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  • 1
    Electronic Resource
    Electronic Resource
    Sirt1 promotes fat mobilization in white adipocytes by repressing PPAR-γ (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 429 (2004), S. 771-776 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Calorie restriction extends lifespan in organisms ranging from yeast to mammals. In yeast, the SIR2 gene mediates the life-extending effects of calorie restriction. Here we show that the mammalian SIR2 orthologue, Sirt1 (sirtuin 1), activates a critical component of calorie restriction in ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02583
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  • 2
    Electronic Resource
    Electronic Resource
    corrigendum: Sirt1 promotes fat mobilization in white adipocytes by repressing PPAR-γ (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 430 (2004), S. 921-921 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Nature 429, 771–776 (2004). It has been drawn to our attention by Vincent Keng that the image in the bottom-left frame of Fig. 1c of this Letter presents identical data to the one above it on the right. A mistake made by the authors ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02892
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  • 3
    Electronic Resource
    Electronic Resource
    Unstable integration of transfected DNAs into embryonal carcinoma cells (1994)
    Springer
    Somatic cell and molecular genetics 20 (1994), S. 529-540 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Plasmid DNA can be efficiently transfected into embryonal carcinoma cells but it is difficult to isolate clones of cells stably expressing genes present on the transfected plasmids. Even in clonal populations derived from transfected cells, the introduced genes are expressed in some but not all cells. Cotransfection with a region of thePgk-1 gene results in more efficient, stable cotransformation due to increased numbers of copies of the transfected plasmids integrated into the genomic DNA. ThePgK-1 genomic sequences did not allow the plasmid DNA to replicate autonomously but seemed to enhance the ligation of transfected plasmids before their integration into the host genome. Our results suggest a model in which the plasmid DNAs are able to integrate and subsequently excise from the host genome by recombination events enhanced by transcription through the tandemly repeated sequences of the transfected plasmids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02255843
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  • 4
    Electronic Resource
    Electronic Resource
    A Role for RNA Processing in Regulating Expression from Transfected Genes (1998)
    Springer
    Somatic cell and molecular genetics 24 (1998), S. 203-215 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We have examined the expression of cloned genes following their stable integration into the genome of pluripotent embryonal carcinoma stem cells. Transfected genes integrate into the genome as tandem arrays. Expression of reporter genes from these tandem arrays in embryonal carcinoma cells is inefficient probably because genes are subject to repeat-induced gene silencing. We found that expression of reporter genes was significantly enhanced if co-transfected with cloned fragments derived from the murine Pgk-1 gene. The enhanced expression required (a) that the Pgk-1 fragment carries an active promoter, (b) that the promoter drives transcription through a region of more than 12 kbp, and (c) that this transcribed region contains both introns and exons. Reporter gene activity did not require specific Pgk-1 DNA sequences suggesting that the coupled processes of transcription and RNA processing conferred activity on neighboring genes probably by influencing local chromatin structure. Consistent with this idea, the effect of the Pgk-1 gene could be mimicked by exposing cells to butyrate or trichostatin A, inhibitors of histone deacetylase. Thus, the effect of the co-transfected Pgk-1 gene is to inhibit the process of gene inactivation possibly by functioning like an insulator or boundary element in the chromatin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/B:SCAM.0000007123.70630.40
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  • 5
    Electronic Resource
    Electronic Resource
    DNA methylation of two X chromosome genes in female somatic and embryonal carcinoma cells (1991)
    Springer
    Somatic cell and molecular genetics 17 (1991), S. 35-47 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The extent of methylation of DNA sequences upstream and within the two X-linked genes,Pgk-1 andHprt, was analyzed in male and female somatic cells and in female embryonal carcinoma cells carrying either two active X chromosomes (Xa) or one active and one inactive X chromosome (Xi). Sites upstream and within the first intron of bothPgk-1 andHprt were heavily methylated on the Xi in somatic cells and in embryonal carcinoma cells with an Xi. Reactivation of this Xi was accompanied by extensive demethylation of these sites. In female embryonal carcinoma cells with two active X chromosomes, one X inactivates during differentiation in culture; however, methylation did not occur during differentiation, consistent with the idea that DNA methylation does not play a role in the initiation of X inactivation but may be involved in maintaining inactivation of those genes on the Xi.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01233203
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  • 6
    Electronic Resource
    Electronic Resource
    Genes transfected into embryonal carcinoma stem cells are both lost and inactivated at high frequency (1996)
    Springer
    Somatic cell and molecular genetics 22 (1996), S. 383-392 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Embryonal carcinoma (EC) cells can be efficiently transfected with cloned DNAs but there is a strong tendency for expression from transfected genes to be lost from stably transformed cells. To investigate the mechanism responsible for this loss of expression, we transfected P19 EC cells with a gene encoding theE. coli β-galactosidase and examined expression of this gene in clonal populations of cells. Cells that carry and express the β-galactosidase gene give rise to cells that do not express at a rate of about 0.02 events per cell per cell division. These non-expressing cells were of two types, some had lost the transfected genes while others had inactivated them. In those cells that retained but inactivated the transfected genes, the inactive state was stable and suppression was at the level of transcription initiation but not associated with increased DNA methylation. Because transfected DNAs integrate into the genome as tandem arrays, the gene loss and inactivation seen in EC cells may be analogous to the repeat-induced gene inactivation seen in lower eukaryotes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02369894
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  • 7
    Electronic Resource
    Electronic Resource
    Reactivation ofhprt on the inactive X chromosome with DNA demethylating agents (1989)
    Springer
    Somatic cell and molecular genetics 15 (1989), S. 421-434 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The C86 line of female embryonal carcinoma cells contains one active and one inactive X chromosome. Following methylnitrosourea mutagenesis, a clone called C86AGM2 was isolated that carries a mutated hprtgene on the active X chromosome. This hprtm allele encodes an HPRT enzyme that has less than 1% normal enzyme activity, is thermolabile, and has an altered isoelectric point. Following treatment with drugs that demethylate DNA, the hprt+ gene from the inactive X chromosome in C86AGM2 cells became active as determined by the appearance of HPRT activity with the thermodenaturation and electrofocusing characteristics of the normal enzyme. No expression of this hprt+ gene occurred if C86AGM2 cells were induced to differentiate prior to DNA demethylation. Stable lines of C86AGM2 cells expressing both the hprtm and hprt+ genes did not inactivate either gene following differentiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01534893
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  • 8
    Electronic Resource
    Electronic Resource
    Formation and fate of heterokaryons involving embryonal carcinoma cells (1982)
    Springer
    Somatic cell and molecular genetics 7 (1982), S. 205-217 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We have shown that murine embryonal carcinoma (EC) cells will readily fuse to non-EC cells following treatment with polyethylene glycol (PEG). Heterokaryons were detected by autoradiography and by the induction of premature chromosome condensation (PCC). Those heterokaryons formed between EC cells and certain of the non-EC cell types did not proliferate to form viable hybrids. For example, hybrids were not recovered from EC/HeLa heterokaryons in spite of the fact that both EC/3T3 and HeLa/3T3 heterokaryons gave rise to hybrids at high frequency. No hybrids were recovered from fusion mixtures involving Chinese hamster (CHO) cells and EC; however, if the differentiated progeny of the EC cells were used, hybrids were recovered. These results suggest that both developmental and phylogenetic differences between parental cells may contribute to the ability of heterokaryons to proliferate indefinitely.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01567658
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  • 9
    Electronic Resource
    Electronic Resource
    Xist is expressed in female embryonal carcinoma cells with two active X chromosomes (1994)
    Springer
    Somatic cell and molecular genetics 20 (1994), S. 171-182 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract TheXist gene resides on the X chromosome and is expressed in female but not male somatic cells. In female cells, only theXist allele on the inactive X chromosome is transcribed. We investigated the expression ofXist in diploid P10 female embryonal carcinoma cells that have two active X chromosomes.Xist RNA was present in these P10 cells. The X chromosomes in P10 cells carry differentXist alleles whose transcripts can be distinguished by restriction digestion of their cDNAs. Both alleles were expressed. Clones of P10 cells that had lost an X chromosome did not expressXist from the remaining allele. ThusXist is expressed in cultured cells developmentally arrested prior to X chromosome inactivation, indicating that theXist transcript is not always derived from an inactive X chromosome. Therefore,Xist expression per se cannot be a sufficient signal to inactivate an X chromosome.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02254758
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  • 10
    Electronic Resource
    Electronic Resource
    Intragenic regions of the murinePgk-1 locus enhance integration of transfected DNAs into genomes of embryonal carcinoma cells (1994)
    Springer
    Somatic cell and molecular genetics 20 (1994), S. 515-528 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Introduction of recombinant genes into mammalian cells in culture has been an important procedure in establishing the molecular mechanisms of various cellular processes. The efficiency with which plasmid borne recombinant genes are expressed following stable integration into genomes of embryonal carcinoma cells is low. Using the P19 embryonal carcinoma cells as recipients, we found that constructs carrying the promoter and intragenic regions of the murinePgk-1 gene were expressed with high efficiency. This elevated expression was associated with increased numbers of copies of the transfected plasmid DNA stably associated with the genomes of recipient cells. The elevated plasmid copy numbers may result from enhanced ligation of transfected plasmids because cotransfected plasmids were also integrated in increased numbers. The enhanced integration and expression of transfected plasmids required active transcription through an intragenic region ofPgk-1, perhaps resulting in more recombinogenic plasmid DNAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02255842
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