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Testis |
a Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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developmental biology, gamete biology, male reproductive tract, Sertoli cells, spermatogenesis
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The majority of information regarding stem cell/niche interaction has been obtained through studies in the hematopoietic system, for which both a functional stem cell assay and partial in vitro reconstitution of the stem cell microenvironment are available [11, 12]. Using these techniques, it has been shown that stem cells require direct contact with stromal cells to facilitate survival, growth, and differentiation [12]. If HSCs are prevented from attaching to stromal cells, they die. Although these studies involving the hematopoietic system provided valuable information regarding stem cell/niche interaction, the in vivo location of the HSC niche in the bone marrow is relatively inaccessible, thus complicating experimental manipulations. The ability to transplant the bone marrow stromal cell compartment has been the subject of controversy [12–14]. Despite its clear importance in stem cell biology, much remains unknown about the identity or characteristics of the niche in the hematopoietic and other self-renewing systems.
Spermatogenesis is a complex and highly productive system for generating male gametes, and it begins shortly after birth, with the transformation of gonocytes into spermatogonial stem cells and type A spermatogonia [15, 16]. These primitive cells produce differentiated progenitor cells in a stepwise, synchronous manner. By the time mature spermatozoa appear, approximately 35 days postpartum in mice, spermatogenic cells have established a unique cellular organization in the seminiferous tubule. Postnatal development of the spermatogenic compartment is accompanied by coordinate changes in the stem cell microenvironment [16]. The primary somatic cells of the seminiferous tubules are myoid and Sertoli cells that support and nourish germ cells, form the tubule wall, and define a niche for spermatogonial stem cells. Sertoli cells constitute approximately 3% of cells in adult mouse seminiferous tubules [17] and are the only somatic cell type that directly contacts germ cells.
Because Sertoli cells interact with many stages of germ cell differentiation, their role in regulating germ line development is complex. Their close association with spermatogonial stem cells suggests that Sertoli cells play a key role in maintaining the undifferentiated and pluripotent state of these stem cells while simultaneously supporting germ cell differentiation and spermatogenesis. Sertoli cell proliferation in the mouse reaches a peak shortly before birth and continues in the prepubertal testis until 10–12 days postpartum [18]. Formation of tight junctions between neighboring Sertoli cells occurs between 10 and 16 days postpartum [19], and this separates the seminiferous tubule into basal and adluminal compartments. Thus, development of the postnatal mouse testis is characterized by unique temporal and spatial differentiation patterns of both germ line and somatic cell types, and Sertoli cells create a special microenvironment for spermatogonial stem cells that is located on the basement membrane of the seminiferous tubule [20].
In the present study, we describe a novel technique to examine the stem cell microenvironment in vivo. Donor testis cells, containing stem cells and Sertoli cells, were transplanted into the seminiferous tubules of recipient mice. Tubule-like structures were produced and spermatogenesis occurred from transplanted stem cells supported by donor Sertoli cells, demonstrating that the stem cell niche of a self-renewing system can engraft to support complete differentiation from donor stem cells. Thus, this technique will be useful for understanding how the niche develops and interacts with stem cells in the testis, and it provides a new opportunity to manipulate the stem cell microenvironment.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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In the first experiment, donor cells were obtained from the transgenic mouse line B6; 129S-Gtrosa26, designated ROSA26-129 (The Jackson Laboratory, Bar Harbor, ME), that expresses the Escherichia coli LacZ (E. Coli lacZ) gene in many cell types, including all stages of spermatogenesis [21, 22]. Donor testis cells derived from this line can be unequivocally identified in recipient testes by staining with the ß-galactosidase substrate 5-bromo-4-chloro-3-indolyl ß-D-galactoside (X-gal). In the second experiment, donor cells were obtained from the transgenic mouse line B6. 129S7-Gtrosa26 (ROSA26-B6), or from wild-type C57BL/6 mice. The ROSA26-129 and ROSA26-B6 donor mice were maintained on C57BL/6 x 129SvCP or C57BL/6 genetic backgrounds, respectively. Single-cell suspensions were prepared from donor testes obtained from perinatal (Embryonic Day 19 to 2 days postpartum) or adult (age, 4–8 wk) mice using an enzymatic digestion procedure, as previously described[23].
Recipient Mice and Analysis
In the first experiment, C57BL/6 x 129SvCP F1 hybrid mice (B6/129) were treated with busulfan (50 mg/kg i.p.) at 4–6 wk of age and were used as immunologically compatible recipients of ROSA26-129 donor testis cells. Approximately 10 µl of donor cell suspension could be introduced into each testis through the efferent ducts of busulfan-treated mice [23]. One month after busulfan treatment, the seminiferous tubules of some recipient mice were injected with approximately 10 µl of cadmium sulfate solution ([3 CdSO4 · 8 H20], 0.1 mg/ml of Cd (Sigma, St. Louis, MO) to remove endogenous Sertoli cells. Donor cell suspensions (
50 µl) were injected into cadmium-treated testes between 2 and 3 wk after the cadmium treatment; the donor testis cell volume that could be injected was increased after removal of endogenous germ and Sertoli cells.
In the second experiment, ROSA26-B6 or C57BL/6 donor testis cells were transplanted into immunologically compatible Steel/Steeldickie (Sl/Sld) recipients (The Jackson Laboratory), which lack endogenous spermatogenesis because of a Sertoli cell defect caused by a mutation in the Sl gene encoding the ligand for the c-kit-receptor tyrosine kinase [24, 25]. Seminiferous tubules of some Sl/Sld recipient mice were treated with cadmium sulfate to remove endogenous Sertoli cells. Because these mutant mice have smaller testes than wild-type mice, approximately 3 µl of cadmium sulfate solution (0.4 mg/ml) was introduced into each testis through the efferent ducts. A higher concentration of cadmium solution (0.4 mg/ml) was used to prepare Sl/Sld recipients compared to wild-type recipients (0.1 mg/ml), because Sertoli cells in Sl/Sld testis were more resistant to the effects of cadmium (data not shown). Two to three weeks after cadmium treatment, 15 µl of donor cell suspension were injected into each recipient testis.
For both experiments, recipient testes were recovered 2 mo after donor cell transplantation. Testes from mice that had received ROSA26-129 donor cells were fixed in 4% (w/v) paraformaldehyde and stained with X-gal to visualize donor cell colonization [22]. Three histological sections (5 µm) were analyzed from the testes of each mouse, with 100-µm intervals between sections. Sections were stained with periodic acid-Schiff and viewed at a magnification of 400x to determine the extent of spermatogenesis in recipient mouse testes. The number and percentage of tubule cross-sections with minitubules, minitubules with donor germ cells (defined by blue staining and distinct morphology), and tubules/minitubules with spermatozoa were recorded for three sections from each testis. Student t-test was used to identify statistical differences in recipient testis weight. To test for differences in the number of minitubules, minitubules with germ cells, or minitubules with spermatozoa, Pearson chi-square or Fisher exact test was used.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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To examine whether Sertoli cells can colonize recipient seminiferous tubules, donor cells were collected from the testes of perinatal and adult ROSA26-129 mice. Adult testes contain all types of spermatogenic cells and mitotically quiescent Sertoli cells; perinatal testes contain gonocytes and dividing Sertoli cells. Both donor cell populations (4 x 107 cells/ml) were microinjected into the seminiferous tubules of busulfan-treated recipient mice. Expression of the lacZ transgene in the germ cells and Sertoli cells of ROSA26-129 testes allowed donor cells to be identified in recipient testes by staining with X-gal. Donor cell colonization of recipient testes was evaluated 2 mo after transplantation. Spermatogenic colonies derived from adult testis cells appeared as distinctive blue segments (Fig. 1A). These colonies generally had a deep blue region in the center flanked by weakly stained regions that are the hallmark of expanding spermatogenic colonies (Fig. 1B). The dark blue region in the middle of the colony suggests multiple donor cell layers, and the pale blue regions at the colony margins indicate a monolayer network of proliferating spermatogonia, as previously described [26]. Histological study confirmed that these colonies consist of several spermatogenic cell layers and elongated spermatids (Fig. 1, C and D).
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Transplantation of perinatal testis cells generated two types of donor cell colonies in the recipient testis (regular [similar to the one shown in Fig. 1B from adult donors] and irregular [as shown in Fig. 1F] donor-derived spermatogenic colonies). Some colonies consisted of a blue stretch of tubule with weakly staining margins that appeared very similar to the germ cell colonies derived from adult donor cells. In contrast, many colonies were irregular in size and staining pattern (Fig. 1, E and F). These colonies were adherent to seminiferous tubules, because they did not change position when pressure was applied to the tubule. However, colonies derived from perinatal donors differed from typical adult-derived colonies, because they contained dense clusters of blue cells and lacZ staining ended abruptly at the colony margins (Fig. 1F). Colonies derived from perinatal donors were variable in length, thickness, and overall appearance. These areas of seminiferous tubules, however, appeared to be intact despite the unphysiological expansion of donor cell colonies. Histological analysis of the recipient testes revealed colonization by perinatal testicular somatic cells (Fig. 1, G and H). Tubular structures closely resembling normal seminiferous tubules were apparently generated by reassociation of donor (blue stain) Sertoli cells (Fig. 1G). This structure or "minitubule" was often embedded in clusters of donor-derived cells that appeared similar to fibroblastic or peritubular cells (Fig. 1H). Several areas of recipient tubules contained two donor-derived minitubules, where the tubule diameter was markedly increased compared to that of seminiferous tubules in wild-type mice (Fig. 1G). Most minitubules did not contain germ cells, but a few spermatogonial cells were occasionally observed on the basement membrane of the minitubules. These results suggest that Sertoli cells from perinatal testes can colonize and have the morphogenic capacity to form tubule-like structures after transplantation into germ cell-depleted testes.
Removal of Endogenous Sertoli Cells by Intratubular Injection of Cadmium
In previous studies, administration of cadmium destroyed various types of testicular cells, including both germ and Sertoli cells [27]. To improve the efficiency of donor Sertoli cell colonization, we attempted to remove endogenous Sertoli cells by cadmium treatment, thereby creating "space" for colonization by donor Sertoli cells. Recipient mice were first treated with busulfan to remove the endogenous germ cells (compare Fig. 2, A and E, with Fig. 2, B and F). Approximately 1 mo later, the mice were further microinjected with cadmium solution through the efferent ducts. Following an inflammatory reaction that lasted for the first several days [27; present study], a large portion of recipient seminiferous tubule content was replaced by cellular debris at approximately 2 wk after the cadmium treatment (Fig. 2, C and G). In gross appearance, cadmium-treated testes were smaller than untreated or busulfan-treated testes (Fig. 2, top and legend). Histological analyses revealed that cadmium injection completely destroyed most Sertoli cells in the seminiferous tubule and that tubules contained amorphous cellular debris (Fig. 2G). Relative to intratubular cells, the interstitial cells were less affected by 2 wk after cadmium injection, despite the initial manifestations of hyperemia and mild hemorrhage. By 4 weeks, however, the basal membrane of individual tubules appeared to disintegrate, and peritubular cells began to migrate toward the lumen of empty tubules (Fig. 2H). The tubules were generally shrunken, and some were completely collapsed. Fibroblast cells proliferated, predominantly in the interstitial area. These results indicate that cadmium treatment can effectively remove Sertoli cells in the seminiferous tubules.
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Transplantation of Testis Cells into the Busulfan + Cadmium-Treated Recipient Testes
Two experiments were performed to examine the level of Sertoli cell colonization and donor-derived spermatogenesis in the busulfan + cadmium-treated recipient. Recipients were prepared by microinjecting cadmium solution into the seminiferous tubules of busulfan-treated mice. Perinatal and adult testis cells were prepared from ROSA26-129 animals, and equal concentrations of cells (108 cells/ml) were transplanted 2–3 wk after cadmium injection.
Recipient testes were stained with X-gal 2 mo after transplantation to assess donor cell colonization. Colonization of cadmium-treated recipients by adult donor cells was limited. Very few minitubules were observed in the recipient testes, and fibroblasts appeared to be the predominant donor cell type (Fig. 3B). Although donor-derived germ cells were occasionally observed in the minitubules in recipients of adult testis cells (Table 1), no spermatozoa were found. In contrast, weights of testes that received perinatal donor cells were significantly (P < 0.05) larger than those that received adult testis cells (Table 1), and the difference in appearance of testes that had received adult and perinatal testis cells was striking (Fig. 3, A and C).
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Perinatal donor testis cells covered greater than half the surface area (Fig. 3C) and appeared as dark-stained, thick tubules, whereas adult donor cells covered a significantly smaller area and their colonization sometimes appeared as thin blue segments (Fig. 3A). Histological analysis revealed that minitubule formation in busulfan + cadmium-treated recipient testes by perinatal donor cells was significantly (P < 0.0001) greater than that by adult donor cells (Fig. 3D and Table 1). The size of the minitubules varied, the pattern was irregular, and more than one minitubule was often found in a single recipient tubule (Fig. 3D). Donor-derived germ cells of various differentiation stages were observed in recipient tubules. Most minitubules with germ cells contained premeiotic, spermatogonial cells, but occasionally, areas that contained spermatocytes or spermatids were observed. The percentage of minitubules with germ cells was significantly (P = 0.0002) greater for busulfan + cadmium-treated recipients of perinatal donor testis cells than for recipients of adult cells (Table 1). Rarely, mature spermatozoa could also be identified (Table 1). Because gonocytes are the only germ cells in the perinatal donor cell population and busulfan + cadmium-treated recipients are devoid of endogenous Sertoli and germ cells, these results strongly suggest that spermatogenesis was initiated and differentiation occurred from donor gonocytes in donor cell-derived minitubules after transplantation. Minitubules appear to be comprised of donor myoid, Sertoli, and germ cells. Blue staining indicates donor origin. Myoid and germ cells were recognized by distinct morphology, and generation of spermatogenesis provided functional confirmation that Sertoli cells were also present. These results demonstrate that perinatal donor cells reconstitute the spermatogonial stem cell niche in busulfan + cadmium-treated recipient testes more efficiently than adult donor cells.
Transplantation of Testis Cells into Sl/Sld testes
The success with Sertoli cell transplantation led us to examine whether the technique could generate spermatogenesis in congenitally infertile Sl/Sld mice. Testes of Sl/Sld mice have few germ cells, and endogenous Sertoli cells cannot support spermatogenesis because of the lack of the membrane-bound form of stem cell factor on Sertoli cells [25]. Therefore, any spermatogenesis in Sl/Sld recipients indicates colonization by healthy donor Sertoli cells and provides definitive evidence for transplantation and reconstitution of the spermatogonial stem cell niche. A two-by-two factorial experiment was used in which donor cells from perinatal or adult testes were transplanted into untreated or cadmium-treated Sl/Sld recipients. Adult donor testis cells were collected from ROSA26-B6 mice and perinatal testis cells from wild-type B6 or ROSA26-B6 mice, because the number of cells that could be collected from perinatal testes was limited and wild-type B6 donors were more readily available. Donor cells from either immature or mature testes were transplanted at a concentration of 108 cells/ml.
Two months after transplantation, some of the recipient testes were recovered and stained for ß-galactosidase activity. When adult ROSA26-B6 testis cells were transplanted into untreated Sl/Sld recipient testes, transplanted donor cells formed networks or patches on the basal membrane, which is a typical cellular arrangement indicative of undifferentiated spermatogonia [26], and no differentiation occurred toward the adluminal compartment of the recipient seminiferous tubule (Fig. 4, A and B). Histological examination of cadmium-treated recipients revealed that most colonizing adult cells appeared to be fibroblastic, and no spermatogenesis was noted in any of the recipients (Table 2). Thus, these results show that adult donor cells cannot initiate spermatogenesis in Sl/Sld recipients, which is in agreement with the results of previous studies [20].
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In contrast to adult donors, perinatal donor cells showed extensive colonization in Sl/Sld recipients. Perinatal cells transplanted in untreated Sl/Sld recipients were able to make minitubules in 4 of 12 testes (33%), and normal spermatogenesis was found in 5 of 12 testes (42%) (Table 2). The donor cell colonization and level of spermatogenesis were markedly enhanced in cadmium-treated Sl/Sld recipients (Fig. 4C), in which 11 of 12 testes (92%) contained minitubules and 8 of 12 testes (67%) contained tubules with spermatozoa (Table 2). Whereas the number of tubules with minitubules was higher in cadmium-treated than in untreated recipients (55% vs. 1.1%, P < 0.0001), the proportion of minitubules with germ cells was not different (P = 0.3) (Table 2). In addition, a smaller percentage of minitubules contained spermatozoa in cadmium-treated recipients (3%) compared to untreated (35%) recipients (P < 0.0001), although the former contained spermatogenesis in areas where no minitubules were apparent and, overall, cadmium-treated testes contained more tubules with spermatozoa than untreated recipients (1.8% vs. 0.4%, data not shown). Endogenous Sertoli cells in Sl/Sld recipient testes cannot support spermatogenesis; therefore, these results indicate that transplanted perinatal wild-type Sertoli cells functionally reconstituted the recipient seminiferous tubule and supported spermatogenesis (Fig. 4D). Thus, the spermatogonial stem cell niche can be transplanted, can correct the defective microenvironment of congenitally infertile recipient animals, and can generate donor-derived spermatogenesis, which is enhanced by previous treatment of the recipient with cadmium.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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In the present study, spermatogonial stem cell/niche interactions in the mouse testis were evaluated functionally by transplantation of wild-type perinatal and adult testis cells into four types of recipients: 1) busulfan-treated, wild-type mice that are devoid of endogenous germ cells but have an intact and functional Sertoli cell compartment; 2) busulfan + cadmium-treated, wild-type mice that are essentially devoid of germ cells and Sertoli cells; 3) Sl mice that cannot support spermatogenesis because of a Sertoli cell defect and contain only undifferentiated germ cells; and 4) cadmium-treated Sl mice that are devoid of Sertoli and germ cells. Spermatogenesis in recipient testes depends on the functional activities of both the germ line stem cell and Sertoli cell (i.e., niche) compartments. The results of these studies clearly show that donor testis cells can reconstitute the tubular microenvironment by producing minitubules within the luminae or re-establishing Sertoli cells on the basement membrane of host seminiferous tubules. This morphogenic activity was enhanced when perinatal donor cells were used and endogenous Sertoli cells were removed by cadmium treatment of recipient tubules (Tables 1 and 2); in some cases, complete spermatogenesis was restored (Tables 1 and 2 and Fig. 4D). The minitubules appeared similar to structures reported by Jiang and Short [30, 31], who transplanted fetal and neonatal rat testis cells into the seminiferous tubules of busulfan-treated, wild-type recipient rat testes and coined the term minitubule. Functional reconstitution of the stem cell niche from transplanted donor Sertoli cells was clearly demonstrated when Sl mutant mice were used as recipients. Endogenous Sertoli cells are defective in this model, so spermatogenesis could only occur among donor Sertoli cells. Donor-derived spermatogenesis was most often found in minitubules, but occasionally, donor cells colonized the basement membrane of cadmium-cleared recipient seminiferous tubules and produced morphologically normal spermatogenesis (Table 2 and Fig. 4D). Because any committed progenitor germ cells in the donor population would have differentiated to mature sperm by 35 days in mice [15], spermatogenesis in recipient testes 2 mo after transplantation must have originated from spermatogonial stem cells, indicating successful reconstitution of the stem cell niche.
The ability to transplant the spermatogonial stem cell niche depended on both donor and recipient factors. Donor cells prepared from perinatal testes in the present experiment efficiently generated spermatogenesis after transplantation into busulfan + cadmium-treated recipients. Differences in the stem cell and/or Sertoli cell populations are two factors that might explain the superiority of the perinatal donor testis cell population compared to the adult donor population. Because stem cells are the only cell type in the testis with the capacity to produce and maintain colonies of spermatogenesis, stem cell activity in the transplanted population is an important determinant for successful donor-derived spermatogenesis. Modest differences in stem cell activity were observed in previous studies, demonstrating that neonatal testes contain an approximately 50% higher stem cell concentration than adult testes [9, 26] and that colonies derived from neonatal stem cells are approximately 50% larger than adult-derived colonies by 3 mo after transplantation [9]. Developmental differences in Sertoli cell activity may be the major factor affecting the success of stem cell and niche engraftment in recipient testes. Whereas mature Sertoli cells are mitotically quiescent [15] and constitute only 3% of cells in adult seminiferous tubules [17], immature Sertoli cells are proliferative [16] and comprise >80% of cells in perinatal seminiferous tubules [17]. Therefore, compared to adult testes, perinatal testes appear to have a slight advantage in stem cell activity but a large advantage in Sertoli cell number and proliferative activity, and the Sertoli cell factors likely played the major role in enhancing donor cell-derived spermatogenesis in recipient seminiferous tubules.
A second critical factor was the conditioning of recipients. Although immature Sertoli cells were able to colonize a germ cell-deficient environment in the seminiferous tubules of busulfan-treated mice, removal of endogenous Sertoli cells by cadmium treatment significantly enhanced the colonization level. Cadmium has long been known to cause testicular damage and infertility in a variety of species [27], and subcutaneous or intratesticular injection of small amounts of cadmium are effective. Cadmium is thought to act on the lining of the blood vessels of the pampiniform plexus [27], causing acute inflammation and necrosis of the testicular cells. Whereas other antifertility treatments, such as radiation or alkylating agents, remove only mitotic cells (i.e., germ cells), cadmium can destroy all cell types in the seminiferous tubules, including Sertoli cells, which are quiescent in the adult testis [15] and, therefore, refractory to antimitotic treatments. In the present experiments, we found sequential busulfan and cadmium treatments to be effective in removing germ cells and Sertoli cells from the seminiferous tubule. Because removal of endogenous stromal cells has not been possible in other self-renewing systems, the availability of both germ cell and Sertoli cell toxicants provides a unique opportunity to modify the stem cell microenvironment in the testis and enables transplantation of the spermatogonial stem cell niche.
Successful donor-derived spermatogenesis in busulfan + cadmium-treated recipients indicates that 1) niche can be recreated despite dissociation of testis tubules into single cells; 2) donor Sertoli cell colonization is increased by creating "space" in the recipient (by cadmium treatment), as previously demonstrated for stem cell transplantation [32, 33]; and 3) niche function is demonstrated by the presence of complete donor-derived spermatogenesis in busulfan + cadmium-cleared seminiferous tubules. Whereas Sertoli cell colonization had a normal appearance in some tubules, most resulted in minitubule formation, as previously described for the rat [30, 31]. Interestingly, mature spermatozoa appeared in a limited number of minitubules, with many minitubules containing only immature germ cells. The low efficiency of spermatogenesis in minitubules might be explained by environmental differences between wild-type seminiferous tubules and donor-derived reconstructed minitubules. For example, in the adult testis, a species-specific, fixed, numerical relationship exists between the germ cells and Sertoli cells [16]. Therefore, the inefficient spermatogenesis in minitubules may reflect an imbalance between germ cell and Sertoli cell numbers. In addition, the heterogeneous donor testis cell population contained Leydig and myoid cells that are not normally found in the seminiferous epithelial environment. These cells may have interfered with the balance between germ cell and endocrine compartments, which is essential for spermatogonial differentiation [34] and Sertoli cell function [35]. Thus, both the relative numbers and types of donor cells likely are responsible for the inefficient sperm production in the minitubules, and identification of factors contributing to spermatogenesis will provide insight regarding how stem cell/niche interactions develop in the testis. Because methods to isolate individual types of testis cells are now available [17, 36], transplantation of specific cell types from different maturational stages or variation of the number and proportion of donor cell populations would likely impact the degree of donor-derived spermatogenesis and allow new experimental possibilities to investigate germ cell/niche interactions in the testis.
Clinically, the present technique may be useful for treatment of male infertility, which can be caused either by defective germ cells or environment. Because differentiation of germ cells depends on close interaction with Sertoli cells, a defect of either would disrupt spermatogenesis and cause infertility. Whereas several assisted reproductive techniques, such as in vitro fertilization or intracytoplasmic sperm injection [37], are now available for patients with few spermatozoa, infertile patients with Sertoli cell defects have limited options. If the Sertoli cell defect can be attributed to a deficiency in a single gene, then it might be corrected by application of gene therapy, as recently demonstrated using adenovirus and lentivirus to deliver the Sl gene into the Sertoli cells of infertile Sl/Sld mutant mice [38, 39]. If the defect is multigenic or the genetic basis is not known, then our results may provide a new opportunity to replace defective Sertoli cells with healthy Sertoli cells, and reintroduction of the original stem cell population may initiate normal spermatogenesis in the testes of these patients. Stem cells in testes with defective environments may retain the capacity to generate spermatogenesis under the appropriate conditions. Recent studies have demonstrated that spermatogonial stem cells recovered from testes of infertile Sl/Sld mice could produce spermatozoa and offspring after transplantation to a healthy environment [40]. Thus, Sertoli cell transplantation will be useful not only for the study of the stem cell niche but also may provide an approach for the treatment of male infertility.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Corespondence: R.L. Brinster, School of Veterinary Medicine, University of Pennsylvania, 3850 Baltimore Avenue, Philadelphia, PA 19104. FAX: 215 898 0667
3 Current address: Department of Medical Chemistry, Graduate School of Medicine, Kyoto University, Yoshida-Konoe, Sakyo-ku, Kyoto, Japan 606-8501
Received: 2 August 2002.
First decision: 26 August 2002.
Accepted: 16 October 2002.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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