心音信号噪声消除的小波变换方法

心音信号幅值小,干扰多,采用常规的时、频域滤波方法往往不能收到良好的效果,本文根据信号和干扰在小波变换下的不同变化特性,利用二进小波变换的模极大值识别出心音信号中的干扰噪声的位置,剔除其相应的小波变换系数后,再通过小波逆变换重构出心音信号,并根据心音信号的特点选取了适当的母小波和分解尺度,给出了利用小波方法去噪前后的实际结果,结果表明,小波变换方法可有效地消除心音信号中的噪声干扰。     

Internal pH of human neutrophil lysosomes

We focus this report on the relationship between signal II fast and slow during a flash sequence for Tris-washed chloroplasts at different pH-values. The pH influences both the redox state and spectral form of signal II slow in dark-adapted chloroplasts. At pH 6.0, signal II slow is oxidized and does not influence the kinetics of signal II fast equally formed on each flash. At pH 8.5, signal II slow in mainly reduced in the dark and the first flash produces signal II slow and no signal fast. Signal II fast appears on the following flashes only. Signals II fast and slow are connected to the same center and signal II fast is observed only if signal II slow is oxidized.     

Principles behind the multifarious control of signal transduction. ERK phosphorylation and kinase/phosphatase control

General and simple principles are identified that govern signal transduction. The effects of kinase and phosphatase inhibition on a MAP kinase pathway are first examined in silico. Quantitative measures for the control of signal amplitude, duration and integral strength are introduced. We then identify and prove new principles, such that total control on signal amplitude and on final signal strength must amount to zero, and total control on signal duration and on integral signal intensity must equal -1. Collectively, kinases control amplitudes more than duration, whereas phosphatases tend to control both. We illustrate and validate these principles experimentally: (a) a kinase inhibitor affects the amplitude of EGF-induced ERK phosphorylation much more than its duration and (b) a phosphatase inhibitor influences both signal duration and signal amplitude, in particular long after EGF administration. Implications for the cellular decision between growth and differentiation are discussed.     

How does environmental variation translate into biological processes?

Birth and death rates, as so many other biological processes, are usually not linearly related to environmental variation. Common examples of non-linear response forms include unimodal "optimum-type" responses and various saturating responses. These responses filter the signal coming from the environment to a corresponding biological process. We explored how different types of environmental signal may be transformed to a biological process. We were interested in the effect of the filter on modulation of (1) the variance of the signal, on (2) the variance-covariance structure between the signal and the filtered signal, and on (3) the match between the power spectra of the signal and the filtered signal. We found that the filters will change the frequency distribution (mean, variance, modality) of the signal. Especially symmetric filters that have a single peak of optimum will change signal structure so that there either exists or does not exist a correlation between the signal and the filtered signal. When the correlation exists it may be either positive or negative depending on the signal's mode relative to the filter structure. Also, the power spectrum properties of the signal may be dramatically transformed after passing the filter, e.g., blue noise can turn into red noise. Our results strongly suggest that studies on the influence of external signals on biological processes, such as population dynamics, should explicitly consider how the signal is transferred to biological processes.     

Type I signal peptidases of Gram-positive bacteria

Proteins that are exported from the cytoplasm to the periplasm and outer membrane of Gram-negative bacteria, or the cell wall and growth medium of Gram-positive bacteria, are generally synthesized as precursors with a cleavable signal peptide. During or shortly after pre-protein translocation across the cytoplasmic membrane, the signal peptide is removed by signal peptidases. Importantly, pre-protein processing by signal peptidases is essential for bacterial growth and viability. This review is focused on the signal peptidases of Gram-positive bacteria, Bacillus and Streptomyces species in particular. Evolutionary concepts, current knowledge of the catalytic mechanism, substrate specificity requirements and structural aspects are addressed. As major insights in signal peptidase function and structure have been obtained from studies on the signal peptidase LepB of Escherichia coli, similarities and differences between this enzyme and known Gram-positive signal peptidases are highlighted. Notably, while the incentive for previous research on Gram-positive signal peptidases was largely based on their role in the biotechnologically important process of protein secretion, present-day interest in these essential enzymes is primarily derived from the idea that they may serve as targets for novel anti-microbials.     

Wild type and mutant signal peptides of Escherichia coli outer membrane lipoprotein interact with equal efficiency with mammalian signal recognition particle

The signal peptide of the outer membrane lipoprotein (OMLP) of Escherichia coli was shown to be capable of promoting protein translocation across mammalian microsomal membranes in vitro. We assayed translocation of a fusion protein containing the OMLP signal peptide and nine amino acids of OMLP fused in frame to beta-lactamase. The efficiency with which the mammalian translocation machinery recognizes and accepts the OMLP signal peptide as substrate is indistinguishable from that of mammalian secretory proteins. Upon translocation mammalian signal peptidase processes the pre-OMLP-beta-lactamase protein at different sites than are utilized in vivo by E. coli OMLP signal peptidase (signal peptidase II) but that can be predicted as mammalian signal peptidase cleavage sites. Mutants in the OMLP signal peptide were tested for their ability to promote translocation of the fusion protein in this assay system. It has been shown previously that mutants in the positively charged amino acids at the amino terminus of the signal peptide severely delay the translocation of OMLP in vivo in E. coli. However, these mutants had no detectable effect either on signal recognition by mammalian signal recognition particle or on the efficiency of translocation itself.     

Examination of optical depth effects on fluorescence imaging of cardiac propagation

Optical mapping with voltage-sensitive dyes provides a high-resolution technique to observe cardiac electrodynamic behavior. Although most studies assume that the fluorescent signal is emitted from the surface layer of cells, the effects of signal attenuation with depth on signal interpretation are still unclear. This simulation study examines the effects of a depth-weighted signal on epicardial activation patterns and filament localization. We simulated filament behavior using a detailed cardiac model, and compared the signal obtained from the top (epicardial) layer of the spatial domain with the calculated weighted signal. General observations included a prolongation of the action upstroke duration, early upstroke initiation, and reduction in signal amplitude in the weighted signal. A shallow filament was found to produce a dual-humped action potential morphology consistent with previously reported observations. Simulated scroll wave breakup exhibited effects such as the false appearance of graded potentials, apparent supramaximal conduction velocities, and a spatially blurred signal with the local amplitude dependent upon the immediate subepicardial activity; the combination of these effects produced a corresponding change in the accuracy of filament localization. Our results indicate that the depth-dependent optical signal has significant consequences on the interpretation of epicardial activation dynamics.     

In vivo effect of asparagine in the hydrophobic region of the signal sequence

On the basis of the biophysical studies on the synthetic mutant (Ile-8----Asn) OmpA signal peptide in the preceding paper (Hoyt, D. C., and Gierasch, L.M. (1991) J. Biol. Chem. 266, 14406-14412), the in vivo effects of the same mutation were examined by fusing the mutant OmpA signal sequence to Staphylococcus aureus nuclease or TEM beta-lactamase. The mutation in which the isoleucine residue at position 8 of the OmpA signal sequence of Escherichia coli was replaced with a neutral polar residue, asparagine, resulted in a defective signal peptide. The mutant signal sequence was unable to be processed, and the precursor molecule accumulated in the cytoplasmic as well as in the membrane fractions, indicating that the Ile-8----Asn OmpA signal sequence is not competent for translocating nuclease A or beta-lactamase across the membrane. This result is consistent with the in vitro studies on the Ile-8----Asn OmpA signal peptide, which indicated that the mutant signal peptide was unable to penetrate into the hydrophobic core of the lipid bilayer. Other asparagine or glutamine substitution mutations in the hydrophobic region of the OmpA signal sequence were also examined. Interestingly, the OmpA signal sequence with either Ile-8----Gln, Val-10----Asn, or Leu-12----Asn mutation was completely defective as the Ile-8----Asn OmpA signal sequence, while the Ile-6----Asn and Ala-9----Asn OmpA nucleases were able to be processed to secrete nuclease, although the processing occurred at a much slower rate than the wild-type OmpA nuclease. These results indicate that the defects depend on the position of the lesion in the hydrophobic core of the OmpA signal sequence.     

THERMOREGULATION CONSTRAINS EFFECTIVE WARNING SIGNAL EXPRESSION

Evolution of conspicuous signals may be constrained if animal coloration has nonsignaling as well as signaling functions. In aposematic wood tiger moth ( Parasemia plantaginis ) larvae, the size of a warning signal (orange patch on black body) varies phenotypically and genetically. Although a large warning signal is favored as an antipredator defense, we hypothesized that thermoregulation may constrain the signal size in colder habitats. To test this hypothesis, we conducted a factorial rearing experiment with two selection lines for larval coloration (small and large signal) and with two temperature manipulations (high and low temperature environment). Temperature constrained the size and brightness of the warning signal. Larvae with a small signal had an advantage in the colder environment, which was demonstrated by a faster development time and growth rate in the low temperature treatment, compared to larvae with a large signal. Interestingly, the larvae with a small signal were found more often on the plant than the ones with a large signal, suggesting higher basking activity of the melanic (small signal) individuals in the low temperature. We conclude that the expression of aposematic display is not only defined by its efficacy against predators; variation in temperature may constrain evolution of a conspicuous warning signal and maintain variation in it.     

A functional interaction between the signal peptide and the translation apparatus is detected by the use of a single point mutation which blocks translocation across mammalian endoplasmic reticulum

A functional interaction between the signal sequence and the translation apparatus which may serve as a first step in chain targeting to the membrane is described. To this end, we exploited the powerful technique of molecular cloning in a procaryotic system and the well characterized translocation system of mammalian endoplasmic reticulum. The signal peptide of subunit B of the heat labile enterotoxin of Escherichia coli (EltB) was fused to several proteins. Single base substitutions were introduced in the signal peptide and their effect on protein synthesis and translocation was studied. We sought a single amino acid substitution which may define certain steps in the coordinated regulation of chain synthesis and targeting to the membrane. The substitution of proline for leucine at residue -8 in the signal peptide abolished all known functions of the signal peptide. In contrast to wild type signal peptide, the mutant signal peptide did not lead to arrest of nascent chain synthesis by signal recognition particle or translocation of the precursor protein across the membrane of the endoplasmic reticulum. Furthermore, the mutant signal peptide was not cleaved by purified E. coli signal peptidase. Interestingly, the mutation resulted in about a 2-fold increase in the rate of synthesis of the precursor protein, suggesting a role for the signal peptide in regulating the synthesis of the nascent secretory chain as a means of ensuring early and efficient targeting of this chain to the membrane. This role might involve interaction of the signal peptide with components of the translation apparatus and/or endogenous signal recognition particle. These results were obtained with three different fusion proteins carrying the signal peptide of EltB thus leading to the conclusion that the effect of the mutation on the structure and function of the signal peptide is independent of the succeeding sequence to which the signal peptide is attached.     

Sympatry drives colour and song evolution in wood-warblers (Parulidae)

Closely related species often exhibit similarities in appearance and behaviour, yet when related species exist in sympatry, signals may diverge to enhance species recognition. Prior comparative studies provided mixed support for this hypothesis, but the relationship between sympatry and signal divergence is likely nonlinear. Constraints on signal diversity may limit signal divergence, especially when large numbers of species are sympatric. We tested the effect of sympatric overlap on plumage colour and song divergence in wood-warblers (Parulidae), a speciose group with diverse visual and vocal signals. We also tested how number of sympatric species influences signal divergence. Allopatric species pairs had overall greater plumage and song divergence compared to sympatric species pairs. However, among sympatric species pairs, plumage divergence positively related to the degree of sympatric overlap in males and females, while male song bandwidth and syllable rate divergence negatively related to sympatric overlap. In addition, as the number of species in sympatry increased, average signal divergence among sympatric species decreased, which is likely due to constraints on warbler perceptual space and signal diversity. Our findings reveal that sympatry influences signal evolution in warblers, though not always as predicted, and that number of sympatric species can limit sympatry''s influence on signal evolution.     

Selection on signal–reward correlation: limits and opportunities to the evolution of deceit in Turnera ulmifolia L

Because pollinators are unable to directly assess the amount of rewards offered by flowers, they rely on the information provided by advertising floral traits. Thus, having a lower intra-individual correlation between signal and reward (signal accuracy) than other plants in the population provides the opportunity to reduce investment in rewards and cheat pollinators. However, pollinators' cognitive capacities can impose a limit to the evolution of this plant cheating strategy if they can punish those plants with low signal accuracy. In this study, we examined the opportunity for cheating in the perennial weed Turnera ulmifolia L. evaluating the selective value of signal accuracy, floral display and reward production in a natural population. We found that plant reproductive success was positively related to signal accuracy and floral display, but not to nectar production. The intensity of selection on floral display was more than three times higher than on signal accuracy. The pattern of selection indicated that pollinators can select for signal accuracy provided by plants and suggests that learning abilities of pollinators can limit the evolution of deceptive strategies in T. ulmifolia.     

Structural requirement of C‐terminal region of chicken lysozyme signal peptide

Abstract

The mechanisms of signal peptide cleavage has not been fully elucidated yet. In previous investigation, we have examined the effect of chicken lysozyme signal peptide mutations on the secretion of human lysozyme. During this study, we determined that the hydrophobic bulky amino acid Val at position ‐1 inhibited the function of signal peptide. To determine why the ‐1Val suppressed the function of signal peptide, turn‐promoting amino acids Pro and Gly were introduced after ‐lVal to prevent the signal peptide from forming α‐helix and induce β‐turn around the cleavage site. This mutation resulted in no processing of signal peptide and no secretion of human lysozyme. However, the replacement of ‐1Val with Ala permitted a functional signal. Based on these results, three dimensional models around the cleavage site of each signal peptide were made, which show that bulky side chain at ‐1 residue of signal peptide limits the reaction space for signal peptidase and suppresses cleavage by steric hindrance. We suggest that the bulky side chain at ‐1 residue suppresses the signal peptide cleavage by its local steric hindrance and not by a change in whole structure around the cleavage site. On the other hand, introduction of Pro at position +1 did not inhibit signal cleavage completely resulting in poor secretion and processing efficiency although Pro in position +1 has been recently reported to block cleavage of the prokaryotic signal peptide. The mechanism of cleavage of prokaryotic signal may be different than that of eukaryotic signal.     

Sources of Selection on Signal Timing in a Tree Frog

Signal-timing adjustment is common in communally signaling species, and there is large variation in signal-timing formats found in nature. We conducted a survey of geographic variation in female signal-timing preferences and male signaling behavior of a tree frog to test predictions of two hypotheses about the sources of selection acting on signal-timing behavior. We found that female preferences are important in shaping male signal timing, affecting the absolute placement of signals relative to the temporal limits of female preferences. Variation in other signal characters, particularly signal period, also affects signal timing, albeit in a more complicated pattern: the influence of signal period on signal timing varied between populations. Overall, our findings indicate that the evolution of male signal-timing behavior is strongly influenced by female preferences and by an interaction with other aspects of male signaling behavior such as male signal period.     

应力作用下软骨细胞信号传导的研究进展

研究显示应力刺激对软骨细胞生长及基质代谢具重要作用。软骨正常结构形态以及应力下的软骨细胞形态和基质代谢的变化是力-生物信号转化的基础,信号分子及信号通路则是应力信号传导的核心,二者是对软骨细胞应力下信号传导过程深入了解不可或缺的信息组成,了解应力对软骨细胞的作用方式及作用机制有助于软骨相关疾病诊治、组织工程等领域的研究,本文就这两个方面研究进展做一综述。     

Two intercellular signals required for fruiting body formation in Myxococcus xanthus act sequentially but non‐hierarchically

Starvation‐induced fruiting body formation in Myxococcus xanthus depends on intercellular signalling. A‐signal functions after 2 h of starvation and its synthesis depends on the asg genes. C‐signal functions after 6 h of starvation and is generated by proteolytic cleavage of a precursor by the protease PopC. Previous gene expression studies suggested that the A‐ and C‐signal lie on a hierarchical pathway. Here we explored the causal relationship between the A‐ and C‐signal. The asgA and asgB mutants have reduced popC expression, PopC accumulation and C‐signal accumulation. popC expression was shown not to depend on A‐signal but on the AsgA and AsgB proteins. Restored popC expression in the two mutants rescued PopC and C‐signal accumulation as well as C‐signalling and the developmental defects of the two mutants without restoring A‐signalling. Based on these results we suggest that A‐ and C‐signal do not lie on a hierarchical, dependent pathway. Instead the A‐ and C‐signal act sequentially and without a causal relationship suggesting that they are linked by a shared timing mechanism, which ensures the early and late onset of A‐signalling and C‐signalling, respectively, during starvation. This pathway topology represents a novel architecture for bacterial intercellular signalling systems involving more than one signal.     

Induction kinetics of heat emission before and after photoinhibition in cotyledons of Raphanus sativus

Heat emitted during non-radiative de-excitation was determined in vivo by the photoacoustic method. The dependence of the photoacoustic signal on the length of the pulses (modulation frequency) of the excitation light and the effect of continuous light, which saturates photosynthesis but does not directly contribute to the signal, are described. The induction kinetic of heat emission measured with intact leaves differed only slightly from the induction kinetic of fluorescence (Kautsky effect) detected in parallel. The photoacoustic signal at high modulation frequencies (279 Hz), which represents the signal of heat emission, and the photoacoustic signal at low modulation frequencies (17 Hz), interpreted as a signal of pulsed oxygen evolution superimposed on the heat emission, were measured with leaves before and after photoinhibition. It was demonstrated that after photoinhibition the decrease in fluorescence yield and in photosynthetic activity (here detected as photoacoustic signal at 17 Hz) are paralleled by an increase in the yield of non-radiative deexcitation (photoacoustic signal at 279 Hz). The increase of heat emission, which has been hypothized for photoinhibited leaves, could now be proved by measuring the induction kinetics of the photoacoustic signal.