Junction restructuring and spermatogenesis: the biology, regulation, and implication in male contraceptive development

Inositol hexakisphosphate kinase 1 is essential for cell junction integrity in the mouse seminiferous epithelium

Inositol hexakisphosphate kinases (IP6Ks) are enzymes that catalyse the synthesis of the inositol pyrophosphate 5-IP7 which is involved in the regulation of many physiological processes in mammals. The IP6K paralog IP6K1 is expressed at high levels in the mammalian testis, and its deletion leads to sterility in male mice. Here, we show that the loss of IP6K1 in mice causes a delay in the first wave of spermatogenesis. Testes from juvenile Ip6k1 knockout mice show downregulation of transcripts that are involved in cell adhesion and formation of the testis-specific inter-Sertoli cell impermeable junction complex known as the blood-testis barrier (BTB). We demonstrate that loss of IP6K1 in the mouse testis causes BTB disruption associated with transcriptional misregulation of the tight junction protein claudin 3, and subcellular mislocalization of the gap junction protein connexin 43. In addition to BTB disruption, we also observe a loss of germ cell adhesion in the seminiferous epithelium of Ip6k1 knockout mice, ultimately resulting in premature sloughing of round spermatids into the epididymis. Mechanistically, we show that loss of IP6K1 in the testis enhances cofilin dephosphorylation in conjunction with increased AKT/ERK and integrin signalling, resulting in destabilization of the actin-based cytoskeleton in Sertoli cells and germ cell loss.

Ferritin-Nanocaged ATP Traverses the Blood-Testis Barrier and Enhances Sperm Motility in an Asthenozoospermia Model

Sperm motility can be enhanced by adding ATP exogenously during in vitro fertilization. However, administering exogenous ATP to the testis to improve sperm motility for in vivo asthenozoospermia treatment has not been investigated yet. Inspired by the recent advances in nanomedicine, we investigated whether the capability of drug delivery nanocarriers to traverse the blood-testis barrier (BTB) can facilitate ATP-dependent asthenozoospermia treatment. We found that the human H-ferritin (HFn) nanocarrier possesses the capability to traverse the BTB and specifically targets the head of elongated sperm cells. Specifically, the HFn nanocarrier traversed the BTB and accumulated in the sperm heads by binding with the HFn receptor (HFR), whose expression was relatively low in Sertoli cells but high in sperm heads. In a gossypol-induced mouse asthenozoospermia model, the administration of an ATP-loaded HFn nanocage through a tail vein injection significantly improved sperm motility. Moreover, the HFn nanocarrier was not toxic to mice in the short (1d) and long terms (30d, 90d) nor did it affect their reproductive health. Thus, the ATP-loaded HFn nanocarrier can potentially serve as a drug-delivery system for treating asthenozoospermia.

Human tissue kallikrein-1 protects against the development of erectile dysfunction in a rat model of hyperhomocysteinemia

The aim of this study was to investigate the mechanism by which a diet inducing high hyperhomocysteinemia (HHcy) leads to the deterioration of erectile function in rats and whether this is inhibited by expression of the human tissue kallikrein-1 (hKLK1) gene. We established a rat model of HHcy by feeding methionine (Met)-rich diets to male Sprague-Dawley (SD) rats. Male wild-type SD rats (WTRs) and transgenic rats harboring the hKLK1 gene (TGRs) were fed a normal diet until 10 weeks of age. Then, 30 WTRs were randomly divided into three groups as follows: the control (n = 10) group, the low-dose (4% Met, n = 10) group, and the high-dose (7% Met, n = 10) group. Another 10 age-matched TGRs were fed the high-dose diet and designated as the TGR+7% Met group. After 30 days, in all four groups, erectile function was measured and penile tissues were harvested to determine oxidative stress, endothelial cell content, and penis fibrosis. Compared with the 7% Met group, the TGR+7% Met group showed diminished HHcy-induced erectile dysfunction (ED), indicating the improvement caused by hKLK1. Regarding corpus cavernosum endothelial cells, hKLK1 preserved endothelial cell-cell junctions and endothelial cell content, and activated protein kinase B/endothelial nitric oxide synthase (Akt/eNOS) signaling. Fibrosis assessment indicated that hKLK1 preserved normal penis structure by inhibiting apoptosis in the corpus cavernosum smooth muscle cells. Taken together, these findings showed that oxidative stress, impaired corpus cavernosum endothelial cells, and severe penis fibrosis were involved in the induction of ED by HHcy in rats, whereas hKLK1 preserved erectile function by inhibiting these pathophysiological changes.

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.

Regulation of the blood-testis barrier by a local axis in the testis: role of laminin α2 in the basement membrane

Laminin α2 is one of the constituent components of the basement membrane (BM) in adult rat testes. Earlier studies that used a mouse genetic model have shown that a deletion of laminin α2 impedes male fertility by disrupting ectoplasmic specialization (ES; a testis-specific, actin-rich anchoring junction) function along the length of Sertoli cell in the testis. This includes ES at the Sertoli cell-elongating/elongated spermatid interface, which is known as apical ES and possibly the Sertoli-Sertoli cell interface, known as basal ES, at the blood-testis barrier (BTB). Studies have also illustrated that there is a local regulatory axis that functionally links cellular events of spermiation that occur near the luminal edge of tubule lumen at the apical ES and the basal ES/BTB remodeling near the BM at opposite ends of the seminiferous epithelium during the epithelial cycle, known as the apical ES-BTB-BM axis. However, the precise role of BM in this axis remains unknown. Here, we show that laminin α2 in the BM serves as the crucial regulator in this axis as laminin α2, likely its 80-kDa fragment from the C terminus, was found to be transported across the seminiferous epithelium at stages VIII-IX of the epithelial cycle, from the BM to the luminal edge of the tubule, possibly being used to modulate apical ES restructuring at these stages. Of more importance, a knockdown of laminin α2 in Sertoli cells was shown to induce the Sertoli cell tight junction permeability barrier disruption via changes in localization of adhesion proteins at the tight junction and basal ES at the Sertoli cell BTB. These changes were found to be mediated by a disruption of F-actin organization that was induced by changes in the spatiotemporal expression of actin binding/regulatory proteins. Furthermore, laminin α2 knockdown also perturbed microtubule (MT) organization by considerable down-regulation of MT polymerization via changes in the spatiotemporal expression of EB1 (end-binding protein 1), a +TIP (MT plus-end tracking protein). In short, laminin α2 in the BM seems to play a crucial role in the BTB-BM axis by modulating BTB dynamics during spermatogenesis.-Gao, Y., Mruk, D., Chen, H., Lui, W.-Y., Lee, W. M., Cheng, C. Y. Regulation of the blood-testis barrier by a local axis in the testis: role of laminin α2 in the basement membrane.

New insights into germ cell migration and survival/apoptosis in spermatogenesis: Lessons from CD147

CD147, also named basigin (Bsg) or extracellular matrix (ECM) metalloproteinase inducer (EMMPRIN), is a highly glycosylated protein first identified as a tumor cell surface molecule. In cancer, it is well established that CD147 promotes metastasis by stimulating the production of MMPs. Recent studies have also suggested that it may be associated with tumor growth and angiogenesis. Interestingly, CD147 is expressed in germ cells of different development stages in the testis and its knockout mice are infertile, indicating an essential role of CD147 in spermatogenesis. While the detailed involvement of CD147 in spermatogenesis remains elusive, our recent findings have revealed a dual role of CD147 in germ cell development. On the one hand, it regulates the migration of spermatogonia and spermatocytes via the induction of MMP-2 production; on the other hand, it specifically regulates the survival/apoptosis of spermatocytes but not spermatogonia through a p53-independent pathway. In this review, we aim to provide an overview on the functions of CD147, comparing its roles in cancer and the testis, thereby providing new insights into the regulatory mechanisms underlying the process of spermatogenesis.

Testin and actin are key molecular targets of adjudin, an anti-spermatogenic agent, in the testis

Earlier studies have shown adjudin to cause aspermatogenesis by depleting virtually all germ cells from the seminiferous epithelium, leading to transient infertility; spermatogenesis and fertility were re-established several weeks later after germ cell proliferation and differentiation were reinitiated by spermatogonia. While adjudin is known to exert its initial effects at the apical ectoplasmic specialization (a testis-specific atypical anchoring junction), thereby perturbing spermatid adhesion, its molecular target(s) at this site is not known. Herein, we report the production of a specific antibody against adjudin after this compound was conjugated to an adjuvant (i.e., keyhole limpet hemocyanin) to maximize immune response in rabbits. This antibody was utilized for co-immunoprecipitation by using an affinity resin to pull-down the binding partners of adjudin. Using this approach coupled with mass spectrometry and immunoblotting, we show testin (a protein largely restricted to the apical ES in the adult testis) and actin-myosin to be molecular targets of adjudin. These findings provide a platform for future functional studies, not only to better understand the molecular mechanism behind adjudin-induced germ cell loss from the seminiferous epithelium, but also to understand the molecular basis of spermiation.

The loss of αSNAP downregulates the expression of occludin in the intestinal epithelial cell of acute pancreatitis model

BACKGROUND AND OBJECTIVE

Intestinal barrier damage is an important event during the occurrence and progression of severe acute pancreatitis. The expression of occludin, one of the main components of the intestinal barrier proteins, is regulated by various factors related to intestinal barrier formation and the remodeling process. The αSNAP, as a novel membrane protein, is ubiquitously expressed in intestinal epithelial cells. This study aimed to investigate the role of αSNAP in acute pancreatitis and the relationship between occludin and αSNAP.

METHODS

Mild and severe acute pancreatitis models were established by retrograde injections of 0.5% and 3.8% sodium taurocholate solutions, respectively, into rat pancreaticobiliary ducts. The animals were killed at 1, 2, and 3 days after the injection, and the pathological changes of the pancreas and intestinal mucosa, the changes in intestinal permeability, and the protein expression of occludin and αSNAP were assessed. Cultured epithelial IEC-6 cells were further infected with lentiviral αSNAP shRNA, cell apoptosis was determined with flow cytometry (FCM), and any changes in occludin expression were detected by Western blotting and immunofluorescent staining.

RESULTS

This pathologic study of a rat acute pancreatitis model indicated pancreatic tissue necrosis and inflammatory cell infiltration; the intestinal villi in the severe acute pancreatitis (SAP) group demonstrated edema, lodging, atrophy, and intestinal epithelial cell necrosis, and shedding. The intestinal permeability in rats with pancreatitis increased significantly. The SAP group showed significantly increased levels of serum TNF-α and endotoxins. The results of immunofluorescent staining and Western blotting revealed that compared with the SO (sham operation) and MAP (mild acute pancreatitis) groups, the SAP group displayed significantly downregulated protein expressions of αSNAP and occludin in the intestinal epithelial cells. After the lentiviral transduction of αSNAP shRNA, apoptosis in IEC-6 cells was drastically increased, whereas the expression of occludin was decreased significantly.

CONCLUSION

The downregulated expression of αSNAP in intestinal epithelial cells leads to reduced occludin expression and enhanced apoptosis of intestinal epithelial cells. Hence, the permeability of the intestinal barrier may be increased in a severe acute pancreatitis model.

ARX/Arx is expressed in germ cells during spermatogenesis in both marsupial and mouse

The X-linked aristaless gene, ARX, is essential for the development of the gonads, forebrain, olfactory bulb, pancreas, and skeletal muscle in mice and humans. Mutations cause neurological diseases, often accompanied by ambiguous genitalia. There are a disproportionately high number of testis and brain genes on the human and mouse X chromosomes. It is still unknown whether the X chromosome accrued these genes during its evolution or whether genes that find themselves on the X chromosome evolve such roles. ARX was originally autosomal in mammals and remains so in marsupials, whereas in eutherian mammals it translocated to the X chromosome. In this study, we examined autosomal ARX in tammars and compared it with the X-linked Arx in mice. We detected ARX mRNA in the neural cells of the forebrain, midbrain and hindbrain, and olfactory bulbs in developing tammars, consistent with the expression in mice. ARX was detected by RT-PCR and mRNA in situ hybridization in the developing tammar wallaby gonads of both sexes, suggestive of a role in sexual development as in mice. We also detected ARX/Arx mRNA in the adult testis in both tammars and mice, suggesting a potential novel role for ARX/Arx in spermiogenesis. ARX transcripts were predominantly observed in round spermatids. Arx mRNA localization distributions in the mouse adult testis suggest that it escaped meiotic sex chromosome inactivation during spermatogenesis. Our findings suggest that ARX in the therian mammal ancestor already played a role in male reproduction before it was recruited to the X chromosome in eutherians.

Regulation of blood-testis barrier (BTB) dynamics during spermatogenesis via the "Yin" and "Yang" effects of mammalian target of rapamycin complex 1 (mTORC1) and mTORC2

In mammalian testes, haploid spermatozoa are formed from diploid spermatogonia during spermatogenesis, which is a complicated cellular process. While these cellular events were reported in the 1960s and 1970s, the underlying molecular mechanism(s) that regulates these events remained unexplored until the past ∼10 years. For instance, adhesion proteins were shown to be integrated components at the Sertoli cell-cell interface and/or the Sertoli-spermatid interface in the late 1980s. But only until recently, studies have demonstrated that some of the adhesion proteins serve as the platform for signal transduction that regulates cell adhesion. In this chapter, a brief summary and critical discussion are provided on the latest findings regarding these cell-adhesion proteins in the testis and their relationship to spermatogenesis. Moreover, antagonistic effects of two mammalian target of rapamycin (mTOR) complexes, known as mTORC1 and mTORC2, on cell-adhesion function in the testis are discussed. Finally, a hypothetic model is presented to depict how these two mTOR-signaling complexes having the "yin" and "yang" antagonistic effects on the Sertoli cell tight junction (TJ)-permeability barrier can maintain the blood-testis barrier (BTB) integrity during the epithelial cycle while preleptotene spermatocytes are crossing the BTB.

Structure and regulation of intestinal epithelial tight junctions: current concepts and unanswered questions

Intestinal epithelium serves as a key interface between internal body compartments and the gut lumen. The epithelial layer forms a physical barrier that protects the body from the harmful environment of the lumen and also mediates vectorial fluxes of fluids, nutrients and waste. Increased permeability of the epithelial barrier is a common manifestation of different gastrointestinal diseases that enhances body exposure to external pathogens thereby exaggerating mucosal inflammation. Barrier properties of the intestinal epithelium are regulated by specialized adhesive plasma membrane structures known as tight junctions (TJs). It is gengrally believed that disease-related increase in intestinal permeability is caused by defects in TJ structure and functions. This chapter describes the molecular composition of intestinal epithelial TJs, basic mechanisms that regulate TJ functions in healthy gut mucosa as well as molecular events that contribute to increased mucosal permeability during intestinal inflammation. The chapter outlines our current understanding of TJ structure and dynamics and highlights several unresolved questions regarding regulation of this junctional complex under normal conditions and in gastroenterological diseases.

Effects of exposure to bisphenol A during pregnancy and lactation on the testicular morphology and caspase-3 protein expression of ICR pups

Bisphenol A (BPA), a xenoestrogen and endocrine-disrupting chemical, is a cause for concern due to its being a potential human carcinogen. The aim of this study was to investigate the effects of continued maternal exposure to BPA on the testicular structures and expression of caspase-3 protein in male ICR offspring during pregnancy and lactation and explore its possible mechanism. Pregnant ICR mice were divided into two control groups, which were either given or not given the solvent dimethyl sulfoxide (DMSO) and three treatment groups, which were gavaged with water-soluble BPA dissolved in DMSO at three different concentrations from gestational day 0 to weaning on postnatal day (PND) 21. The number of mice pups and ratios of males to females were recorded. On PND 21, male offspring were sacrificed to measure their wet weights and testicular coefficients. Electron microscopy was used to observe testicular morphological changes, Hoechst 33258 staining to detect cell apoptosis and immunohistochemistry to measure caspase-3 expression. Although there was no significant difference between offspring of the control group and the treatment group in litter size and male-female ratio (P>0.05), the testicular viscera coefficient in the latter decreased (P<0.01). Specifically, compared with offspring of the control group, in addition to increased cell apoptosis, those of the treatment groups were found to have changes in mitochondrial and endoplasmic reticulum in their spermatogenous, Sertoli, Leydig and peritubular myoid cells, which were concomitant with an elevated expression of caspase-3 in the cytoplasm (P<0.01). In conclusion, exposure of pregnant mice to BPA during pregnancy and lactation has some toxic effects on the testes of male ICR offspring and these may originate from increased apoptosis.

Intercellular adhesion molecules (ICAMs) and spermatogenesis

BACKGROUND

During the seminiferous epithelial cycle, restructuring takes places at the Sertoli-Sertoli and Sertoli-germ cell interface to accommodate spermatogonia/spermatogonial stem cell renewal via mitosis, cell cycle progression and meiosis, spermiogenesis and spermiation since developing germ cells, in particular spermatids, move 'up and down' the seminiferous epithelium. Furthermore, preleptotene spermatocytes differentiated from type B spermatogonia residing at the basal compartment must traverse the blood-testis barrier (BTB) to enter the adluminal compartment to prepare for meiosis at Stage VIII of the epithelial cycle, a process also accompanied by the release of sperm at spermiation. These cellular events that take place at the opposite ends of the epithelium are co-ordinated by a functional axis designated the apical ectoplasmic specialization (ES)-BTB-basement membrane. However, the regulatory molecules that co-ordinate cellular events in this axis are not known.

METHODS

Literature was searched at http://www.pubmed.org and http://scholar.google.com to identify published findings regarding intercellular adhesion molecules (ICAMs) and the regulation of this axis.

RESULTS

Members of the ICAM family, namely ICAM-1 and ICAM-2, and the biologically active soluble ICAM-1 (sICAM-1) are the likely regulatory molecules that co-ordinate these events. sICAM-1 and ICAM-1 have antagonistic effects on the Sertoli cell tight junction-permeability barrier, involved in Sertoli cell BTB restructuring, whereas ICAM-2 is restricted to the apical ES, regulating spermatid adhesion during the epithelial cycle. Studies in other epithelia/endothelia on the role of the ICAM family in regulating cell movement are discussed and this information has been evaluated and integrated into studies of these proteins in the testis to create a hypothetical model, depicting how ICAMs regulate junction restructuring events during spermatogenesis.

CONCLUSIONS

ICAMs are crucial regulatory molecules of spermatogenesis. The proposed hypothetical model serves as a framework in designing functional experiments for future studies.

Long-term vitamin A deficiency induces alteration of adult mouse spermatogenesis and spermatogonial differentiation: direct effect on spermatogonial gene expression and indirect effects via somatic cells

The objective of this study was to further understand the genetic mechanisms of vitamin A deficiency (VAD) induced arrest of spermatogonial stem-cell differentiation. Vitamin A and its derivatives (the retinoids) participate in many physiological processes including vision, cellular differentiation and reproduction. VAD affects spermatogenesis, the subject of our present study. Spermatogenesis is a highly regulated process of differentiation and complex morphologic alterations that leads to the formation of sperm in the seminiferous epithelium. VAD causes early cessation of spermatogenesis, characterized by degeneration of meiotic germ cells, leading to seminiferous tubules containing mostly type A spermatogonia and Sertoli cells. These observations led us to the hypothesis that VAD affects not only germ cells but also somatic cells. To investigate the effects of VAD on spermatogenesis in mice we used adult Balb/C mice fed with Control or VAD diet for an extended period of time (6-28 weeks). We first observed the chronology, then the extent of the effects of VAD on the testes. Using microarray analysis of isolated pure populations of spermatogonia, Leydig and Sertoli cells from control and VAD 18- and 25-week mice, we examined the effects of VAD on gene expression and identified target genes involved in the arrest of spermatogonial differentiation and spermatogenesis. Our results provide a more precise definition of the chronology and magnitude of the consequences of VAD on mouse testes than the previously available literature and highlight direct and indirect (via somatic cells) effects of VAD on germ cell differentiation.

Nonredundant roles of cytoplasmic β- and γ-actin isoforms in regulation of epithelial apical junctions

The functional effects of cytoplasmic actins on epithelial junctions are examined by using isoform-specific siRNAs and cell-permeable inhibitory peptides. Unique roles of cytoplasmic actin isoforms in regulating structure and remodeling of adherens and tight junctions are revealed.

Association with the actin cytoskeleton is critical for normal architecture and dynamics of epithelial tight junctions (TJs) and adherens junctions (AJs). Epithelial cells express β-cytoplasmic (β-CYA) and γ-cytoplasmic (γ-CYA) actins, which have different cellular localization and functions. This study elucidates the roles of cytoplasmic actins in regulating structure and remodeling of AJs and TJs in model intestinal epithelia. Immunofluorescence labeling and latrunculin B treatment reveal affiliation of dynamic β-CYA filaments with newly assembled and mature AJs, whereas an apical γ-CYA pool is composed of stable perijunctional bundles and rapidly turning-over nonjunctional filaments. The functional effects of cytoplasmic actins on epithelial junctions are examined by using isoform-specific small interfering RNAs and cell-permeable inhibitory peptides. These experiments demonstrate unique roles of β-CYA and γ-CYA in regulating the steady-state integrity of AJs and TJs, respectively. Furthermore, β-CYA is selectively involved in establishment of apicobasal cell polarity. Both actin isoforms are essential for normal barrier function of epithelial monolayers, rapid AJ/TJ reassembly, and formation of three-dimensional cysts. Cytoplasmic actin isoforms play unique roles in regulating structure and permeability of epithelial junctions.

Tubulobulbar complex: cytoskeletal remodeling to release spermatozoa

Tubulobulbar complexes (TBCs) are actin-based structures that help establish close contact between Sertoli-Sertoli cells or Sertoli-mature germ cells (spermatids) in the seminiferous tubules of the testes. They are actin-rich push-through devices that eliminate excess spermatid cytoplasm and prepare mature spermatids for release into the tubular lumen. Just prior to spermiation, the elongated spermatid interacts with the Sertoli cell via an extensive structure comprising various adhesion molecules called the apical ectoplasmic specialization which is partially replaced by the apical TBC, on the concave surface of the spermatid head. The sperm release process involves extensive restructuring, namely the disassembly and reassembly of junctions at the Sertoli-spermatid interface in the seminiferous epithelium. Based on the presence of different classes of molecules in the TBCs or the defects observed in the absence of TBCs, the main functions attributed to TBCs are elimination of excess spermatid cytoplasm, endocytosis and recycling of junctional molecules, shaping of the spermatid acrosome, and forming transient anchoring devices for mature spermatids before they are released. This review summarizes the recent findings that focus on the role of TBCs in cell cytoskeleton restructuring during sperm release in the testes and the molecular mechanism involved.

A membrane fusion protein αSNAP is a novel regulator of epithelial apical junctions

Tight junctions (TJs) and adherens junctions (AJs) are key determinants of the structure and permeability of epithelial barriers. Although exocytic delivery to the cell surface is crucial for junctional assembly, little is known about the mechanisms controlling TJ and AJ exocytosis. This study was aimed at investigating whether a key mediator of exocytosis, soluble N-ethylmaleimide sensitive factor (NSF) attachment protein alpha (αSNAP), regulates epithelial junctions. αSNAP was enriched at apical junctions in SK-CO15 and T84 colonic epithelial cells and in normal human intestinal mucosa. siRNA-mediated knockdown of αSNAP inhibited AJ/TJ assembly and establishment of the paracellular barrier in SK-CO15 cells, which was accompanied by a significant down-regulation of p120-catenin and E-cadherin expression. A selective depletion of p120 catenin effectively disrupted AJ and TJ structure and compromised the epithelial barrier. However, overexpression of p120 catenin did not rescue the defects of junctional structure and permeability caused by αSNAP knockdown thereby suggesting the involvement of additional mechanisms. Such mechanisms did not depend on NSF functions or induction of cell death, but were associated with disruption of the Golgi complex and down-regulation of a Golgi-associated guanidine nucleotide exchange factor, GBF1. These findings suggest novel roles for αSNAP in promoting the formation of epithelial AJs and TJs by controlling Golgi-dependent expression and trafficking of junctional proteins.

The blood-testis barrier and its implications for male contraception

The blood-testis barrier (BTB) is one of the tightest blood-tissue barriers in the mammalian body. It divides the seminiferous epithelium into the basal and the apical (adluminal) compartments. Meiosis I and II, spermiogenesis, and spermiation all take place in a specialized microenvironment behind the BTB in the apical compartment, but spermatogonial renewal and differentiation and cell cycle progression up to the preleptotene spermatocyte stage take place outside of the BTB in the basal compartment of the epithelium. However, the BTB is not a static ultrastructure. Instead, it undergoes extensive restructuring during the seminiferous epithelial cycle of spermatogenesis at stage VIII to allow the transit of preleptotene spermatocytes at the BTB. Yet the immunological barrier conferred by the BTB cannot be compromised, even transiently, during the epithelial cycle to avoid the production of antibodies against meiotic and postmeiotic germ cells. Studies have demonstrated that some unlikely partners, namely adhesion protein complexes (e.g., occludin-ZO-1, N-cadherin-β-catenin, claudin-5-ZO-1), steroids (e.g., testosterone, estradiol-17β), nonreceptor protein kinases (e.g., focal adhesion kinase, c-Src, c-Yes), polarity proteins (e.g., PAR6, Cdc42, 14-3-3), endocytic vesicle proteins (e.g., clathrin, caveolin, dynamin 2), and actin regulatory proteins (e.g., Eps8, Arp2/3 complex), are working together, apparently under the overall influence of cytokines (e.g., transforming growth factor-β3, tumor necrosis factor-α, interleukin-1α). In short, a "new" BTB is created behind spermatocytes in transit while the "old" BTB above transiting cells undergoes timely degeneration, so that the immunological barrier can be maintained while spermatocytes are traversing the BTB. We also discuss recent findings regarding the molecular mechanisms by which environmental toxicants (e.g., cadmium, bisphenol A) induce testicular injury via their initial actions at the BTB to elicit subsequent damage to germ-cell adhesion, thereby leading to germ-cell loss, reduced sperm count, and male infertility or subfertility. Moreover, we also critically evaluate findings in the field regarding studies on drug transporters in the testis and discuss how these influx and efflux pumps regulate the entry of potential nonhormonal male contraceptives to the apical compartment to exert their effects. Collectively, these findings illustrate multiple potential targets are present at the BTB for innovative contraceptive development and for better delivery of drugs to alleviate toxicant-induced reproductive dysfunction in men.

The apical ectoplasmic specialization-blood-testis barrier functional axis is a novel target for male contraception

The blood-testis barrier (BTB), similar to other blood-tissue barriers, such as the blood-brain barrier and the blood-retinal barrier, is used to protect the corresponding organ from harmful substances (e.g., xenobiotics) including drugs and foreign compounds. More importantly, the BTB allows postmeiotic spermatid development to take place in an immune privileged site at the adluminal (or apical) compartment to avoid the production of antibodies against spermatid-specific antigens, many of which express transiently during spermiogenesis and spermiation. The BTB, however, also poses an obstacle in developing nonhormonal-based male contraceptives by sequestering drugs (e.g., adjudin) that exert their effects on germ cells in the adluminal compartment. The effects of these drugs include disruption of germ cell cycle progression and development, apoptosis, cell adhesion, metabolism and others. Recent studies have demonstrated that there is a functional axis that operates locally in the seminiferous epithelium to co-ordinate different cellular events across the Sertoli cell epithelium, such as spermiation and BTB restructuring during the seminiferous epithelial cycle of spermatogenesis. Components of this functional axis, such as the apical ectoplasmic specialization (apical ES, a testis-specific atypical anchoring junction type) and the BTB, in particular their constituent protein complexes, such as alpha6beta1-integrin and occludin at the apical ES and the BTB, respectively, can be the target of male contraception. In this chapter, we highlight recent advances regarding the likely mechanism of action of adjudin in this functional axis with emphasis on the use of molecular modeling technique to facilitate the design of better compounds in male contraceptive development.

In vitro assessment of reproductive toxicity on rats induced by organic contaminants of source water

The safety of drinking water attracts more and more attention these years. This study focused on the reproductive toxicity of source water in Jiangsu Province, China. The organic contaminants of source water are capable of bioaccumulating and cause health effects on human beings. The toxicological tests on Spermatogenic cells, Sertoli cells and Leydig cells of male rats showed that source water extracts can reduce testicular cells membrane integrity and depress cell viability significantly. Among these testicular cells, Leydig cells are most sensitive to organic contaminants and the testosterone secretion of Leydig cells is evidently disturbed correspondingly. The phenols in the source water may be chiefly responsible for the reproductive toxicity. These data indicated that chronic reproductive toxicity of source water cannot be overlooked and action should be taken to protect human health from the threat of organic pollution of source water.

Interactions of laminin β3 fragment with β1-integrin receptor: A revisit of the apical ectoplasmic specialization-blood-testis-barrier-hemidesmosome functional axis in the testis

Recent studies have demonstrated the presence of a functional axis that coordinates the events of spermiation and blood-testis barrier (BTB) restructuring which take place simultaneously at the opposite ends of the seminiferous epithelium at stage VIII of the epithelial cycle of spermatogenesis in the rat testis. In short, the disruption of the apical ectoplasmic specialization (apical ES) at the Sertoli cell-elongated spermatid interface, which facilitates the release of sperm at spermiation near the tubule lumen, is coordinated with restructuring at the BTB to accommodate the transit of preleptotene spermatocytes across the immunological barrier near the basement membrane. These two events are likely coordinated by a functional axis involving hemidesmosome at the Sertoli cell-basement membrane interface, and it was designated the apical ES-BTB-hemidesmosome axis. It was demonstrated that fragments of laminin chains (e.g., laminin β3 or γ3 chains) derived from the α6β1-integrin-laminin333 protein complex at the apical ES, which were likely generated via the action of MMP-2 (matrix metalloprotease-2, MMP2) prior to spermiation, acted as biologically active peptides to perturb the BTB permeability function by accelerating protein endocytosis (e.g., occludin) at the site, thereby destabilizing the BTB integrity to facilitate the transit of preleptotene spermatocytes. These laminin fragments also perturbed hemidesmosome function via their action on β1-integrin, a component of hemidesmosome in the testis, which in turn, sent a signal to further destabilize the BTB function. As such, the events of spermiation and BTB restructuring are coordinated via this functional axis. Recent studies using animal models treated with toxicants, such as mono-(2-ethylhexyl) phthalate (MEHP), or adjudin, a male contraceptive under investigation, have also supported the presence of this functional axis in the mouse. In this short review, we critically evaluate the role of this local functional axis in the seminiferous epithelium in spermatogenesis. We also provide molecular modeling information on the interactions between biologically active laminin fragments and β1-integrin, which will be important to assist in the design of more potent laminin-based peptides to disrupt this axis, thereby perturbing spermatogenesis for male contraception and to understand the underlying biology that coordinates spermiation and BTB restructuring during spermatogenesis.

An in vitro system to study Sertoli cell blood-testis barrier dynamics

The use of an in vitro system based on primary cultures of Sertoli cells isolated from rat testes has greatly facilitated the study of the blood-testis barrier in recent years. Herein, we summarize the detailed procedures on the isolation of undifferentiated Sertoli cells from 20-day-old rat testes, the culture of these cells as a monolayer on Matrigel-coated bicameral units, the characterization of these cultured cells, and the use of the Sertoli cell epithelium for monitoring the integrity of the Sertoli cell blood-testis barrier. This information is based on the routine use of this system in our laboratory to study the Sertoli cell blood-testis barrier in the past two decades, which should be helpful for investigators in the field.

Spermiation: The process of sperm release

Spermiation is the process by which mature spermatids are released from Sertoli cells into the seminiferous tubule lumen prior to their passage to the epididymis. It takes place over several days at the apical edge of the seminiferous epithelium, and involves several discrete steps including remodelling of the spermatid head and cytoplasm, removal of specialized adhesion structures and the final disengagement of the spermatid from the Sertoli cell. Spermiation is accomplished by the co-ordinated interactions of various structures, cellular processes and adhesion complexes which make up the "spermiation machinery". This review addresses the morphological, ultrastructural and functional aspects of mammalian spermiation. The molecular composition of the spermiation machinery, its dynamic changes and regulatory factors are examined. The causes of spermiation failure and their impact on sperm morphology and function are assessed in an effort to understand how this process may contribute to sperm count suppression during contraception and to phenotypes of male infertility.

Characterization and functionality of proliferative human Sertoli cells

It has long been thought that mammalian Sertoli cells are terminally differentiated and nondividing postpuberty. For most previous in vitro studies immature rodent testes have been the source of Sertoli cells and these have shown little proliferative ability when cultured. We have isolated and characterized Sertoli cells from human cadaveric testes from seven donors ranging from 12 to 36 years of age. The cells proliferated readily in vitro under the optimized conditions used with a doubling time of approximately 4 days. Nuclear 5-ethynyl-2'-deoxyuridine (EdU) incorporation confirmed that dividing cells represented the majority of the population. Classical Sertoli cell ultrastructural features, lipid droplet accumulation, and immunoexpression of GATA-4, Sox9, and the FSH receptor (FSHr) were observed by electron and fluorescence microscopy, respectively. Flow cytometry revealed the expression of GATA-4 and Sox9 by more than 99% of the cells, and abundant expression of a number of markers indicative of multipotent mesenchymal cells. Low detection of endogenous alkaline phosphatase activity after passaging showed that few peritubular myoid cells were present. GATA-4 and SOX9 expression were confirmed by reverse transcription polymerase chain reaction (RT-PCR), along with expression of stem cell factor (SCF), glial cell line-derived neurotrophic factor (GDNF), and bone morphogenic protein 4 (BMP4). Tight junctions were formed by Sertoli cells plated on transwell inserts coated with fibronectin as revealed by increased transepithelial electrical resistance (TER) and polarized secretion of the immunoregulatory protein, galectin-1. These primary Sertoli cell populations could be expanded dramatically in vitro and could be cryopreserved. The results show that functional human Sertoli cells can be propagated in vitro from testicular cells isolated from adult testis. The proliferative human Sertoli cells should have important applications in studying infertility, reproductive toxicology, testicular cancer, and spermatogenesis, and due to their unique biological properties potentially could be useful in cell therapy.

Differential effects of testosterone and TGF-β3 on endocytic vesicle-mediated protein trafficking events at the blood-testis barrier

The intricate interaction between protein endocytosis, transcytosis, recycling and endosome- or ubiquitin-mediated protein degradation determines the junction integrity in epithelial cells including Sertoli cells at the blood-testis barrier (BTB). Studies have shown that androgens and cytokines (e.g., TGF-β3) that are known to promote and disrupt BTB integrity, respectively, accelerate protein endocytosis at the BTB. We hypothesized that testosterone-induced endocytosed proteins are transcytosed and recycled back to the Sertoli cell surface, whereas cytokine-induced endocytosed proteins are degraded so that androgens and cytokines have opposing effects on BTB integrity. Herein, we report that both testosterone and TGF-β3 induced the steady-state level of clathrin, an endocytic vesicle protein. Testosterone and TGF-β3 also induced the association between internalized occludin (a BTB integral membrane protein) and clathrin, as well as early endosome antigen-1 (EEA-1). Interestingly, testosterone, but not TGF-β3, also induced the levels of proteins that regulate protein transcytosis (e.g., caveolin-1) and recycling (e.g., Rab11), and their association with internalized occludin and N-cadherin from the cell surface. In contrast, TGF-β3, but not testosterone, induced the level of ubiquitin-conjugating enzyme E2 J1 (Ube2j1), a protein crucial to the intracellular protein degradation pathway, and its association with internalized occludin. Based on these findings and recent reports in the field, we hypothesize that the concerted effects of testosterone and TGF-β3 likely facilitate the transit of preleptotene spermatocytes at the BTB while maintaining the immunological barrier in that testosterone induces the assembly of "new" tight junction (TJ)-fibrils below migrating spermatocytes via protein transcytosis and recycling before cytokines induce the disassembly of "old" TJ-fibrils above spermatocytes via endocytic vesicle-mediated degradation of internalized proteins. This thus provides a unique mechanism in the testis to facilitate the transit of preleptotene spermatocytes, many of which are connected in "clones" via cytoplasmic bridges, at the BTB while maintaining the immunological barrier during stage VIII of the seminiferous epithelial cycle of spermatogenesis.

A local autocrine axis in the testes that regulates spermatogenesis

Spermiation--the release of mature spermatozoa from Sertoli cells into the seminiferous tubule lumen--occurs by the disruption of an anchoring device known as the apical ectoplasmic specialization (apical ES). At the same time, the blood-testis barrier (BTB) undergoes extensive restructuring to facilitate the transit of preleptotene spermatocytes. While these two cellular events take place at opposite ends of the Sertoli cell epithelium, the events are in fact tightly coordinated, as any disruption in either process will lead to infertility. A local regulatory axis exists between the apical ES and the BTB in which biologically active laminin fragments produced at the apical ES by the action of matrix metalloproteinase 2 can regulate BTB restructuring directly or indirectly via the hemidesmosome. Equally important, polarity proteins play a crucial part in coordinating cellular events within this apical ES-BTB-hemidesmosome axis. Additionally, testosterone and cytokines work in concert to facilitate BTB restructuring, which enables the transit of spermatocytes while maintaining immunological barrier function. Herein, we will discuss this important autocrine-based cellular axis that parallels the hormonal-based hypothalamic-pituitary-testicular axis that regulates spermatogenesis. This local regulatory axis is the emerging target for male contraception.

The reproductive toxicity of organic compounds extracted from drinking water sources on Sprague Dawley rats: an in vitro study

The safety of drinking water always causes worldwide concern. Water pollution increases with urban development and industrialization in developing countries. During recent decades, increasing numbers of environmental organic compounds have been found in aquatic environments. These organic compounds are capable of bioaccumulating to much higher concentrations in food webs and cause health effects on human beings. Reproductive impairment is one of the commonest consequences of environmental pollution. Our goal was to investigate the reproductive toxicity of organic compounds extracted from surface water samples collected in drinking water sources. This study focused on the surface water in lower Yangtze River and Taihu Lake, which act as drinking water sources of Jiangsu province, one of the most rapidly developing regions in China. We used solid-phase extraction (SPE) to condense organic compounds by 286 times from natural surface water samples and established in vitro system to evaluate their effects on reproductive system. We found that organic compounds destroyed the plasma membrane integrity of Sertoli cells and Spermatogenic cells to a certain degree and significantly depressed viability of Sertoli cells and Spermatogenic cells as well. Accordingly, the proportion of apoptotic Sertoli cells and dead Spermatogenic cells enhanced markedly. Although viability of organic-compound-treated Leydig cells did not come down remarkably, testosterone production of Leydig cells decreased evidently. These results suggest that accumulated comprehensive effects of organic compounds in surface water of drinking water sources may induce spermatogenesis malfunction and reduction of testosterone production in the long term.

The endocytic recycling regulator EHD1 is essential for spermatogenesis and male fertility in mice

Background

The C-terminal Eps15 homology domain-containing protein 1 (EHD1) is ubiquitously expressed and regulates the endocytic trafficking and recycling of membrane components and several transmembrane receptors. To elucidate the function of EHD1 in mammalian development, we generated Ehd1^-/- mice using a Cre/loxP system.

Results

Both male and female Ehd1^-/- mice survived at sub-Mendelian ratios. A proportion of Ehd1^-/- mice were viable and showed smaller size at birth, which continued into adulthood. Ehd1^-/- adult males were infertile and displayed decreased testis size, whereas Ehd1^-/- females were fertile. In situ hybridization and immunohistochemistry of developing wildtype mouse testes revealed EHD1 expression in most cells of the seminiferous epithelia. Histopathology revealed abnormal spermatogenesis in the seminiferous tubules and the absence of mature spermatozoa in the epididymides of Ehd1^-/- males. Seminiferous tubules showed disruption of the normal spermatogenic cycle with abnormal acrosomal development on round spermatids, clumping of acrosomes, misaligned spermatids and the absence of normal elongated spermatids in Ehd1^-/- males. Light and electron microscopy analyses indicated that elongated spermatids were abnormally phagocytosed by Sertoli cells in Ehd1^-/- mice.

Conclusions

Contrary to a previous report, these results demonstrate an important role for EHD1 in pre- and post-natal development with a specific role in spermatogenesis.

The key role of vitamin A in spermatogenesis

Spermatogenesis in adult mammals is highly organized, with the goal being continual sperm production. Vertebrate testes are arranged into recurring cellular associations that vary with time and distance along the tubule. These changes over time and distance are designated the cycle of the seminiferous epithelium and the spermatogenic wave, respectively. In this Review, we briefly outline the roles that follicle-stimulating hormone (FSH) and testosterone play in regulating spermatogenesis and describe our current understanding of how vitamin A regulates germ cell differentiation and how it may lead to the generation of both the cycle of the seminiferous epithelium and the spermatogenic wave.

Regulation of spermatogenesis in the microenvironment of the seminiferous epithelium: new insights and advances

Spermatogenesis is a complex biochemical event, involving the participation of the hypothalamus and the pituitary gland via secretion of the hypothalamus hormone GnRH, and two pituitary hormones FSH and LH. Thus, the hypothalamic-pituitary-testicular axis is a crucial regulatory axis for testicular function. Recent studies have shown that in the microenvironment of the seminiferous epithelium, wherein each Sertoli cell supports approximately 30-50 germ cells at different stages of development, locally produced autocrine and paracrine factors are also involved in spermatogenesis, in particular at the level of cell junctions. These cell junctions at the Sertoli-Sertoli and Sertoli-germ cell interface are crucial for coordinating different events of spermatogenesis by sending signals back-and-forth between Sertoli and germ cells, in order to precisely regulate spermatogonial cell renewal by mitosis, cell cycle progression, meiosis, spermiogenesis, germ cell movement across the epithelium, spermiation and germ cell apoptosis. In this minireview, we provide an update on these latest findings for an emerging new concept regarding the presence of a local "apical ectoplasmic specialization-blood-testis barrier-hemidesmosome/basement membrane" functional axis that regulates the events of spermiation and blood-testis barrier (BTB) restructuring via paracrine/autocrine factors and polarity proteins produced locally in the seminiferous epithelium. These findings provide a new window of research for investigators in the field to tackle the functional regulation of spermatogenesis.

Regulation of blood-testis barrier dynamics by focal adhesion kinase (FAK): an unexpected turn of events

The blood-testis barrier (BTB) is conferred by co-existing tight junctions (TJs), basal ectoplasmic specializations (basal ES), desmosome-like junctions and gap junctions (GJs) between adjacent Sertoli cells near the basement membrane in the seminiferous epithelium. While the concept of the BTB has been known for more than a century and its significance to spermatogenesis discerned for more than five decades, its regulation has remained largely unknown. Recent studies, however, have demonstrated that focal adhesion kinase (FAK), a modulator of the integrin-based signaling that plays a crucial role in cell movement, apoptosis, cell survival and gene expression at the focal adhesion complex (FAC, also known as focal contact, a cell-matrix anchoring junction type), is an integrated component of the BTB, associated with the TJ-integral membrane protein occludin and its adaptor zonula occludens-1 (ZO-1). Herein, we summarize recent findings in the field regarding the significance of FAK in conferring BTB integrity based on some unexpected observations. We also critically discuss the role of FAK in regulating the timely "opening" and "closing" of the BTB to facilitate the transit of primary preleptotene spermatocytes across the BTB at stage VIII of the seminiferous epithelial cycle of spermatogenesis. Lastly, we describe a working model, which can be used to design future functional experiments to explore the involvement of FAK in BTB dynamics by investigators in the field.

Morphology of testes from transgenic rabbits: histological and ultrastructural aspects

The aim of this study was to compare morphological characteristics of testes from transgenic (the WAP-hFVIII gene) and non-transgenic rabbits with emphasis on the histological and ultrastructural aspects. Samples of testes from both groups were fixed and embedded into Durcupan ACM for transmission electron microscopy. For histological analysis, semi-thin toluidine blue-stained sections were evaluated under a Jenaval light microscope. Male fertility was tested based on egg fecundity and blastocyst yield; transgene transmission was proved using PCR assay. Spermatogenesis in rabbit testes had not been destroyed both in transgenic and non-transgenic rabbits. No significant differences were found in the occurrence of individual cell organelles of the Sertoli cells in transgenic and non-transgenic rabbits. The ultrastructure of Leydig cells in testes of transgenic and non-transgenic rabbits was rather similar. No differences in the occurrence of individual organelles of Leydig cells between transgenic and non-transgenic males were found. These results were in concert with fertilizing capacity of transgenic spermatozoa. The presented status of organelles in this study indicates functional activity of the analysed cells.

An intracellular trafficking pathway in the seminiferous epithelium regulating spermatogenesis: a biochemical and molecular perspective

During spermatogenesis in adult rat testes, fully developed spermatids (i.e. spermatozoa) at the luminal edge of the seminiferous epithelium undergo "spermiation" at stage VIII of the seminiferous epithelial cycle. This is manifested by the disruption of the apical ectoplasmic specialization (apical ES) so that spermatozoa can enter the tubule lumen and to complete their maturation in the epididymis. At the same time, the blood-testis barrier (BTB) located near the basement membrane undergoes extensive restructuring to allow transit of preleptotene spermatocytes so that post-meiotic germ cells complete their development behind the BTB. While spermiation and BTB restructuring take place concurrently at opposite ends of the Sertoli cell epithelium, the biochemical mechanism(s) by which they are coordinated were not known until recently. Studies have shown that fragments of laminin chains are generated from the laminin/integrin protein complex at the apical ES via the action of MMP-2 (matrix metalloprotease-2) at spermiation. These peptides serve as the local autocrine factors to destabilize the BTB. These laminin peptides also exert their effects on hemidesmosome which, in turn, further potentiates BTB restructuring. Thus, a novel apical ES-BTB-hemidesmosome regulatory loop is operating in the seminiferous epithelium to coordinate these two crucial cellular events of spermatogenesis. This functional loop is further assisted by the Par3/Par6-based polarity protein complex in coordination with cytokines and testosterone at the BTB. Herein, we provide a critical review based on the latest findings in the field regarding the regulation of these cellular events. These recent findings also open up a new window for investigators studying blood-tissue barriers.

Zona occludens-2 is critical for blood-testis barrier integrity and male fertility

Tight junction integral membrane proteins such as claudins and occludin are tethered to the actin cytoskeleton by adaptor proteins, notably the closely related zonula occludens (ZO) proteins ZO-1, ZO-2, and ZO-3. All three ZO proteins have recently been inactivated in mice. Although ZO-3 knockout mice lack an obvious phenotype, animals deficient in ZO-1 or ZO-2 show early embryonic lethality. Here, we rescue the embryonic lethality of ZO-2 knockout mice by injecting ZO-2(-/-) embryonic stem (ES) cells into wild-type blastocysts to generate viable ZO-2 chimera. ZO-2(-/-) ES cells contribute extensively to different tissues of the chimera, consistent with an extraembryonic requirement for ZO-2 rather than a critical role in epiblast development. Adult chimera present a set of phenotypes in different organs. In particular, male ZO-2 chimeras show reduced fertility and pathological changes in the testis. Lanthanum tracer experiments show a compromised blood-testis barrier. Expression levels of ZO-1, ZO-3, claudin-11, and occludin are not apparently affected. ZO-1 and occludin still localize to the blood-testis barrier region, but claudin-11 is less well restricted and the localization of connexin-43 is perturbed. The critical role of ZO-2 for male fertility and blood-testis barrier integrity thus provides a first example for a nonredundant role of an individual ZO protein in adult mice.

Mitogen-activated protein kinases in male reproductive function

Recent studies have shown that male reproductive function is modulated via the mitogen-activated protein kinase (MAPK) cascade. The MAPK cascade is involved in numerous male reproductive processes, including spermatogenesis, sperm maturation and activation, capacitation and acrosome reaction, before fertilization of the oocyte. In this review, we discuss the latest findings in this rapidly developing field regarding the role of MAPK in male reproduction in animal models and in human spermatozoa in vitro. This research will facilitate the design of future studies in humans, although much work is needed before this information can be used to manage male infertility and environmental toxicant-induced testicular injury in men, such as blood-testis-barrier disruption.

Cadmium-induced testicular injury

Cadmium (Cd) is an environmental toxicant and an endocrine disruptor in humans and rodents. Several organs (e.g., kidney, liver) are affected by Cd and recent studies have illustrated that the testis is exceedingly sensitive to Cd toxicity. More important, Cd and other toxicants, such as heavy metals (e.g., lead, mercury) and estrogenic-based compounds (e.g., bisphenols) may account for the recent declining fertility in men among developed countries by reducing sperm count and testis function. In this review, we critically discuss recent data in the field that have demonstrated the Cd-induced toxicity to the testis is probably the result of interactions of a complex network of causes. This is likely to involve the disruption of the blood-testis barrier (BTB) via specific signal transduction pathways and signaling molecules, such as p38 mitogen-activated protein kinase (MAPK). We also summarize current studies on factors that confer and/or regulate the testis sensitivity to Cd, such as Cd transporters and metallothioneins, the impact of Cd on the testis as an endocrine disruptor and oxidative stress inducer, and how it may disrupt the Zn(2+) and/or Ca(2+) mediated cellular events. While much work is needed before a unified mechanistic pathway of Cd-induced testicular toxicity emerges, recent studies have helped to identify some of the likely mechanisms and/or events that take place during Cd-induced testis injury. Furthermore, some of the recent studies have shed lights on potential therapeutic or preventive approaches that can be developed in future studies by blocking or minimizing the destructive effects of Cd to testicular function in men.

TGF-beta3 and TNFalpha perturb blood-testis barrier (BTB) dynamics by accelerating the clathrin-mediated endocytosis of integral membrane proteins: a new concept of BTB regulation during spermatogenesis

In adult mammals such as rats, the blood-testis barrier (BTB) conferred by adjacent Sertoli cells in the seminiferous epithelium segregates post-meiotic germ cell development from the systemic circulation and is one of the tightest blood-tissue barriers. Yet it must "open" transiently at stages VIII to IX of the epithelial cycle to accommodate the migration of preleptotene/leptotene spermatocytes. While this is a vital event of spermatogenesis, the mechanism(s) that regulates BTB dynamics is virtually unknown. Recent studies have suggested that transforming growth factor-beta3 (TGF-beta3) and tumor necrosis factor alpha (TNFalpha) secreted by Sertoli and germ cells into the microenvironment of the BTB are capable of inducing reversible BTB disruption in vivo, apparently by reducing the steady-state levels of occludin and zonula occludens-1 (ZO-1) at the BTB via the p38 mitogen activated protein (MAP) kinase signaling pathway. In this study, local administration of TGF-beta3 (200 ng/testis) to the testis was shown to reversibly perturb the BTB integrity in vivo. We next sought to delineate the mechanism by which these cytokines maintain the steady-state level of integral membrane proteins: occludin, junctional adhesion molecule-A (JAM-A) and N-cadherin at the BTB. Primary Sertoli cells cultured in vitro were shown to establish intact tight junctions and functional BTB within two days when assessed by transepithelial electrical resistance (TER) measurement across the cell epithelium. Sertoli cell integral membrane protein internalization at the BTB was assessed by biotinylation of cell surface proteins, to be followed by tracking the endocytosed/biotinylated proteins by using specific antibodies. Both TGF-beta3 (3 ng/ml) and TNFalpha (10 ng/ml) were shown to significantly accelerate the kinetics of internalization of JAM-A, N-cadherin, and occludin versus controls. Treatment of cells with phenylarsine oxide (PAO) at 10 microM that blocks clathrin-mediated endocytosis was shown to inhibit the TGF-beta3-induced protein internalization. This inhibition of TGF-beta3-mediated protein endocytosis was further validated by silencing of clathrin. The specific effect of TGF-beta3 on protein internalization was further confirmed by RNAi using specific TGF-beta receptor I (TbetaR1) siRNA duplexes. When TbetaR1 was knocked down, the TGF-beta3-induced increase in the kinetics of JAM-A and occludin endocytosis was abolished, making them indistinguishable from controls, illustrating the specificity of the TGF-beta3 effects on protein endocytosis. In summary, this report demonstrates for the first time that BTB dynamics are regulated by TGF-beta3 and TNFalpha via an enhancement of protein endocytosis at the BTB.

The role of thyroid hormone in testicular development and function

Thyroid hormone is a critical regulator of growth, development, and metabolism in virtually all tissues, and altered thyroid status affects many organs and systems. Although for many years testis has been regarded as a thyroid hormone unresponsive organ, it is now evident that thyroid hormone plays an important role in testicular development and function. A considerable amount of data show that thyroid hormone influences steroidogenesis as well as spermatogenesis. The involvement of tri-iodothyronine (T(3)) in the control of Sertoli cell proliferation and functional maturation is widely accepted, as well as its role in postnatal Leydig cell differentiation and steroidogenesis. The presence of thyroid hormone receptors in testicular cells throughout development and in adulthood implies that T(3) may act directly on these cells to bring about its effects. Several recent studies have employed different methodologies and techniques in an attempt to understand the mechanisms underlying thyroid hormone effects on testicular cells. The current review aims at presenting an updated picture of the recent advances made regarding the role of thyroid hormones in male gonadal function.

Sphingomyelin synthases and testicular function

Sphingomyelin synthase (SMS) is a cellular enzyme that catalyzes de novo synthesis of sphingomyelin (SM), which is a vital lipid component of cell membranes. Both members of the SMS family, SMS1 and SMS2, are found in mammalian testes and they are located in distinctive subcellular compartments, with SMS1 in the Golgi apparatus and SMS2 in the plasma membrane. At present, the precise function of SMS in the testis remains unknown. Recent studies have demonstrated an unique association of SMS2 with spermatids, particularly near developing acrosomes and the junction restructuring site at the apical ectoplasmic specialization (a testis-specific atypical adherens junction type) and Leydig cells in the rat testis. These data illustrate the possible involvement of SMS2 in spermiogenesis and, perhaps, steroidogenesis in male reproductive function. This review summarizes the latest findings on SMS in the field, particularly its role in testicular function.

An autocrine axis in the testis that coordinates spermiation and blood-testis barrier restructuring during spermatogenesis

The mechanism(s) that regulate and coordinate the events of spermiation and blood-testis barrier (BTB) restructuring in the seminiferous epithelium that occur concurrently at stage VIII of the seminiferous epithelial cycle of spermatogenesis are unknown. In this report, fragments derived from the laminin complex composed of laminin alpha3, beta3, and gamma3 chains (laminin-333) at the apical ectoplasmic specialization (apical ES) were shown to modulate BTB dynamics directly and/or indirectly via hemidesmosome. Experiments were performed using cultured Sertoli cells with functional tight junction (TJ) barrier and the ultrastructural features of the BTB but not apical ES. Recombinant protein fragments of laminin beta3 and gamma3 chains were shown to reduce the protein levels of occludin and beta1-integrin dose dependently at the Sertoli-Sertoli and Sertoli-basement membrane interface, respectively, thereby destabilizing the BTB permeability function. These results were corroborated by transient overexpression of laminin fragments in Sertoli cells. To further assess the role of beta1-integrin in hemidesmosome, knockdown of beta1-integrin in Sertoli cells by RNAi was found to associate with occludin redistribution at the Sertoli-Sertoli cell interface, wherein occludin moved away from the cell surface and became associated with endosomes, thereby destabilizing the BTB. In short, an apical ES-BTB-hemidesmosome autocrine regulatory axis was identified in testes, coordinating the events of spermiation and BTB restructuring that occur at the opposite ends of the seminiferous epithelium during spermatogenesis.

On the necessity of different statistical treatment for Illumina BeadChip and Affymetrix GeneChip data and its significance for biological interpretation

Background

The original spotted array technology with competitive hybridization of two experimental samples and measuring relative expression levels is increasingly displaced by more accurate platforms that allow determining absolute expression values for a single sample (for example, Affymetrix GeneChip and Illumina BeadChip). Unfortunately, cross-platform comparisons show a disappointingly low concordance between lists of regulated genes between the latter two platforms.

Results

Whereas expression values determined with a single Affymetrix GeneChip represent single measurements, the expression results obtained with Illumina BeadChip are essentially statistical means from several dozens of identical probes. In the case of multiple technical replicates, the data require, therefore, different stistical treatment depending on the platform. The key is the computation of the squared standard deviation within replicates in the case of the Illumina data as weighted mean of the square of the standard deviations of the individual experiments. With an Illumina spike experiment, we demonstrate dramatically improved significance of spiked genes over all relevant concentration ranges. The re-evaluation of two published Illumina datasets (membrane type-1 matrix metalloproteinase expression in mammary epithelial cells by Golubkov et al. Cancer Research (2006) 66, 10460; spermatogenesis in normal and teratozoospermic men, Platts et al. Human Molecular Genetics (2007) 16, 763) significantly identified more biologically relevant genes as transcriptionally regulated targets and, thus, additional biological pathways involved.

Conclusion

The results in this work show that it is important to process Illumina BeadChip data in a modified statistical procedure and to compute the standard deviation in experiments with technical replicates from the standard errors of individual BeadChips. This change leads also to an improved concordance with Affymetrix GeneChip results as the spermatogenesis dataset re-evaluation demonstrates.

Reviewers

This article was reviewed by I. King Jordan, Mark J. Dunning and Shamil Sunyaev.

Advances in male contraception

Despite significant advances in contraceptive options for women over the last 50 yr, world population continues to grow rapidly. Scientists and activists alike point to the devastating environmental impacts that population pressures have caused, including global warming from the developed world and hunger and disease in less developed areas. Moreover, almost half of all pregnancies are still unwanted or unplanned. Clearly, there is a need for expanded, reversible, contraceptive options. Multicultural surveys demonstrate the willingness of men to participate in contraception and their female partners to trust them to do so. Notwithstanding their paucity of options, male methods including vasectomy and condoms account for almost one third of contraceptive use in the United States and other countries. Recent international clinical research efforts have demonstrated high efficacy rates (90-95%) for hormonally based male contraceptives. Current barriers to expanded use include limited delivery methods and perceived regulatory obstacles, which stymie introduction to the marketplace. However, advances in oral and injectable androgen delivery are cause for optimism that these hurdles may be overcome. Nonhormonal methods, such as compounds that target sperm motility, are attractive in their theoretical promise of specificity for the reproductive tract. Gene and protein array technologies continue to identify potential targets for this approach. Such nonhormonal agents will likely reach clinical trials in the near future. Great strides have been made in understanding male reproductive physiology; the combined efforts of scientists, clinicians, industry and governmental funding agencies could make an effective, reversible, male contraceptive an option for family planning over the next decade.