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  • 1
    Electronic Resource
    Electronic Resource
    Trafficking of sulfated glycoprotein-1 (prosaposin) to lysosomes or to the extracellular space in rat Sertoli cells (1996)
    Springer
    Cell & tissue research 283 (1996), S. 385-394 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Sertoli cells ; Lysosomes ; SGP-1 ; Prosaposin ; Cathepsin L ; Golgi complex ; Secretion ; Rat (Sprague Dawley)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Sulfated glycoprotein-1 (prosaposin) exists in 2 forms: a 65 kDa form targeted to lysosomes and a 70 kDa form secreted extracellularly. In order to understand the sorting and targeting mechanisms of the two forms of SGP-1, we have compared their maturation, processing, and secretion in rat Sertoli cells in vivo. Metabolic labeling experiments in vivo demonstrated that the 65 kDa form is synthesized first, then post-translationally modified to the 70 kDa form of SGP-1. Subcellular fractionation of testicular homogenate was used to obtain Golgi fractions containing up to 50-fold enrichment in galactosyltransferase. Permeabilization of enriched Golgi fractions with saponin released the 70 kDa form, but did not affect the 65 kDa protein. While excess free mannose 6-phosphate did not release lysosomal SGP-1, it released the 35 kDa cathepsin L from Golgi membranes. Using quantitative electron-microscopic immunocytochemistry, the lysosomal contents of SGP-1 were shown to increase significantly after the administration of tunicamycin in vivo. Therefore, the trafficking of the 65 kDa form of SGP-1 to the lysosomes appears to be independent of the M6P-receptor pathway. The 70 kDa form of SGP-1 was found to aggregate within perforated Golgi fractions in a process which depends on low pH and calcium ions. We conclude that the targeting of the 65 kDa form of SGP-1 to the lysosomes involves an early association with Golgi membrane that is independent of mannose 6-phosphate receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050549
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  • 2
    Electronic Resource
    Electronic Resource
    Role of sulfated glycoprotein-1 (SGP-1) in the disposal of residual bodies by sertoli cells of the rat (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 40 (1995), S. 91-102 
    Details
    ISSN: 1040-452X
    Keywords: Sertoli cells ; Phagocytosis ; Lysosomes ; SGP-1 ; Prosaposin ; Saposins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Sulfated glycoprotein-1 (SGP-1) is a polypeptide secreted by Sertoli cells in the rat. Sequence analysis revealed a 76% sequence similarity with human prosaposin produced by various cell types. Human prosaposin is a 70 kDa protein which is cleaved in the lysosomes into four 10-15 kDa polypeptides termed saposins A, B, C, and D. The function of lysosomal saposins is to either solubilize certain membrane glycolipids or to form complexes with lysosomal enzymes and/or their glycolipid substrate to facilitate their hydrolysis. The present investigation dealt with the delivery of SGP-1 into the phagosomes of Sertoli cells; these phagosomes contain the residual bodies which detach from the late spermatids at the time of spermiation. Immunogold labeling with anti-SGP-1 antibody was found over Sertoli cell lysosomes, but was absent from phagosomes formed after phagocytosis of spermatid residual bodies in the apical Sertoli cell cytoplasm in stages VIII and early IX of the cycle of the seminiferous epithelium. The phagosomes found later in the basal Sertoli cell cytoplasm in stages IX and X of the cycle became labeled with the antibody as the components of the residual bodies rapidly underwent lysis and disappeared from the Sertoli cells. Sertoli cell lysosomes isolated by cell fractionation (estimated purity of 80%) were found to contain a 65 kDa form of SGP-1 or prosaposin, as well as the 15 kDa polypeptides or saposins. Thus, it appears that this unique lysosomal form of SGP-1 reached the Sertoli cell phagosomes and that their derived polypeptides, the saposins, must play a role in the hydrolysis of membrane glycolipids found in phagocytosed residual bodies. © 1995 Wiley-Liss, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080400112
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  • 3
    Electronic Resource
    Electronic Resource
    Variations in the level of transferrin and SGP-2 mRNAs in Sertoli cells of vitamin A-deficient rats (1991)
    Springer
    Cell & tissue research 263 (1991), S. 125-130 
    Details
    ISSN: 1432-0878
    Keywords: Transferrin ; Sulfated glycoprotein-2 ; Sertoli cells ; In-situ hybridization ; Rat (Sprague-Dawley)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Stage-specific levels and long-term effects of vitamin A deficiency on transferrin and sulfated glycoprotein-2 (SGP-2) mRNAs were analyzed in normal rats and in rats fed a vitamin A-deficient diet for 49 days (49 day VAD) and 77 days (77 day VAD). Histological sections of testes from these animals were hybridized in situ with single stranded 3H-labeled RNA probes complementary to the transferrin and SGP-2 (clusterin) mRNAs prepared from specific cDNAs subcloned in the SP65 vector. In all cases the probes were visualized and quantified by radioautography. Vitamin A deficiency (49 day VAD rats) differentially affected the levels of these mRNAs by increasing significantly the level of SGP-2 transcripts and decreasing the level of transferrin mRNA. However, in both cases the stage-specific pattern characteristic of the normal testes remained cyclic indicating that the specific interactions between germ cells and Sertoli cells may play an important role in modulating the cyclic activities of Sertoli cells. The data also indicated that dividing spermatocytes, secondary spermatocytes and steps 13–14 spermatids were associated with Sertoli cells expressing high levels of transferrin mRNA, while steps 7, 8 and particularly 19 spermatids were associated with Sertoli cells expressing high levels of SGP-2 mRNA. In contrast to the shorter term, a longer term of vitamin A deficiency (77 day VAD rats) produced a significant decrease in the levels of both transferrin and SGP-2 mRNAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318407
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  • 4
    Electronic Resource
    Electronic Resource
    Receptor-mediated endocytosis of testicular transferrin by germinal cells of the rat testis (1992)
    Springer
    Cell & tissue research 267 (1992), S. 45-55 
    Details
    ISSN: 1432-0878
    Keywords: Transferrin ; Transferrin receptor ; Ferritin ; Gerrninal cells ; Sertoli cells ; Rat (Sprague-Dawley)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The present study examines events of the Sertoli cell iron delivery pathway following the secretion of diferric testicular transferrin (tTf) into the adluminal compartment of the rat seminiferous epithelium. The unidirectional secretion of tTf by Sertoli cells was verified, in vivo, and it was shown that this protein is internalized by adluminal germ cells. It was further determined by Scatchard analysis that this internalization was mediated by high affinity transferrin binding sites on the surface of round spermatids, numbering 1453/cell and displaying a Kd=0.6×10-9 M. Northern blot analysis of RNA isolated from adluminal germ cells, namely spermatocytes, round spermatids and elongating spermatids, indicated that these cells expressed Tf receptor mRNA and ferritin mRNA in levels inversely related to their stage of maturation. Finally it was determined that following binding and internalization in round spermatids, Tf became associated with the endosomal compartment and was recycled back to the cell surface. This study illustrates the immediate fate of tTf once it is secreted by the Sertoli cell. Thus, diferric tTf binds of Tf receptor on the surface of adluminal germ cells, is internalized by receptor-mediated endocytosis and the apo Tf-Tf receptor complex is recycled back to the cell surface where apotTf is released into the adluminal fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318690
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