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G Hager

Publications and source records attributed to G Hager.

At least 37 records · Page 2Linked to original sources
PubMed1998

Characterization of BCE-1, a transcriptional enhancer regulated by prolactin and extracellular matrix and modulated by the state of histone acetylation.

We have previously described a 160-bp enhancer (BCE-1) in the bovine beta-casein gene that is activated in the presence of prolactin and extracellular matrix (ECM). Here we report the characterization of the enhancer by deletion and site-directed mutagenesis, electrophoretic mobility shift analysis, and in vivo footprinting. Two essential regions were identified by analysis of mutant constructions: one binds C/EBP-beta and the other binds MGF/STAT5 and an as-yet-unidentified binding protein. However, no qualitative or quantitative differences in the binding of these proteins were observed in electrophoretic mobility shift analysis using nuclear extracts derived from cells cultured in the presence or absence of ECM with or without prolactin, indicating that prolactin- and ECM-induced transcription was not dependent on the availability of these factors in the functional cell lines employed. An in vivo footprinting analysis of the factors bound to nuclear chromatin in the presence or absence of ECM and/or prolactin found no differences in the binding of C/EBP-beta but did not provide definitive results for the other factors. Neither ECM nor prolactin activated BCE-1 in transient transfections, suggesting that the chromosomal structure of the integrated template may be required for ECM-induced transcription. Further evidence is that treatment of cells with inhibitors of histone deacetylase was sufficient to induce transcription of integrated BCE-1 in the absence of ECM. Together, these results suggest that the ECM induces a complex interaction between the enhancer-bound transcription factors, the basal transcriptional machinery, and a chromosomally integrated template responsive to the acetylation state of the histones.

Acetylation↗
PubMed1997

Purification and nucleic-acid-binding properties of a Saccharomyces cerevisiae protein involved in the control of ploidy.

Scp160p (Saccharomyces cerevisiae protein involved in the control of ploidy), a polypeptide with a molecular mass of around 160 kDa, is associated with the nuclear envelope and the endoplasmic reticulum. The most noteworthy phenotype of SCP160 deletion mutants is a decrease in viability and an increased number of chromosomes in the surviving cells [Wintersberger, U., Kühne, C. & Karwan, A. (1995) Yeast 11, 929-944]. Scp160p contains 14 KH domains, conserved motifs that have lately been identified in a variety of RNA-binding proteins. In this report, we demonstrate that the Scp160p sequence shows nearly perfect colinearity with the putative gene product of C08H9.2 from the nematode Caenorhabditis elegans as well as with the vigilins, vertebrate RNA-binding proteins with a cellular location similar to that of Scp160p. Moreover, we found that Scp160p contains a potential nuclear-export signal (NES) near its N-terminus and a potential nuclear-localization signal (NLS) between KH domains 3 and 4. To determine whether the protein is able to bind to RNA, we purified Scp160p from yeast cell extract by DNA-cellulose and anti-Scp160p affinity chromatography. In northwestern blotting experiments, the electrophoretically homogeneous protein bound to ribohomopolymers and ribosomal RNA as well as to single-stranded and double-stranded DNA. Subcellular fractionation studies revealed that the major part of Scp160p is membrane associated via ionic interactions and can be released from the membrane fraction under conditions that lead to a dissociation of ribosomes. Together, our findings suggest that Scp160p is the yeast homologue of the vigilins, and point to a role for Scp160p in nuclear RNA export or in RNA transport within the cytoplasm.

Amino Acid Sequence↗
PubMed1997

Retinoid-induced chromatin structure alterations in the retinoic acid receptor beta2 promoter.

Transcription of the retinoic acid receptor beta2 (RARbeta2) gene is induced by retinoic acid (RA) in mouse P19 embryonal carcinoma (EC) cells. Here we studied RA-induced chromatin structure alterations in the endogenous RARbeta2 promoter and in an integrated, multicopy RARbeta2 promoter in EC cells. RA markedly increased restriction site accessibility within the promoter, including a site near the RA responsive element (RARE) to which the nuclear receptor retinoid X receptor (RXR)-RAR heterodimer binds. These changes coincided with RA-induced alterations in the DNase I hypersensitivity pattern in and around the promoter. These changes became undetectable upon removal of RA, which coincided with the extinction of transcription. Analyses with receptor-selective ligands and an antagonist showed that increase in restriction site accessibility correlates with transcriptional activation, which parallels the RA-induced in vivo footprint of the promoter. Despite these changes, the micrococcal nuclease digestion profile of this promoter was not altered by RA. These results indicate that concurrent with the binding of the RXR-RAR heterodimer to the RARE, the local chromatin structure undergoes dynamic, reversible changes in and around the promoter without globally affecting the nucleosomal organization.

Animals↗
PubMed1997

Pattern of differentiated nerve cells in hydra is determined by precursor migration.

The nervous system of the fresh water polyp hydra is built up as a nerve net spread over the whole body, with higher densities in the head and the foot. In adult hydra, as a result of continuous growth, new nerve cell differentiation takes place continuously. The pattern of nerve cell differentiation and the role of nerve cell precursor migration in establishing the pattern have been observed in vivo by vitally labelling precursor cells with DiI. The results indicate that nerve cell precursors arise directly from stem cells, complete a final cell cycle and divide, giving rise to two daughter cells, which differentiate into nerve cells. A subpopulation of the nerve cell precursors are migratory for a brief interval at the onset of the terminal cell cycle, then complete the cell cycle and divide at the site of differentiation. Labelling small patches of tissue in the head, body column and peduncle/foot with DiI indicated that formation of nerve cell precursors was nearly constant at all three positions. However, at least half of the labelled precursors in the body column migrated to the head or foot before differentiating; by contrast, precursors in head and foot differentiated in situ without significant migration. This redistribution leads to a net increase of nerve cell precursors in head and foot compared to body column and thus to the higher density of nerve cells in these regions.

Animals↗
PubMed1995

Domain-specific antibodies against the B2 chain of laminin inhibit neuronal migration in the neonatal rat cerebellum.

Although the spatial and temporal patterns of neuronal migration have been analyzed in great detail, little direct evidence is available as to what extracellular matrix molecules are involved. Because there is indirect evidence implicating the extracellular matrix protein laminin in neuronal migration, we investigated the effects of antibodies against a synthetic peptide derived from a neurite outgrowth domain of the B2 chain of laminin on neuronal migration in living cerebellar slices. We show by using infrared video microscopy that divalent Fab2 fragments of these antibodies inhibit granule neuronal movement in living slices of (P8) rat cerebellum. This inhibition of neuronal movement manifests itself by cessation of both radial and horizontal translocations of nuclei inside the granule neuronal processes. Fab2 fragments of antibodies against the intact (native) laminin molecule or Fab2 fragments from the preimmune serum do not affect nuclear translocation. Immunocytochemistry shows binding of the divalent Fab2 fragments of the B2 chain-specific antibodies to the Purkinje and Bergmann glial cell areas, and as punctate deposits in between the cells of the external granule cell layer. Native laminin antibodies bind to the basement membranes, and binding of the Fab2 fragments from the preimmune sera cannot be demonstrated. These results indicate that neuronal migration in the postnatal rat cerebellum in vivo involves nuclear translocation that can be inhibited by antibodies against a neurite outgrowth domain of the B2 chain of laminin. Thus, migration of cerebellar granule neurons may depend on the interaction between a neurite outgrowth domain of the B2 chain of laminin and neuronal cytoskeleton involved in nuclear movement.

Animals↗
PubMed1995

Novel forms of neuronal migration in the rat cerebellum.

Infrared video microscopy of neonatal rat cerebellum (P0-P14) was used to directly visualize migrating granule neurons in relation to other cerebellar cells in a brain slice for up to 24 hr. Initially (P0-P5), granule neurons move along radial migration pathways of other neuronal fibers. These pathways are probably established by the bipolar granule neurons that attach to the external basement membrane via one process and extend another process toward the Purkinje cell layer. At P5-P8, a substantial number of granule neurons move horizontally and extend long parallel fibers. Both radially and horizontally migrating granule neurons move by nuclear translocation inside their preformed processes with a speed that varies between 6 and 120 microns/hr. In P10-P12 animals, the horizontally oriented granule neurons start to migrate radially. They move into the internal granule cell layer either along the radial pathways of other neuronal fibers or in contact with the matured glial processes. The radial neuronal migration pathways disappear by P14 whereas the glial cell processes are maintained and reach the basal lamina. These results describe novel radial and horizontal modes of neuronal migration that proceed independently of the physical glial guidance.

Animals↗
PubMed1994

Formation of a primitive nervous system: nerve cell differentiation in the polyp hydra.

Nerve cell differentiation in the polyp Hydra is strikingly patterned: head and basal disk contain high densities of nerve cells. The pattern is formed by migration of interstitial cell precursors from the gastric region to sites of nerve cell differentiation in the head and basal disk. Migration occurs early in the final cell cycle of precursors and appears to be coincident with commitment to nerve cell differentiation. Following migration, each precursor divides and gives rise to a pair of nerve cells. Treatment of whole hydra with a neuropeptide stimulates formation of nerve cell precursors; differentiation of these precursors is regulated by a second signal, which is provided in vivo by budding or in vitro by injuring tissue.

Animals↗
PubMed1993

Direct observation of neurotoxicity in brain slices with infrared videomicroscopy.

We employed the novel technique of infrared videomicroscopy to study the morphological changes induced by the neurotoxicity of high concentrations of L-glutamate and by anoxia. The infrared videomicroscopy system described uses an inverted microscope and employs a combination of infrared illumination, differential interference contrast (DIC) and contrast enhancement by video. With this system, we were able to observe swelling of neurons 50 microns deep in rat neocortical slices after bath application of glutamatergic agonists or during anoxia. By recording in time lapse mode it was possible to visualize the dynamics of cell swelling and to demonstrate neuroprotection by glutamatergic antagonists. The method may be of use in screening of potential neuroprotective drugs for stroke therapy.

Animals↗
PubMed1987

Expression of H-ras correlates with metastatic potential: evidence for direct regulation of the metastatic phenotype in 10T1/2 and NIH 3T3 cells.

Using three independent approaches, we studied the effects of H-ras on metastasis formation. Analysis of five in vitro-ras-transfected 10T1/2 clones with either flat or refractile morphologies revealed a relationship between metastatic potential, H-ras expression, and anchorage-independent growth. Four metastatic variants derived from a poorly metastatic, low-H-ras-expressing line all expressed high levels of H-ras RNA and grew efficiently in soft agar. Activation of H-ras expression in the metastatic tumors had occurred through amplification and rearrangement of H-ras sequences. In addition, preinduction of p21 synthesis in NIH 3T3 line 433, which contains v-H-ras under transcriptional control of the glucocorticoid-sensitive mouse mammary tumor virus long terminal repeat, significantly increased metastatic efficiency. Glucocorticoid treatment of normal or pEJ-transformed NIH 3T3 cells did not affect metastatic potential. These data reveal a direct relationship between ras expression and metastasis formation and suggest that metastatic and transformed phenotypes may be coregulated in ras-transformed 10T1/2 and NIH 3T3 cells.

Animals↗
PubMed1986

Cell cycle-dependent expression of a stable episomal human histone gene in a mouse cell.

We have constructed a recombinant plasmid that includes a cell cycle-dependent human H4 histone gene with 650 base pairs of 5' and 900 base pairs of 3' flanking sequences and the 69% transforming fragment of bovine papilloma virus. When transfected into C127 mouse cells, this plasmid is maintained as a stable episome with approximately 20 copies per cell. Micrococcal nuclease digestion indicates that the episomal human histone gene is packaged as chromatin. The human H4 histone transcript is initiated at the correct 5' start site and undergoes selective destabilization when DNA synthesis is inhibited. When C127 cells containing the episomal H4 histone gene are synchronized, the human H4 histone mRNA levels are regulated coordinately with DNA replication and parallel those of transcripts from the murine chromosomal H4 histone genes. Our results suggest that the regulatory sequences and/or regulatory molecules associated with murine and human histone genes are compatible. The human histone gene-bovine papillomavirus episome is therefore a viable system for studying cell cycle-regulated histone gene expression under conditions where control is not influenced at the site of chromosomal integration by cis-acting elements of genes normally not contiguous.

Animals↗
PubMed1982

Sequence comparison in the crossover region of an oncogenic avian retrovirus recombinant and its nononcogenic parent: genetic regions that control growth rate and oncogenic potential.

NTRE 7 is an avian retrovirus recombinant of the endogenous nononcogenic Rous-associated virus-0 (RAV-0) and the oncogenic, exogenous, transformation-defective (td) Prague strain of Rous sarcoma virus B (td-PrRSV-B). Oligonucleotide mapping had shown that the recombinant virus is indistinguishable from its RAV-0 parent except for the 3'-end sequences, which were derived from td-PrRSV-B. However, the virus exhibits properties which are typical of an exogenous virus: it grows to high titers in tissue culture, and it is oncogenic in vivo. To accurately define the genetic region responsible for these properties, we determined the nucleotide sequences of the recombinant and its RAV-0 parent by using molecular clones of their DNA. These were compared with sequences already available for PrRSV-C, a virus closely related to the exogenous parent td-PrRSV-B. The results suggested that the crossover event which generated NTRE 7 took place in a region -501 to -401 nucleotides from the 3' end of the td-PrRSV parental genome and that sequences to the right of the recombination region were responsible for its growth properties and oncogenic potential. These sequences included a 148-base-pair exogenous-virus-specific region that was absent from the RAV-0 genome and the U3 region of the long terminal repeat. Since the exogenous-virus-specific sequences are expected to be missing from transformation-defective mutants of the Schmidt-Ruppin strain of RSV, which, like other exogenous viruses, grow to high titers in tissue culture and are oncogenic in vivo, we concluded that the growth properties and oncogenic potential of the exogenous viruses are determined by sequences in the U3 region of the long terminal repeat. However, we propose that the exogenous-virus-specific region may play a role in determining the oncogenic spectrum of a given oncogenic virus.

Animals↗
PubMed1978

[Ultrastructural and histochemical aspects of the rodlet cells from the bulbus arteriosus of Cyprinus carpio L. (Pisces: Cyprinidae) (author's transl)].

Morphological details of the "Stäbchendrüsenzellen" (PLEHN), rodlet cells syn. pear-shaped cells of the endothel from the Bulbus arterious of carps were studied in the electron microscope. From morphological characteristics, especially from the development of desmosomes with adjacent endothelial cells, it becomes evident, that the cells in question, which are very common in Teleostei, are not of parasitic nature. Specific protrusions of the apical cell poles towards the arterial lumen are indicative of a holocrine type of secretion.

Animals↗
PubMed1975

[Indications and results of operative exposure of traumatically damaged optic nerves (author's transl)].

The indications for operative treatment of traumatically damaged optic nerves are given and the results from microsurgical transethmoid approaches are communicated. This operation method has such a low risk, that it can be also used on patients with recent head injuries. The early diagnosis of traumatic optic nerve damage and the earliest possible exposure of the nerve with pressure relief of the traumatised optic nerves are important for possible success. The development of microsurgery of the orbit, the possibility of a low-risk anaesthetic, the use of modern post-operative therapy and observation make older treatments such as waiting for spontaneous return of vision out of date. During the operation undiagnosed dural tears and other secondary damage are often found, which can be repaired at the same time. This is a further argument for a broadly-based indication to operation.

Adolescent↗