The acrosomal protein Dickkopf-like 1 (DKKL1) facilitates sperm penetration of the zona pellucida

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.

Analyzing the effect of heparin on in vitro capacitation and spermatozoal RNA population in goats

Heparin is a glycosaminoglycan polymer that is commonly used as an anticoagulant. Heparin also induces in vitro capacitation in spermatozoa, although its molecular mechanism is elusive. This study investigated the effect of heparin on in vitro capacitation and spermatozoal RNA (spRNA) population in goats. Goat spermatozoa were treated with 20 μM heparin for 0-6 h and evaluated for motility, capacitation, acrosome reaction, and spRNA population by RNA sequencing (RNA-seq). It was observed that heparin enhanced sperm motility up to 6 h of incubation (p < 0.05). Heparin also induced capacitation and acrosome reaction within 4 h. RNA-seq identified 1254 differentially expressed genes (DEGs) between heparin-treated and control spermatozoa. Most DEGs (1251 nos.) were upregulated and included 1090 protein-coding genes. A few genes (PRND, ITPR1, LLCFC1, and CHRM2) showed >5-fold increased expression in heparin-treated spermatozoa compared to the control. The upregulated genes were found to be involved in cAMP-PKA, PI3-Akt, calcium, MAPK signaling, and oxidative stress pathways. DCFDA staining confirmed the increased oxidative stress in heparin-treated spermatozoa compared to the control (p < 0.05). In conclusion, the results of the present study suggest that heparin enhances sperm motility and induces capacitation by upregulation of the spRNA population and oxidative stress pathway.

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.

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.

[Expression of DKKL1 in spermatozoa of men with asthenospermia]

OBJECTIVE

To compare the expression of DKKL1 in ejaculated spermatozoa of normal fertile men and men with asthenospermia and investigate the role of DKKL1 in the pathogenesis of asthenospermia.

METHODS

The characteristics of semen samples collected from normal fertile men and men with asthenospermia were analyzed using computer-assisted sperm analysis according to WHO criteria. The ejaculated sperms were isolated by Percoll discontinuous density gradients to detect the expression of DKKL1 mRNA and protein using real-time PCR and Western blotting.

RESULTS

The expression of DKKL1 mRNA was significantly down-regulated by 11.1 times in asthenospermic men as compared with that in normal fertile men (P<0.01). Western blotting showed that the expression of DKKL1 protein was down-regulated by 2.4 times in asthenospermic men compared to normal fertile men.

CONCLUSION

The expression of DKKL1, which may play an important role in sperm motility,is significantly decreased in ejaculated spermatozoa of men with asthenospermia.

Allele-specific splicing effects on DKKL1 and ZNF419 transcripts in HeLa cells

Allele-specific splicing is the production of different RNA isoforms from different alleles of a gene. Altered splicing patterns such as exon skipping can have a dramatic effect on the final protein product yet have traditionally proven difficult to predict. We investigated the splicing effects of a set of nine single nucleotide polymorphisms (SNPs) which are predicted to have a direct impact on mRNA splicing, each in a different gene. Predictions were based on SNP location relative to splice junctions and intronic/exonic splicing elements, combined with an analysis of splice isoform expression data from public sources. Of the nine genes tested, six SNPs led to direct impacts on mRNA splicing as determined by the splicing reporter minigene assay and RT-PCR in human HeLa cells, of which four were allele-specific effects. These included previously unreported alternative splicing patterns in the genes ZNF419 and DKKL1. Notably, the SNP in ZNF419, a transcription factor, leads to the deletion of a DNA-binding domain from the protein and is associated with an expression QTL, while the SNP in DKKL1 leads to shortened transcripts predicted to produce a truncated protein. We conclude that the impact of SNP mutations on mRNA splicing, and its biological relevance, can be predicted by integrating SNP position with available data on relative isoform abundance in human cell lines.

Cause and consequence of cancer/testis antigen activation in cancer

Tumor cells frequently exhibit widespread epigenetic aberrations that significantly alter the repertoire of expressed proteins. In particular, it has been known for nearly 25 years that tumors frequently reactivate genes whose expression is typically restricted to germ cells. These gene products are classified as cancer/testis antigens (CTAs) owing to their biased expression pattern and their immunogenicity in cancer patients. While these genes have been pursued as targets for anticancer vaccines, whether these reactivated testis proteins have roles in supporting tumorigenic features is less studied. Recent evidence now indicates that these proteins can be directly employed by the tumor cell regulatory environment to support cell-autonomous behaviors. Here, we review the history of the CTA field and present recent findings indicating that CTAs can play functional roles in supporting tumorigenesis.

Safety, efficacy and efficiency of laser-assisted IVF in subfertile mutant mouse strains

In the present report we studied the safety, efficacy and efficiency of using an infrared laser to facilitate IVF by assessing fertilization, development and birth rates after laser-zona drilling (LZD) in 30 subfertile genetically modified (GM) mouse lines. We determined that LZD increased the fertilization rate four to ten times that of regular IVF, thus facilitating the derivation of 26 of 30 (86.7%) GM mouse lines. Cryopreserved two-cell stage embryos derived by LZD-assisted IVF were recovered and developed to blastocysts in vitro at the same rate as frozen-thawed embryos derived by regular IVF. Surprisingly after surgical transfer to pseudopregnant recipients the birth rate of embryos derived by LZD-assisted IVF was significantly lower than that of embryos derived by regular IVF. However this result could be completely mitigated by the addition of 0.25 M sucrose to the culture medium during LZD which caused the oocyte to shrink in volume relative to the perivitelline space. By increasing the distance from the laser target site on the zona pellucida, we hypothesize that the hyperosmotic effect of sucrose reduced the potential for laser-induced cytotoxic thermal damage to the underlying oocytes. With appropriate preparation and cautious application, our results indicate that LZD-assisted IVF is a safe, efficacious and efficient assisted reproductive technology for deriving mutant mouse lines with male factor infertility and subfertility caused by sperm-zona penetration defects.

Region-specific expression of Dickkopf-like1 in the adult brain. Abbreviated title: Dkkl1 in the adult brain

In the adult, the dickkopf family member Dickkopf-like1 (Dkkl1) has been described as a testicular protein involved in the regulation of spermatocyte apoptosis. However, microarray studies additionally suggested that Dkkl1 regulation is involved in various tumors including high grade gliomas. Since investigations of Dkkl1 in the adult central nervous system are lacking, we analyzed Dkkl1 expression in the adult mouse brain and found a region specific expression pattern with a profoundly high cortical expression. Analysis of transgenic mice in which the lacZ gene was inserted into the Dkkl1 locus further pointed to NeuN-positive neurons as the main source of Dkkl1 in the normal adult brain. In Dkkl1(-/-) mutant mice, gross brain morphology as well as hippocampal and cortical lamination appeared normal. Similarly, neuronal density in cortical layer V was not altered. Thus, Dkkl1 may not be essential for normal brain organization, but could exert import functions during pathological conditions such as tumorigenesis and cancer progression.

Evolution of genes involved in gamete interaction: evidence for positive selection, duplications and losses in vertebrates

Genes encoding proteins involved in sperm-egg interaction and fertilization exhibit a particularly fast evolution and may participate in prezygotic species isolation [1], [2]. Some of them (ZP3, ADAM1, ADAM2, ACR and CD9) have individually been shown to evolve under positive selection [3], [4], suggesting a role of positive Darwinian selection on sperm-egg interaction. However, the genes involved in this biological function have not been systematically and exhaustively studied with an evolutionary perspective, in particular across vertebrates with internal and external fertilization. Here we show that 33 genes among the 69 that have been experimentally shown to be involved in fertilization in at least one taxon in vertebrates are under positive selection. Moreover, we identified 17 pseudogenes and 39 genes that have at least one duplicate in one species. For 15 genes, we found neither positive selection, nor gene copies or pseudogenes. Genes of teleosts, especially genes involved in sperm-oolemma fusion, appear to be more frequently under positive selection than genes of birds and eutherians. In contrast, pseudogenization, gene loss and gene gain are more frequent in eutherians. Thus, each of the 19 studied vertebrate species exhibits a unique signature characterized by gene gain and loss, as well as position of amino acids under positive selection. Reflecting these clade-specific signatures, teleosts and eutherian mammals are recovered as clades in a parsimony analysis. Interestingly the same analysis places Xenopus apart from teleosts, with which it shares the primitive external fertilization, and locates it along with amniotes (which share internal fertilization), suggesting that external or internal environmental conditions of germ cell interaction may not be the unique factors that drive the evolution of fertilization genes. Our work should improve our understanding of the fertilization process and on the establishment of reproductive barriers, for example by offering new leads for experiments on genes identified as positively selected.

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.

Evidence for the inhibition of fertilization in vitro by anti-ZP3 antisera derived from DNA vaccine

Previously we have found that DNA vaccine, pCMV4-rZPC' can generate specific antibodies against rabbit ZPC (amino acid 263-415, rZPC'), which binds to ovarian ZP and leads to a significant reduction of fertility in vivo. The purpose of this study was to evaluate the effect of antisera from pCMV4-rZPC(')-immunized mice on sperm-oocyte interaction in vitro. The effect of antisera from DNA vaccine-immunized mice on fertilization and early embryonic development was studied using an in vitro fertilization system. The results showed that the antisera supplemented in fertilization medium (10%, v/v) significantly decreased the rate of fertilization compared to that of control groups (P<0.05); whereas the antisera showed no significant effect on the rate of fertilization when ZP-free eggs were used. Moreover, the antisera pre-neutralized with mouse soluble zona pellucida lost the capacity to inhibit fertilization when compared with that of control groups. In addition, the antisera showed no detrimental effect on early developmental potential of mouse embryos in vitro. Taken together, our study provided herein direct evidence showing that antisera generated by DNA vaccine can block sperm-egg recognition during fertilization via targeting the oocyte ZP proteins.

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.

Assembly of large genomes using second-generation sequencing

Second-generation sequencing technology can now be used to sequence an entire human genome in a matter of days and at low cost. Sequence read lengths, initially very short, have rapidly increased since the technology first appeared, and we now are seeing a growing number of efforts to sequence large genomes de novo from these short reads. In this Perspective, we describe the issues associated with short-read assembly, the different types of data produced by second-gen sequencers, and the latest assembly algorithms designed for these data. We also review the genomes that have been assembled recently from short reads and make recommendations for sequencing strategies that will yield a high-quality assembly.

Fertilization: a sperm's journey to and interaction with the oocyte

Mammalian fertilization comprises sperm migration through the female reproductive tract, biochemical and morphological changes to sperm, and sperm-egg interaction in the oviduct. Recent gene knockout approaches in mice have revealed that many factors previously considered important for fertilization are largely dispensable, or if they are essential, they have an unexpected function. These results indicate that what has been observed in in vitro fertilization (IVF) differs significantly from what occurs during "physiological" fertilization. This Review focuses on the advantages of studying fertilization using gene-manipulated animals and highlights an emerging molecular mechanism of mammalian fertilization.

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.