Structure and control of a cell-cell adhesion complex associated with spermiation in rat seminiferous epithelium

ERK/CREB and p38 MAPK/MMP14 Signaling Pathway Influences Spermatogenesis through Regulating the Expression of Junctional Proteins in Eriocheir sinensis Testis

The hemolymph-testis barrier (HTB) is a reproduction barrier in Crustacea, guaranteeing the safe and smooth process of spermatogenesis, which is similar to the blood-testis barrier (BTB) in mammals. The MAPK signaling pathway plays an essential role in spermatogenesis and maintenance of the BTB. However, only a few studies have focused on the influence of MAPK on crustacean reproduction. In the present study, we knocked down and inhibited MAPK in Eriocheir sinensis. Increased defects in spermatogenesis were observed, concurrently with a damaged HTB. Further research revealed that es-MMP14 functions downstream of ERK and p38 MAPK and degrades junctional proteins (Pinin and ZO-1); es-CREB functions in the ERK cascade as a transcription factor of ZO-1. In addition, when es-MMP14 and es-CREB were deleted, the defects in HTB and spermatogenesis aligned with abnormalities in the MAPK. However, JNK impacts the integrity of the HTB by changing the distribution of intercellular junctions. In summary, the MAPK signaling pathway maintains HTB integrity and spermatogenesis through es-MMP14 and es-CREB, which provides insights into the evolution of gene function during barrier evolution.

Hormone Regulation in Testicular Development and Function

The testes serve as the primary source of androgens and the site of spermatogenesis, with their development and function governed by hormonal actions via endocrine and paracrine pathways. Male fertility hinges on the availability of testosterone, a cornerstone of spermatogenesis, while follicle-stimulating hormone (FSH) signaling is indispensable for the proliferation, differentiation, and proper functioning of Sertoli and germ cells. This review covers the research on how androgens, FSH, and other hormones support processes crucial for male fertility in the testis and reproductive tract. These hormones are regulated by the hypothalamic-pituitary-gonad (HPG) axis, which is either quiescent or activated at different stages of the life course, and the regulation of the axis is crucial for the development and normal function of the male reproductive system. Hormonal imbalances, whether due to genetic predispositions or environmental influences, leading to hypogonadism or hypergonadism, can precipitate reproductive disorders. Investigating the regulatory network and molecular mechanisms involved in testicular development and spermatogenesis is instrumental in developing new therapeutic methods, drugs, and male hormonal contraceptives.

Myosin VI stabilizes intercellular junctions in the testis through the LHR and MAPK signalling pathway during spermatogenesis in Eriocheir sinensis

The myosin motor protein myosin VI plays an essential role in mammalian spermatogenesis, however, the effects of myosin VI on male reproduction in Crustacea remain obscure. We identified the macromolecule es-Myosin VI in Eriocheir sinensis, and studied it by multiple methods. It co-localized with F-actin and was highly expressed in the testis. We interfered es-Myosin VI using dsRNA in vivo, an apparent decrease in spermatozoa count was detected. We also found that the MAPK signalling pathway was changed, subsequently causing disruption of intercellular junctions and damage to the functional hemolymph-testis barrier. We observed that luteinizing hormone receptor es-LHR was located within seminiferous tubules, which was different from the expression in mammals. Es-LHR could bind with es-Myosin VI in testis of E. sinensis, its localization was significantly altered when es-Myosin VI was deleted. Moreover, we obtained consistent results for the MAPK signalling pathway and spermatogenesis defects between the es-LHR and es-Myosin VI knockdown groups. In summary, our research demonstrated that knockdown of es-Myosin VI disturbed the intercellular junction and HTB function via the MAPK signalling pathway by changing the localization of es-LHR in the testis of E. sinensis, which was the potential reason for its negative impact on spermatogenesis.

PFN4 is required for manchette development and acrosome biogenesis during mouse spermiogenesis

Profilin 4 (Pfn4) is expressed during spermiogenesis and localizes to the acrosome-acroplaxome-manchette complex. Here, we generated PFN4-deficient mice, with sperm displaying severe impairment in manchette formation. Interestingly, HOOK1 staining suggests that the perinuclear ring is established; however, ARL3 staining is disrupted, suggesting that lack of PFN4 does not interfere with the formation of the perinuclear ring and initial localization of HOOK1, but impedes microtubular organization of the manchette. Furthermore, amorphous head shape and flagellar defects were detected, resulting in reduced sperm motility. Disrupted cis- and trans-Golgi networks and aberrant production of proacrosomal vesicles caused impaired acrosome biogenesis. Proteomic analysis showed that the proteins ARF3, SPECC1L and FKBP1, which are involved in Golgi membrane trafficking and PI3K/AKT pathway, are more abundant in Pfn4^−/− testes. Levels of PI3K, AKT and mTOR were elevated, whereas AMPK level was reduced, consistent with inhibition of autophagy. This seems to result in blockage of autophagic flux, which could explain the failure in acrosome formation. In vitro fertilization demonstrated that PFN4-deficient sperm is capable of fertilizing zona-free oocytes, suggesting a potential treatment for PFN4-related human infertility.

Summary: PFN4-deficient male mice exhibit impaired acrosome formation and malformation of the manchette, leading to amorphous sperm head shape, flagellar abnormalities and sterility.

Chronic stress inhibits testosterone synthesis in Leydig cells through mitochondrial damage via Atp5a1

Stress is one of the leading causes of male infertility, but its exact function in testosterone synthesis has scarcely been reported. We found that adult male rats show a decrease in bodyweight, genital index and serum testosterone level after continual chronic stress for 21 days. Two-dimensional gel electrophoresis (2-DE) and MALDI-TOF-MS analysis identified 10 differentially expressed proteins in stressed rats compared with controls. A strong protein interaction network was found to be centred on Atp5a1 among these proteins. Atp5a1 expression significantly decreased in Leydig cells after chronic stress. Transfection of Atp5a1 siRNAs decreased StAR, CYP11A1, and 17β-HSD expression by damaging the structure of mitochondria in TM3 cells. This study confirmed that chronic stress plays an important role in testosterone synthesis by regulating Atp5a1 expression in Leydig cells.

What Does Androgen Receptor Signaling Pathway in Sertoli Cells During Normal Spermatogenesis Tell Us?

Androgen receptor signaling pathway is necessary to complete spermatogenesis in testes. Difference between androgen binding location in Sertoli cell classifies androgen receptor signaling pathway into classical signaling pathway and non-classical signaling pathway. As the only somatic cell type in seminiferous tubule, Sertoli cells are under androgen receptor signaling pathway regulation via androgen receptor located in cytoplasm and plasma membrane. Androgen receptor signaling pathway is able to regulate biological processes in Sertoli cells as well as germ cells surrounded between Sertoli cells. Our review will summarize the major discoveries of androgen receptor signaling pathway in Sertoli cells and the paracrine action on germ cells. Androgen receptor signaling pathway regulates Sertoli cell proliferation and maturation, as well as maintain the integrity of blood-testis barrier formed between Sertoli cells. Also, Spermatogonia stem cells achieve a balance between self-renewal and differentiation under androgen receptor signaling regulation. Meiotic and post-meiotic processes including Sertoli cell - Spermatid attachment and Spermatid development are guaranteed by androgen receptor signaling until the final sperm release. This review also includes one disease related to androgen receptor signaling dysfunction named as androgen insensitivity syndrome. As a step further ahead, this review may be conducive to develop therapies which can cure impaired androgen receptor signaling in Sertoli cells.

Cdc42 localized in the CatSper signaling complex regulates cAMP-dependent pathways in mouse sperm

Sperm acquire the ability to fertilize in a process called capacitation and undergo hyperactivation, a change in the motility pattern, which depends on Ca²⁺ transport by CatSper channels. CatSper is essential for fertilization and it is subjected to a complex regulation that is not fully understood. Here, we report that similar to CatSper, Cdc42 distribution in the principal piece is confined to four linear domains and this localization is disrupted in CatSper1-null sperm. Cdc42 inhibition impaired CatSper activity and other Ca²⁺ -dependent downstream events resulting in a severe compromise of the sperm fertilizing potential. We also demonstrate that Cdc42 is essential for CatSper function by modulating cAMP production by soluble adenylate cyclase (sAC), providing a new regulatory mechanism for the stimulation of CatSper by the cAMP-dependent pathway. These results reveal a broad mechanistic insight into the regulation of Ca²⁺ in mammalian sperm, a matter of critical importance in male infertility as well as in contraception.

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.

Androgen Actions in the Testis and the Regulation of Spermatogenesis

Testosterone is essential for spermatogenesis and male fertility. In this review, topics related to testosterone control of spermatogenesis are covered including testosterone production and levels in the testis, classical and nonclassical testosterone signaling pathways, cell- and temporal-specific expression of the androgen receptor in the testis and autocrine and paracrine signaling of testis cells in the testis. Also discussed are the contributions of testosterone to testis descent, the blood-testis barrier, control of gonocyte numbers and spermatogonia expansion, completion of meiosis and attachment and release of elongaed spermatids. Testosterone-regulated genes identified in various mouse models of idsrupted Androgen receptor expression are discussed. Finally, examples of synergism and antagonism between androgen and follicle-stimulating hormone signaling pathways are summarized.

Filamentous actin disorganization and absence of apical ectoplasmic specialization disassembly during spermiation upon interference with retinoid signaling†

Spermiation is a multiple-step process involving profound cellular changes in both spermatids and Sertoli cells. We have observed spermiation defects, including abnormalities in spermatid orientation, translocation and release, in mice deficient in the retinoic acid receptor alpha (RARA) and upon treatment with a pan-RAR antagonist. To elucidate the role of retinoid signaling in regulating spermiation, we first characterized the time course of appearance of spermiogenic defects in response to treatment with the pan-RAR antagonist. The results revealed that defects in spermiation are indeed among the earliest abnormalities in spermatogenesis observed upon inhibition of retinoid signaling. Using fluorescent dye-conjugated phalloidin to label the ectoplasmic specialization (ES), we showed for the first time that these defects involved improper formation of filamentous actin (F-actin) bundles in step 8–9 spermatids and a failure of the actin-surrounded spermatids to move apically to the lumen and to disassemble the ES. The aberrant F-actin organization is associated with diminished nectin-3 expression in both RARA-deficient and pan-RAR antagonist-treated testes. An abnormal localization of both tyrosinated and detyrosinated tubulins was also observed during spermatid translocation in the seminiferous epithelium in drug-treated testes. These results highlight a crucial role of RAR receptor-mediated retinoid signaling in regulating microtubules and actin dynamics in the cytoskeleton rearrangements, required for proper spermiation. This is critical to understand in light of ongoing efforts to inhibit retinoid signaling as a novel approach for male contraception and may reveal spermiation components that could also be considered as new targets for male contraception.

Sperm Differentiation: The Role of Trafficking of Proteins

Sperm differentiation encompasses a complex sequence of morphological changes that takes place in the seminiferous epithelium. In this process, haploid round spermatids undergo substantial structural and functional alterations, resulting in highly polarized sperm. Hallmark changes during the differentiation process include the formation of new organelles, chromatin condensation and nuclear shaping, elimination of residual cytoplasm, and assembly of the sperm flagella. To achieve these transformations, spermatids have unique mechanisms for protein trafficking that operate in a coordinated fashion. Microtubules and filaments of actin are the main tracks used to facilitate the transport mechanisms, assisted by motor and non-motor proteins, for delivery of vesicular and non-vesicular cargos to specific sites. This review integrates recent findings regarding the role of protein trafficking in sperm differentiation. Although a complete characterization of the interactome of proteins involved in these temporal and spatial processes is not yet known, we propose a model based on the current literature as a framework for future investigations.

Alterations in seminal plasma proteomic profile in men with primary and secondary infertility

Proteome of seminal plasma provides profound information related to the male reproductive health. This pilot study was conducted to characterize proteomic profile of seminal plasma from men with primary, or secondary infertility and compare it with proven fertile men. Study participants (n = 59) were recruited at the Cleveland Clinic and divided according to their fertility status: proven fertile (n = 39); primary infertility (n = 11) and secondary infertility (n = 9). Proteomic shotgun analysis revealed a total of 515 peptides common to primary infertility and control group; whereas 523 peptides were common to secondary infertility and control group. Bioinformatic analysis revealed dysregulation of biological processes such as cell secretion and vesicle mediated transport in primary infertility, whereas immune system response, regulation of proteolysis and iron homeostasis were dysregulated in secondary infertility. Western blot validation showed overexpression of ANXA2 and CDC42, and underexpression of SEMG2 proteins in primary infertility; and overexpression of ANXA2 and APP proteins in secondary infertility. This study elucidates the potential role of differentially expressed proteins in the seminal plasma as diagnostic biomarker for primary and secondary infertility. Furthermore, our results suggest maturation failure and immune reaction response as the main cause of infertility in men with primary and secondary infertility, respectively. Additional validation of the proteins involved in the above pathways is warranted.

Neurofibromin haploinsufficiency results in altered spermatogenesis in a mouse model of neurofibromatosis type 1

The fertility of men with neurofibromatosis 1 (NF1) is reduced. Despite this observation, gonadal function has not been examined in patients with NF1. In order to assess the role of reduced neurofibromin in the testes, we examined testicular morphology and function in an Nf1+/- mouse model. We found that although Nf1+/- male mice are able to reproduce, they have significantly fewer pups per litter than Nf1+/+ control males. Reduced fertility in Nf1+/- male mice is associated with disorganization of the seminiferous epithelium, with exfoliation of germ cells and immature spermatids into the tubule lumen. Morphometric analysis shows that these alterations are associated with decreased Leydig cell numbers and increased spermatid cell numbers. We hypothesized that hyper-activation of Ras in Nf1+/- males affects ectoplasmic specialization, a Sertoli-spermatid adherens junction involved in spermiation. Consistent with this idea, we found increased expression of phosphorylated ERK, a downstream effector of Ras that has been shown to alter ectoplasmic specialization, in Nf1+/- males in comparison to control Nf1+/+ littermates. These data demonstrate that neurofibromin haploinsufficiency impairs spermatogenesis and fertility in a mouse model of NF1.

CDC42 Negatively Regulates Testis-Specific SEPT12 Polymerization

Septin (SEPT) genes encode well-preserved polymerizing GTP-binding cytoskeletal proteins. The cellular functions of SEPTs consist of mitosis, cytoskeletal remodeling, cell polarity, and vesicle trafficking through interactions with various types of cytoskeletons. We discovered that mutated SEPTIN12 in different codons resulted in teratozoospermia or oligozoospermia. In mouse models with a defective Septin12 allele, sperm morphology was abnormal, sperm count decreased, and sperms were immotile. However, the regulators of SEPT12 are completely unknown. Some studies have indicated that CDC42 negatively regulates the polymerization of SEPT2/6/7 complexes in mammalian cell lines. In this study, we investigated whether CDC42 modulates SEPT12 polymerization and is involved in the terminal differentiation of male germ cells. First, through scanning electron microscopy analysis, we determined that the loss of Septin12 caused defective sperm heads. This indicated that Septin12 is critical for the formation of sperm heads. Second, CDC42 and SEPT12 were similarly localized in the perinuclear regions of the manchette at the head of elongating spermatids, neck region of elongated spermatids, and midpiece of mature spermatozoa. Third, wild-type CDC42 and CDC42Q61L (a constitutive-acting-mutant) substantially repressed SEPT12 polymerization, but CDC42T17N (a dominant-negative-acting mutant) did not, as evident through ectopic expression analysis. We concluded that CDC42 negatively regulates SEPT12 polymerization and is involved in terminal structure formation of sperm heads.

Functional insights into the role of seminal plasma proteins on sperm motility of buffalo

The objective of the present study was to describe the proteins from the seminal plasma of buffalo and correlate these proteins with sperm motility. Ejaculates from sixteen Murrah buffalo were used. Semen collection was performed by electroejaculation, and the ejaculate was evaluated by macroscopic (volume) and microscopic analysis (subjective motility and vigor, as well as sperm concentration). After the analysis, the samples were centrifuged (800g for 10 min and 10,000 for 30 min at 4 °C), and the supernatant (seminal plasma) was used to determine total protein concentration by the Bradford method. Based on total protein concentration, an aliquot (50 μg) was taken to conduct protein in-solution digestion for nano-LC-ESI-Q-TOF mass spectrometry analysis. Samples were divided into two groups, minimal (little sperm motility) and greater (typical sperm motility), based on non-hierarchical clustering considering motility and emPAI protein value. The data were analyzed by multivariate statistical analysis using principal component analysis (PCA) and partial analysis of minimum squares discrimination (PLS-DA). Forty-eight proteins were detected in the seminal plasma, and fifteen were common to two groups. There were six proteins that were significantly different between the groups. The main functions of proteins in seminal plasma were catalytic and binding activity. Spermadhesin protein, ribonuclease, 14-3-3 protein zeta/delta and acrosin inhibitor were in greater amounts in seminal plasma from the group with greater sperm motility; prosaposin and peptide YY were in greater amounts in the group with little sperm motility. The proteins detected in the greater motility group were correlated with sperm protection, including protection against oxidative stress, lipid peroxidation, protease inhibition and prevention of premature capacitation and acrosome reaction. In the group with little sperm motility, one of the identified proteins is considered to be an antifertility factor, whereas the function of other identified protein is not definitive. Results from the present study add to the knowledge base about the molecular processes related with sperm motility, and these findings can be used for determining potential markers of semen quality.

Endocrine regulation of sperm release

Spermiation (sperm release) is the culmination of a spermatid’s journey in the seminiferous epithelium. After a long association with the Sertoli cell, spermatids have to finally ‘let go’ of the support from Sertoli cells in order to be transported to the epididymis. Spermiation is a multistep process characterised by removal of excess spermatid cytoplasm, recycling of junctional adhesion molecules by endocytosis, extensive cytoskeletal remodelling and final spermatid disengagement. Successful execution of all these events requires coordinated regulation by endocrine and paracrine factors. This review focuses on the endocrine regulation of spermiation. With the aim of delineating how hormones control the various aspects of spermiation, this review provides an analysis of recent advances in research on the hormonal control of molecules associated with the spermiation machinery. Because spermiation is one of the most sensitive phases of spermatogenesis to variations in hormone levels, understanding their molecular control is imperative to advance our knowledge of the nuances of spermatogenesis and male fertility.

Morphology of the Fetal Rat Testis Preserved in Different Fixatives

Histopathological examination of the testes of exposed fetuses and neonates is important in assessing the developmental effects of environmental toxins, including sex hormone modulators. Modified Davidson’s fluid (mDF) has been suggested as a superior substitute for Bouin’s fluid for fixation of adult animal testes. We compared the morphology of fetal rat testes stained with hematoxylin and eosin (H&E) or immunochemically after fixation in 10% neutral buffered formalin (NBF), Bouin’s fluid, or mDF. Fixation in mDF resulted in more sharply defined nuclear detail and better preservation of cellular cytoplasm on H&E-stained sections of rat testes on gestation day 19. Use of Bouin’s fluid did not allow satisfactory detection of apoptotic cells by fluorescent terminal deoxynucleotide transferase-mediated deoxy-UTP nick labeling. Staining with the immunoperoxidase system and the conventional chromogen diaminobenzidine tetrahydrochloride to visualize 5-bromo-2-deoxyuridine-positive cells demonstrated that the number of positive nuclei and intensity of staining were similar with all 3 fixatives. Immunostaining for cytoskeletal protein vimentin was more intense and provided better details of the Sertoli cell cytoplasm with formalin fixation than with mDF. Our study demonstrates that fixation in mDF provided better morphologic detail in the fetal rat testis compared with 10% NBF and Bouin’s fluid and illustrates the importance of establishing the correct fixation conditions for each immunostaining protocol.

Estrogen and androgen regulate actin-remodeling and endocytosis-related genes during rat spermiation

Spermiation, the sperm release process, is imperative to male fertility and reproduction. Morphologically, it is characterized by removal of atypical adherens junctions called ectoplasmic specializations, and formation of transient endocytic devices called tubulobulbar complexes requiring cytoskeleton remodeling and recruitment of proteins needed for endocytosis. Earlier, estrogen administration to adult male rats was seen to cause spermiation failure due to disruption of tubulobulbar complexes. This was accompanied by reduction in intratesticular testosterone levels and increase in intratesticular estrogen along with deregulation of genes involved in cytoskeleton remodeling (Arpc1b, Evl and Capg) and endocytosis (Picalm, Eea1 and Stx5a). In the present study, we aim to understand the role of estrogen and androgen in regulating these genes independently using seminiferous tubule culture system treated with estrogen, androgen or agonists and antagonists of estrogen receptors. We find that transcripts of Arpc1b, Evl and Picalm are responsive to estrogen while those of Picalm, Eea1 and Stx5a are responsive to androgen. We also find that the estrogen regulation of Arpc1b and Evl is mediated through estrogen receptor β and that of Picalm occurs through estrogen receptors α and β. Localization of these proteins at or in the vicinity of tubulobulbar complexes reveals that ARPC1B, EVL, PICALM, EEA1 and STX5A seem to be involved in spermiation. Thus, estrogen and androgen regulate specific genes in seminiferous tubules that could play a role in spermiation.

Kinases as targets for chemical modulators: Structural aspects and their role in spermatogenesis

Protein phosphorylation and de-phosphorylation events are crucial in deciding the fate of cells. They regulate cellular growth, differentiation and cell death, and kinases are the key players of these events. The members of ser/thr kinases and tyrosine kinases form the majority of protein kinase family, exerting their regulatory mechanism in almost all cells. In testis, they impact signal transduction events, regulate all stages of sperm development from mitosis through fertilization. Understanding the function of these kinases at the structural level and studying their interactions with inhibitors can help in understanding the machinery of spermatogenesis. In view of this, we have reviewed some of the prominent kinases that are known to play a role in spermatogenesis. A better understanding of the impacts of kinase inhibition on spermatogenesis should aid in the interpretation of lesions and hopefully further the development of more efficient and potent drug candidates.

Mechanisms of spermiogenesis and spermiation and how they are disturbed

Haploid round spermatids undergo a remarkable transformation during spermiogenesis. The nucleus polarizes to one side of the cell as the nucleus condenses and elongates, and the microtubule-based manchette sculpts the nucleus into its species-specific head shape. The assembly of the central component of the sperm flagellum, known as the axoneme, begins early in spermiogenesis, and is followed by the assembly of secondary structures needed for normal flagella. The final remodelling of the mature elongated spermatid occurs during spermiation, when the spermatids line up along the luminal edge, shed their residual cytoplasm and are ultimately released into the lumen. Defects in spermiogenesis and spermiation are manifested as low sperm number, abnormal sperm morphology and poor motility and are commonly observed during reproductive toxicant administration, as well as in genetically modified mouse models of male infertility. This chapter summarizes the major physiological processes and the most commonly observed defects in spermiogenesis and spermiation, to aid in the diagnosis of the potential mechanisms that could be perturbed by experimental manipulation such as reproductive toxicant administration.

Testosterone signaling and the regulation of spermatogenesis

Spermatogenesis and male fertility are dependent upon the presence of testosterone in the testis. In the absence of testosterone or the androgen receptor, spermatogenesis does not proceed beyond the meiosis stage. The major cellular target and translator of testosterone signals to developing germ cells is the Sertoli cell. In the Sertoli cell, testosterone signals can be translated directly to changes in gene expression (the classical pathway) or testosterone can activate kinases that may regulate processes required to maintain spermatogenesis (the non-classical pathway). Contributions of the classical and non-classical testosterone signaling pathways to the maintenance of spermatogenesis are discussed. Studies that may further elaborate the mechanisms by with the pathways support spermatogenesis are proposed.

p70 S6 kinase and actin dynamics: A perspective

p70 S6 kinase (p70^S6K), a member of the AGC serine/threonine kinase family, was initially identified as a key player, together with its downstream effector S6, in the regulation of cellular growth and survival. The p70^S6K protein has emerged in recent years as a multifunctional protein which also regulates the actin cytoskeleton and thus plays a role in cell migration. This new function is through two important activities of p70^S6K, namely actin cross-linking and Rac1 and Cdc42 activation. The testis is critically dependent on an intricate balance of fundamental cellular processes such as adhesion, migration, and differentiation. It is increasingly evident that Rho GTPases and actin binding proteins play fundamental roles in regulating spermatogenesis within the testis. In this review, we will discuss current findings of p70^S6K in the control of actin cytoskeleton dynamics. In addition, the potential role of p70^S6K in spermatogenesis and testicular function will be highlighted.

Actin binding proteins and spermiogenesis: Some unexpected findings

Drebrin E, an actin-binding protein lacking intrinsic activity in the regulation of actin dynamics (e.g., polymerization, capping, nucleation, branching, cross-linking, bundling and severing), is known to recruit actin regulatory proteins to a specific cellular site. Herein, we critically evaluate recent findings in the field which illustrate that drebrin E works together with two other actin-binding proteins, namely Arp3 (actin-related protein 3, a component of the Arp2/3 complex that simultaneously controls actin nucleation for polymerization and branching of actin filaments) and Eps8 (epidermal growth factor receptor pathway substrate 8 that controls capping of the barbed ends of actin filaments, as well as actin filament bundling) to regulate the homeostasis of F-actin filament bundles at the ectoplasmic specialization (ES), a testis-specific atypical adherens junction (AJ) in the seminiferous epithelium. This is mediated by the strict temporal and spatial expression of these three actin-binding proteins at the apical and basal ES at the Sertoli cell-spermatid (step 8-19) and Sertoli-Sertoli cell interface, respectively, during the seminiferous epithelial cycle of spermatogenesis. In this Commentary, we put forth a possible model by which drebrin E may be acting as a platform upon which proteins (e.g., Arp3) that are needed to alter the conformation of actin filament bundles at the ES can be recruited to the site, thus facilitating changes in cell shape and cell position in the epithelium during spermiogenesis and spermiation. In short, drebrin E may be acting as a "logistic" distribution center to manage different regulatory proteins at the apical ES, thereby regulating the dynamics of actin filament bundles and modulating the plasticity of the apical ES. This would allow adhesion to be altered continuously throughout the epithelial cycle to accommodate spermatid movement in the seminiferous epithelium during spermiogenesis and spermiation. We also describe a hypothetical model, upon which functional studies can be designed in the future.

The stage-specific testicular germ cell apoptotic response to low-dose radiation and 2,5-hexanedione combined exposure. II: qRT-PCR array analysis reveals dose dependent adaptive alterations in the apoptotic pathway

Testicular effects of chemical mixtures may differ from those of the individual chemical constituents. This study assessed the co-exposure effects of the model germ cell- and Sertoli cell-specific toxicants, X-irradiation (x-ray), and 2,5-hexanedione (HD), respectively. In high-dose studies, HD has been shown to attenuate x-ray-induced germ cell apoptosis. Adult rats were exposed to different levels of x-ray (0.5 Gy, 1 Gy, and 2 Gy) or HD (0.33%), either alone or in combination. To assess cell type-specific attenuation of x-ray effects with HD co-exposure, we used laser capture microdissection (LCM) to enrich the targeted cell population and examine a panel of apoptosis-related transcripts using PCR arrays. The apoptosis PCR arrays identified significant dose-dependent treatment effects on several genes, with downregulation of death receptor 5 (DR5), Naip2, Sphk2, Casp7, Aven, Birc3, and upregulation of Fas. The greatest difference in transcript response to exposure was seen with 0.5 Gy x-ray exposure, and the attenuation effect seen with the combined high-dose x-ray and HD did not persist into the low-dose range. Examination of protein levels in staged tubules revealed a significant upregulation in DR5, following high-dose co-exposure. These results provide insight into the testis cell-specific apoptotic response to low-dose co-exposures of model testicular toxicants.

The regulation of spermatogenesis by androgens

Testosterone is essential for maintaining spermatogenesis and male fertility. However, the molecular mechanisms by which testosterone acts have not begun to be revealed until recently. With the advances obtained from the use of transgenic mice lacking or overexpressing the androgen receptor, the cell specific targets of testosterone action as well as the genes and signaling pathways that are regulated by testosterone are being identified. In this review, the critical steps of spermatogenesis that are regulated by testosterone are discussed as well as the intracellular signaling pathways by which testosterone acts. We also review the functional information that has been obtained from the knock out of the androgen receptor from specific cell types in the testis and the genes found to be regulated after altering testosterone levels or androgen receptor expression.

Proteomic changes in rat spermatogenesis in response to in vivo androgen manipulation; impact on meiotic cells

The production of mature sperm is reliant on androgen action within the testis, and it is well established that androgens act on receptors within the somatic Sertoli cells to stimulate male germ cell development. Mice lacking Sertoli cell androgen receptors (AR) show late meiotic germ cell arrest, suggesting Sertoli cells transduce the androgenic stimulus co-ordinating this essential step in spermatogenesis. This study aimed to identify germ cell proteins responsive to changes in testicular androgen levels and thereby elucidate mechanisms by which androgens regulate meiosis. Testicular androgen levels were suppressed for 9 weeks using testosterone and estradiol-filled silastic implants, followed by a short period of either further androgen suppression (via an AR antagonist) or the restoration of intratesticular testosterone levels. Comparative proteomics were performed on protein extracts from enriched meiotic cell preparations from adult rats undergoing androgen deprivation and replacement in vivo. Loss of androgenic stimulus caused changes in proteins with known roles in meiosis (including Nasp and Hsp70–2), apoptosis (including Diablo), cell signalling (including 14-3-3 isoforms), oxidative stress, DNA repair, and RNA processing. Immunostaining for oxidised DNA adducts confirmed spermatocytes undergo oxidative stress-induced DNA damage during androgen suppression. An increase in PCNA and an associated ubiquitin-conjugating enzyme (Ubc13) suggested a role for PCNA-mediated regulation of DNA repair pathways in spermatocytes. Changes in cytoplasmic SUMO1 localisation in spermatocytes were paralleled by changes in the levels of free SUMO1 and of a subunit of its activating complex, suggesting sumoylation in spermatocytes is modified by androgen action on Sertoli cells. We conclude that Sertoli cells, in response to androgens, modulate protein translation and post-translational events in spermatocytes that impact on their metabolism, survival, and completion of meiosis.

17Beta-estradiol signaling and regulation of proliferation and apoptosis of rat Sertoli cells

The aim of the present study was to investigate the intracellular signaling events downstream of the classical estrogen receptors (ESRs) and G protein-coupled estrogen receptor 1 (GPER) involved in regulation of proliferation and apoptosis of rat Sertoli cells, in which we have previously described ESR1, ESR2, and GPER. ESRs play a role in Sertoli cell proliferation, and GPER, but not ESRs, plays a role modulating gene expression involved with apoptosis. The present study shows that 17beta-estradiol (E2) and the GPER-selective agonist G-1 rapidly activate phosphatidylinositol 3-kinase (PIK3)/serine threonine protein kinase (AKT) and cyclic AMP response element-binding (CREB) phosphorylation. E2 and the ESR1-selective agonist 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT) increase the expression of cyclin D1 (CCND1), whereas the ESR2-selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) and G-1 do not change the expression of this protein, suggesting that ESR1 is the upstream receptor regulating Sertoli cell proliferation. E2- or PPT-ESR1, through activation of epidermal growth factor receptor (EGFR)/mitogen-activated protein kinase 3/1 (MAPK3/1) and PIK3 pathways, induces upregulation of CCND1. KG-501, the compound that disrupts the phospho-CREB/CREB binding protein (CBP) complex, does not change E2- or PPT-ESR1-mediated CCND1 expression, suggesting that phospho-CREB/cyclic AMP response element/CBP is not involved in the expression of this protein. E2- or G-1-GPER, through activation of EGFR/MAPK3/1 and PIK3 pathways, may be involved in the upregulation of antiapoptotic proteins BCL2 and BCL2L2. E2- or G-1-GPER/EGFR/MAPK3/1/phospho-CREB decreases BAX expression. Taken together, these results show a differential effect of E2-GPER on the CREB-mediated transcription of proapoptotic and antiapoptotic genes of the same BCL2 gene family. ESR1 and GPER can mediate the rapid E2 actions in the Sertoli cells, which in turn can modulate nuclear transcriptional events important for Sertoli cell function and maintenance of normal testis development and homeostasis. Our findings are important to clarify the role of estrogen in a critical period of testicular development, and to direct further studies, which may contribute to better understanding of the causes of male infertility.

The biology of interleukin-1: emerging concepts in the regulation of the actin cytoskeleton and cell junction dynamics

Interleukin (IL)-1 is a proinflammatory cytokine with important roles in innate immunity, as well as in normal tissue homeostasis. Interestingly, recent studies have also shown IL-1 to function in the dynamics of the actin cytoskeleton and cell junctions. For example, treatment of different epithelia with IL-1α often results in the restructuring of the actin network and cell junctions, thereby leading to junction disassembly. In this review, we highlight new and interesting findings that show IL-1 to be a critical player of restructuring events in the seminiferous epithelium of the testis during spermatogenesis.

Global proteomics analysis of testis and ovary in adult zebrafish (Danio rerio)

The molecular mechanisms controlling sex determination and differentiation in zebrafish (Danio rerio) are largely unknown. A genome-wide analysis may provide comprehensive insights into the processes involved. The mRNA expression in zebrafish gonads has been fairly well studied, but much less data on the corresponding protein expression are available, although the proteins are considered to be more relevant markers of gene function. Because mRNA and protein abundances rarely correlate well, mRNA profiles need to be complemented with the information on protein expression. The work presented here analyzed the proteomes of adult zebrafish gonads by a multidimensional protein identification technology, generating the to-date most populated lists of proteins expressed in mature zebrafish gonads. The acquired proteomics data partially confirmed existing transcriptomics information for several genes, including several novel transcripts. However, disagreements between mRNA and protein abundances were often observed, further stressing the necessity to assess the expression on different levels before drawing conclusions on a certain gene's expression and function. Several gene groups expressed in a sexually dimorphic way in zebrafish gonads were identified. Their potential importance for gonad development and function is discussed. The data gained in the current study provide a basis for further work on elucidating processes occurring during zebrafish development with use of high-throughput proteomics.

The blood-testis barrier: the junctional permeability, the proteins and the lipids

The elucidation of how individual components of the Sertoli cell junctional complexes form and are dismantled to allow not only individual cells but whole syncytia of germinal cells to migrate from the basal to the lumenal compartment of the seminiferous epithelium without causing a permeability leak in the blood-testis barrier is amongst the most enigmatic yet, challenging and timely questions in testicular physiology. The intriguing key event in this process is how the barrier modulates its permeability during the periods of formation and dismantling of individual Sertoli cell junctions. The purpose of this review is therefore to first provide a reliable account on the normal formation, maintenance and dismantling process of the Sertoli cells junctions, then to assess the influence of the expression of their individual proteins, of the cytoskeleton associated with the junctions, and of the lipid content in the seminiferous tubules on the regulation of the their permeability barrier function. To help focus on the formation and dismantling of the Sertoli cell junctions, several considerations are based on data gleaned not only from rodents but from seasonal breeders as well because these animal models are characterized by exhaustive periods of junction assembly during development and the onset of the seasonal re-initiation of spermatogenesis as well as by an extensive junction dismantling period at the beginning of testicular regression, something unavailable in normal physiological conditions in continual breeders. Thus, the modulation of the permeability barrier function of the Sertoli cell junctions is analyzed in the physiological context of the blood-epidydimis barrier and in particular of the blood-testis barrier rather than in the context of a detailed account of the molecular composition and signalisation pathways of cell junctions. Moreover, the considerations discussed in this review are based on measurements performed on seminiferous tubule-enriched fractions gleaned at regular time intervals during development and the annual reproductive cycle.

Hormonal regulation of sertoli cell micro-RNAs at spermiation

Spermatogenesis is absolutely dependent on FSH and androgens; suppression of these hormones inhibits germ cell development and thus sperm production. The final release of spermatids by the Sertoli cell, a process known as spermiation, is particularly sensitive to hormone suppression. To define the molecular mechanisms that mediate FSH and androgen effects in the Sertoli cell, we investigated the expression and regulation of micro-RNAs (miRNAs), small noncoding RNAs that regulate protein translation and modify cellular responses. By array analysis, we identified 23 miRNAs up-regulated more than 2-fold after hormone suppression in vivo and in vitro in primary Sertoli cell cultures. The regulation of four of these miRNAs (miR-23b, -30c, -30d, and -690) was confirmed by quantitative RT-PCR. Bioinformatic analysis of potential targets of hormonally regulated miRNAs identified genes important for focal adhesion and regulation of the actin cytoskeleton, processes known to be intimately associated with adhesion of spermatids to Sertoli cells. Two of the identified genes, Pten, an intracellular phosphatase, and Eps15, a mediator of endocytosis, were down-regulated by the withdrawal of hormones in vivo and possess miR-23b target sites in their 3'-untranslated regions. Overexpression of miR-23b in vitro resulted in decreased translation of PTEN and EPS15 protein as assessed by Western blot and luciferase analysis. We conclude that FSH and androgens act on Sertoli cells in stage VIII to control the expression of miRNAs that operate in a coordinated manner to regulate cell adhesion pathways and male fertility and that miRNA transcription is a new paradigm in the hormone dependence of spermiation.

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.

Regulation of Sertoli-germ cell adhesion and sperm release by FSH and nonclassical testosterone signaling

Testosterone and FSH act in synergy to produce the factors required to maximize the production of spermatozoa and male fertility. However, the molecular mechanisms by which these hormones support spermatogenesis are not well established. Recently, we identified a nonclassical mechanism of testosterone signaling in cultured rat Sertoli cells. We found that testosterone binding to the androgen receptor recruits and activates Src tyrosine kinase. Src then causes the activation of the epidermal growth factor receptor, which results in the phosphorylation and activation of the ERK MAPK and the cAMP response element-binding protein transcription factor. In this report, we find that FSH inhibits testosterone-mediated activation of ERK and the MAPK pathway in Sertoli cells via the protein kinase A-mediated inhibition of Raf kinase. In addition, FSH, as well as inhibitors of Src and ERK kinase activity, reduced germ cell attachment to Sertoli cells in culture. Using pathway-specific androgen receptor mutants we found that the nonclassical pathway is required for testosterone-mediated increases in germ cell attachment to Sertoli cells. Studies of seminiferous tubule explants determined that Src kinase, but not ERK kinase, activity is required for the release of sperm from seminiferous tubule explants. These findings suggest the nonclassical testosterone-signaling pathway acts via Src and ERK kinases to facilitate the adhesion of immature germ cells to Sertoli cells and through Src to permit the release of mature spermatozoa. In contrast, FSH acts to limit testosterone-mediated ERK kinase activity and germ cell attachment.

Mechanism of hCG-induced spermiation in the toad Rhinella arenarum (Amphibia, Anura)

In Rhinella arenarum spermiation occurs as a consequence of LH/FSH increase during the amplexus or by a single dose of hCG, among other gonadotropins. The present study employs an in vitro system to study the mechanism of action of hCG in the spermiation of R. arenarum. Testicular fragments were incubated for 2h at 28°C in the presence or absence of 20IU hCG with or without different PKA/PKC inhibitors and activators as well as ouabain and amiloride as Na(+)/K(+) ATPase and transcellular Na(+) transport inhibitors, respectively. Ouabain did not induce spermiation in absence of hCG and inhibited hCG-induced spermiation in a dose-dependent manner, reaching 90% inhibition with the higher concentration. In contrast, amiloride neither affected spermiation nor steroidogenesis. Activation of PKA with 8Br-cAMP induced spermiation in the absence of hCG while its inhibition with H89 blocked hCG action. On the other hand, PKC inhibition with Bi or STP did not affect hCG-induced spermiation although PKC activation significantly decreased hCG-dependent sperm release. These results suggest that PKC inhibits spermiation but also that the inhibition exerted by the kinase could be blocked by hCG. Taken together, these observations could indicate that PKA is involved in the mechanism of the gonadotropin action, mechanism also requiring the activation of a non-pumping Na(+)/K(+) ATPase pathway.

Sertoli-germ cell junctions in the testis: a review of recent data

Spermatogenesis is a process that involves an array of cellular and biochemical events, collectively culminating in the formation of haploid spermatids from diploid precursor cells known as spermatogonia. As germ cells differentiate from spermatogonia into elongated spermatids, they also progressively migrate across the entire length of the seminiferous epithelium until they reach the luminal edge in anticipation of spermiation at late stage VIII of spermatogenesis. At the same time, these germ cells must maintain stable attachment with Sertoli cells via testis-unique intermediate filament- (i.e. desmosome-like junctions) and actin- (i.e. ectoplasmic specializations, ESs) based cell junctions to prevent sloughing of immature germ cells from the seminiferous epithelium, which may result in infertility. In essence, both desmosome-like junctions and basal ESs are known to coexist between Sertoli cells at the level of the blood-testis barrier where they cofunction with the well-studied tight junction in maintaining the immunological barrier. However, the type of anchoring device that is present between Sertoli and germ cells depends on the developmental stage of the germ cell, i.e. desmosome-like junctions are present between Sertoli and germ cells up to, but not including, step 8 spermatids after which this junction type is replaced by the apical ES. While little is known about the biology of the desmosome-like junction in the testis, we have a relatively good understanding of the molecular architecture and the regulation of the ES. Here, we discuss recent findings relating to these two junction types in the testis, highlighting prospective areas that should be investigated in future studies.

Cytoskeletal dynamics and spermatogenesis

Different cellular events occur during spermatogenesis, and these include (i) mitosis for self-renewal of spermatogonia, (ii) differentiation of type A spermatogonia into type B and commitment of type B spermatogonia to develop into preleptotene primary spermatocytes, (iii) transit of preleptotene/leptotene spermatocytes across the blood-testis barrier in coordination with germ cell cycle progression and meiosis, (iv) spermiogenesis and spermiation. These events also associate with extensive changes in cell shape and size, and germ cell movement. The cytoskeleton, which comprises actin, microtubules and intermediate filaments, is believed to function in these cellular events. However, few studies have been conducted by investigators in the past decades to unfold the role of the cytoskeleton during spermatogenesis. This review summarizes recent advances in the field relating to cytoskeletal dynamics in the testis, and highlights areas of research that require additional emphasis so that new approaches for male contraception, as well as therapeutic approaches to alleviate environmental toxicant-induced reproductive dysfunction in men, can possibly be developed.

Non-classical actions of testosterone and spermatogenesis

Testosterone is essential to maintain spermatogenesis and male fertility. In the absence of testosterone stimulation, spermatogenesis does not proceed beyond the meiosis stage. After withdrawal of testosterone, germ cells that have progressed beyond meiosis detach from supporting Sertoli cells and die, whereas mature sperm cannot be released from Sertoli cells resulting in infertility. The classical mechanism of testosterone action in which testosterone activates gene transcription by causing the androgen receptor to translocate to and bind specific DNA regulatory elements does not appear to fully explain testosterone regulation of spermatogenesis. This review discusses two non-classical testosterone signalling pathways in Sertoli cells and their potential effects on spermatogenesis. Specifically, testosterone-mediated activation of phospholipase C and calcium influx into Sertoli cells is described. Also, testosterone activation of Src, EGF receptor and ERK kinases as well as the activation of the CREB transcription factor and CREB-mediated transcription is reviewed. Regulation of germ cell adhesion to Sertoli cells and release of mature sperm from Sertoli cells by kinases regulated by the non-classical testosterone pathway is discussed. The evidence accumulated suggests that classical and non-classical testosterone signalling contribute to the maintenance of spermatogenesis and male fertility.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

Cortactin/tyrosine-phosphorylated cortactin interaction with connexin 43 in mouse seminiferous tubules

Deletion of the cortactin gene leads to male infertility. Considering that cortactin is an actin filament (F-actin)-binding protein associated with intercellular junctions, we measured changes in the expression and distribution of cortactin and tyrosine phosphorylated cortactin (P-cortactin) in the seminiferous epithelium of developing and adult mice to address the physiological significance of cortactin to germ cell differentiation. Cortactin was expressed in neonatal and developing Sertoli cells. Cortactin levels decreased early during puberty, while P-cortactin increased. Cortactin labeling was intense in the basal and apical thirds of the epithelium. Sertoli cell cytoplasmic processes facing spermatogonia, preleptotene spermatocytes, and step 8-13 spermatids were intensely labeled by both cortactin and P-cortactin. In contrast, the middle region of Sertoli cells exhibited diffuse cortactin labeling but no P-cortactin. This is consistent with the view that plasma membrane segments facing germ cells are part of the continuum of Sertoli cell junctional complexes that extend over lateral and apical membranes of supporting cells. Moreover, F-actin and P-cortactin share a common location in the seminiferous epithelium. The increased P-cortactin levels detected during puberty may be related to the modulatory effect of cortactin tyrosine phosphorylation on actin assembly at sites of selected Sertoli cell-germ cell contacts. Cortactin and connexin 43 (Cx43) were physically linked in seminiferous tubule homogenates and their colocalization in the basal and apical thirds of the seminiferous epithelium was stage-dependent. Our results suggest that cortactin-Cx43 interaction helps coordinate formation of cell-to-cell junctions and organization of the subsurface actin cytoskeleton in specific regions of the epithelium.

14-3-3 and its binding partners are regulators of protein-protein interactions during spermatogenesis

During spermatogenesis, spermiation takes place at the adluminal edge of the seminiferous epithelium at stage VIII of the epithelial cycle during which fully developed spermatids (i.e. spermatozoa) detach from the epithelium in adult rat testes. This event coincides with the migration of preleptotene/leptotene spermatocytes across the blood-testis barrier from the basal to the apical (or adluminal) compartment. At stage XIV of the epithelial cycle, Pachytene spermatocytes (diploid, 2n) differentiate into diplotene spermatocytes (tetraploid, 4n) in the apical compartment of the epithelium, which begin meiosis I to be followed by meiosis II to form spermatids (haploid, 1n) at stage XIV of the epithelial cycle. These spermatids, in turn, undergo extensive morphological changes and traverse the seminiferous epithelium until they differentiate into elongated spermatids. Thus, there are extensive changes at the Sertoli-Sertoli and Sertoli-germ cell interface via protein 'coupling' and 'uncoupling' between cell adhesion protein complexes, as well as changes in interactions between integral membrane proteins and their peripheral adaptors, regulatory protein kinases and phosphatases, and the cytoskeletal proteins. These precisely coordinated protein-protein interactions affect cell adhesion and cell movement. In this review, we focus on the 14-3-3 protein family, whose members have different binding partners in the seminiferous epithelium. Recent studies have illustrated that 14-3-3 affects protein-protein interactions in the seminiferous epithelium, and regulates cell adhesion possibly via its effects on intracellular protein trafficking and cell-polarity proteins. This review provides a summary on the latest findings regarding the role of 14-3-3 family of proteins and their potential implications on spermatogenesis. We also highlight research areas that deserve attentions by investigators.

cAMP-Epac2-mediated activation of Rap1 in developing male germ cells: RA-RhoGAP as a possible direct down-stream effector

Rap1 is a small GTPase that functions as a positional signal and organizer of cell architecture. Recently Rap1 is emerged to play a critical role during sperm differentiation since its inactivation in haploid cells leads to a premature release of spermatids from the supporting Sertoli cell resulting in male infertility. How Rap1 is activated in spermatogenic cells has not yet been determined. Our objective was to investigate on a possible cAMP-mediated activation of Rap1 employing a cAMP analogue selective to Epac, the Rap1 activator directly responsive to cAMP, for stimulating cultured testis germ cells. Here we provide biochemical, cellular and functional evidence that the Epac variant known as Epac2 is expressed as both a transcript and a protein and that it is able to promote Rap1 activation in the cultured cells. A time course immunofluorescence analysis carried out on stimulated cells revealed the translocation of endogenous Epac2, which is cytosolic, towards the site where Rap1 is located, i.e., the Golgi complex, thus documenting the effective Rap1-Epac2 protein interaction 'in vivo' leading to Rap1-GTP loading. A combination of biochemical and molecular techniques supported the immunofluorescence data. The search for the presence of a putative Rap1 downstream effector, described in differentiating somatic cells as a target of cAMP-Epac-activated Rap1, revealed the presence in spermatogenic cells of RA-RhoGAP, a Rap1-activated Rho GTPase-activating protein. Taken together, our results, obtained with endogenously expressed proteins, are consistent with a cAMP/Epac2/Rap1-mediated signaling that could exert its action, among others, through RA-RhoGAP to promote the progression of spermatogenesis.

Delta6-desaturase (FADS2) deficiency unveils the role of omega3- and omega6-polyunsaturated fatty acids

Mammalian cell viability is dependent on the supply of the essential fatty acids (EFAs) linoleic and alpha-linolenic acid. EFAs are converted into omega3- and omega6-polyunsaturated fatty acids (PUFAs), which are essential constituents of membrane phospholipids and precursors of eicosanoids, anandamide and docosanoids. Whether EFAs, PUFAs and eicosanoids are essential for cell viability has remained elusive. Here, we show that deletion of delta6-fatty acid desaturase (FADS2) gene expression in the mouse abolishes the initial step in the enzymatic cascade of PUFA synthesis. The lack of PUFAs and eicosanoids does not impair the normal viability and lifespan of male and female fads2 -/- mice, but causes sterility. We further provide the molecular evidence for a pivotal role of PUFA-substituted membrane phospholipids in Sertoli cell polarity and blood-testis barrier, and the gap junction network between granulosa cells of ovarian follicles. The fads2 -/- mouse is an auxotrophic mutant. It is anticipated that FADS2 will become a major focus in membrane, haemostasis, inflammation and atherosclerosis research.

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.

Anchoring junctions as drug targets: role in contraceptive development

In multicellular organisms, cell-cell interactions are mediated in part by cell junctions, which underlie tissue architecture. Throughout spermatogenesis, for instance, preleptotene leptotene spermatocytes residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier to enter the adluminal compartment for continued development. At the same time, germ cells must also remain attached to Sertoli cells, and numerous studies have reported extensive restructuring at the Sertoli-Sertoli and Sertoli-germ cell interface during germ cell movement across the seminiferous epithelium. Furthermore, the proteins and signaling cascades that regulate adhesion between testicular cells have been largely delineated. These findings have unveiled a number of potential "druggable" targets that can be used to induce premature release of germ cells from the seminiferous epithelium, resulting in transient infertility. Herein, we discuss a novel approach with the aim of developing a nonhormonal male contraceptive for future human use, one that involves perturbing adhesion between Sertoli and germ cells in the testis.

Mechanism of action of l-CDB-4022, a potential nonhormonal male contraceptive, in the seminiferous epithelium of the rat testis

The present study was conducted to elucidate the possible molecular mechanisms involved in the antispermatogenic activity of l-CDB-4022, an indenopyridine. In this study 45-d-old male Sprague-Dawley rats were treated with a single oral dose of l-CDB-4022 (2.5 mg/kg) or vehicle, and blood and testes were collected at various time points. The rate of body weight gain was not affected, but a significant loss of testes weight was induced by l-CDB-4022. Serum hormones were assayed using specific RIAs or ELISAs, and testicular protein and RNA were analyzed by Western blotting and RT-PCR, respectively. There was a significant decrease in inhibin B and concomitant increase in FSH in serum from l-CDB-4022-treated rats, but serum levels of activin A, testosterone, and LH were unchanged. Western analysis of testicular lysates from l-CDB-4022-treated rats exhibited phosphorylation of ERK1/2 at 4 h and later time points. Loss of nectin/afadin complex occurred at 48 h, but there was an increase in levels of integrin-beta1, N-cadherin, alpha-catenin, and beta-catenin protein at 24 h and later time points. Increase in expression of Fas ligand and Fas receptor was detected 8 and 24 h after l-CDB-4022 treatment. The ratio of the membrane to soluble form of stem cell factor mRNA was decreased. Immunohistochemical analysis of testicular sections indicated a dramatic disruption of the Sertoli cell microtubule network in l-CDB-4022-treated rats. Collectively, these results suggest that l-CDB-4022 activates the MAPK pathway, reduces expression of prosurvival factors such as the membrane form of stem cell factor, alters expression of Sertoli-germ cell adherens junction proteins, disrupts Sertoli cell microtubule structure, and induces the proapoptotic factor, Fas, culminating in germ cell loss from the seminiferous epithelium.

Review of the histological effects of the anti-androgen, flutamide, on mouse testis

This is a mini-review summarizing recent findings on the effect of flutamide (FLUT), an anti-androgenic toxicant, on the mouse testis, particularly on the ectoplasmic specialization (ES) in the testis. FLUT induces a reduction in the weight of male reproductive tissues, such as the prostate, because it inhibits the formation of the androgen receptors and testosterone retention. The present review summarizes the abnormal histological changes produced in the mouse testis by FLUT. In addition, we outline the effect of FLUT on the expression of cortactin, an actin-binding protein, in the mouse testis. FLUT is often used as a positive control for the identification of endocrine disrupting chemicals having anti-androgenic activities; therefore, a detailed understanding of the adverse effects of FLUT is important for the analysis of the risks to spermatogenesis by anti-androgen-like endocrine disruptors.

Biology and regulation of ectoplasmic specialization, an atypical adherens junction type, in the testis

Anchoring junctions are cell adhesion apparatus present in all epithelia and endothelia. They are found at the cell-cell interface (adherens junction (AJ) and desmosome) and cell-matrix interface (focal contact and hemidesmosome). In this review, we focus our discussion on AJ in particular the dynamic changes and regulation of this junction type in normal epithelia using testis as a model. There are extensive restructuring of AJ (e.g., ectoplasmic specialization, ES, a testis-specific AJ) at the Sertoli-Sertoli cell interface (basal ES) and Sertoli-elongating spermatid interface (apical ES) during the seminiferous epithelial cycle of spermatogenesis to facilitate the migration of developing germ cells across the seminiferous epithelium. Furthermore, recent findings have shown that ES also confers cell orientation and polarity in the seminiferous epithelium, illustrating that some of the functions initially ascribed to tight junctions (TJ), such as conferring cell polarity, are also part of the inherent properties of the AJ (e.g., apical ES) in the testis. The biology and regulation based on recent studies in the testis are of interest to cell biologists in the field, in particular their regulation, which perhaps is applicable to tumorigenesis.