Association of snRNA genes with coiled bodies is mediated by nascent snRNA transcripts.
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BACKGROUND: Coiled bodies are nuclear organelles that are highly enriched in small nuclear ribonucleoproteins (snRNPs) and certain basal transcription factors. Surprisingly, coiled bodies not only contain mature U snRNPs but also associate with specific chromosomal loci, including gene clusters that encode U snRNAs and histone messenger RNAs. The mechanism(s) by which coiled bodies associate with these genes is completely unknown. RESULTS: Using stable cell lines, we show that artificial tandem arrays of human U1 and U2 snRNA genes colocalize with coiled bodies and that the frequency of the colocalization depends directly on the transcriptional activity of the array. Association of the genes with coiled bodies was abolished when the artificial U2 arrays contained promoter mutations that prevent transcription or when RNA polymerase II transcription was globally inhibited by alpha-amanitin. Remarkably, the association was also abolished when the U2 snRNA coding regions were replaced by heterologous sequences. CONCLUSIONS: The requirement for the U2 snRNA coding region indicates that association of snRNA genes with coiled bodies is mediated by the nascent U2 RNA itself, not by DNA or DNA-bound proteins. Our data provide the first evidence that association of genes with a nuclear organelle can be directed by an RNA and suggest an autogenous feedback regulation model. (+info)
Deletion analysis of the Drosophila Inscuteable protein reveals domains for cortical localization and asymmetric localization.
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The Drosophila Inscuteable protein acts as a key regulator of asymmetric cell division during the development of the nervous system [1] [2]. In neuroblasts, Inscuteable localizes into an apical cortical crescent during late interphase and most of mitosis. During mitosis, Inscuteable is required for the correct apical-basal orientation of the mitotic spindle and for the asymmetric segregation of the proteins Numb [3] [4] [5], Prospero [5] [6] [7] and Miranda [8] [9] into the basal daughter cell. When Inscuteable is ectopically expressed in epidermal cells, which normally orient their mitotic spindle parallel to the embryo surface, these cells reorient their mitotic spindle and divide perpendicularly to the surface [1]. Like the Inscuteable protein, the inscuteable RNA is asymmetrically localized [10]. We show here that inscuteable RNA localization is not required for Inscuteable protein localization. We found that a central 364 amino acid domain - the Inscuteable asymmetry domain - was necessary and sufficient for Inscuteable localization and function. Within this domain, a separate 100 amino acid region was required for asymmetric localization along the cortex, whereas a 158 amino acid region directed localization to the cell cortex. The same 158 amino acid fragment could localize asymmetrically when coexpressed with the full-length protein, however, and could bind to Inscuteable in vitro, suggesting that this domain may be involved in the self-association of Inscuteable in vivo. (+info)
Evidence for F-actin-dependent and -independent mechanisms involved in assembly and stability of the medial actomyosin ring in fission yeast.
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Cell division in a number of eukaryotes, including the fission yeast Schizosaccharomyces pombe, is achieved through a medially placed actomyosin-based contractile ring. Although several components of the actomyosin ring have been identified, the mechanisms regulating ring assembly are still not understood. Here, we show by biochemical and mutational studies that the S.pombe actomyosin ring component Cdc4p is a light chain associated with Myo2p, a myosin II heavy chain. Localization of Myo2p to the medial ring depended on Cdc4p function, whereas localization of Cdc4p at the division site was independent of Myo2p. Interestingly, the actin-binding and motor domains of Myo2p are not required for its accumulation at the division site although the motor activity of Myo2p is essential for assembly of a normal actomyosin ring. The initial assembly of Myo2p and Cdc4p at the division site requires a functional F-actin cytoskeleton. Once established, however, F-actin is not required for the maintenance of Cdc4p and Myo2p medial rings, suggesting that the attachment of Cdc4p and Myo2p to the division site involves proteins other than actin itself. (+info)
Deletion of a region that is a candidate for the difference between the deletion forms of hereditary persistence of fetal hemoglobin and deltabeta-thalassemia affects beta- but not gamma-globin gene expression.
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The analysis of a number of cases of beta-globin thalassemia and hereditary persistence of fetal hemoglobin (HPFH) due to large deletions in the beta-globin locus has led to the identification of several DNA elements that have been implicated in the switch from human fetal gamma- to adult beta-globin gene expression. We have tested this hypothesis for an element that covers the minimal distance between the thalassemia and HPFH deletions and is thought to be responsible for the difference between a deletion HPFH and deltabeta-thalassemia, located 5' of the delta-globin gene. This element has been deleted from a yeast artificial chromosome (YAC) containing the complete human beta-globin locus. Analysis of this modified YAC in transgenic mice shows that early embryonic expression is unaffected, but in the fetal liver it is subject to position effects. In addition, the efficiency of transcription of the beta-globin gene is decreased, but the developmental silencing of the gamma-globin genes is unaffected by the deletion. These results show that the deleted element is involved in the activation of the beta-globin gene perhaps through the loss of a structural function required for gene activation by long-range interactions. (+info)
The disulfide-bonded loop of chromogranin B mediates membrane binding and directs sorting from the trans-Golgi network to secretory granules.
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The disulfide-bonded loop of chromogranin B (CgB), a regulated secretory protein with widespread distribution in neuroendocrine cells, is known to be essential for the sorting of CgB from the trans-Golgi network (TGN) to immature secretory granules. Here we show that this loop, when fused to the constitutively secreted protein alpha1-antitrypsin (AT), is sufficient to direct the fusion protein to secretory granules. Importantly, the sorting efficiency of the AT reporter protein bearing two loops (E2/3-AT-E2/3) is much higher compared with that of AT with a single disulfide-bonded loop. In contrast to endogenous CgB, E2/3-AT-E2/3 does not undergo Ca2+/pH-dependent aggregation in the TGN. Furthermore, the disulfide-bonded loop of CgB mediates membrane binding in the TGN and does so with 5-fold higher efficiency if two loops are present on the reporter protein. The latter finding supports the concept that under physiological conditions, aggregates of CgB are the sorted units of cargo which have multiple loops on their surface leading to high membrane binding and sorting efficiency of CgB in the TGN. (+info)
Optical mapping of Plasmodium falciparum chromosome 2.
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Detailed restriction maps of microbial genomes are a valuable resource in genome sequencing studies but are toilsome to construct by contig construction of maps derived from cloned DNA. Analysis of genomic DNA enables large stretches of the genome to be mapped and circumvents library construction and associated cloning artifacts. We used pulsed-field gel electrophoresis purified Plasmodium falciparum chromosome 2 DNA as the starting material for optical mapping, a system for making ordered restriction maps from ensembles of individual DNA molecules. DNA molecules were bound to derivatized glass surfaces, cleaved with NheI or BamHI, and imaged by digital fluorescence microscopy. Large pieces of the chromosome containing ordered DNA restriction fragments were mapped. Maps were assembled from 50 molecules producing an average contig depth of 15 molecules and high-resolution restriction maps covering the entire chromosome. Chromosome 2 was found to be 976 kb by optical mapping with NheI, and 946 kb with BamHI, which compares closely to the published size of 947 kb from large-scale sequencing. The maps were used to further verify assemblies from the plasmid library used for sequencing. Maps generated in silico from the sequence data were compared to the optical mapping data, and good correspondence was found. Such high-resolution restriction maps may become an indispensable resource for large-scale genome sequencing projects. (+info)
Inducible long-term gene expression in brain with adeno-associated virus gene transfer.
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Recombinant adeno-associated virus (rAAV) vectors hold promise for treating a number of neurological disorders due to the ability to deliver long-term gene expression without toxicity or immune response. Critical to these endeavors will be controlled expression of the therapeutic gene in target cells. We have constructed and tested a dual cassette rAAV vector carrying a reporter gene under the control of the tetracycline-responsive system and the tetracycline transactivator. Transduction in vitro resulted in stable expression from the vector that can be suppressed 20-fold by tetracycline treatment. In vivo experiments, carried out to 6 weeks, demonstrated that vector-transduced expression is sustained until doxycycline administration upon which reporter gene expression is reduced. Moreover, the suppression of vector-driven expression can be reversed by removal of the drug. These studies demonstrate long-term regulated gene expression from rAAV vectors. This system will provide a valuable approach for controlling vector gene expression both in vitro and in vivo. (+info)
Transcriptional regulation and induction of apoptosis: implications for the use of monomeric p53 variants in gene therapy.
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The p53 tumour suppressor protein is a transcriptional activator, which can induce cell cycle arrest and apoptosis. p53 Gene mutations occur in more than 50% of all human tumours. Reintroduction of wild-type p53 but also of oligomerisation-independent p53 variants into tumour cells by gene transfer methods has been considered. We have investigated the biological properties of two carboxy-terminal deletion mutants of p53, p53 delta 300 (comprising amino acids 1-300) and p53 delta 326 (amino acids 1-326), to evaluate their potential deployment in gene therapy. Transactivation was measured in transiently transfected HeLa and SKBR3 cells. Both monomeric variants showed reduced activities compared with wild-type p53. Individual promoters were differently affected. In contrast to wild-type p53, monomeric variants were not able to induce apoptosis. We also provided wild-type p53 and p53 delta 326 with tetracycline-regulated promoters and stably introduced these constructs into Saos2 and SKBR3 cells. Upon induction, wild-type p53 expressing cells, but not p53 delta 326 expressing cells underwent apoptosis. Consistently, only wild-type p53 expressing cells accumulated p21/waf1/cip1 mRNA and protein and showed increased bax, Gadd45 and mdm2 mRNA. Neither wild-type p53 nor p53 delta 326 repressed the transcription of the IGF-1R gene in these cell lines. We conclude that the transactivation potential of monomeric, carboxy-terminally truncated p53 is not sufficient to cause induction of the endogenous target genes which trigger apoptosis. (+info)