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Query: UNIPROT:P10721 (c-kit)
 6,575 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the postnatal testis, the c-kit transmembrane tyrosine-kinase receptor is expressed in type A spermatogonia, and its transcription ceases at the meiotic phase of spermatogenesis. Alternative, shorter c-kit transcripts are expressed in post-meiotic germ cells. These transcripts should encode a truncated version of the c-kit protein, lacking the extracellular, the transmembrane and part of the intracellular tyrosine-kinase domains. The 5' end of the alternative c-kit transcripts maps within an intron of the mouse c-kit gene. We now show that this intron contains a promoter active in nuclear extracts of round spermatids, and that two discrete sequences upstream of the transcriptional start site bind spermatid-specific nuclear factors. Deletion of both these sequences abolishes activity of the promoter in vitro. We have also established that this promoter is functional in vivo, in a tissue-and cell-specific fashion, since intronic sequences drive the expression of the E. coli lacZ reporter gene in transgenic mice specifically in the testis. Transgene expression is confined to haploid germ cells of seminiferous tubules, starting from spermatids at step 9, and disappearing at step 13, indicating that cryptic promoter within the 16th intron of the mouse c-kit gene is active in a short temporal window at the end of the transcriptional phase of spermiogenesis. In agreement with these data, western blot experiments using an antibody directed against the carboxy-terminal portion of the mouse c-kit protein showed that a polypeptide, of the size predicted by the open reading frame of the spermatid-specific c-kit cDNA, accumulates in the latest stages of spermatogenesis and in epididymal spermatozoa. An immunoreactive protein of the same size can be produced in both eukaryotic and prokaryotic artificial expression systems.
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PMID:A cell- and developmental stage-specific promoter drives the expression of a truncated c-kit protein during mouse spermatid elongation. 862 Aug 56

The c-KIT proto-oncogene encodes for a transmembrane receptor and is associated with maturation of several cell types, including germ cells. The ligand of the receptor has been identified as stem cell factor (SCF). Loss or alteration of the expression of either of these factors leads to anemia, albinism, and/or sterility in mice. We examined the expression of c-KIT and SCF by immunohistochemistry in specimens from normal and infertile human testis. All specimens were obtained in the evaluation of male subfertility. We were able to demonstrate staining for c-KIT in Leydig cells in all specimens. Normal testis stained for c-KIT in the cytoplasm of early spermatogenic cells, as well as the acrosomal granules of the round spermatids and the acrosome of testicular spermatozoa. However, staining in testis demonstrating maturation arrest failed to demonstrate acrosomal staining, and Sertoli-only specimens demonstrated staining for c-KIT in Leydig cells only. The results for SCF demonstrated an overall uniform staining of Leydig cells in all specimens. The intensity of staining of Sertoli cells increased from normal to maturation arrest to Sertoli-only specimens. Germ cell staining was consistently negative. We hypothesize that these staining patterns for SCF are due to either lack of staining of the receptor-ligand complex or overexpression of the kit ligand in tissue that does not express the kit receptor. It appears that the c-kit receptor is expressed in the acrosome of developing germ cells, as well as in Leydig cells and early spermatogenic cells, suggesting a role in the acrosome reaction, as well as germ cell maturation and differentiation.
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PMID:Expression of c-KIT and its ligand, stem cell factor, in normal and subfertile human testicular tissue. 888 3

Microinjection of a truncated form of the c-kit tyrosine kinase present in mouse spermatozoa (tr-kit) activates mouse eggs parthenogenetically, and tr-kit- induced egg activation is inhibited by preincubation with an inhibitor of phospholipase C (PLC) (Sette, C., A. Bevilacqua, A. Bianchini, F. Mangia, R. Geremia, and P. Rossi. 1997. Development [Camb.]. 124:2267-2274). Co-injection of glutathione-S-transferase (GST) fusion proteins containing the src-homology (SH) domains of the gamma1 isoform of PLC (PLCgamma1) competitively inhibits tr-kit- induced egg activation. A GST fusion protein containing the SH3 domain of PLCgamma1 inhibits egg activation as efficiently as the whole SH region, while a GST fusion protein containing the two SH2 domains is much less effective. A GST fusion protein containing the SH3 domain of the Grb2 adaptor protein does not inhibit tr-kit-induced egg activation, showing that the effect of the SH3 domain of PLCgamma1 is specific. Tr-kit-induced egg activation is also suppressed by co-injection of antibodies raised against the PLCgamma1 SH domains, but not against the PLCgamma1 COOH-terminal region. In transfected COS cells, coexpression of PLCgamma1 and tr-kit increases diacylglycerol and inositol phosphate production, and the phosphotyrosine content of PLCgamma1 with respect to cells expressing PLCgamma1 alone. These data indicate that tr-kit activates PLCgamma1, and that the SH3 domain of PLCgamma1 is essential for tr-kit-induced egg activation.
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PMID:Involvement of phospholipase Cgamma1 in mouse egg activation induced by a truncated form of the C-kit tyrosine kinase present in spermatozoa. 972 17

Although spermatogenesis is essential for reproduction, little is known about spermatogonial stem cells. These cells provide the basis for spermatogenesis throughout adult life by undergoing self-renewal and by providing progeny that differentiate into spermatozoa. A major impediment to our understanding of the biology of these stem cells is the inability to distinguish them from spermatogonia that are committed to differentiation. We made use of the known association of stem cells with basement membranes and our spermatogonial transplantation assay system to identify specific molecular markers on the stem cell surface. Selection of mouse testis cells with anti-beta1- or anti-alpha6-integrin antibody, but not anti-c-kit antibody, produced cell populations with a significantly enhanced ability to colonize recipient testes and generate donor cell-derived spermatogenesis. We demonstrate spermatogonial stem cell-associated antigens by using an assay system based on biological function. Furthermore, the presence of surface integrins on spermatogonial stem cells suggests that these cells share elements of a common molecular machinery with stem cells in other tissues.
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PMID:beta1- and alpha6-integrin are surface markers on mouse spermatogonial stem cells. 1031 13

The spermatogonial stem cell initiates and maintains spermatogenesis in the testis. To perform this role, the stem cell must self replicate as well as produce daughter cells that can expand and differentiate to form spermatozoa. Despite the central importance of the spermatogonial stem cell to male reproduction, little is known about its morphological or biochemical characteristics. This results, in part, from the fact that spermatogonial stem cells are an extremely rare cell population in the testis, and techniques for their enrichment are just beginning to be established. In this investigation, we used a multiparameter selection strategy, combining the in vivo cryptorchid testis model with in vitro fluorescence-activated cell sorting analysis. Cryptorchid testis cells were fractionated by fluorescence-activated cell sorting analysis based on light-scattering properties and expression of the cell surface molecules alpha6-integrin, alphav-integrin, and the c-kit receptor. Two important observations emerged from these analyses. First, spermatogonial stem cells from the adult cryptorchid testis express little or no c-kit. Second, the most effective enrichment strategy, in this study, selected cells with low side scatter light-scattering properties, positive staining for alpha6-integrin, and negative or low alphav-integrin expression, and resulted in a 166-fold enrichment of spermatogonial stem cells. Identification of these characteristics will allow further purification of these valuable cells and facilitate the investigation of molecular mechanisms governing spermatogonial stem cell self renewal and hierarchical differentiation.
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PMID:Spermatogonial stem cell enrichment by multiparameter selection of mouse testis cells. 1090 1

The c-kit gene plays a fundamental role during the establishment, the maintenance and the function of germ cells. In the embryonal gonad the c-kit tyrosine kinase receptor and its ligand Stem Cell Factor (SCF) are required for the survival and proliferation of primordial germ cells. In the postnatal animal, c-kit/SCF are required for the production of the mature gametes in response to gonadotropic hormones, i.e. for the survival and/or proliferation of the only proliferating germ cells of the testis, the spermatogonia, and for the growth and maturation of the oocytes. Finally, a truncated c-kit product, tr-kit, specifically expressed in post-meiotic stages of spermatogenesis and present in mature spermatozoa, causes parthenogenetic activation when microinjected into mouse eggs, suggesting that it might play a role in the final function of the gametes, fertilization.
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PMID:The role of stem cell factor and of alternative c-kit gene products in the establishment, maintenance and function of germ cells. 1106 23

The tyrosine-kinase receptor c-kit and its ligand, stem cell factor (SCF), are essential for the maintenance of primordial germ cells (PGCs) in both sexes. However, c-kit and a post-meiotic-specific alternative c-kit gene product play important roles also during post-natal stages of spermatogenesis. In the adult testis, the c-kit receptor is re-expressed in differentiating spermatogonia, but not in spermatogonial stem cells, whereas SCF is expressed by Sertoli cells under FSH stimulation. SCF stimulates DNA synthesis in type A spermatogonia cultured in vitro, and injection of anti-c-kit antibodies blocks their proliferation in vivo. A point mutation in the c-kit gene, which impairs SCF-mediated activation of phosphatidylinositol 3-kinase, does not cause any significant reduction in PGCs number during embryonic development, nor in spermatogonial stem cell populations. However males are completely sterile due to a block in the initial stages of spermatogenesis, associated to abolishment of DNA-synthesis in differentiating A1-A4 spermatogonia. With the onset of meiosis c-kit expression ceases, but a truncated c-kit product, tr-kit, is specifically expressed in post-meiotic stages of spermatogenesis, and is accumulated in mature spermatozoa. Microinjection of tr-kit into mouse eggs causes their parthenogenetic activation, suggesting that it might play a role in the final function of the gametes, fertilization.
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PMID:Role of c-kit in mammalian spermatogenesis. 1107 57

Dazl encodes an RNA-binding protein essential for spermatogenesis. Mice that are deficient for Dazl are infertile, lacking any formation of spermatozoa, and the only germ cells present are spermatogonia and a few spermatocytes. To gain more insight regarding the timing of the spermatogenic arrest in Dazl -/- mice, we studied the spermatogonial cell types present in testis sections and in seminiferous tubular whole mounts. Most of the seminiferous tubular cross-sections contained A spermatogonia as the most advanced cell type, with only very few containing cells up to pachytene spermatocytes. Both 5-bromodeoxy-uridine incorporation and mitotic index indicated that the remaining A spermatogonia were actively proliferating. C-kit immunohistochemical studies showed that most of the A spermatogonia were positively stained for the c-Kit protein ( approximately 80%). The clonal composition of the A spermatogonia in tubular whole mounts indicated these cells to be A(single) (A(s)), A(paired) (A(pr)), and A(aligned) (A(al)) spermatogonia. It is concluded that the prime spermatogenic defect in the Dazl -/- mice is a failure of the great majority of the A(al) spermatogonia to differentiate into A(1) spermatogonia. As a result, most seminiferous tubules of Dazl -/- mice only contain actively proliferating A(s), A(pr), and A(al) spermatogonia, with cell production being equaled by apoptosis of these cells.
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PMID:Nature of the spermatogenic arrest in Dazl -/- mice. 1151 40

To determine if the expression of green fluorescent protein (GFP) during spermatogenesis can compromise the fertility of transgenic animals, we have produced mouse transgenic lines expressing GFP in the testis under the control of the potent immediate early promoter and enhancer region of the human cytomegalovirus (CMV). GFP expression was detected in the germ cells with no apparent effect on the fertility of any of the five transgenic lines studied. We demonstrate that the CMV promoter is transcriptionally active in the testes of mice aged 7 days. However, protein could be visually detected only after day 10. GFP was not found either in mature spermatozoa or in Sertoli cells, but it was evident in round spermatids from seminiferous tubules and in cytoplasmic drops of spermatozoa from the epididymis. We also detected GFP in spermatogonia expressing c-kit, which indicates that GFP expression driven by the CMV promoter takes place during the proliferative phase of spermatogenesis. The expression of GFP during spermatogenesis did not affect the fertility of transgenic mice.
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PMID:CMV-driven expression of green fluorescent protein (GFP) in male germ cells of transgenic mice and its effect on fertility. 1155 88

Histamine synthesis in male reproductive tissues remains largely unknown. The interaction between stem cell factor and its receptor, c-Kit, has been found to be essential for the maturation of male germ cells and peripheral mast cells. Based on this analogy, we investigated the expression of histidine decarboxylase (HDC), the rate-limiting enzyme of histamine synthesis, in mouse male germ cells. Immunohistochemical analyses revealed that HDC is localized in the acrosomes of spermatids and spermatozoa. In the testis, epididymis, and spermatozoa, a significant amount of histamine and HDC activity were detected. W/W(V) mice, known to lack most of their germ cells in the seminiferous tubules, were found to lack HDC protein expression as well as HDC activity in the testis. An in vitro acrosome reaction induced by a calcium ionophore, caused the release of histamine from epididymal spermatozoa. Our observations indicate that histamine is produced in and released from the acrosomes.
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PMID:Expression of L-histidine decarboxylase in mouse male germ cells. 1182 77


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