DkkL1 (Soggy), a Dickkopf family member, localizes to the acrosome during mammalian spermatogenesis

Comparative genomic survey and functional analysis of DKKL1 during spermatogenesis in the Chinese soft-shelled turtle (Pelodiscus sinensis)

A feature of the Chinese soft-shelled turtle (Pelodiscus sinensis) is seasonal spermatogenesis; however, the underlying molecular mechanism is not well clarified. Here, we firstly cloned and characterized P. sinensis DKKL1, and then performed comparative genomic studies, expression analysis, and functional validation. P. sinensis DKKL1 had 2 putative N-glycosylation sites and 16 phosphorylation sites. DKKL1 also had classic transmembrane structures that were extracellularly localized. DKKL1's genetic distance was close to turtles, followed by amphibians and mammals, but its genetic distance was far from fishes. DKKL1 genes from different species shared distinct genomic characteristics. Meanwhile, they were also relatively conserved among themselves, at least from the perspective of classes. Notably, the transcription factors associated with spermatogenesis were also identified, containing CTCF, EWSR1, and FOXL2. DKKL1 exhibited sexually dimorphic expression only in adult gonads, which was significantly higher than that in other somatic tissues (P < 0.001), and was barely expressed in embryonic gonads. DKKL1 transcripts showed a strong signal in sperm, while faint signals were detected in other male germ cells. DKKL1 in adult testes progressively increased per month (P < 0.05), displaying a seasonal expression trait. DKKL1 was significantly downregulated in testes cells after the sex hormones (17β-estradiol and 17α-methyltestosterone) and Wnt/β-catenin inhibitor treatment (P < 0.05). Likewise, the Wnt/β-catenin inhibitor treatment dramatically repressed CTCF, EWSR1, and FOXL2 expression. Conversely, they were markedly upregulated after the 17β-estradiol and 17α-methyltestosterone treatment, suggesting that the three transcription factors might bind to different promoter regions, thereby negatively regulating DKKL1 transcription in response to the changes in the estrogen and androgen pathways, and positively controlling DKKL1 transcription in answer to the alterations in the Wnt/β-catenin pathway. Knockdown of DKKL1 significantly reduced the relative expression of HMGB2 and SPATS1 (P < 0.01), suggesting that it may be involved in seasonal spermatogenesis of P. sinensis through a positive regulatory interaction with these two genes. Overall, our findings provide novel insights into the genome evolution and potential functions of seasonal spermatogenesis of P. sinensis DKKL1.

Whole-Transcriptome Analysis Identifies Gender Dimorphic Expressions of Mrnas and Non-Coding Rnas in Chinese Soft-Shell Turtle (Pelodiscus sinensis)

In aquaculture, the Chinese soft-shelled turtle (Pelodiscus sinensis) is an economically important species with remarkable gender dimorphism in its growth patterns. However, the underlying molecular mechanisms of this phenomenon have not been elucidated well. Here, we conducted a whole-transcriptome analysis of the female and male gonads of P. sinensis. Overall, 7833 DE mRNAs, 619 DE lncRNAs, 231 DE circRNAs, and 520 DE miRNAs were identified. Some "star genes" associated with sex differentiation containing dmrt1, sox9, and foxl2 were identified. Additionally, some potential genes linked to sex differentiation, such as bmp2, ran, and sox3, were also isolated in P. sinensis. Functional analysis showed that the DE miRNAs and DE ncRNAs were enriched in the pathways related to sex differentiation, including ovarian steroidogenesis, the hippo signaling pathway, and the calcium signaling pathway. Remarkably, a lncRNA/circRNA-miRNA-mRNA interaction network was constructed, containing the key genes associated with sex differentiation, including fgf9, foxl3, and dmrta2. Collectively, we constructed a gender dimorphism profile of the female and male gonads of P. sinensis, profoundly contributing to the exploration of the major genes and potential ncRNAs involved in the sex differentiation of P. sinensis. More importantly, we highlighted the potential functions of ncRNAs for gene regulation during sex differentiation in P. sinensis as well as in other turtles.

Dkk3/REIC Deficiency Impairs Spermiation, Sperm Fibrous Sheath Integrity and the Sperm Motility of Mice

The role of Dickkopf-3 (Dkk3)/REIC (The Reduced Expression in Immortalized Cells), a Wnt-signaling inhibitor, in male reproductive physiology remains unknown thus far. To explore the functional details of Dkk3/REIC in the male reproductive process, we studied the Dkk3/REIC knock-out (KO) mouse model. By examining testicular sections and investigating the sperm characteristics (count, vitality and motility) and ultrastructure, we compared the reproductive features between Dkk3/REIC-KO and wild-type (WT) male mice. To further explore the underlying molecular mechanism, we performed RNA sequencing (RNA-seq) analysis of testicular tissues. Our results showed that spermiation failure existed in seminiferous tubules of Dkk3/REIC-KO mice, and sperm from Dkk3/REIC-KO mice exhibited inferior motility (44.09 ± 8.12% vs. 23.26 ± 10.02%, p < 0.01). The Ultrastructure examination revealed defects in the sperm fibrous sheath of KO mice. Although the average count of Dkk3/REIC-KO epididymal sperm was less than that of the wild-types (9.30 ± 0.69 vs. 8.27 ± 0.87, ×10⁶), neither the gap (p > 0.05) nor the difference in the sperm vitality rate (72.83 ± 1.55% vs. 72.50 ± 0.71%, p > 0.05) were statistically significant. The RNA-seq and GO (Gene Oncology) enrichment results indicated that the differential genes were significantly enriched in the GO terms of cytoskeleton function, cAMP signaling and calcium ion binding. Collectively, our research demonstrates that Dkk3/REIC is involved in the process of spermiation, fibrous sheath integrity maintenance and sperm motility of mice.

Identification of an immunogenic DKK1 long peptide for immunotherapy of human multiple myeloma

Dickkopf-1 (DKK1), broadly expressed by tumor cells from human multiple myeloma (MM) and other cancers but absent from most normal tissues, may be an ideal target for immunotherapy. Our previous studies have shown that DKK1 (peptide)-specific cytotoxic T lymphocytes can effectively lyse primary MM cells in vitro. To develop DKK1-based vaccines that can be easily and inexpensively made and used by all patients, we identified a DKK1 long peptide (LP), DKK13-76-LP, that contains 74 amino acids and epitopes that can potentially bind to all major MHC class I and II molecules. Using HLA-A*0201- and HLA-DR*4-transgenic mouse models, we found that DKK1-specific CD4+ and CD8+ T-cell responses, detected by DKK1 short peptide (P20 and P66v)-HLA-A*0201 tetramer staining and cytotoxic assay for CD8+ T cells or by carboxyfluorescein diacetate succinimidyl ester (CSFE) dilution and IFN-g secretion for CD4+ T cells, respectively, can be induced in vivo by immunizing mice with the DKK13-76-LP. In addition, DKK13-76-LP also induced anti-DKK1 humoral immunity in the transgenic mice and the DKK1 antibodies were functional. Finally, DKK13-76-LP stimulated human blood T cells ex vivo to generate DKK1-specific CD4+ and CD8+ T-cell responses from 8 out of 10 MM patients with different MHC backgrounds. The generated DKK1-specific CD8+ cells efficiently lysed autologous MM cells from these patients. Thus, these results confirm the immunogenicity of the DKK13-76-LP in eliciting DKK1-specific CD4+ and CD8+ T-cell responses in vitro and in vivo, and suggest that the DKK13-76-LP can be used for immunotherapy of MM and other cancers.

The role of Wnt signaling in male reproductive physiology and pathology

Accumulating evidence has shown that Wnt signaling is deeply involved in male reproductive physiology, and malfunction of the signal path can cause pathological changes in genital organs and sperm cells. These abnormalities are diverse in manifestation and have been constantly found in the knockout models of Wnt studies. Nevertheless, most of the research solely focused on a certain factor in the Wnt pathway, and there are few reports on the overall relation between Wnt signals and male reproductive physiology. In our review, Wnt findings relating to the reproductive system were sought and summarized in terms of Wnt ligands, Wnt receptors, Wnt intracellular signals and Wnt regulators. By sorting out and integrating relevant functions, as well as underlining the controversies among different reports, our review aims to offer an overview of Wnt signaling in male reproductive physiology and pathology for further mechanistic studies.

Low-dose tamoxifen treatment in juvenile males has long-term adverse effects on the reproductive system: implications for inducible transgenics

The tamoxifen-inducible Cre system is a popular transgenic method for controlling the induction of recombination by Cre at a specific time and in a specific cell type. However, tamoxifen is not an inert inducer of recombination, but an established endocrine disruptor with mixed agonist/antagonist activity acting via endogenous estrogen receptors. Such potentially confounding effects should be controlled for, but >40% of publications that have used tamoxifen to generate conditional knockouts have not reported even the minimum appropriate controls. To highlight the importance of this issue, the present study investigated the long-term impacts of different doses of a single systemic tamoxifen injection on the testis and the wider endocrine system. We found that a single dose of tamoxifen less than 10% of the mean dose used for recombination induction, caused adverse effects to the testis and to the reproductive endocrine system that persisted long-term. These data raise significant concerns about the widespread use of tamoxifen induction of recombination, and highlight the importance of including appropriate controls in all pathophysiological studies using this means of induction.

Does murine spermatogenesis require WNT signalling? A lesson from Gpr177 conditional knockout mouse models

Wingless-related MMTV integration site (WNT) proteins and several other components of the WNT signalling pathway are expressed in the murine testes. However, mice mutant for WNT signalling effector β-catenin using different Cre drivers have phenotypes that are inconsistent with each other. The complexity and overlapping expression of WNT signalling cascades have prevented researchers from dissecting their function in spermatogenesis. Depletion of the Gpr177 gene (the mouse orthologue of Drosophila Wntless), which is required for the secretion of various WNTs, makes it possible to genetically dissect the overall effect of WNTs in testis development. In this study, the Gpr177 gene was conditionally depleted in germ cells (Gpr177^flox/flox, Mvh-Cre; Gpr177^flox/flox, Stra8-Cre) and Sertoli cells (Gpr177^flox/flox, Amh-Cre). No obvious defects in fertility and spermatogenesis were observed in these three Gpr177 conditional knockout (cKO) mice at 8 weeks. However, late-onset testicular atrophy and fertility decline in two germ cell-specific Gpr177 deletion mice were noted at 8 months. In contrast, we did not observe any abnormalities of spermatogenesis and fertility, even in 8-month-old Gpr177^flox/flox, Amh-Cre mice. Elevation of reactive oxygen species (ROS) was detected in Gpr177 cKO germ cells and Sertoli cells and exhibited an age-dependent manner. However, significant increase in the activity of Caspase 3 was only observed in germ cells from 8-month-old germ cell-specific Gpr177 knockout mice. In conclusion, GPR177 in Sertoli cells had no apparent influence on spermatogenesis, whereas loss of GPR177 in germ cells disrupted spermatogenesis in an age-dependent manner via elevating ROS levels and triggering germ cell apoptosis.

CKAP4 is identified as a receptor for Dickkopf in cancer cells

The secretory protein Dickkopf-1 (DKK-1) is a known Wnt antagonist and has been shown to suppress tumorigenesis in some cancer cells; however, it is also upregulated in many types of cancer and associated with poor prognosis. Wnt-independent mechanisms by which DKK-1 promotes cancer cell proliferation are not well understood. In this issue of the JCI, Kimura and colleagues demonstrate that DKK-1 interacts with cytoskeleton-associated protein 4 (CKAP4) to promote activation of AKT. They show that both DKK-1 and CKAP4 are frequently upregulated in pancreatic and lung cancers. Importantly, targeting this interaction with an anti-CKAP4 antibody prevented tumor formation in murine xenograft models. These results identify a previously unrecognized DKK-1-mediated pathway and suggest CKAP4 as a potential therapeutic target for certain cancers.

VEGF/VEGFR2 Signaling Regulates Germ Cell Proliferation in vitro and Promotes Mouse Testicular Regeneration in vivo

Vascular endothelial growth factor (VEGF) plays fundamental roles in testicular development; however, its function on testicular regeneration remains unknown. The objective of this study was to explore the roles VEGF/VEGFR2 signaling plays in mouse germ cells and in mouse testicular regeneration. VEGF and the VEGFR2 antagonist SU5416 were added to culture medium to evaluate their effects on spermatogonial stem cell line (C18-4 cells) proliferation. Testicular cells obtained from newborn male ICR mice were grafted into the dorsal region of male BALB/c nude mice. VEGF and SU5416 were injected into the graft sites to assess the effects of the VEGF and VEGFR2 signaling pathways on testicular reconstitution. The grafts were analyzed after 8 weeks. We found that VEGF promoted C18-4 proliferation in vitro, indicating its role in germ cell survival. HE staining revealed that seminiferous tubules were reconstituted and male germ cells from spermatogonia to spermatids could be observed in testis-like tissues 8 weeks after grafting. A few advantaged male germ cells, including spermatocytes and spermatids, were found in SU5416-treated grafts. Moreover, VEGF enhanced the expression of genes specific for male germ cells and vascularization in 8-week grafts, whereas SU5416 decreased the expression of these genes. SU5416-treated grafts had a lower expression of MVH and CD31, indicating that blockade of VEGF/VEGFR2 signaling reduces the efficiency of seminiferous tubule reconstitution. Collectively, these data suggest that VEGF/VEGFR2 signaling regulates germ cell proliferation and promotes testicular regeneration via direct action on germ cells and the enhancement of vascularization.

Immunotherapy strategies in multiple myeloma

Multiple myeloma (MM) is a B-cell malignancy characterized by the clonal proliferation of malignant plasma cells in the bone marrow and the development of osteolytic bone lesions. MM has emerged as a paradigm within the cancers for the success of drug discovery and translational medicine. This article discusses immunotherapy as an encouraging option for the goal of inducing effective and long-lasting therapeutic outcome. Divided into two distinct approaches, passive or active, immunotherapy, which targets tumor-associated antigens has shown promising results in multiple preclinical and clinical studies.

Global gene expression during early differentiation of Xenopus (Silurana) tropicalis gonad tissues

African clawed frog Xenopus sp. is used extensively for developmental biology and toxicology research. Amid concerns of environmental pollutants disrupting endocrine systems and causing altered reproductive development in wildlife, eco-toxicology research has led to a focus on linking molecular initiating events to population-level effects. As such, efforts to better understand reproductive development at the molecular level in these model species are warranted. To that end, transcriptomes were characterized in differentiating Xenopus tropicalis gonad tissues at Nieuwkoop and Faber (NF) stage 58 (pro-metamorphosis), NF66 (completion of metamorphosis), 1week post-metamorphosis (1WPM), and 2weeks post-metamorphosis (2WPM). Differential expression analysis between tissue types at each developmental stage revealed a substantial divergence of ovary and testis transcriptomes starting between NF58 and NF66; transcriptomes continued to diverge through 2WPM. Generally, testis-enriched transcripts were expressed at relatively constant levels, while ovary-enriched transcripts were up-regulated within this developmental period. Functional analyses of differentially expressed transcripts allowed linkages to be made between their putative human orthologues and specific cellular processes associated with differentiating gonad tissues. In ovary tissue, genetic programs direct germ cells through meiosis to the diplotene stage when maternal mRNAs are transcribed and trafficked to oocytes for translation following fertilization. In the testis, gene expression is consistent with connective tissue development, tubule formation, and germ cell support (Leydig and Sertoli cells). This dataset exhibited remarkable consistency with transcript profiles previously described in gonad tissues across species, and emphasizes the universal importance of certain transcripts for germ cell development and preparation of these tissues for reproduction.

Cancer-testis genes as candidates for immunotherapy in breast cancer

Cancer-testis (CT) antigens are tumor-associated antigens attracting immunologists for their possible application in the immunotherapy of cancer. Several clinical trials have assessed their therapeutic potentials in cancer patients. Breast cancers, especially triple-negative cancers are among those with significant expression of CT genes. Identification of CT genes with high expression in cancer patients is the prerequisite for any immunotherapeutic approach. CT genes have gained attention not only for immunotherapy of cancer patients, but also for immunoprevention in high-risk individuals. Many CT genes have proved to be immunogenic in breast cancer patients suggesting the basis for the development of polyvalent vaccines.

Vitamin D receptor-mediated control of Soggy, Wise, and Hairless gene expression in keratinocytes

The vitamin D receptor (VDR), but not its hormonal ligand, 1,25-dihydroxyvitamin D3 (1,25D), is required for the progression of the mammalian hair cycle. We studied three genes relevant to hair cycle signaling, DKKL1 (Soggy), SOSTDC1 (Wise), and HR (Hairless), to determine whether their expression is regulated by VDR and/or its 1,25D ligand. DKKL1 mRNA was repressed 49-72% by 1,25D in primary human and CCD-1106 KERTr keratinocytes; a functional vitamin D responsive element (VDRE) was identified at -9590 bp in murine Soggy. Similarly, SOSTDC1 mRNA was repressed 41-59% by 1,25D in KERTr and primary human keratinocytes; a functional VDRE was located at -6215 bp in human Wise. In contrast, HR mRNA was upregulated 1.56- to 2.77-fold by 1,25D in primary human and KERTr keratinocytes; a VDRE (TGGTGAgtgAGGACA) consisting of an imperfect direct repeat separated by three nucleotides (DR3) was identified at -7269 bp in the human Hairless gene that mediated dramatic induction, even in the absence of 1,25D ligand. In parallel, a DR4 thyroid hormone responsive element, TGGTGAggccAGGACA, was identified at +1304 bp in the human HR gene that conferred tri-iodothyronine (T3)-independent transcriptional activation. Because the thyroid hormone receptor controls HR expression in the CNS, whereas VDR functions in concert with the HR corepressor specifically in skin, a model is proposed wherein unliganded VDR upregulates the expression of HR, the gene product of which acts as a downstream comodulator to feedback-repress DKKL1 and SOSTDC1, resulting in integration of bone morphogenic protein and Wnt signaling to drive the mammalian hair cycle and/or influencing epidermal function.

Regulated Wnt/beta-catenin signaling sustains adult spermatogenesis in mice

The importance of Wnt signaling for postnatal testis function has been previously studied in several mouse models, with chronic pathway disruption addressing its function in Sertoli cells and in postmeiotic germ cells. While chronic beta-catenin deletion in Sertoli cells does not profoundly affect testis development, new data indicate that Wnt signaling is required at multiple stages of spermatogenesis. We used two mouse models that allow acute disruption of Wnt signaling to explore the importance of regulated Wnt pathway activity for normal germ cell development in adult male mice. Short-term induction of mutations in Adenomatous polyposis coli (Apc) and beta-catenin (Ctnnbl), which increase and decrease Wnt signaling levels, were generated in AhCre Apc(fl/fl) and AhCre Ctnnb1(fl/fl) mice, respectively. Each exhibited a distinct phenotype of disrupted spermatogenesis that was evident within 24 h and persisted for up to 4 days. Outcomes included germ cell apoptosis and rapid loss and altered blood-testis barrier protein distribution and morphology. The functional significance of nuclear localized beta-catenin protein in spermatocytes and round spermatids, indicative of active Wnt signaling, was highlighted by the profound loss of postmitotic germ cells in both models. Developmentally regulated Wnt signaling mediators identified through transcriptional profiling of wild-type and AhCre Ctnnb1(fl/fl) mouse testes identified Wnt receptors (e.g., Fzd4) and ligands (e.g., Wnt3, Wnt3a, Wnt5b, Wnt7a, and Wnt8b). This demonstration that Wnt signaling control is essential for adult spermatogenesis supports the growing understanding that its disruption may underpin certain cases of male infertility.

Secreted and transmembrane wnt inhibitors and activators

Signaling by the Wnt family of secreted glycoproteins plays important roles in embryonic development and adult homeostasis. Wnt signaling is modulated by a number of evolutionarily conserved inhibitors and activators. Wnt inhibitors belong to small protein families, including sFRP, Dkk, WIF, Wise/SOST, Cerberus, IGFBP, Shisa, Waif1, APCDD1, and Tiki1. Their common feature is to antagonize Wnt signaling by preventing ligand-receptor interactions or Wnt receptor maturation. Conversely, the Wnt activators, R-spondin and Norrin, promote Wnt signaling by binding to Wnt receptors or releasing a Wnt-inhibitory step. With few exceptions, these antagonists and agonists are not pure Wnt modulators, but also affect additional signaling pathways, such as TGF-β and FGF signaling. Here we discuss their interactions with Wnt ligands and Wnt receptors, their role in developmental processes, as well as their implication in disease.

Developmental expression and function of DKKL1/Dkkl1 in humans and mice

BACKGROUND

Experiments were designed to identify the developmental expression and function of the Dickkopf-Like1 (DKKL1/Dkkl1) gene in humans and mice.

METHODS

Mouse testes cDNA samples were collected at multiple postnatal times (days 4, 9, 18, 35, and 54, as well as at 6 months) and hybridized to Affymetrix mouse whole genome Genechips. To further characterize the homologous gene DKKL1 in human beings, the expression profiles between human adult testis and foetal testis were compared using Affymetrix human Genechips. The characteristics of DKKL1/Dkkl1 were analysed using various cellular and molecular biotechnologies.

RESULTS

The expression of Dkkl1 was not detected in mouse testes on days 4 or 9, but was present on days 18, 35, and 54, as well as at 6 months, which was confirmed by RT-PCR and Western blot results. Examination of the tissue distribution of Dkkl1 demonstrated that while Dkkl1 mRNA was abundantly expressed in testes, little to no expression of Dkkl1 was observed in the epididymis or other tissues. In an in vitro fertilization assay, a Dkkl1 antibody was found to significantly reduce fertilization. Human Genechips results showed that the hybridization signal intensity of DKKL1 was 405.56-fold higher in adult testis than in foetal testis. RT-PCR analysis of multiple human tissues indicated that DKKL1 mRNA was exclusively expressed in the testis. Western blot analysis also demonstrated that DKKL1 was mainly expressed in human testis with a molecular weight of approximately 34 kDa. Additionally, immunohistochemical staining showed that the DKKL1 protein was predominantly located in spermatocytes and round spermatids in human testes. An examination of the expression levels of DKKL1 in infertile male patients revealed that while no DKKL1 appeared in the testes of patients with Sertoli cell only syndrome (SCOS) or cryptorchidism, DKKL1 was observed with variable expression in patients with spermatogenic arrest.

CONCLUSIONS

These results, together with previous studies, suggest that DKKL1/Dkkl1 may play an important role in testicular development and spermatogenesis and may be an important factor in male infertility.

Active vaccination with Dickkopf-1 induces protective and therapeutic antitumor immunity in murine multiple myeloma

Dickkopf-1 (DKK1), broadly expressed in myeloma cells but highly restricted in normal tissues, together with its functional roles as an osteoblast formation inhibitor, may be an ideal target for immunotherapy in myeloma. Our previous studies have shown that DKK1 (peptide)-specific CTLs can effectively lyse primary myeloma cells in vitro. The goal of this study was to examine whether DKK1 can be used as a tumor vaccine to elicit DKK1-specific immunity that can control myeloma growth or even eradicate established myeloma in vivo. We used DKK1-DNA vaccine in the murine MOPC-21 myeloma model, and the results clearly showed that active vaccination using the DKK1 vaccine not only was able to protect mice from developing myeloma, but it was also therapeutic against established myeloma. Furthermore, the addition of CpG as an adjuvant, or injection of B7H1-blocking or OX40-agonist Abs, further enhanced the therapeutic effects of the vaccine. Mechanistic studies revealed that DKK1 vaccine elicited a strong DKK1- and tumor-specific CD4+ and CD8+ immune responses, and treatment with B7H1 or OX40 Abs significantly reduced the numbers of IL-10-expressing and Foxp3+ regulatory T cells in vaccinated mice. Thus, our studies provide strong rationale for targeting DKK1 for immunotherapy of myeloma patients.

Targeting the Wnt pathway in cancer: the emerging role of Dickkopf-3

Aberrant activation of the Wnt signaling pathway is a major trait of many human cancers. Due to its vast implications in tumorigenesis and progression, the Wnt pathway has attracted considerable attention at several molecular levels, also with respect to developing novel cancer therapeutics. Indeed, research in Wnt biology has recently provided numerous clues, and evidence is accumulating that the secreted Wnt antagonist Dickkopf-related protein 3 (Dkk-3) and its regulators may constitute interesting therapeutic targets in the most important human cancers. Based on the currently available literature, we here review the knowledge on the biological role of Dkk-3 as an antagonist of the Wnt signaling pathway, the involvement of Dkk-3 in several stages of tumor development, the genetic and epigenetic mechanisms disrupting DKK3 gene function in cancerous cells, and the potential clinical value of Dkk-3 expression/DKK3 promoter methylation as a biomarker and molecular target in cancer diseases. In conclusion, Dkk-3 rapidly emerges as a key player in human cancer with auspicious tumor suppressive capacities, most of all affecting apoptosis and proliferation. Its gene expression is frequently downregulated by promoter methylation in almost any solid and hematological tumor entity. Clinically, evidence is accumulating of Dkk-3 being both a potential tumor biomarker and effective anti-cancer agent. Although further research is needed, re-establishing Dkk-3 expression in cancer cells holds promise as novel targeted molecular tumor therapy.

SLXL1, a novel acrosomal protein, interacts with DKKL1 and is involved in fertilization in mice

Background

Spermatogenesis is a complex cellular developmental process which involves diverse families of genes. The Xlr (X-linked, lymphocyte regulated) family includes multiple members, only a few of which have reported functions in meiosis, post-meiotic maturation, and fertilization of germ cells. Slx-like1 (Slxl1) is a member of the Xlr family, whose expression and function in spermatogenesis need to be elucidated.

Methodology/Principal Findings

The mRNA and protein expression and localization of Slxl1 were investigated by RT-PCR, Western blotting and immunohistochemistry in different tissues and at different stages of spermatogenesis. The interacting partner of SLXL1 was examined by co-immunoprecipitation and co-localization. Assessment of the role of SLXL1 in capacitation, acrosome reaction, zona pellucida binding/penetration, and fertilization was carried out in vitro using blocking antisera. The results showed that Slxl1 mRNA and protein were specifically expressed in the testis. SLXL1 was exclusively located in the acrosome of post-meiotic germ cells and interacts with DKKL1 (Dickkopf-like1), which is an acrosome-associated protein and plays an important role in fertilization. The rates of zona pellucida binding/penetration and fertilization were significantly reduced by the anti-SLXL1 polyclonal antiserum.

Conclusions/Significance

SLXL1 is the first identified member of the XLR family that is associated with acrosome and is involved in zona pellucid binding/penetration and subsequent fertilization. These results, together with previous studies, suggest that Xlr family members participate in diverse processes from meiosis to fertilization during spermatogenesis.

Stage-specific gene expression during spermatogenesis in the dogfish (Scyliorhinus canicula)

In the dogfish testis, the cystic arrangement and polarization of germ cell stages make it possible to observe all stages of spermatogenesis in a single transverse section. By taking advantage of the zonation of this organ, we have used suppressive subtractive libraries construction, real-time PCR, and in situ hybridization to identify 32 dogfish genes showing differential expressions during spermatogenesis. These include homologs of genes already known to be expressed in the vertebrate testis, but found here to be specifically expressed either in pre-meiotic and/or meiotic zones (ribosomal protein S8, high-mobility group box 3, ubiquitin carboxyl-terminal esterase L3, 20beta-hydroxysteroid dehydrogenase, or cyclophilin B) or in post-meiotic zone (speriolin, Soggy, zinc finger protein 474, calreticulin, or phospholipase c-zeta). We also report, for the first time, testis-specific expression patterns for dogfish genes coding for A-kinase anchor protein 5, ring finger protein 152, or F-box only protein 7. Finally, the study highlights the differential expression of new sequences whose identity remains to be assessed. This study provides the first molecular characterization of spermatogenesis in a chondrichthyan, a key species to gain insight into the evolution of this process in gnathostomes.

Constitutive WNT/beta-catenin signaling in murine Sertoli cells disrupts their differentiation and ability to support spermatogenesis

Sertoli and germ cell interactions are essential for spermatogenesis and, thus, male fertility. Sertoli cells provide a specialized microenvironment for spermatogonial stem cells to divide, allowing both self-renewal and spermatogenesis. In the present study, we used mice with a conditional activated allele of the beta-catenin gene (Ctnnb1(tm1Mmt)(/+)) in Sertoli cells expressing Cre recombinase driven by the anti-Müllerian hormone (AMH; also known as Müllerian-inhibiting substance) type II receptor promoter (Amhr2(tm3(cre)Bhr)(/+)) to show that constitutively activated beta-catenin leads to their continuous proliferation and compromised differentiation. Compared to controls, Sertoli cells in mature mutant mice continue to express high levels of both AMH and glial cell-derived neurotrophic factor (GDNF), which normally are expressed only in immature Sertoli cells. We also show evidence that LiCl treatment, which activates endogenous nuclear beta-catenin activity, regulates both AMH and GDNF expression at the transcriptional level. The epididymides were devoid of sperm in the Amhr2(tm3(cre)Bhr)(/+);Ctnnb1(tm1Mmt)(/+) mice at all ages examined. We show that the mutant mice are infertile because of defective differentiation of germ cells and increased apoptosis, both of which are characteristic of GDNF overexpression in Sertoli cells. Constitutive activation of beta-catenin in Amhr2-null mice showed the same histology, suggesting that the phenotype was the result of persistent overexpression of GDNF. These results show that dysregulated wingless-related MMTV integration site/beta-catenin signaling in Sertoli cells inhibits their postnatal differentiation, resulting in increased germ cell apoptosis and infertility.

The acrosomal protein Dickkopf-like 1 (DKKL1) is not essential for fertility

OBJECTIVE

To determine the role of Dkkl1 on mouse development, viability, and fertility.

DESIGN

Prospective experimental study.

SETTING

Government research institution.

ANIMAL(S)

Mice of C57BL/6 and 129X1/SvJ strains, as well as transgenic mice of mixed C57BL/6 and 129X1/SvJ strains were used for the studies.

INTERVENTION(S)

Mice were constructed that lacked a functional Dkkl1 gene.

MAIN OUTCOME MEASURE(S)

Deletion of the gene was confirmed by DNA, RNA, and protein analyses; in vivo fertility was examined by continuous mating scheme.

RESULT(S)

Previous studies have shown that Dkkl1, a gene unique to mammals, is expressed predominantly, if not exclusively, in developing spermatocytes, and the DKKL1 protein accumulates in the acrosome of mature sperm. Subsequent studies (reported in the accompanying article) demonstrate that Dkkl1 also is expressed in the trophectoderm/placental lineage. Taken together, these results strongly suggested that DKKL1 protein is required for terminal differentiation either of trophoblast giant cells or of sperm, both of which are directly involved in fertility. To challenge this hypothesis, conditional targeted mutagenesis was used to ablate the Dkkl1 gene in mice. Surprisingly, Dkkl1 nullizygous embryos developed into viable, fertile adults, despite the fact that they failed to produce any portion of the DKKL1 protein.

CONCLUSION(S)

DKKL1 is a mammalian-specific acrosomal protein that is not essential either for development or fertility.

Effects of FSH on testicular mRNA transcript levels in the hypogonadal mouse

FSH acts through the Sertoli cell to ensure normal testicular development and function. To identify transcriptional mechanisms through which FSH acts in the testis, we have treated gonadotrophin-deficient hypogonadal (hpg) mice with recombinant FSH and measured changes in testicular transcript levels using microarrays and real-time PCR 12, 24 and 72 h after the start of treatment. Approximately 400 transcripts were significantly altered at each time point by FSH treatment. At 12 h, there was a clear increase in the levels of a number of known Sertoli cell transcripts (e.g. Fabp5, Lgals1, Tesc, Scara5, Aqp5). Additionally, levels of Leydig cell transcripts were also markedly increased (e.g. Ren1, Cyp17a1, Akr1b7, Star, Nr4a1). This was associated with a small but significant rise in testosterone at 24 and 72 h. At 24 h, androgen-dependent Sertoli cell transcripts were up-regulated (e.g. Rhox5, Drd4, Spinlw1, Tubb3 and Tsx) and this trend continued up to 72 h. By contrast with the somatic cells, only five germ cell transcripts (Dkkl1, Hdc, Pou5f1, Zfp541 and 1700021K02Rik) were altered by FSH within the time-course of the experiment. Analysis of canonical pathways showed that FSH induced a general decline in transcripts related to formation and regulation of tight junctions. Results show that FSH acts directly and indirectly to induce rapid changes in Sertoli cell and Leydig cell transcript levels in the hpg mouse but that effects on germ cell development must occur over a longer time-span.

A Wnt survival guide: from flies to human disease

It has been two decades since investigators discovered the link between the Drosophila wingless (Wg) gene and the vertebrate oncogene int-1, thus establishing the family of signaling proteins known as Wnts. Since the inception of the Wnt signaling field, there have been 19 Wnt isoforms identified in humans. These secreted glycoproteins can activate at least two distinct signaling pathways in vertebrate cells, leading to cellular changes that regulate a vast array of biological processes, including embryonic development, cell fate, cell proliferation, cell migration, stem cell maintenance, tumor suppression, and oncogenesis. In certain contexts, one subset of Wnt isoforms activates the canonical Wnt/beta-catenin pathway that is characterized by the activation of certain beta-catenin-responsive target genes in response to the binding of Wnt ligand to its cognate receptors. Similarly, a second subset of Wnt isoforms activates beta-catenin-independent pathways, including the Wnt/calcium (Wnt/Ca) pathway and the Wnt/planar cell polarity (Wnt/PCP) pathway, in certain cellular contexts. In addition, research has identified several secreted proteins known to regulate Wnt signaling, including the Dickkopf (DKK) family, secreted Frizzled-related proteins (sFRPs), and Wnt inhibitory factor-1 (WIF-1). The advent of technologies that can provide genome-wide expression data continues to implicate Wnts and proteins that regulate Wnt signaling pathways in a growing number of disease processes. The aim of this review is to provide a context on the Wnt field that will facilitate the interpretation and study of Wnt signaling in the context of human disease.

The multi-copy mouse gene Sycp3-like Y-linked (Sly) encodes an abundant spermatid protein that interacts with a histone acetyltransferase and an acrosomal protein

Deletion analysis has established that genes on the Y chromosome are essential for normal sperm production in humans, mice, and Drosophila. In mice, long-arm deletions have an impact on spermiogenesis, with the most extensive deletions resulting in severe sperm head malformations and infertility. Intriguingly, smaller deletions are compatible with fertility but result in a distorted sex ratio in favor of females, and recently it was found that Y long-arm deletions are also associated with a marked upregulation of several X-encoded and Y-encoded spermatid-expressed genes. The mouse Y long arm encodes a number of distinct transcripts, each of which derives from multiple gene copies. Of these multicopy genes, the recently described Sly has been favored as the gene underlying the spermiogenic defects associated with Y long-arm deletions. To assess the candidacy of Sly, the expression of this gene was examined in the testis at the transcript and protein levels. Sly is transcribed after the first meiotic division in secondary spermatocytes and round spermatids and encodes two transcript variants, Sly_v1 and Sly_v2 (proteins referred to as SLY1 and SLY2). We raised an antibody against SLY1 which detected the protein in round and early elongating spermatids, where it is predominantly cytoplasmic. Yeast two-hybrid and coimmunoprecipitation studies demonstrated that SLY1 interacts with the acrosomal protein DKKL1, the histone acetyltransferase KAT5 (also known as TIP60), and the microtubule-associated protein APPBP2. Together, these data suggest SLY1 may be involved in multiple processes during spermiogenesis, including the control of gene expression and the development or function of the acrosome.

Dickkopf-like1 regulates postpubertal spermatocyte apoptosis and testosterone production

Dickkopf-like1 (Dkkl1) encodes a glycoprotein secreted by postmeiotic male germ cells. We report here that adult Dkkl1-deficient males have elevated sperm counts caused by a decrease in postpubertal spermatocyte apoptosis and display, upon aging, increased local production of testosterone. Molecular analyses identified the Fas death ligand (FasL) as a target for Dkkl1 pro-apoptotic activity in adult mice. Accordingly, adult FasL-deficient gld mice display an increased sperm count and decreased spermatocyte apoptosis phenotype similar to the one observed in Dkkl1-deficient mice. We also show that the elevated testosterone level observed in aging Dkkl1-deficient males is secondary to increased expression in Leydig cells of CYP11A and CYP17, two genes implicated in steroidogenesis. Furthermore, treatment of Leydig cells with Dkkl1 decreases DNA binding and transcriptional activity of steroidogenic factor 1, a pivotal regulator of gene expression in testis. Thus, this study establishes Dkkl1 as a negative regulator of adult testis homeostasis and identifies a novel, Dkkl1/FasL-dependent, regulation that specifically controls the number of postpubertal spermatocytes.

Acrosome biosynthesis in spermatocytes and spermatids revealed by HPA lectin cytochemistry

The origin of the acrosome is controversial, because of both its lysosomal nature and at the moment of its appearance, which seems to be species-specific. Considering the amazing organization shown by the acrosome of some urodele amphibians, HPA-colloidal gold cytochemistry was used to analyze the biogenesis of the acrosome in the urodele Pleurodeles waltl at electron microscopy level. The results showed that HPA-labeling is useful to label the acrosome and its precursor vesicles and, consequently, HPA-histochemistry could be used as a marker of acrosomal content. Labeling of the Golgi apparatus and precursor vesicles was seen in primary spermatocytes and round (stage I) spermatids, thus contributing solid evidence for the beginning of acrosome biogenesis before meiosis. In both primary spermatocytes and round spermatids, an enigmatic vesicle, probably related to the biosynthesis of the neck piece or the tail, was also labeled. Labeling in elongating spermatids (stage II-IV), showed a homogeneous distribution of colloidal gold particles in the acrosomal cap, but the perforatorium was not positive to the lectin. However, in mature (stage V-VI) spermatids, a regional distribution of labeling in the acrosome was seen, with the apical knob showing a stronger labeling than the lateral barb, and the lateral barb showing a stronger labeling than the principal piece of the acrosomal cap. This regional distribution of the labeling suggests that the acrosome develops several domains with different glycoconjugate compositions.

Function and biological roles of the Dickkopf family of Wnt modulators

Dickkopf (Dkk) genes comprise an evolutionary conserved small gene family of four members (Dkk1-4) and a unique Dkk3-related gene, Dkkl1 (soggy). They encode secreted proteins that typically antagonize Wnt/beta-catenin signaling, by inhibiting the Wnt coreceptors Lrp5 and 6. Additionally, Dkks are high affinity ligands for the transmembrane proteins Kremen1 and 2, which also modulate Wnt signaling. Dkks play an important role in vertebrate development, where they locally inhibit Wnt regulated processes such as antero-posterior axial patterning, limb development, somitogenesis and eye formation. In the adult, Dkks are implicated in bone formation and bone disease, cancer and Alzheimer's disease.

In vitro generation of germ cells from murine embryonic stem cells

The demonstration of germ cell and haploid gamete development from embryonic stem cells (ESCs) in vitro has engendered a unique set of possibilities for the study of germ cell development and the associated epigenetic phenomenon. The process of embryoid body (EB) differentiation, like teratoma formation, signifies a spontaneous differentiation of ESCs into cells of all three germ layers, and it is from these differentiating aggregates of cells that putative primordial germ cells (PGCs) and more mature gametes can be identified and isolated. The differentiation system presented here requires the differentiation of murine ESCs into EBs and the subsequent isolation of PGCs as well as haploid male gametes from EBs at various stages of differentiation. It serves as a platform for studying the poorly understood process of germ cell allocation, imprint erasure and gamete formation, with 4-6 weeks being required to isolate PGCs as well as haploid cells.