Lingual Epithelial Stem Cells and Organoid Culture of Them.

As tongue cancer is one of the major malignant cancers in the world, understanding the mechanism of maintenance of lingual epithelial tissue, which is known to be the origin of tongue cancer, is unquestionably important. However, the actual stem cells that are responsible for the long-term maintenance of the lingual epithelium have not been identified. Moreover, a simple and convenient culture method for lingual epithelial stem cells has not yet been established. Recently, we have shown that Bmi1-positive cells, residing at the second or third layer of the epithelial cell layer at the base of the interpapillary pit (IPP), were slow-cycling and could supply keratinized epithelial cells for over one year, indicating that Bmi1-positive cells are long-term lingual epithelial stem cells. In addition, we have developed a novel lingual epithelium organoid culture system using a three-dimensional matrix and growth factors. Here, we discuss current progress in the identification of lingual stem cells and future applications of the lingual culture system for studying the regulatory mechanisms of the lingual epithelium and for regenerative medicine.

Maintenance of sweat glands by stem cells located in the acral epithelium.

The skin is responsible for a variety of physiological functions and is critical for wound healing and repair. Therefore, the regenerative capacity of the skin is important. However, stem cells responsible for maintaining the acral epithelium had not previously been identified. In this study, we identified the specific stem cells in the acral epithelium that participate in the long-term maintenance of sweat glands, ducts, and interadnexal epidermis and that facilitate the regeneration of these structures following injury. Lgr6-positive cells and Bmi1-positive cells were found to function as long-term multipotent stem cells that maintained the entire eccrine unit and the interadnexal epidermis. However, while Lgr6-positive cells were rapidly cycled and constantly supplied differentiated cells, Bmi1-positive cells were slow to cycle and occasionally entered the cell cycle under physiological conditions. Upon irradiation-induced injury, Bmi1-positive cells rapidly proliferated and regenerated injured epithelial tissue. Therefore, Bmi1-positive stem cells served as reservoir stem cells. Lgr5-positive cells were rapidly cycled and maintained only sweat glands; therefore, we concluded that these cells functioned as lineage-restricted progenitors. Taken together, our data demonstrated the identification of stem cells that maintained the entire acral epithelium and supported the different roles of three cellular classes.

Mouse mesenchymal stem cells can support human hematopoiesis both in vitro and in vivo: the crucial role of neural cell adhesion molecule.

BACKGROUND: We previously established a mesenchymal stem cell line (FMS/PA6-P) from the bone marrow adherent cells of fetal mice. The cell line expresses a higher level of neural cell adhesion molecule and shows greater hematopoiesis-supporting capacity in mice than other murine stromal cell lines. DESIGN AND METHODS: Since there is 94% homology between human and murine neural cell adhesion molecule, we examined whether FMS/PA6-P cells support human hematopoiesis and whether neural cell adhesion molecules expressed on FMS/PA6-P cells contribute greatly to the human hematopoiesis-supporting ability of the cell line. RESULTS: When lineage-negative cord blood mononuclear cells were co-cultured on the FMS/PA6-P cells, a significantly greater hematopoietic stem cell-enriched population (CD34(+)CD38(-) cells) was obtained than in the culture without the FMS/PA6-P cells. Moreover, when lineage-negative cord blood mononuclear cells were cultured on FMS/PA6-P cells and transplanted into SCID mice, a significantly larger proportion of human CD45(+) cells and CD34(+)CD38(-) cells were detected in the bone marrow of SCID mice than in the bone marrow of SCID mice that had received lineage-negative cord blood mononuclear cells cultured without FMS/PA6-P cells. Furthermore, we found that direct cell-to-cell contact between the lineage-negative cord blood mononuclear cells and the FMS/PA6-P cells was essential for the maximum expansion of the mononuclear cells. The addition of anti-mouse neural cell adhesion molecule antibody to the culture significantly inhibited their contact and the proliferation of lineage-negative cord blood mononuclear cells. CONCLUSIONS: These findings suggest that neural cell adhesion molecules expressed on FMS/PA6-P cells play a crucial role in the human hematopoiesis-supporting ability of the cell line.

Preferential expansion of human umbilical cord blood-derived CD34-positive cells on major histocompatibility complex-matched amnion-derived mesenchymal stem cells.

BACKGROUND: We previously found in a murine hematopoietic system that hematopoietic stem cells show high differentiation and proliferation capacity on bone marrow-derived mesenchymal stem cells/stromal cells (microenvironment) with "self" major histocompatibility complex (MHC). DESIGN AND METHODS: We examined whether amnion-derived adherent cells have the characteristics of mesenchymal stem cells, and whether these adherent cells can support the proliferation of umbilical cord blood-derived lineage-negative and CD34-positive cells (Lin(-)CD34(+) cells) obtained from the same fetus to a greater extent than those derived from other fetuses. RESULTS: Culture-expanded amnion-derived adherent cells expressed mesenchymal stem cell markers and HLA-ABC molecules and could differentiate into osteoblasts, adipocytes and chondrocyte-like cells, indicating that the cells have the characteristics of mesenchymal stem cells. The Lin(-)CD34(+) cells purified from the frozen umbilical cord blood were strongly positive for HLA-ABC, and contained a large number of hematopoietic stem cells. When the Lin(-)CD34(+) cells were cultured on the autologous (MHC-matched) or MHC-mismatched amnion-derived adherent cells in short-term assays (hematopoietic stem cell-proliferation) and long-term culture-initiating cell assays, greater expansion of the Lin(-)CD34(+) cells was observed in the MHC-matched combination than in MHC-mismatched combinations. The concentration of granulocyte-macrophage colony-stimulating factor in the culture supernatants of the long-term culture-initiating cell assays was significantly higher in the MHC-matched combination than in MHC-mismatched combinations. CONCLUSIONS: IT is likely that a MHC restriction exists between hematopoietic stem cells and mesenchymal stem cells/stromal cells in the human hematopoietic system and that granulocute-macropage colony-stimulating factor contributes to some extent to the preferential hematopoiesis-supporting ability of the MHC-matched amnion-derived adherent cells.

Organoid Culture of Lingual Epithelial Cells in a Three-Dimensional Matrix.

A novel lingual epithelial organoid culture system using a three-dimensional (3D) matrix and growth factors has recently been established. In the culture system, organoids with multilayered squamous keratinized epithelium and typical morphological features of filiform papillae are generated from single lingual epithelial cells at a high efficiency. The culture system is created in order to observe the differentiation and maturation process of each lingual epithelial stem cell and to observe abnormal organoid formation from malignant cells obtained from carcinogen-treated mice. Thus, our culture system will contribute to the advancement of research into the regulatory mechanism of lingual epithelium and the underlying mechanisms of carcinogenesis.

Facilitation of hematopoietic recovery by bone grafts with intra-bone marrow-bone marrow transplantation.

We have previously shown that T cells can acquire donor-type major histocompatibility complex (MHC) restriction and can interact with both donor-type antigen-presenting cells (APCs) and B cells, when adult donor bones are co-grafted with intravenous (IV) injection of bone marrow cells (BMCs) in order to supply donor bone marrow (BM) stromal cells. We have also found that the direct injection of donor BMCs into recipient BM (intra-bone marrow-bone marrow transplantation: IBM-BMT) produces more rapid reconstitution (including T-cell functions) and higher survival rates than IV injection (IV-BMT) even in chimerism-resistant combinations. In the present study, we show that the co-administration of bones from suckling (2-3 days old) donor mice is also effective in the IBM-BMT system. Even when a relatively low number of BMCs were injected into adult (more than 15 weeks old) mice, complete reconstitution was achieved in the mice that had received IBM-BMT+bone grafts, but not in the mice that had received IBM-BMT alone. Most BM and splenic adherent cells obtained from the recipients that had received IBM-BMT+bone grafts were reconstituted by donor-type cells. Both T-cell proliferation and plaque-forming cell assays indicated that the T cells of such mice showed donor-type MHC restriction. Moreover, the analyses of thymic sections using confocal microscopy revealed that donor BM stromal cells had migrated into the thymus. Thus, the co-administration of donor bones has great advantages for allogeneic BMT in adult mice.

Prevention of osteoporosis and hypogonadism by allogeneic ovarian transplantation in conjunction with intra-bone marrow-bone marrow transplantation.

BACKGROUND: We investigated the effects of ovarian allograft in conjunction with intra-bone marrow-bone marrow transplantation (IBM-BMT) on estrogen deficiency in mice. METHODS: Female C57BL/6 mice underwent ovariectomy (OvX). After 3 months, the mice were irradiated at 9.5 Gy, and the bone marrow cells (BMCs) of female BALB/c mice (8 weeks old) were then injected into the bone cavity of the B6 mice. Simultaneously, allogeneic ovaries from BALB/c mice were transplanted under the renal capsules of the B6 mice. RESULTS: Three months after the transplantation, the hematolymphoid cells were found to be completely reconstituted with donor-derived cells. The transplanted ovary tissues under the renal capsules were accepted without using immunosuppressants; there were a large number of growing follicles at different stages of development. Atrophic endometrium and its glands were also recovered by ovarian transplantation (OT). The transplanted allogeneic ovaries secreted estrogen at normal levels. Furthermore, bone loss was prevented to a certain extent. CONCLUSIONS: These findings suggest that IBM-BMT+OT will become a valuable strategy for young women with malignant tumors to prevent premature senescence, including hypogonadism and osteoporosis, after radiochemotherapy.

The characteristics of hematopoietic stem cells from autoimmune-prone mice and the role of neural cell adhesion molecules in abnormal proliferation of these cells in MRL/lpr mice.

BACKGROUND AND OBJECTIVES: Using various animal models for autoimmune diseases, we have previously shown that such diseases are stem cell disorders.1 In order to understand how autoimmune diseases develop, we investigated the distinct qualitative differences between hematopoietic stem cells (HSC) from normal and autoimmune-prone mice. DESIGN AND METHODS: We studied the major histocompatibility complex (MHC) restriction between HSC and stromal cells in vitro and in vivo. We also examined the ability of HSC to adhere to a stromal cell line and, using flow cytometry, analyzed the expression of various adhesion molecules in HSC before and after the onset of autoimmune disease. In addition, the effect of antibodies to anti-adhesion molecules on the proliferation of HSC was investigated. RESULTS: The abnormal HSC of MRL/lpr mice showed no MHC restriction (or preference) with stromal cells either in vitro or in vivo, although there was MHC restriction between normal HSC and stromal cells, as we previously reported.2,3 The abnormal HSC of MRL/lpr mice exhibited enhanced adhesion to stromal cells in vitro and expressed a higher amount of adhesion molecules such as neural cell adhesion molecule (NCAM). Interestingly, the proliferation of HSC in MRL/lpr mice was significantly suppressed by anti-NCAM monoclonaal antibodies. INTERPRETATION AND CONCLUSIONS: Abnormal HSC of MRL/lpr mice are more resilient than normal HSC. Furthermore, among various adhesion molecules, only NCAM shows increased expression on HSC of MRL/lpr mice after the onset of autoimmune diseases, and these molecules contribute to the enhanced proliferation capacity of abnormal HSC in MRL/lpr mice. The present findings suggest that there are intrinsic qualitative differences between HSC from normal and autoimmune-prone MRL/lpr mice.

An innovative approach to bone marrow collection and transplantation in a patient with beta-thalassemia major: marrow collection using a perfusion method followed by intra-bone marrow injection of collected bone marrow cells.

Using small animals (mice and rats) and monkeys, we have found that the combination of bone marrow collection using the perfusion method (PM) and intra-bone marrow-bone marrow transplantation (IBM-BMT) of the collected cells is safe and effective in treating various intractable diseases. Based on these findings, we attempted to apply this method to humans. We report here the first case of a patient (6 years old) with beta-thalassemia major who underwent allogeneic BMT using this new PM + IBM-BMT method. The white blood cell counts of the patient gradually increased to more than 1500/microL by day 47 and continued to increase, reaching the highest level (8600/microL) on day +55. Fluorescence in situ hybridization data on day +33 showed that 98% of the peripheral blood cells were from the donor. Notably, there were no symptoms of graft-versus-host disease (GvHD). However, on day +56, the patient regrettably died of asphyxia resulting from sticky sputum. There was no evidence of infection (in the lung or liver) or GvHD (in the skin) by necropsy. We hope that this case report will help make our new strategies more readily available for the treatment of patients with various intractable diseases.

Intestinal cancer stem cells marked by Bmi1 or Lgr5 expression contribute to tumor propagation via clonal expansion.

Although the existence of cancer stem cells in intestine tumors has been suggested, direct evidence has not been yet provided. Here, we showed, using the multicolor lineage-tracing method and mouse models of intestinal adenocarcinoma and adenoma that Bmi1- or Lgr5- positive tumorigenic cells clonally expanded in proliferating tumors. At tumor initiation and during tumor propagation in the colon, the descendants of Lgr5-positive cells clonally proliferated to form clusters. Clonal analysis using ubiquitous multicolor lineage tracing revealed that colon tumors derived from Lgr5-positive cells were monoclonal in origin but eventually merged with neighboring tumors, producing polyclonal tumors at the later stage. In contrast, the origin of small intestine tumors was likely polyclonal, and during cancer progression some clones were eliminated, resulting in the formation of monoclonal tumors, which could merge similar to colon tumors. These results suggest that in proliferating intestinal neoplasms, Bmi1- or Lgr5-positive cells represent a population of cancer stem cells, whereas Lgr5-positive cells also function as cells-of-origin for intestinal tumors.

Intestinal stem cells contribute to the maturation of the neonatal small intestine and colon independently of digestive activity.

The murine intestine, like that of other mammalians, continues to develop after birth until weaning; however, whether this occurs in response to an intrinsic developmental program or food intake remains unclear. Here, we report a novel system for the allotransplantation of small intestine and colon harvested from Lgr5 EGFP-IRES-CreERT2/+; Rosa26 rbw/+ mice immediately after birth into the subrenal capsule of wild-type mice. By histological and immunohistochemical analysis, the developmental process of transplanted small intestine and colon was shown to be comparable with that of the native tissues: mature intestines equipped with all cell types were formed, indicating that these organs do not require food intake for development. The intestinal stem cells in transplanted tissues were shown to self-renew and produce progeny, resulting in the descendants of the stem cells occupying the crypt-villus unit of the small intestine or the whole crypt of the colon. Collectively, these findings indicate that neonatal intestine development follows an intrinsic program even in the absence of food stimuli.

Bmi1-positive cells in the lingual epithelium could serve as cancer stem cells in tongue cancer.

We recently reported that the polycomb complex protein Bmi1 is a marker for lingual epithelial stem cells (LESCs), which are involved in the long-term maintenance of lingual epithelial tissue in the physiological state. However, the precise role of LESCs in generating tongue tumors and Bmi1-positive cell lineage dynamics in tongue cancers are unclear. Here, using a mouse model of chemically (4-nitroquinoline-1-oxide: 4-NQO) induced tongue cancer and the multicolor lineage tracing method, we found that each unit of the tumor was generated by a single cell and that the assembly of such cells formed a polyclonal tumor. Although many Bmi1-positive cells within the tongue cancer specimens failed to proliferate, some proliferated continuously and supplied tumor cells to the surrounding area. This process eventually led to the formation of areas derived from single cells after 1-3 months, as determined using the multicolor lineage tracing method, indicating that such cells could serve as cancer stem cells. These results indicate that LESCs could serve as the origin for tongue cancer and that cancer stem cells are present in tongue tumors.

Treatment of streptozotocin-induced diabetes mellitus in rats by transplantation of islet cells from two major histocompatibility complex disparate rats in combination with intra bone marrow injection of allogeneic bone marrow cells.

BACKGROUND: We have established a new method for the transplantation of allogeneic pancreatic islets obtained from two different rat strains in combination with a newly developed bone marrow transplantation (BMT) method in which bone marrow cells (BMCs) are directly injected into the bone marrow cavity (intra bone marrow BMT [IBM-BMT]). METHODS: Streptozotocin-induced diabetic Brown Norway (BN: RT1A(n)) rats were injected with fludarabine, irradiated with 5.0 Gy x 2, and BMCs from two allogeneic rat strains, Fischer 344 (F344: RT1A(1)) and PVG (PVG: RT1A(c)), were then directly injected into the bone marrow cavity (IBM-BMT). Simultaneously, approximately 600 pancreatic islets (PIs) from F344 and PVG rats were mixed and transplanted into the liver by way of the portal vein. RESULTS: All the recipients thus treated showed normoglycemia 30 days after the treatment. Hematolymphoid cells were completely reconstituted with the two donor-type cells, and immunologic tolerance to F344 and PVG major histocompatibility complex (MHC) determinants were induced. CONCLUSIONS: The transplantation of PIs from two MHC-disparate donors was completely achieved in combination with IBM-BMT, resulting in the improvement of blood glucose levels and the amelioration of diabetes mellitus.

Intra-bone marrow-bone marrow transplantation facilitates hemopoietic recovery including dendritic cells.

In this report, we provide evidence using a serial bone marrow transplantation (BMT) protocol that intra-bone marrow (IBM)-BMT (IBM-BMT) can efficiently reconstitute the hemopoietic system with cells of donor origin, in contrast to conventional intravenous (IV)-BMT (IV-BMT). Furthermore, the hematolymphoid system of secondary recipients that had received bone marrow cells (BMCs) from primary recipients treated with IBM-BMT recovered earlier than that of the secondary recipients of BMCs from primary recipients treated with IV-BMT. This was the case when the Lin-/c-kit+ progenitor cells of the secondary and tertiary recipients were examined. These findings indicate that IBM-BMT can facilitate the development of not only cells of various lineages but also the effective generation and, more importantly, the maintenance of the progenitor cells. Furthermore, we show that IBM-BMT can reconstitute the dendritic cell (DC) subsets (myeloid and lymphoid DCs), which are critical for the initiation of both adaptive and innate immune responses. The frequency of both myeloid and lymphoid DC subsets was approximately equal to that of normal age-matched untreated controls and, after second and third BMT, this ratio was close to that observed in the normal controls. However, the lymphoid DCs were clearly reduced in the secondary and tertiary recipients of BMCs from mice that had received IV-BMT. Therefore, the development of DC subsets is also normally maintained in the IBM-BMT group.

Expression and localization of cartilage-specific matrix protein chondromodulin-I mRNA in salivary pleomorphic adenomas.

Pleomorphic adenoma is the most common epithelial tumor in the salivary glands. This tumor frequently exhibits "mesenchyme"-like components, including myxoid or chondroid areas. Recently, using immunohistochemical techniques, we reported that cartilage-specific matrix protein, chondromodulin-I (ChM-I), was deposited on the inter-territorial matrix of the chondroid area in salivary pleomorphic adenomas and that ChM-I, which is also a strong angio-inhibitory factor, plays an important role in the avascular nature of the chondroid area and the chondroid formation in this type of tumor. To elucidate which cells express ChM-I mRNA in pleomorphic adenomas, we examined the expression and localization of ChM-I mRNA in this type of tumor using an in situ hybridization technique. Immunoreactivity for ChM-I was observed in the inter-territorial matrix of the chondroid area, especially around the lacunae, and in the cytoplasm of neoplastic myoepithelial cells of the myxoid element of pleomorphic adenomas. On in situ hybridization analysis, strong signals for ChM-I mRNA were detected in the cytoplasm of the lacuna cells of the chondroid element, and moderate to marked signals were observed in the cytoplasm of the neoplastic myoepithelial cells of the myxoid element. Signals for ChM-I mRNA were also seen in the cytoplasm of the spindle-shaped neoplastic myoepithelial cells in the transitional areas between the myxoid and chondroid elements of this tumor. Signals for ChM-I mRNA were not seen in the inner ductal cells or the fibrous element. These findings indicate that lacuna cells and neoplastic myoepithelial cells express ChM-I mRNA and that mature ChM-I, which lacuna cells and neoplastic myoepithelial cells translate, is deposited in the chondroid matrix of pleomorphic adenomas. In conclusion, lacuna cells and neoplastic myoepithelial cells express ChM-I mRNA ectopically in pleomorphic adenoma, and this plays an important role in chondroid formation and hypovascularity in this type of tumor.

Ectopic pituitary adenoma with malignant transformation.

We report here a case of ectopic pituitary adenoma with malignant transformation after repeated relapses. First, an ectopic pituitary adenoma producing follicle-stimulating hormone was found in the nasal cavity extending to the frontal cranial fossa. Despite repeated surgical resections of the tumor, it recurred three times in 2 years. The tumor gradually showed cellular atypia, mitosis, and necrosis. Immunohistochemical analyses revealed that the expressions of proliferating cell nuclear antigen and MIB-1 increased progressively. Moreover, the expression of p53 was detected at the second recurrence. Finally, at the third recurrence the tumor showed dissemination to the subarachnoid space and multiple metastases in the brain. The patient died of the tumor 10 months after the last resection. These findings indicate that the ectopic pituitary adenoma became malignant. To our knowledge, this is the first report on malignant transformation of ectopic pituitary adenoma. It is important to know that ectopic pituitary adenomas show malignant transformation and that the above parameters (proliferating cell nuclear antigen, MIB-1, and p53) may be useful indicators of the malignant potential of both ectopic and sellar pituitary tumors.

Kimura's disease with unusual eosinophilic epithelioid granulomatous reaction: a finding possibly related to eosinophil apoptosis.

We report and discuss a case of Kimura's disease with an unusual eosinophilic epithelioid granulomatous reaction. A 3-year-old Japanese boy with eosinophilia and a high concentration of IgE developed lymphadenopathy and multiple cervical masses. A lymph node biopsy demonstrated the infiltration of eosinophils in the stroma, which is consistent with the findings of Kimura's disease. Interestingly, a number of apoptotic eosinophils was detected in the infiltrating eosinophils. Multiple epithelioid granulomas with central eosinophilic abscesses and necrosis were also observed. Macrophages and giant cells had phagocytosed the apoptotic eosinophils at the edge of the granulomas. In situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) assay showed that the TUNEL-positive eosinophils were both in the macrophages and in the central eosinophilic abscesses of the granulomas. These findings suggest that the eosinophils had undergone an accelerated apoptosis in this case of Kimura's disease, and that the epithelioid granulomas were produced by phagocytosis of the apoptotic eosinophils by macrophages.

Pulmonary sclerosing hemangioma associated with familial adenomatous polyposis.

A 45-year-old woman presented with asymptomatic solid tumor in the lower right lobe of the lung. Histologically, the tumor comprised a monolayer of surface cells and round stromal cells displaying sclerotic areas. Immunohistochemical studies suggested a diagnosis of sclerosing hemangioma. Interestingly, morular lesions were also observed. Analyses of the gastrointestinal (GI) tract showed mild familial adenomatous polyposis (FAP) and numerous fundal gland polyps, indicating attenuated FAP (AFAP). All components of the sclerosing hemangioma displayed aberrant nuclear and cytoplasmic expression of beta-catenin. However, such findings were much weaker in adenomas of the GI tract and were barely observed in fundal gland polyps. These results strongly suggest an association between sclerosing hemangioma and the AFAP. To the best of our knowledge, this is only the second report of lung tumor associated with FAP and is the first describing an association with sclerosing hemangioma. A new category of FAP-associated lung tumors may be indicated.

Developmentally regulated expression of Neuro-p24 and its possible function in neurite extension.

Process extension is a most marked and characteristic neuronal feature that is observed during the development, regeneration and plasticity of nervous system tissues. Neuro-p24, a novel membranous protein with a molecular weight of 24 kDa, is specifically localized in neurons, particularly in the neurites. Based on its molecular structure and distribution pattern in the brain we proposed that Neuro-p24 plays a role in neurite extension. In the present study we have made several findings that support this hypothesis; first, Neuro-p24 was abundant in motor axonal fibers, neurites of dorsal root ganglia neurons and apical dendrites of cerebral cortex neurons when their extension or arborization was proceeding very actively. Secondly, when COS-7 epithelial cells were transfected with either wild-type or deletion-mutated Neuro-p24 cDNAs, ectopic expression of wild-type cDNA caused morphological alterations resulting in a neuron-like appearance. These observations firmly support our proposal and indicate that Neuro-p24 plays an important role in the nervous tissue.

Bmi1 expression in long-term germ stem cells.

Asingle cells in undifferentiated spermatogonia are considered to be the most primitive forms of germ stem cells (GSCs). Although GFRα1 is thought to be a marker of Asingle cells, we found that Bmi1(High) is more specific than GFRα1 for Asingle cells. Bmi1(High) expression in Asingle cells is correlated with seminiferous stages, and its expression was followed by the proliferative stage of Asingle GSCs. In contrast, GFRα1 expression was seminiferous stage-independent. Fate analyses of EdU-positive Bmi1(High)-positive cell-derived Asingle cells revealed that these cells self-renewed or generated transient amplifying Apaired cells. Bmi1(High)-positive cells were resistant to irradiation-induced injury, after which they regenerated. Elimination of Bmi1(High)-positive cells from seminiferous tubules resulted in the appearance of tubules with seminiferous stage mismatches. Thus, in this study, we found that Bmi1(High) is a seminiferous stage-dependent marker for long-term GSCs and that Bmi1(High)-positive cells play important roles in maintaining GSCs and in regenerating spermatogenic progenitors after injury.