bluuebunny/crossref_metadata_2025 huggingface dataset:
Exportin-5, a novel karyopherin, mediates nuclear export of double-stranded RNA binding proteins
Authors: Brownawell Amy M. , Macara Ian G.
Published: July 2002

We have identified a novel human karyopherin (Kap)β family member that is related to human Crm1 and the Saccharomyces cerevisiae protein, Msn5p/Kap142p. Like other known transport receptors, this Kap binds specifically to RanGTP, interacts with nucleoporins, and shuttles between the nuclear and cytoplasmic compartments. We report that interleukin enhancer binding factor (ILF)3, a double-stranded RNA binding protein, associates with this Kap in a RanGTP-dependent manner and that its double-stranded RNA binding domain (dsRBD) is the limiting sequence required for this interaction. Importantly, the Kap interacts with dsRBDs found in several other proteins and binding is blocked by double-stranded RNA. We find that the dsRBD of ILF3 functions as a novel nuclear export sequence (NES) in intact cells, and its ability to serve as an NES is dependent on the expression of the Kap. In digitonin-permeabilized cells, the Kap but not Crm1 stimulated nuclear export of ILF3. Based on the ability of this Kap to mediate the export of dsRNA binding proteins, we named the protein exportin-5. We propose that exportin-5 is not an RNA export factor but instead participates in the regulated translocation of dsRBD proteins to the cytoplasm where they interact with target mRNAs.
Genetic analysis of the role of G protein–coupled receptor signaling in electrotaxis
Authors: Zhao Min , Jin Tian , McCaig Colin D. , Forrester John V. , Devreotes Peter N.
Published: July 2002

Cells display chemotaxis and electrotaxis by migrating directionally in gradients of specific chemicals or electrical potential. Chemotaxis in Dictyostelium discoideum is mediated by G protein–coupled receptors. The unique Gβ is essential for all chemotactic responses, although different chemoattractants use different receptors and Gα subunits. Dictyostelium amoebae show striking electrotaxis in an applied direct current electric field. Perhaps electrotaxis and chemotaxis share similar signaling mechanisms? Null mutation of Gβ and cAMP receptor 1 and Gα2 did not abolish electrotaxis, although Gβ-null mutations showed suppressed electrotaxis. By contrast, G protein signaling plays an essential role in chemotaxis. G protein–coupled receptor signaling was monitored with PHcrac–green fluorescent protein, which translocates to inositol phospholipids at the leading edge of cells during chemotaxis. There was no intracellular gradient of this protein during electrotaxis. However, F-actin was polymerized at the leading edge of cells during electrotaxis. We conclude that reception and transduction of the electrotaxis signal are largely independent of G protein–coupled receptor signaling and that the pathways driving chemotaxis and electrotaxis intersect downstream of heterotrimeric G proteins to invoke cytoskeletal elements.
Secretory traffic in the eukaryotic parasite Toxoplasma gondii
Authors: Joiner Keith A. , Roos David S.
Published: July 2002

Name a single-celled eukaryote that boasts a small genome size, is easily cultivated in haploid form, for which a wide variety of molecular genetic tools are available, and that exhibits a simple, polarized secretory apparatus with a well-defined endoplasmic reticulum and Golgi that can serve as a model for understanding secretion. Got it? Now name a cell with all these attributes that contains at least a dozen distinct and morphologically well-defined intracellular organelles, including three distinct types of secretory vesicles and two endosymbiotic organelles. Not so sure anymore?
Regulation of the Interleukin (IL)-12R β2 Subunit Expression in Developing T Helper 1 (Th1) and Th2 Cells
Authors: Szabo Susanne J. , Dighe Anand S. , Gubler Ueli , Murphy Kenneth M.
Published: July 2002

The developmental commitment to a T helper 1 (Th1)- or Th2-type response can significantly influence host immunity to pathogens. Extinction of the IL-12 signaling pathway during early Th2 development provides a mechanism that allows stable phenotype commitment. In this report we demonstrate that extinction of IL-12 signaling in early Th2 cells results from a selective loss of IL-12 receptor (IL-12R) β2 subunit expression. To determine the basis for this selective loss, we examined IL-12R β2 subunit expression during Th cell development in response to T cell treatment with different cytokines. IL-12R β2 is not expressed by naive resting CD4+ T cells, but is induced upon antigen activation through the T cell receptor. Importantly, IL-4 and IFN-γ were found to significantly modify IL-12 receptor β2 expression after T cell activation. IL-4 inhibited IL-12R β2 expression leading to the loss of IL-12 signaling, providing an important point of regulation to promote commitment to the Th2 pathway. IFN-γ treatment of early developing Th2 cells maintained IL-12R β2 expression and restored the ability of these cells to functionally respond to IL-12, but did not directly inhibit IL-4 or induce IFN-γ production. Thus, IFN-γ may prevent early Th cells from premature commitment to the Th2 pathway. Controlling the expression of the IL-12R β2 subunit could be an important therapeutic target for the redirection of ongoing Th cell responses.
Peptide-independent Recognition by Alloreactive Cytotoxic T Lymphocytes (CTL)
Authors: Smith Pamela A. , Brunmark Anders , Jackson Michael R. , Potter Terry A.
Published: July 2002

We have isolated several H-2Kb–alloreactive cytotoxic T cell clones and analyzed their reactivity for several forms of H-2Kb. These cytotoxic T lymphocytes (CTL) were elicited by priming with a skin graft followed by in vitro stimulation using stimulator cells that express an H-2Kb molecule unable to bind CD8. In contrast to most alloreactive T cells, these CTL were able to recognize H-2Kb on the surface of the antigen processing defective cell lines RMA-S and T2. Furthermore, this reactivity was not increased by the addition of an extract containing peptides from C57BL/6 (H-2b) spleen cells, nor was the reactivity decreased by treating the target cells with acid to remove peptides bound to MHC molecules. The CTL were also capable of recognizing targets expressing the mutant H-2Kbm8 molecule. These findings suggested that the clones recognized determinants on H-2Kb that were independent of peptide. Further evidence for this hypothesis was provided by experiments in which H-2Kb produced in Drosophila melanogaster cells and immobilized on the surface of a tissue culture plate was able to stimulate hybridomas derived from these alloreactive T cells. Precursor frequency analysis demonstrated that skin graft priming, whether with skin expressing the wild-type or the mutant H-2Kb molecule, is a strong stimulus to elicit peptide-independent CTL. Moreover, reconstitution experiments demonstrated that the peptide-independent CTL clones were capable of mediating rapid and complete rejection of H-2–incompatible skin grafts. These findings provide evidence that not all allorecognition is peptide dependent.
Nonlymphocyte-Derived Tumor Necrosis Factor Is Required for Induction of Colitis in Recombination Activating Gene (Rag)2−/− Mice upon Transfer of Cd4+Cd45rbhi T Cells
Authors: Corazza Nadia , Eichenberger Susanne , Eugster Hans-Pietro , Mueller Christoph
Published: July 2002

In this study, we addressed the role of tumor necrosis factor (TNF)-α and lymphotoxin (LT)-α in the development of colitis and defined the cellular sources (T cells versus non-T cells) of TNF (TNF-α and LT-α) relevant to disease development. After adoptive transfer of TNF+/+ CD4+CD45RBhi splenocytes into TNF+/+ recombination activating gene (RAG)2−/− mice, the recipients develop massive inflammation of the large intestinal mucosa concurrent with massive weight loss. In contrast, clinical signs of disease are completely absent in TNF−/−RAG2−/− recipients of TNF−/− CD4+CD45RBhi T cells, although elevated numbers of interferon-γ–producing cells are present in the colonic mucosa. Surprisingly, upon transfer of TNF−/−CD4+CD45RBhi T cells into TNF+/+RAG2−/− recipients, colitis develops with kinetics similar to those upon transfer of TNF+/+CD4+CD45RBhi donor cells. In contrast, no clinical signs of colitis are observed in TNF−/−RAG2−/− recipients of TNF+/+CD4+CD45RBhi T cells. This protection from colitis is not a consequence of the absence of LT-α, as TNF-α−/−RAG2−/− recipients of TNF-α−/− CD4+CD45RBhi T cells are also protected from colitis induction. These results demonstrate the importance of TNF production by non-T cells of the colonic mucosa in the pathogenesis of colitis and provide direct evidence for a nonredundant role of TNF-α in this mouse model of colitis.
The Src Homology 2 Domain of Vav Is Required for Its Compartmentation to the Plasma Membrane and Activation of C-Jun Nh2-Terminal Kinase 1
Authors: Arudchandran Ramachandran , Brown Martin J. , Peirce Matthew J. , Song James S. , Zhang Juan , Siraganian Reuben P. , Blank Ulrich , Rivera Juan
Published: July 2002

Vav is a hematopoietic cell–specific guanine nucleotide exchange factor (GEF) whose activation is mediated by receptor engagement. The relationship of Vav localization to its function is presently unclear. We found that Vav redistributes to the plasma membrane in response to Fc∈ receptor I (Fc∈RI) engagement. The redistribution of Vav was mediated by its Src homology 2 (SH2) domain and required Syk activity. The Fc∈RI and Vav were found to colocalize and were recruited to glycosphingolipid-enriched microdomains (GEMs). The scaffold protein, linker for activation of T cells (LAT), and Rac1 (a target of Vav activity) were constitutively present in GEMs. Expression of an SH2 domain–containing COOH-terminal fragment of Vav inhibited Vav phosphorylation and movement to the GEMs but had no effect on the tyrosine phosphorylation of the adaptor protein, SLP-76 (SH2 domain–containing leukocyte protein of 76 kD), and LAT. However, assembly of the multiprotein complex containing these proteins was inhibited. In addition, Fc∈RI-dependent activation of c-Jun NH2-terminal kinase 1 (JNK1) was also inhibited. Thus, Vav localization to the plasma membrane is mediated by its SH2 domain and may serve to regulate downstream effectors like JNK1.
In Vivo Evidence for the Contribution of Human Histocompatibility Leukocyte Antigen (Hla)-Dq Molecules to the Development of Diabetes
Authors: Wen Li , Wong F. Susan , Tang Jie , Chen Ning-Yuan , Altieri Martha , David Chella , Flavell Richard , Sherwin Robert
Published: July 2002

Although DQA1*0301/DQB1*0302 is the human histocompatibility leukocyte antigen (HLA) class II gene most commonly associated with human type 1 diabetes, direct in vivo experimental evidence for its diabetogenic role is lacking. Therefore, we generated C57BL/6 transgenic mice that bear this molecule and do not express mouse major histocompatibility complex (MHC) class II molecules (DQ8+/mII−). They did not develop insulitis or spontaneous diabetes. However, when DQ8+/mII− mice were bred with C57BL/6 mice expressing costimulatory molecule B7-1 on β cells (which normally do not develop diabetes), 81% of the DQ8+/mII−/B7-1+ mice developed spontaneous diabetes. The diabetes was accompanied by severe insulitis composed of both T cells (CD4+ and CD8+) and B cells. T cells from the diabetic mice secreted large amounts of interferon γ, but not interleukin 4, in response to DQ8+ islets and the putative islet autoantigens, insulin and glutamic acid decarboxylase (GAD). Diabetes could also be adoptively transferred to irradiated nondiabetic DQ8+/mII−/B7-1+ mice. In striking contrast, none of the transgenic mice in which the diabetes protective allele (DQA1*0103/DQB1*0601, DQ6 for short) was substituted for mouse MHC class II molecules but remained for the expression of B7-1 on pancreatic β cells (DQ6+/mII−/B7-1+) developed diabetes. Only 7% of DQ−/mII−/B7-1+ mice developed diabetes at an older age, and none of the DQ−/mII+/B7-1+ mice or DQ8+/mII+/B7-1+ mice developed diabetes. In conclusion, substitution of HLA-DQA1*0301/DQB1*0302, but not HLA-DQA1*0103/DQB1*0601, for murine MHC class II provokes autoimmune diabetes in non–diabetes-prone rat insulin promoter (RIP).B7-1 C57BL/6 mice. Our data provide direct in vivo evidence for the diabetogenic effect of this human MHC class II molecule and a unique “humanized” animal model of spontaneous diabetes.
Multiple Genetic Alterations Cause Frequent and Heterogeneous Human Histocompatibility Leukocyte Antigen Class I Loss in Cervical Cancer
Authors: Koopman Louise A. , Corver Willem E. , van der Slik Arno R. , Giphart Marius J. , Fleuren Gert Jan
Published: July 2002

The nature and frequency of human histocompatibility leukocyte antigen (HLA) class I loss mechanisms in primary cancers are largely unknown. We used flow cytometry and molecular analyses to concurrently assess allele-specific HLA phenotypes and genotypes in subpopulations from 30 freshly isolated cervical tumor cell suspensions.

Tumor-associated HLA class I alterations were present in 90% of the lesions tested, comprising four altered pheno/genotype categories: (a) HLA-A or -B allelic loss (17%), mostly associated with gene mutations; (b) HLA haplotype loss, associated with loss of heterozygosity at 6p (50%). This category included cases with additional loss of a (third) HLA-A or -B allele due to mutation, as well as one case with an HLA class I–negative tumor cell subpopulation, caused by a β2-microglobulin gene mutation; (c) Total HLA class I antigen loss and retention of heterozygosity (ROH) at 6p (10%); and (d) B locus or HLA-A/B downregulation associated with ROH and/or allelic imbalance at 6p (10%). Normal HLA phenotypes and ROH at 6p were observed in 10% of the cases. One case could not be classified (3%).

Altered HLA class I antigen expression occurs in most cervical cancers, is diverse, and is mainly caused by genetic changes. Combined with widespread tumor heterogeneity, these changes have profound implications for natural immunity and T cell–based immunotherapy in cervical cancer.
Absence of γ-Interferon–inducible Lysosomal Thiol Reductase in Melanomas Disrupts T Cell Recognition of Select Immunodominant Epitopes
Authors: Haque M. Azizul , Li Ping , Jackson Sheila K. , Zarour Hassane M. , Hawes John W. , Phan Uyen T. , Maric Maja , Cresswell Peter , Blum Janice S.
Published: July 2002

Long-lasting tumor immunity requires functional mobilization of CD8+ and CD4+ T lymphocytes. CD4+ T cell activation is enhanced by presentation of shed tumor antigens by professional antigen-presenting cells (APCs), coupled with display of similar antigenic epitopes by major histocompatibility complex class II on malignant cells. APCs readily processed and presented several self-antigens, yet T cell responses to these proteins were absent or reduced in the context of class II+ melanomas. T cell recognition of select exogenous and endogenous epitopes was dependent on tumor cell expression of γ-interferon–inducible lysosomal thiol reductase (GILT). The absence of GILT in melanomas altered antigen processing and the hierarchy of immunodominant epitope presentation. Mass spectral analysis also revealed GILT's ability to reduce cysteinylated epitopes. Such disparities in the profile of antigenic epitopes displayed by tumors and bystander APCs may contribute to tumor cell survival in the face of immunological defenses.
Rapid Cytotoxic T Lymphocyte Activation Occurs in the Draining Lymph Nodes After Cutaneous Herpes Simplex Virus Infection as a Result of Early Antigen Presentation and Not the Presence of Virus
Authors: Mueller Scott N. , Jones Claerwen M. , Smith Chris M. , Heath William R. , Carbone Francis R.
Published: July 2002

Localized cutaneous herpes simplex virus type 1 (HSV-1) infection leads to arming and initial expansion of cytotoxic T lymphocytes (CTLs) in the draining popliteal lymph nodes (PLNs) followed by migration and further proliferation in the spleen. To accurately characterize the sequence of events involved in the activation and generation of anti-HSV CTLs, we used T cell receptor (TCR) transgenic mice specific for the immunodominant epitope from HSV glycoprotein B (gB498–505). We describe the detection of the initiation of antigen presentation in the draining lymph nodes by 4–6 h after infection with HSV-1. Analysis of CD69 up-regulation revealed activation of gB-specific CD8+ T cells by 6–8 h after infection. Furthermore, we show that T cell proliferation begins no sooner than 24 h after activation and is marked by the concurrent appearance of CTL activity in the PLNs. These events are not dependent on the presence of virus in the draining lymph nodes, and suggest a requirement for recruitment of professional antigen-presenting cells to the site of T cell activation. Consequently, we have defined the initiation of the CD8+ T cell–mediated response to cutaneous HSV-1 infection, demonstrating that the immune response to localized viral infection depends only on the appearance of cells presenting virus-derived antigen and commences with remarkable swiftness.
Fast and Slow Gating Relaxations in the Muscle Chloride Channel Clc-1
Authors: Accardi Alessio , Pusch Michael
Published: July 2002

Gating of the muscle chloride channel CLC-1 involves at least two processes evidenced by double-exponential current relaxations when stepping the voltage to negative values. However, there is little information about the gating of CLC-1 at positive voltages. Here, we analyzed macroscopic gating of CLC-1 over a large voltage range (from −160 to +200 mV). Activation was fast at positive voltages but could be easily followed using envelope protocols that employed a tail pulse to −140 mV after stepping the voltage to a certain test potential for increasing durations. Activation was biexponential, demonstrating the presence of two gating processes. Both time constants became exponentially faster at positive voltages. A similar voltage dependence was also seen for the fast gate time constant of CLC-0. The voltage dependence of the time constant of the fast process of CLC-1, τf, was steeper than that of the slow one, τs (apparent activation valences were zf ∼ −0.79 and zs ∼ −0.42) such that at +200 mV the two processes became kinetically distinct by almost two orders of magnitude (τf ∼ 16 μs, τs ∼ 1 ms). This voltage dependence is inconsistent with a previously published gating model for CLC-1 (Fahlke, C., A. Rosenbohm, N. Mitrovic, A.L. George, and R. Rüdel. 1996. Biophys. J. 71:695–706). The kinetic difference at 200 mV allowed us to separate the steady state open probabilities of the two processes assuming that they reflect two parallel (not necessarily independent) gates that have to be open simultaneously to allow ion conduction. Both open probabilities could be described by Boltzmann functions with gating valences around one and with nonzero “offsets” at negative voltages, indicating that the two “gates” never close completely. For comparison with single channel data and to correlate the two gating processes with the two gates of CLC-0, we characterized their voltage, pHint, and [Cl]ext dependence, and the dominant myotonia inducing mutation, I290M. Assuming a double-barreled structure of CLC-1, our results are consistent with the identification of the fast and slow gating processes with the single-pore and the common-pore gate, respectively.
On the set of points with a dense orbit
Authors: Bernardes Nilson
Published: July 2002

Under certain conditions on the topological space

X
X

we prove that for every continuous map

f
:
X
→
X

f : X \to X

the set of all points with a dense orbit has empty interior in

X
X

. This result implies a negative answer to two problems proposed by M. Barge and J. Kennedy.
Complex specializations of the reduced Gassner representation of the pure braid group
Authors: Abdulrahim Mohammad
Published: July 2002

We will give a necessary and sufficient condition for the specialization of the reduced Gassner representation

G

n

(
z
)
:

P

n

→
G

L

n
−
1

(

C

)

G_{n}(z): P_{n} \to GL_{n-1}(\mathbb {C})

to be irreducible. It will be shown that for

z
=
(

z

1

,
…
,

z

n

)
∈
(

C

∗

)

n

z=(z_{1},\ldots ,z_{n})\in (\mathbb {C}^{*})^{n}

,

G

n

(
z
)

G_{n}(z)

is irreducible if and only if

z

1

…

z

n

≠
1

z_{1}\ldots z_{n} \neq 1

.
Polynomial approximation with varying weights on compact sets of the complex plane
Authors: Pritsker Igor
Published: July 2002

For a compact set

E
E

with connected complement, let

A
(
E
)

A(E)

be the uniform algebra of functions continuous on

E
E

and analytic interior to

E
.

E.

We describe

A
(
E
,
W
)
,

A(E,W),

the set of uniform limits on

E
E

of sequences of the weighted polynomials

{

W
n

(
z
)

P
n

(
z
)

}

n
=
0

∞

,

\{W^n(z)P_n(z)\}_{n=0}^{\infty },

as

n
→
∞
,

n \to \infty ,

where

W
∈
A
(
E
)

W \in A(E)

is a nonvanishing weight on

E
.

E.

If

E
E

has empty interior, then

A
(
E
,
W
)

A(E,W)

is completely characterized by a zero set

Z
W

⊂
E
.

Z_W \subset E.

However, if

E
E

is a closure of Jordan domain, the description of

A
(
E
,
W
)

A(E,W)

also involves an inner function. In both cases, we exhibit the role of the support of a certain extremal measure, which is the solution of a weighted logarithmic energy problem, played in the descriptions of

A
(
E
,
W
)
.

A(E,W).
Sieving for rational points on hyperelliptic curves
Authors: Siksek Samir
Published: July 2002

We give a new and efficient method of sieving for rational points on hyperelliptic curves. This method is often successful in proving that a given hyperelliptic curve, suspected to have no rational points, does in fact have no rational points; we have often found this to be the case even when our curve has points over all localizations

Q

p

\mathbb {Q}_p

. We illustrate the practicality of the method with some examples of hyperelliptic curves of genus

1
1

.
Product integration for Volterra integral equations of the second kind with weakly singular kernels
Authors: Orsi Annamaria
Published: July 2002

We introduce a new numerical approach for solving Volterra integral equations of the second kind when the kernel contains a mild singularity. We give a convergence result. We also present numerical examples which show the performance and efficiency of our method.
Structure of a Hecke algebra quotient
Authors: Fan C.
Published: July 2002

Let

W
W

be a Coxeter group with Coxeter graph

γ
\gamma

. Let

H

\mathcal {H}

be the associated Hecke algebra. We define a certain ideal

I

\mathcal {I}

in

H

\mathcal {H}

and study the quotient algebra

H

¯

=

H

/

I

\bar {\mathcal {H}} = \mathcal {H}/\mathcal {I}

. We show that when

γ
\gamma

is one of the infinite series of graphs of type

E
E

, the quotient is semi-simple. We examine the cell structures of these algebras and construct their irreducible representations. We discuss the case where

γ
\gamma

is of type

B
B

,

F
F

, or

H
H

.
Tarski’s problem about the elementary theory of free groups has a positive solution
Authors: Kharlampovich Olga , Myasnikov Alexei
Published: July 2002

We prove that the elementary theories of all nonabelian free groups coincide and that the elementary theory of a free group is decidable. These results answer two old questions that were raised by A. Tarski around 1945.
Multiple Active States and Oligomerization of CCR5 Revealed by Functional Properties of Monoclonal Antibodies
Authors: Blanpain Cédric , Vanderwinden Jean-Marie , Cihak Josef , Wittamer Valérie , Le Poul Emmanuel , Issafras Hassan , Stangassinger Manfred , Vassart Gilbert , Marullo Stefano , Schlo∸ndorff Detlef , Parmentier Marc , Mack Matthias
Published: July 2002

CC-chemokine receptor 5 (CCR5) is the principal coreceptor for macrophage-tropic strains of human immunodeficiency virus type 1 (HIV-1). We have generated a set of anti-CCR5 monoclonal antibodies and characterized them in terms of epitope recognition, competition with chemokine binding, receptor activation and trafficking, and coreceptor activity. MC-4, MC-5, and MC-7 mapped to the amino-terminal domain, MC-1 to the second extracellular loop, and MC-6 to a conformational epitope covering multiple extracellular domains. MC-1 and MC-6 inhibited regulated on activation normal T cell expressed and secreted (RANTES), macrophage inflammatory polypeptide-1β, and Env binding, whereas MC-5 inhibited macrophage inflammatory polypeptide-1β and Env but not RANTES binding. MC-6 induced signaling in different functional assays, suggesting that this monoclonal antibody stabilizes an active conformation of CCR5. Flow cytometry and real-time confocal microscopy showed that MC-1 promoted strong CCR5 endocytosis. MC-1 but not its monovalent isoforms induced an increase in the transfer of energy between CCR5 molecules. Also, its monovalent isoforms bound efficiently, but did not internalize the receptor. In contrast, MC-4 did not prevent RANTES binding or subsequent signaling, but inhibited its ability to promote CCR5 internalization. These results suggest the existence of multiple active conformations of CCR5 and indicate that CCR5 oligomers are involved in an internalization process that is distinct from that induced by the receptor's agonists.
Interactions of Elongation Factor 1α with F-Actin and β-Actin mRNA: Implications for Anchoring mRNA in Cell Protrusions
Authors: Liu Gang , Grant Wayne M. , Persky Daniel , Latham Vaughan M. , Singer Robert H. , Condeelis John
Published: July 2002

The targeting of mRNA and local protein synthesis is important for the generation and maintenance of cell polarity. As part of the translational machinery as well as an actin/microtubule-binding protein, elongation factor 1α (EF1α) is a candidate linker between the protein translation apparatus and the cytoskeleton. We demonstrate in this work that EF1α colocalizes with β-actin mRNA and F-actin in protrusions of chicken embryo fibroblasts and binds directly to F-actin and β-actin mRNA simultaneously in vitro in actin cosedimentation and enzyme-linked immunosorbent assays. To investigate the role of EF1α in mRNA targeting, we mapped the two actin-binding sites on EF1α at high resolution and defined one site at the N-terminal 49 residues of domain I and the other at the C-terminal 54 residues of domain III. In vitro actin-binding assays and localization in vivo of recombinant full-length EF1α and its various truncates demonstrated that the C terminus of domain III was the dominant actin-binding site both in vitro and in vivo. We propose that the EF1α–F-actin complex is the scaffold that is important for β-actin mRNA anchoring. Disruption of this complex would lead to delocalization of the mRNA. This hypothesis was tested by using two dominant negative polypeptides: the actin-binding domain III of EF1α and the EF1α-binding site of yeast Bni1p, a protein that inhibits EF1α binding to F-actin and also is required for yeast mRNA localization. We demonstrate that either domain III of EF1α or the EF1α-binding site of Bni1p inhibits EF1α binding to β-actin mRNA in vitro and causes delocalization of β-actin mRNA in chicken embryo fibroblasts. Taken together, these results implicate EF1α in the anchoring of β-actin mRNA to the protrusion in crawling cells.
RNAi is antagonized by A→I hyper‐editing
Authors: Scadden A D J , Smith Christopher W J
Published: July 2002

RNA interference (RNAi) and adenosine to inosine conversion are both mechanisms that respond to double‐stranded RNA (dsRNA) and have been suggested to have antiviral roles. RNAi involves processing of dsRNA to short interfering RNAs (siRNAs), which subsequently mediate degradation of the cognate mRNAs. Deamination of adenosines changes the coding capacity of the RNA, as inosine is decoded as guanosine, and alters the structure because A–U base pairs are replaced by I·U wobble pairs. Here we show that RNAi is inhibited if the triggering dsRNA is first deaminated by ADAR2. Moreover, we show that production of siRNAs is progressively inhibited with increasing deamination and that this is sufficient to explain the inhibition of RNAi upon hyper‐editing of dsRNAs.
Wnt signals are transmitted through N‐terminally dephosphorylated β‐catenin
Authors: Staal Frank J T , van Noort Mascha , Strous Ger J , Clevers Hans C
Published: July 2002

β‐catenin mediates Wnt signaling by acting as the essential co‐activator for TCF transcription factors. Wnt signaling increases the half‐life and therefore the absolute level of β‐catenin in responding cells. The current model states that these changes in β‐catenin stability set the threshold for Wnt signaling. However, we find that pharmacological inhibition of proteasome activity by ALLN leads to accumulation of cytosolic β‐catenin but not to increased TCF‐mediated transcription. In addition, in temperature‐sensitive ubiquitylation mutant CHO cells inhibition of ubiquitylation increases β‐catenin levels, but does not induce transcriptional activation of TCF reporter genes. Using an antibody specific for β‐catenin dephosphorylated at residues Ser37 and Thr41, we show that Wnt signals specifically increase the levels of dephosphorylated β‐catenin, whereas ALLN does not. We conclude that changes in the phosphorylation status of the N‐terminus of β‐catenin that occur upon Wnt signaling independently affect the signaling properties and half‐life of β‐catenin. Hence, Wnt signals are transduced via N‐terminally dephosphorylated β‐catenin.
On imputing function to structure from the behavioural effects of brain lesions
Authors: Young Malcolm P. , Hilgetag Claus–C. , Scannell Jack W.
Published: July 2002

What is the link, if any, between the patterns of connections in the brain and the behavioural effects of localized brain lesions? We explored this question in four related ways. First, we investigated the distribution of activity decrements that followed simulated damage to elements of the thalamocortical network, using integrative mechanisms that have recently been used to successfully relate connection data to information on the spread of activation, and to account simultaneously for a variety of lesion effects. Second, we examined the consequences of the patterns of decrement seen in the simulation for each type of inference that has been employed to impute function to structure on the basis of the effects of brain lesions. Every variety of conventional inference, including double dissociation, readily misattributed function to structure. Third, we tried to derive a more reliable framework of inference for imputing function to structure, by clarifying concepts of function, and exploring a more formal framework, in which knowledge of connectivity is necessary but insufficient, based on concepts capable of mathematical specification. Fourth, we applied this framework to inferences about function relating to a simple network that reproduces intact, lesioned and paradoxically restored orientating behaviour. Lesion effects could be used to recover detailed and reliable information on which structures contributed to particular functions in this simple network. Finally, we explored how the effects of brain lesions and this formal approach could be used in conjunction with information from multiple neuroscience methodologies to develop a practical and reliable approach to inferring the functional roles of brain structures. of brain lesions.
Molecular genetics of xanthophyll–dependent photoprotection in green algae and plants
Authors: Baroli Irene , Niyogi Krishna K.
Published: July 2002

The involvement of excited and highly reactive intermediates in oxygenic photosynthesis inevitably results in the generation of reactive oxygen species. To protect the photosynthetic apparatus from oxidative damage, xanthophyll pigments are involved in the quenching of excited chlorophyll and reactive oxygen species, namely
1
Chl*,
3
Chl*, and
1
1O
2
*. Quenching of
1
Chl* results in harmless dissipation of excitation energy as heat and is measured as non–photochemical quenching (NPQ) of chlorophyll fluorescence. The multiple roles of xanthophylls in photoprotection are being addressed by characterizing mutants of
Chlamydomonas reinhardtii
and
Arabidopsis thaliana
. Analysis of
Arabidopsis
mutants that are defective in
1
Chl* quenching has shown that, in addition to specific xanthophylls, the psbS gene is necessary for NPQ. Double mutants of
Chlamydomonas
and
Arabidopsis
that are deficient in zeaxanthin, lutein and NPQ undergo photo–oxidative bleaching in high light. Extragenic suppressors of the
Chlamydomonas npq1 lor1
double mutant identify new mutations that restore varying levels of zeaxanthin accumulation and allow survival in high light.
Zanamivir: an alternative translation
Authors: Collier Joe
Published: July 2002

This paper offers an alternative view to that given elsewhere regarding the value of zanamivir as an agent for treating patients who develop influenza symptoms. The position taken here has developed as a result of an analysis of the data that was undertaken by the journal
Drug and Therapeutics Bulletin
.
Electric field distributions in a phased‐array applicator with 12 channels: Measurements and numerical simulations
Authors: Wust Peter , Beck Rudolf , Berger Jörn , Fähling Horst , Seebass Martin , Wlodarczyk Waldemar , Hoffmann Werner , Nadobny Jacek
Published: July 2002

In this paper we examine the SIGMA‐Eye hyperthermia applicator (BSD Medical Corp., Salt Lake City, Utah 84119) with respect to the control of electric field distributions. This applicator is equipped with 12 pairs of antennas fed by 12 amplifiers, allowing the individual adjustment of phase and power for each of them. Measurements were conducted using phantoms with well‐defined electrical properties. Specific electro‐optical sensors, capable of measuring both electric field amplitudes and phases, have been developed, and a system for data acquisition and analysis has been set up. In its initial state the applicator appeared not to be satisfactorily matched at 100 MHz for the phantom used, with return losses up to 20% in power. By tuner readjustments we achieved values below 5%. For various settings of the amplifiers' control parameters we measured field distributions, both in the phantom and in the surrounding water bolus. The experimental results were compared with numerical simulations based on finite difference and finite element methods. Measured and calculated electric fields exhibit deviations of 10% on average, allowing, in principle, a satisfactory prediction of fields by numerical simulations or as well by on‐line measurements at selected locations of the applicator at antenna proximity. However, to obtain this satisfactory agreement a modification of the control parameters in the calculations (phases and amplitudes in the feed points of the antennas) was necessary. The origin of these problems is mainly attributed to cross‐talk phenomena and other characteristics of the transforming network, which need to be scrutinized further for a full understanding.
Quantification of the effect of kVp on edge‐enhancement index in phase‐contrast radiography
Authors: Donnelly Edwin F. , Price Ronald R.
Published: July 2002

This study was performed to measure the dependence of edge‐enhancement in polychromatic phase‐contrast radiography on x‐ray tube operating voltage. Measurements of edge enhancement were made at tube voltages from 40 to 86 kVp using a tungsten anode x‐ray tube with a nominal focal spot size of 100 micrometers. A relatively weak attenuating, sharp edge consisting of a thin lucite sheet (3 mm) in air was imaged utilizing phase‐contrast radiography (PC‐R). PC‐R images were acquired at different radiographic techniques in which x‐ray tube voltage was varied from 40 to 86 kVp. The image receptor was a single emulsion x‐ray mammography cassette. Optical density profiles across the edge of the object were obtained using a film digitizer and edge‐enhancement indices were calculated. Increasing kVp resulted in a gradual decrease of the edge‐enhancement index. Even at the highest kVp (86), however, important edge‐enhancement effects were evident. While there is some degradation in the edge‐enhancement effect of phase‐contrast radiography at higher kVps, the decrease from 40 to 86 kVp is relatively small (11%). Our results suggest that further investigation into the role of phase‐contrast imaging at higher kVp values for the purpose of patient dose reduction while still realizing the advantage of phase‐contrast effects for improved soft‐tissue detectability is warranted.
An accurate measurement of g using falling balls
Authors: Wick Kurt , Ruddick Keith
Published: July 2002

We describe an experiment to determine the acceleration due to gravity, g, with an accuracy of about 1 part in 104. The experiment was designed to expose students to critical thinking in collecting, selecting, and analyzing data, and interpreting the results.
Sound absorption of cellular metals with semiopen cells
Authors: Lu Tian J. , Chen Feng , He Deping
Published: July 2002

A combined experimental and theoretical study is presented for the feasibility of using aluminum foams with semiopen cells for sound-absorption applications. The foams are processed via negative-pressure infiltration, using a preform consisting of water-soluble spherical particles. An analytical model is developed to quantify the dependence of pore connectivity on processing parameters, including infiltration pressure, particle size, wetting angle, and surface tension of molten alloy. Normal sound-absorption coefficient and static flow resistance are measured for samples having different porosity, pore size, and pore opening. A theory is developed for idealized semiopen metallic foams, with a regular hexagonal hollow prism having one circular aperture on each of its eight surfaces as the unit cell. The theory is built upon the acoustic impedance of the circular apertures (orifices) and cylindrical cavities due to viscous effects, and the principle of electroacoustic analogy. The predicted sound-absorption coefficients are compared with those measured. To help select processing parameters for producing semiopen metallic foams with desirable sound-absorbing properties, emphasis is placed on revealing the correlation between sound absorption and morphological parameters such as pore size, pore opening, and porosity.
Complex-image approximations to the half-space acousto-elastic Green’s function
Authors: Fawcett John A.
Published: July 2002

In this paper the complex-image method is used to efficiently approximate the half-space Green’s function for acousto-elastic propagation. This approximation is valid for both the near and far fields and hence should be very useful in scattering codes.
Functional magnetic resonance imaging measurements of sound-level encoding in the absence of background scanner noise
Authors: Hall Deborah A. , Haggard Mark P. , Summerfield A. Quentin , Akeroyd Michael A. , Palmer Alan R. , Bowtell Richard W.
Published: July 2002

Effects of sound level on auditory cortical activation are seen in neuroimaging data. However, factors such as the cortical response to the intense ambient scanner noise and to the bandwidth of the acoustic stimuli will both confound precise quantification and interpretation of such sound-level effects. The present study used temporally “sparse” imaging to reduce effects of scanner noise. To achieve control for stimulus bandwidth, three schemes were compared for sound-level matching across bandwidth: component level, root-mean-square power and loudness. The calculation of the loudness match was based on the model reported by Moore and Glasberg [Acta Acust. 82, 335–345 (1996)]. Ten normally hearing volunteers were scanned using functional magnetic resonance imaging (fMRI) while listening to a 300-Hz tone presented at six different sound levels between 66 and 91 dB SPL and a harmonic-complex tone (F0=186 Hz) presented at 65 and 85 dB SPL. This range of sound levels encompassed all three bases of sound-level matching. Activation in the superior temporal gyrus, induced by each of the eight tone conditions relative to a quiet baseline condition, was quantified as to extent and magnitude. Sound level had a small, but significant, effect on the extent of activation for the pure tone, but not for the harmonic-complex tone, while it had a significant effect on the response magnitude for both types of stimulus. Response magnitude increased linearly as a function of sound level for the full range of levels for the pure tone. The harmonic-complex tone produced greater activation than the pure tone, irrespective of the matching scheme for sound level, indicating that bandwidth had a greater effect on the pattern of auditory activation than sound level. Nevertheless, when the data were collapsed across stimulus class, extent and magnitude were significantly correlated with the loudness scale (measured in phons), but not with the intensity scale (measured in SPL). We therefore recommend the loudness formula as the most appropriate basis of matching sound level to control for loudness effects when cortical responses to other stimulus attributes, such as stimulus class, are the principal concern.
Development of panel loudspeaker system: Design, evaluation and enhancement
Authors: Bai Mingsian R. , Huang Talung
Published: July 2002

Panel speakers are investigated in terms of structural vibration and acoustic radiation. A panel speaker primarily consists of a panel and an inertia exciter. Contrary to conventional speakers, flexural resonance is encouraged such that the panel vibrates as randomly as possible. Simulation tools are developed to facilitate system integration of panel speakers. In particular, electro-mechanical analogy, finite element analysis, and fast Fourier transform are employed to predict panel vibration and the acoustic radiation. Design procedures are also summarized. In order to compare the panel speakers with the conventional speakers, experimental investigations were undertaken to evaluate frequency response, directional response, sensitivity, efficiency, and harmonic distortion of both speakers. The results revealed that the panel speakers suffered from a problem of sensitivity and efficiency. To alleviate the problem, a woofer using electronic compensation based on H2 model matching principle is utilized to supplement the bass response. As indicated in the result, significant improvement over the panel speaker alone was achieved by using the combined panel-woofer system.
Extraction of acoustic normal mode depth functions using vertical line array data
Authors: Neilsen Tracianne B. , Westwood Evan K.
Published: July 2002

A method for extracting the normal modes of acoustic propagation in the shallow ocean from sound recorded on a vertical line array (VLA) of hydrophones as a source travels nearby is presented. The mode extraction is accomplished by performing a singular value decomposition (SVD) of individual frequency components of the signal’s temporally averaged, spatial cross-spectral density matrix. The SVD produces a matrix containing a mutually orthogonal set of basis functions, which are proportional to the depth-dependent normal modes, and a diagonal matrix containing the singular values, which are proportional to the modal source excitations and mode eigenvalues. The conditions under which the method is expected to work are found to be (1) sufficient depth sampling of the propagating modes by the VLA receivers; (2) sufficient source–VLA range sampling, and (3) sufficient range interval traversed by the source. The mode extraction method is applied to data from the Area Characterization Test II, conducted in September 1993 in the Hudson Canyon Area off the New Jersey coast. Modes are successfully extracted from cw tones recorded while (1) the source traveled along a range-independent track with constant bathymetry and (2) the source traveled up-slope with gradual changes in bathymetry. In addition, modes are successfully extracted at multiple frequencies from ambient noise.
Analytical method for describing the paraxial region of finite amplitude sound beams
Authors: Hamilton Mark F. , Khokhlova Vera A. , Rudenko Oleg V.
Published: July 2002

A special analytical method, which combines the parabolic approximation (KZ equation) with nonlinear geometrical acoustics, is developed to model nonlinear and diffraction effects near the axis of a finite amplitude sound beam. The corresponding system of nonlinear equations describing waveform evolution is derived. For the case of an initially sinusoidal wave radiated by a Gaussian source, an analytic solution of the coupled equations is obtained for the paraxial region of the beam. The axial solution is expressed in both the time and frequency domains, and is analyzed in detail for both unfocused and focused beams in their preshock regions. Harmonic propagation curves are compared with finite difference solutions of the KZ equation, and good agreement is obtained for a variety of parameter values.
Visualization of acoustic particle interaction and agglomeration: Theory evaluation
Authors: Hoffmann Thomas L. , Koopmann Gary H.
Published: July 2002

In this paper experimentally observed trajectories of particles undergoing acoustically induced interaction and agglomeration processes are compared to and validated with numerically generated trajectories based on existing agglomeration theories. Models for orthokinetic, scattering, mutual radiation pressure, and hydrodynamic particle interaction are considered in the analysis. The characteristic features of the classical orthokinetic agglomeration hypothesis, such as collision processes and agglomerations due to the relative entrainment motion, are not observed in the digital images. The measured entrainment rates of the particles are found to be consistently lower than the theoretically predicted values. Some of the experiments reveal certain characteristics which may possibly be related to mutual scattering interaction. The study’s most significant discovery is the so-called tuning fork agglomeration [T. L. Hoffmann and G. H. Koopmann, J. Acoust. Soc. Am. 99, 2130–2141 (1996)]. It is shown that this phenomenon contradicts the theories for mutual scattering interaction and mutual radiation pressure interaction, but agrees with the acoustic wake effect model in its intrinsic feature of attraction between particles aligned along the acoustic axis. A model by Dianov et al. [Sov. Phys. Acoust. 13 (3), 314–319 (1968)] is used to describe this effect based on asymmetric flow fields around particles under Oseen flow conditions. It is concluded that this model is consistent with the general characteristics of the tuning fork agglomerations, but lacks certain refinements with respect to accurate quantification of the effect.
A unified framework for mode filtering and the maximum a posteriori mode filter
Authors: Buck John R. , Preisig James C. , Wage Kathleen E.
Published: July 2002

A unified framework is presented for examining the performance of linear mode filtering algorithms. Two common mode filters, samples of the mode shapes and the pseudo-inverse of the mode shapes, are presented in this framework as a tradeoff between sensitivity to other modes and sensitivity to white noise. The maximum a posteriori mode filter is presented as an alternative which gracefully transitions between these extremes, and attains the minimum mean squared error when the modes to be estimated are well modeled as samples of a Gaussian random process. Numerical simulations in both shallow and deep water environments confirm the analytically derived properties of these mode filters.