Localization and expression of the c-kit receptor protein in human and rodent testis and sperm

scRNA-seq reveals that origin recognition complex subunit 6 regulates mouse spermatogonial cell proliferation and apoptosis via activation of Wnt/β-catenin signaling

ABSTRACT

The regulation of spermatogonial proliferation and apoptosis is of great significance for maintaining spermatogenesis. The single-cell RNA sequencing (scRNA-seq) analysis of the testis was performed to identify genes upregulated in spermatogonia. Using scRNA-seq analysis, we identified the spermatogonia upregulated gene origin recognition complex subunit 6 (Orc6), which is involved in DNA replication and cell cycle regulation; its protein expression in the human and mouse testis was detected by western blot and immunofluorescence. To explore the potential function of Orc6 in spermatogonia, the C18-4 cell line was transfected with control or Orc6 siRNA. Subsequently, 5-ethynyl-2-deoxyuridine (EdU) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays, flow cytometry, and western blot were used to evaluate its effects on proliferation and apoptosis. It was revealed that ORC6 could promote proliferation and inhibit apoptosis of C18-4 cells. Bulk RNA sequencing and bioinformatics analysis indicated that Orc6 was involved in the activation of wingless/integrated (Wnt)/ β-catenin signaling. Western blot revealed that the expression of β-catenin protein and its phosphorylation (Ser675) were significantly decreased when silencing the expression of ORC6. Our findings indicated that Orc6 was upregulated in spermatogonia, whereby it regulated proliferation and apoptosis by activating Wnt/β-catenin signaling.

Detection of spermatogonial stem cells in testicular tissue of dogs with chronic asymptomatic orchitis

Chronic asymptomatic idiopathic orchitis (CAO) is an important but neglected cause of acquired infertility due to non-obstructive azoospermia (NOA) in male dogs. The similarity of the pathophysiology in infertile dogs and men supports the dog's suitability as a possible animal model for studying human diseases causing disruption of spermatogenesis and evaluating the role of spermatogonial stem cells (SSCs) as a new therapeutic approach to restore or recover fertility in cases of CAO. To investigate the survival of resilient stem cells, the expression of the protein gene product (PGP9.5), deleted in azoospermia like (DAZL), foxo transcription factor 1 (FOXO1) and tyrosine-kinase receptor (C-Kit) were evaluated in healthy and CAO-affected canine testes. Our data confirmed the presence of all investigated germ cell markers at mRNA and protein levels. In addition, we postulate a specific expression pattern of FOXO1 and C-Kit in undifferentiated and differentiating spermatogonia, respectively, whereas DAZL and PGP9.5 expressions were confirmed in the entire spermatogonial population. Furthermore, this is the first study revealing a significant reduction of PGP9.5, DAZL, and FOXO1 in CAO at protein and/or gene expression level indicating a severe disruption of spermatogenesis. This means that chronic asymptomatic inflammatory changes in CAO testis are accompanied by a significant loss of SSCs. Notwithstanding, our data confirm the survival of putative stem cells with the potential of self-renewal and differentiation and lay the groundwork for further research into stem cell-based therapeutic options to reinitialize spermatogenesis in canine CAO-affected patients.

The effect of imatinib administered in the prenatal period on testis development in rats

BACKGROUND

The purpose of this study was to examine the effects of exposure to imatinib in the prenatal period on testis development in rats.

METHODS

Although all the study groups received intraperitoneal imatinib on prenatal days 1-8, no pregnancy occurred in the Imatinib-80 group. Immunohistochemical analysis, TUNEL, c-kit and PDGF staining revealed no difference between the groups in terms of positivity scoring.

RESULTS

A significant decrease was detected in total sperm counts in the Imatinib-20 group compared to the control group, but the sperm count was higher in the Imatinib-60 group than in the Imatinib-20 group. At biochemical measurements, the drug increased oxidative stress in the testis and serum in the Imatinib-20 group, but caused a decrease in tissue in the Imatinib-60 group. Thiol measurements revealed a decrease in the testis and serum in the Imatinib-60 group, while an increase in serum measurements was observed in the Imatinib-40 group. Analysis revealed no difference between the groups in terms of protamine and histone gene expression levels in testis tissue exposed to imatinib.

CONCLUSION

Our findings show that prenatal exposure to imatinib can lead to histopathological and biochemical changes in testis tissue, but that no adverse effect occurs in nuclear maturation of germ cells during spermiogenesis.

Mechanisms of extramedullary relapse in acute lymphoblastic leukemia: Reconciling biological concepts and clinical issues

Long-term survival rates in childhood acute lymphoblastic leukemia (ALL) are currently above 85% due to huge improvements in treatment. However, 15-20% of children still experience relapses. Relapses can either occur in the bone marrow or at extramedullary sites, such as gonads or the central nervous system (CNS), formerly referred to as ALL-blast sanctuaries. The reason why ALL cells migrate to and stay in these sites is still unclear. In this review, we have attempted to assemble the evidence concerning the microenvironmental factors that could explain why ALL cells reside in such sites. We present criteria that make extramedullary leukemia niches and solid tumor metastatic niches comparable. Indeed, considering extramedullary leukemias as metastases could be a useful approach for proposing more effective treatments. In this context, we conclude with several examples of potential niche-based therapies which could be successfully added to current treatments of ALL.

KIT as a therapeutic target for non-oncological diseases

KIT is a receptor tyrosine kinase that after binding to its ligand stem cell factor activates signaling cascades linked to biological processes such as proliferation, differentiation, migration and cell survival. Based on studies performed on SCF and/or KIT mutant animals that presented anemia, sterility, and/or pigmentation disorders, KIT signaling was mainly considered to be involved in the regulation of hematopoiesis, gametogenesis, and melanogenesis. More recently, novel animal models and ameliorated cellular and molecular techniques have led to the discovery of a widen repertoire of tissue compartments and functions that are being modulated by KIT. This is the case for the lung, heart, nervous system, gastrointestinal tract, pancreas, kidney, liver, and bone. For this reason, the tyrosine kinase inhibitors that were originally developed for the treatment of hemato-oncological diseases are being currently investigated for the treatment of non-oncological disorders such as asthma, rheumatoid arthritis, and alzheimer's disease, among others. The beneficial effects of some of these tyrosine kinase inhibitors have been proven to depend on KIT inhibition. This review will focus on KIT expression and regulation in healthy and pathologic conditions other than cancer. Moreover, advances in the development of anti-KIT therapies, including tyrosine kinase inhibitors, and their application will be discussed.

Expression profiling of c-kit and its impact after esiRNA silencing during gonadal development in catfish

Receptor, c-Kit is a member of a family of growth factor receptors that have tyrosine kinase activity, and are involved in the transduction of growth regulatory signals across plasma membrane by activation of its ligand, kitl/scf. The present study analyzed mRNA and protein expression profiles of c-kit in the gonads of catfish, Clarias gariepinus, using real time PCR, in situ hybridization and immunohistochemistry. Tissue distribution analysis revealed higher expression mainly in the catfish gonads. Ontogeny studies showed minimal expression during early developmental stages and highest during 50-75 days post hatch, and the dimorphic expression in gonads decreased gradually till adulthood, which might suggest an important role for this gene around later stages of sex differentiation and gonadal development. Expression of c-kit was analyzed at various phases of gonadal cycle in both male and female, which showed minimal expression during the resting phase, and higher expression during the pre-spawning phase in male compared to females. In vitro and in vivo induction using human chorionic gonadotropin elevated the expression of c-kit indicating the regulatory influence of hypothalamo-hypophyseal axis. In vivo transient gene silencing using c-kit-esiRNA in adult catfish during gonadal recrudescence showed a decrease in c-kit expression, which affected the expression levels of germ cell meiotic marker sycp3, as well as several factors and steroidogenic enzyme genes that are involved in germ cell development. Decrease in the levels of 11-ketotestosterone and testosterone in serum were also observed after esiRNA silencing. The findings suggests that c-kit has an important role in the process of germ cell proliferation, development and maturation during gonadal development and recrudescence in catfish.

Differentiation of human umbilical cord mesenchymal stem cells into germ-like cells in mouse seminiferous tubules

Our previous study demonstrated that human umbilical cord mesenchymal stem cells (HUMSCs) were capable of differentiation into germ cells in vitro. To assess this potential in vivo, HUMSCs were microinjected into the lumen of seminiferous tubules of immunocompetent mice, which were treated with busulfan to destroy endogenous spermatogenesis. Bromodeoxyuridine labeling studies demonstrated that HUMSCs survived in the tubule for at least 120 days, exhibited a round cell shape typical of proliferating or differentiating germ cells, migrated to the basement of the tubule, where proliferating spermatogonia reside and returned to the luminal compartment, where differentiating spermatids and spermatozoa reside. The migration pattern resembled that of germ cell development in vivo. Immunohistochemical and colocalization studies revealed that transplanted HUMSCs expressed the germ cell markers octamer-binding transcription factor 4, α6 integrin, C-kit and VASA, confirming the germ cell differentiation. In addition, it was observed that tubules transplanted with HUMSCs exhibited marked improvement in the histological features damaged by the chemotherapeutic busulfan, as judged by morphology and quantitative histology. Taken together, these data demonstrated the capacity of HUMSCs to form germ cells in the testes and to repair testicular tissue. These findings suggest a potential utility of HUMSCs to treat the infertility and testicular insufficiency caused by cancer therapeutics.

Intratubular spermatocytic seminomas in 2 sprague-dawley rats

This report describes 2 cases of spontaneous intratubular spermatocytic seminomas in Sprague-Dawley rats. These rats were sacrificed at 10 weeks old (case 1) and 40 weeks old (case 2), respectively. Macroscopically, there were no remarkable changes in either case. Microscopically, tumor cells were observed within a single seminiferous tubule (case 1) or several seminiferous tubules (case 2). The proliferating tumor cells were a tripartite cell population comprising small lymphocyte-like, intermediate-sized or large-sized cells, with frequent mitoses, arranged in sheets or forming a basal layer around a tubule or tubules. Immunohistochemically, the tumor cells were strongly positive for proliferating cell nuclear antigen and weakly positive for c-kit, neuron specific enolase and VASA. Our cases provide valuable background control information for the occurrence of seminoma in rats.

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.

Lentiviral vector transduction of spermatozoa as a tool for the study of early development

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Sperm are mature cell types that can be transduced by lentiviral vectors.

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Lentiviral integration in sperm has been demonstrated.

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Lentivirally transduced sperm is useful for the study of early development.

Spermatozoa and lentiviruses are two of nature’s most efficient gene delivery vehicles. Both can be genetically modified and used independently for the generation of transgenic animals or gene transfer/therapy of inherited disorders. Here we show that mature spermatozoa can be directly transduced with various pseudotyped lentiviral vectors and used in in vitro fertilisation studies. Lentiviral vectors encoding Green Fluorescent Protein (GFP) were shown to be efficiently processed and expressed in sperm. When these transduced sperm were used in in vitro fertilisation studies, GFP expression was observed in arising blastocysts. This simple technique of directly transducing spermatozoa has potential to be a powerful tool for the study of early and pre-implantation development and could be used as a technique in transgenic development and vertical viral transmission studies.

Expression of stem cell markers: OCT4, KIT, ITGA6, and ITGB1 in the male germinal epithelium

Efforts have been made for the isolation and characterization of human stem spermatogonia (SG) which would be of major interest for fertility preservation in oncologic patients. We evaluated the expression of mammalian SG stem cell markers, KIT, OCT4, integrin alpha 6 (ITGA6), and integrin beta 1 (ITGB1) as possible indicators for the isolation of those cells in humans. Two different types of SG were individually isolated by micromanipulation from testicular biopsies of men with conserved spermatogenesis. Expression of mRNA showed the absence of KIT and ITGB1 markers in SG. By immunocytochemistry (IC), protein expression for KIT and integrins revealed two types of SG populations, negative (type-1) and positive (type-2). By immunohistochemistry (IH), protein expression for KIT and ITGB1 also revealed two kinds of SG populations, negative (SG A-dark) and positive (SG A-pale). Results suggest that in humans it may be possible to obtain pure populations of stem SG by using negative KIT((-))/ITGB1((-)) sorting.

Differentiation of human umbilical cord Wharton's jelly-derived mesenchymal stem cells into germ-like cells in vitro

Recent studies have demonstrated that mesenchymal stem cells could differentiate into germ cells under appropriate conditions. We sought to determine whether human umbilical cord Wharton's jelly-derived mesenchymal stem cells (HUMSCs) could form germ cells in vitro. HUMSCs were induced to differentiate into germ cells in all-trans retinoic acid, testosterone and testicular-cell-conditioned medium prepared from newborn male mouse testes. HUMSCs formed "tadpole-like" cells after induction with different reagents and showed both mRNA and protein expression of germ-cell-specific markers Oct4 (POUF5), Ckit, CD49(f) (alpha6), Stella (DDPA3), and Vasa (DDX4). Our results may provide a new route for reproductive therapy involving HUMSCs and a novel in vitro model to investigate the molecular mechanisms that regulate the development of the mammalian germ lineage.

Stage-specific localization and expression of c-kit in the adult human testis

The c-kit receptor (KIT) and its ligand, stem cell factor (SCF), represent one of the key regulators of testicular formation, development, and function and have been extensively studied in various animal models. The present study was undertaken to characterize the pattern of localization and expression of c-kit in normal adult human testis. Immunohistochemical analysis showed that KIT is expressed in the cytoplasm of spermatogonia, acrosomal granules of spermatids, and Leydig cells. Interestingly, a rather heterogenous pattern of expression of the protein along the basement membrane was observed. Intense protein localization in spermatogonia was detected in stages I-III, whereas low expression was observed in stages IV-VI of the seminiferous epithelium, indicating that the expression of the molecule was stage specific. In situ hybridization studies revealed that the transcripts of the gene were also localized in a similar non-uniform pattern. To the best of our knowledge, such a stage-specific expression of KIT has not been reported previously in the human testis. The results of the present study may expand current knowledge about the c-kit/SCF system in human spermatogenesis.

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.

MAGE-A, mMage-b, and MAGE-C proteins form complexes with KAP1 and suppress p53-dependent apoptosis in MAGE-positive cell lines

The MAGE-A, MAGE-B, and MAGE-C protein families comprise the class-I MAGE/cancer testes antigens, a group of highly homologous proteins whose expression is suppressed in all normal tissues except developing sperm. Aberrant expression of class I MAGE proteins occurs in melanomas and many other malignancies, and MAGE proteins have long been recognized as tumor-specific targets; however, their functions have largely been unknown. Here, we show that suppression of class I MAGE proteins induces apoptosis in the Hs-294T, A375, and S91 MAGE-positive melanoma cell lines and that members of all three families of MAGE class I proteins form complexes with KAP1, a scaffolding protein that is known as a corepressor of p53 expression and function. In addition to inducing apoptosis, MAGE suppression decreases KAP1 complexing with p53, increases immunoreactive and acetylated p53, and activates a p53 responsive reporter gene. Suppression of class I MAGE proteins also induces apoptosis in MAGE-A-positive, p53wt/wt parental HCT 116 colon cancer cells but not in a MAGE-A-positive HCT 116 p53-/- variant, indicating that MAGE suppression of apoptosis requires p53. Finally, treatment with MAGE-specific small interfering RNA suppresses S91 melanoma growth in vivo, in syngenic DBA2 mice. Thus, class I MAGE protein expression may suppress apoptosis by suppressing p53 and may actively contribute to the development of malignancies and by promoting tumor survival. Because the expression of class I MAGE proteins is limited in normal tissues, inhibition of MAGE antigen expression or function represents a novel and specific treatment for melanoma and diverse malignancies.

Stem cell factor affects fate determination of human gonocytes in vitro

The stem cell factor (SCF), binding its tyrosine kinase receptor c-Kit, has been shown to play essential roles in the proliferation, differentiation, and survival of germline cells. However, few reports are available about the effect of SCF on the development of human gonocytes within the fetal testis. The objective of this study was to investigate whether SCF affects the biological behaviors of human gonocytes before or after they enter the mitotic arrest stage. Employing an organ culture system, we observed that addition of exogenous SCF could influence the morphology of human gonocytesin vitro. Moreover, SCF was able to trigger the colony formation of round gonocytes, which were characterized positive for alkaline phosphatase activity, Oct-4, SSEA-4, and c-Kit as well. We found that SCF exerted actions in a dose- and age-dependent manner, although the stimulatory effect lasted no more than 14 days. We also showed that SCF played a role in suppressing the apoptosis of human gonocytes. Blocking of SCF signaling with either phosphatidylinositol 3-kinase or mitogen-activated protein kinase inhibitor resulted in similar apoptotic features as well as the SCF-withdrawal cultures. Taken together, we report that SCF acts as a potent regulator in the fate determination of human gonocytes. Our studies should form the basis forin vitrostudies and facilitate investigation of the molecular mechanisms underlying this unique stage.

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.

Epigenetic control of MAGE gene expression by the KIT tyrosine kinase

The Class I MAGE proteins include the MAGE-A, MAGE-B, and MAGE-C antigens, which are normally expressed only in male germ cells but may be aberrantly expressed in melanomas and other tumors. It is known that MAGE gene expression is epigenetically repressed by promoter region methylation in most cells but factors controlling MAGE gene promoter methylation have not been identified. Using transcript microarray analysis and immunoblotting we found that MAGE-A and MAGE-C mRNA and protein are selectively downregulated by pharmacologic inhibition of KIT in KIT-dependent mast cell lines. Methylation-specific polymerase chain reaction studies showed that the MAGE-A3 and MAGE-C2 gene promoter regions were de-methylated in the presence of activated KIT but became methylated on inhibition of KIT, consistent with the downregulation of mRNA and protein. This is early evidence of a tyrosine kinase affecting MAGE gene promoter region methylation and expression, and represents early evidence of a tyrosine kinase in the epigenetic control of gene expression. MAGE proteins suppress apoptosis and promote tumor survival, and are novel targets for functional manipulation and immunotherapy. Understanding the factors controlling MAGE gene expression may allow more effective therapeutic strategies targeting MAGE antigens.

Identification and distribution of a novel platelet-derived growth factor receptor beta variant: effect of retinoic acid and involvement in cell differentiation

We have shown previously that neonatal testicular gonocytes express platelet-derived growth factor receptors (PDGFR) alpha and beta. We report the expression of a novel PDGFRbeta (V1-PDGFRbeta) transcript in gonocytes of 3-d-old rat testes. V1-PDGFRbeta nucleotide sequence spans from intron 6 to exon 23 of the PDGFRbeta gene, and is predicted to encode a protein lacking part of the extracellular domain. V1-PDGFRbeta transcripts are expressed preferentially in developing gonads. The embryonic teratocarcinoma F9 cells, in which differentiation is driven by retinoic acid (RA), express V1-PDGFRbeta, but not wild-type PDGFRbeta. Green fluorescent protein-tagged V1-PDGFRbeta localized mainly in cytosol of F9, MA-10, and COS-1 cells. FLAG and green fluorescent protein-tagged V1-PDGFRbeta displayed tyrosine kinase activities and contain phosphotyrosine residues, suggesting that V1-PDGFRbeta is a cytosolic tyrosine kinase. Treatment of F9 cells with RA induced V1-PDGFRbeta gene expression, concomitant with changes in morphology and increased mRNA expression of collagen IV and laminin B1, suggesting that V1-PFGRbeta is involved in cell differentiation. Similarly, treatment of postnatal d 3 rat gonocytes with RA induced a dose-dependent increase in V1-PDGFRbeta expression together with an increase in c-kit and Stra8, markers of more differentiated germ cells and a concomitant decrease in GFRalpha1, a marker of spermatogonial stem cells. However, an excess of V1-PDGFRbeta inhibited RA-mediated collagen IV and laminin B1 expression and altered both RA-dependent and RA-independent morphological changes in F9 cells, while increasing cell survival. These results suggest that the expression of V1-PDGFRbeta is tightly regulated during differentiation and that it may play an active role in germ cell differentiation.

Risk of germ cell malignancy in children with XY intersex versus isolated cryptorchidism by immunohistochemistry

The risk of subsequent development of testicular germ cell neoplasia is related to presence of underlying developmental defects such as cryptorchidism, in which the risk is around 0.5%, and XY intersex with abdominal testes, in which the risk may be as high as 20-25%. We examined the hypothesis that the increased risk of germ cell malignancy in intersex testes with Y chromosome was a direct consequence of an abnormal increase in number of PLAP/CD117+ immature germ cells into postnatal life. Archival cases of uncomplicated cryptorchidism (CO) and XY intersex (INT) were identified and anonymized, and a subgroup of aged-matched cases had sections immunostained with placental alkaline phosphatase (PLAP) and CD117. From a total of 89 intersex and 105 cryptorchid cases identified, a power calculation to detect a 20% difference in expression between groups (alpha = 0.05, power = 80%) determined that 18 intersex and 36 cryptorchid cases were required. Thus, 58 cases were examined, median age 3 (range birth-11) years, including 39 CO and 19 INT. The prevalence of any PLAP+ germ cells was 2/39 (5.1%) versus 3/19 (15.7%), respectively. (Z = 1.4, p = 0.17). In contrast, 94% of cases showed presence of any CD117+ germ cells, but the frequency of CD117+ cells was not significantly different between groups (t = 0.56, p = 0.58). CD117 and PLAP identify different populations of germ cells in pediatric testes. The extent of increased risk of malignancy in XY INT is not simply related to increased numbers of immature PLAP+/CD117+ germ cells present; additional factors play a pathogenic role.

Insulin-dependent diabetes affects testicular function by FSH- and LH-linked mechanisms

A study was conducted to form a unified hypothesis regarding the gonadotropin-related mechanisms that underlie alterations in the male reproductive system in individuals with diabetes. Streptozotocin-induced diabetes resulted in reduced fertility, prolificacy, and libido. Testes showed a marked decrease in the number and function of Leydig cells, the latter manifested as changes in the expression of biochemical markers, including the GLUT-3 hexose transporter, c-kit, insulin-like growth factor I (IGF-I), androgen receptors, and overall tyrosine phosphorylation, as assessed by Western blot and immunocytochemical analyses. The expression of c-kit, IGF-I, insulin, and follicle-stimulating hormone (FSH) receptors in the seminiferous tubules was also affected. Serum levels of luteinizing hormone (LH), FSH, and testosterone significantly decreased. There was a significant (P <.05) correlation between the serum levels of insulin and FSH. No significant correlation was found between the serum levels of insulin or glucose and LH. On the basis of our results, we conclude that, in insulin-dependent diabetes, 1) Leydig cell function and testosterone production decrease because of the absence of the stimulatory effect of insulin on these cells and an insulin-dependent decrease in FSH, which, in turn, reduces LH levels; and 2) sperm output and fertility are reduced because of a decrease in FSH caused by a reduction in insulin.

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.

Expression of proto-oncogene c-kit receptor in rats (Rattus norvegicus) and identification of a mutant mRNA transcript implicated in spermatogenic failure

The pleiotropic proto-oncogene c-kit receptor, implicated in hematopoiesis and melanogenesis, is also known to play an important role in germ cell proliferation and differentiation although the mechanisms for the latter remain unknown. We studied c-kit expression by RT-PCR in various tissues of both fertile and infertile Brown Norway rats. Using different sets of primers, several regions from within the extracellular domain were amplified, cloned, and sequenced. One set of primers, in addition to the expected 352-bp amplicon, revealed a 276-bp transcript, although its biological functions remain unknown. These two transcripts showed varying levels of expression in different tissues of infertile rats against nearly uniform expression in the fertile animals. Significantly, the 352 bp testis transcript showed mutational hotspots from nucleotide 84-266 in the infertile rats. Analysis of testis and brain genomic DNA from these infertile rats showed mutations only in the testis suggesting this to be a postzygotic event. In contrast, no mutation was detected in the genomic DNA of testis and brain of the fertile rats. Protein expression studies showed complete absence of the cytoplasmic kinase domain and soluble c-kit protein in one of the infertile rats. Histological examination of testis of these infertile animals showed stem cell depletion resulting in fewer germ cells. Based on these results, we infer that 352-bp mutant mRNA transcript is implicated in the spermatogenic failure.

Involvement of death receptor Fas in germ cell degeneration in gonads of Kit-deficient Wv/Wv mutant mice

Kit and its ligand stem cell factor (SCF) play a fundamental role in hematopoiesis, melanogenesis and gametogenesis. Homozygous W(v) mutant mice with a mutation in kit show abnormalities in these cell lineages. Fas is a member of the death receptor family inducing apoptosis. In this study, we generated double-mutant mice (W(v)/W(v):Fas(-/-)) and analyzed histologically their reproductive organs. In testes and ovaries of the double-mutant mice, testicular germ cells and oocytes were detected, respectively, whereas the same-aged W(v)/W(v) mice contained neither cells. In addition, inhibition of Kit signals by administration of anti-Kit mAb, which induces degeneration of testicular germ cells in vivo in wild-type mice, did not cause degeneration in Fas-deficient mice. In testicular germ cells of W(v)/W(v) mutant mice, an increase of Fas expression was observed in spermatogonia. Further, in vitro treatment with SCF was shown to downregulate Fas on fibroblasts expressing exogenous Kit through activation of PI3-kinase/Akt. All the results clearly indicate that Fas-mediated apoptosis is involved in germ cell degeneration accompanied by defects in Kit-mediated signals, and Kit signaling negatively regulates Fas-mediated apoptosis in vivo.

Identification of c-kit-positive cells in the mouse ureter: the interstitial cells of Cajal of the urinary tract

The existence of a pacemaker system in the urinary tract capable of orchestrating the movement of filtrated urine from the ureteral pelvis to the distal ureter and lower urinary tract seems intuitive. The coordinated activity necessary for such movement or "peristalsis" would likely require an intricate network of cells with pacemaker-like activity, as is the case with the interstitial cells of Cajal (ICC) of the gut. We investigated whether these putative pacemaker cells of the urinary tract are antigenically similar to ICC of the gut by using immunofluorescence staining for c-kit, a cell-surface marker specific for ICC. Ureteral, urinary bladder, and urethral tissues were harvested from female mice of the WBB6F1 strain, and fixed sections were prepared and stained for c-kit. Cell networks composed of stellate-appearing, c-kit-positive, ICC-like cells were found in the lamina propria and at the interface of the inner longitudinal and outer circular muscle layers of the ureteral pelvis but not in the urinary bladder or urethra. Thus, like in the gut, c-kit-positive, ICC-like cells are present in the urinary tract but appear to be restricted to the proximal ureter of this murine species.

Localization of protein kinase C theta immunoreactivity to interstitial cells of Cajal in guinea-pig gastrointestinal tract

In the gastrointestinal tract, interstitial cells of Cajal (ICC) are located between nerve fibres and muscle cells and have a role in neuromuscular transmission and muscle contractility. Protein kinase C (PKC) is involved in modulation of muscle contractility by neurotransmitters, but it is not known if PKC has a role in ICC. There are 11 different PKC isoforms. The presence of PKC isoforms in ICC in guinea-pig gastrointestinal tract was examined using fluorescence immunohistochemistry and confocal microscopy. Segments of guinea-pig stomach, duodenum, ileum, proximal and distal colon were fixed in zambonis fixative. Frozen sections and wholemounts were incubated with anti-PKC antibodies (alpha, beta, delta, epsilon, gamma, iota, lambda, mu, theta) followed by fluorescent secondary antibody. Only PKC theta (theta) immunoreactivity was found in ICC. None of the other PKC isoforms (alpha, beta, delta, epsilon, gamma, iota, lambda, mu) localized to the ICC. PKC theta immunoreactivity was prominent in ICC located between the circular and longitudinal muscle layers (ICC-MY) in all regions except stomach and within the circular muscle (ICC-IM) in the large intestine. PKC theta was not present in ICC in the deep muscular plexus in either duodenum or ileum. PKC theta immunoreactivity was present in the cell body and proximal processes of the ICC. The cells containing PKC theta also contained cKit confirming the cells were ICC. ICC-MY in the ileum also contained the neurokinin (NK) 1 receptor. In conclusion, PKC theta is present in pacemaker ICC, but its function is not yet known. Functional studies will be needed to determine the role of this kinase in ICC. Knowing the second messenger cascades and being able to manipulate subpopulations of ICC will add to our understanding of the molecular and cell biology of ICC networks within the gastrointestinal tract and may ultimately help in understanding the aetiology of some gastrointestinal motor pathologies.

The stem cell factor-c-kit system and mast cells in human pancreatic cancer

Stem cell factor (SCF) and its receptor c-kit take part in the regulation of developmental processes of mast cells, hematopoietic stem cells, and melanocytes, as well as in the growth control of human malignancies. To explore the possible role of the SCF-c-kit system and of mast cells in pancreatic cancer, the concomitant expression and distribution of the two molecules were examined in 17 normal and 26 cancerous human pancreatic tissues and in 6 cultured pancreatic cancer cell lines. Mast cell distribution was also evaluated in the same tissue samples. In addition, the effects of SCF and of the c-kit tyrosine-kinase inhibitor STI571 on the growth of the cancer cell lines and of the normal pancreatic ductal cell line TAKA-1 were assessed. SCF immunoreactivity was absent in acinar, ductal, and islet cells of the normal pancreas and faint in pancreatic cancer tissues and cell lines. In contrast, c-kit was clearly present in some normal and hyperplastic ducts of the normal pancreas, in the cancer cells of 73% of the tumor samples, and in all the cell lines tested. Mast cells, identified by tryptase and chymase immunostaining on consecutive tissue sections, showed immunoreactivity for SCF and c-kit in both normal and cancerous specimens and their number was significantly increased (p = 0.03) in pancreatic cancer compared with the normal pancreas. SCF showed a dose-dependent growth inhibitory effect on TAKA-1 cells (p < 0.001), whereas pancreatic cancer cells were resistant to the SCF-induced growth inhibition. Nonetheless, the growth of TAKA-1 cells and pancreatic cancer cells was inhibited by the c-kit tyrosine kinase inhibitor STI571. In conclusion, the SCF-c-kit system, possibly with the contribution of mast cells, may have a growth-regulating role in the normal pancreas, which is altered during malignant transformation.

Expression of L-histidine decarboxylase in mouse male germ cells

Histamine synthesis in male reproductive tissues remains largely unknown. The interaction between stem cell factor and its receptor, c-Kit, has been found to be essential for the maturation of male germ cells and peripheral mast cells. Based on this analogy, we investigated the expression of histidine decarboxylase (HDC), the rate-limiting enzyme of histamine synthesis, in mouse male germ cells. Immunohistochemical analyses revealed that HDC is localized in the acrosomes of spermatids and spermatozoa. In the testis, epididymis, and spermatozoa, a significant amount of histamine and HDC activity were detected. W/W(V) mice, known to lack most of their germ cells in the seminiferous tubules, were found to lack HDC protein expression as well as HDC activity in the testis. An in vitro acrosome reaction induced by a calcium ionophore, caused the release of histamine from epididymal spermatozoa. Our observations indicate that histamine is produced in and released from the acrosomes.

Mast cell distribution and activation in chronic pancreatitis

Chronic pancreatitis (CP) is characterized by mononuclear inflammatory cell infiltration and replacement of the destroyed parenchyma by fibrous tissue. Recently, mast cells have been implicated in chronic inflammatory processes with fibrous tissue deposition. Therefore, the number and distribution of mast cells and their state of activation were evaluated in 12 normal specimens and in 46 specimens of CP with different causes (alcoholic, tropical, and idiopathic). Furthermore, the presence of stem cell factor (SCF), the main mast cell growth factor, and of its receptor, c-kit, was also assessed. In CP tissues, mast cells were localized both in the fibrotic areas and in the residual acinar parenchyma. The total number of mast cells was significantly higher in CP than in the normal pancreas (P < .0001) and correlated positively with the extent of fibrosis and the intensity of inflammation. Immunoglobulin E (IgE)-dependent mast cell activation was higher in CP than in the normal pancreas. No differences in mast cell number or IgE positivity were found among the 3 causes of CP. SCF-and c-kit immunoreactive mast cells were mostly localized in fibrous tissue and around regenerating ducts, which were also positive for c-kit but were negative for SCF. These results suggest that mast cells, activated by an IgE-dependent mechanism and/or by an SCF-c-kit autocrine loop, are a relevant component of the inflammatory infiltrate in CP, independent of the underlying cause. Their localization near degenerating acini and regenerating ducts might indicate that they play a crucial role in tissue destruction and remodeling in CP.

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.

The histopathological differential diagnosis of gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GISTs), initially presumed to be of "true" smooth muscle origin, encompass a heterogeneous, and as yet incompletely understood, group of mesenchymal tumours with respect to their origin, cellular differentiation, and prognosis. Cellular morphology ranges from predominantly spindle shaped to epithelioid in character, whereas differentiation pathways, as determined primarily by immunohistochemistry and ultrastructure, can vary from indeterminate to myoid and/or neural. Recent work has indicated that the interstitial cells of Cajal, a complex cellular network postulated to act as pacemaker cells of the gastrointestinal tract, which exhibit both myoid and neural features, could be candidates for tumour histogenesis. This would provide a plausible and attractive explanation for the variable differentiation pathways identified in the GIST category to date. Nevertheless, the occasional but undisputed location of GISTs outside the gastrointestinal tract (omentum, peritoneum, and retroperitoneum) might mitigate against such an origin, and their histogenesis remains open to debate. The c-kit proto-oncogene, encoding a growth factor receptor with tyrosine kinase activity, has been postulated to play an important role in tumorigenesis because "gain of function" mutations in this gene, localised to chromosome 4q11-21, are being increasingly identified in hereditary and sporadic cases. Monoclonal and polyclonal antibodies directed at the c-kit gene product expressed on the cell surface (CD117/c-kit) appear to be increasingly helpful in resolving the histopathological differential diagnosis between GISTs and true gastrointestinal smooth muscle neoplasms, schwannomas, and other far less frequently occurring mesenchymal tumours at this site. Although tumours with a clinically benign course appear to be more common than their malignant counterparts, no specific histological criteria have as yet been identified to enable an unambiguous prediction of biological behaviour. Increasing tumour size and mitotic activity favour aggressive tumour behaviour, whereas the prognostic value of germline and somatic mutations within the c-kit proto-oncogene remains to be elucidated further. It is the aim of this synopsis to highlight the relevant fundamental and diagnostic developments with respect to this complex group of neoplasms.

Deficiency of Trp53 rescues the male fertility defects of Kit(W-v) mice but has no effect on the survival of melanocytes and mast cells

Mutations of the receptor tyrosine kinase, Kit, or its ligand, mast growth factor (Mgf), affect three unrelated cell populations: melanocytes, germ cells, and mast cells. Kit signaling is required initially to prevent cell death in these lineages both in vitro and in vivo. Mgf appears to play a role in the survival of some hematopoietic cells in vitro by modulating the activity of p53. Signaling by Mgf inhibits p53-induced apoptosis of erythroleukemia cell lines and suppresses p53-dependent radiation-induced apoptosis of bone marrow cells. We tested the hypothesis that cell survival in Kit mutant mice would be enhanced by p53 deficiency in vivo. Double-mutant mice, which have greatly reduced Kit receptor tyrosine kinase activity and also lack Trp53, were generated and the affected cell lineages examined. Mast cell, melanoblast, and melanocyte survival in the double Kit(W-v/W-v):Trp53(-/-) mutants was not increased compared to the single Kit(W-v/W-v):Trp53(+/+) mutants. However, double-mutant males showed an increase in sperm viability and could father litters, in contrast to their homozygous Kit mutant, wild-type p53 littermates. This germ cell rescue appears to be male specific, as female ovaries were similar in mice homozygous for the Kit mutant allele with or without p53. We conclude that defective Kit signaling in vivo results in apoptosis by a p53-independent pathway in melanocyte and mast cell lineages but that in male germ cells apoptosis in the absence of Kit is p53-dependent.

'Paracrine' control of spermatogenesis

Spermatogenesis is a remarkably complex but precise process yielding highly differentiated haploid germ cells from diploid stem cells. Although many factors have been implicated in the paracrine control of spermatogenesis, functional proof is only available for a few regulators. Among those are androgens, growth factors and stem cell factor. Cell- and organ-specific genetargeting will provide important insights into the relevance of local factors controlling male gametogenesis. As testicular communication frequently occurs between rather remote cells and compartments, it is proposed that the term 'local' rather than 'paracrine' mediators/factors should be used, since the latter term refers to communication amongst neighbouring cells (and mainly via diffusion).

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.