Male germ cell specification and differentiation

The BNB-GLID module regulates germline fate determination in Marchantia polymorpha

Germline fate determination is a critical event in sexual reproduction. Unlike animals, plants specify the germline by reprogramming somatic cells at the late stages of their development. However, the genetic basis of germline fate determination and how it evolved during the land plant evolution are still poorly understood. Here, we report that the plant homeodomain finger protein GERMLINE IDENTITY DETERMINANT (GLID) is a key regulator of the germline specification in liverwort, Marchantia polymorpha. Loss of the MpGLID function causes failure of germline initiation, leading to the absence of sperm and egg cells. Remarkably, the overexpression of MpGLID in M. polymorpha induces the ectopic formation of cells with male germline cell features exclusively in male thalli. We further show that MpBONOBO (BNB), with an evolutionarily conserved function, can induce the formation of male germ cell-like cells through the activation of MpGLID by directly binding to its promoter. The Arabidopsis (Arabidopsis thaliana) MpGLID ortholog, MALE STERILITY1 (AtMS1), fails to replace the germline specification function of MpGLID in M. polymorpha, demonstrating that a derived function of MpGLID orthologs has been restricted to tapetum development in flowering plants. Collectively, our findings suggest the presence of the BNB-GLID module in complex ancestral land plants that has been retained in bryophytes, but rewired in flowering plants for male germline fate determination.

Long Noncoding RNA LncPGCR Mediated by TCF7L2 Regulates Primordial Germ Cell Formation in Chickens

Simple Summary

The potential of primordial germ cells (PGCs) for multidirectional differentiation, together with their unique regeneration ability, makes them one of the most promising seed cells in clinical medicine and tissue engineering research. However, not enough PGCs can be obtained to meet the demand, which limits their application. We defined a novel long noncoding RNA (lncRNA) mediated by epigenetics, which could activate the miR-6577-5p/Btrc pathway to promote the formation of PGCs. The technical system we have established is a useful tool to obtain sufficient PGCs for scientific research. Our study offers great theoretical and practical value in the production of transgenic animals or genomic imprinting in poultry. We believe that our study will help researchers in the fields of agricultural production, developmental biology, and cell biology.

Abstract

Although lncRNAs have been identified as playing critical roles in the development of germ cells, their potential involvement in the development of PGCs in chickens remains poorly understood. Differentially expressed lncRNAs (DELs) from previous RNA-seq of embryonic stem cells (ESCs), PGCs, and spermatogonial stem cells (SSCs) were analyzed by K-means clustering, from which a key candidate, lncRNA (lncRNA PGC regulator, LncPGCR) was obtained. We confirmed that LncPGCR plays a positive role in the development of PGCs by increasing the expression of the PGC marker gene (Cvh and C-kit), while downregulating the pluripotency-associated gene (Nanog) in vitro and in vivo. The activation and expression of LncPGCR are regulated by histone acetylation, and transcription factor TCF7L2. Mechanistically, a rescue assay was performed to further confirm that LncPGCR contributed to the development of PGCs by regulating the gga-miR-6577-5p/Btrc signaling pathway. Adsorption of gga-miR-6577-5p activated the WNT signaling cascade by relieving the gga-miR-6577-5p-dependent inhibition of Btrc expression. Taken together, our study discovered the growth-expedited role of LncPGCR in PGCs development, showing the potential LncPGCR/miR-6577-5p/Btrc pathway. The results and findings provide a novel insight into the development of PGCs.

Preliminary Investigation on the Ameliorative Role Exerted by D-Aspartic Acid in Counteracting Ethane Dimethane Sulfonate (EDS) Toxicity in the Rat Testis

Simple Summary

For proper fertility, the production of good-quality spermatozoa is essential. Nowadays, many environmental pollutants affect the spermatogenetic process, at different levels. For this reason, new approaches are needed to prevent/counteract these toxic effects. Here, we showed that the excitatory amino acid D-aspartic acid (D-Asp) prevents the deadly action of ethane dimethane sulfonate (EDS) on the testosterone-secreting Leydig cells in rat testis. We found that EDS, probably via the reduced testosterone level, alters the normal histology of the seminiferous epithelium, leading to germ cells death and to the decreased protein level of two Leydig cell “markers”: steroidogenic acute regulatory and prolyl endopeptidase. In addition, the same analysis performed on rats that were pre-treated with D-Asp revealed a protective role of this compound, since all the above parameters were quite normal. Moreover, we found that the protective mechanism of action involved in this scenario may be due to the ability of D-Asp to reduce the oxidative stress induced by EDS. Based on these findings, we could affirm that D-Asp may be an encouraging candidate to be used to alleviate the harmful action due to environmental pollutants exposure, in order to maintain appropriate fertility.

Abstract

Herein is reported the first evidence of the protective role of D-aspartic acid (D-Asp) in preventing the toxic effect exerted by the alkylating agent ethane dimethane sulfonate (EDS) in the rat testis. We confirmed that EDS treatment specifically destroyed Leydig cells (LC), resulting in the drastic decrease of the serum testosterone level and producing morphological changes in the germinal tubules, i.e., altered organization of the epithelium, loss of cell contacts and the consequent presence of empty spaces between them, and a reduce number of spermatozoa. Moreover, an increase of TUNEL-positive germ cells, other than alteration in the protein level and localization of two LC “markers”, StAR and PREP, were observed. Interestingly, results obtained from rats pre-treated with D-Asp for 15 days before EDS-injection showed that all the considered parameters were quite normal. To explore the probable mechanism(s) involved in the protection exerted by D-Asp, we considered the increased oxidative stress induced by EDS and the D-Asp antioxidant effects. Thiobarbiturc acid-reactive species (TBARS) levels increased following EDS-injection, while no change was observed in the D-Asp + EDS treated rats. Our results showed that D-Asp may be used as a strategy to mitigate the toxic effects exerted by environmental pollutants, as endocrine disrupters, in order to preserve the reproductive function.

EH domain binding protein 1-like 1 (EHBP1L1), a protein with calponin homology domain, is expressed in the rat testis

In this paper, with the aim to find new genes involved in mammalian spermatogenesis, we isolated, for the first time in the rat testis, a partial cDNA clone that encoded EH domain binding protein 1-like 1 (Ehbp1l1), a protein that has a single calponin homology domain (CH). Bioinformatic analysis showed that EHBP1l1 contains three domains: the N-terminal C2-like, the CH and the C-terminal bivalent Mical/EHBP Rab binding (bMERB) domains, which are evolutionarily conserved in vertebrates. We found that Ehbp1l1 mRNA was expressed in several rat tissues, including the liver, intestine, kidney and also in the testis during its development, with a higher level in testis from 12-month-old animals. Interestingly, in situ hybridization experiments revealed that Ehbp1l1 is specifically expressed by types I and II spermatocytes, this result was validated by RT-PCR performed on total RNA obtained from enriched fractions of different testicular cell types. As EHBP1l1 has been described as linked to vesicular transport to the actin cytoskeleton and as an effector of the small GTPase Rab8, we hypothesized that it could participate both in cytoskeletal remodelling and in the regulation of vesicle sorting from the trans-Golgi network to the apical plasma membrane. Our findings provide a better understand of the molecular mechanisms of the differentiation process of spermatogenesis; Ehbp1l1 may also be used as a new marker of testicular activity.

D-Aspartate Upregulates DAAM1 Protein Levels in the Rat Testis and Induces Its Localization in Spermatogonia Nucleus

Cell differentiation during spermatogenesis requires a proper actin dynamic, regulated by several proteins, including formins. Disheveled-Associated-Activator of Morphogenesis1 (DAAM1) belongs to the formins and promotes actin polymerization. Our results showed that oral D-Aspartate (D-Asp) administration, an excitatory amino acid, increased DAAM1 protein levels in germ cells cytoplasm of rat testis. Interestingly, after the treatment, DAAM1 also localized in rat spermatogonia (SPG) and mouse GC-1 cells nuclei. We provided bioinformatic evidence that DAAM1 sequence has two predicted NLS, supporting its nuclear localization. The data also suggested a role of D-Asp in promoting DAAM1 shuttling to the nuclear compartment of those proliferative cells. In addition, the proliferative action induced by D-Asp is confirmed by the increased levels of PCNA, a protein expressed in the nucleus of cells in the S phase and p-H3, a histone crucial for chromatin condensation during mitosis and meiosis. In conclusion, we demonstrated, for the first time, an increased DAAM1 protein levels following D-Asp treatment in rat testis and also its localization in the nucleus of rat SPG and in mouse GC-1 cells. Our results suggest an assumed role for this formin as a regulator of actin dynamics in both cytoplasm and nuclei of the germ cells.

Post-transcriptional gene regulation regulates germline stem cell to oocyte transition during Drosophila oogenesis

During oogenesis, several developmental processes must be traversed to ensure effective completion of gametogenesis including, stem cell maintenance and asymmetric division, differentiation, mitosis and meiosis, and production of maternally contributed mRNAs, making the germline a salient model for understanding how cell fate transitions are mediated. Due to silencing of the genome during meiotic divisions, there is little instructive transcription, barring a few examples, to mediate these critical transitions. In Drosophila, several layers of post-transcriptional regulation ensure that the mRNAs required for these processes are expressed in a timely manner and as needed during germline differentiation. These layers of regulation include alternative splicing, RNA modification, ribosome production, and translational repression. Many of the molecules and pathways involved in these regulatory activities are conserved from Drosophila to humans making the Drosophila germline an elegant model for studying the role of post-transcriptional regulation during stem cell differentiation and meiosis.

Evaluation of testis hormonal and histopathological alterations in type I and type II diabetic rats

BACKGROUND

Diabetes is a devastating metabolic disease that causes long-term damage to various organs. An important leading complication of diabetes is a degenerative effect on the reproductive system including infertility and gonadal dysfunction. This study aimed to evaluate the effects of experimental type I and II diabetes on the levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone.

METHODS

Male Wistar rats were randomly divided into four separate groups: (1) type I diabetes (T1DM), (2) type II diabetes (T2DM), (3) cetrorelix acetate-treated nondiabetic control group, and (4) normal untreated group (n = 6). T1DM was experimentally induced by a single injection of alloxan (135 mg/kg) while T2DM was induced by feeding the animals with drinking water enriched with fructose (10%). Cetrorelix acetate (100 mg/kg, intraperitoneal for 1 week) treatment group was used as a positive control. All rats were killed and blood and testes were collected after 8 weeks of the study. The effects of induced diabetes on the levels of blood glucose and insulin were assessed. The levels of sex hormones and insulin were determined by radioimmunoassay. Histological staining was used to check abnormal patterns of testicular morphology, the diameter of seminiferous tubules, testicular diameter, and germinal layer thickness.

RESULTS

A significant reduction in the testosterone, FSH, and LH levels were observed in T1DM, T2DM, and also in cetrorelix acetate-treated groups. Analysis of testicular histology sections revealed significantly reduced thickness of cell layer in T1DM and cetrorelix acetate-treated groups compared with the T2DM group. In T2DM, the cell numbers, the thickness of cell layer, the diameter of seminiferous tubules, and weight of testicles were slightly increased. In contrast, total tubules of empty seminiferous increased significantly in T1D and cetrorelix treated groups compared with the control group.

CONCLUSION

Overall, diabetes can induce hypothalamus-pituitary-gonad axis dysfunction, affects hormonal secretion, and causes histological damage to testes, collectively leading to deleterious effects on male fertility.

Obtaining and characterization of anti-testis monoclonal antibodies: Invaluable tools toward the identification of testis antigens involved in fertilization

BACKGROUND

Generation and utilization of the specific monoclonal antibodies against testis antigens is reported to identify the antigens that are important in reproductive field.

OBJECTIVE

Current study aimed to introduce a hybridoma that producing a specific anti-testis monoclonal antibody to identify the testis antigens that can be important in the reproduction field.

METHODS

To make hybridoma against testis antigens, mice were immunized with testis cell lysate. After cell fusion, resulted hybridomas were screened by indirect ELISA, then cloned by limiting dilution and finally the produced monoclonal antibody were characterized by some of the molecular laboratory techniques such as immunohistochemistry, immunocytochemistry and western blot.

RESULTS

By using hybridoma technique, cell fusion was performed and ten (8A11, 8D6, 8D7, 9F6, 9G11, 10C3, 10B3, 10B2, 10C2 and 10H7) antibodies specific to the testis antigens were produced finally. Among the produced antibodies, 10C3 was found to cross-react with testis, but not detected in other tissues. mAb 10C3 recognized the sperm and testis antigens, specifically the intertestitial tissue of testis, spermatogonia, primary and secondary spermatocyte antigens, so they were most likely the target of generated mAb. Also our mAb could totally detect the mouse sperm antigens and the specific antigens of head and tail of human sperm. In western blotting analysis, mAb 10C3 could recognize the specific protein bands of sperm and testis extracts. Also in this study the testis specific genes that were target of generated mAb, were selected according to the mouse EST profile available at UniGene part of NCBI.

CONCLUSIONS

So this stable anti-testis mAb has a potential for laboratory researches and also for diagnostic procedures in fertilization. Thus it could be exploited as a suitable tool for target-specific diagnosis and research in several diseases.

Characterization and localization of primordial germ cells in Totoaba macdonaldi

The totoaba, Totoaba macdonaldi, is an endangered fish of the Gulf of California with high economic and ecological potential. Therefore, our purpose was to characterize the Primordial Germ Cells (PGCs) of this Sciaenid with two objectives: (1) to provide the basis for PGCs cryopreservation to preserve the genetic resources and (2) to take the first step to know the gonadal genesis and sex differentiation of totoaba. Immunofluorescence analysis performed from 2-cell stage to 8-day after hatch (DAH) shows that Vasa protein is specific for PGCs. These cells were first observed in the peripheral and dorsal regions of the blastodisc at approximately the 50%-epiboly stage and migrated to both sides of embryo body during the development. Finally, at 7 DAH the PGCs of the hatching embryo reached the place where the gonad will be developed. Histology analysis of larvae showed a genital ridge with enclosed PGCs on the dorsal side of the peritoneum at 9 DAH, gonadal primordium growth was observed at 11 DAH as a result of the interaction between PGCs and somatic cells derived from the peritoneum. Results of qPCR showed that vasa expression was restricted to the embryonic and early larval development, highest values were observed in 2-cell and mid-blastula stage suggesting the maternal inheritance of vasa mRNA. These findings support the hypothesis of preformation in T. macdonaldi PGCs. The migration pattern of PGCs allow us to recommend the isolation and subsequent cryopreservation of these cells before 7 DAH when the embryonic and larval development is given at 21 °C.

Evolutionary conservation and divergence of Vasa, Dazl and Nanos1 during embryogenesis and gametogenesis in dark sleeper (Odontobutis potamophila)

Germline-specific genes, Vasa, Dazl and Nanos1, have highly conserved functions in germline development and fertility across animal phyla. In this study, the full-length sequences of Opvasa, Opdazl and Opnanos1 were cloned and characterized from the dark sleeper (Odontobutis potamophila). Gonad-specific expression patterns of Opvasa and Opdazl were confirmed in adult tissues by quantitative real-time PCR (qRT-PCR). Different from Opvasa and Opdazl, the expression of Opnanos1 was ubiquitously detected in all examined tissues except for the liver and spleen. Time-course dynamic expressions during embryogenesis were assessed, and all three genes (Opvasa, Opdazl and Opnanos1) persisted at a high level until gastrulation. qRT-PCR and Western blotting analyses revealed that all three genes were highly expressed throughout gametogenesis. In testis, the expressions of all three genes at the mRNA and protein levels were down-regulated during spermatogenesis. In ovary, different expression patterns were found, and all three genes had a differential role in translational regulation during oogenesis. The expressions of Opvasa, Opdazl and Opnanos1 at the mRNA but not the protein level were high in stage IV. Different expression patterns were found in premeiotic gonads treated by HPG axis hormones (HCG and LHRH-A). Immunolocalization analysis demonstrated that in testis, Opvasa, Opdazl and Opnanos1 were detected in spermatogonia and spermatocytes but absent in the meiotic products, such as spermatids and spermatozoa. In ovary, Opvasa, Opdazl and Opnanos1 persisted at a high level throughout oogenesis. These findings indicated that Opvasa, Opdazl and Opnanos1 played an important role in mitotic and early meiotic phases of oogenesis and spermatogenesis, and they functioned as maternal factors in early embryogenesis. Their proteins could be used as three new markers for germ cells during gametogenesis in O. potamophila gonad. Our data laid a good foundation for improving the breeding efficiency of O. potamophila.

Physiological and pathological implications of 5-hydroxymethylcytosine in diseases

Gene expression is the prerequisite of proteins. Diverse stimuli result in alteration of gene expression profile by base substitution for quite a long time. However, during the past decades, accumulating studies proved that bases modification is involved in this process. CpG islands (CGIs) are DNA fragments enriched in CpG repeats which mostly locate in promoters. They are frequently modified, methylated in most conditions, thereby suggesting a role of methylation in profiling gene expression. DNA methylation occurs in many conditions, such as cancer, embryogenesis, nervous system diseases etc. Recently, 5-hydroxymethylcytosine (5hmC), the product of 5-methylcytosine (5mC) demethylation, is emerging as a novel demethylation marker in many disorders. Consistently, conversion of 5mC to 5hmC has been proved in many studies. Here, we reviewed recent studies concerning demethylation via 5hmC conversion in several conditions and progress of therapeutics-associated with it in clinic. We aimed to unveil its physiological and pathological significance in diseases and to provide insight into its clinical application potential.

Neuronal signaling repertoire in the mammalian sperm functionality

The common embryonic origin has been a recurrent explanation to understand the presence of "neural receptors" in sperm. However, this designation has conditioned a bias marked by the classical neurotransmission model, dismissing the possibility that neurotransmitters can play specific roles in the sperm function by themselves. For instance, the launching of acrosome reaction, a fundamental sperm function, includes several steps that recall the process of presynaptic secretion. Unlike of postsynaptic neuron, whose activation is mediated by molecular interaction between neurotransmitter and postsynaptic receptors, the oocyte activation is not mediated by receptors, but by cytosolic translocation of sperm phospholipase (PLCζ). Thus, the sperm has a cellular design to access and activate the oocyte and restore the ploidy of the species by an "allogenic pronuclear fusion." At subcellular level, the events controlling sperm function, particularly the capacitation process, are activated by chemical signals that trigger ion fluxes, sterol oxidation, synthesis of cyclic adenosine monophosphate, protein kinase A activation, tyrosine phosphorylations and calcium signaling, which correspond to second messengers similar to those associated with exocytosis and growth cone guidance in neurons. Classically, the sperm function associated with neural signals has been analyzed as a unidimensional approach (single ligand-receptor effect). However, the in vivo sperm are exposed to multidimensional signaling context, for example, the GABAergic, monoaminergic, purinergic, cholinergic, and melatoninergic, to name a few. The aim of this review is to present an overview of sperm functionality associated with "neuronal signaling" and possible cellular and molecular mechanisms involved in their regulation.

Probing spermiogenesis: a digital strategy for mouse acrosome classification

Classification of morphological features in biological samples is usually performed by a trained eye but the increasing amount of available digital images calls for semi-automatic classification techniques. Here we explore this possibility in the context of acrosome morphological analysis during spermiogenesis. Our method combines feature extraction from three dimensional reconstruction of confocal images with principal component analysis and machine learning. The method could be particularly useful in cases where the amount of data does not allow for a direct inspection by trained eye.

Control of Anther Cell Differentiation by the Small Protein Ligand TPD1 and Its Receptor EMS1 in Arabidopsis

A fundamental feature of sexual reproduction in plants and animals is the specification of reproductive cells that conduct meiosis to form gametes, and the associated somatic cells that provide nutrition and developmental cues to ensure successful gamete production. The anther, which is the male reproductive organ in seed plants, produces reproductive microsporocytes (pollen mother cells) and surrounding somatic cells. The microsporocytes yield pollen via meiosis, and the somatic cells, particularly the tapetum, are required for the normal development of pollen. It is not known how the reproductive cells affect the differentiation of these somatic cells, and vice versa. Here, we use molecular genetics, cell biological, and biochemical approaches to demonstrate that TPD1 (TAPETUM DETERMINANT1) is a small secreted cysteine-rich protein ligand that interacts with the LRR (Leucine-Rich Repeat) domain of the EMS1 (EXCESS MICROSPOROCYTES1) receptor kinase at two sites. Analyses of the expressions and localizations of TPD1 and EMS1, ectopic expression of TPD1, experimental missorting of TPD1, and ablation of microsporocytes yielded results suggesting that the precursors of microsporocyte/microsporocyte-derived TPD1 and pre-tapetal-cell-localized EMS1 initially promote the periclinal division of secondary parietal cells and then determine one of the two daughter cells as a functional tapetal cell. Our results also indicate that tapetal cells suppress microsporocyte proliferation. Collectively, our findings show that tapetal cell differentiation requires reproductive-cell-secreted TPD1, illuminating a novel mechanism whereby signals from reproductive cells determine somatic cell fate in plant sexual reproduction.

The differentiation of distinct somatic and reproductive cells in flowers is required for the successful sexual reproduction of plants. The anther produces reproductive microsporocytes (pollen mother cells) that give rise to pollen (male gametophytes), as well as surrounding somatic cells (particularly the tapetal cells) that support the normal development of pollen. In animals, signals from somatic cells are known to influence reproductive cell fate determination, and vice versa. However, little is known about the molecular mechanisms underlying somatic and reproductive cell fate determination in plants. In this paper, we demonstrate that TPD1 (TAPETUM DETERMINANT1) is processed into a small secreted cysteine-rich protein ligand for the EMS1 (EXCESS MICROSPOROCYTES1) leucine-rich repeat receptor-like kinase (LRR-RLK). TPD1 is secreted from reproductive cells to the plasma membrane of somatic cells, where activated TPD1-EMS1 signaling first promotes periclinal cell division and then determines tapetal cell fate. Moreover, tapetal cells suppress microsporocyte proliferation. Our findings illuminate a novel mechanism by which reproductive cells determine somatic cell fate, and somatic cells in turn limit reproductive cell proliferation. Plants extensively employ LRR-RLKs to control growth, development, and defense. Our identification of TPD1 as the first small protein ligand for all LRR-RLKs characterized to date will provide a valuable system for studying how small protein ligands activate LRR-RLK signaling complexes.

Analysis of POU5F1, c-Kit, PLAP, AP2γ and SALL4 in gonocytes of patients with cryptorchidism

Cryptorchidism is a risk factor for the development of testicular germ cell tumors (TGCTs). The most common type of TGCT in cryptorchidism is seminoma. The intratubular germ cell neoplasia unclassified (ITGCNU) is a histological pattern preceding the development of seminomas and non-seminomas. It was suggested that in patients with cryptorchidism, the gonocytes remained undifferentiated with pluripotent abilities expressing proteins like POU domain class 5 transcription factor 1 (POU5F1), tyrosine kinase receptor c-Kit, placental-like alkaline phosphatase (PLAP), the transcription factor AP2γ and sal-like protein 4 (SALL4) that confer to the gonocytes this ability and therefore make them susceptible to develop ITGCNU. The aim of the present study was to determine if the gonocytes of patients with cryptorchidism express POU5F1, c-Kit, PLAP, AP2γ and SALL4 proteins after their differentiation period. Based on this, we evaluated samples of testicular tissue from newborns to 16-year old subjects with or without cryptorchidism in search of POU5F1, c-Kit, PLAP, AP2γ and SALL4 using immunocytochemical method, the results of which were validated by RT-PCR. The results showed that control subjects witnessed a down-regulation in the expression of these five proteins in the first year of life, which eventually disappeared. On the other hand, it was determined that 21.6% (8/37) of the patients with cryptorchidism continued to express, at least, one of the proteins analyzed in this study after the second year of life. And only 5.4% (2/37) of the patients were positive to the five markers. These data sustain the proposed hypothesis that in cryptorchid patients, ITGCNU arises from gonocytes that fail in their differentiation process to spermatogonia with conservation of the proteins (POU5F1, c-Kit, PLAP, AP2γ and SALL4) that maintain pluripotency and undifferentiated characteristics and which are responsible for making the gonocytes susceptible to malignancy. However, we cannot guarantee that these patients present neoplastic transformation.

Mammalian gonocyte and spermatogonia differentiation: recent advances and remaining challenges

The production of spermatozoa relies on a pool of spermatogonial stem cells (SSCs), formed in infancy from the differentiation of their precursor cells, the gonocytes. Throughout adult life, SSCs will either self-renew or differentiate, in order to maintain a stem cell reserve while providing cells to the spermatogenic cycle. By contrast, gonocytes represent a transient and finite phase of development leading to the formation of SSCs or spermatogonia of the first spermatogenic wave. Gonocyte development involves phases of quiescence, cell proliferation, migration, and differentiation. Spermatogonia, on the other hand, remain located at the basement membrane of the seminiferous tubules throughout their successive phases of proliferation and differentiation. Apoptosis is an integral part of both developmental phases, allowing for the removal of defective cells and the maintenance of proper germ–Sertoli cell ratios. While gonocytes and spermatogonia mitosis are regulated by distinct factors, they both undergo differentiation in response to retinoic acid. In contrast to postpubertal spermatogenesis, the early steps of germ cell development have only recently attracted attention, unveiling genes and pathways regulating SSC self-renewal and proliferation. Yet, less is known on the mechanisms regulating differentiation. The processes leading from gonocytes to spermatogonia have been seldom investigated. While the formation of abnormal gonocytes or SSCs could lead to infertility, defective gonocyte differentiation might be at the origin of testicular germ cell tumors. Thus, it is important to better understand the molecular mechanisms regulating these processes. This review summarizes and compares the present knowledge on the mechanisms regulating mammalian gonocyte and spermatogonial differentiation.

Stage-specific signaling pathways during murine testis development and spermatogenesis: A pathway-based analysis to quantify developmental dynamics

Shifting the field of developmental toxicology toward evaluation of pathway perturbation requires a quantitative definition of normal developmental dynamics. This project examined a publicly available dataset to quantify pathway dynamics during testicular development and spermatogenesis and anchor toxicant-perturbed pathways within the context of normal development. Genes significantly changed throughout testis development in mice were clustered by their direction of change using K-means clustering. Gene Ontology terms enriched among each cluster were identified using MAPPfinder. Temporal pathway dynamics of enriched terms were quantified based on average expression intensity for all genes associated with a given term. This analysis captured processes that drive development, including the peak in steroidogenesis known to occur around gestational day 16.5 and the increase in meiosis and spermatogenesis-related pathways during the first wave of spermatogenesis. Our analysis quantifies dynamics of pathways vulnerable to toxicants and provides a framework for quantifying perturbation of these pathways.

Germ cell loss is associated with fading Lin28a expression in a mouse model for Klinefelter's syndrome

Klinefelter's syndrome is a male sex-chromosomal disorder (47,XXY), causing hypogonadism, cognitive and metabolic deficits. The majority of patients are infertile due to complete germ cell loss after puberty. As the depletion occurs during development, the possibilities to study the underlying causes in humans are limited. In this study, we used the 41,XXY* mouse model to characterise the germ line postnatally. We examined marker expression of testicular cells focusing on the spermatogonial stem cells (SSCs) and found that the number of germ cells was approximately reduced fivefold at day 1pp in the 41,XXY* mice, indicating the loss to start prenatally. Concurrently, immunohistochemical SSC markers LIN28A and PGP9.5 also showed decreased expression on day 1pp in the 41,XXY* mice (48.5 and 38.9% of all germ cells were positive), which dropped to 7.8 and 7.3% on 3dpp, and were no longer detectable on days 5 and 10pp respectively. The differences in PCNA-positive proliferating cells in XY* and XXY* mice dramatically increased towards day 10pp. The mRNA expression of the germ cell markers Lin28a (Lin28), Pou5f1 (Oct4), Utf1, Ddx4 (Vasa), Dazl, and Fapb1 (Sycp3) was reduced and the Lin28a regulating miRNAs were deregulated in the 41,XXY* mice. We suggest a model for the course of germ cell loss starting during the intrauterine period. Neonatally, SSC marker expression by the already lowered number of spermatogonia is reduced and continues fading during the first postnatal week, indicating the surviving cells of the SSC population to be disturbed in their stem cell characteristics. Subsequently, the entire germ line is then generally lost when entering meiosis.

Sperm parameters: paradigmatic index of good health and longevity

Since the discovery of spermatozoon by Anton van Leeuwenhoek in 1677, there has been an ever increasing understanding of its role in reproduction. Many factors adversely affect sperm quality, including varicocele, accessory gland infection, immunological factors, congenital abnormalities, and iatrogenic systemic and endocrine causes, such as diabetes mellitus, obesity, metabolic syndrome, and smoking. The mechanisms responsible for the association between poor sperm parameters and ill health may include oxidative stress, low-grade inflammation, low testosterone, and low sex-hormone-binding globulin. Oxidative stress in the testicular microenvironment may result in decreased spermatogenesis and sperm DNA damage, loss of sperm motility, and abnormal sperm morphology. Low testosterone caused by advanced age, visceral obesity, and inflammation is associated with the development of cardiovascular disease. Hence, semen analysis has an important role in the routine evaluation of idiopathic male infertility, usually manifested as low sperm counts, impaired sperm motility, or absence of sperm, and remains the most common single diagnostic tool. Several studies have shown an inverse relationship between semen quality and medical disorders. This review elucidates the effect of medical disorders and social habits on sperm quality, the mechanisms that are involved in the impairment of sperm quality, and whether or not sperm quality can be used as an index of good health and longevity in a man.

Small RNAs in germline development

One of the most important and evolutionarily conserved strategies to control gene expression in higher metazoa is posttranscriptional regulation via small regulatory RNAs such as microRNAs (miRNAs), endogenous small interfering RNAs (endo-siRNAs), and piwi-interacting RNAs (piRNAs). Primordial germ cells, which are defined by their totipotent potential and noted for their dependence on posttranscriptional regulation by RNA-binding proteins, rely on these small regulatory RNAs for virtually every aspect of their development, including specification, migration, and differentiation into competent gametes. Here, we review current knowledge of the roles miRNAs, endo-siRNAs, and piRNAs play at all stages of germline development in various organisms, focusing on studies in the mouse.

New routes for transgenesis of the mouse

Transgenesis refers to the molecular genetic techniques for directing specific insertions, deletions and point mutations in the genome of germ cells in order to create genetically modified organisms (GMO). Genetic modification is becoming more practicable, efficient and predictable with the development and use of a variety of cell and molecular biology tools and DNA sequencing technologies. A collection of plasmidial and viral vectors, cell-type specific promoters, positive and negative selectable markers, reporter genes, drug-inducible Cre-loxP and Flp/FRT recombinase systems are available which ensure efficient transgenesis in the mouse. The technologies for the insertion and removal of genes by homologous-directed recombination in embryonic stem cells (ES) and generation of targeted gain- and loss-of function alleles have allowed the creation of thousands of mouse models of a variety of diseases. The engineered zinc finger nucleases (ZFNs) and small hairpin RNA-expressing constructs are novel tools with useful properties for gene knockout free of ES manipulation. In this review we briefly outline the different approaches and technologies for transgenesis as well as their advantages and disadvantages. We also present an overview on how the novel integrative mouse and human genomic databases and bioinformatics approaches have been used to understand genotype-phenotype relationships of hundreds of mutated and candidate disease genes in mouse models. The updating and continued improvements of the genomic technologies will eventually help us to unraveling the biological and pathological processes in such a way that they can be translated more efficiently from mouse to human and vise-versa.

RNA-binding proteins, RNA granules, and gametes: is unity strength?

Changes in mRNA translation and degradation represent post-transcriptional processes operating during gametogenesis and early embryogenesis to ensure regulated protein synthesis. Numerous mRNA-binding proteins (RBPs) have been described in multiple animal models that contribute to the control of mRNA translation and decay during oogenesis and spermatogenesis. An emerging view from studies performed in germ cells and somatic cells is that RBPs associate with their target mRNAs in RNA–protein (or ribonucleoprotein) complexes (mRNPs) that assemble in various cytoplasmic RNA granules that communicate with the translation machinery and control mRNA storage, triage, and degradation. In comparison withXenopus, Caenorhabditis elegans, orDrosophila, the composition and role of cytoplasmic RNA-containing granules in mammalian germ cells are still poorly understood. However, regained interest for these structures has emerged with the recent discovery of their role in small RNA synthesis and transposon silencing through DNA methylation. In this review, we will briefly summarize our current knowledge on cytoplasmic RNA granules in murine germ cells and describe the role of some of the RBPs they contain in regulating mRNA metabolism and small RNA processing during gametogenesis.

Spermatogonial stem cells, infertility and testicular cancer

The spermatogonial stem cells (SSCs) are responsible for the transmission of genetic information from an individual to the next generation. SSCs play critical roles in understanding the basic reproductive biology of gametes and treatments of human infertility. SSCs not only maintain normal spermatogenesis, but also sustain fertility by critically balancing both SSC self-renewal and differentiation. This self-renewal and differentiation in turn is tightly regulated by a combination of intrinsic gene expression within the SSC as well as the extrinsic gene signals from the niche. Increased SSCs self-renewal at the expense of differentiation result in germ cell tumours, on the other hand, higher differentiation at the expense of self-renewal can result in male sterility. Testicular germ cell cancers are the most frequent cancers among young men in industrialized countries. However, understanding the pathogenesis of testis cancer has been difficult because it is formed during foetal development. Recent studies suggest that SSCs can be reprogrammed to become embryonic stem (ES)-like cells to acquire pluripotency. In the present review, we summarize the recent developments in SSCs biology and role of SSC in testicular cancer. We believe that studying the biology of SSCs will not only provide better understanding of stem cell regulation in the testis, but eventually will also be a novel target for male infertility and testicular cancers.

Germ cell differentiation and proliferation in the developing testis of the South American plains viscacha, Lagostomus maximus (Mammalia, Rodentia)

Cell proliferation and cell death are essential processes in the physiology of the developing testis that strongly influence the normal adult spermatogenesis. We analysed in this study the morphometry, the expression of the proliferation cell nuclear antigen (PCNA), cell pluripotency marker OCT-4, germ cell marker VASA and apoptosis in the developing testes of Lagostomus maximus, a rodent in which female germ line develops through abolished apoptosis and unrestricted proliferation. Morphometry revealed an increment in the size of the seminiferous cords with increasing developmental age, arising from a significant increase of PCNA-positive germ cells and a stable proportion of PCNA-positive Sertoli cells. VASA showed a widespread cytoplasmic distribution in a great proportion of proliferating gonocytes that increased significantly at late development. In the somatic compartment, Leydig cells increased at mid-development, whereas peritubular cells showed a stable rate of proliferation. In contrast to other mammals, OCT-4 positive gonocytes increased throughout development reaching 90% of germ cells in late-developing testis, associated with a conspicuous increase in circulating FSH from mid- to late-gestation. TUNEL analysis was remarkable negative, and only a few positive cells were detected in the somatic compartment. These results show that the South American plains viscacha displays a distinctive pattern of testis development characterized by a sustained proliferation of germ cells throughout development, with no signs of apoptosis cell demise, in a peculiar endocrine in utero ambiance that seems to promote the increase of spermatogonial number as a primary direct effect of FSH.

Separase phosphosite mutation leads to genome instability and primordial germ cell depletion during oogenesis

To ensure equal chromosome segregation and the stability of the genome during cell division, Separase is strictly regulated primarily by Securin binding and inhibitory phosphorylation. By generating a mouse model that contained a mutation to the inhibitory phosphosite of Separase, we demonstrated that mice of both sexes are infertile. We showed that Separase deregulation leads to chromosome mis-segregation, genome instability, and eventually apoptosis of primordial germ cells (PGCs) during embryonic oogenesis. Although the PGCs of mutant male mice were completely depleted, a population of PGCs from mutant females survived Separase deregulation. The surviving PGCs completed oogenesis but produced deficient initial follicles. These results indicate a sexual dimorphism effect on PGCs from Separase deregulation, which may be correlated with a gender-specific discrepancy of Securin. Our results reveal that Separase phospho-regulation is critical for genome stability in oogenesis. Furthermore, we provided the first evidence of a pre-zygotic mitotic chromosome segregation error resulting from Separase deregulation, whose sex-specific differences may be a reason for the sexual dimorphism of aneuploidy in gametogenesis.

Zebrafish models of germ cell tumor

Germ cell tumors are neoplasms arising from pluripotent germ cells. In humans, these tumors occur in infants, children and young adults. The tumors display a wide range of histologic differentiation states which exhibit different clinical behaviors. Information about the molecular basis of germ cell tumors, and representative animal models of these neoplasms, are lacking. Germline development in zebrafish and humans is broadly conserved, making the fish a useful model to probe the connections between germ cell development and tumorigenesis. Here, we provide an overview of germline development and a brief review of germ cell tumor biology in humans and zebrafish. We also outline some methods for studying the zebrafish germline.

Revisiting rat spermatogenesis with MALDI imaging at 20-microm resolution

Matrix-assisted laser desorption/ionization (MALDI) molecular imaging technology attracts increasing attention in the field of biomarker discovery. The unambiguous correlation between histopathology and MALDI images is a key feature for success. MALDI imaging mass spectrometry (MS) at high definition thus calls for technological developments that were established by a number of small steps. These included tissue and matrix preparation steps, dedicated lasers for MALDI imaging, an increase of the robustness against cell debris and matrix sublimation, software for precision matching of molecular and microscopic images, and the analysis of MALDI imaging data using multivariate statistical methods. The goal of these developments is to approach single cell resolution with imaging MS. Currently, a performance level of 20-μm image resolution was achieved with an unmodified and commercially available instrument for proteins detected in the 2-16-kDa range. The rat testis was used as a relevant model for validating and optimizing our technological developments. Indeed, testicular anatomy is among the most complex found in mammalian bodies. In the present study, we were able to visualize, at 20-μm image resolution level, different stages of germ cell development in testicular seminiferous tubules; to provide a molecular correlate for its well established stage-specific classification; and to identify proteins of interest using a top-down approach and superimpose molecular and immunohistochemistry images.

Microarray-based analysis of cell-cycle gene expression during spermatogenesis in the mouse

Mammalian spermatogenesis is a continuum of cellular differentiation in a lineage that features three principal stages: 1) a mitotically active stage in spermatogonia, 2) a meiotic stage in spermatocytes, and 3) a postreplicative stage in spermatids. We used a microarray-based approach to identify changes in expression of cell-cycle genes that distinguish 1) mitotic type A spermatogonia from meiotic pachytene spermatocytes and 2) pachytene spermatocytes from postreplicative round spermatids. We detected expression of 550 genes related to cell-cycle function in one or more of these cell types. Although a majority of these genes were expressed during all three stages of spermatogenesis, we observed dramatic changes in levels of individual transcripts between mitotic spermatogonia and meiotic spermatocytes and between meiotic spermatocytes and postreplicative spermatids. Our results suggest that distinct cell-cycle gene regulatory networks or subnetworks are associated with each phase of the cell cycle in each spermatogenic cell type. In addition, we observed expression of different members of certain cell-cycle gene families in each of the three spermatogenic cell types investigated. Finally, we report expression of 221 cell-cycle genes that have not previously been annotated as part of the cell cycle network expressed during spermatogenesis, including eight novel genes that appear to be testis-specific.

Cloning and differential expression pattern of vasa in the developing and recrudescing gonads of catfish, Clarias gariepinus

Vasa gene codes for a DEAD box family protein, which plays a crucial role in primordial germ cell proliferation. In this study, we report cloning of vasa from gonads of air-breathing catfish, Clarias gariepinus, a seasonally reproducing teleost fish. We studied the expression pattern of vasa during gametogenesis using real-time PCR. We also examined the hormonal regulation on vasa in gonads of catfish. RT-PCR analysis revealed that vasa was detectable only in the gonads. Further, real-time PCR results showed that expression of vasa was seen throughout the development from embryonic stage to adult. However, the expression was more in ovary than in testis during gonadal development. In adult testis, the vasa transcripts were significantly high during spermatogenesis and it declined during spermiation. On the other hand, during ovarian recrudescence, vasa transcripts were high in immature oocytes (stages I and II oocytes) when compared to mature oocytes (stages III and IV oocytes). Human chorionic gonadotropin treatment in recrudescing ovary (in vivo) as well as in testicular slices (in vitro) resulted in up regulation of vasa mRNA in a time-dependent manner. These results together suggest that vasa gene has got an important role to play in spermatogenesis and oogenesis during recrudescence in addition to development.

BRIT1/MCPH1 is essential for mitotic and meiotic recombination DNA repair and maintaining genomic stability in mice

BRIT1 protein (also known as MCPH1) contains 3 BRCT domains which are conserved in BRCA1, BRCA2, and other important molecules involved in DNA damage signaling, DNA repair, and tumor suppression. BRIT1 mutations or aberrant expression are found in primary microcephaly patients as well as in cancer patients. Recent in vitro studies suggest that BRIT1/MCPH1 functions as a novel key regulator in the DNA damage response pathways. To investigate its physiological role and dissect the underlying mechanisms, we generated BRIT1^−/− mice and identified its essential roles in mitotic and meiotic recombination DNA repair and in maintaining genomic stability. Both BRIT1^−/− mice and mouse embryonic fibroblasts (MEFs) were hypersensitive to γ-irradiation. BRIT1^−/− MEFs and T lymphocytes exhibited severe chromatid breaks and reduced RAD51 foci formation after irradiation. Notably, BRIT1^−/− mice were infertile and meiotic homologous recombination was impaired. BRIT1-deficient spermatocytes exhibited a failure of chromosomal synapsis, and meiosis was arrested at late zygotene of prophase I accompanied by apoptosis. In mutant spermatocytes, DNA double-strand breaks (DSBs) were formed, but localization of RAD51 or BRCA2 to meiotic chromosomes was severely impaired. In addition, we found that BRIT1 could bind to RAD51/BRCA2 complexes and that, in the absence of BRIT1, recruitment of RAD51 and BRCA2 to chromatin was reduced while their protein levels were not altered, indicating that BRIT1 is involved in mediating recruitment of RAD51/BRCA2 to the damage site. Collectively, our BRIT1-null mouse model demonstrates that BRIT1 is essential for maintaining genomic stability in vivo to protect the hosts from both programmed and irradiation-induced DNA damages, and its depletion causes a failure in both mitotic and meiotic recombination DNA repair via impairing RAD51/BRCA2's function and as a result leads to infertility and genomic instability in mice.

The repair of DNA breaks in cells is critical for maintaining genomic integrity and suppressing tumor development. DNA breaks can arise from exogenous agents such as ionizing radiation (IR) or can form during the process of germ cell (sperm and egg) generation. BRIT1 protein (also known as MCPH1) is a recently identified DNA damage responding protein, and its mutations or reduced expression are found in primary microcephaly (small brain) patients, as well as in cancer patients. To investigate BRIT1's physiological functions and dissect the underlying molecular mechanism, we used a genetic approach (gene targeting technology) to delete BRIT1 gene in mice and generated a mouse model with BRIT1 deficiency (called BRIT1-knockout mice). Here, we showed that BRIT1 knockout mice are more sensitive to IR due to their inability to repair the IR-induced DNA breaks. These mice are also infertile, and their DNA repair during the process of germ cell generation was impaired substantially. Thus, in this study, we generated a novel mouse model (BRIT1 knockout mice) with striking phenotypes related to defective DNA repair and clearly demonstrated the essential role of BRIT1 in DNA repair at organism level.

Identification, isolation, and RT-PCR analysis of single stage-specific spermatogenetic cells obtained from portions of seminiferous tubules classified by transillumination microscopy

The protocol here described allows the analysis of gene expression in single specific mouse spermatogenetic cells. Germ cells were singularly isolated by microdissection of portions of seminiferous tubules classified, based on their transillumination pattern, into four distinct zones along their length. Single portions of a seminiferous tubule, corresponding to specific zones, were mechanically disaggregated into single cells that were (1) identified as spermatogonia, spermatocytes, round or elongated spermatids, (2) isolated using a micromanipulator, and (3) singularly transferred into a test tube for retro-transcription PCR analysis. On each single isolated cell, we have determined the quantitative profile of expression of Gapdh, an endogenous housekeeping gene known to be expressed throughout spermatogenesis. The protocol described allows an accurate analysis of the temporal and quantitative profile of gene expression throughout the whole male gamete differentiation process which so far has mainly been performed on enriched population of cells.

Derivation of male germ cell-like lineage from human fetal bone marrow stem cells

Mesenchymal stem cells derived from bone marrow are a well characterized population of adult stem cells that can be maintained and propagated in culture for a long time with the capacity to form a variety of cell types. Reports have shown that murine and human embryonic stem cells can differentiate into primordial germ cells and then to early gametes. Evidence has indicated that some adult stem cells also have the potential to differentiate into germ cells. Currently, there are no reports on directed differentiation of human mesenchymal stem cells into germ cells. This study investigated the ability of retinoic acid and testicular extracts to induce human bone marrow stem cells (hBMSC) to differentiate into male germ cells. It was found that a small population of hBMSC seem to transdifferentiate into male germ cell-like cells. These cells expressed early germ cell markers OCT4, STELLA, NANOG and VASA, and male germ-ceil-specific markers such as DAZL, TH2, c-kit, beta(1)-integrin, ACR, PRMl, FSHR, STRA8 and SCP3, as analysed by reverse transcription-polymerase chain reaction and immunohistochemistry. These results demonstrated that hBMSC may differentiate into male germ cells and the same could be used as a potential source of cells for reproductive toxicological studies.

CLPH, a novel casein kinase 2-phosphorylated disordered protein, is specifically associated with postmeiotic germ cells in rat spermatogenesis

In a recent proteomic study of rat spermatogenesis, we identified CLPH (for Casein-Like PHosphoprotein), a new testis-specific protein expressed exclusively in postmeiotic germ cells. In situ hybridization showed that the CLPH transcript was mainly present in round spermatids, whereas the protein was specifically detected by immunohistochemistry in elongated spermatids and in residual bodies. Electron microscopy showed the protein to be mostly cytoplasmic, but also frequently associated with the mitochondrial inner membrane during the last steps of spermatid differentiation. The Clph gene was found to be present solely in mammalian genomes, in a chromosomal region syntenic to the mammalian cluster of secretory calcium-binding phosphoprotein (SCPP) genes. CLPH has several distinctive properties in common with SCPPs: calcium overlay experiments showed that CLPH was a calcium-binding protein, whereas trypsin digestion assay, circular dichroism and fluorescence experiments demonstrated its intrinsically disordered structure. We also showed that CLPH was phosphorylated in vitro and in vivo by casein kinase 2, an enzyme critical for spermatid elongation. Given the specific and strong production of CLPH during rat spermiogenesis, together with the particular biochemical properties of this protein, we suggest that CLPH is involved in the extremely complex structural rearrangements occurring in haploid germ cells during spermiogenesis.

Differentiations of transplanted mouse spermatogonial stem cells in the adult mouse renal parenchyma in vivo

AIM

Spermatogonial stem cells can initiate the process of cellular differentiation to generate mature spermatozoa, but whether it possess the characteristic of pluripotency and plasticity, similar to embryonic stem cells, has not been elucidated. This study was designed to evaluate the differentiation potential of spermatogonial stem cells into renal cells in vivo.

METHODS

Neonatal mouse spermatogonial stem cells were transplanted into mature male mice lacking endogenous spermatogenesis. The restoration of fertility in recipient males was observed. Spermatogonial stem cells were then injected into renal parenchyma of mature female mice to make a new extracellular environment for differentiation. Fluorescence in situ hybridization technology (FISH) was used to detect the expression of chromosome Y in recipient renal tissues. To determine the type of cells differentiated from spermatogonial stem cells, the expression of ricinus communis agglutinin, vimentin, CD45, and F(4/80) proteins were examined in the renal tissues by immunohistochemistry.

RESULTS

The proliferation of seminiferous epithelial cells was distinctly observed in seminiferous tubules of transplanted testes, whereas no regeneration of spermatogenesis was observed in non-transplanted control testes. In transplanted female renal tissues, FISH showed a much stronger immuno-fluorescence signal of chromosome Y in the nucleolus of epithelial cells of the renal tubule and podocytes of the glomerulus.

CONCLUSION

The spermatogonial stem cells were successfully purified from mouse testicles. This finding demonstrated that spermatogonial stem cells could not only restore damaged spermatogenesis, but were also capable of differentiating into mature renal parenchyma cells in vivo.

Culture of rodent spermatogonial stem cells, male germline stem cells of the postnatal animal

Spermatogonial stem cells (SSCs), postnatal male germline stem cells, are the foundation of spermatogenesis, during which an enormous number of spermatozoa is produced daily by the testis throughout life of the male. SSCs are unique among stem cells in the adult body because they are the only cells that undergo self-renewal and transmit genes to subsequent generations. In addition, SSCs provide an excellent and powerful model to study stem cell biology because of the availability of a functional assay that unequivocally identifies the stem cell. Development of an in vitro culture system that allows an unlimited supply of SSCs is a crucial technique to manipulate genes of the SSC to generate valuable transgenic animals, to study the self-renewal mechanism, and to develop new therapeutic strategies for infertility. In this chapter, we describe a detailed protocol for the culture of mouse and rat SSCs. A key factor for successful development of the SSC culture system was identification of in vitro growth factor requirements for the stem cell using a defined serum-free medium. Because transplantation assays using immunodeficient mice demonstrated that extrinsic factors for self-renewal of SSCs appear to be conserved among many mammalian species, culture techniques for SSCs of other species, including farm animals and humans, are likely to be developed in the coming 5-10 years.