Cell Junction Dynamics in the Testis: Sertoli-Germ Cell Interactions and Male Contraceptive Development

Loss of connexin43 in murine Sertoli cells and its effect on blood-testis barrier formation and dynamics

Connexin43 (Cx43) is the predominant testicular gap junction protein and in cases of impaired spermatogenesis, Cx43 expression has been shown to be altered in several mammals. Amongst other functions, Cx43 is supposed to regulate junction formation of the blood-testis barrier (BTB). The aim of the present study was to investigate the expression pattern of different tight junction (TJ) proteins of the murine BTB using SC-specific Cx43 knockout mice (SCCx43KO). Adult homozygous male SCCx43KO mice (SCCx43KO-/-) predominantly show an arrest of spermatogenesis and SC-only tubules that might have been caused by an altered BTB assembly, composition or regulation. TJ molecules claudin-3, -5 and -11 were examined in adult wild type (WT) and SCCx43KO-/- mice using immunohistochemistry (IHC) and quantitative real-time PCR (qRT-PCR). In this context, investigation of single tubules with residual spermatogenesis in SCCx43KO-/- mice was particularly interesting to identify a potential Cx43-independent influence of germ cells (GC) on BTB composition and dynamics. In tubules without residual spermatogenesis, a diffuse cytoplasmic distribution pattern for claudin-11 protein could be demonstrated in mutant mice. Nevertheless, claudin-11 seems to form functional TJ. Claudin-3 and -5 could not be detected immunohistochemically in the seminiferous epithelium of those tubules. Correspondingly, claudin-3 and -5 mRNA expression was decreased, providing evidence of generally impaired BTB dynamics in adult KO mice. Observations of tubules with residual spermatogenesis suggested a Cx43-independent regulation of TJ proteins by GC populations. To determine initial BTB formation in peripubertal SCCx43KO-/- mice, immunohistochemical staining and qRT-PCR of claudin-11 were carried out in adolescent SCCx43KO-/- and WT mice. Additionally, BTB integrity was functionally analysed using a hypertonic glucose fixative. These analyses revealed that SCCx43KO-/- mice formed an intact BTB during puberty in the same time period as WT mice, which however seemed to be accelerated.

Sertoli cell-specific ablation of miR-17-92 cluster significantly alters whole testis transcriptome without apparent phenotypic effects

MicroRNAs are frequently organized into polycistronic clusters whose transcription is controlled by a single promoter. The miR-17-92 cluster is expressed in most embryonic and postnatal organs. It is a potent oncogene associated to several types of cancer and it is involved in several important developmental processes. In the testis, expression of the miR-17-92 cluster in the germ cells is necessary to maintain normal spermatogenesis. This cluster is also expressed in Sertoli cells (the somatic cells of the seminiferous tubules), which require miRNAs for correct cell development and survival. To study the possible role of miR-17-92 in Sertoli cell development and function and, in order to overcome the postnatal lethality of miR-17-92-/ mice, we conditionally deleted it in embryonic Sertoli cells shortly after the sex determination stage using an Amh-Cre allele. Mutant mice developed apparently normal testes and were fertile, but their testis transcriptomes contained hundreds of moderately deregulated genes, indicating that testis homeostasis is tightly controlled in mammals and that miR-17-92 expression in Sertoli cells contribute to maintain normal gene expression levels, but is unnecessary for testis development and function. Our results show that significant deregulation of hundreds of genes might have no functional consequences.

ADAMTS1 and ADAMTS5 metalloproteases produced by Sertoli cells: a potential diagnostic marker in azoospermia

In this study, our aim was to detect protein levels of A Disintegrin and Metalloproteinase with Thrombospondin Motifs 1 and 5 (ADAMTS1 and ADAMTS5) proteases and to examine the effect of in vitro FSH supplementation on protease production in cultured Sertoli cells. The expression of metalloproteases, ADAMTS1, and ADAMTS5 were investigated in Sertoli cell cultures as well as in ejaculate of azoospermic men which then were compared with ejaculates of the fertile control group. A total of 15 azoospermic men, diagnosed as obstructive (OA, n = 5) and nonobstructive (NOA, n = 10) azoospermia were included in the study. ADAMTS1, ADAMTS5 and FSH receptors (FSHR) were found to be expressed 2.56, 2.10, and 2.66-fold less in Sertoli cells of NOA patients, than those of OA (p < 0.05). After rFSH was added onto Sertoli cell cultures of NOA patients, their expression did not increase significantly and did not reach to levels of control group. Evaluation of ejaculates revealed that the expression of ADAMTS1 and ADAMTS5 were insignificantly 1.03 and 1.1-fold higher in OA group (p > 0.05), respectively; however, in the NOA group, their expression were 1.70 and 1.96-fold lower, respectively, when compared with the fertile control group (p < 0.05) which was statistically significant. As a conclusion, the present study has revealed that insufficiency of ADAMTS1 and ADAMTS5 expression in Sertoli cells may have an important role in the etiology of male infertility. As expected due to low FSHR expression, rFSH response is impaired in NOA patients with relatively low ADAMTS expression response; therefore, such patients might hardly benefit from rFSH treatment. Further studies with larger cohorts may reveal ADAMTSs' potential use as a predictive marker for positive sperm retrieval in azoospermic patients who are scheduled to undergo testicular sperm extraction. Abbreviations: ADAM: A Disintegrin and Metalloproteinase; ADAMTS1 and ADAMTS5: A Disintegrin and Metalloproteinase with 10 Thrombospondin Motifs 1 and 5; ADAMTS: A Disintegrin and Metalloproteinase with Thrombospondin; ABP: androgen binding protein; CAMs: cell adhesion molecules; ECM: extracellular matrix; FSH: follicle stimulating hormone; FSHR: FSH receptors; HRP: horseradish peroxidase; MMP: matrix metalloproteinases; MP: metalloproteinases; NOA: nonobstructive azoospermia; OA: obstructive azoospermia; TIMP-1: tissue inhibitor of metalloproteinase-1.

Junctional adhesion molecule-A: functional diversity through molecular promiscuity

Cell adhesion molecules (CAMs) of the immunoglobulin superfamily (IgSF) regulate important processes such as cell proliferation, differentiation and morphogenesis. This activity is primarily due to their ability to initiate intracellular signaling cascades at cell-cell contact sites. Junctional adhesion molecule-A (JAM-A) is an IgSF-CAM with a short cytoplasmic tail that has no catalytic activity. Nevertheless, JAM-A is involved in a variety of biological processes. The functional diversity of JAM-A resides to a large part in a C-terminal PDZ domain binding motif which directly interacts with nine different PDZ domain-containing proteins. The molecular promiscuity of its PDZ domain motif allows JAM-A to recruit protein scaffolds to specific sites of cell-cell adhesion and to assemble signaling complexes at those sites. Here, we review the molecular characteristics of JAM-A, including its dimerization, its interaction with scaffolding proteins, and the phosphorylation of its cytoplasmic domain, and we describe how these characteristics translate into diverse biological activities.

Actin nucleator Spire 1 is a regulator of ectoplasmic specialization in the testis

Germ cell differentiation during the epithelial cycle of spermatogenesis is accompanied by extensive remodeling at the Sertoli cell-cell and Sertoli cell-spermatid interface to accommodate the transport of preleptotene spermatocytes and developing spermatids across the blood-testis barrier (BTB) and the adluminal compartment of the seminiferous epithelium, respectively. The unique cell junction in the testis is the actin-rich ectoplasmic specialization (ES) designated basal ES at the Sertoli cell-cell interface, and the apical ES at the Sertoli-spermatid interface. Since ES dynamics (i.e., disassembly, reassembly and stabilization) are supported by actin microfilaments, which rapidly converts between their bundled and unbundled/branched configuration to confer plasticity to the ES, it is logical to speculate that actin nucleation proteins play a crucial role to ES dynamics. Herein, we reported findings that Spire 1, an actin nucleator known to polymerize actins into long stretches of linear microfilaments in cells, is an important regulator of ES dynamics. Its knockdown by RNAi in Sertoli cells cultured in vitro was found to impede the Sertoli cell tight junction (TJ)-permeability barrier through changes in the organization of F-actin across Sertoli cell cytosol. Unexpectedly, Spire 1 knockdown also perturbed microtubule (MT) organization in Sertoli cells cultured in vitro. Biochemical studies using cultured Sertoli cells and specific F-actin vs. MT polymerization assays supported the notion that a transient loss of Spire 1 by RNAi disrupted Sertoli cell actin and MT polymerization and bundling activities. These findings in vitro were reproduced in studies in vivo by RNAi using Spire 1-specific siRNA duplexes to transfect testes with Polyplus in vivo-jetPEI as a transfection medium with high transfection efficiency. Spire 1 knockdown in the testis led to gross disruption of F-actin and MT organization across the seminiferous epithelium, thereby impeding the transport of spermatids and phagosomes across the epithelium and perturbing spermatogenesis. In summary, Spire 1 is an ES regulator to support germ cell development during spermatogenesis.

Essential roles of Akt/Snail pathway in microcystin-LR-induced tight junction toxicity in Sertoli cell

Microcystin (MC)-LR is a cyclic heptapeptide that acts as a potent reproductive system toxin. However, the underlying pathways of MCLR-induced reproductive system toxicity have not been well elucidated. The blood-testis barrier is mainly constituted by tight junctions (TJs) between adjacent Sertoli cells in the seminiferous epithelium near the basement membrane. The present study was designed to investigate changes in TJs and the underlying pathway in MC-LR-induced TJs toxicity in Sertoli cell. In our study, the transepithelial electrical resistance (TER) value was decreased in a dose dependent manner due to the markers of TJs occludin, claudin and zonula occludens-1 (ZO-1) expression decline. MC-LR is shown to induce cytotoxicity by inhibiting protein phosphatase 2A (PP2A) activity. Our results also showed that the PP2A activity presented a dose-dependent decline. Moreover, MC-LR stimulated protein expression of snail by Akt/GSK-3β activation. The activated Akt/GSK-3β and snail signaling pathway largely accounted for MC-LRinduced TJs toxicity, which could be partially reversed by snail siRNA interference or AKT chemical inhibitor in TM4 cells. These findings indicated that MC-LR inhibit the protein expression of TJs, and the activation of Akt/Snail signaling pathways due to PP2A inhibition is proposed to participate in this process.

Molecular Mechanisms and Signaling Pathways Involved in the Nutritional Support of Spermatogenesis by Sertoli Cells

Sertoli cells play a central role in spermatogenesis. They maintain the blood-testis barrier, an essential feature of seminiferous tubules which creates the proper environment for the occurrence of the spermatogenesis. However, this confinement renders germ cells almost exclusively dependent on Sertoli cells' nursing function and support. Throughout spermatogenesis, differentiating sperm cells become more specialized, and their biochemical machinery is insufficient to meet their metabolic demands. Although the needs are not the same at all differentiation stages, Sertoli cells are able to satisfy their needs. In order to maintain the seminiferous tubule energetic homeostasis, Sertoli cells react in response to several metabolic stimuli, through signaling cascades. The AMP-activated kinase, sensitive to the global energetic status; the hypoxia-inducible factors, sensitive to oxygen concentration; and the peroxisome proliferator-activated receptors, sensitive to fatty acid availability, are pathways already described in Sertoli cells. These cells' metabolism also reflects the whole-body metabolic dynamics. Metabolic diseases, including obesity and type II diabetes mellitus, induce changes that, both directly and indirectly, affect Sertoli cell function and, ultimately, (dys)function in male reproductive health. Insulin resistance, increased estrogen synthesis, vascular disease, and pubic fat accumulation are examples of metabolic-related conditions that affect male fertility potential. On the other hand, malnutrition can also induce negative effects on male sexual function. In this chapter, we review the molecular mechanisms associated with the nutritional state and male sexual (dys)function and the central role played by the Sertoli cells.

Preparation of Testicular Samples for Histology and Immunohistochemistry

One approach to visualize internal structures of the testis is histological sectioning of the material. The use of testicular samples allows a detailed analysis of the structure of both seminiferous tubules and the interstitial space. It is worth noting that key role in the control of germ cell development is assigned to Sertoli cells. Thus, in this chapter the special reference is made on visualization of Sertoli cells in the seminiferous epithelium in which they create a specialized microenvironment to support the germ cell development through the formation of the blood-testis barrier (BTB). The use of transmission electron microscopy (TEM) allows a deeper insight into the BTB morphology, especially the organization of the basal ectoplasmic specialization (ES) and coexisting intercellular junctions.Equally important, immunohistochemistry (IHC) is an appropriate technique to detect the localization of various proteins in paraffin-embedded and fixed tissues, i.e. testicular samples. A proper fixation allows to stabilize structure of the seminiferous tubules and preserve cells against irreversible damage. As such localization of various junction proteins connecting adjoined Sertoli cells and present in germ cell-Sertoli cell interfaces is possible. Also immunofluorescence (IF) is helpful to detect the distribution and relative abundance of the junctional proteins, while immunocytochemistry (ICC) is a valuable technique to show a protein distribution within a single cell (e.g. in Sertoli cell culture).

T-2 toxin induces cytotoxicity and disrupts tight junction barrier in SerW3 cells

T-2 toxin, which is produced in grain and grain products as a secondary metabolite by Fusarium species, is also potentially dangerous for human health. Up to date, no study was reported the cytotoxicity of T-2 toxin on SerW3 cells in the perspective of junctional barriers. This study focused on revealing the cytotoxic effects of T-2 on Sertoli cells associated with cell junctional barriers. In the present study, SerW3 cells were exposed to T-2 toxin at 12, 120 and 1200ng/ml doses for 24 and 48h. Cytotoxicity tests including cell viability (MTT), lactate dehydrogenase (LDH) cytotoxicity test and trypan blue exclusion assay were performed. Occludin, ZO-1, N-cadherin and β-catenin were immunolabelled, expressions of occludin and N-cadherin were determined by western blotting. SerW3 cell barrier integrity was measured by transepithelial electrical resistance (TEER). Cytotoxicity caused by T-2 toxin increased in a dose dependent manner, expressions of proteins and TEER measurement decreased. This study may underlie the early targets of T-2 toxin on SerW3 cells mimicking blood-testis barrier in vitro.

Regulation of cell polarity by cell adhesion receptors

The ability of cells to polarize is an intrinsic property of almost all cells and is required for the devlopment of most multicellular organisms. To develop cell polarity, cells integrate various signals derived from intrinsic as well as extrinsic sources. In the recent years, cell-cell adhesion receptors have turned out as important regulators of cellular polarization. By interacting with conserved cell polarity proteins, they regulate the recruitment of polarity complexes to specific sites of cell-cell adhesion. By initiating intracellular signaling cascades at those sites, they trigger their specific subcellular activation. Not surprisingly, cell-cell adhesion receptors regulate diverse aspects of cell polarity, including apico-basal polarity in epithelial and endothelial cells, front-to-rear polarity in collectively migrating cells, and planar cell polarity during organ development. Here, we review the recent developments highlighting the central roles of cell-cell adhesion molecules in the development of cell polarity.

Signaling pathways regulating blood-tissue barriers - Lesson from the testis

Signaling pathways that regulate blood-tissue barriers are important for studying the biology of various blood-tissue barriers. This information, if deciphered and better understood, will provide better therapeutic management of diseases particularly in organs that are sealed by the corresponding blood-tissue barriers from systemic circulation, such as the brain and the testis. These barriers block the access of antibiotics and/or chemotherapeutical agents across the corresponding barriers. Studies in the last decade using the blood-testis barrier (BTB) in rats have demonstrated the presence of several signaling pathways that are crucial to modulate BTB function. Herein, we critically evaluate these findings and provide hypothetical models regarding the underlying mechanisms by which these signaling molecules/pathways modulate BTB dynamics. This information should be carefully evaluated to examine their applicability in other tissue barriers which shall benefit future functional studies in the field. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

TSSK6 is required for γH2AX formation and the histone-to-protamine transition during spermiogenesis

Spermiogenesis includes transcriptional silencing, chromatin condensation and extensive morphological changes as spermatids transform into sperm. Chromatin condensation involves histone hyperacetylation, transitory DNA breaks, histone H2AX (also known as H2AFX) phosphorylation at Ser139 (γH2AX), and replacement of histones by protamines. Previously, we have reported that the spermatid protein kinase TSSK6 is essential for fertility in mice, but its specific role in spermiogenesis is unknown. Here, we show that TSSK6 expression is spatiotemporally coincident with γH2AX formation in the nuclei of developing mouse spermatids. RNA-sequencing analysis demonstrates that genetic ablation of Tssk6 does not impact gene expression or silencing in spermatids. However, loss of TSSK6 blocks γH2AX formation, even though the timing and level of the transient DNA breaks is unaltered. Further, Tssk6-knockout sperm contained increased levels of histones H3 and H4, and protamine 2 precursor and intermediate(s) indicative of a defective histone-to-protamine transition. These results demonstrate that TSSK6 is required for γH2AX formation during spermiogenesis, and also link γH2AX to the histone-to-protamine transition and male fertility.

Basement Membrane Laminin α2 Regulation of BTB Dynamics via Its Effects on F-Actin and Microtubule Cytoskeletons Is Mediated Through mTORC1 Signaling

A local axis connects the apical ectoplasmic specialization (ES) at the Sertoli-spermatid interface, the basal ES at the blood-testis barrier (BTB), and the basement membrane across the seminiferous epithelium functionally in rat testes. As such, cellular events that take place simultaneously across the epithelium such as spermiation and BTB remodeling that occur at the apical ES and the basal ES, respectively, at stage VIII of the cycle are coordinated. Herein, laminin α2, a structural component of the basement membrane, was found to regulate BTB dynamics. Sertoli cells were cultured in vitro to allow the establishment of a tight junction (TJ) barrier that mimicked the BTB in vivo. Knockdown of laminin α2 by transfecting Sertoli cells with laminin α2-specific short hairpin RNA vs the nontargeting negative control was shown to perturb the Sertoli cell TJ barrier, illustrating laminin α2 was involved in regulating BTB dynamics. This regulatory effect was mediated through mammalian target of rapamycin complex 1 (mTORC1) signaling because the two mTORC1 downstream signaling molecules ribosomal protein S6 and Akt1/2 were activated and inactivated, respectively, consistent with earlier findings that mTORC1 is involved in promoting BTB remodeling. Also, laminin α2 knockdown induced F-actin and microtubule (MT) disorganization through changes in the spatial expression of F-actin regulators actin-related protein 3 and epidermal growth factor receptor pathway substrate 8 vs end-binding protein 1 (a MT plus-end tracking protein, +TIP). These laminin α2 knockdown-mediated effects on F-actin and MT organization was blocked by exposing Sertoli cells to rapamycin, an inhibitor of mTORC1 signaling, and also SC79, an activator of Akt. In summary, laminin α2-mediated regulation on Sertoli cell BTB dynamics is through mTORC1 signaling.

Toxic effects of TiO2 nanoparticles in primary cultured rat sertoli cells are mediated via a dysregulated Ca2+ /PKC/p38 MAPK/NF-κB cascade

Although numerous studies have demonstrated that titanium dioxide nanoparticles (TiO₂ NPs) can be accumulated in various animal organs and can cause toxicity, there is currently only limited data regarding reproductive toxicity especially on the toxic mechanisms of TiO₂ NPs in Sertoli cells. In order to investigate the mechanism of reproductive toxicity, primary cultured rat Sertoli cells were exposed to 5, 15, or 30 μg/mL TiO₂ NPs for 24 h, and TiO₂ NPs internalization, expression of PKC (p-PKC) and p38 MAPK (p-p38 MAPK) as well as calcium homeostasis were examined. Our findings demonstrated that TiO₂ NPs crossed the membrane into the cytoplasm or nucleus, and significantly suppressed cell viability of primary cultured rat Sertoli cells in a concentration-dependent manner. Furthermore, immunological dysfunction caused by TiO₂ NPs was involved in the increased expression of NF-κB, TNF-α, and IL-1β, and decreased IκB expression. TiO₂ NPs significantly decreased Ca²⁺ -ATPase and Ca²⁺ /Mg²⁺ -ATPase activity and enhanced intracellular Ca²⁺ levels, and up-regulated the expression of p-PKC and p-p38 MAPK in a dose-dependent manner in primary cultured rat Sertoli cells. Taken together, these findings indicate that TiO₂ NPs may induce immunological dysfunction of primary cultured rat Sertoli cells by stimulating the Ca²⁺ /PKC/p38 MAPK cascade, which triggers NF-κB activation and ultimately induces the expression of inflammatory cytokines in primary cultured rat Sertoli cells. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1374-1382, 2017.

Beneficial effects of quercetin on titanium dioxide nanoparticles induced spermatogenesis defects in mice

Many recent studies have demonstrated that most nanoparticles (NPs) have an adverse or toxic action on male germ cells. In present study, protective effect of quercetin (Que) on titanium dioxide nanoparticle (NTiO₂)-induced spermatogenesis defects in mice was investigated. Thirty-two Naval Medical Research Institute (NMRI) mice were randomly divided into four groups. Que group received 75 mg/kg of Que for 42 days. NTiO₂ group received 300 mg/kg NTiO₂ for 35 days. NTiO₂ + Que group initially received 75 mg/kg Que for 7 days and was followed by concomitant administration of 300 mg/kg NTiO₂ for 35 days. Control group received only normal saline for 42 days. Sperm parameters, testosterone concentration, histological criteria, and apoptotic index were assessed. Product of lipid peroxidation (MDA), superoxide dismutase (SOD), and catalase (CAT) activities were also evaluated for oxidative stress in testicular tissue. Administration of NTiO₂ significantly induced histological changes in testicular tissue; increased apoptotic index; and decreased testicular weight, testosterone concentration, and sperm quality (p < 0.01). In the testis, NTiO₂ increased oxidative stress through an increase in lipid peroxidation and a decrease in SOD and CAT activities (p < 0.05). Que pretreatment could significantly attenuate testicular weight; apoptotic index; and histological criteria including vacuolization, detachment, and sloughing of germ cells in seminiferous tubules. Serum and tissue testosterone levels were significantly increased in Que-pretreated mice (p < 0.01). Sperm parameters including sperm number, motility, and percentage of abnormality were also effectively improved by Que pretreatment (p < 0.01). Pretreatment of Que significantly ameliorated oxidative stress and increased the activities of SOD and CAT in testicular tissue. These results indicate that sperm production can be increased by Que pretreatment in NTiO₂-intoxicated mice. The improved sperm quality and reverse testis histology by Que pretreatment may be a consequence of elevation testosterone concentration, reduction in germ cell apoptosis, and suppression of oxidative stress in testicular tissue.

Drebrin and Spermatogenesis

Drebrin is a family of actin-binding proteins with two known members called drebrin A and E. Apart from the ability to stabilize F-actin microfilaments via their actin-binding domains near the N-terminus, drebrin also regulates multiple cellular functions due to its unique ability to recruit multiple binding partners to a specific cellular domain, such as the seminiferous epithelium during the epithelial cycle of spermatogenesis. Recent studies have illustrated the role of drebrin E in the testis during spermatogenesis in particular via its ability to recruit branched actin polymerization protein known as actin-related protein 3 (Arp3), illustrating its involvement in modifying the organization of actin microfilaments at the ectoplasmic specialization (ES) which includes the testis-specific anchoring junction at the Sertoli-spermatid (apical ES) interface and at the Sertoli cell-cell (basal ES) interface. These data are carefully evaluated in light of other recent findings herein regarding the role of drebrin in actin filament organization at the ES. We also provide the hypothetical model regarding its involvement in germ cell transport during the epithelial cycle in the seminiferous epithelium to support spermatogenesis.

Effects of Morinda officinalis Polysaccharide on Experimental Varicocele Rats

Morinda officinalis is a traditional Chinese herbal medicine, which has been used to tonify the kidney and strengthen yang for a long time in China. In this study, the effects of M. officinalis Polysaccharide (MOP) on experimental varicocele adolescent rats were investigated. The result showed that varicocele destroyed the structure of the seminiferous epithelium and decreased the TJ protein expression (Occludin, Claudin-11, and ZO-1), testosterone (T) concentration in the left testicular tissue and serum, and serum levels of inhibin B (INHB), while increasing the levels of cytokines (TGF-β3 and TNF-α) in the left testicular tissue, as well as serum levels of gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and antisperm antibody (AsAb). MOP repaired the damaged seminiferous epithelium and TJ and reduced the levels of cytokines (TGF-β3 and TNF-α) as well as serum levels of GnRH, FSH, LH, and AsAb, while upregulating TJ protein expression, T level in the left testicular tissue and serum, and serum INHB levels. In summary, we conclude that MOP promotes spermatogenesis and counteracts the varicocele-induced damage to the seminiferous epithelium and TJ, probably via decreasing cytokines (TGF-β3 and TNF-α) levels and regulating the abnormal sex hormones levels in experimental varicocele rats.

MiRNA-133b promotes the proliferation of human Sertoli cells through targeting GLI3

Sertoli cells play critical roles in regulating spermatogenesis and they can be reprogrammed to the cells of other lineages, highlighting that they have significant applications in reproductive and regenerative medicine. The fate determinations of Sertoli cells are regulated precisely by epigenetic factors. However, the expression, roles, and targets of microRNA (miRNA) in human Sertoli cells remain unknown. Here we have for the first time revealed that 174 miRNAs were distinctly expressed in human Sertoli cells between Sertoli-cell-only syndrome (SCOS) patients and obstructive azoospermia (OA) patients with normal spermatogenesis using miRNA microarrays and real time PCR, suggesting that these miRNAs may be associated with the pathogenesis of SCOS. MiR-133b is upregulated in Sertoli cells of SCOS patients compared to OA patients. Proliferation assays with miRNA mimics and inhibitors showed that miR-133b enhanced the proliferation of human Sertoli cells. Moreover, we demonstrated that GLI3 was a direct target of miR-133b and the expression of Cyclin B1 and Cyclin D1 was enhanced by miR-133b mimics but decreased by its inhibitors. Gene silencing of GLI3 using RNA inference stimulated the growth of human Sertoli cells. Collectively, miR-133b promoted the proliferation of human Sertoli cells by targeting GLI3. This study thus sheds novel insights into epigenetic regulation of human Sertoli cells and the etiology of azoospermia and offers new targets for treating male infertility

Transport of germ cells across the seminiferous epithelium during spermatogenesis-the involvement of both actin- and microtubule-based cytoskeletons

The transport of germ cells from the base of the seminiferous epithelium toward the luminal edge of the tubule lumen in the adluminal compartment during the epithelial cycle is an essential cellular event to support spermatogenesis. Thus, fully developed elongated spermatids (i.e., spermatozoa) can be released at spermiation in late stage VIII in rodents versus late stage II in humans. Earlier studies to examine the molecular mechanism(s) that support germ cell transport, most notably the transport of preleptotene spermatocytes across the blood-testis barrier (BTB), and the transport of elongating spermatids across the adluminal compartment during spermiogenesis, is focused on the adhesion protein complexes at the cell-cell interface. It is generally accepted that cell junctions at the Sertoli cell-cell interface at the BTB, including the actin-based tight junction (TJ), basal ectoplasmic specialization (basal ES, a testis-specific adherens junction) and gap junction (GJ), as well as the intermediate filament-based desmosome undergo constant remodeling to accommodate the transport of preleptotene spermatocytes across the barrier. On the other hand, similar junction dynamics (i.e., disassembly, reassembly and stabilization/maintenance) take place at the Sertoli-spermatid interface. Emerging evidence has shown that junction dynamics at the Sertoli cell-cell vs. Sertoli-germ cell interface are supported by the 2 intriguingly coordinated cytoskeletons, namely the F-actin- and microtubule (MT)-based cytoskeletons. Herein, we provide a brief summary and critically evaluate the recent findings. We also provide an updated hypothetical concept regarding germ cell transport in the testis utilizing the MT-conferred tracks and the MT-specific motor proteins. Furthermore, this cellular event is also supported by the F-actin-based cytoskeleton.

Distinct purinergic signaling pathways in prepubescent mouse spermatogonia

Spermatogenesis ranks among the most complex, yet least understood, developmental processes. The physiological principles that control male germ cell development in mammals are notoriously difficult to unravel, given the intricate anatomy and complex endo- and paracrinology of the testis. Accordingly, we lack a conceptual understanding of the basic signaling mechanisms within the testis, which control the seminiferous epithelial cycle and thus govern spermatogenesis. Here, we address paracrine signal transduction in undifferentiated male germ cells from an electrophysiological perspective. We identify distinct purinergic signaling pathways in prepubescent mouse spermatogonia, both in vitro and in situ. ATP-a dynamic, widespread, and evolutionary conserved mediator of cell to cell communication in various developmental contexts-activates at least two different spermatogonial purinoceptor isoforms. Both receptors operate within nonoverlapping stimulus concentration ranges, display distinct response kinetics and, in the juvenile seminiferous cord, are uniquely expressed in spermatogonia. We further find that spermatogonia express Ca(2+)-activated large-conductance K(+) channels that appear to function as a safeguard against prolonged ATP-dependent depolarization. Quantitative purine measurements additionally suggest testicular ATP-induced ATP release, a mechanism that could increase the paracrine radius of initially localized signaling events. Moreover, we establish a novel seminiferous tubule slice preparation that allows targeted electrophysiological recordings from identified testicular cell types in an intact epithelial environment. This unique approach not only confirms our in vitro findings, but also supports the notion of purinergic signaling during the early stages of spermatogenesis.

Does cell polarity matter during spermatogenesis?

Cell polarity is crucial to development since apico-basal polarity conferred by the 3 polarity protein modules (or complexes) is essential during embryogenesis, namely the Par (partition defective)-, the CRB (Crumbs)-, and the Scribble-based polarity protein modules. While these protein complexes and their component proteins have been extensively studied in Drosophila and C. elegans and also other mammalian tissues and/or cells, their presence and physiological significance in the testis remain unexplored until the first paper on the Par-based protein published in 2008. Since then, the Par-, the Scribble- and the CRB-based protein complexes and their component proteins in the testis have been studied. These proteins are known to confer Sertoli and spermatid polarity in the seminiferous epithelium, and they are also integrated components of the tight junction (TJ) and the basal ectoplasmic specialization (ES) at the Sertoli cell-cell interface near the basement membrane, which in turn constitute the blood-testis barrier (BTB). These proteins are also found at the apical ES at the Sertoli-spermatid interface. Thus, these polarity proteins also play a significant role in regulating Sertoli and spermatid adhesion in the testis through their actions on actin-based cytoskeletal function. Recent studies have shown that these polarity proteins are having antagonistic effects on the BTB integrity in which the Par6- and CRB3-based polarity complexes promotes the integrity of the Sertoli cell TJ-permeability barrier, whereas the Scribble-based complex promotes restructuring/remodeling of the Sertoli TJ-barrier function. Herein, we carefully evaluate these findings and provide a hypothetic model regarding their role in the testis in the context of the functions of these polarity proteins in other epithelia, so that better experiments can be designed in future studies to explore their significance in spermatogenesis.

From the Cover: Sperm Molecular Biomarkers Are Sensitive Indicators of Testicular Injury following Subchronic Model Toxicant Exposure

Traditional testis histopathology endpoints remain the gold standard for evaluating testicular insult and injury in a non-clinical setting, but are invasive and unfeasible for monitoring these effects clinically in humans. Assessing testicular injury in humans relies on semen and serum hormone analyses, both of which are insensitive and poor indicators of effect. Therefore, we hypothesized that sperm messenger RNA (mRNA) transcripts and DNA methylation marks can be used as translatable and sensitive indicators or testicular injury. Dose-response studies using adult male Fischer 344 rats subchronically exposed to model Sertoli cell toxicants (0.14, 0.21, and 0.33% 2,5-hexanedione, and 30, 50, and 70 mg/kg/day carbendazim), and a model germ cell toxicant (1.4, 3.4, and 5.1 mg/kg/day cyclophosphamide) for 3 months were evaluated for testicular injury by traditional histopathological endpoints, changes in sperm mRNA transcript levels using custom PCR arrays, and alterations in sperm DNA methylation via reduced representation bisulfite sequencing. Testis histopathological evaluation and PCR array analysis of the sperm transcriptome identified dose-dependent changes elicited by toxicant exposure (P < 0.05). Global sperm DNA methylation analysis of subchronic 0.33% 2,5-hexandione and 5.1 mg/kg/day cyclophosphamide exposure using a Monte Carlo approach did not identify differentially methylated regions (methylation difference > 10% and q < 0.05) with robust signatures. Overall, these results suggest that sperm mRNA transcripts are sensitive indicators of low dose toxicant-induced testicular injury in the rat, while sperm DNA methylation changes are not. Additionally, the Monte Carlo analysis is a powerful approach that can be used to assess the robustness of signals resulting from -omic studies.

Rescue of perfluorooctanesulfonate (PFOS)-mediated Sertoli cell injury by overexpression of gap junction protein connexin 43

Perfluorooctanesulfonate (PFOS) is an environmental toxicant used in developing countries, including China, as a stain repellent for clothing, carpets and draperies, but it has been banned in the U.S. and Canada since the late 2000s. PFOS perturbed the Sertoli cell tight junction (TJ)-permeability barrier, causing disruption of actin microfilaments in cell cytosol, perturbing the localization of cell junction proteins (e.g., occluden-ZO-1, N-cadherin-ß-catenin). These changes destabilized Sertoli cell blood-testis barrier (BTB) integrity. These findings suggest that human exposure to PFOS might induce BTB dysfunction and infertility. Interestingly, PFOS-induced Sertoli cell injury associated with a down-regulation of the gap junction (GJ) protein connexin43 (Cx43). We next investigated if overexpression of Cx43 in Sertoli cells could rescue the PFOS-induced cell injury. Indeed, overexpression of Cx43 in Sertoli cells with an established TJ-barrier blocked the disruption in PFOS-induced GJ-intercellular communication, resulting in the re-organization of actin microfilaments, which rendered them similar to those in control cells. Furthermore, cell adhesion proteins that utilized F-actin for attachment became properly distributed at the cell-cell interface, resealing the disrupted TJ-barrier. In summary, Cx43 is a good target that might be used to manage PFOS-induced reproductive dysfunction.

Polarity protein Crumbs homolog-3 (CRB3) regulates ectoplasmic specialization dynamics through its action on F-actin organization in Sertoli cells

Crumbs homolog 3 (or Crumbs3, CRB3) is a polarity protein expressed by Sertoli and germ cells at the basal compartment in the seminiferous epithelium. CRB3 also expressed at the blood-testis barrier (BTB), co-localized with F-actin, TJ proteins occludin/ZO-1 and basal ES (ectoplasmic specialization) proteins N-cadherin/β-catenin at stages IV-VII only. The binding partners of CRB3 in the testis were the branched actin polymerization protein Arp3, and the barbed end-capping and bundling protein Eps8, illustrating its possible role in actin organization. CRB3 knockdown (KD) by RNAi in Sertoli cells with an established tight junction (TJ)-permeability barrier perturbed the TJ-barrier via changes in the distribution of TJ- and basal ES-proteins at the cell-cell interface. These changes were the result of CRB3 KD-induced re-organization of actin microfilaments, in which actin microfilaments were truncated, and extensively branched, thereby destabilizing F-actin-based adhesion protein complexes at the BTB. Using Polyplus in vivo-jetPEI as a transfection medium with high efficiency for CRB3 KD in the testis, the CRB3 KD testes displayed defects in spermatid and phagosome transport, and also spermatid polarity due to a disruption of F-actin organization. In summary, CRB3 is an actin microfilament regulator, playing a pivotal role in organizing actin filament bundles at the ES.

Overexpression of plastin 3 in Sertoli cells disrupts actin microfilament bundle homeostasis and perturbs the tight junction barrier

Throughout the epithelial cycle of spermatogenesis, actin microfilaments arranged as bundles near the Sertoli cell plasma membrane at the Sertoli cell-cell interface that constitute the blood-testis barrier (BTB) undergo extensive re-organization by converting between bundled and unbundled/branched configuration to give plasticity to the F-actin network. This is crucial to accommodate the transport of preleptotene spermatocytes across the BTB. Herein, we sought to examine changes in the actin microfilament organization at the Sertoli cell BTB using an in vitro model since Sertoli cells cultured in vitro is known to establish a functional tight junction (TJ)-permeability barrier that mimics the BTB in vivo. Plastin 3, a known actin microfilament cross-linker and bundling protein, when overexpressed in Sertoli cells using a mammalian expression vector pCI-neo was found to perturb the Sertoli cell TJ-barrier function even though its overexpression increased the overall actin bundling activity in these cells. Furthermore, plastin 3 overexpression also perturbed the localization and distribution of BTB-associated proteins, such as occludin-ZO1 and N-cadherin-β-catenin, this thus destabilized the barrier function. Collectively, these data illustrate that a delicate balance of actin microfilaments between organized in bundles vs. an unbundled/branched configuration is crucial to confer the homeostasis of the BTB and its integrity.

GATA4 Regulates Blood-Testis Barrier Function and Lactate Metabolism in Mouse Sertoli Cells

Conditional deletion of Gata4 in Sertoli cells (SCs) of adult mice has been shown to increase permeability of the blood-testis barrier (BTB) and disrupt spermatogenesis. To gain insight into the molecular underpinnings of these phenotypic abnormalities, we assessed the impact of Gata4 gene silencing in cell culture models. Microarray hybridization identified genes dysregulated by siRNA-mediated inhibition of Gata4 in TM4 cells, an immortalized mouse SC line. Differentially expressed genes were validated by quantitative RT-PCR analysis of primary cultures of Gata4(flox/flox) mouse SCs that had been subjected to cre-mediated recombination in vitro. Depletion of GATA4 in TM4 cells and primary SCs was associated with altered expression of genes involved in key facets of BTB maintenance, including tight/adherens junction formation (Tjp1, Cldn12, Vcl, Tnc, Csk) and extracellular matrix reorganization (Lamc1, Col4a1, Col4a5, Mmp10, Mmp23, Timp2). Western blotting and immunocytochemistry demonstrated reduced levels of tight junction protein-1, a prototypical tight junction protein, in GATA4-depleted cells. These changes were accompanied by a loss of morphologically recognizable junctional complexes and a decline in epithelial membrane resistance. Furthermore, Gata4 gene silencing was associated with altered expression of Hk1, Gpi1, Pfkp, Pgam1, Gls2, Pdk3, Pkd4, and Ldhb, genes regulating the production of lactate, a key nutrient that SCs provide to developing germ cells. Comprehensive metabolomic profiling demonstrated impaired lactate production in GATA4-deficient SCs. We conclude that GATA4 plays a pivotal role in the regulation of BTB function and lactate metabolism in mouse SCs.

Ezrin: a regulator of actin microfilaments in cell junctions of the rat testis

Ezrin, radixin, moesin and merlin (ERM) proteins are highly homologous actin-binding proteins that share extensive sequence similarity with each other. These proteins tether integral membrane proteins and their cytoplasmic peripheral proteins (e.g., adaptors, nonreceptor protein kinases and phosphatases) to the microfilaments of actin-based cytoskeleton. Thus, these proteins are crucial to confer integrity of the apical membrane domain and its associated junctional complex, namely the tight junction and the adherens junction. Since ectoplasmic specialization (ES) is an F-actin-rich testis-specific anchoring junction-a highly dynamic ultrastructure in the seminiferous epithelium due to continuous transport of germ cells, in particular spermatids, across the epithelium during the epithelial cycle-it is conceivable that ERM proteins are playing an active role in these events. Although these proteins were first reported almost 25 years and have since been extensively studied in multiple epithelia/endothelia, few reports are found in the literature to examine their role in the actin filament bundles at the ES. Studies have shown that ezrin is also a constituent protein of the actin-based tunneling nanotubes (TNT) also known as intercellular bridges, which are transient cytoplasmic tubular ultrastructures that transport signals, molecules and even organelles between adjacent and distant cells in an epithelium to coordinate cell events that occur across an epithelium. Herein, we critically evaluate recent data on ERM in light of recent findings in the field in particular ezrin regarding its role in actin dynamics at the ES in the testis, illustrating additional studies are warranted to examine its physiological significance in spermatogenesis.

Autophagy is required for ectoplasmic specialization assembly in sertoli cells

The ectoplasmic specialization (ES) is essential for Sertoli-germ cell communication to support all phases of germ cell development and maturity. Its formation and remodeling requires rapid reorganization of the cytoskeleton. However, the molecular mechanism underlying the regulation of ES assembly is still largely unknown. Here, we show that Sertoli cell-specific disruption of autophagy influenced male mouse fertility due to the resulting disorganized seminiferous tubules and spermatozoa with malformed heads. In autophagy-deficient mouse testes, cytoskeleton structures were disordered and ES assembly was disrupted. The disorganization of the cytoskeleton structures might be caused by the accumulation of a negative cytoskeleton organization regulator, PDLIM1, and these defects could be partially rescued by Pdlim1 knockdown in autophagy-deficient Sertoli cells. Altogether, our works reveal that the degradation of PDLIM1 by autophagy in Sertoli cells is important for the proper assembly of the ES, and these findings define a novel role for autophagy in Sertoli cell-germ cell communication.

The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Prenatal and lactation nicotine exposure affects Sertoli cell and gonadotropin levels in rats

Nicotine is largely consumed in the world as a component of cigarettes. It can cross the placenta and reach the milk of smoking mothers. This drug induces apoptosis, affects sex hormone secretion, and leads to male infertility. To investigate the exposure to nicotine during the whole intrauterine and lactation phases in Sertoli cells, pregnant rats received nicotine (2 mg/kg per day) through osmotic minipumps. Male offsprings (30, 60, and 90 days old) had blood collected for hormonal analysis (FSH and LH) and their testes submitted for histophatological study, analysis of the frequency of the stages of seminiferous epithelium cycle, immunolabeling of apoptotic epithelial cells (TUNEL and Fas/FasL), analysis of the function and structure of Sertoli cells (respectively using transferrin and vimentin immunolabeling), and analysis of Sertoli-germ cell junctional molecule (β-catenin immunolabeling). The exposure to nicotine increased the FSH and LH plasmatic levels in adult rats. Although nicotine had not changed the number of apoptotic cells, neither in Fas nor FasL expression, it provoked an intense sloughing of epithelial cells and also altered the frequency of some stages of the seminiferous epithelium cycle. Transferrin and β-catenin expressions were not changed, but vimentin was significantly reduced in the early stages of the seminiferous cycle of the nicotine-exposed adult rats. Thus, we concluded that nicotine exposure during all gestational and lactation periods affects the structure of Sertoli cells by events causing intense germ cell sloughing observed in the tubular lumen and can compromise the fertility of the offspring.

Step-specific Sorting of Mouse Spermatids by Flow Cytometry

The differentiation of mouse spermatids is one critical process for the production of a functional male gamete with an intact genome to be transmitted to the next generation. So far, molecular studies of this morphological transition have been hampered by the lack of a method allowing adequate separation of these important steps of spermatid differentiation for subsequent analyses. Earlier attempts at proper gating of these cells using flow cytometry may have been difficult because of a peculiar increase in DNA fluorescence in spermatids undergoing chromatin remodeling. Based on this observation, we provide details of a simple flow cytometry scheme, allowing reproducible purification of four populations of mouse spermatids fixed with ethanol, each representing a different state in the nuclear remodeling process. Population enrichment is confirmed using step-specific markers and morphological criterions. The purified spermatids can be used for genomic and proteomic analyses.

AKAP9, a Regulator of Microtubule Dynamics, Contributes to Blood-Testis Barrier Function

The blood-testis barrier (BTB), formed between adjacent Sertoli cells, undergoes extensive remodeling to facilitate the transport of preleptotene spermatocytes across the barrier from the basal to apical compartments of the seminiferous tubules for further development and maturation into spermatozoa. The actin cytoskeleton serves unique structural and supporting roles in this process, but little is known about the role of microtubules and their regulators during BTB restructuring. The large isoform of the cAMP-responsive scaffold protein AKAP9 regulates microtubule dynamics and nucleation at the Golgi. We found that conditional deletion of Akap9 in mice after the initial formation of the BTB at puberty leads to infertility. Akap9 deletion results in marked alterations in the organization of microtubules in Sertoli cells and a loss of barrier integrity despite a relatively intact, albeit more apically localized F-actin and BTB tight junctional proteins. These changes are accompanied by a loss of haploid spermatids due to impeded meiosis. The barrier, however, progressively reseals in older Akap9 null mice, which correlates with a reduction in germ cell apoptosis and a greater incidence of meiosis. However, spermiogenesis remains defective, suggesting additional roles for AKAP9 in this process. Together, our data suggest that AKAP9 and, by inference, the regulation of the microtubule network are critical for BTB function and subsequent germ cell development during spermatogenesis.

Regulation of blood-testis barrier by actin binding proteins and protein kinases

The blood-testis barrier (BTB) is an important ultrastructure in the testis, since the onset of meiosis and spermiogenesis coincides with the establishment of a functional barrier in rodents and humans. It is also noted that a delay in the assembly of a functional BTB following treatment of neonatal rats with drugs such as diethylstilbestrol or adjudin also delays the first wave of spermiation. While the BTB is one of the tightest blood-tissue barriers, it undergoes extensive remodeling, in particular, at stage VIII of the epithelial cycle to facilitate the transport of preleptotene spermatocytes connected in clones across the immunological barrier. Without this timely transport of preleptotene spermatocytes derived from type B spermatogonia, meiosis will be arrested, causing aspermatogenesis. Yet the biology and regulation of the BTB remains largely unexplored since the morphological studies in the 1970s. Recent studies, however, have shed new light on the biology of the BTB. Herein, we critically evaluate some of these findings, illustrating that the Sertoli cell BTB is regulated by actin-binding proteins (ABPs), likely supported by non-receptor protein kinases, to modulate the organization of actin microfilament bundles at the site. Furthermore, microtubule-based cytoskeleton is also working in concert with the actin-based cytoskeleton to confer BTB dynamics. This timely review provides an update on the unique biology and regulation of the BTB based on the latest findings in the field, focusing on the role of ABPs and non-receptor protein kinases.

Formin 1 Regulates Ectoplasmic Specialization in the Rat Testis Through Its Actin Nucleation and Bundling Activity

During spermatogenesis, developing spermatids and preleptotene spermatocytes are transported across the adluminal compartment and the blood-testis barrier (BTB), respectively, so that spermatids line up near the luminal edge to prepare for spermiation, whereas preleptotene spermatocytes enter the adluminal compartment to differentiate into late spermatocytes to prepare for meiosis I/II. These cellular events involve actin microfilament reorganization at the testis-specific, actin-rich Sertoli-spermatid and Sertoli-Sertoli cell junction called apical and basal ectoplasmic specialization (ES). Formin 1, an actin nucleation protein known to promote actin microfilament elongation and bundling, was expressed at the apical ES but limited to stage VII of the epithelial cycle, whereas its expression at the basal ES/BTB stretched from stage III to stage VI, diminished in stage VII, and was undetectable in stage VIII tubules. Using an in vitro model of studying Sertoli cell BTB function by RNA interference and biochemical assays to monitor actin bundling and polymerization activity, a knockdown of formin 1 in Sertoli cells by approximately 70% impeded the tight junction-permeability function. This disruptive effect on the tight junction barrier was mediated by a loss of actin microfilament bundling and actin polymerization capability mediated by changes in the localization of branched actin-inducing protein Arp3 (actin-related protein 3), and actin bundling proteins Eps8 (epidermal growth factor receptor pathway substrate 8) and palladin, thereby disrupting cell adhesion. Formin 1 knockdown in vivo was found to impede spermatid adhesion, transport, and polarity, causing defects in spermiation in which elongated spermatids remained embedded into the epithelium in stage IX tubules, mediated by changes in the spatiotemporal expression of Arp3, Eps8, and palladin. In summary, formin 1 is a regulator of ES dynamics.

Obif, a Transmembrane Protein, Is Required for Bone Mineralization and Spermatogenesis in Mice

BACKGROUND

Various kinds of transmembrane and secreted proteins play pivotal roles in development through cell-cell communication. We previously reported that Obif (Osteoblast induction factor, Tmem119), encoding a single transmembrane protein, is expressed in differentiating osteoblasts, and that Obif-/- mice exhibit significantly reduced bone volume in the femur. In the current study, we characterized the Obif protein and further investigated the biological phenotypes of a variety of tissues in Obif-/- mice.

RESULTS

First, we found that O-glycosylation of the Obif protein occurs at serine residue 36 in the Obif extracellular domain. Next, we observed that Obif-/- mice exhibit bone dysplasia in association with significantly increased osteoid volume per osteoid surface (OV/OS) and osteoid maturation time (Omt), and significantly decreased mineral apposition rate (MAR) and bone formation rate per bone surface (BFR/BS). In addition, we observed that Obif-/- mice show a significant decrease in testis weight as well as in sperm number. By histological analysis, we found that Obif is expressed in spermatocytes and spermatids in the developing testis and that spermatogenesis is halted at the round spermatid stage in the Obif-/- testis that lacks sperm. However, the number of litters fathered by male mice was slightly reduced in Obif-/- mice compared with wild-type mice, although this was not statistically significant.

CONCLUSIONS

Our results, taken together with previous observations, indicate that Obif is a type Ia transmembrane protein whose N-terminal region is O-glycosylated. In addition, we found that Obif is required for normal bone mineralization and late testicular differentiation in vivo. These findings suggest that Obif plays essential roles in the development of multiple tissues.

FH535 inhibited metastasis and growth of pancreatic cancer cells

FH535 is a small-molecule inhibitor of the Wnt/β-catenin signaling pathway, which a substantial body of evidence has proven is activated in various cancers, including pancreatic cancer. Activation of the Wnt/β-catenin pathway plays an important role in tumor progression and metastasis. We investigated the inhibitory effect of FH535 on the metastasis and growth of pancreatic cancer cells. Western blotting and luciferase reporter gene assay indicated that FH535 markedly inhibited Wnt/β-catenin pathway viability in pancreatic cancer cells. In vitro wound healing, invasion, and adhesion assays revealed that FH535 significantly inhibited pancreatic cancer cell metastasis. We also observed the inhibitory effect of FH535 on pancreatic cancer cell growth via the tetrazolium and plate clone formation assays. Microarray analyses suggested that changes in the expression of multiple genes could be involved in the anti-cancer effect of FH535 on pancreatic cancer cells. Our results indicate for the first time that FH535 inhibits pancreatic cancer cell metastasis and growth, providing new insight into therapy of pancreatic cancer.

Formins: Actin nucleators that regulate cytoskeletal dynamics during spermatogenesis

Formins are a growing class of actin nucleation proteins that promote the polymerization of actin microfilaments, forming long stretches of actin microfilaments to confer actin filament bundling in mammalian cells. As such, microfilament bundles can be formed in specific cellular domains, in particular in motile mammalian cells, such as filopodia. Since ectoplasmic specialization (ES), a testis-specific adherens junction (AJ), at the Sertoli cell-cell and Sertoli-spermatid interface is constituted by arrays of actin microfilament bundles, it is likely that formins are playing a significant physiological role on the homeostasis of ES during the epithelial cycle of spermatogenesis. In this Commentary, we provide a timely discussion on formin 1 which was recently shown to be a crucial regulator of actin microfilaments at the ES in the rat testis (Li N et al. Endocrinology, 2015, in press; DOI: 10.1210/en.2015-1161, PMID:25901598). We also highlight research that is needed to unravel the functional significance of formins in spermatogenesis.

Actin-bundling protein plastin 3 is a regulator of ectoplasmic specialization dynamics during spermatogenesis in the rat testis

Ectoplasmic specialization (ES) is an actin-rich adherens junction in the seminiferous epithelium of adult mammalian testes. ES is restricted to the Sertoli-spermatid (apical ES) interface, as well as the Sertoli cell-cell (basal ES) interface at the blood-testis barrier (BTB). ES is typified by the presence of an array of bundles of actin microfilaments near the Sertoli cell plasma membrane. These actin microfilament bundles require rapid debundling to convert them from a bundled to branched/unbundled configuration and vice versa to confer plasticity to support the transport of 1) spermatids in the adluminal compartment and 2) preleptotene spermatocytes at the BTB while maintaining cell adhesion. Plastin 3 is one of the plastin family members abundantly found in yeast, plant and animal cells that confers actin microfilaments their bundled configuration. Herein, plastin 3 was shown to be a component of the apical and basal ES in the rat testis, displaying spatiotemporal expression during the epithelial cycle. A knockdown (KD) of plastin 3 in Sertoli cells by RNA interference using an in vitro model to study BTB function showed that a transient loss of plastin 3 perturbed the Sertoli cell tight junction-permeability barrier, mediated by changes in the localization of basal ES proteins N-cadherin and β-catenin. More importantly, these changes were the result of an alteration of the actin microfilaments, converting from their bundled to branched configuration when examined microscopically, and validated by biochemical assays that quantified actin-bundling and polymerization activity. Moreover, these changes were confirmed by studies in vivo by plastin 3 KD in the testis in which mis-localization of N-cadherin and β-catenin was also detected at the BTB, concomitant with defects in the transport of spermatids and phagosomes and a disruption of cell adhesion most notably in elongated spermatids due to a loss of actin-bundling capability at the apical ES, which in turn affected localization of adhesion protein complexes at the site. In summary, plastin 3 is a regulator of actin microfilament bundles at the ES in which it dictates the configuration of the filamentous actin network by assuming either a bundled or unbundled/branched configuration via changes in its spatiotemporal expression during the epithelial cycle.

Actin binding proteins in blood-testis barrier function

PURPOSE OF REVIEW

The present review examines the role of actin binding proteins (ABPs) on blood-testis barrier (BTB), an androgen-dependent ultrastructure in the testis, in particular their involvement on BTB remodeling during spermatogenesis.

RECENT FINDINGS

The BTB divides the seminiferous epithelium into the basal and the adluminal compartments. The BTB is constituted by coexisting actin-based tight junction, basal ectoplasmic specialization, and gap junction, and also intermediate filament-based desmosome between Sertoli cells near the basement membrane. Junctions at the BTB undergo continuous remodeling to facilitate the transport of preleptotene spermatocytes residing in the basal compartment across the immunological barrier during spermatogenesis. Thus, meiosis I/II and postmeiotic spermatid development take place in the adluminal compartment behind the BTB. BTB remodeling also regulates exchanges of biomolecules between the two compartments. As tight junction, basal ectoplasmic specialization, and gap junction use F-actin for attachment, actin microfilaments rapidly convert between their bundled and unbundled/branched configuration to confer BTB plasticity. The events of actin reorganization are regulated by two major classes of ABPs that convert actin microfilaments between their bundled and branched/unbundled configuration.

SUMMARY

We provide a model on how ABPs regulate BTB remodeling, shedding new light on unexplained male infertility, such as environmental toxicant-induced reproductive dysfunction since the testis, in particular the BTB, is sensitive to environmental toxicants, such as cadmium, bisphenol A, phthalates, and PFOS (perfluorooctanesulfonic acid or perfluorooctane sulfonate).

Origin and function of embryonic Sertoli cells

In the adult testis, Sertoli cells (SCs) are the epithelial supporting cells of the seminiferous tubules that provide germ cells (GCs) with the required nutrients and structural and regulatory support to complete spermatogenesis. SCs also form the blood-testis barrier, phagocytose apoptotic spermatocytes and cell debris derived from spermiogenesis, and produce and secrete numerous paracrine and endocrine signals involved in different regulatory processes. In addition to their essential functions in the adult testis, SCs play a pivotal role during testis development. They are the first cells to differentiate in the embryonic XY gonadal primordium and are involved in the regulation of testis-specific differentiation processes, such as prevention of GC entry into meiosis, Leydig and peritubular myoid cell differentiation, and regression of the Müllerian duct, the anlagen of the uterus, oviducts, and the upper part of the vagina. Expression of the Y-linked gene SRY in pre-SCs initiates a genetic cascade that leads to SC differentiation and subsequently to testis development. Since the identification of the SRY gene, many Sertoli-specific transcription factors and signals underlying the molecular mechanisms of early testis differentiation have been identified. Here, we review the state of the art of the molecular interactions that commit the supporting cell lineage of the gonadal primordium to differentiate as SCs and the subsequent Sertoli-specific signaling pathways involved in early testis differentiation.