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At least 1,315 records · Page 73Linked to original sources
PubMed1987

A spatial template for the shape of tuning curves in the mammalian cochlea.

The shape of the tuning curve of primary auditory neurons of four mammals is characterized using a simple exponential model. The regression analysis formalizes a distinction between the characteristic frequency of a neuron and its "nominal" characteristic frequency in cases of temporary threshold loss in high-frequency neurons. Second, the model offers a stronger quality test for sharpness of tuning than the Q10dB since it takes into account the threshold of the neuron at its characteristic frequency and its "characteristic place" of origin along the cochlear partition. Third, the model reveals that the low-frequency side of the tip segment of the tuning curve is bounded by a constraint or template which is most simply expressed in spatial terms. The template describes the basal-side boundary of an "excitatory region" whose length along the cochlear partition is proportional to the square root of the sound pressure. Tuning curve variability arises because biological dependencies influence the basic template. A "spatial-filter" hypothesis is developed and its generality is discussed, particularly in regard to the case of the acoustic "fovea" of the horseshoe bat. Finally, the possibility is discussed that the template possesses a simple physiological correlate in the form of a spatially localized region marked by a "dc" shift of the mean position of the basilar membrane which sets the sensitivity of the tuning mechanism [E.L. LePage, J. Acoust. Soc. Am. 82, 139-154 (1987)].

Animals↗
PubMed2003

A bacterial cell-cycle regulatory network operating in time and space.

Transcriptional regulatory circuits provide only a fraction of the signaling pathways and regulatory mechanisms that control the bacterial cell cycle. The CtrA regulatory network, important in control of the Caulobacter cell cycle, illustrates the critical role of nontranscriptional pathways and temporally and spatially localized regulatory proteins. The system architecture of Caulobacter cell-cycle control involves top-down control of modular functions by a small number of master regulatory proteins with cross-module signaling coordinating the overall process. Modeling the cell cycle probably requires a top-down modeling approach and a hybrid control system modeling paradigm to treat its combined discrete and continuous characteristics.

Bacterial Physiological Phenomena↗
PubMed2004

Substructure in the circumstellar disk around the young star AU Microscopii.

Keck adaptive optics imaging with a physical resolution of 0.4 astronomical units (AU) resolves the inner (15 to 80 AU) disk of AU Microscopii (AU Mic, GJ 803, HD 197481), the nearest known scattered light disk to Earth. The inner disk is asymmetric and possesses a sharp change in structure at 35 AU. The disk also shows spatially localized enhancements and deficits at 25- to 40-AU separations. The overall morphology points to the influence of unseen larger bodies and resembles structures expected from recent planet formation. AU Mic is coeval with the archetypical debris disk system beta Pictoris, and the similarities between their two disks point to synchronous disk evolution. Multiple indications of substructure appear to be common in circumstellar disks at an age of approximately 12 million years.

Journal Article↗
PubMed1999

Role of the S. typhimurium actin-binding protein SipA in bacterial internalization.

Entry of the bacterium Salmonella typhimurium into host cells requires membrane ruffling and rearrangement of the actin cytoskeleton. Here, it is shown that the bacterial protein SipA plays a critical role in this process. SipA binds directly to actin, decreases its critical concentration, and inhibits depolymerization of actin filaments. These activities result in the spatial localization and more pronounced outward extension of the Salmonella-induced membrane ruffles, thereby facilitating bacterial uptake.

Actins↗
PubMed1999

Transcriptional coregulators in development.

Small differences in the levels of an extracellular signaling molecule can specify cell fate during development. Threshold responses are often determined at the level of transcription. Cell-specific and spatially localized patterns of gene expression depend on combinations of sequence-specific activators and repressors that bind to extensive cis-regulatory regions. Different mechanisms for integrating this complex regulatory information are discussed, particularly the role of coregulatory proteins, which are recruited to the DNA template by sequence-specific transcription factors. Recent studies suggest that a growing set of coactivators and corepressors mediate communication between diverse upstream regulatory proteins and the core RNA polymerase II transcription complex.

Animals↗
PubMed1999

Microfabrication inside capillaries using multiphase laminar flow patterning

The reaction of species in solutions flowing laminarly (without turbulent mixing) inside capillaries was used as the basis for a broadly applicable method of microfabrication. In this method, patterning occurs as a result of transport of reactive species to interfaces within the capillary by laminar flow. A wide range of chemistries can be used to generate structures with feature sizes of less than 5 micrometers and with spatial localization to within 5 micrometers. The method is applicable to the patterning of metals, organic polymers, inorganic crystals, and ceramics on the inner walls of preformed capillaries, using both additive and subtractive processes.

Journal Article↗
PubMed1987

Intracellular topography of rhodopsin bleaching.

In a vertebrate eye, the photoreceptor cells are aligned so that most of the light passes through them lengthwise. At the light-transducing outer segment region of the photoreceptor, photons are absorbed in a time-varying, spatially dependent fashion. Because the transduction event is spatially localized around the site of photon absorption, the spatiotemporal patterns of light absorption in outer segments are an important receiver input characteristic. This aspect of receptor biophysics has now been measured; the results were consistent with a theoretical model proposed for bleaching of a pigment in an unstirred layer.

Animals↗
PubMed1985

Noninvasive study of high-energy phosphate metabolism in human heart by depth-resolved 31P NMR spectroscopy.

Phosphorus-31 nuclear magnetic resonance (NMR) spectra showing the relative concentrations of high-energy phosphate metabolites have been recorded noninvasively from the human heart in vivo. Spectral data were spatially localized by combining a pulsed magnetic field gradient with surface NMR excitation-detection coils. The location of the selected spectral region was determined by conventional proton NMR imaging immediately before examination by phosphorus-31 NMR spectroscopy.

Adenine Nucleotides↗
PubMed1993

A traveling-wave amplifier model of the cochlea.

A two-mode model of the cochlea that uses active intermode feedback has been developed that quantitatively accounts for the motion of the basilar membrane in response to single tones and qualitatively accounts for cochlear emission phenomena. In contrast to existing single-mode models, this model amplifies the mechanical traveling wave in spatially localized cochlear regions where an approximate match occurs between the traveling-wave velocities of each of the two traveling-wave lines or modes.

Acoustic Stimulation↗
PubMed1977

A phantom-motion aftereffect.

Motion aftereffects, typically found to result only from localized retinal stimulation, were obtained within regions of the visual field that had not been stimulated by moving contours. "Phantom" stripes are seen moving through a physically homogeneous (empty) region of the visual field when vertical stripes move above and below that region. Immediately afterward, stationary stripes in the previously empty region appear to move in the opposite direction. This phantom-motion aftereffect provides a novel instance of the way global structure affects processes that have been assumed to be influenced only by simpler local spatial and temporal variables.

Afterimage↗
PubMed2002

KSR--a regulator and scaffold protein of the MAPK pathway.

Raabe and Rapp discuss how the scaffolding proteins may spatially localize mitogen-activated protein kinase (MAPK) signaling cassettes to allow signaling specificity. They focus on the adaptor kinase suppressor of Ras (KSR) and describe how the interactions between KSR and other proteins and the subcellular localization of KSR are regulated by phosphorylation.

Animals↗
PubMed2004

Flirting in little space: the ER/mitochondria Ca2+ liaison.

Mitochondria have long been known to accumulate Ca2+; the apparent inconsistency between the low affinity of mitochondrial Ca2+ uptake mechanisms, the low concentration of global Ca2+ signals observed in cytoplasm, and the efficiency in intact cells of mitochondrial Ca2+ uptake led to the formulation of the "hotspot hypothesis." This hypothesis proposes that mitochondria preferentially accumulate Ca2+ at microdomains of elevated Ca2+ concentration ([Ca2+]) that exist near endoplasmic reticulum (ER) Ca2+ release sites and other Ca2+ channels. Physiological Ca2+ signals may affect mitochondrial function--both by stimulating key metabolic enzymes and, under some conditions, by promoting apoptosis. Mitochondria in turn may affect both Ca2+ release from the ER and capacitative Ca2+ entry across the plasma membrane, thereby shaping the size and duration of the intracellular Ca2+ signal. Interactions between mitochondria and the ER are critically dependent on the spatial localization of mitochondria within the cell. The molecular mechanisms that define the organization of mitochondria with regard to the ER and other Ca2+ sources, and the extent to which mitochondrial function varies among different cell types, are open questions whose answers remain to be determined.

Animals↗
PubMed2006

Deciphering the underlying mechanism of specification and differentiation: the sea urchin gene regulatory network.

The regulatory genome functions as a vast information processor through development. It processes the initial conditions that are set by asymmetric distributions of cellular components in the egg and translates them into the onset of spatially localized specification states. It regulates the timely differential activation of signaling molecules and transcription factors that divide the emerging domains into subdomains. It also governs the activation of groups of differentiation genes, the genes that encode, at the protein level, the functional and the structural properties of a cell type. The sea urchin endomesoderm gene regulatory network provides a window into the different levels of the regulatory apparatus. It demonstrates how the static physical genomic components define functional connections between the various regulatory genes that act together to conduct the dynamical developmental program.

Animals↗
PubMed2002

Identification of novel Plasmodium gallinaceum zygote- and ookinete-expressed proteins as targets for blocking malaria transmission.

The development of transmission-blocking vaccines is one approach to malaria control. To identify novel Plasmodium zygote- and ookinete-secreted proteins as targets of blocking malaria transmission, monoclonal antibodies (MAbs) were produced against parasite-secreted proteins found in Plasmodium gallinaceum ookinete culture supernatants. Four MAbs-1A6, 2A5, 2B5, and 4B6-were identified that bound to P. gallinaceum zygotes and ookinetes in diverse patterns in terms of spatial localization on parasites, time course of antigen expression, and Western immunoblot patterns. MAbs 2A5 and 4B6 recognized more than one protein band as detected by Western immunoblot of P. gallinaceum ookinete supernatants. Beginning at 0 h postfertilization, MAb 2A5 recognized a diverse set of antigens; at 10 h postfertilization, MAb 4B6 recognized several antigens as well. MAb 1A6 recognized a single approximately 17-kDa protein, and 2B5 recognized a single approximately 32-kDa protein at 15 h postfertilization. In membrane feeding assays to assess the effect of these MAbs on P. gallinaceum infectivity for Aedes aegypti mosquitoes, the addition of MAbs 1A6 and 2B5 to infectious blood meals significantly inhibited oocyst development in the mosquito midgut. In contrast, MAb 2A5 seemed to enhance infectivity. These results demonstrate that Plasmodium ookinetes secrete proteins (in addition to previously characterized chitinases) that may be targets for blocking malaria transmission. Future investigation of ookinete-secreted neutralization-sensitive molecules should provide valuable insight into mechanisms by which ookinetes exit the blood meal, penetrate and transverse the peritrophic matrix, and invade the mosquito midgut epithelium.

Aedes↗
PubMed1989

Differential activity of a transposable element in Escherichia coli colonies.

In Escherichia coli colonies, patterns of differential gene expression can be visualized by the use of Mu d(lac) fusion elements. Here we report that patterned beta-galactosidase expression in colonies of strain MS1534 resulted from a novel mechanism, spatially localized replication of the Mu dII1681 element causing lacZ transposition to active expression sites. Mu dII1681 replication did not occur constitutively with a fixed probability but was dependent on the growth history of the bacterial population. The bacteria in which Mu dII1681 replication and lacZ transposition had occurred could no longer form colonies. These results lead to several interesting conclusions about cellular differentiation during colony development and the influence of bacterial growth history on gene expression and genetic change.

Blotting, Southern↗
PubMed1996

Multiple roles of the novel protein tyrosine phosphatase PTP3 during Dictyostelium growth and development.

PTP3, the third nonreceptor protein tyrosine phosphatase identified in Dictyostelium discoideum, has a single catalytic protein tyrosine phosphatase domain. Recombinant PTP3 exhibited phosphatase activity that was inhibited by vanadate. PTP3 is expressed at a moderate level during growth. The level of transcripts increased between growth and 8 h of development and declined thereafter. Expression of lacZ under the control of the PTP3 promoter indicated a spatial localization of PTP3 in the anterior-like and prestalk cell types. There are two copies of the PTP3 gene in this haploid organism. Disruption of one copy led to a slow-growth phenotype. We were unable to obtain a strain with disruptions in both PTP3 genes. Overexpression of wild-type PTP3 led to slower growth rates and the formation of large aggregation streams. These streams split into smaller aggregates, many of which then arrested in development. Overexpression of a catalytically inactive mutation (Cys to Ser) had no effect on growth rate; however, this strain also formed large aggregation streams that later split up into large and small mound structures and became fruiting bodies of various sizes. Antiphosphotyrosine Western blot (immunoblot) analysis of total cell proteins showed that the pattern of protein tyrosine phosphorylation was specifically altered in PTP3 mutants. Addition of growth medium to starving cells and a subsequent replacement with nonnutrient buffer led to reciprocal changes in the pattern of several phosphotyrosine proteins, including a protein of approximately 130 kDa. Analysis of strains overexpressing active or inactive PTP3 suggested that p130 is a potential substrate of PTP3. A transient posttranslational phosphorylation of PTP3 further supported the role of PTP3 in these processes. The data obtained strongly suggest new regulatory functions for PTP3 that are distinct from those described earlier for D. discoideum PTP1 and PTP2.

Amino Acid Sequence↗
PubMed2005

Spatial distribution and function of sterol regulatory element-binding protein 1a and 2 homo- and heterodimers by in vivo two-photon imaging and spectroscopy fluorescence resonance energy transfer.

Sterol regulatory element-binding proteins (SREBPs) are a subfamily of basic helix-loop-helix-leucine zipper proteins that regulate lipid metabolism. We show novel evidence of the in vivo occurrence and subnuclear spatial localization of both exogenously expressed SREBP-1a and -2 homodimers and heterodimers obtained by two-photon imaging and spectroscopy fluorescence resonance energy transfer. SREBP-1a homodimers localize diffusely in the nucleus, whereas SREBP-2 homodimers and the SREBP-1a/SREBP-2 heterodimer localize predominantly to nuclear speckles or foci, with some cells showing a diffuse pattern. We also used tethered SREBP dimers to demonstrate that both homo- and heterodimeric SREBPs activate transcription in vivo. Ultrastructural analysis revealed that the punctate foci containing SREBP-2 are electron-dense nuclear bodies, similar or identical to structures containing the promyelocyte (PML) protein. Immunofluorescence studies suggest that a dynamic interplay exists between PML, as well as another component of the PML-containing nuclear body, SUMO-1, and SREBP-2 within these nuclear structures. These findings provide new insight into the overall process of transcriptional activation mediated by the SREBP family.

CCAAT-Enhancer-Binding Proteins↗
PubMed1986

5'-flanking sequence required for regulated expression of a muscle-specific Drosophila melanogaster actin gene.

We have functionally tested derivatives of a muscle-specific Drosophila melanogaster actin gene in which 5'-flanking sequences have been deleted or rearranged. From our results we conclude that approximately 1,000 nucleotides of 5'-flanking sequence are required for wild-type levels of mRNA accumulation during flight muscle development. Derivatives having 875 or 865 nucleotides of upstream sequence could be expressed normally, but were prone to influence by flanking foreign DNA sequences. Derivatives retaining 600 or fewer nucleotides of flanking DNA did not direct detectable levels of mRNA accumulation. The sequence residing between -919 and -640 could be inverted and yet retain normal function. Deletion of this sequence reduced mRNA accumulation markedly, but did not affect its spatial localization, suggesting that elements which confer tissue specificity reside close to the point of transcription initiation.

Actins↗