Activin receptor mRNA expression in rat testicular cell types

Regulation of activin and inhibin in the adult testis and the evidence for functional roles in spermatogenesis and immunoregulation

Activin A provides a unique link between reproduction and immunity, which is especially significant in the adult testis. This cytokine, together with inhibin B and follistatin acting as regulators of activin A activity, is fundamentally involved in the regulation of spermatogenesis and testicular steroidogenesis. However, activin A also has a much broader role in control of inflammation, fibrosis and immunity. In the Sertoli cell, activin A is regulated by signalling pathways that normally regulate stress and inflammation, signalling pathways that intersect with the classical hormonal regulatory pathways mediated by FSH. Modulation of activin A production and activity during spermatogenesis is implicated in the fine control of the cycle of the seminiferous epithelium. The immunoregulatory properties of activin A also suggest that it may be involved in maintaining testicular immune privilege. Consequently, elevated activin A production within the testis during inflammation and infection may contribute to spermatogenic failure, fibrosis and testicular damage.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

Developmentally regulated SMAD2 and SMAD3 utilization directs activin signaling outcomes

Activin is required for testis development. Activin signals via phosphorylation and nuclear accumulation of SMAD2 and SMAD3. We present novel findings of developmentally regulated activin signaling leading to specific transcriptional outcomes in testicular Sertoli cells. In immature, proliferating, Sertoli cells, activin A induces nuclear accumulation of SMAD3, but not SMAD2, although both proteins become phosphorylated. In postmitotic differentiating cells, both SMAD proteins accumulate in the nucleus. Furthermore, immature Sertoli cells are sensitive to activin dosage; higher concentrations induce maximal SMAD3 nuclear accumulation and a small increase in nuclear SMAD2. Microarray analysis identified distinct transcriptional outcomes correlating with differential SMAD utilization and new activin target genes, including Gja1 and Serpina5, which are essential for Sertoli cell development and male fertility. In transgenic mice with altered activin bioactivity that display fertility phenotypes, Gja1 and Serpina5 are significantly altered. Thus, differential SMAD utilization in response to activin features during Sertoli cell maturation.

Inhibin, activin, follistatin and FSH serum levels and testicular production are highly modulated during the first spermatogenic wave in mice

Testicular development is governed by the combined influence of hormones and proteins, including FSH, inhibins, activins and follistatin (FST). This study documents the expression of these proteins and their corresponding mRNAs, in testes and serum from mice aged 0 through 91 dayspost partum(dpp), using real-time PCR,in situhybridisation, immunohistochemistry, ELISA and RIA. Serum immunoactive total inhibin and FSH levels were negatively correlated during development, with FSH levels rising and inhibin levels falling. Activin A production changed significantly during development, with subunit mRNA and protein levels declining rapidly after 4 dpp, while simultaneously levels of the activin antagonists, FST and inhibin/activin βC, increased. Inhibin/activin βAand βBsubunit mRNAs were detected in Sertoli, germ and Leydig cells throughout testis development, with the βAsubunit also detected in peritubular myoid cells. The α, βA, βBand βCsubunit proteins were detected in Sertoli and Leydig cells of developing and adult mouse testes. While βAand βBsubunit proteins were observed in spermatogonia and spermatocytes in immature testes, βCwas localised to leptotene and zygotene spermatocytes in immature and adult testes. Nuclear βAsubunit protein was observed in primary spermatocytes and nuclear βCsubunit in gonocytes and round spermatids. The changing spatial and temporal distributions of inhibins and activins indicate that their modulated synthesis and action are important during onset of murine spermatogenesis. This study provides a foundation for evaluation of these proteins in mice with disturbed testicular development, enabling their role in normal and perturbed spermatogenesis to be more fully understood.

Hormonal regulation of spermatogenesis and spermiogenesis

Normal testicular function is dependent upon hormones acting through endocrine and paracrine pathways both in vivo and in vitro. Sertoli cells provide factors necessary for the successful progression of spermatogonia into spermatozoa. Sertoli cells have receptors for follicle stimulating hormone (FSH) and testosterone which are the main hormonal regulators of spermatogenesis. Hormones such as testosterone, FSH and luteinizing hormone (LH) are known to influence the germ cell fate. Their removal induces germ cell apoptosis. Proteins of the Bcl-2 family provide one signaling pathway which appears to be essential for male germ cell homeostasis. In addition to paracrine signals, germ cells also depend upon signals derived from Sertoli by direct membrane contact. Somatostatin is a regulatory peptide playing a role in the regulation of the proliferation of the male gametes. Activin A, follistatin and FSH play a role in germ cell maturation during the period when gonocytes resume mitosis to form the spermatogonial stem cells and differentiating germ cell populations. In vitro cultures systems have provided evidence that spermatogonia in advance stage of differentiation have specific regulatory mechanisms that control their fate. This review article provides an overview of the literature concerning the hormonal pathways regulating spermatogenesis.

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).

All in the family: TGF-beta family action in testis development

To achieve and maintain fertility, the adult mammalian testis produces many generations of sperm. While testicular integrity is established in the fetus and develops further in juvenile life, sperm production does not ensue until much later in life, following the onset of puberty. Signals from the transforming growth factor-beta superfamily of proteins are vital for governance of testis development and spermatogenesis, and this review discusses our current understanding of the mechanisms and processes in which they have been implicated with a focus on the fetal and juvenile testis.

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.

Tissue immunoexpression and messenger ribonucleic acid localization of inhibin/activin subunit in human epididymis

OBJECTIVE

To determine the expression of inhibin betaA and betaB subunits and follistatin and the ability of human epididymal epithelium to synthesize these molecules.

DESIGN

The main aim of this study was to investigate the expression of inhibin alpha, betaA, and betaB-subunits and follistatin in human epididymis with immunohistochemistry, in situ hybridization, and Western blotting in adult life.

SETTING

Academic university hospital.

PATIENT(S)

Epididymes were obtained from 10 men undergoing routine vasectomy or surgery for benign disease at the Royal Hallamshire Hospital, Sheffield, United Kingdom.

MAIN OUTCOME MEASURE(S)

Immunoexpression of activin betaA and betaB subunits and follistatin proteins and mRNA in human caput and cauda epididymis.

RESULT(S)

Positive immunoexpression for activin betaA and betaB subunits and follistatin were detected in different parts of the epididymis epithelium. Western blotting under a reducing condition detected a 28-kd band (possibly corresponding to the activin dimer). In situ hybridization indicated positive mRNA localization signal in both caput and cauda epididymal epithelium.

CONCLUSION(S)

Activins betaA and betaB subunits, but not inhibin alpha subunit, were detected in epididymal epithelium. These finding suggest that activins might have a role in the processes of sperm maturation and sperm fertilizing capability during transit and storage.

Changes in circulating and testicular levels of inhibin A and B and activin A during postnatal development in the rat

This study describes the testicular levels of inhibin/activin subunits by Northern analysis and in situ hybridization and serum and testicular levels of inhibins A and B and activin A by enzyme linked immunosorbent assays (ELISA) during postnatal development in the rat. We show that serum inhibin A levels are less than 4 pg/ml throughout postnatal life. Serum inhibin B levels peak at 572 +/- 119 pg/ml (mean +/- se) at d 40 post partum (pp) before falling to 182 +/- 35 pg/ml in mature males. Serum activin A decreases from 294 +/- 29 pg/ml at d 6 to 132 +/- 27 pg/ml at maturity. Within the testis, inhibin A levels fall from 0.330 +/- 0.108 ng/g at d 15 to less than 0.004 ng/g at maturity. Inhibin B levels peak at 43.9 +/- 4.2 ng/g at d 6 before falling to 1.6 +/- 0.13 ng/g at maturity. Testicular activin A levels fall from 18.6 +/- 2.2 ng/g at d 6 to 0.094 +/- 0.013 ng/g at maturity. Northern profiles of testicular inhibin/activin subunits correlate with immunoreactive levels demonstrated by ELISA. In situ hybridization suggests that beta(A) and beta(B) subunit expression is largely restricted to the seminiferous tubule, particularly Sertoli cells, spermatogonia, and primary spermatocytes. These data support the view that inhibin B is the major inhibin in the male rat and that levels relate to Sertoli cell number and activity. Furthermore, the demonstration of high local concentrations of activin A during the period of Sertoli cell proliferation and the onset of spermatogenesis support its proposed role because a modulator of testicular development and function.

Developmental changes in inhibin α and inhibin/activin βA and βB mRNA levels in the gonads during post-hatch prepubertal development of male and female chickens

Dimeric inhibins and activins are barely detectable in the plasma during prepubertal development of male and female chickens. This may be misconstrued to indicate that the proteins are not produced in the gonads and have no functional significance during this period. Very few studies have actually determined the mRNA expression profile of the inhibin and activin subunits in the gonads prior to puberty in order to establish their secretion at the local level and postulate potential roles for the inhibin and activins at this developmental stage. In this study, the expression of the mRNA for the alpha-, betaA-, and betaB-subunits was determined in the ovary and testis of chickens during prepubertal development. Gene expression was determined at 3, 5, 6, 8, 10, 12, 16, and 18 weeks of age by RT-PCR. Messenger RNA level was quantified by competitive RT-PCR at 3, 6, 12, and 18 weeks of age in order to detect any changes with development, suggest potential relationship to the profile of dimeric inhibins and activins reported previously and to suggest potential paracrine and endocrine roles for them. The results show that all the inhibin/activin subunit mRNAs are expressed in the testis of the chicken throughout the period of prepubertal development up to 18 weeks of age. However, in the ovary, only the betaA- and betaB-subunits were detected at all ages whereas the alpha-subunit mRNA could only be detected just before puberty. Quantification of the mRNA levels showed variation of each subunit with age. These temporal changes suggest relationship with paracrine functional role in the ovary or the testis. Quantitative changes in expression levels also suggests that there may be some relationship between mRNA levels and the type and amount of dimeric inhibins and activins produced at any developmental stage. There are major differences between the male and female gonads in the timing of the expression of different subunits. In conclusion, the expression of the mRNA subunits in the testis and ovary suggests that inhibins and activins are being produced but may be principally involved in autocrine/paracrine function within the gonads.

Developmental and stage-specific expression of Smad2 and Smad3 in rat testis

Members of the transforming growth factor beta type (TGFbeta) superfamily and their receptors are expressed in the testis, and are believed to play important paracrine and autocrine roles during testicular development and spermatogenesis. The Smad proteins are downstream mediators for the family of TGFbeta growth factors. Smad2 and Smad3 are associated with both TGFbeta and activin signaling. However, very little is known about the expression and regulation of the Smad signaling proteins in the testis. In the present study, we have determined that Smad2 and Smad3 proteins are expressed in the postnatal testes of rats from 5 days to 60 days of age. Expression levels for both proteins are higher in young rats than in sexually mature rats. Smad2 and Smad3 messenger RNA levels parallel protein expression. Smad2 and Smad3 proteins are mainly localized in the cytoplasm of meiotic germ cells, Sertoli cells, and Leydig cells. Smad3 protein is localized to the nucleus of preleptotene to zygotene primary spermatocytes in young rats. Both proteins are expressed throughout all stages of the cycle of seminiferous tubules but are expressed at their lowest levels at stages VII-VIII in the seminiferous epithelium of adult rats. The presence of these downstream mediators in these cell types supports a role for TGFbeta and activin during spermatogenesis. The difference between the expression of Smad2 and Smad3 suggests that they may have different functions within the testis.

Expression pattern of messenger ribonucleic acid for the activin type II receptors and the inhibin/activin subunits during follicular development in broiler breeder hens

The expression of mRNA for the activin type II receptors (ActRII and ActRIIB), follistatin, and the inhibin/activin subunits was investigated in the follicles of broiler breeder hens. Total RNA was isolated from individual granulosa and theca layers of the F1 through F5 follicles, a pool of the F6 and F7 follicles, the small yellow follicles, and from the combined granulosa and theca layers of the large white follicles from six birds. Northern blot analysis was performed, and two ActRII mRNA transcripts of 6.5 and 3.7 kb were detected in granulosa and theca samples. Both ActRII transcripts were equally expressed in the granulosa samples, but in the theca samples expression of the 3.7-kb transcript was greater than the 6.5-kb transcript. ActRIIB was not detected by Northern analysis in any of the samples. Expression of the mRNA for the activin/inhibin binding protein, follistatin, was detected in theca and granulosa samples with the greatest expression found in small yellow follicle samples for both cell layers. Expression of the inhibin alpha-subunit was detected in the granulosa layer of all the follicles, but expression was greatest in the F6 and F7 follicles. Granulosa from the large hierarchical follicles expressed the most inhibin/activin betaA-subunit, whereas expression of the inhibin/activin betaB-subunit was greatest in the granulosa of small yellow and F6 and F7 follicles. This report is the first, to our knowledge, on detection of activin type II receptor mRNA in the hen ovary and characterization of the expression pattern of the inhibin family in both the theca and granulosa layers throughout follicular development. The presence of activin receptor and follistatin mRNA in the theca and granulosa layers of the small developing follicles suggests that locally produced activin may be highly regulated and have a vital role in early follicular development.

Proliferative phase sertoli cells display a developmentally regulated response to activin in vitro

We have used cultures of highly purified, proliferating rat Sertoli cells collected from d 3, 6, and 9 rat pups to investigate the role of activin A on Sertoli cell division. These studies demonstrate that activin A acts directly on d 6 and 9, but not d 3, Sertoli cells to induce proliferation, both alone and synergistically with FSH. In addition to stimulating proliferation, activin A induces secretion of inhibins A and B as determined by specific ELISAs. We demonstrate that the synergy between activin A and FSH is not due to local actions of secreted inhibin or follistatin. We have used real-time fluorometric RT-PCR to demonstrate that activin regulates expression of activin receptor and follistatin mRNA by Sertoli cells. Saturation binding studies using (125)I-activin A indicate that synergy between activin and FSH may be due to increased numbers of activin receptors on the Sertoli cell. Finally, we show that activin A was secreted at high levels by cultured peritubular cells but was undetectable in high purity proliferating Sertoli cell cultures, suggesting that activin A functions as a paracrine factor during postnatal testis development.

Cytokines and the immune-testicular axis

Cytokines are regulatory proteins involved in haematopoiesis, immune cell development, inflammation and immune responses. Several cytokines have direct effects on testicular cell functions, and a number of these are produced within the testis even in the absence of inflammation or immune activation events. There is compelling evidence that cytokines, in fact, play an important regulatory role in the development and normal function of the testis. Pro-inflammatory cytokines including interleukin-1 and interleukin-6 have direct effects on spermatogenic cell differentiation and testicular steroidogenesis. Stem cell factor and leukaemia inhibitory factor, cytokines normally involved in haematopoiesis, also play a role in spermatogenesis. Anti-inflammatory cytokines of the transforming growth factor-beta family are implicated in testicular development. Consequently, local or systemic up-regulation of cytokine expression during injury, illness or infection may contribute to the disruption of testicular function and fertility that frequently accompanies these conditions. The aim of this review is to provide a very brief summary of the extensive literature dealing with cytokines in testicular biology, and to follow this with some speculation concerning the significance of these molecules in interactions between the immune system and the testis.

Immunohistochemical localization of inhibin subunits in the testis of the bull

The differential localization of the inhibin beta subunits betaA and betaB in the testis of adult bull was studied using specific monoclonal and polyclonal primary antibodies. Inhibin betaA- and betaB-subunits were localized only in the Sertoli cells. The inhibin betaA-subunit was observed in the cytoplasm while the betaB-subunit was localized in the nucleus. No specific findings depending on spermatogenic stages were observed among the seminiferous tubules. Moreover, the inhibin alpha-subunit was not detected in the testis of the bulls. In addition, no inhibin subunits were detected in the Leydig cells and spermatogenic cells. These findings indicate the presence of betaA- and betaB-subunits in the bull, which may suggest a possibility that activin is produced and/or stored in the Sertoli cells and regulates spermatogenesis in an autocrine/paracrine manner. Moreover, the inhibin betaB-subunit may be produced in the nucleus but the functional meaning of this is not yet clear.

Analysis of the testicular phenotype of the follicle-stimulating hormone beta-subunit knockout and the activin type II receptor knockout mice by stereological analysis

This study evaluated the role of FSH and activin A on testicular function using quantitative stereological analysis of testicular cell types in mice with targeted disruption of genes encoding the FSH beta-subunit and the activin type IIA receptor (ActRIIA). Using the optical dissector technique, the numbers of Sertoli cells and germ cells per testis were determined. Testis weights in homozygous males lacking the FSHbeta gene or the ActRIIA gene were decreased approximately 60% compared with wild-type or respective heterozygotes. Sertoli cell numbers decreased in both homozygous mice by 30-39%, and there was a comparable decline in germ cell numbers in both models. The degree of germ cell attrition increased in the later stages of spermatogenesis from a 46% reduction of spermatogonia to a 60% decrease in round spermatids. As the FSH levels are decreased in both models, the cellular lesion in both is most likely due to the FSH deficiency. Although the decrease in the Sertoli cell complement represents one cause of lower germ cell numbers, the ability of Sertoli cells to nurture germ cells is compromised by the lower FSH levels, as shown by a decrease in the round spermatid to Sertoli cell ratios in both homozygous models. We conclude that the defects in FSH beta-subunit gene knockout and ActRIIA knockout mice are related to diminished FSH action on both Sertoli cell proliferation and the capacity of Sertoli cells to nurture germ cells.

Inhibins, activins and follistatin: actions on the testis

While the early studies of the inhibins, activins and follistatins concentrated on their role as endocrine regulators of FSH secretion, recent data has emphasized the local actions of the activins and follistatin. Inhibin, through its capacity to suppress FSH secretion can modulate numerous processes within the testis. However, to date, evidence to support a local role for inhibin is limited. In contrast, activin and its binding protein follistatin are produced by a large number of cell-types within the testis raising the possibility of a range of paracrine and autocrine actions. These include the modulation of androgen production, influence on the proliferation of Sertoli cells and germ cells as well as the capacity to influence the structural and functional features of mitochondria within germ cells. Some of these actions are carefully controlled in a temporal relationship during the development of testicular function in the rat in which there is no separation in time between birth and the onset of spermatogenesis. Given the range of actions of activin in different cell-types, recognition of systems that are designed to modulate its actions are crucial in enhancing our understanding of how these many roles can be compartmentalized.

Activin maintains the condensed type of mitochondria in germ cells

Development of germ cells during spermatogenesis is characterized by a complex series of differentiation events finally leading to the production of spermatozoa. Beside the main hormonal regulators, paracrine interactions are thought to play a major role in this process. Mitochondria in germ cells pass through unique alterations ranging from the 'typical' cristae-rich mitochondria found in spermatogonia to the 'condensed' form in pachytene spermatocytes. This study provides further support that paracrine factors produced by Sertoli cells, most likely activin A, are involved in germ cell differentiation as monitored by the maintenance of the physiological 'condensed' mitochondrial phenotype in primary spermatocytes. Culture of primary spermatocytes in Sertoli cell conditioned medium (SCCM) for 18 h resulted in the maintenance of a high percentage of 'condensed-type' mitochondria in comparison to cells cultured in Dulbecco's minimum essential medium (DMEM). Activin A, a product of Sertoli cells, showed at subnanogram concentrations a similar ability to SCCM to maintain a high percentage of spermatocyte mitochondria in the 'condensed' state, while inhibin had no effect. The addition of an antiserum specific for activin A resulted in a neutralization of the effect caused by activin A or SCCM. This strongly suggested that the active substance in SCCM was activin A. Taken together these data indicate that activin A is the first Sertoli cell product that has been identified to influence differentiation of male meiotic germ cells.

Insertion of Inhbb into the Inhba locus rescues the Inhba-null phenotype and reveals new activin functions

The activins (dimers of betaA or betaB subunits, encoded by the genes Inhba and Inhbb, respectively) are TGF-beta superfamily members that have roles in reproduction and development. Whereas mice homozygous for the Inhba-null allele demonstrate disruption of whisker, palate and tooth development, leading to neonatal lethality, homozygous Inhbb-null mice are viable, fertile and have eye defects. To determine if these phenotypes were due to spatiotemporal expression differences of the ligands or disruption of specific ligand-receptor interactions, we replaced the region of Inhba encoding the mature protein with Inhbb, creating the allele Inhbatm2Zuk (hereafter designated InhbaBK). Although the craniofacial phenotypes of the Inhba-null mutation were rescued by the InhbaBK allele, somatic, testicular, genital and hair growth were grossly affected and influenced by the dosage and bioactivity of the allele. Thus, functional compensation within the TGF-beta superfamily can occur if the replacement gene is expressed appropriately. The novel phenotypes in these mice further illustrate the usefulness of insertion strategies for defining protein function.

Effects of stem cell factor and granulocyte macrophage-colony stimulating factor on survival of porcine type A spermatogonia cultured in KSOM

Spermatogenesis is initiated with the divisions of the type A spermatogonial stem cells; however, the regulation of this stem cell population remains unknown. In order to obtain a better understanding of the biology of these cells, type A spermatogonia were isolated from 80-day-old pig testes by sedimentation velocity at unit gravity. The cells were cultured for up to 120 h in Dulbecco's modified Eagle's medium/Ham's F-12 medium (DMEM/F12) or a potassium-rich medium derived by the simplex optimization method (KSOM). At the end of the 120-h culture period, 30-50% of the spermatogonia were viable in KSOM, whereas in DMEM/F12 very few cells survived. Using KSOM as the culture medium, the effects of stem cell factor (SCF) and granulocyte macrophage-colony stimulating factor (GM-CSF) were studied. SCF significantly enhanced the percentage of cell survival at 100 ng/ml but not at lower concentrations. In comparison, GM-CSF promoted survival at relatively low concentrations (0.01, 0.1, and 1 ng/ml). At a higher dose (10 ng/ml), a significant reduction in percentage of cell survival was observed. The combination of SCF with GM-CSF had no significant effect on the percentage survival of type A spermatogonial cells. These data indicate that SCF and GM-CSF play a role in the regulation of survival and/or proliferation of type A spermatogonia.

Male sterility in transgenic mice expressing activin betaA subunit gene in testis

Activins and inhibins, which are endocrine regulators of anterior pituitary function, have also been reported to participate in the paracrine and autocrine regulation of reproductive function. To determine the in vivo effects of overexpressed activin/inhibin, we generated transgenic mice carrying the human activin/inhibin betaA subunit mini gene under the regulatory control of the mouse methallothionein promoter. In one of the transgenic line analyzed, the betaA subunit gene was preferentially expressed in the testis. Ectopic and allochronic expression of the betaA gene started at 3 weeks after birth and transgenic male mice became sterile in the ensuing several weeks. Histological analysis revealed testicular degeneration in these mice. The results from this transgenic line strongly support the in vivo activity of activin/inhibin in male reproductive functions.

Identification of a nuclear localization signal in activin/inhibin betaA subunit; intranuclear betaA in rat spermatogenic cells

Activin is a dimeric glycoprotein hormone that was initially characterized by its ability to stimulate pituitary FSH secretion and was subsequently recognized as a growth factor with diverse biological functions in a large variety of tissues. In the testis, activin has been implicated in the auto/paracrine regulation of spermatogenesis through its cognate cell membrane receptors on Sertoli and germ cells. In this study we provide evidence for intranuclear activin/inhibin betaA subunit and show its distribution in the rat seminiferous epithelium. We have shown by transient expression in HeLa cells of beta-galactosidase fusion proteins that the betaA subunit precursor contains a functional nuclear localization signal within the lysine-rich sequence corresponding to amino acids 231-244. In all stages of the rat seminiferous epithelial cycle, an intense immunohistochemical staining of nuclear betaA was demonstrated in intermediate or type B spermatogonia or primary spermatocytes in their initial stages of the first meiotic prophase, as well as in pachytene spermatocytes and elongating spermatids primarily in stages IX-XII. In some pachytene spermatocytes, the pattern of betaA immunoreactivity was consistent with the characteristic distribution of pachytene chromosomes. In the nuclei of round spermatids, betaA immunoreactivity was less intense, and in late spermatids it was localized in the residual cytoplasm, suggesting disposal of betaA before spermatozoal maturation. Immunoblot analysis of a protein extract from isolated testicular nuclei revealed a nuclear betaA species with a molecular mass of approximately 24 kDa, which is more than 1.5 times that of the mature activin betaA subunit present in activin dimers. These results suggest that activin/inhibin betaA may elicit its biological functions through two parallel signal transduction pathways, one involving the dimeric molecule and cell surface receptors and the other an alternately processed betaA sequence acting directly within the nucleus. According to our immunohistochemical data, betaA may play a significant role in the regulation of nuclear functions during meiosis and spermiogenesis.

Expression of growth differentiation factor-9 messenger ribonucleic acid in ovarian and nonovarian rodent and human tissues

Growth differentiation factor-9 (GDF-9) is a member of the transforming growth factor-beta family that is reported to be expressed exclusively in the ovary, specifically in the oocyte. Female mice deficient in GDF-9 are infertile, suggesting that GDF-9 receptor agonists and antagonists may specifically modulate fertility. We now report that GDF-9 messenger RNA (mRNA) is expressed in nonovarian tissues in mice, rats, and humans. GDF-9 mRNA was detected in mouse and rat ovary, testis, and hypothalamus by Northern blot and RT-PCR analyses. The localization of GDF-9 mRNA specifically in oocytes of the mouse ovary was confirmed by in situ hybridization histochemistry. In mouse testis, although localization in Sertoli cell cytoplasm could not be ruled out, mRNA expression was observed in large pachytene spermatocytes and round spermatids. The expression of GDF-9 mRNA in human tissues was assessed by Northern blot and RT-PCR analyses. GDF-9 mRNA was observed in ovary and testis and, surprisingly, in diverse nongonadal tissues, including pituitary, uterus, and bone marrow. Therefore, GDF-9 mRNA expression in rodents is not exclusive to the ovary, but includes the testis and hypothalamus. Furthermore, human GDF-9 mRNA is expressed not only in the gonads, but also in several extragonadal tissues. The function and relevance of nongonadal GDF-9 mRNA are not known, but may affect strategies for contraception and fertility that are based on GDF-9 activity.

Testicular germ cell populations in the adult rat after continuous in-vivo testicular infusion of inhibin-A and activin-A

This study investigated the in-vivo effects of inhibin-A and activin-A on germ cell subpopulations in the adult rat testis. Each animal received a total of 2 micrograms (dose 5 ng/0.5 microliter/h) of activin, inhibin or 0.1% bovine serum albumin (vehicle control) delivered intratesticularly into the left testis via a cannula connected to an abdominal minipump implant. To establish whether the hormones exerted any effect on procarbazine-induced germ cell depletion, a single intraperitoneal dose of this agent was given to a group of the rats 24 h after the start of testicular infusion of activin or inhibin. Rats were killed 14 days later. Inhibin treatment caused a reduction in the number of round spermatids without altering serum FSH levels. In procarbazine-treated rats, infusion of inhibin reduced the number of pachytene spermatocytes and reduced blood FSH levels simultaneously. Infusion of activin had no significant effect on the numbers of germ cells, but reduced the number of dead cells in the seminiferous tubules of procarbazine-treated rats. The data would therefore suggest that the effects of inhibin and activin on the seminiferous epithelium are influenced by the testicular microenvironment, and that they are capable of influencing the growth and survival of germ cells by both FSH- and non FSH-mediated mechanisms. Further experiments are needed to identify the physiological role(s) of inhibin and activin in spermatogenesis.

Hybridization histochemical and immunohistochemical localization of inhibin/activin subunits and messenger ribonucleic acids in the rat brain

Inhibin and activin are best known as gonadal glycoprotein hormones but have a broad anatomical distribution. We previously described the central distribution ofinhibin/activin beta A- and beta B-subunit proteins in some neuronal cell bodies, fibers, and nuclei of the rat brain and reported a possible role for central activin in suckling-induced oxytocin secretion and corticotropin releasing factor release. In the present report, we mapped the detailed immunohistochemical localization of inhibin/activin alpha-, beta A-, and beta B-subunits throughout the rat brain to further clarify their central distribution. In addition, the localization and distribution of their corresponding mRNAs was assessed. The results are summarized as follows: 1) Both beta A- and beta B-subunit immunoreactivity are found in neuronal cell bodies in the nucleus of the solitary tract and the dorsal and ventral medullary reticular nuclei, and in fibers and terminals of known projection sites for these nuclei. 2) beta B-subunit immunoreactivity is localized in a group of perifornical neurons in the hypothalamus. 3) beta A-subunit immunoreactivity is present in discrete populations of neuronal cell nuclei scattered throughout the CNS. 4) mRNAs encoding each of the inhibin/activin subunits are expressed in all major brain regions as determined by S1 nuclease assay and in a variety of specific neuroanatomical sites as shown by in situ hybridization. The results suggest that central inhibin and activin proteins are produced in the brain where they may potentially serve inter- and intracellular functions in multiple systems.

Expression and localization of activin beta A-subunit and activin receptors in TM3, a mouse Leydig cell line

We have determined whether TM3 cells, a cell line derived from a murine Leydig cell tumor, (a) transcribe messenger RNAs encoding the beta A-subunits of inhibin/activin, and activin receptors I, II, and IIB, and (b) produce activin-A protein. Messenger RNAs for inhibin/activin beta A-subunits and activin receptors II, and IIB in TM3 cells were localized and expressed using in situ hybridization and the reverse transcription-polymerase chain reaction (RT-PCR) analysis, respectively. The identify of the RT-PCR products was confirmed by DNA sequencing of PCR products. Immunocytochemically, activin-A was localized in these cells. We observed that messenger RNAs encoding activin beta A-subunit as well as activin receptors II, and IIB were expressed and activin protein was produced by TM3 cells. These findings suggest that activin-A may have autocrine functions in TM3 cells and that activin-A may be involved in regulating the growth and differentiation of mouse Leydig cells.

Different phenotypes for mice deficient in either activins or activin receptor type II

Activins are believed to initiate a signal transduction cascade by binding to serine/threonine kinase receptors types I and II. Activins bind to several different receptors in vitro, but the significance of this interaction in vivo has not been confirmed. To test the function of the type II activin receptor (ActRcII) in mammalian development and reproduction, we generated a null mutation in the ActRcII gene in mice using embryonic stem cell technology. We expected ActRcII-deficient mice to phenocopy activin-deficient mice. A few ActRcII-deficient mice had skeletal and facial abnormalities reminiscent of the Pierre-Robin syndrome in humans, but most lacked these defects and developed into adults; their follicle-stimulating hormone was suppressed, and their reproductive performance was defective. These findings confirm a role of ActRcII in activin signalling in pituitary gonadotrophs. The striking lack of overlap between phenotypes of ActRcII-deficient and activin-deficient mice suggests that the ligands that signal through ActRcII during embryonic development are not activins.

mRNAs for activin receptors II and IIB are expressed in mouse oocytes and in the epiblast of pregastrula and gastrula stage mouse embryos

Activin is a potent inducer of mesoderm in frog embryos. We showed previously that in the mouse, activin beta A is expressed in the uterine decidua near the embryo before and during the first appearance of mesoderm (E4.5-E6.5). Here, using Northern blotting and in situ hybridization, we show that mouse oocytes, E6.5 and E7.5 embryos, and E6.5 and E7.5 decidua contain mRNAs for both activin receptors type II and IIB. The expression of activin receptor type IIB is particularly strong in embryonic ectoderm apparent at E5.5 and continuing through E8.5. These results support the hypothesis that activin derived from the decidua promotes development of mesoderm in the period E5.5-E6.5.

Bovine activin receptor type II cDNA: cloning and tissue expression

The cDNA encoding the bovine activin type II receptor has been cloned by reverse transcription-polymerase chain reaction (RT-PCR) amplification of a bovine testicular RNA preparation. Sequence comparisons of the bovine activin type II receptor with its human, mouse and rat homologues show strong evolutionary conservation at the nucleotide level of 94.9%, 93.5%, 92.9% and at the amino acid level of 98.6%, 99.0%, 98.8%, respectively. Bovine activin type II receptor mRNA is widely but not strongly expressed in reproductive tissues, with a major RNA band at 6 kb and minor bands at 5 kb and 3 kb. The differential levels of expression observed in these tissues suggest that levels of bActRII gene expression are regulated. Furthermore, we have observed decreasing levels of the bovine activin type II receptor mRNA with testes maturation.

Localization of mRNAs by in-situ hybridization to the residual body at stages IX-X of the cycle of the rat seminiferous epithelium: fact or artefact?

Several recent articles have reported localization of specific mRNAs in the rat testis to stage IX and X seminiferous tubules using in-situ hybridization. In all cases the expression was located basally in the tubules and appeared as discrete round clusters of grains close to the lamina propria. The localization was interpreted as being in Sertoli cells or leptotene spermatocytes. In this study we demonstrate that this pattern is most probably due to artefactual binding of probes to the residual body (RB). In the present study testicular tissue, perfusion-fixed with Bouin's and embedded in paraffin, was used, as this resulted in excellent morphological preservation such that RBs within tubules at stages VIII-X were clearly distinguishable. RNA content of the RBs was demonstrated at stages VIII-X using methyl green pyronin staining, and could be eliminated by pretreatment with RNAse or trichloroacetic acid. Localization of mRNAs for 11 seminiferous tubule proteins was assessed using 35S-labelled and digoxigenin-labelled riboprobes (activin receptor-II, alpha-inhibin, transferrin, androgen-binding protein (ABP), cyclic protein-2 (CP-2), CREM, sulphated glycoproteins 1 and 2 (SGP-1 and SGP-2), transition protein 2 (TP-2) and cystatin-C), and digoxigenin-labelled oligonucleotide probes (transition protein-1 (TP-1), TP-2 and protamine-1). All of these probes showed localization to the correct cell type(s) within the seminiferous epithelium. In addition, six antisense riboprobes (activin receptor-II, CREM, SGP-2, CP-2, cystatin C and alpha-inhibin) showed hybridization to basally located residual bodies in tubules at stages IX-X on one or more occasions, whereas residual bodies around the edge of the lumen (stage VIII) or in transit through the seminiferous epithelium showed no hybridization; sense probes showed no localization to residual bodies. A common feature of the probes which localized to the basal RBs was that they had been prepared using cDNA cloned into Bluescript SK- vector such that the antisense strand was generated from the T7 polymerase promotor. A cRNA prepared using T7 polymerase and Bluescript vector alone and a GC-rich 27mer oligonucleotide corresponding to the region of the multiple cloning site of Bluescript adjacent to the T7 site both localized uniquely to basal RB. It is concluded that the hybridization seen within RBs is probably a subtle artefact unique to RBs undergoing dissolution following fusion with Sertoli cell lysosomes, and may reflect nonspecific hybridization to GC-rich fragments of RNA.

Inhibins, activins, their binding proteins and receptors: interactions underlying paracrine activity in the testis

The inhibin-related peptides are present in the testis from early gestation through adulthood. They are produced from multiple testicular sites in a highly regulated manner, suggesting important paracrine roles. Similarly, receptors for these peptides are located in specific stages of the seminiferous tubule and on particular cell types, and an additional level of control is afforded by specific binding proteins, such as follistatin, which may regulate bioavailability. The actions of these factors include the modulation of interstitial cell function and the increase of spermatogonial proliferation in vitro. It thus appears that activin and inhibin are significant factors in the local control of testicular function.

Welcome to the family: the anti-müllerian hormone receptor

Anti-müllerian hormone (AMH) is a member of the superfamily of peptide growth/differentiation factors which includes the activins and TGF-beta s. The putative AMH type II receptor, which was cloned recently (Baarends et al., 1994), is a member of the superfamily of transmembrane serine/threonine kinase receptors. In hypothetical evolutionary relationship dendrograms, both AMH and its putative receptor take isolated positions relative to their respective family members. The prenatal expression pattern of this putative AMH receptor is in accordance with the expected endocrine action of AMH on the mesenchymal cells located adjacent to the müllerian duct, and with known effects of AMH on gonadal differentiation. Postnatal expression of mRNA encoding this receptor in granulosa and Sertoli cells provides a new stimulus to study possible functions of AMH in the gonads.

MIP-1 alpha is a regulator of mitotic and meiotic DNA synthesis during spermatogenesis

To find out whether macrophage inflammatory protein-1 alpha (MIP-1 alpha) has a role in the regulation of germ cell development, we studied its effects on spermatogenic stage-specific DNA synthesis in vitro. MIP-1 alpha increased the DNA synthesis of primitive type A2-4 spermatogonia and of premeiotic cells, whereas the DNA synthesis of more differentiated intermediate and type B spermatogonia was inhibited when cultured in the presence of MIP-1 alpha. An antibody against MIP-1 alpha cross-reacted with a protein of 15 kDa from every spermatogenic stage of rat seminiferous epithelium. Immunohistochemical studies with the same antibody revealed a complex pattern of MIP-1 alpha localization both in primitive and advanced spermatogenic cells. These observations suggest that MIP-1 alpha is a local regulator of mitotic and meiotic DNA synthesis.

A novel member of the transmembrane serine/threonine kinase receptor family is specifically expressed in the gonads and in mesenchymal cells adjacent to the mullerian duct

The activin and TGF-beta type II receptors are members of a separate subfamily of transmembrane receptors with intrinsic protein kinase activity, which also includes the recently cloned TGF-beta type I receptor. We have isolated and characterized a cDNA clone (C14) encoding a new member of this subfamily. The domain structure of the C14-encoded protein corresponds with the structure of the other known transmembrane serine/threonine kinase receptors. It also contains the two inserts in the kinase domain that are characteristic for this subfamily. Using in situ hybridization, C14 mRNA was detected in the mesenchymal cells located adjacent to the mullerian ducts of males and females at day 15 (E15) of embryonic development. Marked C14 mRNA expression was also detected in the female gonads. In female E16 embryos, the C14 mRNA expression pattern remained similar to that in E15 embryos. However, in male E16 embryos C14 mRNA was detected in a circular area that includes the degenerating mullerian duct. The expression of C14 mRNA was also studied using RNase protection assays. At E15 and E16, C14 mRNA is expressed in the female as well as in the male urogenital ridge. However, at E19, a high C14 mRNA level in the female urogenital ridge contrasts with a lack of C14 mRNA in the male urogenital ridge. This correlates with the almost complete degeneration of the mullerian ducts in male embryos at E19. C14 mRNA expression was also detected in embryonic testes at E15, E16 and E19 using RNase protection assays, but at much lower levels than those found in the developing ovaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of receptor tyrosine kinases in the rat testis

Evidence of receptor/ligand interactions that regulate testis cell function was sought in order to broaden the current understanding of the molecular basis of testis cell function. Using reverse transcription and the polymerase chain reaction, we have obtained novel evidence for the expression of three mRNAs encoding receptor tyrosine kinases in the adult rat testis: the platelet-derived growth factor type A receptor (PDGF-RA), the basic fibroblast growth factor receptor (flg), and fetal liver kinase 1 (Flk-1). A 6.8 kb transcript encoding the PDGF-RA was observed in RNA prepared from testes of rats aged day 5 through adult, with a decline in relative abundance with increasing age after day 17. Analysis of mRNA from isolated cell preparations (day 21 Sertoli cells, adult Leydig cells, round spermatids, and primary spermatocytes) and testes depleted of specific cell types [ethane dimethane sulfonate (EDS)-treated and cryptorchid] indicated that the Leydig cell was the predominant source of this mRNA in the adult testis. The addition of PDGF-BB to cultures of highly purified adult rat Leydig cell preparations resulted in a 40% increase in LH-stimulated testosterone production, confirming a role for this growth factor in regulation of Leydig cell function. These data indicate that the Leydig cell is a principal site of action of PDGF in the testis.

Inhibin/activin subunits and activin receptor are co-expressed in Leydig tumor cells

The expression of genes encoding inhibin/activin subunits and activin receptor was examined in four cultured Leydig tumor cells (MA-10, I-10, R2C, and LC-540). Inhibin alpha-subunit gene was highly expressed in Leydig tumor cell lines except LC-540. Both inhibin beta-A- and beta-B-subunit mRNAs were present in low levels. The 6.5-kb beta-A-subunit mRNA was detected in MA-10, R2C and LC-540 cells, and not in I-10 cells. The expression of the two species of beta-B-subunit mRNA is cell specific. In MA-10 and I-10 cells, 4.4-kb beta-B-subunit mRNA was the predominant species, while in R2C and LC-540 cells both 4.4-kb and 3.3-kb mRNA were present in equal quantities. By contrast, two species (6 and 3 kb) of activin receptor ActRII mRNA were identified in equal intensity in all four Leydig tumor cell lines. Addition of cAMP derivative to MA-10 cells at 0.1 mM for 17 h or 1 mM for 5 h produced a two-fold increase in inhibin alpha-subunit mRNA levels, and small or no significant change in inhibin beta-B-subunit and ActRII mRNAs. However, a 70-80% reduction in inhibin beta-A-subunit mRNA was observed by 1 mM cAMP for 5 h. We concluded that: (1) the inhibin/activin subunit genes and activin receptor gene are co-expressed in Leydig tumor cell lines, and (2) the three inhibin/activin subunit genes are expressed differently, while the activin receptor gene is expressed identically in the four cell lines.

Effect of epidermal growth factor/transforming growth factor alpha on lactate production in porcine Sertoli cells: glucose transport and lactate dehydrogenase isozymes as potential sites of action

Germ cell development is dependent upon the delivery of essential nutriments such as lactate originating from Sertoli cells. Lactate production is under the systemic control but probably also under a local control exerted via certain growth factors. By using a model of porcine cultured Sertoli cells, we have characterized the action of epidermal growth factor (EGF) on lactate production and further delineated the potential biochemical mechanisms involved in the EGF action. EGF stimulated lactate production in a time and dose dependent manner with a half-maximal (ED50) and maximal effects, respectively with 3.8 (0.6 x 10(-9) M) and 22 ng/ml of EGF. Lactate formation involves several biochemical steps among which the glucose substrate uptake and transport system as well as the lactate dehydrogenase (LDH) activity appear to play key roles. We report here that EGF increased the uptake of glucose evaluated through that of 2-deoxy-D-glucose (2-DOG), a non-metabolizable glucose analog. Such an increase in glucose substrate uptake occurs both after a long term (48 h) and a short term treatment (ED50 = 6.4 ng/ml, 1.1 x 10(-9) M EGF). Moreover, EGF was also able to enhance the activity of the Sertoli cell LDH. The maximal effect of the growth factor on LDH activity was observed after a long term (24 h) treatment with an ED50 of 7 ng/ml (1.2 x 10(-9) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes of testicular activin and FSH receptor mRNA and plasma FSH and inhibin levels in the rat

To investigate the changes in the FSH receptor and the activin receptor during sexual maturation in rat testes, we examined the mRNA levels of the receptors by Northern blot analysis. With a full length rat activin receptor cRNA probe in this study, Northern blot analysis revealed two activin receptor mRNAs (6Kb and 3Kb) in testes. The large messenger (6Kb) was low on day 7, and gradually increased by day 35. On the other hand, the small messenger (3Kb) was low on day 7, began to increase on day 21, and had increased dramatically by day 35. Therefore, compared with our previous data, developmental changes in the mRNA of the activin receptor of male and female gonads showed certain differences. The expression of 3Kb activin receptor mRNA in rat testis may be relevant to the stimulated spermatogenesis in this period. 2.4Kb and 5.5Kb FSH receptor mRNA were revealed on day 7 and decreased to 80% on day 14 and remained at the same level. The Scatchard plots of FSH binding data showed that the binding affinities of testicular FSH were constant at each stage of development. Changes in the mRNA level in FSH receptor were followed by changes in the concentration of FSH receptor in testis. The rise in the plasma FSH level was concomitant with the decrease in the plasma inhibin level by day 14.