Biologically active kit ligand growth factor is produced by mouse Sertoli cells and is defective in SId mutant mice

Xenotransplantation of canine spermatogonial stem cells (cSSCs) regulated by FSH promotes spermatogenesis in infertile mice

Background

Xenotransplantation of spermatogonial stem cells (SSCs) has become a popular topic in various research fields because manipulating these cells can provide insights into the mechanisms associated with germ cell lines and the entire spermatogenesis process; moreover, these cells can be used in several biotechnology applications. To achieve successful xenotransplantation, the in vitro microenvironment in which SSCs are cultured should be an ideal microenvironment for self-renewal and similar to the in vivo testicular microenvironment. The age of the donor, the correct spermatogenesis cycle, and the quality of the donor tissue are also important. Although cell culture-related factors, such as the in vitro supplementation of hormonal factors, are known to promote successful xenotransplantation in mice, little is known about the influence of these factors on SSCs in vitro or in vivo in other mammalian species, such as dogs (Canis lupus familiaris). In this context, the goals of this study were to test the effect of follicle-stimulating hormone (FSH) on canine spermatogonial stem cell (cSSC) cultures since this hormone is related to the glial cell-derived neurotrophic factor (GDNF) signaling pathway, which is responsible for the self-renewal and maintenance of these cells in vivo, and to investigate the microenvironment of the SSC culture after FSH supplementation. Additionally, in vivo analyses of transplanted FSH-supplemented cSSCs in the testes of infertile mice were performed to assess the capacity of cSSCs to develop, maintain, and restore spermatogenesis.

Methods

SSCs from canine prepubertal testes (aged 3 months) were cultured in vitro in the presence of FSH (10 IU L⁻¹). GFRA1 transcript expression was detected to confirm the spermatogonia population in culture and the effect of FSH on these cells. The protein and transcript levels of late germ cell markers (GFRA1, DAZL, STRA8, PLZF, and CD49f) and a pluripotency marker (OCT4) were detected at 72 and 120 h to confirm the cSSC phenotype. In vivo experiments were performed by transplanting GFP+ cSSCs into infertile mice, and a 10-week follow-up was performed. Histological and immunofluorescence analyses were performed to confirm the repopulation capacity after cSSC xenotransplantation in the testis.

Results

Supplementation with FSH in cell culture increased the number of cSSCs positive for GFRA1. The cSSCs were also positive for the pluripotency and early germline marker OCT4 and the late germline markers PLZF, DAZL, C-kit, and GFRA-1. The in vivo experiments showed that the cSSCs xenotransplanted into infertile mouse testes were able to repopulate germline cells in the seminiferous tubules of mice.

Conclusions

In conclusion, our results showed for the first time that the treatment of cSSC cultures with FSH can promote in vitro self-renewal, increase the population of germline cells, and possibly influence the success of spermatogenesis in infertile mice in vivo.

The SCF/c-KIT system in the male: Survival strategies in fertility and cancer

Maintaining the delicate balance between cell survival and death is of the utmost importance for the proper development of germ cells and subsequent fertility. On the other hand, the fine regulation of tissue homeostasis by mechanisms that control cell fate is a factor that can prevent carcinogenesis. c-KIT is a type III receptor tyrosine kinase activated by its ligand, stem cell factor (SCF). c-KIT signaling plays a crucial role in cell fate decisions, specifically controlling cell proliferation, differentiation, survival, and apoptosis. Indeed, deregulating the SCF/c-KIT system by attenuation or overactivation of its signaling strength is linked to male infertility and cancer, and rebalancing its activity via c-KIT inhibitors has proven beneficial in treating human tumors that contain gain-of-function mutations or overexpress c-KIT. This review addresses the roles of SCF and c-KIT in the male reproductive tract, and discusses the potential application of c-KIT target therapies in disorders of the reproductive system.

Characterization of the testis-specific proteasome subunit α4s in mammals

The 26 S proteasome is responsible for regulated proteolysis in eukaryotic cells. It is composed of one 20 S core particle (CP) flanked by one or two 19 S regulatory particles. The CP is composed of seven different α-type subunits (α1-α7) and seven different β-type subunits, three of which are catalytic. Vertebrates encode four additional catalytic β subunits that are expressed predominantly in immune tissues and produce distinct subtypes of CPs particularly well suited for the acquired immune system. In contrast, the diversity of α subunits remains poorly understood. Recently, another α subunit, referred to as α4s, was reported. However, little is known about α4s. Here we provide a detailed characterization of α4s and the α4s-containing CP. α4s is exclusively expressed in germ cells that enter the meiotic prophase and is incorporated into the CP in place of α4. A comparison of structural models revealed that the differences in the primary sequences between α4 and α4s are located on the outer surface of the CP, suggesting that α4s interacts with specific molecules via these unique regions. α4s-containing CPs account for the majority of the CPs in mouse sperm. The catalytic β subunits in the α4s-containing CP are β1, β2, and β5, and immunosubunits are not included in the α4s-containing CP. α4s-containing CPs have a set of peptidase activities almost identical to those of α4-containing CPs. Our results provide a basis for understanding the role of α4s and male germ cell-specific proteasomes in mammals.

Effects of testicular interstitial fluid on the proliferation of the mouse spermatogonial stem cells in vitro

Spermatogenesis is a process in adult male mammals supported by spermatogonial stem cells (SSCs). The cultivation of SSCs has potential value, for example for the treatment of male infertility or spermatogonial transplantation. Testicular interstitial fluid was added to culture medium to a final concentration of 5, 10, 20, 30 or 40%, in order to investigate its effects on proliferation of mouse SSCs in vitro, Alkaline phosphatase (AKP) assay, reverse transcription polymerase chain reaction (RT-PCR) analysis and indirect immunofluorescence of cells were performed to identify SSCs, and the proliferation rate and diameters of the SSCs colonies were measured. The results showed that the optimal addition of testicular interstitial fluid to culture medium was 30%. When medium supplemented with 30% testicular interstitial fluid was used to culture mouse SSCs, the optimum proliferation rate and diameter of the cell colonies were 72.53% and 249 μm, respectively, after 8 days in culture, values that were significant higher than those found for other groups (P < 0.05). In conclusion, proliferation of mouse SSCs could be promoted significantly by supplementation of the culture medium with 30% testicular interstitial fluid. More research is needed to evaluate and understand the precise physiological role of testicular interstitial fluid during cultivation of SSCs.

c-kit and its related genes in spermatogonial differentiation

Spermatogenesis is the process of production of male gametes from SSCs. The SSCs are the stem cells that differentiate into male gametes in the testis. in the mean time, the Spg are remarkable for their potential multiple trans-differentiations, which make them greatly invaluable for clinical applications. However, the molecular mechanism controlling differentiation of the Spg is still not clear. Among the discovered spermatogenesis-related genes, c-kit seems to be expressed first by the Spgs thus may play a central role in switching on the differentiation process. Expression of Kit and the activation of the Kit/Kitl pathway coincide with the start of differentiation of Spgs. Several genes have been discovered to be related to the Kit/Kitl pathway. in this review, we have summarized the recent discoveries of c-kit and the Kit/Kitl pathway-related genes in the spermatogenic cells during different stages of spermatogenesis.

Control of KIT signalling in male germ cells: what can we learn from other systems?

The KIT ligand (KITL)/KIT-signalling system is among several pathways known to be essential for fertility. In the postnatal testis, the KIT/KITL interaction is crucial for spermatogonial proliferation, differentiation, survival and subsequent entry into meiosis. Hence, identification of endogenous factors that regulate KIT synthesis is important for understanding the triggers driving germ cell maturation. Although limited information is available regarding local factors in the testicular microenvironment that modulate KIT synthesis at the onset of spermatogenesis, knowledge from other systems could be used as a basis for identifying how KIT function is regulated in germ cells. This review describes the known regulators of KIT, including transcription factors implicated in KIT promoter regulation. In addition, specific downstream outcomes in biological processes that KIT orchestrates are addressed. These are discussed in relationship to current knowledge of mammalian germ cell development.

The reproductive activity in the testis of Podarcis s. sicula involves D-aspartic acid: a study on c-kit receptor protein, tyrosine kinase activity and PCNA protein during annual sexual cycle

The current study provides substantial evidence that the pattern of synthesis of D-aspartic acid (D-Asp) in the testes of lizard Podarcis s. sicula throughout the reproductive cycle is in parallel with seasonal variations of testosterone, c-kit receptor protein, tyrosine kinase activity, and proliferating cell nuclear antigen (PCNA) protein. Although the trend is the same in all phases of the sexual cycle, the peaks of these three molecules are detectable only during the reproductive period. Using Western blot technique, we demonstrated that both polyclonal c-kit and PCNA antibodies specifically recognized bands with molecular mass of approximately 150 and approximately 36 kDa, respectively. By immunocytochemical methods, D-Asp immunopositivity appeared spread in the germinal epithelium as well as in the interstitial compartment of the testes. We also found specific c-kit labeling in I and II spermatogonia (SPG), in I and II spermatocytes (SPC), in the elongated spermatides, in spermatozoa, in Sertoli and Leydig cells. Like c-kit, PCNA positivity was located in the germinal epithelium pattern. Furthermore, we investigated the relationship between testosterone, c-kit receptor, tyrosine kinases activity and PCNA following treatment with D-Asp. In vivo experiments, entailing a single injection of D-Asp (2.0 micromol/g body weight), demonstrated that this amino acid significantly accumulated in the testes. After 3 h, its uptake was accompanied by an increase in testosterone levels and in the expression and intensity of immunostaining of c-kit receptor protein. Furthermore, at 6 h, exogenous D-Asp affected the phosphorylation of tyrosine kinases, whose activation was positively correlated with the temporal uptake of both D-Asp and testosterone detected in the testes. Thereafter, between 6 and 15 h, the expression of PCNA was induced and an increase in its immunolabeling intensity was observed. Taken all together, these results provide new insights into the testicular activity during the reproductive cycle of Podarcis s. sicula, suggesting that a sequential cascade of a functional relationship between testosterone levels, c-kit receptor protein, tyrosine kinase activity and PCNA could be partly mediated by D-aspartic acid.

The roles of pericystic cells and Sertoli cells in spermatogonial proliferation stimulated by some growth factors in organ culture of newt (Cynops pyrrhogaster) testis

We have previously shown FSH promotes spermatogonial proliferation and their differentiation into primary spermatocytes in organ culture of newt testicular fragments. Several growth factors identified in newt testis, such as stem cell factor (SCF), insulin-like growth factor (IGF)-I, and neuregulin (NRG)1, also stimulate spermatogonial proliferation in the organ culture. However, any growth factor added in vitro might not work on spermatogonia directly, but act on somatic cells such as Sertoli cells or pericystic cells, because size-selective barrier exists around a cyst which is enclosed by Sertoli cells. In order to determine the target somatic cells of the growth factors as well as the role of pericystic cells in spermatogonial proliferation and differentiation, we searched for agents that kill pericystic cells selectively. We found that treatment of the testicular fragments with trypan blue (TB) caused cell death of only pericystic cells and significant abolishment of the activity of SCF to stimulate spermatogonial proliferation, while the activities of neither IGF-I nor NRG1 were affected. In addition, the potency of neither IGF-I nor FSH to stimulate the differentiation of spermatogonia into primary spermatocytes was abolished by TB treatment. Consistent with these results, only the mRNA expression of c-kit was reduced by TB treatment, whereas those of FSH receptor, SCF, IGF-I, IGF-I receptor, Immunoglobulin-like domain-containing NRG1, ErbB2, and ErbB4 were unaffected. These results indicate that SCF stimulates pericystic cells, while IGF-I and NRG1, as well as FSH, activate Sertoli cells, resulting in stimulation of spermatogonial proliferation in organ culture of testicular fragments.

Promotion of spermatogonial proliferation by neuregulin 1 in newt (Cynops pyrrhogaster) testis

We have previously shown that mammalian follicle-stimulating hormone (FSH) promotes the proliferation of spermatogonia and their differentiation into primary spermatocytes in organ culture of newt testis. In the current study, we performed microarray analysis to isolate local factors secreted from somatic cells upon FSH treatment and acting on the germ cells. We identified neuregulin 1 (NRG1) as a novel FSH-upregulated clone homologous to mouse NRG1 known to control cell proliferation, differentiation and survival in various tissues. We further isolated cDNAs encoding two different clones. Amino acid sequences of the two clones were 75% and 94% identical to Xenopus leavis immunoglobulin (Ig)-type and cysteine-rich domain (CRD)-type NRG1, respectively, which had distinct sequences in their N-terminal region but identical in their epidermal growth factor (EGF)-like domain. Semi-quantitative and quantitative PCR analyses indicated that both clones were highly expressed at spermatogonial stage than at spermatocyte stage. In vitro FSH treatment increased newt Ig-NRG1 (nIg-NRG1) mRNA expression markedly in somatic cells, whereas newt CRD-NRG1 (nCRD-NRG1) mRNA was only slightly increased by FSH. To elucidate the function of newt NRG1 (nNRG1) in spermatogenesis, recombinant EGF domain of nNRG1 (nNRG1-EGF) was added to organ and reaggregated cultures with or without somatic cells: it promoted spermatogonial proliferation in all cases. Treatment of the cultures with the antibody against nNRG1-EGF caused remarkable suppression of spermatogonial proliferation activated by FSH. These results indicated that nNRG1 plays a pivotal role in promoting spermatogonial proliferation by both direct effect on spermatogonia and indirect effect via somatic cells in newt testes.

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

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

Sohlh2 knockout mice are male-sterile because of degeneration of differentiating type A spermatogonia

The spermatogenesis and oogenesis-specific transcription factor Sohlh2 is normally expressed only in premeiotic germ cells. In this study, Sohlh2 and several other germ cell transcripts were found to be induced in mouse embryonic stem cells when cultured on a feeder cell line that overexpresses bone morphogenetic protein 4. To study the function of Sohlh2 in germ cells, we generated mice harboring null alleles of Sohlh2. Male Sohlh2-deficient mice were infertile because of a block in spermatogenesis. Although normal prior to birth, Sohlh2-null mice had reduced numbers of intermediate and type B spermatogonia by postnatal day 7. By day 10, development to the preleptotene spermatocyte stage was severely disrupted, rendering seminiferous tubules with only Sertoli cells, undifferentiated spermatogonia, and degenerating colonies of differentiating spermatogonia. Degenerating cells resembled type A2 spermatogonia and accumulated in M-phase prior to death. A similar phenotype was observed in Sohlh2-null mice on postnatal days 14, 21, 35, 49, 68, and 151. In adult Sohlh2-mutant mice, the ratio of undifferentiated type A spermatogonia (DAZL+/PLZF+) to differentiating type A spermatogonia (DAZL+/PLZF-) was twice normal levels. In culture, undifferentiated type A spermatogonia isolated from Sohlh2-null mice proliferated normally but linked the mutant phenotype to aberrant cell surface expression of the receptor-tyrosine kinase cKit. Thus, Sohlh2 is required for progression of differentiating type A spermatogonia into type B spermatogonia. One conclusion originating from these studies would be that testicular factors normally regulate the viability of differentiating spermatogonia by signaling through Sohlh2. This regulation would provide a crucial checkpoint to optimize the numbers of spermatocytes entering meiosis during each cycle of spermatogenesis. Disclosure of potential conflicts of interest is found at the end of this article.

Kit ligand 2 promotes murine oocyte growth in vitro

Oocyte-granulosa cell communication, mediated by paracrine factors, is essential for oocyte development. Kit ligand (KITL) is expressed in granulosa cells as soluble (KITL1) or membrane-associated (KITL2) proteins. However, the relative biopotency of each isoform during oocyte development is unknown. Our initial results showed that Kitl2 was down-regulated in cultured granulosa cells. To determine the effect of the two isoforms of KITL on oocyte growth, Kitl-deficient fibroblasts were transfected with constructs expressing either KITL1 or KITL2, and growing oocytes were isolated from 12-day-old mice and cultured on the transfected fibroblasts for 2 days. At the end of culture, oocyte diameters were measured, the incidence of spontaneous germinal vesicle breakdown (GVBD) was noted, and oocytes were analyzed for KIT receptor expression. Oocyte growth occurred only in the presence of the KITL2-producing fibroblasts, and suppression of KITL2 expression impaired oocyte growth. Up-regulation of KIT expression occurred in the presence of KITL2 but not KITL1. The presence of KITL2 inhibited spontaneous GVBD. Meiosis inhibitors did not attenuate the GVBD that occurred in the absence of KITL2, suggesting that this process reflects oocyte degeneration rather than meiotic progression. These results indicate that KITL2 is the principal KITL isoform required for oocyte growth and survival in vitro.

The c-kit receptor protein in the testis of green frog Rana esculenta: seasonal changes in relationship to testosterone titres and spermatogonial proliferation

The green frog Rana esculenta is a seasonal breeder. The cyclic changes between almost arrested and highly activated spermatogenesis offer an ideal model to study basic mechanisms of spermatogenesis. In this study, we demonstrated, to our knowledge for the first time, c-kit receptor positive cells in the testis of this amphibian. The presence of c-kit receptor protein was confirmed by western blotting (Wb) analyses carried out in the testis during all the three main phases of the sexual cycle. The antibody recognized a band of about 150 kDa that was correlated with the positive staining in the germinal epithelium. The immunolabelling for c-kit receptor, evaluated by immunohistochemistry (IHC), was localized in I and II spermatogonia (SPG), in I and II spermatocytes, in both elongating spermatids and spermatozoa and in the Leydig cells. Furthermore, c-kit expression showed a seasonal pattern connected with both testicular and plasma profiles of testosterone during the reproductive cycle. The highest expression of c-kit receptor occurred during the reproductive period, when the testis exhibited the maximum concentration of testosterone. In this period, the mitotic activity of germ cell, assessed by both Wb and IHC analyses for proliferating cell nuclear antigen (PCNA), was intensive. Indeed, during the post-reproductive period, testosterone titres were the lowest and the expression of both PCNA and c-kit receptor protein in the testis, although present, is minor when compared with the reproductive phase. This evidence suggests that cell division can continue sufficiently to accumulate SPG for the next spring, when new germinal cells undergo multiplication. Finally, during the pre-reproductive period, testosterone levels begin to increase and mitotic activity of germinal epithelium is comparably enhanced. These events seem to precede the period of maximum stimulated spermatogonial proliferation, i.e. the reproductive period. These results suggest that the c-kit receptor may play a role in germ cell proliferation and provide a basis for future detailed investigation of regulatory factors of the proliferation of SPG.

The radiation-induced block in spermatogonial differentiation is due to damage to the somatic environment, not the germ cells

Radiation and chemotherapeutic drugs cause permanent sterility in male rats, not by killing most of the spermatogonial stem cells, but by blocking their differentiation in a testosterone-dependent manner. However, it is not known whether radiation induces this block by altering the germ or the somatic cells. To address this question, we transplanted populations of rat testicular cells containing stem spermatogonia and expressing the green fluorescent protein (GFP) transgene into various hosts. Transplantation of the stem spermatogonia from irradiated adult rats into the testes of irradiated nude mice, which do not show the differentiation block of their own spermatogonia, permitted differentiation of the rat spermatogonia into spermatozoa. Conversely transplantation of spermatogonial stem cells from untreated prepubertal rats into irradiated rat testes showed that the donor spermatogonia were able to colonize along the basement membrane of the seminiferous tubules but could not differentiate. Finally, suppression of testosterone in the recipient irradiated rats allowed the differentiation of the transplanted spermatogonia. These results conclusively show that the defect caused by radiation in the rat testes that results in the block of spermatogonial differentiation is due to injury to the somatic compartment. We also observed colonization of tubules by transplanted Sertoli cells from immature rats. The present results suggest that transplantation of spermatogonia, harvested from prepubertal testes to adult testes that have been exposed to cytotoxic therapy might be limited by the somatic damage and may require hormonal treatments or transplantation of somatic elements to restore the ability of the tissue to support spermatogenesis.

Impairment of spermatogenesis leading to infertility

Highly differentiated spermatozoa are generated through multiple cellular and molecular processes maintained by Sertoli cells. The cellular events associated with germ cells include proliferation, protein folding and transportation, as well as sequential changes in chromatin and cell organelles. These processes are strictly controlled by the expression of specific genes, including transcription and DNA replication/repair. This complex spermatogenesis is impaired by a mutation such as gene knockout, which leads to a variety of morphological and functional abnormalities found in mature spermatozoa. An overview of spermatogenesis impairment induced by gene knockout is provided in the present review.

Effects of dibromoacetic acid on murine spermatozoa and testis

Background and Aims:   Bromoacetic acids are a by-product of water ozonation and dibromoacetic acid (DBAA) in particular, which is a by-product of disinfection, inhibits male reproductive functions. In order to understand its effects, the spermatozoa and testes of mice were exposed to DBAA. Methods:   Twelve-week-old ICR mice were exposed to 10 p.p.m. DBAA. They were examined in regards to effects on the weights of body, testis and epididymis, the histological changes of tesits and the protein expression in testis. Results:   Neither the bodyweight nor the weights of the testis and epididymis of the exposed mice was affected, but approximately 13% of spermatozoa obtained from the cauda epididymis were motile with a drop-shaped head, and structures resembling residual bodies were found in the testis. Moreover, the expression of two testis proteins was changed by exposure to DBAA. Conclusions:   It was likely that DBAA inhibited male reproductive functions by disturbance of spermatogenesis via change of protein expression. (Reprod Med Biol 2004; 3: 85-93).

The testicular-derived Sertoli cell: cellular immunoscience to enable transplantation

There is a renewed enthusiasm for the potential of cellular transplantation as a therapy for numerous clinical disorders. The revived interest is largely due to the unprecedented success of the "Edmonton protocol," which produced a 100% cure rate for type I diabetics following the transplantation of human islet allografts together with a modified immunosuppressive regimen. While these data provide a clear and unequivocal demonstration that transplantation is a viable treatment strategy, the shortage of suitable donor tissue together with the debilitating consequences of lifelong immunosuppression necessitate a concerted effort to develop novel means to enable transplantation on a widespread basis. This review outlines the use of Sertoli cells to provide local immunoprotection to cografted discordant cells, including those from xenogeneic sources. Sertoli cells are normally found in the testes where one of their functions is to provide local immunologic protection to developing germ cells. Isolated Sertoli cells 1) engraft and self-protect when transplanted into allogeneic and xenogeneic environments, 2) protect cografted allogeneic and xenogeneic cells from immune destruction, 3) protect islet grafts to reverse diabetes in animal models, 4) enable survival and function of cografted foreign dopaminergic neurons in rodent models of Parkinson's disease (PD), and 5) promote regeneration of damaged striatal dopaminergic circuitry in those same PD models. These benefits are discussed in the context of several potential underlying biological mechanisms. While the majority of work to date has focused on Sertoli cells to facilitate transplantation for diabetes and PD, the generalized ability of these unique cells to potently suppress the local immune environment opens additional clinical possibilities.

C-kit receptor and its possible function in human spermatozoa

The presence and role of the c-kit proto-oncogene protein was investigated in the mature sperm of the human. A polyclonal antibody against the c-kit peptide was used to perform immunohistochemical (IHC) staining, electron microscopy (EM) studies, and Western blot analysis. The acrosomal region of fresh sperm specifically stained with the antibody. No acrosomal staining or staining limited to the equatorial region was noted in the acrosome-reacted (AR) sperm. EM studies demonstrated immunogold label on the plasma membrane (PM) of the acrosome, and confirmed the lack of binding following the acrosome reaction. A 150 kDa band was detected by Western blot analysis. This protein was released from the sperm surface during sperm capacitation and the acrosome reaction. Antibody against the c-kit receptor significantly inhibited the acrosome reaction and increased sperm agglutination, but did not significantly inhibit sperm motility. These results suggest that the c-kit receptor protein is present in mature human sperm and is released during capacitation and/or the acrosome reaction. The assessment of the c-kit receptor may also be a useful assay for sperm function in male infertility.

2,5-hexanedione-induced testicular injury

Now in its third decade of mechanistic investigation, testicular injury caused by 2,5-hexanedione (2,5-HD) exposure is a well-studied model with a rich database. The development of this model reflects the larger changes that have moved biology from a branch of chemistry into the molecular age. Critically examined in this review is the proposed mechanism for 2,5-HD-induced testicular injury in which germ cell maturation is disrupted owing to alterations in Sertoli cell microtubule-mediated functions. The goal is to evaluate the technical and conceptual approaches used to assess 2,5-HD-induced testicular injury, to highlight unanswered questions, and to identify fruitful avenues of future research.

The role of the c-kit receptor in the regenerative differentiation of rat Leydig cells

To determine the physiological role of the c-kit receptor, which is highly expressed in Leydig cells, the regenerative differentiation of Leydig cells was studied following transient degeneration induced by ethane dimethyl sulphonate (EDS) in c-kit-deficient mutant rats (Ws/Ws). EDS caused the destruction of Leydig cells; their functional recovery was evaluated by the weight change of the target organs of androgens, which occurred at the same rate in Ws/Ws and wild-type rats. These results indicate that the tyrosine kinase activity of the c-kit receptor does not play an essential role in the regenerative differentiation of Leydig cells.

Development of a conditionally immortalized testicular Sertoli cell line RTS3-3 from adult transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen gene

Transgenic mice and rats harboring temperature-sensitive simian virus 40 (tsSV40) large T-antigen gene are useful for establishing cell lines from tissues. We succeeded in establishing a conditionally immortalized testicular Sertoli cell line, RT3-3, from adult transgenic rats harboring the oncogene. The cells grew at permissive (33 degrees C) and intermediate (37 degrees C) temperatures but not at nonpermissive temperature (39 degrees C). Large T-antigen was expressed at 33 and 37 degrees C, whereas the expression level was gradually decreased at 39 degrees C, suggesting that the temperature-sensitive growth characteristics arise as a result of the function of tsSV40 large T-antigen. The cells showed biochemical features associate with normal Sertoli cells including expressions of mRNAs of sulfated glycoprotein-2 (SGP-2), transferrin (TF) and steel factor. Quantitative polymerase chain reaction revealed that nonpermissive temperature induced increase in the level of SGP-2. Moreover, levels of SGP-2 and/or TF were significantly elevated in the cells treatment with sodium butyrate and retinoic acid, inducers of cellular differentiation. To our knowledge, this is the first report of the establishment of a testicular Sertoli cell line from the transgenic rats. Thus, the conditionally immortalized cell line RTS3-3 with unique characteristics may serve as good experimental in vitro models for basic and applied biology of testicular Sertoli cells.

Anandamide activity and degradation are regulated by early postnatal aging and follicle-stimulating hormone in mouse Sertoli cells

Anandamide (AEA), a prominent member of the endogenous ligands of cannabinoid receptors (endocannabinoids), is known to adversely affect female fertility. However, a potential role of AEA in male reproductive functions is unknown. Here we report evidence that immature mouse Sertoli cells have the biochemical tools to bind and inactivate AEA, i.e. a functional type-2 cannabinoid receptor (CB2R), a selective AEA membrane transporter, and an AEA-degrading enzyme fatty acid amide hydrolase. We show that, unlike CB2R, the activity of AEA membrane transporter and the activity and expression of FAAH decrease, whereas the apoptosis-inducing activity of AEA increases with age during the neonatal period. We also show that FSH reduces the apoptotic potential of AEA, but not that of its nonhydrolyzable analog methanandamide. Concomitantly, FSH enhances FAAH activity in a manner dependent on mRNA transcription and protein synthesis and apparently involving cAMP. These data demonstrate that Sertoli cells partake in the peripheral endocannabinoid system, and that FSH reduces the apoptotic potential of AEA by activating FAAH. Taken together, it can be suggested that the endocannabinoid network plays a role in the hormonal regulation of male fertility.

Human recombinant stem cell factor promotes spermatogonial proliferation, but not meiosis initiation in organ culture of newt testis fragments

We previously showed that mammalian FSH stimulates the proliferation of newt spermatogonia and induces their differentiation into primary spermatocytes in vitro. In the current study, to examine a possibility that stem cell factor (SCF) is involved in the proliferation of newt spermatogonia and/or their differentiation into primary spermatocytes, human recombinant SCF (rhSCF) was added to organ culture of testicular fragments. rhSCF was found to stimulate the spermatogonial proliferation and the spermatogonia progressed to the seventh generation that is the penultimate stage before primary spermatocyte stage. However, the spermatogonia did not differentiate into primary spermatocytes, but instead died of apoptosis. These results indicate that rhSCF promotes the proliferation of newt spermatogonia, but not the initiation of meiosis.

Developmental study of the different effects on the hybrid sterility of Kit and KitW-v alleles paired with Kit from Mus spretus

The combination of the KitW or KitW-n mutant alleles and KitS from Mus spretus results in male hybrid sterility with small testes. In the present study, reproduction of the combination between KitW-v and KitS alleles was examined. The KitW-v/KitS male was fertile and the histologic structure was normal; the seminiferous tubules showed all of the normal stages of spermatogenesis. The postnatal development of the testis at 8, 12, 16 and 20 days was also studied in the fertile +Kit/+Kit and KitW-v/KitS males and the sterile KitW/KitS. The results showed that at 8 days there was no noticeable difference among the three genotype combinations, while from 12 to 20 days spermatogenesis in the KitW/KitS male nearly stopped before the meiosis stage. The expression of Kit receptor protein from the KitS allele in the sterile testis of the KitW/KitS male was confirmed using western blot analysis. The Kit ligand derived from M. spretus showed two amino acid changes in the extracellular domain compared with that from C57BL and it appears that the ligand-receptor interaction between C57BL and SPR may influence the male hybrid sterility of KitW/KitS.

Differential expression of growth factors in irradiated mouse testes

PURPOSE

By using as an experimental model the male mouse gonad, which contains both radiosensitive (germ) and radioresistant (somatic) cells, we have studied the growth factor (and/or receptor) expression of transforming growth factor-beta receptor (TGFbeta RI), stem cell factor (SCF), c-kit, Fas-L, Fas, tumor necrosis factor receptor (TNF R55), and leukemia inhibiting factor receptor (LIF-R) after local irradiation.

METHODS AND MATERIALS

Adult male mice were locally irradiated on the testes. Induction of apoptosis in the different testicular cell types following X-ray radiation was identified by the TdT-mediated dUTP Nick End Labeling (TUNEL) approach. Growth factor expression was evidenced by semiquantitative RT-PCR and Western blot analyses.

RESULTS

Apoptosis, identified through the TUNEL approach, occurred in radiosensitive testicular (premeotic) germ cells with the following kinetics: the number of apoptotic cells increased after 24 h (p < 0.001) and was maximal 48 h after a 2-Gy ionizing radiation (p < 0.001). Apoptotic cells were no longer observed 72 h after a 2-Gy irradiation. The number of apoptotic cells increased with the dose of irradiation (1-4 Gy). In the seminiferous tubules, the growth factor expression in premeiotic radiosensitive germ cells was modulated by irradiation. Indeed Fas, c-kit, and LIF-R expression, which occurs in (radiosensitive) germ cells, decreased 24 h after a 2-Gy irradiation, and the maximal decrease was observed with a 4-Gy irradiation. The decrease in Stra8 expression occurred earlier, at 4 h after a 2-Gy irradiation. In addition, a significant (p < 0.03) decrease in Stra8 mRNA levels was observed at the lowest dose used (0.5 Gy, 48 h). Moreover, concerning a growth factor receptor, such as TGFbeta RI, which is expressed both in radiosensitive and radioresistant cells, we observed a differential expression depending on the cell radiosensitivity after irradiation. Indeed, TGFbeta RI expression was increased after irradiation in interstitial radioresistant testicular cells in a dose- and time-dependent manner, while it decreased in seminiferous radiosensitive (germ cells) testicular cells. Such a differential expression between radioresistant and radiosensitive cells in TGFbeta RI levels was observed in terms of both mRNA and protein. In contrast, the growth factors specifically expressed in the somatic radioresistant (Sertoli) cells in the seminiferous tubules (SCF, Fas-L, TNF R55) were not affected by ionizing radiation (up to 4 Gy, 72 h).

CONCLUSION

Growth factor expression decreased in the radiosensitive testicular cells after irradiation. Such a decrease occurred before the detection of apoptosis using the TUNEL approach. TGFbeta RI mRNA levels decreased in the radiosensitive cells, whereas it increased in the radioresistant cells, suggesting that TGFbeta RI may represent a biomarker of the intrinsic radiosensitivity of cells.

Stem cell factor functions as a survival factor for mature Leydig cells and a growth factor for precursor Leydig cells after ethylene dimethane sulfonate treatment: implication of a role of the stem cell factor/c-Kit system in Leydig cell development

The significance of the interaction between Sertoli cell-produced stem cell factor (SCF) and its receptor, c-kit, on Leydig cells (LCs) during LC development and differentiation is unknown. In the present study, we investigated the potential role of the SCF/c-kit system in LC apoptosis and precursor LC proliferation after ethylene dimethane sulfonate (EDS) treatment in rats. A function-blocking anti-c-kit antibody, ACK-2, was used to block SCF/c-kit interaction at four time points, corresponding to the peak of LC apoptosis and three waves of proliferation of precursor LCs. Blockade of SCF/c-kit interaction by ACK-2 accelerated LC apoptosis and inhibited proliferation of precursor LCs during the first two waves of precursor LC proliferation around days 3-4 and day 10, but not the third wave of precursor LC proliferation around day 20 after EDS treatment. The data suggest that the soluble SCF might act as a survival factor for mature LCs and a growth factor for precursor LCs after EDS-induced LC depletion. This is also supported by a close correlation between the oscillating levels of soluble SCF mRNA and the profiles of LC apoptosis and regeneration. Since regeneration of the LC population after EDS treatment resembles the development of adult-type LCs during prepubertal life, the present findings imply that soluble SCF might participate in regulation of the formation of the LC population during testicular development. Our data also support a model in which delicate and reciprocal regulation exists between soluble SCF production by Sertoli cells, testosterone production by LCs, and pituitary gonadotropins.

Role of c-kit in mammalian spermatogenesis

The tyrosine-kinase receptor c-kit and its ligand, stem cell factor (SCF), are essential for the maintenance of primordial germ cells (PGCs) in both sexes. However, c-kit and a post-meiotic-specific alternative c-kit gene product play important roles also during post-natal stages of spermatogenesis. In the adult testis, the c-kit receptor is re-expressed in differentiating spermatogonia, but not in spermatogonial stem cells, whereas SCF is expressed by Sertoli cells under FSH stimulation. SCF stimulates DNA synthesis in type A spermatogonia cultured in vitro, and injection of anti-c-kit antibodies blocks their proliferation in vivo. A point mutation in the c-kit gene, which impairs SCF-mediated activation of phosphatidylinositol 3-kinase, does not cause any significant reduction in PGCs number during embryonic development, nor in spermatogonial stem cell populations. However males are completely sterile due to a block in the initial stages of spermatogenesis, associated to abolishment of DNA-synthesis in differentiating A1-A4 spermatogonia. With the onset of meiosis c-kit expression ceases, but a truncated c-kit product, tr-kit, is specifically expressed in post-meiotic stages of spermatogenesis, and is accumulated in mature spermatozoa. Microinjection of tr-kit into mouse eggs causes their parthenogenetic activation, suggesting that it might play a role in the final function of the gametes, fertilization.

Inhibitory effect of sodium salicylate on nitric oxide production from TM4 sertoli cells

Nitric oxide (NO) has been proposed to play a role in a variety of inflammatory diseases. Sodium salicylate (NaSal) is the most commonly used anti-inflammatory agent. We investigated whether NaSal can diminish the production of NO in TM4 Sertoli cells. TM4 Sertoli cells produced a small amount of NO upon treatment with recombinant interferon-gamma (rIFN-gamma). The effect of rIFN-gamma was enhanced markedly by the addition of recombinant TNF-alpha (rTNF-alpha) in a dose-dependent manner. NaSal (10 and 20 mM) significantly inhibited NO production from TM4 Sertoli cells induced by rIFN-gamma plus rTNF-alpha. In addition, rIFN-gamma in combination with rTNF-alpha showed a marked increase of the expression of inducible NO synthase (iNOS) protein. Western blot analysis revealed that NaSal (10 and 20 mM) blocked a step of iNOS protein synthesis. The rIFN-gamma plus rTNF-alpha-induced nuclear factor-kappaB (NF-kappaB) activation was significantly blocked by NaSal (10 and 20 mM). On the other hand, neither staurosporine nor polymyxin B significantly inhibited NO production from TM4 Sertoli cells induced by rIFN-gamma plus rTNF-alpha. The present results indicate that NaSal inhibits rIFN-gamma plus rTNF-alpha-induced NO production in TM4 Sertoli cells via the signal transduction pathway of NF-kappaB activation.

Regulation of proliferation and differentiation in spermatogonial stem cells: the role of c-kit and its ligand SCF

To study self-renewal and differentiation of spermatogonial stem cells, we have transplanted undifferentiated testicular germ cells of the GFP transgenic mice into seminiferous tubules of mutant mice with male sterility, such as those dysfunctioned at Steel (Sl) locus encoding the c-kit ligand or Dominant white spotting (W) locus encoding the receptor c-kit. In the seminiferous tubules of Sl/Sl(d) or Sl(17H)/Sl(17H) mice, transplanted donor germ cells proliferated and formed colonies of undifferentiated c-kit (−) spermatogonia, but were unable to differentiate further. However, these undifferentiated but proliferating spermatogonia, retransplanted into Sl (+) seminiferous tubules of W mutant, resumed differentiation, indicating that the transplanted donor germ cells contained spermatogonial stem cells and that stimulation of c-kit receptor by its ligand was necessary for maintenance of differentiated type A spermatogonia but not for proliferation of undifferentiated type A spermatogonia. Furthermore, we have demonstrated that their transplantation efficiency in the seminiferous tubules of Sl(17H)/Sl(17H) mice depended upon the stem cell niche on the basement membrane of the recipient seminiferous tubules and was increased by elimination of the endogenous spermatogonia of mutant mice from the niche by treating them with busulfan.

The potential role of stem cell factor and its receptor c-kit in the mouse blastocyst implantation

Embryo implantation is a complex process that requires the interaction of embryo and endometrium. Several growth factors and cytokines appear to be involved in this process. Stem cell factor (SCF) and its receptor c-kit regulate the proliferation and survival of germ cells and play an important role in follicular development. However, little information is available on the role of SCF and c-kit in the process of blastocyst implantation. In the present study, we examined the expression of SCF and c-kit mRNA in mouse embryos and in the stromal and epithelial cells of the uterine endometrium by reverse transcription-polymerase chain reaction (RT-PCR). SCF mRNA was expressed in the spreading blastocysts and endometrial cells, with especially strong expression occurring in the stromal cells. Expression of c-kit mRNA was detected in the blastocysts and spreading blastocysts, as well as in the endometrial cells. By immunocytochemical studies, staining for c-kit protein was observed in the in-vitro spreading trophoblasts. We found that 50-100 ng/ml SCF significantly promoted the expansion of the surface area of the spreading blastocysts (P < 0.01). These results are consistent with the hypothesis that SCF derived from endometrial cells and the implanting embryo exerts paracrine and/or autocrine action on the process of implantation by stimulating trophoblast outgrowth through its receptor c-kit.

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.

Enhanced Retroviral Transduction of 5-Fluorouracil–Resistant Human Bone Marrow (Stem) Cells Using a Genetically Modified Packaging Cell Line

Pluripotent hematopoietic stem cells (PHSC) are rare cells capable of multilineage differentiation, long-term reconstituting activity and extensive self-renewal. Such cells are the logical targets for many forms of corrective gene therapy, but are poor targets for retroviral mediated gene transfer owing to their quiescence, as retroviral transduction requires that the target cells be cycling. To try and surmount this problem we have constructed a retroviral producer line that expresses the membrane-bound form of human stem cell factor (SCF) on its cell surface. These cells are capable, therefore, of delivering a growth signal concomitant with recombinant retroviral vector particles. In this report we describe the use of this cell line to transduce a highly quiescent population of cells isolated from adult human bone marrow using the 5-fluorouracil (FU) resistance technique of Berardi et al. Quiescent cells selected using this technique were transduced by cocultivation with retroviral producers expressing surface bound SCF or with the parent cell line that does not. Following coculture, the cells were plated in long-term bone marrow culture for a further 5 weeks, before plating the nonadherent cells in semisolid media. Colonies forming in the semisolid media over the next 14 days were analyzed by polymerase chain reaction for the presence of the retroviral vector genome. Over six experiments, the transduction frequency of the quiescent 5-FU resistant cells using the SCF-expressing producer line averaged about 20%, whereas those transduced using the parent producer line showed evidence of reduced levels or no transduction.

The c-kit receptor and its possible signaling transduction pathway in mouse spermatozoa

The presence and role of the c-kit protein was investigated in the mature sperm of the mouse. The c-kit monoclonal antibody (mAb) ACK2 reacted specifically with the acrosomal region and the principal piece of fixed noncapacitated sperm but did not react with the acrosome region in acrosome-reacted sperm. ACK2 significantly inhibited the acrosome reaction; this inhibition was relieved by the calcium ionophore A23187. The kit ligand stem cell factor (SCF) significantly increased the percentage of sperm undergoing acrosome reaction. This increase was partially inhibited by the calcium channel inhibitor (verapamil), the PI3k inhibitor (wortmannin), and the PLC inhibitor (U-73122). ACK2 predominantly recognized c-kit proteins of 33, 48, and 150 kDa by Western blotting of mouse sperm extracts. The 48- and 150-kDa protein bands were released into the media and tyrosine autophosphorylated at low basal levels during acrosome reaction. On stimulation with SCF, the level of c-kit phosphorylation increased significantly. These findings suggest that c-kit is present in mature sperm, and its binding to SCF may result in the activation of PLC gamma 1 and PI3K, leading to receptor autophosphorylation, and ultimately may play a role in capacitation and/or the acrosome reaction.

Leuprolide, a gonadotropin-releasing hormone agonist, reestablishes spermatogenesis after 2,5-hexanedione-induced irreversible testicular injury in the rat, resulting in normalized stem cell factor expression

2,5-Hexanedione (2,5-HD) exposure in the rat produces irreversible testicular atrophy, a model of human male infertility that can be used for mechanistic and therapeutic studies. Following testicular injury by 2,5-HD, stem cell factor (SCF), a Sertoli cell-derived growth factor that binds the c-kit receptor on spermatogonia, is altered in its expression, changing from predominantly membrane SCF to predominantly soluble SCF. The goals of this study were 2-fold: first, evaluate leuprolide, a GnRH agonist, as a therapy for 2,5-HD-induced testicular atrophy, and second, examine changes in SCF expression during testicular injury and following recovery from injury. Rats exposed to 2,5-HD showed a nearly complete testicular atrophy that could be reversed by leuprolide therapy. Using RT-PCR, preferential expression of membrane SCF was associated with spermatogenesis, whereas soluble SCF expression was associated with atrophy. In conclusion, 2,5-HD exposure altered the form of SCF expressed and disrupted spermatogenesis; leuprolide therapy allowed recovery of spermatogenesis, which correlated with a normalization in growth factor expression in an otherwise irreversibly atrophic testis.

Coexpression of multiple Sertoli cell and Leydig cell marker genes in the spontaneous testicular tumor of F344 rat: evidence for phenotypical bifurcation of the interstitial cell tumor

The development of testicular tumor has been frequently observed in some laboratory rat strains. In the present study, we have further characterized the testicular tumor that spontaneously develops in the F344 rat (F344/Jcl). Tumor cells first appeared in the interstitium and developed into multifocal nodular lesions. In the later stage, the whole testes were occupied by tumor cells that consisted of three different types of cells in morphological appearance: large clear type, small eosinophilic type and intermediate type. To determine the character of these cells, we examined the expression of marker genes for Sertoli cells (e.g., transferrin) and Leydig cells (e.g., 3 beta-hydroxysteroid dehydrogenase 1 (3 beta-HSD 1)). Transferrin and 3 beta-HSD 1 mRNAs were found in all 8 tumor samples analyzed by northern blotting. By in situ hybridization, we observed a substantial amount of 3 beta-HSD 1 mRNA and little or no transferrin mRNA in the large clear cells. In contrast, the small eosinophilic cells showed little or no 3 beta-HSD 1 mRNA and a large amount of transferrin mRNA, suggesting that the tumor was a mixture of at least two types of cells. Other Sertoli cell marker genes, such as cyclic protein 2 and sulfated glycoprotein 2, were expressed in all 8 tumors analyzed, and testin and steel factor (SLF), the c-kit receptor ligand, were also expressed in some of the tumors (testin, 75%; SLF, 25%), while other Leydig cell markers, LH receptor and c-kit, were expressed in 87% and 80% of the tumors, respectively. These results indicate that the spontaneous testicular tumor of F344 rat is of interstitium origin, showing phenotypical bifurcation possibly via transdifferentiation.

Hormonally regulated expression and alternative splicing of kit ligand may regulate kit-induced inhibition of meiosis in rat oocytes

Mutations in the genes encoding the Kit tyrosine kinase receptor or kit ligand (KL) cause numerous phenotypic defects, including sterility. In the postnatal ovary, Kit is expressed on the oocyte surface and KL is produced by the surrounding granulosa cells, but its function in these cells is still unknown. The purpose of this study was to determine the role KL/Kit interactions play in the regulation of oocyte meiosis. Here, we demonstrate that meiotically arrested rat oocytes that are microinjected with Kit antisense oligonucleotides have decreased Kit expression. This decreased expression is associated with an increased ability of these oocytes to resume meiosis compared with those microinjected with missense oligonucleotides or buffer alone. In addition, oocytes cultured in the presence of KL were delayed in their resumption of meiosis, but KL could not enhance the meiosis inhibitory effects of dibutyryl cAMP, suggesting that KL operates through a mechanism that is independent of cAMP. Human chorionic gonadotropin-induced meiotic resumption in oocytes was accompanied by a shift in follicular granulosa cell KL expression from membrane-bound to soluble forms and a loss of expression of both forms of KL in cumulus cells. Thus, KL-activated Kit inhibits meiotic progression, and the in vivo luteinizing hormone-stimulated resumption of meiosis may negate Kit activity by a localized decrease in KL expression and by altering the form of KL produced within the follicle.

Cloning and characterization of the 5' flanking region of the stem cell factor gene in rat Sertoli cells

In order to elucidate the molecular basis of stem cell factor (SCF, or steel factor/kit ligand) expression in Sertoli cells of rat testis, 1.5 kb of the 5' flanking region of the SCF gene was isolated and characterized. The transcriptional start point (tsp) was identified by primer extension assay and a rapid amplification of cDNA ends (RACE) assay. A TATA box was found 29 base pairs (bp) upstream from the tsp, and a number of transcription factor consensus sequences, including several AP2 and Spl sites, were identified. The transcriptional activity of the 1.5 kb 5' flanking region was analyzed by deletion constructs using a firefly luciferase-encoding gene (luc) expression vector transiently transfected into primary rat Sertoli cells and other SCF positive and negative cell lines. For all the cells and cell lines examined, a -119 bp to +43 bp fragment including the tsp was sufficient for SCF promoter activity, and the core promoter activity was not significantly changed by inclusion of upstream sequences as far as -1461 bp. These results indicate that additional sites outside of this promoter region are needed to define the cell-specific regulatory elements of SCF expression. The transcriptional activities of all SCF deletion constructs treated with cyclic adenosine 3',5'-monophosphate (cAMP) and forskolin were increased two- to threefold, indicating that SCF transcription in Sertoli cells is regulated by a cAMP-dependent pathway in the proximal promoter region.

The dominant white spotting oncogene allele Kit(W-42J) exacerbates XY(DOM) sex reversal

The Y chromosome from certain populations of M. m. domesticus is incapable of normal testis determination in the B6 inbred strain resulting in XY hermaphrodites or XY females (XY(DOM) sex reversal). B6 consomic strains have been developed with either transient (B6-Y(AKR)) or severe (B6-Y(TIR)) XY(DOM) sex reversal. We report that a point mutation, the dominant white spotting oncogene allele, Kit(W-42J), exacerbates XY(DOM) sex reversal. In B6-Y(AKR), penetrance of the trait is low; however, in B6-Y(TIR), Kit(W-42J) exacerbated sex reversal to such an extent that almost all XY progeny developed into females. The exacerbation of sex reversal was not linked to retardation of early fetal growth or reduction of testis size. Furthermore, semiquantitative RT-PCR for the testis-determining gene, Sry, suggests that exacerbation of sex reversal in B6-Y(TIR) is not due to blockade of Sry expression, a substantial delay in initiation of Sry expression, or exceptionally low levels of Sry mRNAs. We propose that Kit(W-42J) enhances sex reversal by adversely affecting a critical step in testis differentiation that is downstream of Sry.

Mammalian oocyte growth in vitro is stimulated by soluble factor(s) produced by preantral granulosa cells and by Sertoli cells

We have evaluated the possibility that mouse oocyte growth in vitro could be achieved under the influence of soluble compound(s) released by different somatic cell types. For this purpose, zona-free denuded oocytes from 12-day-old mice were cultured on monolayers of NIH-3T3 fibroblasts, which are able to establish gap junctional communications with them, in the presence or absence of media conditioned by preantral granulosa cells or by Sertoli cells, plated at increasing concentrations from 0.3-1 x 10(6) ml-1 cells. After 3 days, no increase in vitellus diameter was recorded from fibroblast-coupled oocytes maintained in culture medium or in the presence of media conditioned by 0.3 x 10(6) ml-1 Sertoli cells. By contrast, increasing proportions of coupled oocytes grew, provided the continuous presence of media conditioned by 0.5 or 1 x 10(5) ml-1 Sertoli cells, or by 0.3, 0.5, and 1 x 10(5) ml-1 preantral granulosa cells. Since the ligand of c-kit, the growth factor KL, promotes the growth in vitro of oocytes cultured in follicles from 8-day-old mice, an antibody against mouse KL was used to evaluate whether in our culture conditions KL might also be responsible for the growth of oocytes from 12-day-old mice. No inhibition of growth was evident in oocytes cultured directly on preantral granulosa or Sertoli-cell monolayers. Furthermore, the growth of fibroblast-coupled oocytes cultured in media conditioned by preantral granulosa cells was not significantly affected by the presence of this antibody during culture. By contrast, a high percentage of oocytes cultured on fibroblasts in the presence of media conditioned by Sertoli cells showed a significant inhibition of growth and no metabolic cooperativity. It was concluded that, besides KL, other bioactive factor(s) released by either preantral granulosa or Sertoli cells can induce a significant stimulation of mouse oocyte growth in vitro.

Hormonal regulation of the ligand for c-kit in the rat ovary and its effects on spontaneous oocyte meiotic maturation

Kit ligand (KL, c-kit ligand) mRNA was detected in the ovaries of 26-day-old prepubertal rats using in situ hybridization. In antral follicles there was a gradient in the intensity of the hybridization signal across the layers of granulosa cells, with greatest intensity observed in the cumulus granulosa cells enclosing the oocyte, and less signal occurring in the granulosa cells furthest from the oocyte. In age-matched rats 40 hr after injection of pregnant mare serum gonadotropin (PMSG), the pattern of distribution of KL resembled that in the untreated ovaries, although the intensity of the hybridization signal was greater in the PMSG-primed ovaries. This morphological observation was confirmed using Northern blot analysis, which indicated that granulosa cells of PMSG-treated rats had 3.5-fold greater abundance of KL mRNA compared to untreated rats. The abundance of KL mRNA further increased to 7-fold over control levels at 6 hr after PMSG-primed rats were treated with human chorionic gonadotropin (hCG). By contrast, treatment of rats with diethylstilbestrol to stimulate follicular growth did not cause any change in the abundance of KL transcripts. To investigate a potential role for KL in oocyte meiotic maturation, fully grown oocytes were cultured for 24 hr with or without KL (50 or 500 ng/ml). The presence of KL resulted in a significant, albeit transient, delay in the progression of spontaneous meiotic maturation, using the indices of germinal vesicle breakdown and polar body formation. The inhibitory effects of KL were specifically blocked by ACK2, an antibody to the extracellular domain of the c-kit receptor. These results indicate that KL is produced in rat granulosa cells at particularly high levels in the cells closest to the oocyte and that this production may be regulated directly by gonadotropic hormones. Furthermore, KL inhibits the progression of meiosis in cultured oocytes, which suggests a possible role in the maintenance of meiotic arrest that occurs throughout oocyte growth.

Localization of follicle-stimulating hormone (FSH) immunoreactivity and hormone receptor mRNA in testicular tissue of infertile men

Testicular biopsies from 82 oligo- or azoo-spermic male patients were subjected to immunostaining using anti-human FSH antibodies. Histological evaluation showed normal spermatogenesis (nspg) in 7 (FSH: (2.7 +/- 0.7), mixed atrophy (ma) in 63 (FSH:L 5.3 +/- 0.5), and bilateral or unilateral Sertoli Cell Only syndrome (SCO) in 12 (FSH: 21.7 +/- 3.5) patients. For the relationship between FSH values and testicular histology, see Bergmann et al. (1994). FSH immunoreactivity was found exclusively in Sertoli cells and in some interstitial cells. Seminiferous epithelium showing normal or impaired spermatogenesis displayed only weak immunoreactivity compared to intense immunoreaction, i.e. large and numerous vesicles in Sertoli cells of SCO tubules in biopsies showing mixed atrophy or SCO. In addition, h-FSH receptor mRNA was demonstrated by in situ hybridization using biotinylated cDNA antisense oligonucleotides. Hybridization signals were found within the seminiferous epithelium exclusively in Sertoli cell cytoplasm associated with normal spermatogenesis and in epithelia showing different signs of impairment, including SCO. It is concluded that: (1) Sertoli cells are the only cells within the seminiferous epithelium expressing FSH receptors; (2) the accumulation of FSH immunoreactivity in Sertoli cells of SCO tubules appears to be a sign of impaired Sertoli cell function.

Expression of the c-kit protein product in carcinoma-in-situ and invasive testicular germ cell tumours

Carcinoma-in-situ of the testis (CIS) is the precursor of invasive germ cell tumours. It is believed that CIS cells may originate from early fetal gonocytes. Recently, the proto-oncogene c-kit has been implicated as crucial for the development and migration of primordial germ cells. In this study, CIS and overtly invasive human male germ cell tumours were analysed immunohistochemically for expression of the c-kit proto-oncogene protein product. Testicular tissue samples from 36 patients with various types of testicular germ cell neoplasia and 19 control specimens were stained using an indirect immunoperoxidase method. High expression of c-kit was found in almost all cases of CIS, both when the lesion was the only pathology, and when CIS was adjacent to invasive tumours. The Kit staining was retained in seminomas with variable intensity; the majority of cells in tumour mass exhibited c-kit expression in 61% of the samples while focal expression was observed in 39% of the samples studied. No expression of c-kit was detected in non-seminomas or in normal testicular germ cells. High expression of the proto-oncogene in CIS cells supports the hypothesis of their origin from primordial germ cells. In addition, we propose that the c-kit protein product is a new marker for carcinoma-in-situ of the testis.