Transcriptional regulation of genes encoding the selenium-free [NiFe]-hydrogenases in the archaeon Methanococcus voltae involves positive and negative control elements.
(41/4715)
Methanococcus voltae harbors genetic information for two pairs of homologous [NiFe]-hydrogenases. Two of the enzymes contain selenocysteine, while the other two gene groups encode apparent isoenzymes that carry cysteinyl residues in the homologous positions. The genes coding for the selenium-free enzymes, frc and vhc, are expressed only under selenium limitation. They are transcribed out of a common intergenic region. A series of deletions made in the intergenic region localized a common negative regulatory element for the vhc and frc promoters as well as two activator elements that are specific for each of the two transcription units. Repeated sequences, partially overlapping the frc promoter, were also detected. Mutations in these repeated heptanucleotide sequences led to a weak induction of a reporter gene under the control of the frc promoters in the presence of selenium. This result suggests that the heptamer repeats contribute to the negative regulation of the frc transcription unit. (+info)
Modulations of glucocorticoid-induced apoptosis linked to the p53 deletion and to the apoptosis susceptibility gene Rapop1 (Radiation-induced apoptosis 1).
(42/4715)
We have analysed the effects of p53 and of the apoptosis susceptibility gene Rapop1 (Radiation-induced apoptosis 1) located on chromosome 16 on glucocorticoid- and radiation-induced in vivo apoptosis of thymocytes. For those analyses, we used Rapop1 semicongenic mice heterozygous for the STS and BALB/cHeA alleles in the chromosomal segment containing Rapop1 in the BALB/cHeA background, mice bearing a p53 deficient allele in the BALB/cHeA background and the genetic crosses between these mice. The p53 wild type mice with a STS/A allele at the Rapop1 locus were less susceptible to both radiation- and glucocorticoid-induced apoptosis than those with homozygous BALB/cHeA alleles at this locus. Surprisingly, glucocorticoid-induced apoptosis was enhanced in the p53 hemizygous mice and considerably increased in the p53 nullizygous mice. In contrast, a sizable reduction of radiation-induced apoptosis was seen in the p53 hemizygous mice. The low susceptiblity to glucocortocoid-induced apoptosis linked to the STS allele of Rapop1 was less pronounced in the p53 hemizygous mice and a diminished effect of Rapop1 on radiation-induced apoptosis was seen in these mice. Although it remains to be established whether the genes modulating glucocortocoid-induced apoptosis are identical to p53 and Rapop1, our data suggest that p53 and Rapop1 may participate in glucocorticoid-induced apoptosis of thymocytes. (+info)
The ubiquitous transcription factor NF-Y positively regulates the transcription of human p27Kip1 through a CCAAT box located in the 5-upstream region of the p27Kip1 gene.
(43/4715)
Abnormally low levels of the cyclin-dependent kinase inhibitor p27Kip1 are found frequently in human carcinomas, and these levels correlate directly with both histological aggressiveness and patient mortality. p27Kip1 is haplo-insufficient for tumor suppression. Thus, p27Kip1 may be a useful molecule for the development of cancer therapies. To know the possible mechanisms underlying transcriptional control, we previously cloned the promoter region of human p27Kip1 gene. We report here the characterization of the 5'-regulatory region of the human p27Kip1 gene. Promoter analysis using 5'-deletion mutants revealed that a 39-bp region between -549 and -511 was required for maximal promoter activity. Point mutation analysis revealed that a CCAAT box within this region was essential for promoter activity. Gel shift assays and cotransfection experiments using a dominant negative form of the NF-Y transcription factor showed that NF-Y directly regulates p27Kip1 transcription through this CCAAT box. This finding might provide a clue to approach the mechanism of tumorigenesis. (+info)
Reversible inactivation of cell-type-specific regulatory and structural genes in migrating isolated striated muscle cells of jellyfish.
(44/4715)
We have investigated, by RT-PCR and in situ hybridization, expression of genes encoding regulatory and structural proteins in migrating mononucleated striated muscle cells of the medusa Podocoryne carnea. Expression of the three homeobox genes Otx, Cnox1-Pc, and Cnox3-Pc; a specific splice variant of the myosin heavy chain gene (Myo1); and a tropomyosin (Tpm2) is stable in isolated and cultured striated muscle tissue. When grafted onto cell-free extracellular matrix (ECM), muscle cells of the tissue fragments leave their native ECM and migrate as a coherent tissue onto a host ECM until a stretched cell monolayer is formed. Shortly after the first cells of the grafted isolate have made contact with the host ECM, Otx and Cnox1-Pc expression is completely turned off in all cells of the graft, including those still adhering to their native ECM. Myo1 message disappears with a delay while the expression level of Tpm2 is strongly reduced. However, expression of the homeobox gene Cnox3-Pc, a msh-like gene, and of the ubiquitously expressed elongation factor 1 alpha is not affected by the migration process. All genes are reexpressed after 12-24 h, once migration of the cells has ceased. Our results demonstrate that the first few migrating cells induce a change in gene expression which is rapidly communicated throughout the entire tissue. Furthermore, we showed that commitment of striated muscle cells remains stable despite the transient inactivation of cell-type-specific regulatory and structural genes. (+info)
An E box comprises a positional sensor for regional differences in skeletal muscle gene expression and methylation.
(45/4715)
To dissect the molecular mechanisms conferring positional information in skeletal muscles, we characterized the control elements responsible for the positionally restricted expression patterns of a muscle-specific transgene reporter, driven by regulatory sequences from the MLC1/3 locus. These sequences have previously been shown to generate graded transgene expression in the segmented axial muscles and their myotomal precursors, fortuitously marking their positional address. An evolutionarily conserved E box in the MLC enhancer core, not recognized by MyoD, is a target for a nuclear protein complex, present in a variety of tissues, which includes Hox proteins and Zbu1, a DNA-binding member of the SW12/SNF2 gene family. Mutation of this E box in the MLC enhancer has only a modest positive effect on linked CAT gene expression in transfected muscle cells, but when introduced into transgenic mice the same mutation elevates CAT transgene expression in skeletal muscles, specifically releasing the rostral restriction on MLC-CAT transgene expression in the segmented axial musculature. Increased transgene activity resulting from the E box mutation in the MLC enhancer correlates with reduced DNA methylation of the distal transgenic MLC1 promoter as well as in the enhancer itself. These results identify an E box and the proteins that bind to it as a positional sensor responsible for regional differences in axial skeletal muscle gene expression and accessibility. (+info)
Control of CD4 gene expression: connecting signals to outcomes in T cell development.
(46/4715)
The control of CD4 gene expression is essential for proper T lymphocyte development. Signals transmitted from the T-cell antigen receptor (TCR) during the thymic selection processes are believed to be linked to the regulation of CD4 gene expression during specific stages of T cell development. Thus, a study of the factors that control CD4 gene expression may lead to further insight into the molecular mechanisms that drive thymic selection. In this review, we discuss the work conducted to date to identify and characterize the cis-acting transcriptional control elements in the CD4 locus and the DNA-binding factors that mediate their function. From these studies, it is becoming clear that the molecular mechanisms controlling CD4 gene expression are very complex and differ at each stage of development. Thus, the control of CD4 expression is subject to many different influences as the thymocyte develops. (+info)
Identification of the Pseudomonas stutzeri OX1 toluene-o-xylene monooxygenase regulatory gene (touR) and of its cognate promoter.
(47/4715)
Toluene-o-xylene monooxygenase is an enzymatic complex, encoded by the touABCDEF genes, responsible for the early stages of toluene and o-xylene degradation in Pseudomonas stutzeri OX1. In order to identify the loci involved in the transcriptional regulation of the tou gene cluster, deletion analysis and complementation studies were carried out with Pseudomonas putida PaW340 as a heterologous host harboring pFB1112, a plasmid that allowed regulated expression, inducible by toluene and o-xylene and their corresponding phenols, of the toluene-o-xylene monooxygenase. A locus encoding a positive regulator, designated touR, was mapped downstream from the tou gene cluster. TouR was found to be similar to transcriptional activators of aromatic compound catabolic pathways belonging to the NtrC family and, in particular, to DmpR (83% similarity), which controls phenol catabolism. By using a touA-C2,3O fusion reporter system and by primer extension analysis, a TouR cognate promoter (P(ToMO)) was mapped, which showed the typical -24 TGGC, -12 TTGC sequences characteristic of sigma(54)-dependent promoters and putative upstream activating sequences. By using the reporter system described, we found that TouR responds to mono- and dimethylphenols, but not the corresponding methylbenzenes. In this respect, the regulation of the P. stutzeri system differs from that of other toluene or xylene catabolic systems, in which the hydrocarbons themselves function as effectors. Northern analyses indicated low transcription levels of tou structural genes in the absence of inducers. Basal toluene-o-xylene monooxygenase activity may thus transform these compounds to phenols, which then trigger the TouR-mediated response. (+info)
Apoptosis.
(48/4715)
Mechanisms in Hematology is a book with an accompanying interactive CD-ROM designed to assemble basic concepts that underlie clinical understanding and progress. It is presented as a concise text with a series of diagrams that distill diffuse information into a compact form. The interactive CD, in particular, brings many of the processes "to life" as details of the more complex pathways are conveyed in clear visual images. The text begins with the basic molecular biology that underlies hematological and oncological physiology/pathology--cell signaling, adhesion molecules, and apoptosis. This is followed by sections, among others, on hematopoiesis, iron, B12, and folate metabolism, neutrophil function, immunoproteins, chemotherapy, and coagulation. With the permission of the authors and publisher. The Oncologist has reproduced the section on apoptosis, which we think our readers will enjoy. (+info)