Biomedical subjects

I Bach

Publications and source records attributed to I Bach.

At least 19 recordsLinked to original sources

PubMed2005

Effects of triplet exciton confinement induced by reduced conjugation length in polyspirobifluorene copolymers.

Using gated optical spectroscopy at low temperatures, a polyspirobifluorene has been compared with an alternating carbazole-spirobifluorene copolymer in which the backbone conjugation is interrupted due to meta coupling of the carbazole moieties. In the copolymer both singlet and triplet energy levels are blueshifted by 130 meV with respect to the homopolymer, resulting in an unaltered singlet-to-triplet splitting. Though the barrier for triplet exciton migration increases from 4.4 to 6.0 meV for the copolymer compared to the homopolymer, it still remained low enough to ensure efficient triplet diffusion at ambient temperature.

Journal Article↗

PubMed2000

Functional characterization of the gene encoding RLIM, the corepressor of LIM homeodomain factors.

RLIM is a RING H2 zinc finger protein that acts as a negative coregulator for LIM homeodomain transcription factors. We have isolated genomic lambda clones that cover the entire mouse RLIM-encoding Rnf12 gene. The Rnf12 gene encompasses 20 kb and consists of at least five exons and four introns. Several transcriptional start sites within a 24-bp region were mapped around 300 nt upstream of the translational start site. Rnf12-specific mRNA can be detected in many tissues as revealed by Northern blot analysis. Transient cotransfections reveal that the proximal Rnf12 promoter can be activated in vitro by ubiquitously and more restrictively expressed transcription factors, some of which are known mediators of signal transduction pathways, e.g., mammalian Krüppel-like transcription factors, Sox and ets-related proteins, and RBP-J. We isolated a cDNA encoding human RLIM, which is highly conserved with mouse and chick RLIM. By fluorescence in situ hybridization and interspecific backcross analysis, we have localized the Rnf12 gene to the central regions of mouse and human chromosome X.

Animals↗

PubMed2000

The LIM domain: regulation by association.

The LIM domain is a zinc finger structure that is present in several types of proteins, including homeodomain transcription factors, kinases and proteins that consist of several LIM domains. Proteins containing LIM domains have been discovered to play important roles in a variety of fundamental biological processes including cytoskeleton organization, cell lineage specification and organ development, but also for pathological functions such as oncogenesis, leading to human disease. The LIM domain has been demonstrated to be a protein-protein interaction motif that is critically involved in these processes. The recent isolation and analysis of more LIM domain-containing proteins from several species have confirmed and broadened our knowledge about LIM protein function. Furthermore, the identification and characterization of factors that interact with LIM domains illuminates mechanisms of combinatorial developmental regulation.

Animals↗

PubMed1999

Lhx9: a novel LIM-homeodomain gene expressed in the developing forebrain.

A novel LIM-homeodomain gene, Lhx9, was isolated by degenerate RT-PCR followed by mouse embryonic library screening. Lhx9 cDNA encodes a protein that is most closely related to Drosophila apterous and rodent Lhx2 proteins. The Lhx9 spatiotemporal pattern of expression during embryogenesis was similar but distinct from Lhx2. Highest expression levels were found in the diencephalon, telencephalic vesicles, and dorsal mesencephalon. Domains of expression respected the proposed neuromeric boundaries (). Lhx9 was also expressed in the spinal cord, forelimb and hindlimb mesenchyme, and urogenital system. Although Lhx9 expression was sustained in diencephalon and mesencephalon from embryonic day 10.5 (E10.5) to postnatal stages, it was transient in the future cerebral cortex, where it was turned off between E14.5 and E16.5. Lhx9 expression was highest if not exclusively located (depending on the region of interest) in the intermediate and mantle zones, as opposed to the mitotic ventricular zone. Lhx9 protein was tested for interaction with the recently discovered cofactors of LIM-homeodomain proteins and was found to interact strongly both with CLIM1 and CLIM2. The expression pattern and structural characteristics of Lhx9 suggest that it encodes a transcription factor that might be involved in the control of cell differentiation of several neural cell types. Furthermore, Lhx9 protein could act in a combinatorial manner with other LIM-homeodomain factors expressed in overlapping pattern.

Amino Acid Sequence↗

PubMed1999

RLIM inhibits functional activity of LIM homeodomain transcription factors via recruitment of the histone deacetylase complex.

LIM domains are required for both inhibitory effects on LIM homeodomain transcription factors and synergistic transcriptional activation events. The inhibitory actions of the LIM domain can often be overcome by the LIM co-regulator known as CLIM2, LDB1 and NLI (referred to hereafter as CLIM2; refs 2-4). The association of the CLIM cofactors with LIM domains does not, however, improve the DNA-binding ability of LIM homeodomain proteins, suggesting the action of a LIM-associated inhibitor factor. Here we present evidence that LIM domains are capable of binding a novel RING-H2 zinc-finger protein, Rlim (for RING finger LIM domain-binding protein), which acts as a negative co-regulator via the recruitment of the Sin3A/histone deacetylase corepressor complex. A corepressor function of RLIM is also suggested by in vivo studies of chick wing development. Overexpression of the gene Rnf12, encoding Rlim, results in phenotypes similar to those observed after inhibition of the LIM homeodomain factor LHX2, which is required for the formation of distal structures along the proximodistal axis, or by overexpression of dominant-negative CLIM1. We conclude that Rlim is a novel corepressor that recruits histone deacetylase-containing complexes to the LIM domain.

Amino Acid Sequence↗

PubMed1999

Conserved regulation of mesenchymal gene expression by Fgf-8 in face and limb development.

Clim-2 (NLI, Lbd1) is one of two related mouse proteins that interact with Lim-domain homeoproteins. In the mouse, embryonic expression of Clim-2 is particularly pronounced in facial ectomesenchyme and limb bud mesenchyme in association with Lim genes, Lhx-6 and Lmx-1 respectively. We show that in common with both these Lim genes, Clim-2 expression is regulated by signals from overlying epithelium. In both the developing face and the limb buds we identify Fgf-8 as the likely candidate signalling molecule that regulates Clim-2 expression. We show that in the mandibular arch, as in the limb, Fgf-8 functions in combination with CD44, a cell surface binding protein, and that blocking CD44 binding results in inhibition of Fgf8-induced expression of Clim-2 and Lhx-6. Regulation of gene expression by Fgf8 in association with CD44 is thus conserved between limb and mandibular arch development.

Animals↗

PubMed1998

Mouse deformed epidermal autoregulatory factor 1 recruits a LIM domain factor, LMO-4, and CLIM coregulators.

Nuclear LIM domains interact with a family of coregulators referred to as Clim/Ldb/Nli. Although one family member, Clim-2/Ldb-1/Nli, is highly expressed in epidermal keratinocytes, no nuclear LIM domain factor is known to be expressed in epidermis. Therefore, we used the conserved LIM-interaction domain of Clim coregulators to screen for LIM domain factors in adult and embryonic mouse skin expression libraries and isolated a factor that is highly homologous to the previously described LIM-only proteins LMO-1, -2, and -3. This factor, referred to as LMO-4, is expressed in overlapping manner with Clim-2 in epidermis and in several other regions, including epithelial cells of the gastrointestinal, respiratory and genitourinary tracts, developing cartilage, pituitary gland, and discrete regions of the central and peripheral nervous system. Like LMO-2, LMO-4 interacts strongly with Clim factors via its LIM domain. Because LMO/Clim complexes are thought to regulate gene expression by associating with DNA-binding proteins, we used LMO-4 as a bait to screen for such DNA-binding proteins in epidermis and isolated the mouse homologue of Drosophila Deformed epidermal autoregulatory factor 1 (DEAF-1), a DNA-binding protein that interacts with regulatory sequences first described in the Deformed epidermal autoregulatory element. The interaction between LMO-4 and mouse DEAF-1 maps to a proline-rich C-terminal domain of mouse DEAF-1, distinct from the helix-loop-helix and GATA domains previously shown to interact with LMOs, thus defining an additional LIM-interacting domain.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Normalization of fasting glycaemia by intravenous GLP-1 ([7-36 amide] or [7-37]) in type 2 diabetic patients.

Intravenous GLP-1 [7-36 amide] can normalize fasting hyperglycaemia in Type 2 diabetic patients. Whether GLP-1 [7-37] has similar effects and how quickly plasma glucose concentrations revert to hyperglycaemia after stopping GLP-1 is not known. Therefore, 8 patients with Type 2 diabetes (5 female, 3 male; 65+/-6 years; BMI 34.3+/-7.9 kg m(-2); HbA1c 9.6+/-1.2%; treatment with diet alone (n=2), sulphonylurea (n=5), metformin (n=1)) were examined twice in randomized order. GLP-1 [7-36 amide] or [7-37] (1 pmol kg(-1)min(-1) were infused intravenously over 4 h in fasted subjects. Plasma glucose (glucose-oxidase), insulin and C-peptide (ELISA) was measured during infusion and for 4 h thereafter. Indirect calorimetry was performed. Fasting hyperglycaemia was 11.7+/-0.9 [7-36 amide] and 11.3+/-0.9 mmol l(-1) [7-37]. GLP-1 infusions stimulated insulin secretion approximately 3-fold (insulin peak 168+/-32 and 156+/-47 pmol l(-1), p<0.0001 vs basal; C-peptide peak 2.32+/-0.28 and 2.34+/-0.43 nmol l(-1), p<0.0001, respectively, with GLP-1 [7-36 amide] and [7-37]). Four hours of GLP-1 infusion reduced plasma glucose (4.8+/-0.4 and 4.6+/-0.3 mmol l(-1), p<0.0001 vs basal values), and it remained in the non-diabetic fasting range after a further 4 h (5.1+/-0.4 and 5.3+/-0.4 mmol l(-1), for GLP [7-36 amide] and [7-37], respectively). There were no significant differences between GLP-1 [7-36 amide] and [7-37] (glucose, p=0.99; insulin, p=0.99; C-peptide, p=0.99). Neither glucose oxidation nor lipid oxidation (or any other parameters determined by indirect calorimetry) changed during or after the administration of exogenous GLP-1. In conclusion, GLP-1 [7-36 amide] and [7-37] normalize fasting hyperglycaemia in Type 2 diabetic patients. Diabetes therapy (diet, sulphonyl ureas or metformin) does not appear to influence this effect. In fasting and resting patients, the effect persists during administration of GLP-1 and for at least 4 h thereafter, without rebound. Significant changes in circulating substrate concentrations (e.g. glucose) are not accompanied by changes in intracellular substrate metabolism.

Age of Onset↗

PubMed1998

Specificity of resistance to pea seed-borne mosaic potyvirus in transgenic peas expressing the viral replicase (Nlb) gene.

Transgenic pea lines carrying the replicase (NIb) gene of pea seed-borne mosaic potyvirus (PSbMV) were generated and used in experiments to determine the effectiveness of induced resistance upon heterologous isolates. Three pea lines showed inducible resistance in which an initial infection by the homologous isolate (PSbMV-DPD1) was followed by a highly resistant state. Resistance was observed in plants in either the homozygous or hemizygous condition and resulted in no overall yield loss despite the initial infection. Resistance was associated with a loss of both viral and transgene RNA, which is indicative of a mechanism based upon post-transcriptional gene silencing. There was no correlation between the steady-state levels of transgene RNA and ability of the plants to show resistance. To test the specificity of the resistance, plants were also inoculated with the most distantly related sequenced PSbMV isolate, NY. PSbMV-NY varied between experiments in its ability to induce resistance, suggesting that the sequence identity in the NIb gene is borderline for the specificity required for triggering gene silencing. Upon challenge inoculation of virus-free recovered leaves, the specificity of the induced resistance varied between the two isolates and indicated that the virus and transgene additively determined the resistant state. These results suggest that the sequence requirements for triggering gene silencing may differ from those involved in the degradation process.

Cell Transformation, Viral↗

PubMed1997

A family of LIM domain-associated cofactors confer transcriptional synergism between LIM and Otx homeodomain proteins.

The essential roles of LIM homeodomain proteins in cell fate determination during development have been demonstrated in organisms as divergent as Drosophila and higher mammals. We have isolated murine cDNAs encoding two highly homologous proteins that specifically interact with the LIM domains of P-Lim/Lhx3 and several other LIM homeodomain factors. Transcripts encoding these factors can be detected as early as mouse E8.5, with maximal expression observed in regions of the embryo in which the LIM homeodomain factors P-Lim/Lhx3, Isl-1, and LH-2 are selectively expressed. These proteins can potentiate transactivation by P-Lim/Lhx-3 and are required for a synergistic activation of the glycoprotein hormone alpha-subunit promoter by P-Lim/Lhx3 and a pituitary Otx class homeodomain transcription factor, with which they also specifically associate. Our results link LIM homeodomain proteins and members of the Otx class of transcription factors in gene activation events during embryogenesis via the actions of specific cofactors.

Amino Acid Sequence↗

PubMed1996

Transcriptional control of cell phenotypes in the neuroendocrine system.

A fundamental aspect of the development of complex organ systems is a requirement for precise temporal and spatial coordination in the genesis of tissues of distinct embryonic origins, in order to form functional units required for physiological homeostasis and survival. Such a requirement is particularly well exemplified in mammalian development in the formation of the hypothalamic-pituitary axis. Neuronally expressed POU domain factors might exert effects on terminal differentiation events similar to those of Pit-1 in the maturation of anterior pituitary gland cell phenotypes. Neurons comprising the endocrine hypothalamus develop in tandem with their ultimate target, the pituitary gland, and arise from a primordium in which three related class III POU domain factors-Brn-2, Brn-4, and Brn-1-are initially co-expressed. These factors subsequently exhibit stratified patterns of ontogenic expression, correlating with the appearance of distinct neuropeptides that define three major endocrine hypothalamic cell types. Deletion of the Brn-2 genomic locus affects terminal differentiation and/or maintenance of hypothalamic neurosecretory neurons and development of the posterior pituitary gland. Thus, both neuronal and endocrine components of the hypothalamic-pituitary axis are critically dependent upon the action of specific POU domain factors at a penultimate step in the sequential events that underlie the appearance of mature cellular phenotypes.

Amino Acid Sequence↗

PubMed1995

P-Lim, a LIM homeodomain factor, is expressed during pituitary organ and cell commitment and synergizes with Pit-1.

A pituitary LIM homeodomain factor, P-Lim, is expressed as Rathke's pouch forms and as specific pituitary cell phenotypes are established, suggesting functional roles throughout pituitary development. While selectively expressed in both anterior and intermediate pituitary in mature mice, P-Lim is also transiently expressed in the developing ventral neural cord and brainstem. P-Lim binds to and activates the promoter of the alpha-glycoprotein subunit gene, a marker of early pituitary development, and synergizes with Pit-1 in transcriptional activation of genes encoding terminal differentiation markers. The LIM domain of P-Lim specifically interacts with the Pit-1 POU domain and is required for synergistic interactions with Pit-1, but not for basal transcriptional activation events.

Amino Acid Sequence↗

PubMed1993

More potent transcriptional activators or a transdominant inhibitor of the HNF1 homeoprotein family are generated by alternative RNA processing.

We report the isolation of cDNAs from human liver encoding several isoforms of the hepatocyte nuclear factor homeoproteins HNF1 and vHNF1 generated by the differential use of polyadenylation sites and by alternative splicing. In the novel isoforms intron sequences that are excised in the previously described forms are translated in the same frame as exon sequences until the first termination codon is encountered. Hence, the newly found isoforms all contain different C-terminal domains. For HNF1 it has been shown that its C-terminal region is responsible for the activation of transcription. In transient transfection assays the two novel HNF1 isoforms, HNF1-B and -C, transactivate 5-fold better than the previously described HNF1 protein (HNF1-A). The newly isolated isoform of vHNF1, designated vHNF1-C, is unable to transactivate and behaves as a transdominant repressor when cotransfected with HNF1-A, -B or -C. All of the different isoforms of HNF1 and vHNF1 can form homo- and heterodimers and their mRNAs are differentially expressed in fetal and adult human liver, kidney and intestine, suggesting distinct roles during development. Our studies show that the transactivation domain of the members of the HNF1 homeoprotein family is organized in modules which can be exchanged to generate either more potent transcriptional activators or a transdominant repressor.

Alternative Splicing↗

PubMed1993

Physical mapping of DNA markers in the q13-q22 region of the human X chromosome.

DNA probe screening of somatic cell hybrids derived from females with X;autosome translocations has enabled us to define eight new breakpoints within the Xq13-q22 region. Together with other X-chromosome rearrangements that have been described earlier, these breakpoints subdivide the Xq21-q22 region into 20 intervals. Our panel refines the physical assignment of 40 probes in the Xq21-q22 segment. Thus, these X-chromosome rearrangements are useful tools for ordering X-linked markers and genes on the proximal long arm of the human X chromosome.

Amenorrhea↗

PubMed1992

Structure of the gene encoding hepatocyte nuclear factor 1 (HNF1).

Genomic clones have been isolated that cover the entire gene for the transcription factor HNF1 (hepatocyte nuclear factor 1). This protein governs the expression of many genes, synthesized in the liver in a tissue-specific manner. We have determined the intron/exon structure of the HNF1 gene, which is strictly conserved between rat and mouse and estimate that it spans not more than 40kb in the rat genome. Whereas most homeoprotein genes do not contain introns within the homeodomain, HNF1 displays an intron between the regions encoding the second and the third helices. We discuss possible evolutionary mechanisms leading to this homeobox intron/exon pattern.

Amino Acid Sequence↗

PubMed1992

Physical fine mapping of genes underlying X-linked deafness and non fra (X)-X-linked mental retardation at Xq21.

Linkage studies and cytogenetically visible deletions associated with nonspecific X-linked mental retardation (XLMR) and a specific form of deafness (DFN3) have indicated that the genes responsible for these disorders are located at Xq21. Using DNA probes from this region, we have studied several overlapping deletions spanning different parts of Xq21. This has enabled us to assign the DFN3 gene and a gene for nonspecific XLMR to an interval that encompasses the locus DXS232 and that is flanked by DXS26 and DXS121.

Adolescent↗

PubMed1992

Sequences of DNA fragments contacting the nuclear lamina in vivo.

To study the DNA sequences contacting the nuclear lamina (NL) in vivo, Ehrlich ascites tumor cells were UV-irradiated. The NL was purified, and the DNA fragments covalently linked to the lamina proteins in vivo were cloned and sequenced. Although heterogeneous in length and composition, the sequences displayed homology to the introns and/or flanking regions of different genes, suggesting that functionally distinct regions are organized in a topologically defined manner at the nuclear periphery.

Animals↗

PubMed1992

Investigations of the frequency of DNA strand breakage and cross-linking and of sister chromatid exchange frequency in the lymphocytes of patients with multiple myeloma undergoing cytostatic therapy with melphalan and prednisone.

An investigation was made of 17 patients with multiple myeloma using the method of alkaline filter elution for the detection of DNA damage and the determination of sister chromatid exchange (SCE) frequency in peripheral lymphocytes during a course of chemotherapy with melphalan and prednisone. We were able to detect elevated SCE frequencies in pretreated patients that approximately doubled during the therapeutic cycle. An appreciable level of DNA cross-linking was detected by alkaline filter elution; DNA cross-linking scarcely increased during a course of chemotherapy. The increase in the SCE frequency during the first therapy cycle was even greater in the case of patients with newly diagnosed multiple myelomas. The results obtained by alkaline filter elution and measuring SCE frequencies suggest that these techniques are suitable as methods in molecular epidemiology, especially if applied to persons who are chronically exposed to cytostatic drugs. Whether or not the methods could be valuable in evaluating therapy response needs further investigation.

Aged↗