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At least 145 records · Page 8Linked to original sources
PubMed2000

Characterization of a shiga toxin 2e-converting bacteriophage from an Escherichia coli strain of human origin.

An infectious Shiga toxin (Stx) 2e-converting bacteriophage (phiP27) was isolated from Stx2e-producing Escherichia coli ONT:H(-) isolate 2771/97 originating from a patient with diarrhea. The phage could be transduced to E. coli laboratory strain DH5alpha, and we could show that lysogens were able to produce biologically active toxin in a recA-dependent manner. By DNA sequence analysis of a 6,388-bp HindIII restriction fragment of phiP27, we demonstrated that the stx(2e) gene was located directly downstream of ileZ and argO tRNA genes. Although no analogue of an antiterminator Q encoding gene was present on this fragment, a lysis cassette comprising two holin genes which are related to the holin genes of Pseudomonas aeruginosa phage phiCTX and a gene homologous to the endolysin gene gp19 of phage PS3 were detected. The results of our study demonstrated for the first time that Stx2e can be encoded in the genome of an infectious bacteriophage.

Bacterial Toxins↗
PubMed1971

Mapping the gene determining ornithine transcarbamylase and its operator in Escherichia coli B.

The gene determining ornithine transcarbamylase in Escherichia coli B is argI, not argF. The argI gene has been located at 84 min on the linkage map, close to the gene for aspartate transcarbamylase, with neighboring markers in clockwise order fdp pyrB argI valS. A mutation in its operator locus, argO(I), has been mapped between argI and valS, so that this gene, unlike the argCBH portion of the argECBH cluster, appears to be oriented in the same direction as most of the other known E. coli operons.

Arginine↗
PubMed1970

Genetic mapping of a defective bacteriophage on the chromosome of Bacillus subtilis 168.

A genetic marker responsible for the killing activity of PBSX, a defective phage carried by Bacillus subtilis 168, has been located on the bacterial chromosome. Two mutant strains of B. subtilis 168, which produced tailless phage particles upon mitomycin C induction, were shown to carry lesions, designated xtl-1 and xtl-2, which were linked by transformation and PBS1-mediated transduction to metC. The link-age relationship between xtl and adjacent auxotrophic markers was determined by three-factor PBS1 transduction, the suggested order of markers being argO 1 metA metC xtl.

Bacillus subtilis↗
PubMed1987

Interference with viral infection by defective RNA replicase.

RNA-dependent RNA and DNA polymerases have a conserved segment, Tyr-X-Asp-Asp (G. Karmer and P. Argos, Nucleic Acids Res. 12:7269-7282, 1984). To investigate the function of this segment, we changed the Gly residue at position 357 in the conserved sequence Tyr-356-Gly-357-Asp-358-Asp-359 of the replicase of RNA coliphage Q beta to Ala, Ser, Pro, Met, or Val and examined the replicase activity in vivo. Cells carrying the variant plasmids lost the replicase activity and severely inhibited the proliferation of phage Q beta (group III) and related phage SP (group IV) by suppressing phage RNA synthesis. In contrast, substitution of the Gly residue at 390 showed only a slight inhibitory effect, although replicase activity was also lost. These results suggest that the cells harboring an altered replicase at the conserved segment can interfere specifically with the wild-type phage and different but related phage infections.

Coliphages↗
PubMed1997

Intrinsic and extrinsic determinants regulating cell fate decision in developing nervous system.

Cell fate in the nervous system is determined by environmental signals and/or heredity. They can be referred to as extrinsic and intrinsic determinants, respectively. The molecular and cellular mechanisms underlying these processes are well conserved from invertebrates to vertebrates. We have identified both types of determinants through the intensive screening of P-element-induced Drosophila mutants affected in neural development. As a member of the first category, argos gene product which regulates cell-cell interaction in the developing nervous system gives a good example. As a member of the second category, we refer to Drosophila musashi gene encoding a neural RNA-binding protein. The fractions of these gene products and application to the mammalian nervous system will be discussed.

Animals↗
PubMed1989

Class III malocclusion: a cephalometric study of Saudi Arabians.

The records of 500 consecutive Saudi Arabian patients referred for orthodontic treatment were examined clinically and cephalometrically for Class III malocclusion. A control group was drawn at random from the same sample. The incidence of Class III was 9.4 per cent, with mandibular prognathism being the commonest presentation of the malocclusion. The upper and lower incisors exhibited a marked degree of dentoalveolar compensation, on dental bases having mean values of SNA--78.77 degrees and SNB--81.17 degrees. The maxillary length was reduced, as were the saddle and maxillary-mandibular plane angles. The gonial angle (ArGoMe), anterior and posterior facial heights, and mandibular lengths (ArGo, ArPo) were all significantly larger than the control group. The cephalometric values of the control group showed the increased tendency to bimaxillary protrusion in the Saudi Arabian sample.

Adolescent↗
PubMed2003

Egfr signaling regulates ommatidial rotation and cell motility in the Drosophila eye via MAPK/Pnt signaling and the Ras effector Canoe/AF6.

Epidermal Growth Factor-receptor (Egfr) signaling is evolutionarily conserved and controls a variety of different cellular processes. In Drosophila these include proliferation, patterning, cell-fate determination, migration and survival. Here we provide evidence for a new role of Egfr signaling in controlling ommatidial rotation during planar cell polarity (PCP) establishment in the Drosophila eye. Although the signaling pathways involved in PCP establishment and photoreceptor cell-type specification are beginning to be unraveled, very little is known about the associated 90 degrees rotation process. One of the few rotation-specific mutations known is roulette (rlt) in which ommatidia rotate to a random degree, often more than 90 degrees. Here we show that rlt is a rotation-specific allele of the inhibitory Egfr ligand Argos and that modulation of Egfr activity shows defects in ommatidial rotation. Our data indicate that, beside the Raf/MAPK cascade, the Ras effector Canoe/AF6 acts downstream of Egfr/Ras and provides a link from Egfr to cytoskeletal elements in this developmentally regulated cell motility process. We provide further evidence for an involvement of cadherins and non-muscle myosin II as downstream components controlling rotation. In particular, the involvement of the cadherin Flamingo, a PCP gene, downstream of Egfr signaling provides the first link between PCP establishment and the Egfr pathway.

Animals↗
PubMed1996

EGF receptor signaling induces pointed P1 transcription and inactivates Yan protein in the Drosophila embryonic ventral ectoderm.

The induction of different cell fates along the dorsoventral axis of the Drosophila embryo requires a graded activity of the EGF receptor tyrosine kinase (DER). Here we have identified primary and secondary target genes of DER, which mediate the determination of discrete ventral cell fates. High levels of DER activation in the ventralmost cells trigger expression of the transcription factors encoded by ventral nervous system defective (vnd) and pointed P1 (pntPl). Concomitant with the induction of pntP1, high levels of DER activity lead to inactivation of the Yan protein, a transcriptional repressor of Pointed-target genes. These two antagonizing transcription factors subsequently control the expression of secondary target genes such as otd, argos and tartan. The simultaneous effects of the DER pathway on pntP1 induction and Yan inactivation may contribute to the definition of the border of the ventralmost cell fates.

Animals↗
PubMed1996

The Drosophila embryonic midline is the site of Spitz processing, and induces activation of the EGF receptor in the ventral ectoderm.

The Drosophila EGF receptor (DER) is activated by secreted Spitz to induce different cell fates in the ventral ectoderm. Processing of the precursor transmembrane Spitz to generate the secreted form was shown to be the limiting event, but the cells in which processing takes place and the mechanism that may generate a gradient of secreted Spitz in the ectoderm were not known. The ectodermal defects in single minded (sim) mutant embryos, in which the midline fails to develop, suggested that the midline cells contribute to patterning of the ventral ectoderm. This work shows that the midline provides the site for Spitz expression and processing. The Rhomboid and Star proteins are also expressed and required in the midline. The ectodermal defects of spitz, rho or Star mutant embryos could be rescued by inducing the expression of the respective normal genes only in the midline cells. Rho and Star thus function non-autonomously, and may be required for the production or processing of the Spitz precursor. Secreted Spitz is the only sim-dependent contribution of the midline to patterning the ectoderm, since the ventral defects observed in sim mutant embryos can be overcome by expression of secreted Spitz in the ectoderm. While ectopic expression of secreted Spitz in the ectoderm or mesoderm gave rise to ventralization of the embryo, increased expression of secreted Spitz in the midline did not lead to alterations in ectoderm patterning. A mechanism for adjustment to variable levels of secreted Spitz emanating from the midline may be provided by Argos, which forms an inhibitory feedback loop for DER activation. The production of secreted Spitz in the midline, may provide a stable source for graded DER activation in the ventral ectoderm.

Animals↗
PubMed1997

Spitz and Wingless, emanating from distinct borders, cooperate to establish cell fate across the Engrailed domain in the Drosophila epidermis.

A key step in development is the establishment of cell type diversity across a cellular field. Segmental patterning within the Drosophila embryonic epidermis is one paradigm for this process. At each parasegment boundary, cells expressing the Wnt family member Wingless confront cells expressing the homeoprotein Engrailed. The Engrailed-expressing cells normally differentiate as one of two alternative cell types. In investigating the generation of this cell type diversity among the 2-cell-wide Engrailed stripe, we previously showed that Wingless, expressed just anterior to the Engrailed cells, is essential for the specification of anterior Engrailed cell fate. In a screen for additional mutations affecting Engrailed cell fate, we identified anterior open/yan, a gene encoding an inhibitory ETS-domain transcription factor that is negatively regulated by the Rasl-MAP kinase signaling cascade. We find that Anterior Open must be inactivated for posterior Engrailed cells to adopt their correct fate. This is achieved by the EGF receptor (DER), which is required autonomously in the Engrailed cells to trigger the Ras1-MAP kinase pathway. Localized activation of DER is accomplished by restricted processing of the activating ligand, Spitz. Processing is confined to the cell row posterior to the Engrailed domain by the restricted expression of Rhomboid. These cells also express the inhibitory ligand Argos, which attenuates the activation of DER in cell rows more distant from the ligand source. Thus, distinct signals flank each border of the Engrailed domain, as Wingless is produced anteriorly and Spitz posteriorly. Since we also show that En cells have the capacity to respond to either Wingless or Spitz, these cells must choose their fate depending on the relative level of activation of the two pathways.

Animals↗
PubMed1998

EGFR signaling is required for the differentiation and maintenance of neural progenitors along the dorsal midline of the Drosophila embryonic head.

EGFR signaling has been shown in recent years to be involved in the determination, differentiation and maintenance of neural and epidermal cells of the ventral midline (mesectoderm and ventromedial ectoderm). Localized activation of the TGFalpha homolog Spitz (Spi) in the mesectoderm is achieved by the products of the genes rhomboid and Star. Spi binds to its receptor, the Drosophila epidermal growth factor receptor homolog (Egfr), and triggers the Ras pathway which is needed for the survival and differentiation of ventral midline cells. The results reported here indicate that EGFR signaling is also required in a narrow medial domain of the head ectoderm (called 'head midline' in the following) that includes the anlagen of the medial brain, the visual system (optic lobe, larval eye) and the stomatogastric nervous system (SNS). We document that genes involved in EGFR signaling are expressed in the head midline. Loss of EGFR signaling results in an almost total absence of optic lobe and larval eye, as well as severe reduction of SNS and medial brain. The cellular mechanism by which this phenotype arises is a failure of neurectodermal cells to differentiate combined with apoptotic cell death. Overactivity of EGFR signaling, as achieved by heat-shock-driven activation of a wild-type rhomboid (rho) construct, or by loss of function of argos (aos) or yan, results in an hyperplasia and deformity of the head midline structures. We show that, beside their requirement for EGFR signaling, head and ventral midline structures share several morphogenetic and molecular properties.

Animals↗
PubMed1998

Regulation of EGF receptor signaling establishes pattern across the developing Drosophila retina.

Developing epithelia use a variety of patterning mechanisms to place individual cells into their correct positions. However, the means by which pattern elements are established are poorly understood. Here, we report evidence that regulation of Drosophila EGF receptor (DER) activity plays a central role in propagating the evenly spaced array of ommatidia across the developing Drosophila retina. DER activity is essential for establishing the first ommatidial cell fate, the R8 photoreceptor neuron. R8s in turn appear to signal through Rhomboid and Vein to create a patterned array of 'proneural clusters' which contain high levels of phosphorylated ERKA and the bHLH protein Atonal. Finally, secretion by the proneural clusters of Argos represses DER activity in less mature regions to create a new pattern of R8s. Propagation of this process anteriorly results in a retina with a precise array of maturing ommatidia.

Animals↗
PubMed2002

EGFR signalling inhibits Capicua-dependent repression during specification of Drosophila wing veins.

Localised activation of the Ras/Raf pathway by Epidermal Growth Factor Receptor (EGFR) signalling specifies the formation of veins in the Drosophila wing. However, little is known about how the EGFR signal regulates transcriptional responses during the vein/intervein cell fate decision. We provide evidence that EGFR signalling induces expression of vein-specific genes by inhibiting the Capicua (Cic) HMG-box repressor, a known regulator of embryonic body patterning. Lack of Cic function causes ectopic expression of EGFR targets such as argos, ventral veinless and decapentaplegic and leads to formation of extra vein tissue. In vein cells, EGFR signalling downregulates Cic protein levels in the nucleus and relieves repression of vein-specific genes, whereas intervein cells maintain high levels of Cic throughout larval and pupal development, repressing the expression of vein-specific genes and allowing intervein differentiation. However, regulation of some EGFR targets such as rhomboid appears not to be under direct control of Cic, suggesting that EGFR signalling branches out in the nucleus and controls different targets via distinct mediator factors. Our results support the idea that localised inactivation of transcriptional repressors such as Cic is a rather general mechanism for regulation of target gene expression by the Ras/Raf pathway.

Animals↗
PubMed1997

Prey ingestion revealed by oesophagus and stomach temperature recordings in cormorants.

We examined the accuracy of both stomach and oesophagus temperature sensors-deployed on captive Brandt's cormorants-for determination of the mass of food ingested and the number of prey items swallowed. The oesophageal temperature sensor was a better detector of all feeding events, including that of small prey which were missed by the stomach sensor. Adapted to free-ranging animals (and coupled to data loggers for recording seawater temperature), oesophagus temperature recorders, in conjunction with both recordings of energy expenditure (e.g. doubly labelled water, heart rate) and determination of position (e.g. Argos transmitter, time/depth recorder), should provide further important insights into the foraging success of marine endotherms.

Animals↗
PubMed2004

Induction and biochemical purification of RNA-induced silencing complex from Drosophila S2 cells.

The discovery of RNA interference (RNAi) has greatly simplified the process of suppressing genes in many experimental systems, including Caenorhabditis elegans, Drosophila, and mammalian cells. A sequence-specific nuclease complex, called the RNA-induced silencing complex (RISC), can be purified from cells undergoing RNAi. RISC shows RNase activity when exposed to RNAs homologous to the input double-stranded RNA (dsRNAs) but lacks activity in the presence of nontargeted RNAs. We describe the induction of RNAi by dsRNA in cultured Drosophila Schneider-2 (S2) cells and detail procedures for RISC purification from these cells. This purification approach has allowed us to identify several RISC components, including siRNAs, Argo naute 2 (Ago-2), Drosophila Fragile X related protein (dFXR), Vasa intronic gene (VIG), and the micrococcal nuclease family member Tudor-SN (Drosophila CG7008). RNAi is carried out by an endogenous pathway important for normal development in many organisms. In fact, organisms express hundreds of different microRNAs (miRNAs), small hairpin RNAs that function through the RNAi pathway to suppress expression of endogenous genes. The function of miRNAs is poorly understood, and most of their targets are unknown. Purified RISC complexes contain short interfering RNAs and endogenously expressed miRNAs and will be useful for studying many aspects of the RNAi machinery.

Animals↗
PubMed1987

Prediction of the secondary structures of stefins and cystatins, the low-molecular mass protein inhibitors of cysteine proteinases.

A procedure for classifying proteins of known sequence into structurally similar groups was developed on the basis of the Argos parametric approach. It is shown that stefins and cystatins constitute two structurally well resolved, but homologous groups of proteins. Furthermore, it is very probable that segments of secondary structures within each family are conserved, although significant differences between stefins and cystatins are indicated at the level of secondary structure. Next, secondary structures of all sequenced stefins and cystatins were predicted and used in the construction of secondary structures of the "typical stefin" and the "typical cystatin". Results were interpreted in the light of evolution and inhibition mechanism: Alignment of the "typical stefin" versus the "typical cystatin" secondary structure segments suggests that the divergence of stefin and cystatin families did not occur by a gene fusion event, but only by a mechanism of substitution, insertion and/or deletion. The central region of low-molecular mass cystatins, which is assumed to interact with cysteine proteinases, is predicted to be in a beta-sheet conformation. This resembles the beta-sheet in the active site of "standard mechanism" serine proteinases inhibitors.

Amino Acid Sequence↗
PubMed2005

Phylogenetic relationships among major species of japanese coleoid cephalopods (Mollusca: Cephalopoda) using three mitochondrial DNA sequences.

Phylogenetic relationships among 36 species of major coleoid cephalopods from Japanese waters were studied using partial sequences of three mitochondrial genes, 16S rDNA, 12S rDNA, and cytochrome c oxidase subunit I gene. Octopoda and Decapoda were monophylic groups. Within Sepioidea, Sepiadariidae and Sepiolidae were not closely related to Sepiidae, but rather related to Teuthoidea. Sepiidae with a distinct calcareous shell formed a single cluster. Myopsida was closely related to Oegopsida. Within Octopoda, Opisthoteuthis depressa and Argonauta argo diverged earlier than Octopodiidae. The common octopuses in Japanese waters were separated into three clusters. The first cluster occupied a basal position, and includes large-sized octopuses, such as Enteroctopus dofleini and Octopus (Paroctopus) conispadiceus from the continental shelf and upper slope. The second cluster consisted of long-armed octopuses, such as O. ornatus, O. minor, and O. sasakii. The third cluster contained small- to medium-sized octopus, such as Amphioctopus fangsiao, A. areolatus, O. cyaneus, and O. vulgaris, in which several species possess ocelli on the web. The second cluster formed the sister group to the third cluster.

Animals↗