Creating a conditional mutation of Wnt-1 by antisense transgenesis provides evidence that Wnt-1 is not essential for spermatogenesis

Comparative gonad transcriptome analysis in cobia (Rachycentron canadum)

Background: Cobia (Rachycentron canadum) is a species of fish with high commercial potential particularly due to fast growth rates. The evidence of sexual size dimorphism favoring females indicate potential benefits in having a monosex culture. However, the involvement of genetic factors responsible for sexual development and gonadal maintenance that produces phenotypic sex in cobia is largely unknown. Methods: In the present study, we performed transcriptome sequencing of cobia to identify sex-biased significantly differentially expressed genes (DEGs) in testes and ovaries. The reliability of the gonad transcriptome data was validated by qPCR analysis of eight selected significantly differential expressed sex-related candidate genes. Results: This comparative gonad transcriptomic analysis revealed that 7,120 and 4,628 DEGs are up-regulated in testes or ovaries, respectively. Further functional annotation analyses identified 76 important candidate genes involved in sex determination cascades or sex differentiation, including 42 known testis-biased DEGs (dmrt1, amh and sox9 etc.), and 34 known ovary-biased DEGs (foxl2, sox3 and cyp19a etc.). Moreover, eleven significantly enriched pathways functionally related to sex determination and sex differentiation were identified, including Wnt signaling pathway, oocyte meiosis, the TGF-beta signaling pathway and MAPK signaling pathway. Conclusion: This work represents the first comparative gonad transcriptome study in cobia. The putative sex-associated DEGs and pathways provide an important molecular basis for further investigation of cobia's sex determination, gonadal development as well as potential control breeding of monosex female populations for a possible aquaculture setting.

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.

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.

Aberrant Wnt/β-Catenin Signaling Pathway in Testis of Azoospermic Men​

PURPOSE

The Importance and key role of Wnt/β-catenin signaling pathway in spermatogenesis is known. Abnormalities of this pathway in Sertoli and germ cells leads to infertility. Leydig cells play an important role in spermatogenesis and male reproduction. As of now, exact position of the Wnt/β-catenin signaling pathway disorders in the tissue and possible involvement of Leydig cells has not been investigated.

METHODS

Samples of our previous study were used for common Y chromosome microdeletions screening and common CFTR gene mutations.1 β-catenin gene expression were evaluated and compared between testicular tissue obtained by testicular sperm extraction (TESE) in two groups of obstructive (n=10) and non-obstructive (n=10) azoospermic infertile men. Location of β-catenin accumulation was detected by immunofluorescence technic and quantitatively compared in the tissue followed by counterstaining with anti-vimentin antibody. It was used as specific marker of leydig cells to determine and confirm the cells in which this gathering was occurred.

RESULTS

β-catenin gene expression does not have a significant difference between the obstructive azoospermia (0.998) and non-obstructive azoospermia group (0.891). β-catenin was abnormally aggregated in leydig cell of non-obstructive azoospermic men.

CONCLUSION

Gathering β-catenin in cytoplasm of leydig cells can disrupt spermatogenesis and cause infertility in men.

R-spondin 1/dickkopf-1/beta-catenin machinery is involved in testicular embryonic angiogenesis

Testicular vasculogenesis is one of the key processes regulating male gonad morphogenesis. The knowledge of the molecular cues underlining this phenomenon is one of today’s most challenging issues and could represent a major contribution toward a better understanding of the onset of testicular morphogenetic disorders. R-spondin 1 has been clearly established as a candidate for mammalian ovary determination. Conversely, very little information is available on the expression and role of R-spondin 1 during testicular morphogenesis. This study aims to clarify the distribution pattern of R-spondin 1 and other partners of its machinery during the entire period of testicular morphogenesis and to indicate the role of this system in testicular development. Our whole mount immunofluorescence results clearly demonstrate that R-spondin 1 is always detectable in the testicular coelomic partition, where testicular vasculature is organized, while Dickkopf-1 is never detectable in this area. Moreover, organ culture experiments of embryonic male UGRs demonstrated that Dickkopf-1 acted as an inhibitor of testis vasculature formation. Consistent with this observation, real-time PCR analyses demonstrated that DKK1 is able to slightly but significantly decrease the expression level of the endothelial marker Pecam1. The latter experiments allowed us to observe that DKK1 administration also perturbs the expression level of the Pdgf-b chain, which is consistent with some authors’ observations relating this factor with prenatal testicular patterning and angiogenesis. Interestingly, the DKK1 induced inhibition of testicular angiogenesis was rescued by the co-administration of R-spondin 1. In addition, R-spondin 1 alone was sufficient to enhance, in culture, testicular angiogenesis.

Physiopathological aspects of the Wnt/β-catenin signaling pathway in the male reproductive system

The Wnt/β-catenin signaling pathway controls several biological processes throughout development and adult life. Dysregulation of Wnt/β-catenin signaling underlies a wide range of pathologies in animals and humans, including cancer in different tissues. In this review, we provide an update of the Wnt/β-catenin signaling pathway and the possible roles of the Wnt/β-catenin signaling in the biology of testis, epididymis and prostate. Data from our laboratory suggest the involvement of 17β-estradiol and estrogen receptors (ERs) on the regulation of β-catenin expression in rat Sertoli cells. We also provide emerging evidences of the involvement of Wnt/β-catenin pathway in testis and prostate cancer. Our understanding of the role of Wnt/β-Catenin signaling in male reproductive tissues is still evolving, and several questions are open to be addressed in the future.

Sex-specific roles of beta-catenin in mouse gonadal development

Sexually dimorphic development of the gonads is controlled by positive and negative regulators produced by somatic cells. Many Wnt ligands, including ones that signal via the canonical beta-catenin pathway, are expressed in fetal gonads. beta-catenin, a key transcriptional regulator of the canonical Wnt pathway and an element of the cell adhesion complex, is essential for various aspects of embryogenesis. To study the involvement of beta-catenin in sex determination, we ablated beta-catenin specifically in the SF1-positive population of somatic cells. Although beta-catenin was present in gonads of both sexes, it was necessary only for ovarian differentiation but dispensable for testis development. Loss of beta-catenin in fetal testes did not affect Sertoli cell differentiation, testis morphogenesis or masculinization of the embryos. However, we observed molecular and morphological defects in ovaries lacking beta-catenin, including formation of testis-specific coelomic vessel, appearance of androgen-producing adrenal-like cells and loss of female germ cells. These phenotypes were strikingly similar to those found in the R-spondin1 (Rspo1) and Wnt4 knockout ovaries. In the absence of beta-catenin, expression of Wnt4 was down-regulated while that of Rspo1 was not affected, placing beta-catenin as a component in between Rspo1 and Wnt4. Our results demonstrate that beta-catenin is responsible for transducing sex-specific signals in the SF1-positive somatic cell population during mouse gonadal development.

Seminiferous tubule degeneration and infertility in mice with sustained activation of WNT/CTNNB1 signaling in sertoli cells

WNT/CTNNB1 signaling is involved in the regulation of multiple embryonic developmental processes, adult tissue homeostasis, abd cell fate determination and differentiation. Many WNTs and components of the WNT/CTNNB1 signaling pathway are expressed in the testis, but their physiological roles in this organ are largely unknown. To elucidate the role(s) of WNT/CTNNB1 signaling in the testis, transgenic Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ mice were generated to obtain sustained activation of the WNT/CTNNB1 pathway in both Leydig and Sertoli cells. Male Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ mice were sterile because of testicular atrophy starting at 5 wk of age, associated with degeneration of seminiferous tubules and the progressive loss of germ cells. Although Cre activity was expected in Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ Leydig cells, no evidence of Cre-mediated recombination of the floxed allele or of WNT/CTNNB1 pathway activation could be obtained, and testosterone levels were comparable to age-matched controls, suggesting that genetic recombination was inefficient in Leydig cells. Conversely, sustained WNT/CTNNB1 pathway activation was obtained in Ctnnb1 tm1Mmt/+;Amhr2 tm3(cre)Bhr/+ Sertoli cells. The latter often exhibited morphological characteristics suggestive of incomplete differentiation that appeared in a manner coincident with germ cell loss, and this was accompanied by an increase in the expression of the immature Sertoli cell marker AMH. In addition, a poorly differentiated, WT1-positive somatic cell population accumulated in multilayered foci near the basement membrane of many seminiferous tubules. Together, these data suggest that the WNT/CTNNB1 pathway regulates Sertoli cell functions critical to their capacity to support spermatogenesis in the postnatal testis.

The 37 kDa/67 kDa laminin receptor is required for PrP(Sc) propagation in scrapie-infected neuronal cells

The accumulation of PrP(Sc) in scrapie-infected neuronal cells has been prevented by three approaches: (i) transfection of ScMNB cells with an antisense laminin receptor precursor (LRP) RNA-expression plasmid, (ii) transfection of ScN2a cells and ScGT1 cells with small interfering RNAs (siRNAs) specific for the LRP mRNA, and (iii) incubation of ScN2a cells with an anti-LRP/LR antibody. LRP antisense RNA and LRP siRNAs reduced LRP/LR expression and inhibited the accumulation of PrP(Sc) in these cells. The treatments also reduced PrP(c) levels. The anti-LRP/LR antibody, W3, abolished PrP(Sc) accumulation and reduced PrP(c) levels after seven days of incubation. Cells remained free of PrP(Sc) after being cultured for 14 additional days without the antibody, whereas the PrP(c) level was restored. Our results demonstrate the necessity of the laminin receptor (LRP/LR) for PrP(Sc) propagation in cultured cells and suggest that LRP/LR-specific antibodies could be used as powerful therapeutic tools in the treatment of transmissible spongiform encephalopathies.

Antisense transgenics in animals

Antisense transgenesis provides a methodology for ablating gene expression in targeted tissues through the use of tissue-specific or controllable promoters. The two major features to be considered in the design of a construct for injection are (1) the target sequence and (2) the promoter to be used. Information is provided to help the investigator make decisions in these regards. The standard methodology of making transgenics is not replicated but some hints as how best to use a transgenic facility are provided. An overview of methods for studying transgene expression and target gene suppression is given. In summary, antisense transgenesis may provide a more readily achievable method for tissue-specific ablation of a gene's function than controllable knockouts provide.

Controlling your losses: conditional gene silencing in mammals

Methods are now widely used in mice, and to a lesser extent in mammalian-cell culture, for the constitutive silencing of target genes in order to assess their function. For a variety of reasons, not least because many genes are essential for viability, it is important that these methods can be adapted to allow the controlled silencing of target genes. Reviewed here are the ways in which gene-silencing methods can be combined with a growing number of genetic control systems to generate cell lines or mice that are, in effect, conditional mutants. These approaches are still being developed and promise to open up key areas of cell and animal biology to genetic analysis.

Antisense and ribozyme constructs in transgenic animals

Geneticists have long sought the ability to add or subtract individual genes from an organism's genome, or to be able to alter the level of expression of a gene in a targeted, developmentally and tissue-specific manner. The development of transgenic technology realized the possibilities of increasing the expression of a specific gene or the transfer of a new gene into an animal. Homologous recombination techniques allow the deletion or alteration of a gene in vivo. The production of transgenic animals incorporating a gene construct that expresses a complimentary antisense RNA to a targeted gene, or an antisense RNA incorporating a catalytic, ribozyme sequence, have been suggested as a potential mechanism for obtaining the developmentally and tissue-specific down-regulation of expression of a targeted gene in vivo. In this paper we review the current literature with respect to the application of antisense and ribozyme constructs in transgenic animals and conclude that such constructs can effectively downregulate the level of mRNA from a target gene, the amount of protein produced in the cell, and result in phenotypic consequences.

A 252 bp upstream region of the rat spermatocyte-specific hst70 gene is sufficient to promote expression of the hst70-CAT hybrid gene in testis and brain of transgenic mice

The rat hst70 gene belongs to a heat shock hsp70 multigene family and its expression has been detected so far solely in spermatocytes. To investigate the cis-elements responsible for testis-specific expression of the hst70 gene we produced several lines of transgenic mice carrying fragments of the 5'-flanking regions of the hst70 gene fused to the chloramphenicol acetyltransferase (CAT) reporter gene. Hybrid genes of series B were constructed such that, besides the 780 bp, 343 bp and 163 bp 5'-flanking region these plasmids contained no other sequences of the hst70 gene. In hybrid genes of series D the CAT gene was ligated to 343 bp and 252 bp 5'-flanking regions together with the 57 bp of the 5'-end nontranslated (leader) sequences of the hst70 gene. We found that in 780/B, 343/B, 343/D and 252/D adult mice the transgene was specifically and highly expressed in testes. In developing testes the high CAT activity appeared in transgenic mice aged 3 weeks and older. None of the three 163/B transgenic lines exhibited CAT activity in any tissue analyzed. In all CAT expressing lines a weak but significant CAT activity (up to 5% of that in testis) was detected also in the brain. RNase protection assay confirmed that the endogenous hst70 gene transcripts are present in testis as well as in brain of nontransgenic rats and mice. Our data show that the cis-regulatory sequences responsible for testis-specific and developmentally regulated expression of the hst70 gene are localized within the 252 bp region 5' to the gene and neither the 5'-end nor 3'-end nontranslated sequences of the gene are important for this specificity.

Evaluation of an antisense RNA transgene for inhibiting growth hormone gene expression in transgenic rats

We compared the levels of growth hormone (GH) mRNA in the pituitary, plasma GH concentration, and altered phenotype in rats heterozygous and homozygous for an antisense RNA transgene targeted to the rat GH gene, with those in nontransgenic rats. We initially investigated whether the transgene promoter, which is connected to four copies of a thyroid hormone response element (TRE) that increases promoter activity, affected in vivo transgene expression in the pituitary of the transgenic rats. Plasma GH concentration correlated negatively with T3 injection in surgically thyroidectomized heterozygous transgenic rats. There was a reduction of about approximately 35-40% in GH mRNA levels in the pituitary of homozygous animals compared with those in non-transgenic rats. Plasma GH concentration was significantly approximately 25-32 and approximately 29-41% lower in heterozygous and homozygous transgenic rats, respectively, compared with that in nontransgenic animals. Furthermore, the growth rates in homozygous transgenic rats were reduced by approximately 72-81 and approximately 51-70% compared with those of their heterozygous and nontransgenic littermates, respectively. The results of these studies suggested that the biological effect of GH in vivo is modulated dose-dependently by the antisense RNA transgene. The rat GH gene can therefore be targeted by antisense RNA produced from a transgene, as reflected in the protein and RNA levels.

Transcription of circular and noncircular forms of Sry in mouse testes

Although its expression in adult testis was immediately apparent, the role for Sry (sex determining region, Y) in testicular function remains elusive. We have performed transcriptional studies in an effort to elucidate potential roles of Sry by studying the time and location of its transcription in mouse testes. Northern analyses and more sensitive nuclease protection assays detected transcripts in 28-day-old testes and beyond. The highly sensitive technique of reverse transcription polymerase chain reaction (RTPCR) could not detect Sry expression in 14-day testes when primers for the most conserved portion of the gene, the high mobility group (HMG) box, were used, but primers for the circular form detected Sry transcription at all postnatal stages studied. The same HMG box primers were able to detect expression of Sry in XX, Sxra or Sxrb testes. This suggested that Sry is expressed in cells other than germ cells, which was confirmed with studies on fractionated cells--RTPCR detected transcription of Sry in the highly pure interstitial cell fraction. However, Leydig cells and a Leydig cell tumor were negative for Sry expression. We performed in situ studies in an attempt to localize the expression of Sry in the testes. Abundant expression of an Sry cross-hybridizing transcript was found in spermatogonia, in early spermatocytes, and in some interstitial cells with antisense probes to the HMG box or a more specific, 3' region, whereas the sense probe gave little or no hybridization. It is probable that the circular transcripts, which are seen in reverse transcriptase positive (RT+) and RT- reactions by PCR because of the RT activity of Taq polymerase, are responsible for the hybridization seen in spermatogonia and spermatocytes, whereas linear and circular forms are detected later. Thus Sry is expressed in pre- and postmeiotic germ cells and in somatic cells of the testes.