Survival and proliferation of rat gonocytes in vitro

10−7 M genistein partially alleviates 10−7 M MEHP unfavorable effects in a new modified fetal rat testis culture system

Background: Recent studies revealed that some common endocrine-disrupting chemicals (EDCs) including phthalates and phytoestrogens may exhibit low-dose effects properties. However, how low dose of these EDCs and their mixture would affect fetal rat testis development still needs further investigation. Moreover, testis organ culture system also needs further modification to provide an effective tool for ex vivo EDCs study.

Methods: We firstly modified the agarose organ culture system, in which fetal rat testes were cultured for 4 days (d1 to d4) on agarose gels held by Millicell inserts. Then we used the modified agarose culture system to study the combined effects of multiple EDCs exposure. 15.5 dpc fetal rat testes were isolated and treated with vehicle, MEHP (0.1 μmol/L), GEN (0.1 μmol/L) or MEHP (0.1 μmol/L) + GEN (0.1 μmol/L). Parameters concerning testicular cell development and function were evaluated, trying to gain insight into the early molecular events after multiple EDCs exposure.

Results: The development of somatic, germ cells and seminiferous tubule in 15.5 dpc fetal rat testis was better sustained in the modified agarose culture system. Based on the modified system, we found that MEHP at 0.1 μmol/L induced alterations in gonocyte markers, antioxidative enzyme activity as well as transient reduction of testosterone production, accompanied by mitochondria swelling in gonocytes and Sertoli cells. No obvious morphological and histological alterations were observed in all treated groups. However, coadministration of genistein at 0.1 μmol/L partially alleviated MEHP-induced fetal testis damage ex vivo through enhancement of antioxidative action. MEHP at low dose still showed weak endocrine disrupting properties but did not exhibit typical low-dose effects.

Conclusion: Our findings indicated that the modified agarose culture system could better mimic testicular microenvironment without obvious hypoxic cell damage. Furthermore, low dose of MEHP induced mild disruption to fetal testis development, cotreatment of genistein at low dose attenuated MEHP induced fetal testis injuries in part by balancing redox state, indicating that low dose of genistein may partially protect fetal testis from phthalates induced injury.

Low Dose of Genistein Alleviates Mono-(2-Ethylhexyl) Phthalate-Induced Fetal Testis Disorder Based on Organ Culture Model

Mono-(2-ethylhexyl) phthalate (MEHP) and genistein have been classified as endocrine-disrupting chemicals (EDCs) which interfere with the differentiation and development of the male reproductive system. However, how these two EDCs would affect fetal rat testis development at a low dose was rarely studied. In this study, we established the organ culture system and applied it to evaluate testicular effects following multiple EDC exposure at a low dose. 15.5 days postcoitum fetal rat testes were dissected, cultured, and exposed to vehicle (control), GEN (1 μmol/L, G), MEHP (1 μmol/L, M), or GEN (1 μmol/L)+MEHP (1 μmol/L, G+M). Testicular cell markers, testosterone concentration, redox state, testicular histology, and testicular ultrastructure were evaluated. Our results showed that a low dose of MEHP suppressed the development of Sertoli cells, Leydig cells, and gonocytes by triggering oxidative injuries, which was consistent with the ultrastructural findings. However, coadministration of genistein at a low dose could partially attenuate MEHP-induced fetal testis damage through antioxidative action. Cotreatment of genistein at a low dose may have a promising future on its protecting role for attenuating other EDC-induced reproductive disorders during early life. Based on the results, it can be speculated that dietary intake of isoflavones may make the fetal testis less susceptible to phthalate-induced injury.

Live-cell imaging and ultrastructural analysis reveal remarkable features of cultured porcine gonocytes

Gonocytes in the neonatal testis have male germline stem cell potential. The objective of the present study was to examine the behavior and ultrastructure of gonocytes in culture. Neonatal porcine testis cells were cultured for 4 weeks and underwent live-cell imaging to explore real-time interactions among cultured cells. This included imaging every 1 h from day 0 to day 3, every 2 h from day 4 to day 7, and every 1 h for 24 h at days 14, 21, and 28. Samples also underwent scanning electron microscopy, transmission electron microscopy, morphometric evaluations, immunofluorescence, and RT-PCR. Live-cell imaging revealed an active amoeboid-like movement of gonocytes, assisted by the formation of extensive cytoplasmic projections, which, using scanning electron microscopy, were categorized into spike-like filopodia, leaf-like lamellipodia, membrane ruffles, and cytoplasmic blebs. In the first week of culture, gonocytes formed loose attachments on top of a somatic cell monolayer and, in week 2, formed grape-like clusters, which, over time, grew in cell number. Starting at week 3 of culture, some of the gonocyte clusters transformed into large multinucleated embryoid body-like colonies (EBLCs) that expressed both gonocyte- and pluripotent-specific markers. The number and diameter of individual gonocytes, the number and density of organelles within gonocytes, as well as the number and diameter of the EBLCs increased over time (P < 0.05). In conclusion, cultured porcine gonocytes displayed extensive migratory behavior facilitated by their various cytoplasmic projections, propagated, and transformed into EBLCs that increased in size and complexity over time.

Optimization of culture conditions for short-term maintenance, proliferation, and colony formation of porcine gonocytes

Background

Gonocytes give rise to spermatogonial stem cells, and thereby play an essential role in establishing spermatogenesis. Optimized culture conditions for gonocytes provide an opportunity for their study and in vitro manipulation for potential application in reproductive technologies. Using six experiments in a step-wise design, we examined the effects of several culture conditions on the maintenance, proliferation, and colony formation of porcine gonocytes. Testis cells from neonatal piglets were cultured for 7 d in DMEM supplemented with 10% fetal bovine serum. The examined culture conditions included using different cell seeding densities, gonocyte proportions, incubation temperatures, sampling strategies, and medium changing regimens.

Results

Confluency of cells was optimal (>90% by ~6 d) when 3.0 × 10⁴ testis cells/cm² containing ~40% gonocytes were used. Incubating the cells at 35 °C or 37 °C resulted in similar cell number and viability at confluency, but incubation at 35 °C resulted in a delayed confluency. In the first 2 d of culture, gonocytes remained mostly floating in the medium and gradually settled over the next 5 d. Consequently, not changing the medium for 7 d (as opposed to changing it every 2 d) led to a significant increase in the number of gonocyte colonies by reducing the loss of “floating gonocytes”.

Conclusion

We found that gonocytes require the presence of a critical minimum number of somatic cells for settlement, and can proliferate and form growing colonies even in a basic medium. Large numbers of viable gonocytes remain floating in the medium for several days. The optimized culture conditions in the present study included seeding with 3.0 × 10⁴ testis cells/cm² containing ~40% gonocytes, incubating at 37 °C, and without changing the medium in the first week, which can result in improved colony formation of porcine gonocytes.

Adverse effects of endocrine disruptors on the foetal testis development: focus on the phthalates

There are great concerns about the increasing incidence of abnormalities in male reproductive function. Human sperm counts have markedly dropped and the rate of testicular cancer has clearly augmented over the past four decades. Moreover, the prevalence rates of cryptorchidism and hypospadias are also probably increasing. It has been hypothesized that all these adverse trends in male reproduction result from abnormalities in the development of the testis during foetal and neonatal life. Furthermore, many recent epidemiological, clinical and experimental data suggest that these male reproductive disorders could be due to the effects of xenobiotics termed endocrine disruptors, which are becoming more and more concentrated and prevalent in our environment. Among these endocrine disruptors, we chose to focus this review on the phthalates for different reasons: 1) they are widespread in the environment; 2) their concentrations in many human biological fluids have been measured; 3) the experimental data using rodent models suggesting a reprotoxicity are numerous and are the most convincing; 4) their deleterious effects on the in vivo and in vitro development and function of the rat foetal testis have been largely studied; 5) some epidemiological data in humans suggest a reprotoxic effect at environmental concentrations at least during neonatal life. However, the direct effects of phthalates on human foetal testis have never been explored. Thus, as we did for the rat in the 1990s, we recently developed and validated an organ culture system which allows maintenance of the development of the different cell types of human foetal testis. In this system, addition of 10-4 M MEHP (mono-2-ethylhexyl phthalate), the most produced phthalate, had no effect on basal or LH-stimulated production of testosterone, but it reduced the number of germ cells by increasing their apoptosis, without modification of their proliferation. This is the first experimental demonstration that phthalates alter the development of the foetal testis in humans. Using our organotypic culture system, we and others are currently investigating the effect of MEHP in the mouse and the rat, and it will be interesting to compare the results between these species to analyse the relevance of toxicological tests based on rodent models.

Spermatogonial stem cell functions in physiological and pathological conditions

Sperm have a vital role in the continuity of a species by contributing genetic information to the next generation. Production of these specialized gametes in numbers sufficient to confer normal fertility occurs via cycling of the spermatogenic lineage, a process referred to as spermatogenesis. Continuity relies on the activities of a self-renewing reservoir of spermatogonial stem cells (SSCs) from which progenitors will arise that transiently amplify in number before committing to a pathway of terminal differentiation. A primary population of SSCs is established during neonatal development from a pool of quiescent gonocyte precursors that forms in embryogenesis. Disruption of this process has dire consequences on maintenance of a cycling spermatogenic lineage in adulthood. At present, the molecular mechanisms underlying initial formation of the SSC pool are largely undefined. However, several transcription factors and posttranscriptional regulators have been identified as important regulators of SSC self-renewal from studies with mutant mouse models and experimental manipulation within primary cultures of mouse SSCs. Importantly, loss of function of these self-renewal factors may be underlying causes of infertility. Furthermore, disruption in the establishment of the SSC state within gonocytes or misregulation of self-renewal may manifest as testicular germ cell tumors in postnatal life.

Toward a more precise and informative nomenclature describing fetal and neonatal male germ cells in rodents

The germ cell lineages are among the best characterized of all cell lineages in mammals. This characterization includes precise nomenclature that distinguishes among numerous, often subtle, changes in function or morphology as development and differentiation of germ cells proceed to form the gametes. In male rodents, there are at least 41 distinct cell types that occur during progression through the male germ cell lineage that gives rise to spermatozoa. However, there is one period during male germ cell development-that which occurs immediately following the primordial germ cell stage and prior to the spermatogonial stage-for which the system of precise and informative cell type terminology is not adequate. Often, male germ cells during this period are referred to simply as "gonocytes." However, this term is inadequate for multiple reasons, and it is suggested here that nomenclature originally proposed in the 1970s by Hilscher et al., which employs the terms M-, T1-, and T2-prospermatogonia, is preferable. In this Minireview, the history, proper utilization, and advantages of this terminology relative to that of the term gonocytes are described.

Pluripotent cells in farm animals: state of the art and future perspectives

Pluripotent cells, such as embryonic stem (ES) cells, embryonic germ cells and embryonic carcinoma cells are a unique type of cell because they remain undifferentiated indefinitely in in vitro culture, show self-renewal and possess the ability to differentiate into derivatives of the three germ layers. These capabilities make them a unique in vitro model for studying development, differentiation and for targeted modification of the genome. True pluripotent ESCs have only been described in the laboratory mouse and rat. However, rodent physiology and anatomy differ substantially from that of humans, detracting from the value of the rodent model for studies of human diseases and the development of cellular therapies in regenerative medicine. Recently, progress in the isolation of pluripotent cells in farm animals has been made and new technologies for reprogramming of somatic cells into a pluripotent state have been developed. Prior to clinical application of therapeutic cells differentiated from pluripotent stem cells in human patients, their survival and the absence of tumourigenic potential must be assessed in suitable preclinical large animal models. The establishment of pluripotent cell lines in farm animals may provide new opportunities for the production of transgenic animals, would facilitate development and validation of large animal models for evaluating ESC-based therapies and would thus contribute to the improvement of human and animal health. This review summarises the recent progress in the derivation of pluripotent and reprogrammed cells from farm animals. We refer to our recent review on this area, to which this article is complementary.

Coordination of spermatogenic processes in the testis: lessons from cystic spermatogenesis

A common observation in the vertebrate testis is that new germ cell clones enter spermatogenesis proper before previously formed clones have completed their development. The extent to which the developmental advance of any given germ cell clone in any phase of spermatogenesis is dependent on that of neighboring clones and/or on the coordinating influence of associated Sertoli cells in the immediate vicinity or of others further away remains unclear. This review presents an overall synthesis of findings in an ancient vertebrate, the spiny dogfish shark and shows that, even at this phyletic level, the developmental advance of a given germ cell clone is the outcome of various processes emanating from its spatiotemporal relationship with (1) its own complement of Sertoli cells in the anatomically distinct spermatocyst and (2) Sertoli cells associated with other germ cell clones that lie upstream or downstream in the spermatogenic progression and that secrete, among others, androgen and estrogen destined for target sites upstream. Analysis of the protracted spermatogenic cycle shows the coordination in space and time of spermatogenic and steroidogenic events. Furthermore, the natural withdrawal of pituitary gonadotropin support in the dogfish causes a distinct and highly ordered gradient of apoptosis among the spermatogonial generations; this in turn is a major contributing factor to the cyclic nature of sperm production observed in this lower vertebrate. Because of the simplicity of their testicular organization, their cystic spermatogenesis and their phylogenetic position, cartilaginous fishes constitute a valid vertebrate reference system for comparative analysis with higher vertebrates.

Altérations environnementales du développement du testicule foetal: zoom sur les phtalates

L’augmentation de plusieurs anomalies de la fonction de reproduction masculine suscite de grandes inquiétudes. Au cours des quatre dernières décennies, le nombre de spermatozoïdes chez l’homme a nettement diminué, et l’incidence du cancer testiculaire a doublé. De plus, les cas de cryptorchidie et d’hypospadias sont également en augmentation. L’hypothèse la plus couramment admise est que tous ces effets néfastes sur la fonction reproductive masculine résulteraient d’anomalies survenant lors du développement du testicule pendant la vie foetale et néonatale. En outre, de nombreuses données épidémiologiques, cliniques et expérimentales suggèrent que ces troubles pourraient être dus aux effets de xénobiotiques appelés perturbateurs endocriniens qui sont de plus en plus concentrés et présents dans notre environnement. Parmi les perturbateurs endocriniens, nous avons choisi de focaliser cette revue sur les phtalates pour diverses raisons: 1) ils sont très répandus dans l’environnement; 2) leurs concentrations dans de nombreux fluides biologiques humains ont été mesurées y compris pendant la grossesse; 3) les données expérimentales utilisant le modèle rat et suggérant une reprotoxicité sont nombreuses et pertinentes; 4) les effets délétères des phtalates sur le développement et sur les fonctions du testicule foetal de rat ont largement été étudiés; 5) quelques données épidémiologiques humaines suggèrent un effet reprotoxique des phtalates aux concentrations retrouvées dans l’environnement, au moins durant la vie néonatale. Cependant, les effets directs des phtalates sur le testicule foetal humain n’avaient jamais été étudiés. Comme nous l’avions fait chez le rat dans les années 1990, nous avons récemment développé et validé un système de culture organotypique de testicule foetal humain qui permet de maintenir in vitro le développement des différents types cellulaires. Dans ce système, l’ajout de 10−4 M de MEHP (mono-2-éthylhexyl phtalate), le phtalate le plus répandu, n’a aucun effet sur la production de testostérone basale ou stimulée par l’hormone lutéinisante (LH), mais il réduit le nombre de cellules germinales en augmentant leur apoptose et sans modifier leur prolifération. Nos données constituent la première donnée expérimentale montrant que les phtalates altèrent le développement du testicule foetal humain. En outre, en utilisant le même système de culture organotypique, il est intéressant de comparer la réponse au MEHP chez l’Homme et chez les rongeurs pour analyser la pertinence des tests toxicologiques basés sur le modèle rongeur.

In vitro culture of testicular germ cells: regulatory factors and limitations

Spermatogenesis is regulated mainly by endocrine factors and also by testicular paracrine/autocrine growth factors. These factors are produced by Sertoli cells, germ cells, peritubular cells and interstitial cells, mainly Leydig cells and macrophages. The interactions and the ratio between Sertoli and germ cells in the seminiferous tubules ensure successful spermatogenesis. In order to culture spermatogonial stem cells (SSCs) in vitro, researchers tried to overcome some of the obstacles -- such as the low number of stem cells in the testis, absence of specific markers to identify SSCs -- in addition to difficulties in keeping the SSCs alive in culture. Recently, some growth factors important for the proliferation and differentiation of SSCs were identified, such as glial cell line derived neurotrophic factor (GDNF), stem cell factor (SCF) and leukemia inhibitory factor (LIF); also, markers for SSCs at different stages were reported. Therefore, some groups succeeded in culturing SSCs (under limitations), or more differentiated cells and even were able to produce in vitro germ cells from embryonic stem cells. Thus, success in culturing SSCs is dependent on understanding the molecular mechanisms behind self-renewal and differentiation. Culture of SSCs should be a good tool for discovering new therapeutic avenue for some infertile men or for patients undergoing chemotherapy/radiotherapy (pre-puberty or post-puberty).

A new method for toxicity assays on human and mouse fetal testis

Exposure to environmental pollutants (EP) is associated with a wide range of toxic effects, in particular in testis development. Uranium is a potential pollutant of nuclear industry and over the last few years, its environmental concentrations have increased. In animals, the current procedures for evaluating the potential developmental toxicity of uranium are based on in vivo studies. These methods do not allow to know the direct effects on testicular cells and are obviously excluded for human experiments. Consequently, we have developed an in vitro culture system of the whole testis. In the present study we characterized and validated this organ culture system in both mouse fetal testes and human fetal testes recovered during the first trimester (6-12 weeks) of gestation. We compared the histological aspect, the number of germ cells and the testosterone production, before and after culture. Testicular architecture and intercellular communications were preserved, and organ culture appears as a powerful method for studying the early development of testicular gametogenesis and steroidogenesis in both species. Thus by using this method we will be able to investigate the effects of uranium on mouse and human developing testis. The mouse model will allow us to determine the dose range of interest without restriction of material.

Organotypic culture, a powerful model for studying rat and mouse fetal testis development

The key role of the fetal testis in the masculinization of genital organs has been known for a long time. More recently, the observed increases in male reproductive disorders has been postulated to be the result of changes in fetal and neonatal testis development in response to increasing environmental pollution. However, few tools are available for studying fetal testis development and the effects of physiological or toxic substances. We have developed an organ culture system in which rat fetal testis is grown on a filter floating on a synthetic medium containing no serum, hormones or biological factors. In this study, we have compared the long-term morpho-functional development of the various testicular cell types in this system with that observed in vivo and have extended this system to the mouse. Rat Leydig, Sertoli and germ cells and macrophages develop normally over a period of 1-2 weeks in this system. Fewer cells are produced than in vivo but the level of differentiated function is similar. Germ cells, which are difficult to culture in vitro, resume mitosis after a quiescent period, at the same time as in vivo. Similar results have been obtained with mouse fetuses, except that Leydig cells dedifferentiate in vitro if the testis is explanted after 13.5 days post conception. Testicular architecture and intercellular communication are sufficiently preserved for the development of the main fetal and neonatal testicular cell types in vitro with no added factors. Our floating-filter organotypic culture system in synthetic medium therefore allows the morpho-functional development of somatic and germ cells in fetal testis explants taken at all developmental stages in rat and at early stages in mouse. This method is potentially useful for studies of the effects of various factors, and of xenobiotics, in particular.

Efforts to create an artificial testis: culture systems of male germ cells under biochemical conditions resembling the seminiferous tubular biochemical environment

Induction of meiotic and post-meiotic alterations of male germ cells in vitro has been the target of several research efforts since 1960. However, to date, the establishment of an ideal culture system in which spermatogonial stem cells can be maintained and directed to proliferate and undergo meiosis and complete spermiogenesis does not exist. This is attributed to the difficulties concerning the isolation and purification of defined subpopulations of germ cells and the establishment of male germ cell lines. In addition, there is no adequate knowledge regarding the optimal biochemical conditions that promote the survival and differentiation of germ cells in long-term cultures. This review focuses on the methodologies that have been proved sufficient to achieve differentiation of cultured male germ cells. Furthermore, the factors regulating spermatogenesis and the technical prerequisites to achieve differentiation of cultured male germ cells are described. Finally, the role of in vitro cultures of immature diploid germ cells in the therapeutic management of men negative for haploid cells in their testes and the subsequent potential genetic and epigenetic risks are discussed.

Pituitary hormones inhibit the function and differentiation of fetal Sertoli cells

Although the role of pituitary hormones in fetal Sertoli cell proliferation is well understood, their involvement in fetal Sertoli cell differentiation is poorly documented. In this study, we evaluated rat fetal Sertoli cell function by measuring basal transferrin secretion ex vivo and transferrin and anti-Müllerian hormone (AMH) mRNA levels in vivo. The differentiation state of the Sertoli cells was estimated from the amount of transferrin secreted ex vivo after acute stimulation with FSH. Surprisingly, we found that the amount of transferrin secreted by each Sertoli cell in basal condition and after acute FSH stimulation decreased between 18.5 and 21.5 day post coitum (dpc), which corresponds to the onset of pituitary hormone secretion. All of the Sertoli cell parameters measured (basal and FSH-stimulated transferrin secretion ex vivo, transferrin and AMH mRNA levels in vivo) were higher in 21.5-dpc fetuses that had been decapitated on 16.5 dpc than in control littermates. Furthermore, immunostaining for AMH was strongly increased after decapitation. Taken together, these results suggest that pituitary hormones in the fetus and in the immature or adult rat differently regulate Sertoli cells, which suggests that fetal Sertoli cells have their own particular physiology.

Regulation of the proliferation of cocultured gonocytes and Sertoli cells by retinoids, triiodothyronine, and intracellular signaling factors: differences between fetal and neonatal cells

The regulation of early fetal germ cell growth has not been studied in cell culture, probably due to the poor survival of these cells. However, cell culture is the only system in which the control of cell growth can be studied independently of the influence of secreted testicular factors, which are diluted in the medium. We successfully cultured dispersed testicular cells from 16.5-day-old rat fetuses in defined medium and compared the growth of these cells with that of cells from 3-day-old neonates. In this system, fetal gonocytes displayed low levels of mitotic activity and their numbers remained stable. In contrast, neonatal gonocytes displayed high levels of mitotic activity and increased in number, these characteristics resembling those observed in vivo. We found that retinoic acid had deleterious effects on the number of gonocytes but did not affect Sertoli cell proliferation in fetal and neonatal cell cultures. Moreover, in fetal cell cultures, the decrease in the number of gonocytes resulted from a decrease in mitotic activity, probably due to a direct effect of retinoids on fetal gonocytes. Among the selective agonists for the retinoic acid receptor (RARalpha agonist, RARbeta agonist, and RARgamma agonist) and the retinoic X receptor (pan-RXR agonist) tested, only the RARalpha agonist reproduced the effects of retinoic acid at concentrations lower than its Kd value in both fetal and neonatal cell cultures. As both RARalpha and RXRalpha are present in fetal and neonatal gonocytes, we suggest that retinoic acid exerts its effects on gonocytes via a RARalpha-RXRalpha heterodimer, with RARalpha functioning as an active partner and RXRalpha as a passive partner. In this culture system, we show for the first time that triiodothyronine (T3) inhibits testicular fetal Sertoli cell and germ cell growth. We also tested intracellular signaling factors and found that a cAMP analog increased Sertoli cell proliferation and germ cell survival in both fetal and neonatal cells whereas phorbol esters (PMA) strongly inhibited the proliferation of fetal but not of neonatal gonocytes. None of the tested factors (T3, dbcAMP, and PMA) seemed to interact with the all-trans retinoic acid pathway. Thus, fetal gonocytes and neonatal gonocytes differ in intrinsic properties, and their growth is not regulated in the same manner. Despite their low level of mitotic activity, fetal gonocytes were more sensitive to various factors than neonatal gonocytes.

Male germ-line stem cell potential is predicted by morphology of cells in neonatal rat testes

Gonocytes are a transient population of male germ-line stem cells that are derived from primordial germ cells in the embryo and give rise to spermatogonial stem cells, which establish and maintain spermatogenesis in the postnatal testis. In contrast to spermatogonial stem cells, gonocytes can be identified easily in neonatal rat testis cell suspensions based on their large size and distinct morphology. Furthermore, histological analysis of testes from neonatal transgenic rats demonstrated that gonocytes are the only cells that express a lacZ reporter transgene. Two gonocyte subpopulations, designated pseudopod and round, were identified and isolated from neonatal (0-4 days postpartum) rat testis cell suspensions. Male germ-line stem cells, identified by their ability to produce and maintain colonies of spermatogenesis upon transplantation into infertile recipient testes, were present almost exclusively in the pseudopod gonocyte subpopulation. In contrast, annexin V staining indicated that the majority of round gonocytes undergo apoptosis. These results indicate that a nearly pure population of male germ-line stem cells can be prospectively identified in neonatal rat testis cell suspensions by morphological criteria. Together, the pseudopod and round gonocyte populations will provide powerful tools for the study of cellular mechanisms that control cell fates and the establishment of spermatogenesis in the postnatal testis.

Role of Sertoli cells in injury-associated testicular germ cell apoptosis

This review examines experimental models of Sertoli cell injury resulting in germ cell apoptosis. Since germ cells exist in an environment created by Sertoli cells, paracrine signaling between these intimately associated cells must regulate the process of germ cell death. Germ cell apoptosis may be signaled by a decrease in Sertoli cell pro-survival factors, an increase in Sertoli cell pro-apoptotic factors, or both. The different models of Sertoli cell injury indicate that spermatogenesis is susceptible to disruption, and that targeting critical Sertoli cell functions can lead to rapid and massive germ cell death.

Reproliferation and relocation of mouse male germ cells (gonocytes) during prespermatogenesis

In the prespermatogenesis period, male germ cells (gonocytes) begin to reproliferate and move to the basement membrane of the seminiferous tubule. Although these two events-reproliferation and relocation-are important for establishment of spermatogenesis, they have not been greatly analyzed both in a mechanical and in an endocrine or paracrine aspect. In this study, the relationship between reproliferation and relocation of gonocytes was examined, using the thymidine analog bromodeoxyuridine (BrdU) labeling method and transmission electron microscopy (TEM). BrdU was injected into the fetuses [day 13.5 post coitus (dpc) to 18.5 dpc] and pups [day 0. 5 post partum (dpp) to 6.5 dpp] of C57BL/6J mice. Two hours later, BrdU positive gonocytes were examined immunohistochemically and these data were analyzed. TEM and LM observation was carried out as well. Gonocytes began to relocate on the basement membrane from 18.5 dpc (1.4%) while BrdU-labeled gonocytes were first detected on 1.5 dpp (13.6%). Relocated BrdU-negative gonocytes were recognized from 18.5 dpc (1.4%), and relocated BrdU-labeled gonocytes were recognized from 1.5 dpp (8.4%). On the other hand, non-relocated BrdU-labeled gonocytes were detected from 1.5 dpp (5.2%). Gonocyte relocation began 2 days earlier than reproliferation during the late fetal period. After birth, the two events occurred at random. These results indicate that the reproliferation of the gonocyte does not correlate with relocation. The two events may be regulated by different mechanisms.

Apoptosis and mitosis in gonocytes of the rat testis during foetal and neonatal development

This study was undertaken to determine the extent of apoptosis and mitosis in the various testicular cell types throughout rat development from foetal day 14.5 to postnatal days 9-10. Apoptotic activity was studied by detecting DNA fragmentation (TUNEL method) in situ. A TUNEL-positive reaction was detected in gonocytes, while none of the other testicular cells were labelled. The morphology of the TUNEL-positive gonocytes was characteristic of apoptotic cells and was different from that observed in experimentally induced necrosis. The percentage of stained gonocytes peaked on day 15.5-16.5 post-conception (dpc), decreased thereafter and no TUNEL-positive gonocytes were found from foetal day 18.5 onwards. On postnatal day 2, apoptosis resumed and increased to reach a maximum on day 7. Mitosis in the gonocytes, as evaluated by the immunodetection of 5-bromo-2'-deoxyuridine (BrdU) incorporation, was present during the same developmental periods but the ratio of BrdU-positive/TUNEL-positive gonocytes was much greater in the foetal period than in the neonatal period. In an organotypic culture system, the changes in the apoptotic and mitotic activities of the gonocytes in testicular explants from foetuses on days 18.5 and 20.5 or from neonates on day 3, cultured for two days were similar to those observed in vivo. Addition of LH or FSH did not influence either apoptosis or mitosis in the germ cells. These results suggest that both apoptosis and mitosis of gonocytes are independent of gonadotrophins and are mainly controlled by intratesticular factors.

The tao of stem cells in the germline

Germline stem cells (GSCs) are the self-renewing population of germ cells that serve as the source for gametogenesis. GSCs exist in diverse forms, from those that undergo strict self-renewing asymmetric divisions in Drosophila to those that maintain their population by balancing between mitosis and differentiation in Caenorhabditis elegans. Most vertebrate spermatogonial GSCs appear to adopt an intermediate strategy. In most animals, GSCs are established during preadult gonadogenesis following the proliferation and migration of embryonic primordial germ cells. GSCs produce numerous gametes throughout the sexually active period of adult life. The establishment and self-renewing division of GSCs are controlled by extracellular signals such as hormones from the hypothalamic-pituitary axis and local interactions between GSCs and their neighboring cells. These extracellular signals may then influence differential gene expression, cell cycle machinery, and cytoskeletal organization of GSCs for their formation and/or divisional asymmetry. In addition, the GSC mechanism is related to that for germline and sex determination. Current knowledge has provided a solid framework for further study of GSCs and stem cells in general.

Immunomagnetic isolation of fetal rat gonocytes

PROBLEM

An efficient method to obtain highly enriched populations of viable gonocytes from rat embryos at Day 18 and Day 20 postcoitum (pc) is described.

METHOD

Single-cell suspensions with high cell yield were obtained by a collagenase/ trypsin digestion of the decapsulated testis. The gonocytes were purified by a direct immunoseparation technique, using magnetizable beads coated with rat anti-mouse immunoglobulin M (IgM) and a monoclonal antibody 4B6.3E10, which specifically reacted with a differentiation antigen on the fetal germ cells.

RESULTS

Populations of 8.3 +/- 2.7 (x10(3); 18 days pc) or 1.2 +/- 0.25 (x10(4); 20 days pc) viable gonocytes per testis with purities of 91 +/- 6.5% and 92 +/- 4.3%, respectively, as determined by Nomarski microscopy were obtained.

CONCLUSION

The cells were successfully used for culture studies and as starting material for the investigation of gene expression.

Characterization of a novel spermatogenic cell antigen specific for early stages of germ cells in mouse testis

To study the mechanism of spermatogenesis during the premeiotic phase, a hybridoma producing monoclonal antibody (mAb) specific for early stages of spermatogenic cells was obtained. In immunohistochemical staining of adult testis, this mAb, designated as EE2, was able to react with type A to B spermatogonia and early meiotic cells, but not with Sertoli cells, Leydig cells, and other somatic tissues. Precursor cells of type A spermatogonia (gonocytes) were also positive for EE2 in perinatal mouse testis. The antigenic molecule recognized by mAb EE2 was a novel glycoprotein with molecular weight of 114 kDa, which had affinity with Con A and WGA lectins, and was susceptible to N-glycanase, suggesting the presence of asparagine-linked sugar chains. Furthermore, EE2 antigen was found to localize on the germ cell surface. The specific expression of this antigenic molecule suggests that it may play an important role in early spermatogenesis, of which only a little information is available at present.