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M Wegner

Publications and source records attributed to M Wegner.

67 records · Page 4Linked to original sources
PubMed1991

Variable effects of phosphorylation of Pit-1 dictated by the DNA response elements.

Pit-1, a tissue-specific POU domain transcription factor, is required for the activation of the prolactin, growth hormone, and Pit-1 promoters that confer regulation by epidermal growth factor, adenosine 3',5'-monophosphate (cAMP), and phorbol esters. Pit-1 is phosphorylated in pituitary cells at two distinct sites in response to phorbol esters and cAMP. Phosphorylation of Pit-1 modifies its conformation on DNA recognition elements and results in increased binding at certain sites and decreased binding at other sites, dependent on DNA sequences adjacent to the core Pit-1 binding motif. One residue (Thr220), located in the POU homeodomain within a sequence conserved throughout the POU-domain family, confers these responses.

Amino Acid Sequence↗
PubMed1991

DNA replication of human polyomavirus JC is stimulated by NF-I in vivo.

Using a combination of Bal31 deletion mutagenesis and site-directed mutagenesis, we analyzed the sequence requirements for the DNA replication of the human neurotropic polyomavirus JC. In addition to defining the late side boundary of the viral core origin we demonstrated that the viral enhancer stimulates replication in vivo. Three regions within the viral enhancer increased the rate of replication, with sequences directly adjacent to the late side of the core origin exhibiting the strongest effect. These sequences interact with various cellular proteins, among them NF-I. Point mutations within the NF-I site abolished the stimulation of DNA replication concomitant with a strong reduction in NF-I binding. By contrast, point mutations which did not interfere with NF-I binding did not influence the rate of replication in vivo. Stimulation of JCV DNA replication could only be observed in vivo, but not in vitro, indicating a role of NF-I in determining chromatin structure.

Animals↗
PubMed1991

TEF, a transcription factor expressed specifically in the anterior pituitary during embryogenesis, defines a new class of leucine zipper proteins.

We have identified and characterized a new member of the leucine zipper (bZIP) gene family of transcription factors, thyrotroph embryonic factor (TEF). Analysis of the ontogeny of TEF gene expression reveals the presence of TEF transcripts, beginning on embryonic day 14, only in the region of the rat anterior pituitary gland in which thyrotrophs arise. This pattern of gene expression corresponds temporally and spatially to the onset of thyroid-stimulating hormone (TSH beta) gene expression, which defines the thyrotroph phenotype. Coupled with this observation, we find that TEF can bind to and trans-activate the TSH beta promoter. In contrast to this restricted pattern of expression during embryogenesis, TEF transcripts appear in several tissues in the mature organism. We propose that TEF belongs to a new class of bZIP proteins on the basis of the unique homology between TEF and another member of the bZIP gene family, the albumin D box-binding protein (DBP). TEF and DBP transcripts are coexpressed in a pituitary cell line, and these two proteins can readily form heterodimers. The DNA-binding and dimerization domains of TEF correspond to those found in other bZIP proteins. We have however, identified a cluster of basic amino acids, found only in TEF and DBP, that is necessary for the proper DNA-binding site specificity of TEF. A major trans-activation domain of TEF resides outside the region of homology to other bZIP proteins. These data are consistent with a role for a member of a new class of bZIP transcription factors in activating gene expression in the developing thyrotroph.

Amino Acid Sequence↗
PubMed1990

Interaction of a protein with a palindromic sequence from murine rDNA increases the occurrence of amplification-dependent transformation in mouse cells.

muNTS1, an element isolated from the nontranscribed spacer of murine rDNA, increases the occurrence of amplification-dependent transformation in mouse cells when integrated into plasmid DNA containing a selectable marker (Wegner, M., Zastrow, G., Klavinius, A., Schwender, S., Müller, F., Luksza, H., Hoppe, J., Wienberg, J., and Grummt, F. (1989) Nucleic Acids Res. 17, 9909-9932). In an initial attempt to dissect muNTS1 into its structural components we localized part of the transformation increasing activity to a long AT-rich stretch from the 5' region which interacts with HMG-I. Here we identify a second element on muNTS1 which also stimulates the rate of amplification-coupled transformation in cis. It is found in the 3' region of muNTS1 and contains the 11-base pair palindrome ATGGCTGCCAT. It is conserved in the otherwise strongly divergent ribosomal NTS regions from mouse, rat, and man and is also found in the origin/enhancer region of human papovavirus JC. The palindromic sequence interacts specifically with proteins from mouse cell extracts. Protein-DNA interaction was dependent on the presence of zinc ions in the extract. Point-specific mutations within the palindrome reduced protein-DNA complex formation substantially and concomitantly abolished the ability to stimulate the frequency of transformation. The binding activity was purified and shown to consist of two polypeptides with molecular masses of 70 and 73 kDa.

Animals↗
PubMed1990

Netropsin, distamycin and berenil interact differentially with a high-affinity binding site for the high mobility group protein HMG-I.

Netropsin, distamycin, berenil and the chromosomal protein HMG-I share the ability to bind preferentially to AT-rich regions of DNA. We studied the binding behaviour of the chemical agents towards a high-affinity binding site for HMG-I by DNase I and MPE footprinting and analyzed their ability to challenge HMG-I-DNA complexes by competition experiments. Significant differences in the binding affinities and in the efficiencies to abolish HMG-I-DNA complexes were observed for the three drugs. Netropsin proved to be the most avidly binding compound and the most efficient competitor raising the interesting possibility that netropsin affects cell growth by interfering with HMG-I-DNA interaction.

Amidines↗
PubMed1990

An amplification-promoting sequence from mouse genomic DNA: interaction with a trans-acting factor that also affects gene expression.

We previously identified murine DNA sequences that stimulate the amplification of cis-linked plasmid DNA in mouse cells under selective conditions (Holst et al., 1988). Here we focus on the structural features of one of these elements, the 229-bp element 5. The amplification-promoting activity was fully recovered from the middle part of element 5. The active region interacted in a sequence-specific way with a protein from nuclear extracts. Using footprinting analyses the binding region was characterized and subsequently shown to be functionally active as an amplification-promoting sequence, whereas a mutated binding site was inactive. Therefore, cis-acting element 5 functioned via interaction with a trans-acting factor. The same binding site was also active as a promoter element for RNA polymerase II transcription, because it efficiently reconstituted the activity of a truncated herpes simplex virus type 1 (HSV-1) thymidine kinase (tk) gene promoter lacking the distal Sp1 binding site. Thus, the same protein seems to function in both RNA polymerase II transcription and DNA amplification. Possible relationships between both functions are discussed.

Animals↗
PubMed1989

Cis-acting sequences from mouse rDNA promote plasmid DNA amplification and persistence in mouse cells: implication of HMG-I in their function.

Searching for amplification promoting sequences within the murine rDNA cistrons, we isolated two elements from the nontranscribed spacer region. These 370 bp and 423 bp long cis-acting elements, referred to as muNTS1 and muNTS2, are localized 4.1 kb and 4.6 kb upstream the RNA polymerase I transcriptional start site. They contain ca. 50 bp long AT-rich sequences that strongly interact with a protein from nuclear extracts. The protein could be purified and identified as HMG-I. A synthetic oligonucleotide encompassing the AT-rich stretch from muNTS1 is able to substitute for the muNTS elements. A similar sequence from the nontranscribed spacer of rat has previously been reported to be important for the function of the RNA polymerase I enhancer (1). Therefore the interaction of HMG I with the muNTS elements may play a role both in the stimulation of DNA amplification and transcription.

Amino Acid Sequence↗
PubMed1989

Identification of an amplification promoting DNA sequence from the hypotrichous ciliate Stylonychia lemnae.

The macronucleus of the hypotrichous ciliate Stylonychia lemnae contains a 1218 bp long DNA molecule which becomes highly amplified during vegetative growth due to a continuous overreplication over a long time range. The region which is located upstream the open reading frame of the overamplified 1.2kbp Stylonychia DNA molecule enabled plasmids containing an inefficiently transcribed thymidine kinase gene to persist and amplify upon transfection into mouse L fibroblasts under selective conditions. This region contains long AT-rich stretches. The AT-rich sequences interact with a previously characterized HMG-I like protein from mouse Ehrlich ascites tumour cells. A binding activity for AT-rich stretches could also be identified in macronuclear extracts from Stylonychia lemnae. We suggest a common mechanism for overamplification in Stylonychia macronuclei during vegetative growth and amplification of plasmid DNA in heterologous mouse cells under the influence of a common element.

Amino Acid Sequence↗
PubMed1989

Distinct mouse DNA sequences enable establishment and persistence of plasmid DNA polymers in mouse cells.

Distinct elements isolated from mouse genomic DNA confer on plasmid DNA the ability to persist at high copy numbers in mouse L fibroblasts (1). Field inversion gel electrophoresis demonstrated that - in contrast to our previous assumption - the persisting plasmid DNA does not exist extrachromosomally but as clusters of tandem repeats integrated into genomic DNA. Digestion with restriction endonucleases that do not cut within the plasmid DNA results in fragments of 50-300 kb in length indicating reiteration of 10-50 plasmid DNA molecules. Restriction with several enzymes that cut once or twice within the plasmid sequences lead to fragment(s) indicative for head-to-tail tandem repeats. In situ hybridization revealed signals for a long homogeneously staining region (HSR) in one or two chromosomes per cell nucleus. Possibilities how these elements could act in the establishment and/or maintenance of the head-to-tail polymers of plasmid DNA in mouse cells are discussed.

Animals↗
PubMed1988

Müller cell endfeet at the inner surface of the retina: light microscopy.

Using fractions of the protein spectrum of the cat retina as immunogens, we have generated antibodies with substantial specificity for the Müller cells of the retina of cat, rabbit, guinea pig, and rat. The antibodies appear to bind to the filamentous components of the Müller cells and allow demonstration of the pattern of Müller cell endfeet at the inner surface of the retina, best seen in wholemount preparations. In sections and at the edge of wholemount preparations the somas and processes of the cells can be observed. Müller cells are more evenly distributed over the retina than ganglion cells, indicating that their proliferation continues during the differential growth of retina which continues into postnatal life. The morphology and distribution of the endfeet varies with the structures present at the inner surface of the retina. Where the axon bundles are thick, the endfeet are relatively small and are confined to narrow rows between bundles. Müller cell endfeet are also separated widely by large blood vessels. In both situations, it seems likely that Müller cells and astrocytes both contribute, perhaps competitively, to form the glia limitans of the inner surface of the retina. Where the somas of neurones are densely packed in the ganglion cell layer, the endfeet are small and numerous, forming rings around the somas. Where axon bundles, vessels, and somas are sparse, the endfeet appear largest and form a regular array.

Animals↗
PubMedDate not supplied

Muscarinic acetylcholine receptors activate the acetylcholinesterase gene promoter.

The acetylcholinesterase (AChE) gene promoter contains several overlapping binding sites for Sp1 and Egr-1 transcription factors. Cotransfection experiments and promoter assays showed that Egr-1 can potently activate transcription from the human AChE promoter. Muscarinic acetylcholine receptors (mAChR) rapidly activate, via protein kinase C-mediated signaling, expression of the Egr-1 gene, leading to dramatically increased nuclear concentrations of Egr-1 protein, and to increased binding of Egr-1 to specific DNA recognition sequences. These mAChR-induced increases are followed by increased transcription from the human AChE promoter. In vivo studies with intraventricular infusions of the cholinergic immunotoxin 192 IgG saporin showed more than 80% decrease of AChE activity in cholinergic target areas of the hippocampus and brain cortex. The results are compatible with a combination of decreased AChE activity in degenerating subcortical cholinergic projections, and additional decreases in postsynaptic AChE gene expression. Together our data show that mAChR can activate transcription from the AChE promoter via increased synthesis of Egr-1. The results suggest a feedback mechanism by which the AChE gene is activated by cholinergic neurotransmission, possibly leading to increased formation of AChE protein and accelerated degradation of acetylcholine at cholinergic synapses. This possibility suggests testing of cholinomimetic compounds currently in development for the treatment of Alzheimer's disease for their potential ability to increase AChE gene expression.

Acetylcholinesterase↗