bluuebunny/crossref_metadata_2025 huggingface dataset:
Myostatin negatively regulates satellite cell activation and self-renewal
Authors: McCroskery Seumas , Thomas Mark , Maxwell Linda , Sharma Mridula , Kambadur Ravi
Published: September 2003

Satellite cells are quiescent muscle stem cells that promote postnatal muscle growth and repair. Here we show that myostatin, a TGF-β member, signals satellite cell quiescence and also negatively regulates satellite cell self-renewal. BrdU labeling in vivo revealed that, among the Myostatin-deficient satellite cells, higher numbers of satellite cells are activated as compared with wild type. In contrast, addition of Myostatin to myofiber explant cultures inhibits satellite cell activation. Cell cycle analysis confirms that Myostatin up-regulated p21, a Cdk inhibitor, and decreased the levels and activity of Cdk2 protein in satellite cells. Hence, Myostatin negatively regulates the G1 to S progression and thus maintains the quiescent status of satellite cells. Immunohistochemical analysis with CD34 antibodies indicates that there is an increased number of satellite cells per unit length of freshly isolated Mstn−/− muscle fibers. Determination of proliferation rate suggests that this elevation in satellite cell number could be due to increased self-renewal and delayed expression of the differentiation gene (myogenin) in Mstn−/− adult myoblasts. Taken together, these results suggest that Myostatin is a potent negative regulator of satellite cell activation and thus signals the quiescence of satellite cells.
Direct signaling by the BMP type II receptor via the cytoskeletal regulator LIMK1
Authors: Foletta Victoria C. , Lim Mei Ann , Soosairajah Juliana , Kelly April P. , Stanley Edouard G. , Shannon Mark , He Wei , Das Supratik , Massagué Joan , Bernard Ora
Published: September 2003

Bone morphogenetic proteins (BMPs) regulate multiple cellular processes, including cell differentiation and migration. Their signals are transduced by the kinase receptors BMPR-I and BMPR-II, leading to Smad transcription factor activation via BMPR-I. LIM kinase (LIMK) 1 is a key regulator of actin dynamics as it phosphorylates and inactivates cofilin, an actin depolymerizing factor. During a search for LIMK1-interacting proteins, we isolated clones encompassing the tail region of BMPR-II. Although the BMPR-II tail is not involved in BMP signaling via Smad proteins, mutations truncating this domain are present in patients with primary pulmonary hypertension (PPH). Further analysis revealed that the interaction between LIMK1 and BMPR-II inhibited LIMK1's ability to phosphorylate cofilin, which could then be alleviated by addition of BMP4. A BMPR-II mutant containing the smallest COOH-terminal truncation described in PPH failed to bind or inhibit LIMK1. This study identifies the first function of the BMPR-II tail domain and suggests that the deregulation of actin dynamics may contribute to the etiology of PPH.
The roles of microtubule-based motor proteins in mitosis
Authors: Goshima Gohta , Vale Ronald D.
Published: September 2003

Kinesins and dyneins play important roles during cell division. Using RNA interference (RNAi) to deplete individual (or combinations of) motors followed by immunofluorescence and time-lapse microscopy, we have examined the mitotic functions of cytoplasmic dynein and all 25 kinesins in Drosophila S2 cells. We show that four kinesins are involved in bipolar spindle assembly, four kinesins are involved in metaphase chromosome alignment, dynein plays a role in the metaphase-to-anaphase transition, and one kinesin is needed for cytokinesis. Functional redundancy and alternative pathways for completing mitosis were observed for many single RNAi knockdowns, and failure to complete mitosis was observed for only three kinesins. As an example, inhibition of two microtubule-depolymerizing kinesins initially produced monopolar spindles with abnormally long microtubules, but cells eventually formed bipolar spindles by an acentrosomal pole-focusing mechanism. From our phenotypic data, we construct a model for the distinct roles of molecular motors during mitosis in a single metazoan cell type.
Molecular requirements for actin-based lamella formation in Drosophila S2 cells
Authors: Rogers Stephen L. , Wiedemann Ursula , Stuurman Nico , Vale Ronald D.
Published: September 2003

Cell migration occurs through the protrusion of the actin-enriched lamella. Here, we investigated the effects of RNAi depletion of ∼90 proteins implicated in actin function on lamella formation in Drosophila S2 cells. Similar to in vitro reconstitution studies of actin-based Listeria movement, we find that lamellae formation requires a relatively small set of proteins that participate in actin nucleation (Arp2/3 and SCAR), barbed end capping (capping protein), filament depolymerization (cofilin and Aip1), and actin monomer binding (profilin and cyclase-associated protein). Lamellae are initiated by parallel and partially redundant signaling pathways involving Rac GTPases and the adaptor protein Nck, which stimulate SCAR, an Arp2/3 activator. We also show that RNAi of three proteins (kette, Abi, and Sra-1) known to copurify with and inhibit SCAR in vitro leads to SCAR degradation, revealing a novel function of this protein complex in SCAR stability. Our results have identified an essential set of proteins involved in actin dynamics during lamella formation in Drosophila S2 cells.
Real-time single cell analysis of Smac/DIABLO release during apoptosis
Authors: Rehm Markus , Düßmann Heiko , Prehn Jochen H.M.
Published: September 2003

We examined the temporal and causal relationship between Smac/DIABLO release, cytochrome c (cyt-c) release, and caspase activation at the single cell level during apoptosis. Cells treated with the broad-spectrum caspase inhibitor z-VAD-fmk, caspase-3 (Casp-3)–deficient MCF-7 cells, as well as Bax-deficient DU-145 cells released Smac/DIABLO and cyt-c in response to proapoptotic agents. Real-time confocal imaging of MCF-7 cells stably expressing Smac/DIABLO-yellow fluorescent protein (YFP) revealed that the average duration of Smac/DIABLO-YFP release was greater than that of cyt-c-green fluorescent protein (GFP). However, there was no significant difference in the time to the onset of release, and both cyt-c-GFP and Smac/DIABLO-YFP release coincided with mitochondrial membrane potential depolarization. We also observed no significant differences in the Smac/DIABLO-YFP release kinetics when z-VAD-fmk–sensitive caspases were inhibited or Casp-3 was reintroduced. Simultaneous measurement of DEVDase activation and Smac/DIABLO-YFP release demonstrated that DEVDase activation occurred within 10 min of release, even in the absence of Casp-3.
Nup358 integrates nuclear envelope breakdown with kinetochore assembly
Authors: Salina Davide , Enarson Paul , Rattner J.B. , Burke Brian
Published: September 2003

Nuclear envelope breakdown (NEBD) and release of condensed chromosomes into the cytoplasm are key events in the early stages of mitosis in metazoans. NEBD involves the disassembly of all major structural elements of the nuclear envelope, including nuclear pore complexes (NPCs), and the dispersal of nuclear membrane components. The breakdown process is facilitated by microtubules of the mitotic spindle. After NEBD, engagement of spindle microtubules with chromosome-associated kinetochores leads to chromatid segregation. Several NPC subunits relocate to kinetochores after NEBD. siRNA-mediated depletion of one of these proteins, Nup358, reveals that it is essential for kinetochore function. In the absence of Nup358, chromosome congression and segregation are severely perturbed. At the same time, the assembly of other kinetochore components is strongly inhibited, leading to aberrant kinetochore structure. The implication is that Nup358 plays an essential role in integrating NEBD with kinetochore maturation and function. Mitotic arrest associated with Nup358 depletion further suggests that mitotic checkpoint complexes may remain active at nonkinetochore sites.
Juxtaparanodal clustering of Shaker-like K+ channels in myelinated axons depends on Caspr2 and TAG-1
Authors: Poliak Sebastian , Salomon Daniela , Elhanany Hadas , Sabanay Helena , Kiernan Brent , Pevny Larysa , Stewart Colin L. , Xu Xiaorong , Chiu Shing-Yan , Shrager Peter , Furley Andrew J.W. , Peles Elior
Published: September 2003

In myelinated axons, K+ channels are concealed under the myelin sheath in the juxtaparanodal region, where they are associated with Caspr2, a member of the neurexin superfamily. Deletion of Caspr2 in mice by gene targeting revealed that it is required to maintain K+ channels at this location. Furthermore, we show that the localization of Caspr2 and clustering of K+ channels at the juxtaparanodal region depends on the presence of TAG-1, an immunoglobulin-like cell adhesion molecule that binds Caspr2. These results demonstrate that Caspr2 and TAG-1 form a scaffold that is necessary to maintain K+ channels at the juxtaparanodal region, suggesting that axon–glia interactions mediated by these proteins allow myelinating glial cells to organize ion channels in the underlying axonal membrane.
Association of TAG-1 with Caspr2 is essential for the molecular organization of juxtaparanodal regions of myelinated fibers
Authors: Traka Maria , Goutebroze Laurence , Denisenko Natalia , Bessa Maria , Nifli Artemisia , Havaki Sophia , Iwakura Yoichiro , Fukamauchi Fumihiko , Watanabe Kazutada , Soliven Betty , Girault Jean-Antoine , Karagogeos Domna
Published: September 2003

Myelination results in a highly segregated distribution of axonal membrane proteins at nodes of Ranvier. Here, we show the role in this process of TAG-1, a glycosyl-phosphatidyl-inositol–anchored cell adhesion molecule. In the absence of TAG-1, axonal Caspr2 did not accumulate at juxtaparanodes, and the normal enrichment of shaker-type K+ channels in these regions was severely disrupted, in the central and peripheral nervous systems. In contrast, the localization of protein 4.1B, an axoplasmic partner of Caspr2, was only moderately altered. TAG-1, which is expressed in both neurons and glia, was able to associate in cis with Caspr2 and in trans with itself. Thus, a tripartite intercellular protein complex, comprised of these two proteins, appears critical for axo–glial contacts at juxtaparanodes. This complex is analogous to that described previously at paranodes, suggesting that similar molecules are crucial for different types of axo–glial interactions.
Restoration of CD28 Expression in CD28− CD8+ Memory Effector T Cells Reconstitutes Antigen-induced IL-2 Production
Authors: Topp Max S. , Riddell Stanley R. , Akatsuka Yoshiki , Jensen Michael C. , Blattman Joseph N. , Greenberg Philip D.
Published: September 2003

The control of many persistent viral infections by Ag-specific cytolytic CD8+ T cells requires a concurrent virus-specific CD4+ Th cell response. This reflects in part a requirement of activated effector CD8+ T cells for paracrine IL-2 production as a growth and survival factor. In human CMV and HIV infection, the majority of differentiated virus-specific CD8+ T cells notably lose the ability to produce IL-2 but also lose expression of CD28, a costimulatory molecule. Analysis of the fraction of memory CD8+ T cells that continue to express CD28 revealed these cells retain the ability to produce IL-2. Therefore, we examined if IL-2 production by CD28− CD8+ T cells could be restored by introduction of a constitutively expressed CD28 gene. Expression of CD28 in CD28− CD8+ CMV- and HIV-specific CD8+ T cells reconstituted the ability to produce IL-2, which could sustain an autocrine proliferative response after Ag recognition. These results suggest that the loss of CD28 expression during differentiation of memory/effector CD8+ T cells represents a decisive step in establishing regulation of responding CD8+ T cells, increasing the dependence on CD4+ Th for proliferation after target recognition, and has implications for the treatment of viral disease with adoptively transferred CD8+ T cells.
A New Rodent Model to Assess Blood Stage Immunity to the Plasmodium falciparum Antigen Merozoite Surface Protein 119 Reveals a Protective Role for Invasion Inhibitory Antibodies
Authors: de Koning-Ward Tania F. , O'Donnell Rebecca A. , Drew Damien R. , Thomson Russell , Speed Terence P. , Crabb Brendan S.
Published: September 2003

Antibodies capable of inhibiting the invasion of Plasmodium merozoites into erythrocytes are present in individuals that are clinically immune to the malaria parasite. Those targeting the 19-kD COOH-terminal domain of the major merozoite surface protein (MSP)-119 are a major component of this inhibitory activity. However, it has been difficult to assess the overall relevance of such antibodies to antiparasite immunity. Here we use an allelic replacement approach to generate a rodent malaria parasite (Plasmodium berghei) that expresses a human malaria (Plasmodium falciparum) form of MSP-119. We show that mice made semi-immune to this parasite line generate high levels of merozoite inhibitory antibodies that are specific for P. falciparum MSP-119. Importantly, protection from homologous blood stage challenge in these mice correlated with levels of P. falciparum MSP-119–specific inhibitory antibodies, but not with titres of total MSP-119–specific immunoglobulins. We conclude that merozoite inhibitory antibodies generated in response to infection can play a significant role in suppressing parasitemia in vivo. This study provides a strong impetus for the development of blood stage vaccines designed to generate invasion inhibitory antibodies and offers a new animal model to trial P. falciparum MSP-119 vaccines.
Matrilysin-dependent Elastolysis by Human Macrophages
Authors: Filippov Sergey , Caras Ingrid , Murray Richard , Matrisian Lynn M. , Chapman Harold A. , Shapiro Steven , Weiss Stephen J.
Published: September 2003

Human macrophages found in juxtaposition to fragmented elastin in vivo express the elastolytic matrix metalloproteinases (MMPs) progelatinase B, prometalloelastase, and promatrilysin. Though MMPs can degrade a range of extracellular matrix components, increasing evidence suggests that preferred targets in vivo include nonmatrix substrates such as chemokines and growth factors. Hence, the means by which MMPs participate in elastin turnover remain undefined as does the identity of the elastolysins. Herein, human macrophage cultures have been established that express a complement of elastolytic proteinases similar, if not identical, to that found in vivo. Under plasminogen-free conditions, macrophages preferentially use metalloelastase to mediate elastolysis via a process that deposits active enzyme on elastin surfaces. By contrast, in the presence of plasminogen, human macrophages up-regulate proteolysis 10-fold by processing promatrilysin to an active elastolysin via a urokinase-type plasminogen activator-dependent pathway. Matrilysin-deficient human macrophages fail to mediate an elastolytic response despite the continued expression of gelatinase B and metalloelastase. Thus, acting in concert with cosecreted cysteine proteinases whose activities are constrained to sites of macrophage-elastin contact (Punturieri, A., S. Filippov, E. Allen, I. Caras, R. Murray, V. Reddy, and S.J. Weiss. 2000. J. Exp. Med. 192:789–799), matrilysin confers macrophages with their most potent MMP-dependent elastolytic system.
Selective Generation of Gut Tropic T Cells in Gut-associated Lymphoid Tissue (GALT)
Authors: Johansson-Lindbom Bengt , Svensson Marcus , Wurbel Marc-André , Malissen Bernard , Márquez Gabriel , Agace William
Published: September 2003

In the current study, we address the underlying mechanism for the selective generation of gut-homing T cells in the gut-associated lymphoid tissues (GALT). We demonstrate that DCs in the GALT are unique in their capacity to establish T cell gut tropism but in vivo only confer this property to T cells in the presence of DC maturational stimuli, including toll-like receptor-dependent and -independent adjuvants. Thus, DCs from mesenteric LNs (MLNs), but not from spleen, supported expression of the chemokine receptor CCR9 and integrin α4β7 by activated CD8+ T cells. While DCs were also required for an efficient down-regulation of CD62L, this function was not restricted to MLN DCs. In an adoptive CD8+ T cell transfer model, antigen-specific T cells entering the small intestinal epithelium were homogeneously CCR9+α4β7+CD62Llow, and this phenotype was only generated in GALT and in the presence of adjuvant. Consistent with the CCR9+ phenotype of the gut-homing T cells, CCR9 was found to play a critical role in the localization of T cells to the small intestinal epithelium. Together, these results demonstrate that GALT DCs and T cell expression of CCR9 play critical and integrated roles during T cell homing to the gut.
Exactly 𝑘-to-1 maps and hereditarily indecomposable tree-like continua
Authors: Gonzalez Thomas
Published: September 2003

In 1947, W.H. Gottschalk proved that no dendrite is the continuous, exactly

k
k

-to-1 image of any continuum if

k
≥
2

k \geq 2

. Since that time, no other class of continua has been shown to have this same property. It is shown that no hereditarily indecomposable tree-like continuum is the continuous, exactly

k
k

-to-1 image of any continuum if

k
≥
2

k \geq 2

.
A proof of the Generalized Banach Contraction Conjecture
Authors: Arvanitakis Alexander
Published: September 2003

We introduce the notion of

J
J

-continuity, which generalizes both continuity and the hypothesis in the Generalized Banach Contraction Conjecture, and prove that any

J
J

-continuous self-map on a scattered compact space, has an invariant finite set. We use the results and the techniques to prove the Generalized Banach Contraction Conjecture.
Cotilting modules are pure-injective
Authors: Bazzoni S.
Published: September 2003

We prove that a cotilting module over an arbitrary ring is pure-injective.
Global analytic regularity for non-linear second order operators on the torus
Authors: Boiti Chiara , Zanghirati Luisa
Published: September 2003

Assuming a subelliptic a-priori estimate we prove global analytic regularity for non-linear second order operators on a product of tori, using the method of majorant series.
Zeroes of complete polynomial vector fields
Authors: Bustinduy Alvaro
Published: September 2003

We prove that a complete polynomial vector field on

C

2

\mathbb {C}^{2}

has at most one zero, and analyze the possible cases of those with exactly one which is not of Poincaré-Dulac type. We also obtain the possible nonzero first jet singularities of the foliation

F

X

\mathcal {F}_X

at infinity and the nongenericity of completeness. Connections with the Jacobian Conjecture are established.
A reproducing kernel space model for 𝐍_{𝜅}-functions
Authors: Derkach Vladimir , Hassi Seppo
Published: September 2003

A new model for generalized Nevanlinna functions

Q
∈

N

κ

Q\in \mathbf {N}_\kappa

will be presented. It involves Bezoutians and companion operators associated with certain polynomials determined by the generalized zeros and poles of

Q
Q

. The model is obtained by coupling two operator models and expressed by means of abstract boundary mappings and the corresponding Weyl functions.
Inner bounds for the spectrum of quasinormal operators
Authors: Gil’ M.
Published: September 2003

A linear operator in a separable Hilbert space is called a quasinormal one if it is a sum of a normal operator and a compact one. In the paper, bounds for the spectrum of quasinormal operators are established. In addition, the lower estimate for the spectral radius is derived. Under some restrictions, that estimate improves the well-known results. Applications to integral operators and matrices are discussed. Our results are new even in the finite-dimensional case.
Trivial, strongly minimal theories are model complete after naming constants
Authors: Goncharov Sergey , Harizanov Valentina , Laskowski Michael , Lempp Steffen , McCoy Charles
Published: September 2003

We prove that if

M

\mathcal {M}

is any model of a trivial, strongly minimal theory, then the elementary diagram

Th
⁡
(

M

M

)

\operatorname {Th}(\mathcal {M}_M)

is a model complete

L

M

\mathcal {L}_M

-theory. We conclude that all countable models of a trivial, strongly minimal theory with at least one computable model are

0
\boldsymbol {0}

-decidable, and that the spectrum of computable models of any trivial, strongly minimal theory is

Σ
5
0

\Sigma ^0_5

.
A generalization of Filliman duality
Authors: Kuperberg Greg
Published: September 2003

Filliman duality expresses (the characteristic measure of) a convex polytope

P
P

containing the origin as an alternating sum of simplices that share supporting hyperplanes with

P
P

. The terms in the alternating sum are given by a triangulation of the polar body

P

∘

P^{\circ }

. The duality can lead to useful formulas for the volume of

P
P

. A limiting case called Lawrence’s algorithm can be used to compute the Fourier transform of

P
P

.

In this note we extend Filliman duality to an involution on the space of polytopal measures on a finite-dimensional vector space, excluding polytopes that have a supporting hyperplane coplanar with the origin. As a special case, if

P
P

is a convex polytope containing the origin, any realization of

P

∘

P^{\circ }

as a linear combination of simplices leads to a dual realization of

P
P

.
Cyclicity conditions for division algebras of prime degree
Authors: Mahdavi-Hezavehi M. , Tignol J.-P.
Published: September 2003

Let

D
D

be a division algebra of prime degree

p
p

. A set of criteria is given for cyclicity of

D
D

in terms of subgroups of the multiplicative group

D
∗

D^*

of

D
D

. It is essentially shown that

D
D

is cyclic if and only if

D
∗

D^*

contains a nonabelian metabelian subgroup.
Power bounded operators and supercyclic vectors
Authors: Müller V.
Published: September 2003

By the well-known result of Brown, Chevreau and Pearcy, every Hilbert space contraction with spectrum containing the unit circle has a nontrivial closed invariant subspace. Equivalently, there is a nonzero vector which is not cyclic. We show that each power bounded operator on a Hilbert space with spectral radius equal to one has a nonzero vector which is not supercyclic. Equivalently, the operator has a nontrivial closed invariant homogeneous subset. Moreover, the operator has a nontrivial closed invariant positive cone.
Totally knotted Seifert surfaces with accidental peripherals
Authors: Ozawa Makoto , Tsutsumi Yukihiro
Published: September 2003

We show that if there exists an essential accidental surface in the knot exterior, then a closed accidental surface also exists. As its corollary, we know boundary slopes of accidental essential surfaces are integral or meridional. It is shown that an accidental incompressible Seifert surface in knot exteriors in

S
3

S^3

is totally knotted. Examples of satellite knots with arbitrarily high genus Seifert surfaces with accidental peripherals are given, and a Haken 3-manifold which contains a hyperbolic knot with an accidental incompressible Seifert surface of genus one is also given.
On commuting operator exponentials
Authors: Paliogiannis Fotios
Published: September 2003

Let

A
A

,

B
B

be bounded operators on a Banach space with

2
π
i

2\pi i

-congruence-free spectra such that

e
A

e
B

=

e
B

e
A

e^Ae^B=e^Be^A

. E. M. E. Wermuth has shown that

A
B
=
B
A

AB=BA

. Ch. Schmoeger later established this result, using inner derivations and, in a second paper, has shown that: for

a
,
b

a,b

in a complex unital Banach algebra, if the spectrum of

a
+
b

a+b

is

2
π
i

2\pi i

-congruence-free and

e
a

e
b

=

e

a
+
b

=

e
b

e
a

e^ae^b=e^{a+b}=e^be^a

, then

a
b
=
b
a

ab=ba

(and thus, answering an open problem raised by E. M. E. Wermuth). In this paper we use the holomorphic functional calculus to give alternative simple proofs of both of these results. Moreover, we use the Borel functional calculus to give new proofs of recent results of Ch. Schmoeger concerning normal operator exponentials on a complex Hilbert space, under a weaker hypothesis on the spectra.
Perfectly normal non-metrizable non-Archimedean spaces are generalized Souslin lines
Authors: Qiao Yuan-Qing , Tall Franklin
Published: September 2003

In this paper we prove the equivalence between the existence of perfectly normal, non-metrizable, non-archimedean spaces and the existence of “generalized Souslin lines", i.e., linearly ordered spaces in which every collection of disjoint open intervals is

σ
\sigma

-discrete, but which do not have a

σ
\sigma

-discrete dense set. The key ingredient is the observation that every first countable linearly ordered space has a dense non-archimedean subspace.
Principal eigenvalues for indefinite weight problems in all of ℝ^{𝕕}
Authors: Rhouma N.
Published: September 2003

We show the existence of principal eigenvalues of the problem

−
△
u
=
λ
g
u

-\triangle u=\lambda gu

in

R

d

\mathbb {R}^{d}

where

g
g

is an indefinite weight function. The existence of a continuous family of principal eigenvalues is demonstrated. Also, we prove the existence of a principal eigenvalue for which the principal eigenfunction

u
→
0

u\rightarrow 0

at

∞
\infty

.
An example of a 𝐶-minimal group which is not abelian-by-finite
Authors: Simonetta Patrick
Published: September 2003

In 1996 D. Macpherson and C. Steinhorn introduced

C
C

-minimality as an analogue, for valued fields and some groups with a definable chain of normal subgroups with trivial intersection, of the notion of o-minimality. One of the open questions of that paper was the existence of a non abelian-by-finite

C
C

-minimal group. We give here the first example of such a group.
𝑛-inner automorphisms of finite groups
Authors: Szechtman Fernando
Published: September 2003

We refer to an automorphism

g
g

of a group

G
G

as

n
n

-inner if given any subset

S
S

of

G
G

with cardinality less than

n
n

, there exists an inner automorphism of

G
G

agreeing with

g
g

on

S
S

. Hence

g
g

is 2-inner if it sends every element of

G
G

to a conjugate. New examples are given of outer

n
n

-inner automorphisms of finite groups for all natural numbers

n
≥
2

n\geq 2

.
Positive harmonic functions of finite order in a Denjoy type domain
Authors: Aikawa Hiroaki
Published: September 2003

We introduce a Denjoy type domain and prove that the dimension of the cone of positive harmonic functions of finite order in the domain with vanishing boundary values is one or two, whenever the boundary is included in a certain set.
On non-measurability of ℓ_{∞}/𝑐₀ in its second dual
Authors: Burke Dennis , Pol Roman
Published: September 2003

We show that

ℓ
∞

/

c
0

=
C
(

N

∗

)

\ell _\infty /c_0=C(\mathbb {N}^*)

with the weak topology is not an intersection of

ℵ
1

\aleph _1

Borel sets in its Čech-Stone extension (and hence in any compactification). Assuming (CH), this implies that

(
C
(

N

∗

)
,

w
e
a
k

)

(C(\mathbb {N}^*),\mathrm {weak})

has no continuous injection onto a Borel set in a compact space, or onto a Lindelöf space. Under (CH), this answers a question of Arhangel’skiĭ.
On characterizations of commutativity of C*-algebras
Authors: Ji Guoxing , Tomiyama Jun
Published: September 2003

We give three kinds of characterizations of the commutativity of C

∗

^*

- algebras. The first is the one from operator monotone property of functions regarded as the nonlinear version of Stinespring theorem, the second one is the characterization of commutativity of local type from expansion formulae of related functions and the third one is of global type from multiple positivity of those nonlinear positive maps induced from functions.
Simple 𝐴𝐻-algebras of real rank zero
Authors: Lin Huaxin
Published: September 2003

Let

A
A

be a unital simple

A
H

AH

-algebra with real rank zero. It is shown that if

A
A

satisfies a so-called fundamental comparison property, then

A
A

has tracial topological rank zero. Combining some previous results, it is shown that a unital simple

A
H

AH

-algebra with real rank zero, stable rank one and weakly unperforated

K
0

(
A
)

K_0(A)

must have slow dimension growth.
A note on the isoperimetric inequality
Authors: Onninen Jani
Published: September 2003

We show that the sharp integral form on the isoperimetric inequality holds for those orientation-preserving mappingsf∈Wlocn2n+1(Ω,Rn)f\in W^\frac {n^2}{n+1}_{loc}(\Omega , \mathbb {R}^n)whose Jacobians obey the rule of integration by parts.
On the embedding of variational inequalities
Authors: Rouhani B. , Khan A.
Published: September 2003

This work is devoted to the approximation of variational inequalities with pseudo-monotone operators. A variational inequality, considered in an arbitrary real Banach space, is first embedded into a reflexive Banach space by means of linear continuous mappings. Then a strongly convergent approximation procedure is designed by regularizing the embedded variational inequality. Some special cases have also been discussed.
A proof of Nogura’s conjecture
Authors: Todorcevic Stevo
Published: September 2003

Answering a question of T. Nogura (1985), we show using the Open Coloring Axiom that the weak diagonal sequence property is preserved by taking products whenever the products themselves are Fréchet. As an application we show, using the same assumption, that the product of two Fréchet groups is Fréchet provided it is sequential. Recall that the product of two Fréchet groups may not be sequential.
Asymptotic limit for condensate solutions in the Abelian Chern-Simons Higgs model II
Authors: Han Jongmin
Published: September 2003

In this paper we show that the maximal condensate solutions

(

ϕ
ϵ

,

A
ϵ

)

(\phi ^\epsilon , A^\epsilon )

in the Abelian Chern-Simons Higgs model converge to

(

ϕ
∗

,

A
∗

)

(\phi _*,A_*)

in higher norms, where

ϕ
∗

\phi _*

is a harmonic map.
A property of weakly Krull domains
Authors: Anderson D. , Zafrullah Muhammad
Published: September 2003

We show that a weakly Krull domain

D
D

satisfies

(
∗
)

(\ast )

: for every pair

a
,
b
∈
D
∖
{
0
}

a,b\in D\backslash \{0\}

there is an

n
=
n
(
a
,
b
)
∈

N

n=n(a,b)\in \mathbb {N}

such that

(
a
,

b

n

)

(a,b^{n})

is

t
t

-invertible. For

D
D

Noetherian,

D
D

satisfies

(
∗
)

(\ast )

if and only if every grade-one prime ideal of

D
D

is of height one. We also show that a modification of

(
∗
)

(\ast )

can be used to characterize Noetherian domains that are one-dimensional.
Construction of best Bregman approximations in reflexive Banach spaces
Authors: Bauschke Heinz , Combettes Patrick
Published: September 2003

An iterative method is proposed to construct the Bregman projection of a point onto a countable intersection of closed convex sets in a reflexive Banach space.
Une inégalité du type Payne-Polya-Weinberger pour le laplacien brut
Authors: Colbois Bruno
Published: September 2003

Let us consider a riemannian vector bundle

E
E

with compact basis

(
M
,
g
)

(M,g)

and the rough laplacian

Δ
¯

\bar {\Delta }

associated to a connection

D
D

on

E
E

. We prove that the eigenvalues of

Δ
¯

\bar {\Delta }

are bounded above by a function of the first eigenvalue and of the geometry of

(
M
,
g
)

(M,g)

, but independently of the choice of the connection

D
D

.
Degenerating families of rank two bundles
Authors: Kumar N. , Peterson Chris , Rao A.
Published: September 2003

We construct families of rank two bundles

E

t

\mathcal {E}_t

on

P

4

\mathbf {P}^4

, in characteristic two, where for

t
≠
0

t\neq 0

,

E

t

\mathcal {E}_t

is a sum of line bundles, and

E

0

\mathcal {E}_0

is non-split. We construct families of rank two bundles

E

t

\mathcal {E}_t

on

P

3

\mathbf {P}^3

, in characteristic

p
p

, where for

t
≠
0

t\neq 0

,

E

t

\mathcal {E}_t

is a sum of line bundles, and

E

0

\mathcal {E}_0

is non-split.
Isomorphisms of subalgebras of nest algebras
Authors: Lu Fangyan
Published: September 2003

Let

T

\mathcal T

be a subalgebra of a nest algebra

T

(

N

)

\mathcal T(\mathcal N)

. If

T

\mathcal T

contains all rank one operators in

T

(

N

)

\mathcal T(\mathcal N)

, then

T

\mathcal T

is said to be large; if the set of rank one operators in

T

\mathcal T

coincides with that in the Jacobson radical of

T

(

N

)

\mathcal T(\mathcal N)

,

T

\mathcal T

is said to be radical-type. In this paper, algebraic isomorphisms of large subalgebras and of radical-type subalgebras are characterized. Let

N

i

\mathcal N_i

be a nest of subspaces of a Hilbert space

H

i

\mathcal H_i

and

T

i

\mathcal T_i

be a subalgebra of the nest algebra

T

(

N

i

)

\mathcal T(\mathcal N_i)

associated to

N

i

\mathcal N_i

(

i
=
1
,
2

i=1,2

). Let

ϕ
\phi

be an algebraic isomorphism from

T

1

\mathcal T_1

onto

T

2

\mathcal T_2

. It is proved that

ϕ
\phi

is spatial if one of the following occurs: (1)

T

i

\mathcal T_i

(

i
=
1
,
2

i=1,2

) is large and contains a masa; (2)

T

i

\mathcal T_i

(

i
=
1
,
2

i=1,2

) is large and closed; (3)

T

i

\mathcal T_i

(

i
=
1
,
2

i=1,2

) is a closed radical-type subalgebra and

N

i

\mathcal N_i

(

i
=
1
,
2
)

i=1,2)

is quasi-continuous (i.e. the trivial elements of

N

i

\mathcal N_i

are limit points); (4)

T

i

\mathcal T_i

(

i
=
1
,
2

i=1,2

) is large and one of

N

1

\mathcal N_1

and

N

2

\mathcal N_2

is not quasi-continuous.
Fixed points in the family of convex representations of a maximal monotone operator
Authors: Svaiter B.
Published: September 2003

Any maximal monotone operator can be characterized by a convex function. The family of such convex functions is invariant under a transformation connected with the Fenchel-Legendre conjugation. We prove that there exists a convex representation of the operator which is a fixed point of this conjugation.
Induced local actions on taut and Stein manifolds
Authors: Iannuzzi Andrea
Published: September 2003

Let

G
=
(

R

,
+
)

G=({\mathbb {R}},+)

act by biholomorphisms on a taut manifold

X
X

. We show that

X
X

can be regarded as a

G
G

-invariant domain in a complex manifold

X

∗

X^{*}

on which the universal complexification

(

C

,
+
)

({\mathbb {C}},+)

of

G
G

acts. If

X
X

is also Stein, an analogous result holds for actions of a larger class of real Lie groups containing, e.g., abelian and certain nilpotent ones. In this case the question of Steinness of

X

∗

X^{*}

is discussed.
An application of Bochner’s technique to the deformations of the complex structure of ℂℙⁿ
Authors: Ouyang Yong
Published: September 2003

We consider the deformation of the complex structure of

C

P

n

\mathbb C \mathbb P^n

. We show that a harmonic deformation on

C

P

n

\mathbb C \mathbb P^n

equipped with the Fubini-Study metric is trivial if its supernorm is appropriately small.
On a question of Craven and a theorem of Belyi
Authors: Borisov Alexander
Published: September 2003

In this elementary note we prove that a polynomial with rational coefficients divides the derivative of some polynomial which splits in

Q

\mathbb Q

if and only if all of its irrational roots are real and simple. This provides an answer to a question posed by Thomas Craven. Similar ideas also lead to a variation of the proof of Belyi’s theorem that every algebraic curve defined over an algebraic number field admits a map to

P
1

P^1

which is only ramified above three points. As it turned out, this variation was noticed previously by G. Belyi himself and Leonardo Zapponi.
Graph-distance convergence and uniform local boundedness of monotone mappings
Authors: Pennanen Teemu , Revalski Julian , Théra Michel
Published: September 2003

In this article we study graph-distance convergence of monotone operators. First, we prove a property that has been an open problem up to now: the limit of a sequence of graph-distance convergent maximal monotone operators in a Hilbert space is a maximal monotone operator. Next, we show that a sequence of maximal monotone operators converging in the same sense in a reflexive Banach space is uniformly locally bounded around any point from the interior of the domain of the limit mapping. The result is an extension of a similar one from finite dimensions. As an application we give a simplified condition for the stability (under graph-distance convergence) of the sum of maximal monotone mappings in Hilbert spaces.
On alternating analogues of Tornheim’s double series
Authors: Tsumura Hirofumi
Published: September 2003

In this paper, we give some evaluation formulas for alternating analogues of Tornheim’s double series. These can be regarded as alternating analogues of Mordell’s formulas. This gives a partial answer to the problem posed by Subbarao-Sitaramachandrarao.
A note on invertibility preservers on Banach algebras
Authors: Brešar Matej , Fošner Ajda , Šemrl Peter
Published: September 2003

Let

A

{\mathcal {A}}

be

B

{\mathcal {B}}

be semisimple Banach algebras and let

ϕ
:

A

→

B

\phi :\mathcal {A}\to \mathcal {B}

be a unital bijective linear operator that preserves invertibility. If the socle of

A

{\mathcal A}

is an essential ideal of

A

{\mathcal A}

, then

ϕ
\phi

is a Jordan isomorphism.
A “nonlinear” proof of Pitt’s compactness theorem
Authors: Fabian M. , Zizler V.
Published: September 2003

Using Stegall’s variational principle, we present a simple proof of Pitt’s theorem that bounded linear operators from

ℓ
q

\ell _q

into

ℓ
p

\ell _p

are compact for

1
≤
p
>
q
>
+
∞

1\le p>q>+\infty

.
The scenery factor of the [𝑇,𝑇⁻¹] transformation is not loosely Bernoulli
Authors: Hoffman Christopher
Published: September 2003

Kalikow (1982) proved that the

[
T
,

T

−
1

]

[T,T^{-1}]

transformation is not isomorphic to a Bernoulli shift. We show that the scenery factor of the

[
T
,

T

−
1

]

[T,T^{-1}]

transformation is not isomorphic to a Bernoulli shift. Moreover, we show that it is not Kakutani equivalent to a Bernoulli shift.
A 𝑞-analogue of the Whittaker-Shannon-Kotel’nikov sampling theorem
Authors: Ismail Mourad , Zayed Ahmed
Published: September 2003

The Whittaker-Shannon-Kotel’nikov (WSK) sampling theorem plays an important role not only in harmonic analysis and approximation theory, but also in communication engineering since it enables engineers to reconstruct analog signals from their samples at a discrete set of data points. The main aim of this paper is to derive a

q
q

-analogue of the Whittaker-Shannon-Kotel’nikov sampling theorem. The proof uses recent results in the theory of

q
q

-orthogonal polynomials and basic hypergeometric functions, in particular, new results on the addition theorems for

q
q

-exponential functions.
The Diophantine equation 2𝑥²+1=3ⁿ
Authors: Leu Ming-Guang , Li Guan-Wei
Published: September 2003

Let

p
p

be a rational prime and

D
D

a positive rational integer coprime with

p
p

. Denote by

N
(
D
,
1
,
p
)

N(D, 1,p)

the number of solutions

(
x
,
n
)

(x, n)

of the equation

D

x
2

+
1
=

p
n

D x^2 + 1 = p^n

in rational integers

x
≥
1

x \geq 1

and

n
≥
1

n \geq 1

. In a paper of Le, he claimed that

N
(
D
,
1
,
p
)
≤
2

N(D, 1, p) \leq 2

without giving a proof. Furthermore, the statement

N
(
D
,
1
,
p
)
≤
2

N(D, 1, p) \leq 2

has been used by Le, Bugeaud and Shorey in their papers to derive results on certain Diophantine equations. In this paper we point out that the statement

N
(
D
,
1
,
p
)
≤
2

N(D, 1, p) \leq 2

is incorrect by proving that

N
(
2
,
1
,
3
)
=
3

N(2, 1, 3)=3

.
Finer geometric rigidity of limit sets of conformal IFS
Authors: Mayer Volker , Urbański Mariusz
Published: September 2003

We consider infinite conformal iterated function systems in the phase space

R

d

\mathbb {R}^d

with

d
≥
3

d\ge 3

. Let

J
J

be the limit set of such a system. Under a mild technical assumption, which is always satisfied if the system is finite, we prove that either the Hausdorff dimension of

J
J

exceeds the topological dimension

k
k

of the closure of

J
J

or else the closure of

J
J

is a proper compact subset of either a geometric sphere or an affine subspace of dimension

k
k

. A similar dichotomy holds for conformal expanding repellers.
Evolutionary game dynamics
Authors: Hofbauer Josef , Sigmund Karl
Published: September 2003

Evolutionary game dynamics is the application of population dynamical methods to game theory. It has been introduced by evolutionary biologists, anticipated in part by classical game theorists. In this survey, we present an overview of the many brands of deterministic dynamical systems motivated by evolutionary game theory, including ordinary differential equations (and, in particular, the replicator equation), differential inclusions (the best response dynamics), difference equations (as, for instance, fictitious play) and reaction-diffusion systems. A recurrent theme (the so-called ‘folk theorem of evolutionary game theory’) is the close connection of the dynamical approach with the Nash equilibrium, but we show that a static, equilibrium-based viewpoint is, on principle, unable to always account for the long-term behaviour of players adjusting their behaviour to maximise their payoff.
Spectra of hyperbolic surfaces
Authors: Sarnak Peter
Published: September 2003

These notes attempt to describe some aspects of the spectral theory of modular surfaces. They are by no means a complete survey.
On a theorem of Jordan
Authors: Serre Jean-Pierre
Published: September 2003

The theorem of Jordan which I want to discuss here dates from 1872. It is an elementary result on finite groups of permutations. I shall first present its translations in Number Theory and Topology.
Topological obstructions to graph colorings
Authors: Babson Eric , Kozlov Dmitry
Published: September 2003

For any two graphs

G
G

and

H
H

Lovász has defined a cell complex

H
o
m

(
G
,
H
)

\mathtt {Hom} (G,H)

having in mind the general program that the algebraic invariants of these complexes should provide obstructions to graph colorings. Here we announce the proof of a conjecture of Lovász concerning these complexes with

G
G

a cycle of odd length. More specifically, we show that If

Hom
⁡
(

C

2
r
+
1

,
G
)

\operatorname {Hom}(C_{2r+1},G)

is

k
k

-connected, then

χ
(
G
)
≥
k
+
4

\chi (G)\geq k+4

.

Our actual statement is somewhat sharper, as we find obstructions already in the nonvanishing of powers of certain Stiefel-Whitney classes.
Metric tensor estimates, geometric convergence, and inverse boundary problems
Authors: Anderson Michael , Katsuda Atsushi , Kurylev Yaroslav , Lassas Matti , Taylor Michael
Published: September 2003

Three themes are treated in the results announced here. The first is the regularity of a metric tensor, on a manifold with boundary, on which there are given Ricci curvature bounds, on the manifold and its boundary, and a Lipschitz bound on the mean curvature of the boundary. The second is the geometric convergence of a (sub)sequence of manifolds with boundary with such geometrical bounds and also an upper bound on the diameter and a lower bound on injectivity and boundary injectivity radius, making use of the first part. The third theme involves the uniqueness and conditional stability of an inverse problem proposed by Gel’fand, making essential use of the results of the first two parts.
Cusps in complex boundaries of one-dimensional Teichmüller space
Authors: Miyachi Hideki
Published: September 2003

This paper gives a concrete proof of the conjectural phenomena on the complex boundary one-dimensional slices: every rational boundary point is cusp shaped. This paper treats this problem for Bers slices, the Earle slice, and the Maskit slice. In proving this, we also show that every Teichmüller modular transformation acting on a Bers slice can be extended as a quasi-conformal mapping on its ambient space. Furthermore, using this extension, we discuss similarity phenomena on the boundaries of Bers slices, and also compare these phenomena with results in complex dynamics. We will also give a result, related to the theory of L. Keen and C. Series, of pleated varieties in quasifuchsian space of once punctured tori.
The Genetic Basis of Cellular Morphogenesis in the Filamentous FungusNeurospora crassa
Authors: Seiler Stephan , Plamann Michael
Published: September 2003

Cellular polarity is a fundamental property of every cell. Due to their extremely fast growth rate (≥1 μm/s) and their highly elongated form, filamentous fungi represent a prime example of polarized growth and are an attractive model for the analysis of fundamental mechanisms underlying cellular polarity. To identify the critical components that contribute to polarized growth, we developed a large-scale genetic screen for the isolation of conditional mutants defective in this process in the model fungus Neurospora crassa. Phenotypic analysis and complementation tests of ca. 950 mutants identified more than 100 complementation groups that define 21 distinct morphological classes. The phenotypes include polarity defects over the whole hypha, more specific defects localized to hyphal tips or subapical regions, and defects in branch formation and growth directionality. To begin converting this mutant collection into meaningful biological information, we identified the defective genes in 45 mutants covering all phenotypic classes. These genes encode novel proteins as well as proteins which 1) regulate the actin or microtubule cytoskeleton, 2) are kinases or components of signal transduction pathways, 3) are part of the secretory pathway, or 4) have functions in cell wall formation or membrane biosynthesis. These findings highlight the dynamic nature of a fungal hypha and establish a molecular model for studies of hyphal growth and polarity.
Rapid Microtubule-dependent Induction of Neurite-like Extensions in NIH 3T3 Fibroblasts by Inhibition of ROCK and Cbl
Authors: Scaife Robin M. , Job Didier , Langdon Wallace Y.
Published: September 2003

A number of key cellular functions, such as morphological differentiation and cell motility, are closely associated with changes in cytoskeletal dynamics. Many of the principal signaling components involved in actin cytoskeletal dynamics have been identified, and these have been shown to be critically involved in cell motility. In contrast, signaling to microtubules remains relatively uncharacterized, and the importance of signaling pathways in modulation of microtubule dynamics has so far not been established clearly. We report here that the Rho-effector ROCK and the multiadaptor proto-oncoprotein Cbl can profoundly affect the microtubule cytoskeleton. Simultaneous inhibition of these two signaling molecules induces a dramatic rearrangement of the microtubule cytoskeleton into microtubule bundles. The formation of these microtubule bundles, which does not involve signaling by Rac, Cdc42, Crk, phosphatidylinositol 3-kinase, and Abl, is sufficient to induce distinct neurite-like extensions in NIH 3T3 fibroblasts, even in the absence of microfilaments. This novel microtubule-dependent function that promotes neurite-like extensions is not dependent on net changes in microtubule polymerization or stabilization, but rather involves selective elongation and reorganization of microtubules into long bundles.