Glycobiology Advance Access originally published online on January 19, 2005
Glycobiology 2005 15(6):649-654; doi:10.1093/glycob/cwi043
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Glycobiology vol. 15 no. 6 © Oxford University Press 2005; all rights reserved.
Testis-specific sulfoglycolipid, seminolipid, is essential for germ cell function in spermatogenesis
2 Department of Molecular Genetics, Kochi University Medical School, Kochi 783-8505, Japan; 3 Department of Biochemistry, Osaka University Medical School, Osaka 565-0871, Japan; 4 Department of Pathology, Kochi University Medical School, Kochi 783-8505, Japan; and 5 CREST, Japan Science and Technology Agency, Japan
1 To whom correspondence should be addressed; e-mail: proftani{at}biochem.med.osaka-u.ac.jp; khonke{at}med.kochi-u.ac.jp
Received on December 13, 2004; revised on January 14, 2005; accepted on January 15, 2005
 |
Abstract |
|---|
 Top Abstract IntroductionResultsDiscussionMaterials and methodsReferences |
|---|
More than 90% of the glycolipid in mammalian testis consists of a unique sulfated glyceroglycolipid, seminolipid. The sulfation of the molecule is catalyzed by a Golgi membrane-associated sulfotransferase, cerebroside sulfotransferase (CST). Disruption of the Cst gene in mice results in male infertility due to the arrest of spermatogenesis prior to the metaphase of the first meiosis. However, the issue of which side of the cell function—germ cells or Sertoli cells—is deteriorated in this mutant mouse remains unknown. Our findings show that the defect is in the germ cell side, as evidenced by a transplantation analysis, in which wild-type spermatogonia expressing the green fluorescent protein were injected into the seminiferous tubules of CST-null testis. The transplanted GFP-positive cells generated colonies and spermatogenesis proceeded over meiosis in the mutant testis. The findings also clearly show that the seminolipid is expressed on the plasma membranes of spermatogonia, spermatocytes, spermatids, and spermatozoa, as evidenced by the immunostaining of wild-type testes using an anti-sulfogalactolipid antibody, Sulph-1 in comparison with CST-null testes as a negative control, and that seminolipid appears as early as day 8 of age, when Type B spermatogonia emerge.
Key words: cereboroside sulfotransferase / germ cell transplantation / green flourescent protein / knockout mouse / testis
|
Introduction |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Mammalian spermatogenesis is a complex, highly organized process that takes place in the seminiferous tubules of the testis, in which germ cells undergo proliferation and differentiation to become spermatozoa (Dym, 1983
). The proliferation and differentiation of spermatogonial stem cells occur in the basal compartment at the peripheral side of the seminiferous tubules. These differentiated spermatogonia then become spermatocytes and begin meiosis, migrating from the peripheral to the luminal side along somatic Sertoli cells. The mutual interaction between germ cells and Sertoli cells play a crucial role in their differentiation (Jegou, 1993). After spermatogenesis in the testis, spermatozoa are released into the lumen of seminiferous tubules and are transported to the epididymis where they continue to mature.
More than 90% of the glycolipid in the mammalian testis consists of a unique sulfated glycerogalactolipid, seminolipid (Ishizuka, 1997; Ishizuka et al., 1973; Kornblatt et al., 1974; Vos et al., 1994). Its carbohydrate moiety, 3-O-sulfated galactose, is identical to that of sulfatide, which is abundant in the myelin. Seminolipid and sulfatide are synthesized by a sequential reaction of common enzymes, ceramide galactosyltransferase and cerebroside sulfotransferase (CST) (Fujimoto et al., 2000; Honke et al., 1997, 2002). Disruption of the genes for these enzymes in mice results in the complete absence of seminolipid in the testis and male infertility due to the arrest of spermatogenesis at the late stage of the prophase of the first meiosis, indicating that seminolipid is essential for spermatogenesis (Fujimoto et al., 2000; Honke et al., 2002). Indeed, seminolipid is present in germ cells (Ishizuka, 1997; Vos et al., 1994), but the issue of which side of cell function, germ cells or Sertoli cells, is deteriorated in these mutant mice remains unknown. To address this question, we examined whether spermatogenesis is restored or not after testis germ-cell transplantation (Brinster and Zimmermann, 1994; Ogawa et al., 1997; Brinster, 2002), in which wild-type spermatogonial stem cells were injected into the seminiferous tubules of CST-null mice. To demonstrate colonization of donor cells in recipient testes, donor spermatogonia were prepared from Green mice (Okabe et al., 1997) that systemically express the green fluorescent protein (GFP).
Furthermore, to address the molecular mechanisms involved in the action of seminolipid, its localization in the testis was examined by immunohistochemistry using CST-null testis as a negative control. The onset of seminolipid expression during the testicular development was also determined by an reverse transciption polymerase chain reaction (RT-PCR) analysis of the Cst gene and immunohistochemistry of the first wave testes of young age mice.
|
Results |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Spermatogenesis is restored by germline stem cell transplantation into CST-null testis
Disruption of the Cst gene in mice results in a lack of seminolipid and male infertility due to the arrest of spermatogenesis prior to the metaphase of the first meiosis (Honke et al., 2002
). However, the issue of whether germ cells or Sertoli cells are deteriorated in this mutant mouse is not known with certainty. To address this issue, wild-type spermatogonia were injected into seminiferous tubules from the efferent duct according to a previously described method (Brinster and Zimmermann, 1994; Ogawa et al., 1997). Because the testes of 6-day-old mice contain mainly primitive type A spermatogonia (Bellve et al., 1977), donor cells were prepared from the Green mouse testes of this age. The Green mice were found to express GFP in the testis (Figure 1A). After transplantation, GFP-expressing spermatogonial stem cells were found to reside and expand in the seminiferous tubules of CST-null testis (Figure 1B and C). In a histological analysis of the transplanted testis, GFP was observed in the germ cells but not in the somatic cells (Figure 1D), suggesting that only the germ cells are established in the recipient tissues. In addition, the transplanted germ cells were found to express seminolipid on their cell surface, as evidenced by immunostaining using an anti-sulfogalactolipid monoclonal antibody, Sulph-1 (Fredman et al., 1988) (Figure 1E).
|
The staining of the peripheral layer of the seminiferous tubule and Leydig cells may be an artifact, as described here. Three months after transplantation, the size and weight of testis became larger and heavier, and histologically mature spermatozoa were observed in only a portion of the seminiferous tubules and transplanted germ cells continued to proliferate and differentiate in other portions (data not shown). At 5 months after transplantation, ~ 2/3 of the total seminiferous tubules developed and contained mature spermatozoa (Figure 2). These results indicate that wild-type spermatogonia are able to resume spermatogenesis in a normal manner in CST-null testis and that the defect in the mutant mice is in germ cell function. The results also demonstrate that the somatic compartment of the CST-null testes retains functionality.
|
Unexpectedly, these transplanted mice were still infertile, because spermatozoa were absent from the epididymis, suggesting that spermatozoa are unable to enter the epididymis by some currently unknown reason. Considering the possibility that another defect in epididymal function in CST-null mice exists, we investigated the issue of whether sulfoglycolipid is expressed in the epithelia of the epididymis. As shown in Figure 3, reactivity to the Sulph-1 anti-sulfoglycolipid antibody was observed in epithelial cells of the epididymis from wild-type mice, whereas no reactivity was found in those from CST-null mice. The reactivity of the outer layer of the epididymis may be artifact in the staining procedure because it was also observed in CST-null tissues and without the first antibody (data not shown).
|
Seminolipid is expressed on the plasma membranes of spermatogonia, spermatocytes, spermatids, and spermatozoa
To address the molecular mechanisms in which seminolipid is involved, its localization in the testis was examined by immunohistochemistry using Sulph-1. To verify the reactivity of the antibody, CST-null testis was used as a negative control. As shown in Figure 4, the plasma membranes of spermatogonia, spermatocytes, spermatids, and spermatozoa in wild-type testis were all heavily stained by Sulph-1, whereas it did not react with any cells in the seminiferous tubules of CST-null testis. The reactivity of the outer layer of the seminiferous tubule and Leydig cells may be artifact in the staining procedure because it was also observed in CST-null testis and without the first antibody (data not shown).
|
Seminolipid appears at day 8 of age, when Type B spermatogonia emerge during testicular development
To investigate the onset of seminolipid expression during testicular development, CST gene expression was examined in the first wave testes of young mice by means of an RT-PCR analysis in parallel with other spermatogenesis-associated genes including CGT, Oct-4, and c-kit. Oct-4 is a transcription factor that is specifically expressed in mouse primordial germ cells, type A spermatogonia, and undifferentiated ES cells (Yeom et al., 1996). Kit is a tyrosine kinase receptor that is expressed in spermatogonia and spermatocytes (Sette et al., 2000). The Kit-positive type A spermatogonia from 5-day-old mice required the stem cell factor as a ligand for proliferation (Tajima et al., 1994), whereas the Kit-negative undifferentiated type A spermatogonia from 2-day-old mice did not (Ohta et al., 2000). Total RNA was extracted from day 6 through day 18 mouse testes, and cDNA was generated by reverse transcription. The seminiferous epithelia from day 6 mice contain only primitive type A spermatogonia and Sertoli cells (Bellve et al., 1977). Type B spermatogonia appear by day 8, and the meiotic prophase is initiated at day 10. As shown in Figure 5, transcripts of the CST and CGT genes could be clearly observed in day 8 and subsequent testis, indicating that they begin to appear, at the latest, in differentiated spermatogonia.
|
We then investigated the expression of seminolipid in day 6 through day 18 murine testes by immunohistochemistry using the Sulph-1 antibody. No staining was observed in day 6 testis (Figure 6), suggesting that undifferentiated spermatogonia and Sertoli cells do not express sulfoglycolipids. A faint staining was observed in a part of the cross-sections of the seminiferous tubules of day 8 mice. Robust staining was observed in a part of the cross-sections of the seminiferous tubules of day 10 mice. The strength of most of the seminiferous tubules was slightly heterogeneous in day 12 testis. In addition, in day 14 and day18 testes, all of the seminiferous tubules were strongly stained. These results indicate that seminolipid begins to appear in differentiated spermatogonia, a finding that is consistent with the gene expression results.
|
|
Discussion |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Germline stem cell transplantation is a potent tool for evaluating germ cell development in infertile recipient testes (Brinster, 2002
). Actually, it has been clearly shown that the mutant phenotype is the result of a defect in germ cells or in supporting somatic cells (Ohta et al., 2001; Speed et al., 2003), and it has also been shown that spermatozoa obtained after testicular stem cell transplantation retain their full functional capacity to produce normally developing embryos (Goossens et al., 2003; Honaramooz et al., 2003). In the present study, we applied this method to CST-null testes where spermatogenesis is arrested at the late prophase of the first meiosis (Honke et al., 2002) and successfully demonstrated that the defect is in germ cells and that the somatic compartment of the mutant testis retains its functionality.
Although apparently mature spermatozoa were produced in the testis after the transplantation of wild-type germ cells, the CST-null recipients were still infertile, as evidenced by the fact that their epididymides were completely devoid of spermatozoa. There are two possible mechanisms for explaining this. One is that spermatozoa are unable to translocate into the epididymis because of a second defect. The other is that sulfoglycolipids are required for the epithelial function of the epididymis to maintain viable spermatozoa. Although there is no clear-cut evidence to support either mechanism, we addressed the latter possibility by elucidating that sulfoglycolipids are actually expressed in the epithelial cells of the epididymis. This is the first report of the presence of sulfoglycolipid in epididymal epithelia. A further functional assay must await the generation of conditional knockout mice in terms of the Cst gene. The proposed role of seminolipid in gamate interaction (Weerachatyanukul et al., 2003) should also be tested in vivo in the future.
Because seminolipid levels of ejaculated spermatozoa and isolated spermatocytes are much higher than that of the whole testis (Ishizuka, 1997; Ishizuka et al., 1973) and the w/wv mouse testis, in which c-kit is mutated and only undifferentiated spermatogonia are present as germline cells, contains negligible amount of seminolipid (Kornblatt et al., 1974), it is generally thought that seminolipid is expressed in germ cells. By using the same anti-sulfogalactolipid monoclonal antibody as was used in the present study, germ cells were densely stained in the seminiferous tubules of rat testis (Buschard et al., 1994). Our study clearly demonstrates that existence and function of seminolipid in germ cells.
When day 8 through day 12 testes were stained with the anti-sulfogalactolipid antibody, the reactivity was heterogeneous among cross-sections but homogeneous within the same cross-section (Figure 6). Staining was particularly prominent in cross-sections of day 10 testis. These findings suggest that the differentiation of spermatogonia does not occur synchronously and support conclusions reached by Huckins (1971) that ratio of Asingle and Aaligned spermatogonia is variable in different areas of a seminiferous tubule. Because there are no regulatory mechanisms for ensuring an even distribution of spermatogonial stem cells in the spermatogenic epithelium, highly variable numbers of differentiating spermatogonia are produced at different positions along the length of a seminiferous tubule (de Rooij and Grootegoed, 1998).
It has been reported that in the mouse and rat, seminolipid is actively synthesized in spermatocytes (Handa et al., 1974; Kornblatt et al., 1974). Indeed the reactivity of anti-sulfogalactolipid antibody was increased in total after the appearance of spermatocytes in the present study, but when a more sensitive method was used, the findings showed that seminolipid begins to be synthesized, at the latest, in differentiated spermatogonia. The issue of which stage of germ cell lineage seminolipid begins to function remains unknown.
Our studies reveal that seminolipid is essential for germ cell function. We must next elucidate the molecular mechanisms for how seminolipid actually functions in germ cell membranes. To this end, seminolipid-associated molecules should be identified as a first step. Glycosphingolipids self-associate in cellular membranes to form a microdomain, which is referred to as lipid raft (Simons and Ikonen, 1997). Glycosylphosphatidylinositol-anchor proteins and plasmalogens, which contain an ether glycerolipid similar to seminolipid, are also enriched in this microdomain (Rodemer et al., 2003; van Meer, 2002). The fact that seminolipid is recovered in detergent-insoluble floating membrane fractions (Zhang and Honke, unpublished data) suggests that seminolipid is included in the lipid rafts of germ cells. It has been proposed that these microdomains serve as platforms within the plasma membrane for receptor signaling and trafficking (Simons and Ikonen, 1997; van Meer, 2002). Seminolipid may contribute to the organization of such functional platforms on germ cells.
In conclusion, the present study indicates that seminolipid is essential for germ cell function in spermatogenesis. Given that the germ cell differentiation depends on the mutual interactions between germ cells and Sertoli cells, seminolipid may play a critical role as a plasma membrane component.
|
Materials and methods |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Animals
The donor mice for transplantation were a transgenic mouse line rC57BL6/tg14 (act-EGFP-OsbY01) that was bred into C57BL/6 background, designated Green mice (Okabe et al., 1997
), whose spermatogonia and spermatocytes express the enhanced GFP gene. The expression level of the GFP decreases gradually after meiosis (Okabe et al., 1997). Recipient mice were generated by intercrossing of a mouse strain with a targeted mutation TgH(CSTneo)01, in which one of the Cst genes was disrupted by homologous recombination. Cst–/– male mice are sterile because of a block in spermatogenesis before the first meiotic division (Honke et al., 2002). CST-null mice at 1.5–6 months of age were used as the recipient mice. Four to 6 weeks before transplantation, the recipient mice were injected with busulfan (40 mg / kg, IP) to destroy endogenous spermatogenic stem cells, which inhibit the establishment of exogenous stem cells (Brinster and Zimmermann, 1994). All experiments were performed in strict compliance with the Guide for the Care and Use of Laboratory Animals (NIH, 1985). Specific protocols were approved by the Animal Care and Use Committee of Kochi University Medical School (protocol no. 368).
Germ cell transplantation
Donor cells were prepared from Green mice at the age of day 6–12. The mice were anesthetized and the testes rapidly removed. Decapsulated seminiferous tubules were placed in calcium-free phosphate buffered saline (PBS) and washed 3 times with PBS. Seminiferous epithelia were dispersed enzymatically using a previously described method (Izadyar et al., 2002) with minor modifications. In a typical experiment, seminiferous tubules were suspended in 5–8 volumes of 0.25% trypsin/PBS and incubated at 32°C for 20–30 min in a shaking water bath (140 cycles/min). After washing three times with Dulbecco’s modified Eagle’s medium (DMEM), the seminiferous tubules were incubated with DMEM containing collagenase (1 mg/ml) and DNase (200–500 µg/ml) at 32°C for 20–30 min in a shaking water bath (140 cycles/ min). The tubular fragments were then repeatedly pipetted and filtrated through a 77–55 µm nylon filter and washed with DMEM three times. The dispersed cells were precipitated, resuspended in DMEM supplemented with 10% fetal calf serum at a concentration of 105–106 cells/ml, put into 75-cm2 tissue culture flasks in 15 ml/flask, and incubated for 5–6 h at 32°C. After incubation, spermatogonia that remained in suspension were collected. Sertoli cells and myoid cells were removed because they were attached to culture plates during the incubation.
Testicular germ cell transplantation was performed according to a previously described method (Ogawa et al., 1997). Donor cells were injected into the seminiferous tubules through the efferent duct. Four to 7 µl of cell suspension (107–108 cells/ml) including trypan blue was injected per testis.
Analysis of recipient mice
For an analysis of donor testis cell colonization, recipient testes of CST-null mice were collected 45 days after transplantation and observed by fluorescent microscopy (Olympus BX50) at low magnification to observe GFP-expressing germ cells expanding in the seminiferous tubules. To examine whether spermatogenesis proceeds, a histological observation of recipient testes was performed 4–5 months after transplantation. Testes were fixed with 10% formaldehyde at 4°C overnight, embedded in paraffin, and cut into 5-µm-thick sections. The sections were then stained with hematoxylin-eosin.
RT-PCR analysis
Testicular germ cells were prepared from wild-type C57BL6 male mice at days 6, 8, 10, 12, 14, and 18 by the methods already described. Total RNA was extracted with the Trizol reagent (Invitrogen, Carslbad, CA). Total RNA (1 µg) was reverse-trancribed with random hexamer. The resulting cDNA was subjected to PCR with the following primer sets: Cst, 5'-GGGTTTCCTGAGATGAC-3' and 5'-TAGTGCGCGTTGTAGCT-3'; Cgt, 5'-AGAGGCGCTCTCCAACT-3' and 5'-GTCAACCAGTTCAACTG-3'; c-kit, 5'-CCTCATCGAGTGTGATG-3' and 5'-GACACAACAGGGATAGC-3'; Oct4, 5'-TCTCGAACCTGGCTAAG-3' and 5'-TCTGCAGGGCTTTCATG-3'; ßactin, 5'-TTACCAACTGGGACGACATG-3' and 5'-AGGAGCCAGAGCAGTAATCT-3' PCR was carried out for 35 cycles (Cst, Cgt, c-kit, Oct4) or 30 cycles (ß-actin) under condition of denaturing at 95°C for 30 s, annealing at 60°C for 30 s, and extension at 72°C for 1 min. The reaction products were analyzed by agarose gel electrophoresis.
Immunohistochemistry
Seminolipid expression in murine testis was examined by immunofluorescence staining using Sulph-1 (Fredman et al., 1988). Testes were fixed with 4% paraformaldehyde at 4°C overnight, incubated in 10% sucrose/PBS at 4°C for 12–24 h, embedded in OCT compound, and cut into 6-µm-thick sections. The sections were sequentially reacted with Sulph-1 antibody, biotin-conjugated goat anti-mouse IgG F(ab’)2 (DakoCytomation), and FITC-conjugated streptoavidin (DakoCytomation, Carpinteria, CA). Nuclear staining was achieved with 4',6-diamidino-2-phenylindole (DAPI) (Dojindo Laboratories, Kumamoto, Japan).
|
Acknowledgements |
|---|
We thank Dr. Hiroshi Ohta (Center for Developmental Biology, RIKEN, Japan) for his kind instruction of the efferent duct injection technique. This study was supported in part by Grant-in-aid for Scientific Research on Priority Area No. 14082204 and by the 21st Century COE program from the Ministry of Education, Science, Culture, Sports and Technology of Japan.
|
Abbreviations |
|---|
CST, cerebroside sulfotransferase; DAPI, 4',6-diamidino-2-phenylindole; DMEM, Dulbecco’s modified Eagle’s medium; GFP, green fluorescent protein; PBS, phosphate buffered saline; RT-PCR, reverse transciption polymerase chain reaction
|
References |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Bellve, A.R., Cavicchia, J.C., Millette, C.F., O’Brien, D.A., Bhatnagar, Y.M., and Dym, M. (1977) Spermatogenic cells of the prepuberal mouse. Isolation and morphological characterization. J. Cell Biol., 74, 68–85.
Brinster, R.L. (2002) Germline stem cell transplantation and transgenesis. Science, 296, 2174–2176.
Brinster, R.L. and Zimmermann, J.W. (1994) Spermatogenesis following male germ-cell transplantation. Proc. Natl Acad. Sci. USA, 91, 11298–11302.
Buschard, K., Josefsen, K., Hansen, S.V., Horn, T., Marshall, M.O., Persson, H., Mansson, J.E., and Fredman, P. (1994) Sulphatide in islets of Langerhans and in organs affected in diabetic late complications: a study in human and animal tissue. Diabetologia, 37, 1000–1006.[ISI][Medline]
de Rooij, D.G. and Grootegoed, J.A. (1998) Spermatogonial stem cells. Curr. Opin. Cell Biol., 10, 694–701.[CrossRef][ISI][Medline]
Dym, M. (1983) The male reproductive system. In Weiss, L. (Ed.), Histology: cell and tissue biology, 5th ed. Elsevier Science, New York, pp. 1000–1053.
Fredman, P., Mattson, L., Andersson, K., Davidsson, P., Ishizuka, I., Jeansson, S., Mansson, J.-E., and Svennerholm, L. (1988) Characterization of the binding epitope of a monoclonal antibody to sulphatide. Biochem. J., 251, 17–22.[ISI][Medline]
Fujimoto, H., Tadano-Aritomi, K., Tokumasu, A., Ito, K., Hikita, T., Suzuki, K., and Ishizuka, I. (2000) Requirement of seminolipid in spermatogenesis revealed by UDP-galactose: ceramide galactosyltransferase-deficient mice. J. Biol. Chem., 275, 22623–22626.
Goossens, E., Frederickx, V., De Block, G., Van Steirteghem, A.C., and Tournaye, H. (2003) Reproductive capacity of sperm obtained after germ cell transplantation in a mouse model. Hum Reprod., 18, 1874–1880.
Handa, S., Yamato, K., Ishizuka, I., Suzuki, A., and Yamakawa, T. (1974) Biosynthesis of seminolipid: sulfation in vivo and in vitro. J. Biochem. (Tokyo), 75, 77–83.
Honaramooz, A., Behboodi, E., Blash, S., Megee, S.O., and Dobrinski, I. (2003) Germ cell transplantation in goats. Mol. Reprod. Dev., 64, 422–428.[CrossRef][ISI][Medline]
Honke, K., Tsuda, M., Hirahara, Y., Ishii, A., Makita, A., and Wada, Y. (1997) Molecular cloning and expression of cDNA encoding human 3'-phosphoadenylylsulfate:galactosylceramide 3'-sulfotransferase. J. Biol. Chem., 272, 4864–4868.
Honke, K., Hirahara, Y., Dupree, J., Suzuki, K., Popko, B., Fukushima, K., Fukushima, J., Nagasawa, T., Yoshida, N., Wada, Y., and Taniguchi, N. (2002) Paranodal junction formation and spermatogenesis require sulfoglycolipids. Proc. Natl Acad. Sci. USA, 99, 4227–4232.
Huckins, C. (1971) The spermatogonial stem cell population in adult rats. Their morphology, proliferation and maturation. Anat. Rec., 169, 533–558.[CrossRef][Medline]
Ishizuka, I. (1997) Chemistry and functional distribution of sulfoglycolipids. Prog. Lipid Res., 36, 245–319.[CrossRef][ISI][Medline]
Ishizuka, I., Suzuki, M., and Yamakawa, T. (1973) Isolation and characterization of a novel sulfoglycolipid, "seminolipid" from boar testis and spermatozoa. J. Biochem. (Tokyo), 73, 77–87.
Izadyar, F., Spierenberg, G.T., Creemers, L.B., den Ouden, K., and de Rooij, D.G. (2002) Isolation and purification of type A spermatogonia from the bovine testis. Reproduction, 124, 85–94.[Abstract]
Jegou, B. (1993) The sertoli-germ cell communication-network in mammals. Int. Rev. Cytol.,147, 25–96.[ISI][Medline]
Kornblatt, M.J., Knapp, A., Levine, M., Schachter, H., and Murray, R.K. (1974) Studies on the strucuture and formation during spermatogenesis of the sulfoglycerogalactolipid of rat testis. Can. J. Biochem., 52, 689–697.[ISI][Medline]
Ogawa, T., Arechaga, J.M., Avarbock, M.R., and Brinster, R.L. (1997) Transplantation of testis germinal cells into mouse seminiferous tubules. Int. J. Dev. Biol., 41, 111–122.[ISI][Medline]
Ohta, H., Yomogida, K., Dohmae, K., and Nishimune, Y. (2000) Regulation of proliferation and differentiation in spermatogonial stem cells: the role of c-kit and its ligand SCF. Development, 127, 2125–2131.[Abstract]
Ohta, H., Yomogida, K., Tadokoro, Y., Tohda, A., Dohmae, K., and Nishimune, Y. (2001) Defect in germ cells, not in supporting cells, is the cause of male infertility in the cause of spermatogonial stem cells without differentiation. Int. J. Androl., 24, 15–23.[CrossRef][ISI][Medline]
Okabe, M., Ikawa, M., Kominami, K., Nakanishi, T., and Nishimune, Y. (1997) "Green mice" as a source of ubiquitous green cells. FEBS Lett., 407, 313–319.[CrossRef][ISI][Medline]
Rodemer, C., Thai, T.-P., Brugger, B., Kaercher, T., Werner, H., Nave, K.-A., Wieland, F., Gorgas, K., and Just, W.W. (2003) Inactivation of ether lipid biosynthesis causes male infertility, defects in eye development and optic nerve hypoplasia in mice. Hum. Mol. Genet., 12, 1881–1895.
Sette, C., Dolci, S., Geremia, R., and Rossi, P. (2000) The role of stem cell factor and of alternative c-kit gene products in the establishment, maintenance and function of germ cells. Int. J. Dev. Biol., 44, 599–608.[ISI][Medline]
Simons, K. and Ikonen, E. (1997) Functional rafts in cell membranes. Nature, 387, 569–572.[CrossRef][Medline]
Speed, R. R., Taggart, M., and Cooke, H.J. (2003) Spermatogenesis in testes of Dazl null mice after transplantation of wild-type germ cells. Reproduction, 126, 599–604.[Abstract]
Tajima, Y., Sawada, K., Morimoto, T., and Nishimune, Y. (1994) Switching of mouse spermatogonial proliferation from the c-kit receptor-independent type to the receptor-dependent type during differentiation. J. Reprod. Fertil., 102, 117–122.[Abstract]
van Meer, G. (2002) The different hues of lipid rafts. Science, 296, 855–856.
Vos, J.P., Lopes-Cardozo, M., and Gadella, B.M. (1994) Metabolic and functional aspects of sulfogalactolipids. Biochim. Biophys. Acta, 1211, 125–149.[Medline]
Weerachatyanukul, W., Xu, H., Anupriwan, A., Carmona, E., Wade, M., Hermo, L., da Silva, S.M., Rippstein, P., Sobhon, P., Sretarugsa, P., and Tanphaichitr, N. (2003) Acquisition of arylsulfatase A onto the mouse sperm surface during epididymal transit. Biol. Reprod., 69, 1183–1192.
Yeom, Y.I., Fuhrmann, G., Ovitt, C.E., Brehm, A., Ohbo, K., Gross, M., Hubner, K., and Scholer, H.R. (1996) Germline regulatory element of Oct-4 specific for the totipotent cycle of embryonal cells. Development, 122, 881–894.[Abstract]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  M. Rabionet, A. C. van der Spoel, C.-C. Chuang, B. von Tumpling-Radosta, M. Litjens, D. Bouwmeester, C. C. Hellbusch, C. Korner, H. Wiegandt, K. Gorgas, et al. Male Germ Cells Require Polyenoic Sphingolipids with Complex Glycosylation for Completion of Meiosis: A LINK TO CERAMIDE SYNTHASE-3 J. Biol. Chem., May 9, 2008; 283(19): 13357 - 13369. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||