Tissues of Male and Female Mice1

The control of gene expression in reproductive tissues involves a number of unique germ cell-specific transcription factors. One such factor, ALF (TFIIA tau), encodes a protein similar to the large subunit of general transcription factor TFIIA. To understand how this factor is regulated, we characterized transgenic mice that contain the ALF promoter linked to either beta-galactosidase or green fluorescent protein (GFP) reporters. The results show that as little as 133 base pairs are sufficient to drive developmentally accurate and cell-specific expression. Transgene DNA was methylated and inactive in liver, but could be reactivated in vivo by system administration of 5-aza, 2'-deoxycytidine. Fluorescence-activated cell sorting allowed the identification of male germ cells that express the GFP transgene and provides a potential method to collect cells that might be under the control of a nonsomatic transcription system. Finally, we found that transcripts from the endogenous ALF gene and derived transgenes can also be detected in whole ovary and in germinal vesicle-stage oocytes of female mice. The ALF sequence falls into a class of germ cell promoters whose features include small size, high GC content, numerous CpG dinucleotides, and an apparent TATA-like element. Overall, the results define a unique core promoter that is active in both male and female reproductive tissues, and suggest mouse ALF may have a regulatory role in male and female gametogenic gene expression programs.

The Chlamydomonas Fus1 protein is present on the mating type plus fusion organelle and required for a critical membrane adhesion event during fusion with minus gametes

The molecular mechanisms of the defining event in fertilization, gamete fusion, remain poorly understood. The FUS1 gene in the unicellular, biflagellated green alga Chlamydomonas is one of the few sex-specific eukaryotic genes shown by genetic analysis to be essential for gamete fusion during fertilization. In Chlamydomonas, adhesion and fusion of the plasma membranes of activated mt+ and mt- gametes is accomplished via specialized fusion organelles called mating structures. Herein, we identify the endogenous Fus1 protein, test the idea that Fus1 is at the site of fusion, and identify the step in fusion that requires Fus1. Our results show that Fus1 is a approximately 95-kDa protein present on the external surface of both unactivated and activated mt+ gametes. Bioassays indicate that adhesion between mating type plus and mating type minus fusion organelles requires Fus1 and that Fus1 is functional only after gamete activation. Finally, immunofluorescence demonstrates that the Fus1 protein is present as an apical patch on unactivated gametes and redistributes during gamete activation over the entire surface of the microvillous-like activated plus mating structure, the fertilization tubule. Thus, Fus1 is present on mt+ gametes at the site of cell-cell fusion and essential for an early step in the fusion process.

Native tesmin is a 60-kilodalton protein that undergoes dynamic changes in its localization during spermatogenesis in mice

Tesmin is a testis-specific protein. Four mouse tesmin cDNAs so far reported encode a testis-specific, metallothionein-like, 30-kDa protein (tesmin-30). An antibody against tesmin-30, however, detected a protein of 60 kDa (tesmin-60) from the mouse testis. To resolve the relationship between the two, the immunoprecipitated native tesmin-60 was sequenced. The result indicated that tesmin-30 is not full-length but is part of the C-terminal half of tesmin-60. The full-length cDNA (2.2 kilobases [kb]) encoding tesmin-60 (475 amino acid residues) and its genomic DNA (23 kb) were cloned and sequenced. A search of databases indicated that tesmin is a member of the CXC-hinge-CXC family. Immunohistochemistry indicated that tesmin exhibits dynamic subcellular localization changes during spermatogenesis. Before meiosis, it was localized in the cytoplasm of early to late spermatocytes and then translocated into the nucleus just before meiotic division. After meiosis, it appeared in spermatids, starting from the acrosomal vesicles, moving to the nuclear membrane and then to the caudal end as the spermatids elongated, and finally relocating into the cytoplasm. Oxidative stress by cobalt chloride, as well as by diethylmaleate, induced both premature translocation of tesmin from the cytoplasm to the nucleus and apoptotic signals in spermatocytes. The persistent existence of tesmin and its temporally and spatially dynamic localization suggest that tesmin is involved in multiple stages of spermatogenesis and spermiogenesis, possibly during sperm maturation and/or morphogenesis.

Male-enhanced antigen-1 gene flanked by two overlapping genes is expressed in late spermatogenesis

The male-enhanced antigen-1 gene (Mea1) was originally isolated from a murine testicular cDNA library using anti-H-Y antigen antisera and was assigned to chromosome 17. On analysis of its structure and expression, we found that the Mea1 genomic sequence is flanked by two other genes: Ppp2r5d present in its 3'-terminus in a tail-to-tail orientation and a novel gene called Peas in its 5'-terminus in a head-to-head orientation. The coding sequences of the two genes embedded in the Mea1 sequence are located on the opposite DNA strands of Mea1. Cap-site analysis of Mea1 revealed that it is transcribed from at least seven sites. Most splice variants of Mea1 were abundantly expressed in the testis; the d-type was weakly expressed in the other tissues. AP-2-binding motifs were detected in the transcription-initiation sites. In situ hybridization and immunohistochemical studies revealed Mea1 expression in pachytene spermatocytes. This expression was most prominent in spermatids and residual bodies. The Mea1 protein was also localized in the cytoplasm of elongated spermatids and residual bodies. Localization of the Mea1 suggests that it may function in the very late stages of spermiogenesis. The possibility that Mea1 is one of the serologically detectable male antigens is discussed.

Calmegin is required for fertilin alpha/beta heterodimerization and sperm fertility

Loss of the endoplasmic reticulum resident chaperone calmegin leads to the production of sterile sperm that do not bind to the egg zona pellucida (M. Ikawa et al., 1997, Nature 387, 607-611). In the present study, we demonstrate that calmegin -/- sperm were defective in migrating into the oviducts and in binding to the egg plasma membrane. Despite the impaired adhesive function, calmegin -/- sperm could fertilize eggs when zonae pellucidae were partially dissected, and eggs fertilized in this manner could develop normally to term. Since these sperm characteristics were similar to those found in fertilin beta -/- sperm, we investigated the interaction of calmegin with fertilin beta. Using immunoprecipitation techniques, calmegin was found to bind to sperm membrane proteins, fertilin alpha and beta, during spermatogenesis. The binding was specific to calmegin: another endoplasmic reticulum chaperone calnexin, a calmegin homologue, was not able to bind to fertilin alpha and beta. In the calmegin -/- mice, a loss of heterodimerization of fertilin alpha and beta was observed and fertilin beta was not detectable in mature sperm. The data not only explain why the calmegin and fertilin beta knockout mouse lines share a common infertile phenotype, but also reveal the importance of the maturation of sperm membrane proteins in the endoplasmic reticulum.

Lessons from knockout and transgenic mice for infertility in men

This review concentrates on the clear cases where knocking out a gene in mice has caused male infertility and thus comes near to proving that the gene plays a role in the development of sperm. Knockout mice have been created with primary defects at every stage of spermatogenesis thus creating a framework for decoding the genetic hierarchy that causes male germ cell differentiation. As well as defining essential genes in vivo experiments have defined promoter and untranslated sequences responsible for the expression of proteins at all the spermatogenic stages. In conclusion knockout mice remain the ultimate test of spermatogenic hypotheses as well as providing detailed information about this complex process.

A novel 14-base-pair regulatory element is essential for in vivo expression of murine beta4-galactosyltransferase-I in late pachytene spermatocytes and round spermatids

During murine spermatogenesis, beginning in late pachytene spermatocytes, the beta4-galactosyltransferase-I (beta4GalT-I) gene is transcribed from a male germ cell-specific start site. We had shown previously that a 796-bp genomic fragment that flanks the germ cell start site and contains two putative CRE (cyclic AMP-responsive element)-like motifs directs correct male germ cell expression of the beta-galactosidase reporter gene in late pachytene spermatocytes and round spermatids of transgenic mice (N. L. Shaper, A. Harduin-Lepers, and J. H. Shaper, J. Biol. Chem. 269:25165-25171, 1994). We now report that in vivo expression of beta4GalT-I in developing male germ cells requires an essential and previously undescribed 14-bp regulatory element (5'-GCCGGTTTCCTAGA-3') that is distinct from the two CRE-like sequences. This cis element is located 16 bp upstream of the germ cell-specific start site and binds a male germ cell protein that we have termed TASS-1 (transcriptional activator in late pachytene spermatocytes and round spermatids 1). The presence of the Ets signature binding motif 5'-GGAA-3' on the bottom strand of the TASS-1 sequence (underlined sequence) suggests that TASS-1 is a novel member of the Ets family of transcription factors. Additional transgenic analyses established that an 87-bp genomic fragment containing the TASS-1 regulatory element was sufficient for correct germ cell-specific expression of the beta-galactosidase reporter gene. Furthermore, when the TASS-1 motif was mutated by transversion, within the context of the original 796-bp fragment, transgene expression was reduced 12- to 35-fold in vivo.

Characterization of domains in mice of calnexin-t, a putative molecular chaperone required in sperm fertility, with use of glutathione S-transferase-fusion proteins

Calnexin-t (calmegin) is a male germ cell-specific variant of calnexin, a membrane bound-molecular chaperone in the endoplasmic reticulum (ER). Although it is temporally expressed during spermatogenesis, it has recently been shown to be highly involved in sperm fertility. To investigate the biochemical states of calnexin-t during spermatogenesis, we produced a series of glutathione S-transferase-fusion proteins with several specific coding domains of calnexin-t. Immunostaining and 45Ca2+ overlay assays clearly showed that the internal proline-rich repeat region has Ca2+-binding ability and contains an epitope recognized by monoclonal antibody 1C9. Western blot analysis of protein extracts from the testes of 10-, 18-, 26-, and 60-day-old mice revealed only a single 101-kDa protein during testicular development by 1C9. Anti-C, a cytoplasmic domain-specific antibody generated by immunization with recombinant protein, produced the same results, indicating that the 101-kDa form of calnexin-t is prevalent at all stages of spermatogenesis expressing calnexin-t. In paraffin sections of mouse testis, Anti-C stained spermatocytes and spermatids intensely, whereas 1C9 stained spermatocytes only slightly but spermatids intensely, suggesting that the affinity of 1C9 for its epitope is lower in pachytene spermatocytes than in spermatids. Acid phosphatase treatment of the 101-kDa form generated a 93-kDa band that in turn could be recovered to the 101-kDa form by incubation with HeLa cell S100 fraction, indicating that the 101-kDa form is a phosphorylated type of calnexin-t. The sites of phosphorylation were shown to be restricted to the cytoplasmic domain. Our results suggest that the structure of the ER luminal domain of calnexin-t is likely to differ in middle pachytene versus haploid germ cell phases. In addition, the cytoplasmic domain of calnexin-t was shown to be highly phosphorylated immediately after protein synthesis and constitutively phosphorylated during spermatogenesis.

Cloning and characterization of the human Calmegin gene encoding putative testis-specific chaperone

The putative chaperone Calmegin is required for sperm fertility in mouse and the relevance of the gene to certain cases of human male infertility has been suggested. In the present paper, we have isolated and characterized the human homolog cDNA of the mouse germ cell-specific Calmegin. The entire coding region of the human cDNA showed 80% identity with the previously reported mouse Calmegin. The predicted amino acid sequence showed strong conservation of the two sets of internal repetitive sequences (Ca2+ binding motif), and the hydrophilic COOH terminus, which corresponds to the putative endoplasmic reticulum (ER) retention motif. Our finding will support diagnosis of male infertility. Northern blotting analysis of various human tissues showed that the transcript was 3 kb in length and was expressed exclusively in the testis. Using the fluorescence in situ hybridization (FISH) technique, human Calmegin gene was mapped to chromosome 4q28.3-q31.1.

Mapping of eight testis-specific genes to mouse chromosomes

We previously identified eight testis-specific genes using antibodies raised against testicular germ cells. They are expressed during spermatogenesis and are presumed to be involved in testicular germ cell differentiation and sperm formation. We have mapped the genomic loci for these testis-specific genes using restriction fragment length variants in interspecific backcross mice. The calmegin gene (Clgn) was mapped to Chr 8. The synaptonemal complex protein gene 1 (Sycp1) probe hybridized with two sequences on different chromosomes; Sycp1-rs2 was mapped to Chr 3, whereas Sycp1-rs3 was mapped to Chr 7. The relaxin-like factor gene (Rlnl) was mapped to Chr 8, and collapsin response mediator protein 1 (Crmp1) was mapped to Chr 5. Three novel genes encoding testis-specific proteins A2 (Tsga2), A8 (Tsga8), and A12 (Tsga12) were mapped to chromosomes 3, X, and 10, respectively.