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Weak Signal (weak + signal)
Selected AbstractsSpatio-temporal expression of Xenopus vasa homolog, XVLG1, in oocytes and embryos: The presence of XVLG1 RNA in somatic cells as well as germline cellsDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 2 2000Kohji Ikenishi The expression of Xenopus vasa homolog or XVLG1 was examined in oocytes and embryos by whole-mount in situ hybridization and reverse transcription,polymerase chain reaction (RT-PCR). To confirm the results in embryos, both methods were also applied to explants of germ plasm-bearing cells (GPBC) from 32-cell embryos and to those of partial embryos deprived of GPBC. By hybridization, XVLG1 ribonucleic acid (RNA) was shown to be present throughout the cytoplasm in oocytes at stages I,III, except for the mitochondrial cloud. It was barely recognizable in a portion of germline cells of embryos at specific stages, notwithstanding that XVLG1 protein was present in those cells almost throughout their life-span. A weak signal for the RNA was detectable in some of the presumptive primordial germ cells (pPGC, descendants of GPBC from the gastrula stage onward) from the late gastrula (stage 12) to the hatching tadpole stage (stage 33/34), and in some of the PGC at stages 49,50. The results for pPGC were confirmed by the hybridization of explants of GPBC at equivalent stages in control embryos. In contrast, XVLG1 RNA was detected in certain somatic cells of embryos until stage 46. These observations were supported in part by the results of RT-PCR for embryos and explants. The possible role of the product of XVLG1 was reconsidered given its presence in both germline and somatic cells. [source] Noise-improved signal detection in cat primary visual cortex via a well-balanced stochastic resonance-like procedureEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2007Klaus Funke Abstract Adding noise to a weak signal can paradoxically improve signal detection, a process called ,stochastic resonance' (SR). In the visual system, noise might be introduced by the image jitter resulting from high-frequency eye movements, like eye microtremor and microsaccades. To test whether this kind of noise might be beneficial or detrimental for cortical signal detection, we performed single-unit recordings from area 17 of anaesthetized cats while jittering the visual stimulus in a frequency and amplitude range resembling the possible range of eye movements. We used weak, sub- and peri-threshold visual stimuli, on top of which we superimposed noise with variable jitter amplitude. In accordance with the typical SR effect, we found that small noise levels actually increased the signal-to-noise ratio (SNR) of previously weak cortical visual responses, while originally strong responses were little affected or even reduced. Above a certain noise level, the SNR dropped a little, but not as a result of increased background activity , as would be proposed by SR theory , but because of a lowered response to signal and noise. Therefore, it seems that the ascending visual pathway optimally utilizes signal detection improvement by a SR-like process, while at the same time preventing spurious noise-induced activity and keeping the SNR sufficiently high. [source] Localizations of intracellular calcium and Ca2+ -ATPase in hamster spermatogenic cells and spermatozoaMICROSCOPY RESEARCH AND TECHNIQUE, Issue 8 2006H.L. Feng Abstract Calcium plays a predominant role regulating many functional processes of spermatogenesis and fertilization. The purpose of the present study is to define the exact location of calcium as well as examine the role it plays during spermatogenesis and sperm capacitation. Testes and epididymides were obtained from adult healthy male hamsters. Spermatozoa were incubated with modified Tyrode's medium up to 4 h at 37°C for sperm capacitation in vitro. Samples of the testes and sperm cells were analyzed by cytochemical techniques to determine the location of calcium and Ca2+ -ATPase and the percentage of acrosome reactions under light and electron microscopy. The data showed that (1) Sertoli cells exhibited numerous calcium precipitates as large, round, electron-dense bodies distributed throughout the cytoplasm and the mitochondrial matrix. Fine calcium precipitates existed in fewer numbers in the intracellular storage sites of spermatogonia and primary spermatocytes, in sharp distinction to secondary spermatocyte and spermatids, which showed an abundance of large and round calcium precipitates, especially in the mitochondrial matrix of spermatids. More calcium deposits were distributed in the plasma membrane (PM), acrosome membrane, and matrices of the acrosome and mitochondria following capacitation; (2) Ca2+ -ATPase was found in the endoplasmic reticulum system and PM of noncapacitated spermatozoa as well as Sertoli cells. Capacitated spermatozoa showed a weak signal. These results suggest that the presence of calcium in spermatogenic cells might play a role in cell growth and differentiation during spermatogenesis. The Ca2+ -ATPase function may be inhibited during capacitation, leading to an increase in acrosomal calcium level and triggering of acrosomal exocytosis. Microsc. Res. Tech., 2006. © 2006 Wiley-Liss, Inc. [source] Joint FTIR and TPD study of hydrogen desorption from p+ -type porous siliconPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003P. Rivolo Abstract The H-terminated surface of Porous Silicon (PS) has been studied in the past decade basically by means of Fourier transform infrared (FTIR) spectroscopy. In one case only, a temperature programmed desorption (TPD) technique has been applied to an n-type PS sample. However, the evaluation of the amount of hydrogen thermally desorbed has never been attempted. The present work reports the joint FTIR and TPD study of hydrogen desorption from p+ -type PS and estimates the amount of hydrogen desorbed in the range 40,850 °C to be around 2 mmol/g. This suggests a ratio between H atoms and surface Si atoms of about one, giving support to the picture of PS as H-covered: as a consequence, only a few bare Si atoms are exposed at the surface and prone to act as adsorption centres, e.g. of NO2. A weak signal, in the TPD curve, is probably associated with the decomposition of a few Si,H,B bulk complexes. [source] Structure of lobster apocrustacyanin A1 using softer X-raysACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2001M. Cianci The molecular basis of the camouflage colouration of marine crustacea is often provided by carotenoproteins. The blue colour of the lobster carapace, for example, is intricately associated with a multimacromolecular 16-mer complex of protein subunits each with a bound astaxanthin molecule. The protein subunits of crustacyanin fall into two distinct subfamilies, CRTC and CRTA. Here, the crystal structure solution of the A1 protein of the CRTC subfamily is reported. The problematic nature of the structure solution of the CRTC proteins (both C1 and A1) warranted consideration and the development of new approaches. Three putative disulfides per protein subunit were likely to exist based on molecular-homology modelling against known lipocalin protein structures. With two such subunits per crystallographic asymmetric unit, this direct approach was still difficult as it involved detecting a weak signal from these sulfurs and suggested the use of softer X-rays, combined with high data multiplicity, as reported previously [Chayen et al. (2000), Acta Cryst. D56, 1064,1066]. This paper now describes the structure solution of CRTC in the form of the A1 dimer based on use of softer X-rays (2,Å wavelength). The structure solution involved a xenon derivative with an optimized xenon LI edge signal and a native data set. The hand of the xenon SIROAS phases was determined by using the sulfur anomalous signal from a high-multiplicity native data set also recorded at 2,Å wavelength. For refinement, a high-resolution data set was measured at short wavelength. All four data sets were collected at 100,K. The refined structure to 1.4,Å resolution based on 60,276 reflections has an R factor of 17.7% and an Rfree of 22.9% (3137 reflections). The structure is that of a typical lipocalin, being closely related to insecticyanin, to bilin-binding protein and to retinol-binding protein. This A1 monomer or dimer can now be used as a search motif in the structural studies of the oligomeric forms ,- and ,-crustacyanins, which contain bound astaxanthin molecules. [source] New aspects of IFN-,/, signalling in immunity, oncogenesis and bone metabolismCANCER SCIENCE, Issue 5 2003Akinori Takaoka Although interferons (IFNs) were originally identified as humoral factors that confer an antiviral state upon cells, they have been demonstrated to be multifunctional in a variety of biological systems. The IFN-,/, system modulates not only the cellular immune response to viral and bacterial infections, but also the oncogenic process and bone metabolism. Further studies have revealed additional unique facets of the IFN-,/, system. A weak signal by constitutively produced IFN-,/, is critical not only for the regulation of cellular amplification of IFN-,/, production upon viral infection or the enhancement of signalling by other cytokines, but also for the regulation of adaptive immune responses, such as the enhancement of CD8+ T cell activation. Furthermore, IFN-, signalling is critical for the regulation of the bone-resorbing osteo-clasts. In this review, we focus on the newly discovered roles of the IFN-,/, system in host defense and bone remodeling, particularly on the functions of the weak IFN-,/, signalling in the context of what we refer to as the "rewing-up" model. (Cancer Sci 2003; 94: 405,411) [source] Somatic APC mosaicism: a frequent cause of familial adenomatous polyposis (FAP),HUMAN MUTATION, Issue 10 2007Stefan Aretz Abstract Somatic mutational mosaicism presents a challenge for both molecular and clinical diagnostics and may contribute to deviations from predicted genotype,phenotype correlations. During APC mutation screening in 1,248 unrelated patients with familial adenomatous polyposis (FAP), we identified 75 cases with an assumed or confirmed de novo mutation. Prescreening methods (protein truncation test [PTT], DHPLC) indicated the presence of somatic mosaicism in eight cases (11%). Sequencing of the corresponding fragments revealed very weak mutation signals, pointing to the presence of either nonsense or frameshift mutations at low level. All mutations were confirmed and quantified by SNaPshot analysis: in leukocyte DNA from the eight patients, the percentage of mosaicism varied between 5.5% and 77%, while the proportion of the mutation in DNA extracted from adenomas of the respective patient was consistently higher. The eight mutations identified as mosaic are localized within codons 216,1464 of the APC gene. According to the known genotype,phenotype correlation, patients with mutations in this region exhibit typical or severe FAP. However, six of the eight patients presented with an attenuated or atypical polyposis phenotype. Our data demonstrate that in a fraction of FAP patients the causative APC mutation may not be detected due to weak signals or somatic mosaicism that is restricted to tissues other than blood. SNaPshot analysis was proven to be an easy, rapid, and reliable method of confirming low-level mutations and evaluating the degree of mosaicism. Some of the deviations from the expected phenotype in FAP can be explained by the presence of somatic mosaicism. Hum Mutat 28(10), 985,992, 2007. © 2007 Wiley-Liss, Inc. [source] The chemopreventive compound curcumin is an efficient inhibitor of Epstein-Barr virus BZLF1 transcription in Raji DR-LUC cells,MOLECULAR CARCINOGENESIS, Issue 3 2002Manfred Hergenhahn Abstract To characterize the effects of inhibitors of Epstein-Barr virus (EBV) reactivation, we established Raji DR-LUC cells as a new test system. These cells contain the firefly luciferase (LUC) gene under the control of an immediate-early gene promoter (duplicated right region [DR]) of EBV on a self-replicating episome. Luciferase induction thus serves as an intrinsic marker indicative for EBV reactivation from latency. The tumor promoter 12- O -tetradecanoylphorbol-13-acetate (TPA) induced the viral key activator BamH fragment Z left frame 1 (BZLF1) protein ("ZEBRA") in this system, as demonstrated by induction of the BZLF1 protein-responsive DR promoter upstream of the luciferase gene. Conversely, both BZLF1 protein and luciferase induction were inhibited effectively by the chemopreventive agent curcumin. Semiquantitative reverse transcriptase (RT)-polymerase chain reaction (PCR) further demonstrated that the EBV inducers TPA, sodium butyrate, and transforming growth factor-, (TGF-,) increased levels of the mRNA of BZLF1 mRNA at 12, 24, and 48 h after treatment in these cells. TPA treatment also induced luciferase mRNA with similar kinetics. Curcumin was found to be highly effective in decreasing TPA-, butyrate-, and TGF-,-induced levels of BZLF1 mRNA, and of TPA-induced luciferase mRNA, indicating that three major pathways of EBV are inhibited by curcumin. Electrophoretic mobility shift assays (EMSA) showed that activator protein 1 (AP-1) binding to a cognate AP-1 sequence was detected at 6 h and could be blocked by curcumin. Protein binding to the complete BZLF1 promoter ZIII site (ZIIIA+ZIIIB) demonstrated several specific complexes that gave weak signals at 6 h and 12 h but strong signals at 24 h, all of which were reduced after application of curcumin. Autostimulation of BZLF1 mRNA induction through binding to the ZIII site at 24 h was confirmed by antibody-induced supershift analysis. The present results confirm our previous finding that curcumin is an effective agent for inhibition of EBV reactivation in Raji DR-CAT cells (carrying DR-dependent chloramphenicol acetyltransferase), and they show for the first time that curcumin inhibits EBV reactivation mainly through inhibition of BZLF1 gene transcription. © 2002 Wiley-Liss, Inc. [source] Formation of iminium ions by fragmentation of a2 ionsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2004Alex G. Harrison Tandem mass spectrometric experiments have been carried out on the protonated amides H-Gly-Ala-NH2, H-Ala-Gly-NH2, H-Ala-Val-NH2, H-Val-Ala-pNA, H-Leu-Phe-NH2, H-Phe-Leu-NH2, H-Phe-Tyr-NH2 and H-Tyr-Phe-NH2 with particular emphasis on the fragmentation of the isomeric a2 ions derived therefrom. Primary fragmentation reactions of the protonated amides involve formation of the y1, and b2 ions with further fragmentation of the b2 ion to form the a2 ion which fragments to form iminium ions. Collision-induced dissociation studies of the mass-selected a2 ions were carried out. For the Gly-Ala, Ala-Gly and Val-Ala a2 ions, weak signals were observed corresponding to loss of CO from the a2 ion. With the exception of the Gly-Ala, Ala-Gly and Val-Ala a2 ions, both possible iminium ions (a1 and the internal iminium ion) are observed with the most abundant being that formed by proton attachment to the imine of higher proton affinity. The results provide strong support for the recently proposed (El Aribi et al. J. Am. Chem. Soc. 2003; 125: 9229) mechanism of fragmentation of a2 ions which involves elimination of CO from the a2 ion to form a proton-bound complex of two imines. Based on this mechanism ab initio calculations of the total energies of the a2 ions and the transition states for fragmentation have been carried out giving the energy barrier for fragmentation of each a2 ion. The experimental results are interpreted in terms of these energetics data, unimolecular rate constants calculated by using the RRKM theory, and the imine proton affinities. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||