Restricted Arp3 expression in the testis prevents blood-testis barrier disruption during junction restructuring at spermatogenesis

Androgens and Notch signaling cooperate in seminiferous epithelium to regulate genes related to germ cell development and apoptosis

It was reported previously that in adult males disruption of both androgen and Notch signaling impairs spermatid development and germ cell survival in rodent seminiferous epithelium. To explain the molecular mechanisms of these effects, we focused on the interaction between Notch signaling and androgen receptor (AR) in Sertoli cells and investigate its role in the control of proteins involved in apical ectoplasmic specializations, actin remodeling during spermiogenesis, and induction of germ cell apoptosis. First, it was revealed that in rat testicular explants ex vivo both testosterone and Notch signaling modulate AR expression and cooperate in the regulation of spermiogenesis-related genes (Nectin2, Afdn, Arp2, Eps8) and apoptosis-related genes (Fasl, Fas, Bax, Bcl2). Further, altered expression of these genes was found following exposure of Sertoli cells (TM4 cell line) and germ cells (GC-2 cell line) to ligands for Notch receptors (Delta-like1, Delta-like4, and Jagged1) and/or Notch pathway inhibition. Finally, direct interactions of Notch effector, Hairy/enhancer-of-split related with YRPW motif protein 1, and the promoter of Ar gene or AR protein were revealed in TM4 Sertoli cells. In conclusion, Notch pathway activity in Sertoli and germ cells regulates genes related to germ cell development and apoptosis acting both directly and indirectly by influencing androgen signaling in Sertoli cells.

The katanin A-subunits KATNA1 and KATNAL1 act co-operatively in mammalian meiosis and spermiogenesis to achieve male fertility

Katanins, a class of microtubule-severing enzymes, are potent M-phase regulators in oocytes and somatic cells. How the complex and evolutionarily crucial, male mammalian meiotic spindle is sculpted remains unknown. Here, using multiple single and double gene knockout mice, we reveal that the canonical katanin A-subunit KATNA1 and its close paralogue KATNAL1 together execute multiple aspects of meiosis. We show KATNA1 and KATNAL1 collectively regulate the male meiotic spindle, cytokinesis and midbody abscission, in addition to diverse spermatid remodelling events, including Golgi organisation, and acrosome and manchette formation. We also define KATNAL1-specific roles in sperm flagellum development, manchette regulation and sperm-epithelial disengagement. Finally, using proteomic approaches, we define the KATNA1, KATNAL1 and KATNB1 mammalian testis interactome, which includes a network of cytoskeletal and vesicle trafficking proteins. Collectively, we reveal that the presence of multiple katanin A-subunit paralogs in mammalian spermatogenesis allows for 'customised cutting' via neofunctionalisation and protective buffering via gene redundancy.

mTORC1/rpS6 and mTORC2/PKC regulate spermatogenesis through Arp3-mediated actin microfilament organization in Eriocheir sinensis

Mammalian target of rapamycin (mTOR) is a crucial signaling protein regulating a range of cellular events. Numerous studies have reported that the mTOR pathway is related to spermatogenesis in mammals. However, its functions and underlying mechanisms in crustaceans remain largely unknown. mTOR exists as two multimeric functional complexes termed mTOR complex 1 (mTORC1) and mTORC2. Herein, we first cloned ribosomal protein S6 (rpS6, a downstream molecule of mTORC1) and protein kinase C (PKC, a downstream effector of mTORC2) from the testis of Eriocheir sinensis. The dynamic localization of rpS6 and PKC suggested that both proteins may be essential for spermatogenesis. rpS6/PKC knockdown and Torin1 treatment led to defects in spermatogenesis, including germ cell loss, retention of mature sperm and empty lumen formation. In addition, the integrity of the testis barrier (similar to the blood-testis barrier in mammals) was disrupted in the rpS6/PKC knockdown and Torin1 treatment groups, accompanied by changing in expression and distribution of junction proteins. Further study demonstrated that these findings may result from the disorganization of filamentous actin (F-actin) networks, which were mediated by the expression of actin-related protein 3 (Arp3) rather than epidermal growth factor receptor pathway substrate 8 (Eps8). In summary, our study illustrated that mTORC1/rpS6 and mTORC2/PKC regulated spermatogenesis via Arp3-mediated actin microfilament organization in E. sinensis.

Bisphenols as promoters of the dysregulation of cellular junction proteins of the blood-testis barrier in experimental animals: A systematic review of the literature

Daily, people are exposed to chemicals and environmental compounds such as bisphenols (BPs). These substances are present in more than 80% of human fluids. Human exposure to BPs is associated with male reproductive health disorders. Some of the main targets of BPs are intercellular junction proteins of the blood-testis barrier (BTB) in Sertoli cells because BPs alter the expression or induce aberrant localization of these proteins. In this systematic review, we explore the effects of BP exposure on the expression of BTB junction proteins and the characteristics of in vivo studies to identify potential gaps and priorities for future research. To this end, we conducted a systematic review of articles. Thirteen studies met our inclusion criteria. In most studies, animals treated with bisphenol-A (BPA) showed decreased occludin expression at all tested doses. However, bisphenol-AF treatment did not alter occludin expression. Cx43, ZO-1, β-catenin, nectin-3, cortactin, paladin, and claudin-11 expression also decreased in some tested doses of BP, while N-cadherin and FAK expression increased. BP treatment did not alter the expression of α and γ catenin, E-cadherin, JAM-A, and Arp 3. However, the expression of all these proteins was altered when BPA was administered to neonatal rodents in microgram doses. The results show significant heterogeneity between studies. Thus, it is necessary to perform more research to characterize the changes in BTB protein expression induced by BPs in animals to highlight future research directions that can inform the evaluation of risk of toxicity in humans.

Arsenic interferes with spermatogenesis involving Rictor/mTORC2-mediated blood-testis barrier disruption in mice

Ingestion of arsenic interferes with spermatogenesis and increases the risk of male infertility, but the underlying mechanism remines unclear. In this study, we investigated spermatogenic injury with a focus on blood-testis barrier (BTB) disruption by administrating 5 mg/L and 15 mg/L arsenic orally to adult male mice for 60 d. Our results showed that arsenic exposure reduced sperm quality, altered testicular architecture, and impaired Sertoli cell junctions at the BTB. Analysis of BTB junctional proteins revealed that arsenic intake downregulated Claudin-11 expression and increased protein levels of β-catenin, N-cadherin, and Connexin-43. Aberrant localization of these membrane proteins was also observed in arsenic-treated mice. Meanwhile, arsenic exposure altered the components of Rictor/mTORC2 pathway in mouse testis, including inhibition of Rictor expression, reduced phosphorylation of protein kinase Cα (PKCα) and protein kinase B (PKB), and elevated matrix metalloproteinase-9 (MMP-9) levels. Furthermore, arsenic also induced testicular lipid peroxidative damage, inhibited antioxidant enzyme (T-SOD) activity, and caused glutathione (GSH) depletion. Our findings suggest that disruption of BTB integrity is one of the main factors responsible for the decline in sperm quality caused by arsenic. PKCα-mediated rearrangement of actin filaments and PKB/MMP-9-increased barrier permeability jointly contribute to arsenic-induced BTB disruption.

es-Arp3 and es-Eps8 regulate spermatogenesis via microfilaments in the seminiferous tubule of Eriocheir sinensis

Spermatogenesis is a complicated process that includes spermatogonia differentiation, spermatocytes meiosis, spermatids spermiogenesis and final release of spermatozoa. Actin-related protein 3 (Arp3) and epidermal growth factor receptor pathway substrate 8 (Eps8) are two actin binding proteins that regulate cell adhesion in seminiferous tubules during mammalian spermatogenesis. However, the functions of these two proteins during spermatogenesis in nonmammalian species, especially Crustacea, are still unknown. Here, we cloned es-Arp3 and es-Eps8 from the testis of Chinese mitten crab Eriocheir sinensis. es-Arp3 and es-Eps8 were located in spermatocytes, spermatids and spermatozoa. Knockdown of es-Arp3 and es-Eps8 in vivo caused morphological changes to seminiferous tubules including delayed spermatozoa release, shedding of germ cells and vacuoles. Filamentous-actin (F-actin) filaments network was disorganized due to deficiency of es-Arp3 and es-Eps8. Accompanying this, four junctional proteins (α-catenin, β-catenin, pinin and ZO1) displayed abnormal expression levels as well as penetrating biotin signals in seminiferous tubules. We also used the Arp2/3 complex inhibitor CK666 to block es-Arp3 activity and supported es-Arp3 knockdown results. In summary, our study demonstrated for the first time that es-Arp3 and es-Eps8 are important for spermatogenesis via regulating microfilament-mediated cell adhesion in Eriocheir sinensis.

MARK2 and MARK4 Regulate Sertoli Cell BTB Dynamics Through Microtubule and Actin Cytoskeletons

Microtubule affinity-regulating kinases (MARKs) are nonreceptor Ser/Thr protein kinases known to regulate cell polarity and microtubule dynamics in Caenorhabditis elegans, Drosophila, invertebrates, vertebrates, and mammals. An earlier study has shown that MARK4 is present at the ectoplasmic specialization and blood-testis barrier (BTB) in the seminiferous epithelium of adult rat testes. Here, we report the function of MARK4 and another isoform MARK2 in Sertoli cells at the BTB. Knockdown of MARK2, MARK4, or MARK2 and MARK4 by RNAi using the corresponding siRNA duplexes without apparent off-target effects was shown to impair tight junction (TJ)-permeability barrier at the Sertoli cell BTB. It also disrupted microtubule (MT)- and actin-based cytoskeletal organization within Sertoli cells. Although MARK2 and MARK4 were shown to share sequence homology, they likely regulated the Sertoli cell BTB and MT cytoskeleton differently. Disruption of the TJ-permeability barrier following knockdown of MARK4 was considerably more severe than loss of MARK2, though both perturbed the barrier. Similarly, loss of MARK2 affected MT organization in a different manner than the loss of MARK4. Knockdown of MARK2 caused MT bundles to be arranged around the cell periphery, whereas knockdown of MARK4 caused MTs to retract from the cell edge. These differences in effects on the TJ-permeability barrier are likely from the unique roles of MARK2 and MARK4 in regulating the MT cytoskeleton of the Sertoli cell.

Drug transport across the blood-testis barrier

The blood-testis barrier transfers nutrients to spermatogenic tubules to ensure the normal physiological function of the testes. It also restricts the "entry and exit" of biological macromolecules in the testicular lumen and provides a unique microenvironment for spermatogenesis. This makes the testes a safe place for some viruses and tumors, as immune factors cannot function and drugs fail to reach therapeutic concentrations in the testes. This review aimed to describe the factors regulating the structure and physiological function of the blood-testis barrier. By understanding therapeutic mechanisms of action, drugs can be developed to function in the testicles.

FYN regulates cell adhesion at the blood-testis barrier and the apical ectoplasmic specialization via its effect on Arp3 in the mouse testis

FYN is a non-receptor tyrosine kinase of the SRC family that facilitates virus entry across epithelial tight junctions. However, the role of FYN in mammalian testes in maintaining the blood-testis barrier (BTB) integrity and the adhesion of germ cells to Sertoli cells are not well defined. Here, we show that FYN is a component of the BTB and the apical ectoplasmic specialization (ES) at Sertoli-Sertoli and Sertoli-spermatid interfaces, respectively, and is expressed extensively in mouse testes during postnatal development. FYN was shown to be structurally linked to the actin and microtubule-based cytoskeletons. An in vivo model was used to explore the modulatory effect of FYN on BTB and apical ES dynamics within the testes when adult mice were treated intraperitoneally with CdCl₂ (3 mg/kg body weight). The CdCl₂-induced epithelial restructuring was associated with a transient increase in the interaction between FYN and the actin branching/nucleation protein Arp3, as well as an induction of Arp3 phosphorylation, which possibly lead to actin cytoskeleton remodeling, resulting in BTB damage and germ cell loss in the seminiferous epithelium. Based on the results, we propose a model in which FYN and Arp3 form a protein complex that is responsible for junction reorganization events at the apical ES and the BTB. It is also possible for viruses to break through the BTB and enter the immunoprivileged testicular microenvironment via this mechanism.

Focal Adhesion Protein Vinculin Is Required for Proper Meiotic Progression during Mouse Spermatogenesis

The focal adhesion protein Vinculin (VCL) is ascribed to various cytoplasmic functions; however, its nuclear role has so far been ambiguous. We observed that VCL localizes to the nuclei of mouse primary spermatocytes undergoing first meiotic division. Specifically, VCL localizes along the meiosis-specific structure synaptonemal complex (SC) during prophase I and the centromeric regions, where it remains until metaphase I. To study the role of VCL in meiotic division, we prepared a conditional knock-out mouse (VCL^cKO). We found that the VCL^cKO male mice were semi-fertile, with a decreased number of offspring compared to wild-type animals. This study of events in late prophase I indicated premature splitting of homologous chromosomes, accompanied by an untimely loss of SCP1. This caused erroneous kinetochore formation, followed by failure of the meiotic spindle assembly and metaphase I arrest. To assess the mechanism of VCL involvement in meiosis, we searched for its possible interacting partners. A mass spectrometry approach identified several putative interactors which belong to the ubiquitin–proteasome pathway (UPS). The depletion of VLC leads to the dysregulation of a key subunit of the proteasome complex in the meiotic nuclei and an altered nuclear SUMOylation level. Taken together, we show for the first time the presence of VCL in the nucleus of spermatocytes and its involvement in proper meiotic progress. It also suggests the direction for future studies regarding the role of VCL in spermatogenesis through regulation of UPS.

Qiangjing tablets repair of blood-testis barrier dysfunction in rats via regulating oxidative stress and p38 MAPK pathway

BACKGROUND

The blood-testis barrier (BTB) is a physical barrier of the testis to prevent various exogenous substrates from entering apical compartments and provides immune privilege for spermatogenesis, which is essential for normal spermatogenic function of testis. It has been shown that oxidative stress can damage BTB by activating the p38 MAPK pathway. In Traditional Chinese Medicine, Qiangjing tablets (QJT) improve spermatogenesis and increase pregnancy rates. Previous studies have confirmed that QJT can improve sperm quality and have obvious antioxidant effects. In this study, we explore whether QJT contributes to recovery from BTB dysfunction in rats.

METHODS

BTB dysfunction was induced in rats by 1% Cyclophosphamide (CP). The CP-induced rats in the treatment group were given a dose of QJT (0.45 g/kg·d) by gavage. Testis tissues were collected for histopathological and biochemical analysis, and the testis weight was estimated. Levels of BTB-related proteins and antioxidant enzyme were analyzed in the testis tissues.

RESULTS

QJT resolved the pathological injury of rats testis induced by CP. Furthermore, MDA levels were significantly reduced, and the levels of SOD markedly increased in the testicular tissue after QJT treatment. In addition, QJT down-regulated the expression of p38 protein in rat testis and up-regulated the expressions of key proteins ZO-1, occludin and F-actin in BTB.

CONCLUSION

These results demonstrate that QJT exerts protective effects on CP-induced rats with BTB dysfunction, likely by regulating the oxidative stress-mediated p38 MAPK pathway.

PCP Protein Inversin Regulates Testis Function Through Changes in Cytoskeletal Organization of Actin and Microtubules

Inversin is an integrated component of the Frizzled (Fzd)/Dishevelled (Dvl)/Diversin planar cell polarity (PCP) complex that is known to work in concert with the Van Gogh-like protein (eg, Vangl2)/Prickle PCP complex to support tissue and organ development including the brain, kidney, pancreas, and others. These PCP protein complexes are also recently shown to confer developing haploid spermatid PCP to support spermatogenesis in adult rat testes. However, with the exception of Dvl3 and Vangl2, other PCP proteins have not been investigated in the testis. Herein, we used the technique of RNA interference (RNAi) to examine the role of inversin (Invs) in Sertoli cell (SC) and testis function by corresponding studies in vitro and in vivo. When inversin was silenced by RNAi using specific small interfering RNA duplexes by transfecting primary cultures of SCs in vitro or testes in vivo, it was shown that inversin knockdown (KD) perturbed the SC tight junction-barrier function in vitro and in vivo using corresponding physiological and integrity assays. More important, inversin exerted its regulatory effects through changes in the organization of the actin and microtubule cytoskeletons, including reducing the ability of their polymerization. These changes, in turn, induced defects in spermatogenesis by loss of spermatid polarity, disruptive distribution of blood-testis barrier-associated proteins at the SC-cell interface, appearance of multinucleated round spermatids, and defects in the release of sperm at spermiation.

Titanium dioxide nanoparticles perturb the blood-testis barrier via disruption of actin-based cell adhesive function

As one of the most commonly used nanoparticles, titanium dioxide nanoparticles (TiO₂-NPs) are widely used as coating reagents in cosmetics, medicine and other industries. The increasing risk of exposure to TiO₂-NPs raises concerns about their safety. In this study, we investigated the mechanism by which TiO₂-NPs cross the blood-testis barrier (BTB). TM-4 cells were selected as an in vitro Sertoli cell model of BTB. Cell viability, cell morphological changes, apoptosis, oxidative damage, and the expression levels of actin regulatory and tight junction (TJ) proteins were assessed in TM-4 cells treated with 3-nm and 24-nm TiO₂-NPs. Cells treated with 3-nm TiO₂-NPs exhibited increased cytotoxicity and decreased Annexin II expression, whereas cells treated with 24-nm TiO₂-NPs exhibited increased Arp 3 and c-Src expression. Both TiO₂-NPs induced significant oxidative stress, decreased the expression of TJ proteins (occludin, ZO-1 and claudin 5), damaged the TJ structure, and exhibited enlarged gaps between TM-4 cells. Our results indicated that both TiO₂-NPs crossed the BTB by disrupting actin-based adhesive junctions of TM-4 cells; however, apoptosis was not observed. Our results provide new insights into how TiO₂-NPs cross the BTB.

Polystyrene microplastics disrupt the blood-testis barrier integrity through ROS-Mediated imbalance of mTORC1 and mTORC2

It has been found that polystyrene microplastics (PS-MPs) exposure leads to decreased sperm quality and quantity, and we aim to explore the underlying mechanisms. Therefore, we gave 20 mg/kg body weight (bw) and 40 mg/kg bw 4 μm and 10 μm PS-MPs to male Balb/c mice by gavage. RNA sequencing of testes was performed. After PS-MPs exposure, blood-testis barrier (BTB) integrity was impaired. Since cytoskeleton was closely related to BTB integrity maintenance, and cytoskeleton disorganization could be induced by PS-MPs exposure in the testis, which resulted in the truncation of actin filaments and disruption of BTB integrity. Such processes were attributed to the differential expression of Arp3 and Eps8 (two of the most important actin-binding proteins). According to the transcriptome sequencing results, we examined the oxidative stress level in the testes and Sertoli cells. We found that PS-MPs exposure induced increased reactive oxygen species (ROS) level, which destroyed the balance between mTORC1 and mTORC2 (the mTORC1 activity was increased, while the mTORC2 activity was decreased). In conclusion, PS-MPs induced the imbalance of mTORC1 and mTORC2 via the ROS burst, and altered the expression profile of actin-binding proteins, resulting in F-actin disorganization and reduced expression of junctional proteins in the BTB. Eventually PS-MPs led to BTB integrity disruption and spermatogenesis dysfunction.

HIV-1 Establishes a Sanctuary Site in the Testis by Permeating the BTB Through Changes in Cytoskeletal Organization

Studies suggest that HIV-1 invades the testis through initial permeation of the blood-testis barrier (BTB). The selectivity of the BTB to antiretroviral drugs makes this site a sanctuary for the virus. Little is known about how HIV-1 crosses the BTB and invades the testis. Herein, we used 2 approaches to examine the underlying mechanism(s) by which HIV-1 permeates the BTB and gains entry into the seminiferous epithelium. First, we examined if recombinant Tat protein was capable of perturbing the BTB and making the barrier leaky, using the primary rat Sertoli cell in vitro model that mimics the BTB in vivo. Second, we used HIV-1-infected Sup-T1 cells to investigate the activity of HIV-1 infection on cocultured Sertoli cells. Using both approaches, we found that the Sertoli cell tight junction permeability barrier was considerably perturbed and that HIV-1 effectively permeates the BTB by inducing actin-, microtubule-, vimentin-, and septin-based cytoskeletal changes in Sertoli cells. These studies suggest that HIV-1 directly perturbs BTB function, potentially through the activity of the Tat protein.

Wnt5a Regulates Junctional Function of Sertoli cells Through PCP-mediated Effects on mTORC1 and mTORC2

The blood-testis barrier (BTB) and apical ectoplasmic specialization (ES), which are synchronized through the crosstalk of Sertoli cells and Sertoli germ cells, are required for spermatogenesis and sperm release. Here, we show that Wnt5a, a noncanonical Wnt signaling pathway ligand, is predominately expressed in both the BTB and apical ES and has a specific expression pattern during the seminiferous epithelium cycle. We employed siRNA to knockdown Wnt5a expression in testis and Sertoli cells, and then identified elongated spermatids that lost their polarity and were embedded in the seminiferous epithelium. Moreover, phagosomes were found near the tubule lumen. These defects were due to BTB and apical ES disruption. We also verified that the expression level and/or location of BTB-associated proteins, actin binding proteins (ABPs), and F-actin was changed after Wnt5a knockdown in vivo and in vitro. Additionally, we demonstrated that Wnt5a regulated actin dynamics through Ror2-mediated mTORC1 and mTORC2. This study clarified the molecular mechanism of Wnt5a in Sertoli cell junctions through the planar cell polarity (PCP) signaling pathway. Our findings could provide an experimental basis for the clinical diagnosis and treatment of male infertility caused by Sertoli cell junction impairment.

AKAP9 supports spermatogenesis through its effects on microtubule and actin cytoskeletons in the rat testis

In mammalian testes, extensive remodeling of the microtubule (MT) and actin cytoskeletons takes place in Sertoli cells across the seminiferous epithelium to support spermatogenesis. However, the mechanism(s) involving regulatory and signaling proteins remains poorly understood. Herein, A-kinase anchoring protein 9 (AKAP9, a member of the AKAP multivalent scaffold protein family) was shown to be one of these crucial regulatory proteins in the rat testis. Earlier studies have shown that AKAP9 serves as a signaling platform by recruiting multiple signaling and regulatory proteins to create a large protein complex that binds to the Golgi and centrosome to facilitate the assembly of the MT-nucleating γ-tubulin ring complex to initiate MT polymerization. We further expanded our earlier studies based on a Sertoli cell-specific AKAP9 knockout mouse model to probe the function of AKAP9 by using the techniques of immunofluorescence analysis, RNA interference (RNAi), and biochemical assays on an in vitro primary Sertoli cell culture model, and an adjudin-based animal model. AKAP9 robustly expressed across the seminiferous epithelium in adult rat testes, colocalizing with MT-based tracks, and laid perpendicular across the seminiferous epithelium, and prominently expressed at the Sertoli-spermatid cell-cell anchoring junction (called apical ectoplasmic specialization [ES]) and at the Sertoli cell-cell interface (called basal ES, which together with tight junction [TJ] created the blood-testis barrier [BTB]) stage specifically. AKAP9 knockdown in Sertoli cells by RNAi was found to perturb the TJ-permeability barrier through disruptive changes in the distribution of BTB-associated proteins at the Sertoli cell cortical zone, mediated by a considerable loss of ability to induce both MT polymerization and actin filament bundling. A considerable decline in AKAP9 expression and a disruptive distribution of AKAP9 across the seminiferous tubules was also noted during adjudin-induced germ cell (GC) exfoliation in this animal model, illustrating AKAP9 is essential to maintain the homeostasis of cytoskeletons to maintain Sertoli and GC adhesion in the testis.

Spermiation: Insights from Studies on the Adjudin Model

Spermatogenesis is comprised of a series of cellular events that lead to the generation of haploid sperm. These events include self-renewal of spermatogonial stem cells (SSC), proliferation of spermatogonia by mitosis, differentiation of spermatogonia and spermatocytes, generation of haploid spermatids via meiosis I/II, and spermiogenesis. Spermiogenesis consists of a series of morphological events in which spermatids are being transported across the apical compartment of the seminiferous epithelium while maturing into spermatozoa, which include condensation of the genetic materials, biogenesis of acrosome, packaging of the mitocondria into the mid-piece, and elongation of the sperm tail. However, the biology of spermiation remains poorly understood. In this review, we provide in-depth analysis based on the use of bioinformatics tools and an animal model that mimics spermiation through treatment of adult rats with adjudin, a non-hormonal male contraceptive known to induce extensive germ cell exfoliation across the seminiferous epithelium, but nost notably elongating/elongated spermatids. These analyses have shed insightful information regaridng the biology of spermiation.

Myosin VI maintains the actin-dependent organization of the tubulobulbar complexes required for endocytosis during mouse spermiogenesis†‡

Myosin VI (MYO6) is an actin-based motor that has been implicated in a wide range of cellular processes, including endocytosis and the regulation of actin dynamics. MYO6 is crucial for actin/membrane remodeling during the final step of Drosophila spermatogenesis, and MYO6-deficient males are sterile. This protein also localizes to actin-rich structures involved in mouse spermiogenesis. Although loss of MYO6 in Snell's waltzer knock-out (KO) mice causes several defects and shows reduced male fertility, no studies have been published to address the role of MYO6 in sperm development in mouse. Here we demonstrate that MYO6 and some of its binding partners are present at highly specialized actin-based structures, the apical tubulobulbar complexes (TBCs), which mediate endocytosis of the intercellular junctions at the Sertoli cell-spermatid interface, an essential process for sperm release. Using electron and light microscopy and biochemical approaches, we show that MYO6, GIPC1 and TOM1/L2 form a complex in testis and localize predominantly to an early endocytic APPL1-positive compartment of the TBCs that is distinct from EEA1-positive early endosomes. These proteins also associate with the TBC actin-free bulbular region. Finally, our studies using testis from Snell's waltzer males show that loss of MYO6 causes disruption of the actin cytoskeleton and disorganization of the TBCs and leads to defects in the distribution of the MYO6-positive early APPL1-endosomes. Taken together, we report here for the first time that lack of MYO6 in mouse testis reduces male fertility and disrupts spatial organization of the TBC-related endocytic compartment during the late phase of spermiogenesis.

EXOC1 plays an integral role in spermatogonia pseudopod elongation and spermatocyte stable syncytium formation in mice

The male germ cells must adopt the correct morphology at each differentiation stage for proper spermatogenesis. The spermatogonia regulates its differentiation state by its own migration. The male germ cells differentiate and mature with the formation of syncytia, failure of forming the appropriate syncytia results in the arrest at the spermatocyte stage. However, the detailed molecular mechanisms of male germ cell morphological regulation are unknown. Here, we found that EXOC1, a member of the Exocyst complex, is important for the pseudopod formation of spermatogonia and spermatocyte syncytia in mice. EXOC1 contributes to the pseudopod formation of spermatogonia by inactivating the Rho family small GTPase Rac1 and also functions in the spermatocyte syncytia with the SNARE proteins STX2 and SNAP23. Since EXOC1 is known to bind to several cell morphogenesis factors, this study is expected to be the starting point for the discovery of many morphological regulators of male germ cells.

mTORC1/rpS6 and p-FAK-Y407 signaling regulate spermatogenesis: Insights from studies of the adjudin pharmaceutical/toxicant model

In rodents and humans, the major cellular events at spermatogenesis include self-renewal of spermatogonial stem cells and undifferentiated spermatogonia via mitosis, commitment of spermatogonia to differentiation and transformation to spermatocytes, meiosis, spermiogenesis, and the release of spermatozoa at spermiation. While details of the morphological changes during these cellular events have been delineated, knowledge gap exists between the morphological changes in the seminiferous epithelium and the underlying molecular mechanism(s) that regulate these cellular events. Even though many of the regulatory proteins and biomolecules that modulate spermatogenesis are known based on studies using genetic models, the underlying regulatory mechanism(s), in particular signaling pathways/proteins, remain unexplored since much of the information regarding the signaling regulation is unknown. Studies in the past decade, however, have unequivocally demonstrated that the testis is using several signaling proteins and/or pathways to regulate multiple cellular events to modulate spermatogenesis. These include mTORC1/rpS6/Akt1/2 and p-FAK-Y407. While selective inhibitors and/or agonists and antagonists are available to examine some of these signaling proteins, their use have limitations due to their specificities and also potential systemic cytotoxicity. On the other hand, the use of genetic models has had profound implications for our understanding of the molecular regulation of spermatogenesis, and these knockout (null) models have also revealed the factors that are critical for spermatogenesis. Nonetheless, additional studies using in vitro and in vivo models are necessary to unravel the signaling pathways involved in regulating seminiferous epithelial cycle. Emerging data from studies, such as the use of the adjudin pharmaceutical/toxicant model, have illustrated that this non-hormonal male contraceptive drug is utilizing specific signaling pathways/proteins to induce specific defects in spermatogenesis, yielding mechanistic insights on the regulation of spermatogenesis. We sought to review these recent data in this article, highlighting an interesting approach that can be considered for future studies.

Bisphenol S perturbs Sertoli cell junctions in male rats via alterations in cytoskeletal organization mediated by an imbalance between mTORC1 and mTORC2

Bisphenol S (BPS) is now used as an alternative of bisphenol A (BPA), but has been implicated in male reproductive dysfunction-including diminished sperm number and quality and altered hormonal concentrations. However, the mechanisms of action subserving these effects remains unclear. In the present study, BPS at doses of 50 mg/kg bw and 100 mg/kg bw caused defects in the integrity of the blood-testis barrier (BTB) and apical ectoplasmic specialization (ES), and we also delineated an underlying molecular mechanism of action. BPS induced F-actin and α-tubulin disorganization in seminiferous tubules, which in turn led to the truncation of actin filaments and microtubules. Additionally, BPS was found to perturb the expression of the actin-binding proteins Arp3 and Eps8, which are critical for the organization of the actin filaments. mTORC1 and mTORC2 manifest opposing roles in Sertoli cell junctional function, and we demonstrated that mTORC1/rpS6/Akt/MMP9 signaling was increased and that mTORC2/rictor activity was also attenuated. In summary, we showed that BPS-induced disruption of the BTB and apical ES perturbed normal spermatogenic function that was mediated by mTORC1 and mTORC2. The imbalance in mTORC1 and mTORC2, in turn, altered the expression of actin-binding proteins, resulting in the impairment of F-actin and MT organization, and inhibited the expression of junctional proteins at the BTB and apical ES.

Microcystin-leucine-arginine induces apical ectoplasmic specialization disassembly

Microcystin-leucine-arginine (MC-LR) has been identified to be a hazardous material to cause hepatotoxicity. In this study, mice were exposed to MC-LR dissolved in drinking water at doses of 1, 10, 20 and 30 μg/L for 90 and 180 days, respectively. We validated MC-LR accelerated spermatid exfoliation and caused large vacuoles in testes, reducing sperm count and increasing percentage of morphologically abnormal sperm. Furthermore, we found MC-LR induced the apical ectoplasmic specialization (ES) disassembly by disrupting F-actin organization. Further studies identified that downregulation of Palladin, the actin crosslinking protein, might be associated with disassembly of the apical ES in mice testis following MC-LR exposure. We also confirmed that MC-LR disrupted the interaction between Palladin and other actin-related proteins and thus impeded the F-actin organization. Additionally, we found that autophagy initiated by AMPK/ULK1 signaling pathway mediated the degradation of Palladin in Sertoli cells challenged with MC-LR. Following exposure to MC-LR, reduced PP2A activity and upregulated expression of LKB1 and CAMKK2 could activate AMPK. In conclusion, these results revealed MC-LR induced the degradation of Palladin via AMPK/ULK1-mediated autophagy, which might result in the apical ES disorder and spermatid exfoliation from spermatogenic epithelium. Our work may provide a new perspective to understand MC-LR-induced male infertility.

Diverse functions of myosin VI in spermiogenesis

Spermiogenesis is the final stage of spermatogenesis, a differentiation process during which unpolarized spermatids undergo excessive remodeling that results in the formation of sperm. The actin cytoskeleton and associated actin-binding proteins play crucial roles during this process regulating organelle or vesicle delivery/segregation and forming unique testicular structures involved in spermatid remodeling. In addition, several myosin motor proteins including MYO6 generate force and movement during sperm differentiation. MYO6 is highly unusual as it moves towards the minus end of actin filaments in the opposite direction to other myosin motors. This specialized feature of MYO6 may explain the many proposed functions of this myosin in a wide array of cellular processes in animal cells, including endocytosis, secretion, stabilization of the Golgi complex, and regulation of actin dynamics. These diverse roles of MYO6 are mediated by a range of specialized cargo-adaptor proteins that link this myosin to distinct cellular compartments and processes. During sperm development in a number of different organisms, MYO6 carries out pivotal functions. In Drosophila, the MYO6 ortholog regulates actin reorganization during spermatid individualization and male KO flies are sterile. In C. elegans, the MYO6 ortholog mediates asymmetric segregation of cytosolic material and spermatid budding through cytokinesis, whereas in mice, this myosin regulates assembly of highly specialized actin-rich structures and formation of membrane compartments to allow the formation of fully differentiated sperm. In this review, we will present an overview and compare the diverse function of MYO6 in the specialized adaptations of spermiogenesis in flies, worms, and mammals.

The Non-hormonal Male Contraceptive Adjudin Exerts its Effects via MAPs and Signaling Proteins mTORC1/rpS6 and FAK-Y407

Adjudin, 1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide (formerly called AF-2364), is a nonhormonal male contraceptive, since it effectively induces reversible male infertility without perturbing the serum concentrations of follicle stimulating hormone (FSH), testosterone, and inhibin B based on studies in rats and rabbits. Adjudin was shown to exert its effects preferentially by perturbing the testis-specific actin-rich adherens junction (AJ) at the Sertoli-spermatid interface known as apical ectoplasmic specialization (apical ES), thereby effectively inducing spermatid exfoliation. Adjudin did not perturb germ cell development nor germ cell function. Also, it had no effects on Sertoli cell-cell AJ called basal ectoplasmic specialization (basal ES), which, together with tight junction constitute the blood-testis barrier (BTB), unless an acute dose of adjudin was used. Adjudin also did not perturb the population of spermatogonial stem cells nor Sertoli cells in the testis. However, the downstream signaling protein(s) utilized by adjudin to induce transient male infertility remains unexplored. Herein, using adult rats treated with adjudin and monitored changes in the phenotypes across the seminiferous epithelium between 6 and 96 h in parallel with the steady-state protein levels of an array of signaling and cytoskeletal regulatory proteins, recently shown to be involved in apical ES, basal ES and BTB function. It was shown that adjudin exerts its contraceptive effects through changes in microtubule associated proteins (MAPs) and signaling proteins mTORC1/rpS6 and p-FAK-Y407. These findings are important to not only study adjudin-mediated male infertility but also the biology of spermatogenesis.

The Seminiferous Epithelial Cycle of Spermatogenesis: Role of Non-receptor Tyrosine Kinases

Non-receptor tyrosine kinases (NRTKs) are implicated in various biological processes including cell proliferation, differentiation, survival, and apoptosis, as well as cell adhesion and movement. NRTKs are expressed in all mammals and in different cell types, with extraordinarily high expression in the testis. Their association with the plasma membrane and dynamic subcellular localization are crucial parameters in their activation and function. Many NRTKs are found in endosomal protein trafficking pathways, which suggests a novel mechanism to regulate the timely junction restructuring in the mammalian testis to facilitate spermiation and germ cell transport across the seminiferous epithelium.

NC1-Peptide From Collagen α3 (IV) Chains in the Basement Membrane of Testes Regulates Spermatogenesis via p-FAK-Y407

The blood-testis barrier (BTB) in the testis is an important ultrastructure to support spermatogenesis. This blood-tissue barrier undergoes remodeling at late stage VII to early stage IX of the epithelial cycle to support the transport of preleptotene spermatocytes across the BTB to prepare for meiosis I/II at the apical compartment through a mechanism that remains to be delineated. Studies have shown that NC1-peptide-derived collagen α3 (IV) chain in the basement membrane is a bioactive peptide that induces BTB remodeling. It also promotes the release of fully developed spermatids into the tubule lumen. Thus, this endogenously produced peptide coordinates these 2 cellular events across the seminiferous epithelium. Using an NC1-peptide complementary deoxyribonucleic acid (cDNA) construct to transfect adult rat testes for overexpression, NC1-peptide was found to effectively induce germ cell exfoliation and BTB remodeling, which was associated with a surge and activation of p-rpS6, the downstream signaling protein of mTORC1 and the concomitant downregulation of p-FAK-Y407 in the testis. In order to define the functional relationship between p-rpS6 and p-FAK-Y407 signaling to confer the ability of NC1-peptide to regulate testis function, a phosphomimetic (and thus constitutively active) mutant of p-FAK-Y407 (p-FAK-Y407E-MT) was used for its co-transfection, utilizing Sertoli cells cultured in vitro with a functional tight junction (TJ) barrier that mimicked the BTB in vivo. Overexpression of p-FAK-Y407E-MT blocked the effects of NC1-peptide to perturb Sertoli cell BTB function by promoting F-actin and microtubule cytoskeleton function, and downregulated the NC1-peptide-mediated induction of p-rpS6 activation. In brief, NC1-peptide is an important endogenously produced biomolecule that regulates BTB dynamics.

Microtubule Cytoskeleton and Spermatogenesis-Lesson From Studies of Toxicant Models

Studies have shown that mammalian testes, in particular the Sertoli cells, are highly susceptible to exposure of environmental toxicants, such as cadmium, perfluorooctanesulfonate, phthalates, 2,5-hexanedione and bisphenol A. However, important studies conducted by reproductive toxicologists and/or biologists in the past have been treated as toxicology reports per se. Yet, many of these studies provided important mechanistic insights on the toxicant-induced testis injury and reproductive dysfunction, relevant to the biology of the testis and spermatogenesis. Furthermore, recent studies have shown that findings obtained from toxicant models are exceedingly helpful tools to unravel the biology of testis function in particular spermatogenesis, including specific cellular events associated with spermatid transport to support spermiogenesis and spermiation. In this review, we critically evaluate some recent data, focusing primarily on the molecular structure and role of microtubules in cellular function, illustrating the importance of toxicant models to unravel the biology of microtubule cytoskeleton in supporting spermatogenesis, well beyond information on toxicology. These findings have opened up some potential areas of research which should be carefully evaluated in the years to come.

Dysfunction of dimorphic sperm impairs male fertility in the silkworm

Sperm, which have a vital role in sexual reproduction in the animal kingdom, can display heteromorphism in some species. The regulation of sperm dichotomy remains a longstanding puzzle even though the phenomenon has been widely documented for over a century. Here we use Bombyx mori as a model to study a form of sperm dimorphism (eupyrene and apyrene sperm), which is nearly universal among Lepidoptera. We demonstrate that B. mori Sex-lethal (BmSxl) is crucial for apyrene sperm development, and that B. mori poly(A)-specific ribonuclease-like domain-containing 1 (BmPnldc1) is required for eupyrene sperm development. BmSXL is distributed in the nuclei and cytoplasm of somatic cyst cells in a mesh-like pattern and in the cytoplasm of germ cells enclosed in spermatocysts and sperm bundles. Cytological analyses of dimorphic sperm in BmSxl mutants (∆BmSxl) showed deficient apyrene sperm with abnormal nuclei, as well as loss of motility associated with malformed mitochondrial derivatives. We define the crucial function of apyrene sperm in the process of fertilization as assisting the migration of eupyrene spermatozoa from bursa copulatrix to spermatheca. By contrast, BmPnldc1 deficiency (∆BmPnldc1) caused eupyrene sperm abnormalities and impaired the release of eupyrene sperm bundles during spermiation. Although apyrene or eupyrene sperm defects impaired fertility of the mutated males, double copulation of a wild-type female with ∆BmSxl and ∆BmPnldc1 males could rescue the sterility phenotypes induced by single copulation with either gene-deficient male. Our findings demonstrate the crucial functions of BmSxl and BmPnldc1 in the development of sperm dimorphism and the indispensable roles of nonfertile apyrene sperm in fertilization.

Regulation of blood-testis barrier dynamics by the mTORC1/rpS6 signaling complex: An in vitro study

During spermatogenesis, developing germ cells that lack the cellular ultrastructures of filopodia and lamellipodia generally found in migrating cells, such as macrophages and fibroblasts, rely on Sertoli cells to support their transport across the seminiferous epithelium. These include the transport of preleptotene spermatocytes across the blood-testis barrier (BTB), but also the transport of germ cells, in particular developing haploid spermatids, across the seminiferous epithelium, that is to and away from the tubule lumen, depending on the stages of the epithelial cycle. On the other hand, cell junctions at the Sertoli cell–cell and Sertoli–germ cell interface also undergo rapid remodeling, involving disassembly and reassembly of cell junctions, which, in turn, are supported by actin- and microtubule-based cytoskeletal remodeling. Interestingly, the underlying mechanism(s) and the involving biomolecule(s) that regulate or support cytoskeletal remodeling remain largely unknown. Herein, we used an in vitro model of primary Sertoli cell cultures that mimicked the Sertoli BTB in vivo overexpressed with the ribosomal protein S6 (rpS6, the downstream signaling protein of mammalian target of rapamycin complex 1 [mTORC1]) cloned into the mammalian expression vector pCI-neo, namely, quadruple phosphomimetic and constitutively active mutant of rpS6 (pCI-neo/p-rpS6-MT) versus pCI-neo/rpS6-WT (wild-type) and empty vector (pCI-neo/Ctrl) for studies. These findings provide compelling evidence that the mTORC1/rpS6 signal pathway exerted its effects to promote Sertoli cell BTB remodeling. This was mediated through changes in the organization of actin- and microtubule-based cytoskeletons, involving changes in the distribution and/or spatial expression of actin- and microtubule-regulatory proteins.

Integration of whole-genome DNA methylation data with RNA sequencing data to identify markers for bull fertility

Predicting bull fertility prior to breeding is a current challenge for the dairy industry. The use of molecular biomarkers has been previously assessed. However, the integration of this information has not been performed to extract biologically relevant markers. The goal of this study was to integrate DNA methylation data with previously published RNA-sequencing results in order to identify candidate markers for sire fertility. A total of 1765 differentially methylated cytosines were found between high- and low-fertility sires. Ten genes associated with 11 differentially methylated cytosines were found in a previous study of gene expression between high- and low-fertility sires. Additionally, two of these genes code for proteins found exclusively in bull seminal plasma. Collectively, our results reveal 10 genes that could be used in the future as a panel for predicting bull fertility.

JMY expression by Sertoli cells contributes to mediating spermatogenesis in mice

Sertoli cells are crucial for spermatogenesis in the seminiferous epithelium because their actin cytoskeleton supports vesicular transport, cell junction formation, protein anchoring, and spermiation. Here, we show that a junction-mediating and actin-regulatory protein (JMY) affects the blood-tissue barrier (BTB) function through remodeling of the Sertoli cell junctional integrity and it also contributes to controlling endocytic vesicle trafficking. These functions are critical for the maintenance of sperm fertility since loss of Sertoli cell-specific Jmy function induced male subfertility in mice. Specifically, these mice have (a) impaired BTB integrity and spermatid adhesion in the seminiferous tubules; (b) high incidence of sperm structural deformity; and (c) reduced sperm count and poor sperm motility. Moreover, the cytoskeletal integrity was compromised along with endocytic vesicular trafficking. These effects impaired junctional protein recycling and reduced Sertoli cell BTB junctional integrity. In addition, JMY interaction with actin-binding protein candidates α-actinin1 and sorbin and SH3 domain containing protein 2 was related to JMY activity, and in turn, actin cytoskeletal organization. In summary, JMY affects the control of spermatogenesis through the regulation of actin filament organization and endocytic vesicle trafficking in Sertoli cells.

The dynamics and regulation of microfilament during spermatogenesis

Spermatogenesis is a highly complex physiological process which contains spermatogonia proliferation, spermatocyte meiosis and spermatid morphogenesis. In the past decade, actin binding proteins and signaling pathways which are critical for regulating the actin cytoskeleton in testis had been found. In this review, we summarized 5 actin-binding proteins that have been proven to play important roles in the seminiferous epithelium. Lack of them perturbs spermatids polarity and the transport of spermatids. The loss of Arp2/3 complex, Formin1, Eps8, Palladin and Plastin3 cause sperm release failure suggesting their irreplaceable role in spermatogenesis. Actin regulation relies on multiple signal pathways. The PI3K/Akt signaling pathway positively regulate the mTOR pathway to promote actin reorganization in seminiferous epithelium. Conversely, TSC1/TSC2 complex, the upstream of mTOR, is activated by the LKB1/AMPK pathway to inhibit cell proliferation, differentiation and migration. The increasing researches focus on the function of actin binding proteins (ABPs), however, their collaborative regulation of actin patterns and potential regulatory signaling networks remains unclear. We reviewed ABPs that play important roles in mammalian spermatogenesis and signal pathways involved in the regulation of microfilaments. We suggest that more relevant studies should be performed in the future.

NC1-peptide regulates spermatogenesis through changes in cytoskeletal organization mediated by EB1

During the epithelial cycle of spermatogenesis, different sets of cellular events take place across the seminiferous epithelium in the testis. For instance, remodeling of the blood-testis barrier (BTB) that facilitates the transport of preleptotene spermatocytes across the immunological barrier and the release of sperms at spermiation take place at the opposite ends of the epithelium simultaneously at stage VIII of the epithelial cycle. These cellular events are tightly coordinated via locally produced regulatory biomolecules. Studies have shown that collagen α3 (IV) chains, a major constituent component of the basement membrane, release the non-collagenous (NC) 1 domain, a 28-kDa peptide, designated NC1-peptide, from the C-terminal region, via the action of MMP-9 (matrix metalloproteinase 9). NC1-peptide was found to be capable of inducing BTB remodeling and spermatid release across the epithelium. As such, the NC1-peptide is an endogenously produced biologically active peptide which coordinates these cellular events across the epithelium in stage VIII tubules. Herein, we used an animal model, wherein NC1-peptide cloned into the pCI-neo mammalian expression vector was overexpressed in the testis, to better understanding the molecular mechanism by which NC1-peptide regulated spermatogenic function. It was shown that NC1-peptide induced considerable downregulation on a number of cell polarity and planar cell polarity (PCP) proteins, and studies have shown these polarity and PCP proteins modulate spermatid polarity and adhesion via their effects on microtubule (MT) and F-actin cytoskeletal organization across the epithelium. More important, NC1-peptide exerted its effects by downregulating the expression of microtubule (MT) plus-end tracking protein (+TIP) called EB1 (end-binding protein 1). We cloned the full-length EB1 cDNA for its overexpression in the testis, which was found to block the NC1-peptide-mediated disruptive effects on cytoskeletal organization in Sertoli cell epithelium and pertinent Sertoli cell functions. These findings thus illustrate that NC1-peptide is working in concert with EB1 to support spermatogenesis.

Cdc42 is involved in NC1 peptide-regulated BTB dynamics through actin and microtubule cytoskeletal reorganization

Noncollagenous domain 1 (NC1)-peptide is a biologically active peptide derived from the C-terminal region of collagen α3(IV) chain, a structural constituent protein at the basement membrane in the rat testis, likely via proteolytic cleavage of matrix metalloproteinase 9. Studies have shown that this NC1 peptide regulates testis function by inducing Sertoli cell blood-testis barrier (BTB) remodeling and is also capable of inducing elongate spermatid exfoliation through its disruptive effects on the organization of actin- and microtubule (MT)-based cytoskeletons at these cell adhesion sites. However, the underlying molecular mechanism remains unknown. NC1 peptide was found to exert its biologic effects through an activation of small GTPase cell division control protein 42 homolog (Cdc42) because cooverexpression of the dominant negative mutant of Cdc42 [namely, Cdc42-T17N (via a single mutation of amino acid residue 17 from the N terminus from Thr to Asn by site-directed mutagenesis, making it constitutively inactive)] and NC1 peptide was able to block the NC1 peptide-induced Sertoli cell tight junction-permeability barrier disruption. Their cooverexpression also blocked the NC1 peptide-induced misdistribution of BTB-associated proteins at the cell-cell interface and also disruptive cytoskeletal organization of F-actin and MTs through changes in spatial expression of the corresponding actin and MT regulatory proteins. Interestingly, NC1 peptide was also found to induce an up-regulation of phosphorylated (p)-ribosomal protein S6 (rpS6) (namely, p-rpS6-S235/S236) and a concomitant down-regulation of p-Akt1/2 (namely, p-Akt1-S473 and p-Akt2-S474), but these changes could not be blocked by overexpression of Cdc42-T17N. More importantly, NC1 peptide-induced Cdc42 activation was effectively blocked by treatment of Sertoli cell epithelium with a p-Akt1/2 activator SC79, which is also capable of blocking NC1 peptide-induced down-regulation of p-Akt1-S473 and p-Akt2/S474, but not p-rpS6-S235/S236 up-regulation. In summary, these findings illustrate that Cdc42 is working downstream of the mammalian target of rapamycin complex 1/rpS6/Akt1/2 signaling pathway to support NC1 peptide-mediated effects on Sertoli cell function in the testis using the rat as an animal model.-Su, W., Cheng, C. Y. Cdc42 is involved in NC1 peptide-regulated BTB dynamics through actin and microtubule cytoskeletal reorganization.

mTORC1/rpS6 and spermatogenic function in the testis-insights from the adjudin model

mTORC1/rpS6 signaling complex promoted Sertoli blood-testis barrier (BTB) remodeling by perturbing Sertoli cell-cell adhesion site known as the basal ectoplasmic specialization (ES). mTORC1/rpS6 complex also promoted disruption of spermatid adhesion at the Sertoli-spermatid interface called the apical ES. Herein, we performed analyses using the adjudin (a non-hormonal male contraceptive drug under development) model, wherein adjudin was known to perturb apical and basal ES function when used at high dose. Through direct administration of adjudin to the testis, adjudin at doses that failed to perturb BTB integrity per se, overexpression of an rpS6 phosphomimetic (i.e., constitutively active) mutant (i.e., p-rpS6-MT) that modified BTB function considerably potentiated adjudin efficacy. This led to disorderly spatial expression of proteins necessary to maintain the proper cytoskeletal organization of F-actin and microtubules (MTs) across the seminiferous epithelium, leading to germ cell exfoliation and aspermatogenesis. These findings yielded important insights regarding the role of mTORC1/rpS6 signaling complex in regulating BTB homeostasis.

F5-Peptide and mTORC1/rpS6 Effectively Enhance BTB Transport Function in the Testis-Lesson From the Adjudin Model

During spermatogenesis, the blood-testis barrier (BTB) undergoes cyclic remodeling that is crucial to support the transport of preleptotene spermatocytes across the immunological barrier at stage VIII to IX of the epithelial cycle. Studies have shown that this timely remodeling of the BTB is supported by several endogenously produced barrier modifiers across the seminiferous epithelium, which include the F5-peptide and the ribosomal protein S6 [rpS6; a downstream signaling molecule of the mammalian target of rapamycin complex 1 (mTORC1)] signaling protein. Herein, F5-peptide and a quadruple phosphomimetic (and constitutively active) mutant of rpS6 [i.e., phosphorylated (p-)rpS6-MT] that are capable of inducing reversible immunological barrier remodeling, by making the barrier "leaky" transiently, were used for their overexpression in the testis to induce BTB opening. We sought to examine whether this facilitated the crossing of the nonhormonal male contraceptive adjudin at the BTB when administered by oral gavage, thereby effectively improving its BTB transport to induce germ cell adhesion and aspermatogenesis. Indeed, it was shown that combined overexpression of F5-peptide and p-rpS6-MT and a low dose of adjudin, which by itself had no noticeable effects on spermatogenesis, was capable of perturbing the organization of actin- and microtubule (MT)-based cytoskeletons through changes in the spatial expression of actin- and MT-binding/regulatory proteins to the corresponding cytoskeleton. These findings thus illustrate the possibility of delivering drugs to any target organ behind a blood-tissue barrier by modifying the tight junction permeability barrier using endogenously produced barrier modifiers based on findings from this adjudin animal model.

mTORC1/rpS6 signaling complex modifies BTB transport function: an in vivo study using the adjudin model

Studies have shown that the mTORC1/rpS6 signaling cascade regulates Sertoli cell blood-testis barrier (BTB) dynamics. For instance, specific inhibition of mTORC1 by treating Sertoli cells with rapamycin promotes the Sertoli cell barrier, making it "tighter." However, activation of mTORC1 by overexpressing a full-length rpS6 cDNA clone (i.e., rpS6-WT, wild type) in Sertoli cells promotes BTB remodeling, making the barrier "leaky." Also, there is an increase in rpS6 and p-rpS6 (phosphorylated and activated rpS6) expression at the BTB in testes at stages VIII-IX of the epithelial cycle, and it coincides with BTB remodeling to support the transport of preleptotene spermatocytes across the barrier, illustrating that rpS6 is a BTB-modifying signaling protein. Herein, we used a constitutively active, quadruple phosphomimetic mutant of rpS6, namely p-rpS6-MT of p-rpS6-S235E/S236E/S240E/S244E, wherein Ser (S) was converted to Glu (E) at amino acid residues 235, 236, 240, and 244 from the NH2 terminus by site-directed mutagenesis, for its overexpression in rat testes in vivo using the Polyplus in vivo jet-PEI transfection reagent with high transfection efficiency. Overexpression of this p-rpS6-MT was capable of inducing BTB remodeling, making the barrier "leaky." This thus promoted the entry of the nonhormonal male contraceptive adjudin into the adluminal compartment in the seminiferous epithelium to induce germ cell exfoliation. Combined overexpression of p-rpS6-MT with a male contraceptive (e.g., adjudin) potentiated the drug bioavailability by modifying the BTB. This approach thus lowers intrinsic drug toxicity due to a reduced drug dose, further characterizing the biology of BTB transport function.

CAMSAP2 Is a Microtubule Minus-End Targeting Protein That Regulates BTB Dynamics Through Cytoskeletal Organization

During spermatogenesis, microtubule (MT) cytoskeleton in Sertoli cells confers blood-testis barrier (BTB) function, but the regulators and mechanisms that modulate MT dynamics remain unexplored. In this study, we examined the role of calmodulin-regulated spectrin-associated protein (CAMSAP)2 (a member of the CAMSAP/Patronin protein family), and a minus-end targeting protein (-TIP) that binds to the minus-end (i.e., slow-growing end) of polarized MTs involved in determining MT length, in Sertoli cell function. CAMSAP2 was found to localize at discrete sites across the Sertoli cell cytosol, different from end-binding protein 1 (a microtubule plus-end tracking protein that binds to the plus-end of MTs), and colocalized with MTs. CAMSAP2 displayed a stage-specific expression pattern, appearing as tracklike structures across the seminiferous epithelium in adult rat testes that lay perpendicular to the basement membrane. CAMSAP2 knockdown by RNA interference was found to promote Sertoli cell tight junction (TJ) barrier function, illustrating its role in inducing TJ remodeling under physiological conditions. To further examine the regulatory role of CAMSAP2 in BTB dynamics, we used a perfluorooctanesulfonate (PFOS)-induced Sertoli cell injury model for investigations. CAMSAP2 knockdown blocked PFOS-induced Sertoli cell injury by promoting proper distribution of BTB-associated proteins at the cell-cell interface. This effect was mediated by the ability of CAMSAP2 knockdown to block PFOS-induced disruptive organization of MTs, but also F-actin, across cell cytosol through changes in cellular distribution/localization of MT- and actin-regulatory proteins. In summary, CAMSAP2 is a regulator of MT and actin dynamics in Sertoli cells to support BTB dynamics and spermatogenesis.

Myosin VIIa Supports Spermatid/Organelle Transport and Cell Adhesion During Spermatogenesis in the Rat Testis

The biology of transport of spermatids and spermatid adhesion across the seminiferous epithelium during the epithelial cycle remains largely unexplored. Nonetheless, studies have implicated the role of motor proteins in these cellular events. In this article, we report findings to unravel the role of myosin VIIa, an F-actin-based barbed (+)-end-directed motor protein, to support cellular transport and adhesion in the testis. Using RNA interference to knock down myosin VIIa in Sertoli cells cultured in vitro as a study model was shown to perturb the Sertoli cell tight junction permeability barrier, mediated through disorganization of actin- or microtubule (MT)-based cytoskeletons owing to disruptive changes on the spatiotemporal expression of F-actin or MT-regulatory proteins. Consistent with these in vitro findings, knockdown of myosin VIIa in the testis in vivo also induced disorganization of the actin- and MT-based cytoskeletons across the seminiferous epithelium, mediated by disruptive changes in the spatiotemporal expression of actin- and MT-based regulatory proteins. More important, the transport of spermatids and organelles across the epithelium, as well as cell adhesion, was grossly disrupted. For instance, step 19 spermatids failed to be transported to the adluminal compartment near the tubule lumen to undergo spermiation; in this manner, step 19 spermatids were persistently detected in stage IX and XII tubules, intermingling with step 9 and 12 spermatids, respectively. Also, phagosomes were detected near the tubule lumen in stage I to III tubules when they should have been degraded near the base of the seminiferous epithelium via the lysosomal pathway. In summary, myosin VIIa motor protein was crucial to support cellular transport and adhesion during spermatogenesis.

Emerging role for SRC family kinases in junction dynamics during spermatogenesis

SRC family kinases (SFKs) are known regulators of multiple cellular events, including cell movement, differentiation, proliferation, survival and apoptosis. SFKs are expressed virtually by all mammalian cells. They are non-receptor protein kinases that phosphorylate a variety of cellular proteins on tyrosine, leading to the activation of protein targets in response to environmental stimuli. Among SFKs, SRC, YES and FYN are the ubiquitously expressed and best studied members. In fact, SRC, the prototypical SFK, was the first tyrosine kinase identified in mammalian cells. Studies have shown that SFKs are regulators of cell junctions, and function in endocytosis and membrane trafficking to regulate junction restructuring events. Herein, we briefly summarize the recent findings in the field regarding the role of SFKs in the testis in regulating spermatogenesis, particularly in Sertoli-Sertoli and Sertoli-germ cell adhesion. While it is almost 50 years since the identification of the oncogene v-Src encoded by Rous sarcoma transforming virus, the understanding of SFK involvement during spermatogenesis in the testis remains far behind that in other epithelia and tissues. The goal of this review is to bridge this gap.

Regulation of Blood-Testis Barrier (BTB) Dynamics, Role of Actin-, and Microtubule-Based Cytoskeletons

The blood-testis barrier (BTB) is an important ultrastructure in the testis that supports meiosis and postmeiotic spermatid development since a delay in the establishment of a functional Sertoli cell barrier during postnatal development in rats or mice by 17-20 day postpartum (dpp) would lead to a delay of the first wave of meiosis. Furthermore, irreversible disruption of the BTB by toxicants also induces infertility in rodents. Herein, we summarize recent findings that BTB dynamics (i.e., disassembly, reassembly, and stabilization) are supported by the concerted efforts of the actin- and microtubule (MT)-based cytoskeletons. We focus on the role of two actin nucleation protein complexes, namely, the Arp2/3 (actin-related protein 2/3) complex and formin 1 (or the formin 1/spire 1 complex) known to induce actin nucleation, respectively, by conferring plasticity to actin cytoskeleton. We also focus on the MT plus (+)-end tracking protein (+TIP) EB1 (end-binding protein 1) which is known to confer MT stabilization. Furthermore, we discuss in particular how the interactions of these proteins modulate BTB dynamics during spermatogenesis. These findings also yield a novel hypothetical concept regarding the molecular mechanism that modulates BTB function.

Fluoride altered rat's blood testis barrier by affecting the F-actin via IL-1α

Fluoride is known to affect the pro-inflammatory cytokines in the testis. Most of the recent literatures cited that cytokines regulate the blood-testis-barrier (BTB). However, the involvement of cytokines in the fluoride induced toxicity in BTB remains unclear. In order to study this, 60 male Sprague-Dawley (SD) rats were taken and randomly divided into 5 groups which included four fluoride groups exposed to 0, 25, 50, and 100 mg/L NaF in distilled water and one positive control group. On the 29th day of fluoride exposure, the positive control group rats were administered 0.1% CaCl₂ solution. Biotin tracer technology and transmission electron microscopy (TEM) analysis were applied to evaluate the function and ultra-structure of BTB. The expression levels of the BTB associated proteins, actin relative protein 3 (Arp3), interleukin-1 alpha (IL-1α), and transforming growth factor beta-3 (TGF-β3) were determined using Western blotting and Enzyme Linked Immunosorbent Assay (ELISA) respectively, meanwhile the actin filament (F-actin) was detected by fluorescent phalloidin conjugates. Our results revealed that the function and the ultra-structure of BTB in all the fluoride treated groups were damaged with a concomitant significant decreases in basal ectoplasmic specialization (basal ES), associated protein β-catenin, and F-actin. Moreover, Arp3 levels were significantly increased in 50 and 100 mg/L NaF groups. Meanwhile, IL-1α significantly increased in all the fluoride treated groups. In summary, we concluded that an increase in IL-1α induced by NaF significantly decreased the expression of F-actin and the organization of F-actin highly branched, which might facilitate the BTB's functional and ultra-structural variations.

Dynein 1 supports spermatid transport and spermiation during spermatogenesis in the rat testis

In the mammalian testis, spermatogenesis is dependent on the microtubule (MT)-specific motor proteins, such as dynein 1, that serve as the engine to support germ cell and organelle transport across the seminiferous epithelium at different stages of the epithelial cycle. Yet the underlying molecular mechanism(s) that support this series of cellular events remain unknown. Herein, we used RNAi to knockdown cytoplasmic dynein 1 heavy chain (Dync1h1) and an inhibitor ciliobrevin D to inactivate dynein in Sertoli cells in vitro and the testis in vivo, thereby probing the role of dynein 1 in spermatogenesis. Both treatments were shown to extensively induce disruption of MT organization across Sertoli cells in vitro and the testis in vivo. These changes also perturbed the transport of spermatids and other organelles (such as phagosomes) across the epithelium. These changes thus led to disruption of spermatogenesis. Interestingly, the knockdown of dynein 1 or its inactivation by ciliobrevin D also perturbed gross disruption of F-actin across the Sertoli cells in vitro and the seminiferous epithelium in vivo, illustrating there are cross talks between the two cytoskeletons in the testis. In summary, these findings confirm the role of cytoplasmic dynein 1 to support the transport of spermatids and organelles across the seminiferous epithelium during the epithelial cycle of spermatogenesis.

Fluorochloridone perturbs blood-testis barrier/Sertoli cell barrier function through Arp3-mediated F-actin disruption

There are reports of fluorochloridone (FLC)-induced male reproductive toxicity, but the underlying toxicological mechanisms remain unknown. In this study, we looked at how FLC exposure affected the integrity of the blood-testis barrier (BTB) and the Sertoli cell barrier and studied the molecular mechanisms. Male rats received gavage administration of FLC (30 mg/kg/d) for 14 consecutive days with sample collection at the 7th and 14th day; and primary cultured Sertoli cells were treated with 0-10 μM FLC in vitro for 24 h. Our in vivo findings revealed that FLC exposure caused time-dependent testicular injuries, sperm quality decrease as well as adverse changes in BTB integrity, F-actin organization, and expressions of claudin-11 and Arp3. In Sertoli cells isolated from FLC-treated rat testis, Sertoli cell barrier tightness was increased. In Sertoli cells in vitro exposed to FLC, abnormal changes in the barrier permeability were also observed, and the protein expressions of occludin, claudin-11, ZO-1, connexin-43, and Arp3 were significantly decreased in a dose- and time-dependent manner. Furthermore, the FLC-induced adverse changes in Sertoli cell barrier and F-actin were partly alleviated by the induction of Arp3 overexpression. In conclusion, our findings revealed that FLC perturbed BTB/Sertoli cell barrier function through Arp3-mediated F-actin disorganization.

Multiple aspects of male germ cell development and interactions with Sertoli cells require inositol hexakisphosphate kinase-1

Inositol hexakisphosphate kinase-1 (IP6K1) is required for male fertility, but the underlying mechanisms have been elusive. Here, we report that IP6K1 is required for multiple aspects of male germ cell development. This development requires selective interactions between germ cells and Sertoli cells, namely apical ectoplasmic specialization. Spermiation (sperm release) requires tubulobulbar complexes. We found that the apical ectoplasmic specialization and tubulobulbar complexes were poorly formed or disrupted in IP6K1 KOs. Deletion of IP6K1 elicited several aberrations, including: 1, sloughing off of round germ cells; 2, disorientation and malformation of elongating/elongated spermatids; 3, degeneration of acrosomes; 4, defects in germ-Sertoli cell interactions and 5, failure of spermiation. Eventually the sperm cells were not released but phagocytosed by Sertoli cells leading to an absence of sperm in the epididymis.

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.

F5-peptide induces aspermatogenesis by disrupting organization of actin- and microtubule-based cytoskeletons in the testis

During the release of sperm at spermiation, a biologically active F5-peptide, which can disrupt the Sertoli cell tight junction (TJ) permeability barrier, is produced at the site of the degenerating apical ES (ectoplasmic specialization). This peptide coordinates the events of spermiation and blood-testis barrier (BTB) remodeling at stage VIII of the epithelial cycle, creating a local apical ES-BTB axis to coordinate cellular events across the epithelium. The mechanism(s) by which F5-peptide perturbs BTB restructuring, and its involvement in apical ES dynamics remain unknown. F5-peptide, besides perturbing BTB integrity, was shown to induce germ cell release from the epithelium following its efficient in vivo overexpression in the testis. Overexpression of F5-peptide caused disorganization of actin- and microtubule (MT)-based cytoskeletons, mediated by altering the spatiotemporal expression of actin binding/regulatory proteins in the seminiferous epithelium. F5-peptide perturbed the ability of actin microfilaments and/or MTs from converting between their bundled and unbundled/defragmented configuration, thereby perturbing adhesion between spermatids and Sertoli cells. Since apical ES and basal ES/BTB are interconnected through the underlying cytoskeletal networks, this thus provides an efficient and novel mechanism to coordinate different cellular events across the epithelium during spermatogenesis through changes in the organization of actin microfilaments and MTs. These findings also illustrate the potential of F5-peptide being a male contraceptive peptide for men.

mTORC1/rpS6 regulates blood-testis barrier dynamics and spermatogenetic function in the testis in vivo

The blood-testis barrier (BTB), conferred by Sertoli cells in the mammalian testis, is an important ultrastructure that supports spermatogenesis. Studies using animal models have shown that a disruption of the BTB leads to meiotic arrest, causing defects in spermatogenesis and male infertility. To better understand the regulation of BTB dynamics, we report findings herein to understand the role of ribosomal protein S6 (rpS6), a downstream signaling protein of mammalian target of rapamycin complex 1 (mTORC1), in promoting BTB disruption in the testis in vivo, making the barrier "leaky." Overexpression of wild-type rpS6 (rpS6-WT, the full-length cDNA cloned into the mammalian expression vector pCI-neo) and a constitutively active quadruple phosphomimetic mutant cloned into pCI-neo (p-rpS6-MT) vs. control (empty pCI-neo vector) was achieved by transfecting adult rat testes with the corresponding plasmid DNA using a Polyplus in vivo-jetPEI transfection reagent. On the basis of an in vivo functional BTB integrity assay, p-rpS6-MT was found to induce BTB disruption better than rpS6-WT did (and no effects in empty vector control), leading to defects in spermatogenesis, including loss of spermatid polarity and failure in the transport of cells (e.g., spermatids) and organelles (e.g., phagosomes), to be followed by germ exfoliation. More important, rpS6-WT and p-rpS6-MT exert their disruptive effects through changes in the organization of actin- and microtubule (MT)-based cytoskeletons, which are mediated by changes in the spatiotemporal expression of actin- and MT-based binding and regulatory proteins. In short, mTORC1/rpS6 signaling complex is a regulator of spermatogenesis and BTB by modulating the organization of the actin- and MT-based cytoskeletons.