bluuebunny/crossref_metadata_2025 huggingface dataset:
Two living species of coelacanths?
Authors: Holder Mark T. , Erdmann Mark V. , Wilcox Thomas P. , Caldwell Roy L. , Hillis David M.
Published: July 2002

During the period of September 1997 through July 1998, two coelacanth fishes were captured off Manado Tua Island, Sulawesi, Indonesia. These specimens were caught almost 10,000 km from the only other known population of living coelacanths,
Latimeria chalumnae
, near the Comores. The Indonesian fish was described recently as a new species,
Latimeria menadoensis,
based on morphological differentiation and DNA sequence divergence in fragments of the cytochrome
b
and 12S rRNA genes. We have obtained the sequence of 4,823 bp of mitochondrial DNA from the same specimen, including the entire genes for cytochrome
b
, 12S rRNA, 16S rRNA, four tRNAs, and the control region. The sequence is 4.1% different from the published sequence of an animal captured from the Comores, indicating substantial divergence between the Indonesian and Comorean populations. Nine morphological and meristic differences are purported to distinguish
L. menadoensis
and
L. chalumnae
, based on comparison of a single specimen of
L. menadoensis
to a description of five individuals of
L. chalumnae
from the Comores. A survey of the literature provided data on 4 of the characters used to distinguish
L. menadoensis
from
L. chalumnae
from an additional 16 African coelacanths; for all 4 characters, the Indonesian sample was within the range of variation reported for the African specimens. Nonetheless,
L. chalumnae
and
L. menadoensis
appear to be separate species based on divergence of mitochondrial DNA.
Dysfunction of human Rad18 results in defective postreplication repair and hypersensitivity to multiple mutagens
Authors: Tateishi Satoshi , Sakuraba Yoshiyuki , Masuyama Sadaharu , Inoue Hirokazu , Yamaizumi Masaru
Published: July 2002

Postreplication repair functions in gap-filling of a daughter strand on replication of damaged DNA. The yeast
Saccharomyces cerevisiae
Rad18 protein plays a pivotal role in the process together with the Rad6 protein. Here, we have cloned a human homologue of
RAD18
,
hRAD18
. It maps on chromosome 3p24–25, where deletions are often found in lung, breast, ovary, and testis cancers.
In vivo
, hRad18 protein binds to hHR6 protein through a conserved ring-finger motif. Stable transformants with hRad18 mutated in this motif become sensitive to UV, methyl methanesulfonate, and mitomycin C, and are defective in the replication of UV-damaged DNA. Thus,
hRAD18
is a functional homologue of
RAD18
.
Acquired, nonrandom chromosomal abnormalities associated with the development of acute promyelocytic leukemia in transgenic mice
Authors: Zimonjic Drazen B. , Pollock Jessica L. , Westervelt Peter , Popescu Nicholas C. , Ley Timothy J.
Published: July 2002

We previously generated a transgenic mouse model for acute promyelocytic leukemia (APL) by expressing the promyelocytic leukemia (PML)–retinoic acid receptor (RARα) cDNA in early myeloid cells. This fusion protein causes a myeloproliferative disease in 100% of animals, but only 15–20% of the animals develop acute leukemia after a long latency period (6–13 months). PML-RARα is therefore necessary, but not sufficient, for APL development. The coexpression of a reciprocal form of the fusion, RARα-PML, increased the likelihood of APL development (55–60%), but did not shorten latency. Together, these results suggested that additional genetic events are required for the development of APL. We therefore evaluated the splenic tumor cells from 18 transgenic mice with APL for evidence of secondary genetic events, by using spectral karyotyping analysis. Interstitial or terminal deletions of the distal region of one copy of chromosome 2 [del(2)] were found in 1/5 tumors expressing PML-RARα, but in 11/13 tumors expressing both PML-RARα and RARα-PML (P< 0.05). Leukemic cells that contained a deletion on chromosome 2 often contained additional chromosomal gains (especially of 15), chromosomal losses (especially of 11 or X/Y), or were tetraploid (P≤ 0.001). These changes did not commonly occur in nontransgenic littermates, nor in aged transgenic mice that did not develop APL. These results suggest that expression of RARα-PML increases the likelihood of chromosome 2 deletions in APL cells. Deletion 2 appears to predispose APL cells to further chromosomal instability, which may lead to the acquisition of additional changes that provide an advantage to the transformed cells.
Evolution of the bilaterian body plan: What have we learned from annelids?
Authors: Shankland Marty , Seaver Elaine C.
Published: July 2002

Annelids, unlike their vertebrate or fruit fly cousins, are a
bilaterian taxon often overlooked when addressing the question of body
plan evolution. However, recent data suggest that annelids offer unique
insights on the early evolution of spiral cleavage, anteroposterior
axis formation, body axis segmentation, and head versus trunk
distinction.
Identification of EBP50: A PDZ-containing Phosphoprotein that Associates with Members of the Ezrin-Radixin-Moesin Family
Authors: Reczek David , Berryman Mark , Bretscher Anthony
Published: July 2002

Members of the ezrin-radixin-moesin (ERM) family of membrane–cytoskeletal linking proteins have NH2- and COOH-terminal domains that associate with the plasma membrane and the actin cytoskeleton, respectively. To search for ERM binding partners potentially involved in membrane association, tissue lysates were subjected to affinity chromatography on the immobilized NH2-terminal domains of ezrin and moesin, which comprise the ezrin-radixin-moesin–association domain (N-ERMAD). A collection of polypeptides at 50–53 kD from human placenta and at 58-59 kD from bovine brain bound directly to both N-ERMADs. The 50–53-kD placental proteins migrated as a major 50-kD species after phosphatase treatment, indicating that the heterogeneity is due to different phosphorylation states. We refer to these polypeptides as ERM-binding phosphoprotein 50 (EBP50). Sequence analysis of human EBP50 was used to identify an ∼2-kb human cDNA that encodes a 357-residue polypeptide. Recombinant EBP50 binds tightly to the N-ERMADs of ezrin and moesin. Peptide sequences from the brain candidate indicated that it is closely related to EBP50. EBP50 has two PSD-95/DlgA/ZO-1–like (PDZ) domains and is most likely a homologue of rabbit protein cofactor, which is involved in the protein kinase A regulation of the renal brush border Na+/H+ exchanger. EBP50 is widely distributed in tissues, and is particularly enriched in those containing polarized epithelia. Immunofluorescence microscopy of cultured cells and tissues revealed that EBP50 colocalizes with actin and ezrin in the apical microvilli of epithelial cells, and immunoelectron microscopy demonstrated that it is specifically associated with the microvilli of the placental syncytiotrophoblast. Moreover, EBP50 and ezrin can be coimmunoprecipitated as a complex from isolated human placental microvilli. These findings show that EBP50 is a physiologically relevant ezrin binding protein. Since PDZ domains are known to mediate associations with integral membrane proteins, one mode of membrane attachment of ezrin is likely to be mediated through EBP50.
β1 Integrin Is Essential for Teratoma Growth and Angiogenesis
Authors: Bloch Wilhelm , Forsberg Erik , Lentini Sylvia , Brakebusch Cord , Martin Karl , Krell Hans W. , Weidle Ulrich H. , Addicks Klaus , Fässler Reinhard
Published: July 2002

Teratomas are benign tumors that form after ectopic injection of embryonic stem (ES) cells into mice and contain derivatives of all primitive germ layers. To study the role of β1 integrin during teratoma formation, we compared teratomas induced by normal and β1-null ES cells. Injection of normal ES cells gave rise to large teratomas. In contrast, β1-null ES cells either did not grow or formed small teratomas with an average weight of <5% of that of normal teratomas. Histological analysis of β1-null teratomas revealed the presence of various differentiated cells, however, a much lower number of host-derived stromal cells than in normal teratomas. Fibronectin, collagen I, and nidogen were expressed but, in contrast to normal teratomas, diffusely deposited in β1-null teratomas. Basement membranes were present but with irregular shape and detached from the cell surface.

Normal teratomas had large blood vessels with a smooth inner surface, containing both host- and ES cell–derived endothelial cells. In contrast, β1-null teratomas had small vessels that were loosely embedded into the connective tissue. Furthermore, endothelial cells were always of host-derived origin and formed blood vessels with an irregular inner surface. Although β1- deficient endothelial cells were absent in teratomas, β1-null ES cells could differentiate in vitro into endothelial cells. The formation of a complex vasculature, however, was significantly delayed and of poor quality in β1-null embryoid bodies. Moreover, while vascular endothelial growth factor induced proliferation of endothelial cells as well as an extensive branching of blood vessels in normal embryoid bodies, it had no effect in β1-null embryoid bodies.
The Yeast Adaptor Protein Complex, AP-3, Is Essential for the Efficient Delivery of Alkaline Phosphatase by the Alternate Pathway to the Vacuole
Authors: Stepp J. David , Huang Kristen , Lemmon Sandra K.
Published: July 2002

A novel clathrin adaptor-like complex, adaptor protein (AP)-3, has recently been described in yeast and in animals. To gain insight into the role of yeast AP-3, a genetic strategy was devised to isolate gene products that are required in the absence of the AP-3 μ chain encoded by APM3. One gene identified by this synthetic lethal screen was VPS45. The Vps pathway defines the route that several proteins, including carboxypeptidase Y, take from the late Golgi to the vacuole. However, vacuolar alkaline phosphatase (ALP) is transported via an alternate, intracellular route. This suggested that the apm3-Δ vps45 synthetic phenotype could be caused by a block in both the alternate and the Vps pathways. Here we demonstrate that loss of function of the AP-3 complex results in slowed processing and missorting of ALP. ALP is no longer localized to the vacuole membrane by immunofluorescence, but is found in small punctate structures throughout the cell. This pattern is distinct from the Golgi marker Kex2p, which is unaffected in AP-3 mutants. We also show that in the apm3-Δ mutant some ALP is delivered to the vacuole by diversion into the Vps pathway. Class E vps mutants accumulate an exaggerated prevacuolar compartment containing membrane proteins on their way to the vacuole or destined for recycling to the Golgi. Surprisingly, in AP-3 class E vps double mutants these proteins reappear on the vacuole. We suggest that some AP-3–dependent cargo proteins that regulate late steps in Golgi to vacuole transport are diverted into the Vps pathway allowing completion of transfer to the vacuole in the class E vps mutant.
Relocalization of Phospholipase D Activity Mediates Membrane Formation During Meiosis
Authors: Rudge Simon A. , Morris Andrew J. , Engebrecht JoAnne
Published: July 2002

Phospholipase D (PLD) enzymes catalyze the hydrolysis of phosphatidylcholine and are involved in membrane trafficking and cytoskeletal reorganization. The Saccharomyces cerevisiae SPO14 gene encodes a PLD that is essential for meiosis. We have analyzed the role of PLD in meiosis by examining two mutant proteins, one with a point mutation in a conserved residue (Spo14pK→ H) and one with an amino-terminal deletion (Spo14pΔN), neither of which can restore meiosis in a spo14 deletion strain. Spo14pK→ H is enzymatically inactive, indicating that PLD activity is required, whereas Spo14pΔN retains PLD catalytic activity in vitro, indicating that PLD activity is not sufficient for meiosis. To explore other aspects of Spo14 function, we followed the localization of the enzyme during meiosis. Spo14p is initially distributed throughout the cell, becomes concentrated at the spindle pole bodies after the meiosis I division, and at meiosis II localizes to the new spore membrane as it surrounds the nuclei and then expands to encapsulate the associated cytoplasm during the formation of spores. The catalytically inactive protein also undergoes relocalization during meiosis; however, in the absence of PLD activity, no membrane is formed. In contrast, Spo14pΔN does not relocalize properly, indicating that the failure of this protein to complement a spo14 mutant is due to its inability to localize its PLD activity. Furthermore, we find that Spo14p movement is correlated with phosphorylation of the protein. These experiments indicate that PLD participates in regulated membrane formation during meiosis, and that both its catalytic activity and subcellular redistribution are essential for this function.
The Human Homologue of Bub3 Is Required for Kinetochore Localization of Bub1 and a Mad3/Bub1-related Protein Kinase
Authors: Taylor Stephen S. , Ha Edward , McKeon Frank
Published: July 2002

A feedback control mechanism, or cell cycle checkpoint, delays the onset of anaphase until all the chromosomes are correctly aligned on the mitotic spindle. Previously, we showed that the murine homologue of Bub1 is not only required for checkpoint response to spindle damage, but also restrains progression through a normal mitosis (Taylor, S.S., and F. McKeon. 1997. Cell. 89:727–735). Here, we describe the identification of a human homologue of Bub3, a 37-kD protein with four WD repeats. Like Bub1, Bub3 localizes to kinetochores before chromosome alignment. In addition, Bub3 and Bub1 interact in mammalian cells. Deletion mapping was used to identify the domain of Bub1 required for binding Bub3. Significantly, this same domain is required for kinetochore localization of Bub1, suggesting that the role of Bub3 is to localize Bub1 to the kinetochore, thereby activating the checkpoint in response to unattached kinetochores. The identification of a human Mad3/Bub1-related protein kinase, hBubR1, which can also bind Bub3 in mammalian cells, is described. Ectopically expressed hBubR1 also localizes to kinetochores during prometaphase, but only when hBub3 is overexpressed. We discuss the implications of the common interaction between Bub1 and hBubR1 with hBub3 for checkpoint control.
Modulation of Calcium Current in Arteriolar Smooth Muscle by αvβ3 and α5β1 Integrin Ligands
Authors: Wu Xin , Mogford Jon E. , Platts Steven H. , Davis George E. , Meininger Gerald A. , Davis Michael J.
Published: July 2002

Vasoactive effects of soluble matrix proteins and integrin-binding peptides on arterioles are mediated by αvβ3 and α5β1 integrins. To examine the underlying mechanisms, we measured L-type Ca2+ channel current in arteriolar smooth muscle cells in response to integrin ligands. Whole-cell, inward Ba2+ currents were inhibited after application of soluble cyclic RGD peptide, vitronectin (VN), fibronectin (FN), either of two anti–β3 integrin antibodies, or monovalent β3 antibody. With VN or β3 antibody coated onto microbeads and presented as an insoluble ligand, current was also inhibited. In contrast, beads coated with FN or α5 antibody produced significant enhancement of current after bead attachment. Soluble α5 antibody had no effect on current but blocked the increase in current evoked by FN-coated beads and enhanced current when applied in combination with an appropriate IgG. The data suggest that αvβ3 and α5β1 integrins are differentially linked through intracellular signaling pathways to the L-type Ca2+ channel and thereby alter control of Ca2+ influx in vascular smooth muscle. This would account for the vasoactive effects of integrin ligands on arterioles and provide a potential mechanism for wound recognition during tissue injury.
Activation of αVβ3 on Vascular Cells Controls Recognition of Prothrombin
Authors: Byzova Tatiana V. , Plow Edward F.
Published: July 2002

Regulation of vascular homeostasis depends upon collaboration between cells of the vessel wall and blood coagulation system. A direct interaction between integrin αVβ3 on endothelial cells and smooth muscle cells and prothrombin, the pivotal proenzyme of the blood coagulation system, is demonstrated and activation of the integrin is required for receptor engagement. Evidence that prothrombin is a ligand for αVβ3 on these cells include: (a) prothrombin binds to purified αVβ3 via a RGD recognition specificity; (b) prothrombin supports αVβ3-mediated adhesion of stimulated endothelial cells and smooth muscle cells; and (c) endothelial cells, either in suspension and in a monolayer, recognize soluble prothrombin via αVβ3. αVβ3-mediated cell adhesion to prothrombin, but not to fibrinogen, required activation of the receptor. Thus, the functionality of the αVβ3 receptor is ligand defined, and prothrombin and fibrinogen represent activation- dependent and activation-independent ligands. Activation of αVβ3 could be induced not only by model agonists, PMA and Mn2+, but also by a physiologically relevant agonist, ADP. Inhibition of protein kinase C and calpain prevented activation of αVβ3 on vascular cells, suggesting that these molecules are involved in the inside-out signaling events that activate the integrin. The capacity of αVβ3 to interact with prothrombin may play a significant role in the maintenance of hemostasis; and, at a general level, ligand selection by αVβ3 may be controlled by the activation state of this integrin.
The Bipolar Kinesin, KLP61F, Cross-links Microtubules within Interpolar Microtubule Bundles of Drosophila Embryonic Mitotic Spindles
Authors: Sharp David J. , McDonald Kent L. , Brown Heather M. , Matthies Heinrich J. , Walczak Claire , Vale Ron D. , Mitchison Timothy J. , Scholey Jonathan M.
Published: July 2002

Previous genetic and biochemical studies have led to the hypothesis that the essential mitotic bipolar kinesin, KLP61F, cross-links and slides microtubules (MTs) during spindle assembly and function. Here, we have tested this hypothesis by immunofluorescence and immunoelectron microscopy (immunoEM). We show that Drosophila embryonic spindles at metaphase and anaphase contain abundant bundles of MTs running between the spindle poles. These interpolar MT bundles are parallel near the poles and antiparallel in the midzone. We have observed that KLP61F motors, phosphorylated at a cdk1/cyclin B consensus domain within the BimC box (BCB), localize along the length of these interpolar MT bundles, being concentrated in the midzone region. Nonphosphorylated KLP61F motors, in contrast, are excluded from the spindle and display a cytoplasmic localization. Immunoelectron microscopy further suggested that phospho-KLP61F motors form cross-links between MTs within interpolar MT bundles. These bipolar KLP61F MT-MT cross-links should be capable of organizing parallel MTs into bundles within half spindles and sliding antiparallel MTs apart in the spindle midzone. Thus we propose that bipolar kinesin motors and MTs interact by a “sliding filament mechanism” during the formation and function of the mitotic spindle.
An Acidic Motif Retains Vesicular Monoamine Transporter 2 on Large Dense Core Vesicles
Authors: Waites Clarissa L. , Mehta Anand , Tan Philip K. , Thomas Gary , Edwards Robert H. , Krantz David E.
Published: July 2002

The release of biogenic amines from large dense core vesicles (LDCVs) depends on localization of the vesicular monoamine transporter VMAT2 to LDCVs. We now find that a cluster of acidic residues including two serines phosphorylated by casein kinase 2 is required for the localization of VMAT2 to LDCVs. Deletion of the acidic cluster promotes the removal of VMAT2 from LDCVs during their maturation. The motif thus acts as a signal for retention on LDCVs. In addition, replacement of the serines by glutamate to mimic phosphorylation promotes the removal of VMAT2 from LDCVs, whereas replacement by alanine to prevent phosphorylation decreases removal. Phosphorylation of the acidic cluster thus appears to reduce the localization of VMAT2 to LDCVs by inactivating a retention mechanism.
Filamin A, the Arp2/3 complex, and the morphology and function of cortical actin filaments in human melanoma cells
Authors: Flanagan Lisa A. , Chou Janet , Falet Hervé , Neujahr Ralph , Hartwig John H. , Stossel Thomas P.
Published: July 2002

The Arp2/3 complex and filamin A (FLNa) branch actin filaments. To define the role of these actin-binding proteins in cellular actin architecture, we compared the morphology of FLNa-deficient human melanoma (M2) cells and three stable derivatives of these cells expressing normal FLNa concentrations. All the cell lines contain similar amounts of the Arp2/3 complex. Serum addition causes serum-starved M2 cells to extend flat protrusions transiently; thereafter, the protrusions turn into spherical blebs and the cells do not crawl. The short-lived lamellae of M2 cells contain a dense mat of long actin filaments in contrast to a more three-dimensional orthogonal network of shorter actin filaments in lamellae of identically treated FLNa-expressing cells capable of translational locomotion. FLNa-specific antibodies localize throughout the leading lamellae of these cells at junctions between orthogonally intersecting actin filaments. Arp2/3 complex–specific antibodies stain diffusely and label a few, although not the same, actin filament overlap sites as FLNa antibody. We conclude that FLNa is essential in cells that express it for stabilizing orthogonal actin networks suitable for locomotion. Contrary to some proposals, Arp2/3 complex–mediated branching of actin alone is insufficient for establishing an orthogonal actin organization or maintaining mechanical stability at the leading edge.
A subset of yeast vacuolar protein sorting mutants is blocked in one branch of the exocytic pathway
Authors: Harsay Edina , Schekman Randy
Published: July 2002

Exocytic vesicles that accumulate in a temperature-sensitive sec6 mutant at a restrictive temperature can be separated into at least two populations with different buoyant densities and unique cargo molecules. Using a sec6 mutant background to isolate vesicles, we have found that vacuolar protein sorting mutants that block an endosome-mediated route to the vacuole,including vps1, pep12, vps4, and a temperature-sensitive clathrin mutant, missort cargo normally transported by dense exocytic vesicles, such as invertase, into light exocytic vesicles, whereas transport of cargo specific to the light exocytic vesicles appears unaffected. Immunoisolation experiments confirm that missorting, rather than a changed property of the normally dense vesicles, is responsible for the altered density gradient fractionation profile. The vps41Δ and apl6Δmutants, which block transport of only the subset of vacuolar proteins that bypasses endosomes, sort exocytic cargo normally. Furthermore, avps10Δ sec6 mutant, which lacks the sorting receptor for carboxypeptidase Y (CPY), accumulates both invertase and CPY in dense vesicles. These results suggest that at least one branch of the yeast exocytic pathway transits through endosomes before reaching the cell surface. Consistent with this possibility, we show that immunoisolated clathrin-coated vesicles contain invertase.
The Monomeric Guanosine Triphosphatase rab4 Controls an Essential Step on the Pathway of Receptor-mediated Antigen Processing in B Cells
Authors: Lazzarino Deborah A. , Blier Peter , Mellman Ira
Published: July 2002

Each member of the rab guanosine triphosphatase protein family assists in the regulation of a specific step within the biosynthetic or endocytic pathways. We have found that the early endosome-associated rab4 protein controls a step critical for receptor-mediated antigen processing in a murine A20 B cell line. Expression of the dominant negative rab4N121I mutant dramatically inhibited the processing and presentation of ovalbumin, λ cI repressor, or rabbit immunoglobulin G internalized as antigens by B cell antigen receptors or transfected Fc receptors. This defect did not reflect a block in antigen endocytosis or degradation, and transfected cells remained completely capable of presenting exogenously added ovalbumin and λ repressor peptides. Most remarkably, rab4N121I-expressing cells were undiminished in their ability to present each of these antigens when whole proteins were internalized at high concentration by fluid-phase endocytosis. Thus, expression of the rab4N121I selectively inactivated a portion of the endocytic pathway required for the processing of receptor-bound, but not nonspecifically internalized, antigens. These results suggest that elements of the early endosome-recycling pathway play an important and selective role in physiologically relevant forms of antigen processing in B cells.
Bad Can Act as a Key Regulator of  T Cell Apoptosis and T Cell Development
Authors: Mok Chen-Lang , Gil-Gómez Gabriel , Williams Owen , Coles Mark , Taga Samir , Tolaini Mauro , Norton Trisha , Kioussis Dimitris , Brady Hugh J.M.
Published: July 2002

Bad is a distant relative of Bcl-2 and acts to promote cell death. Here, we show that Bad expression levels are greatly increased in thymocytes during apoptosis. We generated bad transgenic mice to study the action of upregulated Bad expression on T cell apoptosis. The T cells from these mice are highly sensitive to apoptotic stimuli, including anti-CD95. The numbers of T cells are greatly depleted and the processes of T cell development and selection are perturbed. We show that the proapoptotic function of Bad in primary T cells is regulated by Akt kinase and that Bad overexpression enhances both cell cycle progression and interleukin 2 production after T cell activation. These data suggest that Bad can act as a key regulator of T cell apoptosis and that this is a consequence of its upregulation after exposure to death stimuli.
Salmonella-Induced Apoptosis of Infected Macrophages Results in Presentation of a Bacteria-Encoded Antigen after Uptake by Bystander Dendritic Cells
Authors: Yrlid Ulf , Wick Mary Jo
Published: July 2002

Salmonella typhimurium is a gram-negative bacterium that survives and replicates inside vacuolar compartments of macrophages. Infection of macrophages with S. typhimurium grown under conditions allowing expression of the type III secretion system results in apoptotic death of the infected cells. Here, we show that infection of bone marrow–derived macrophages (MΦ) with wild-type S. typhimurium 14028 results in presentation of epitopes derived from a bacteria-encoded antigen on major histocompatibility complex (MHC) class I and MHC class II molecules after internalization of apoptotic MΦ by bystander dendritic cells (DCs). In contrast, infection of MΦ with the phoP constitutive mutant strain CS022, which does not induce apoptosis in infected MΦ, does not result in presentation of a bacteria-derived antigen by bystander DCs unless the infected MΦ are induced to undergo apoptosis by treatment with lipopolysaccharide and ATP. DCs appear to be unique in their ability to present antigens derived from MΦ induced to undergo apoptosis by Salmonella, as bystander MΦ are not capable of presenting the bacteria-derived antigen despite the fact that they efficiently internalize the apoptotic cells. These data suggest that apoptosis induction by bacterial infection of MΦ may not be a quiescent death that allows the bacteria to escape recognition by the immune system, but rather may contribute to an antimicrobial immune response upon engulfment by bystander DCs.
Targeted Disruption of the Leukotriene B4Receptor in Mice Reveals Its Role in Inflammation and Platelet-Activating Factor–Induced Anaphylaxis
Authors: Haribabu Bodduluri , Verghese Margrith W. , Steeber Douglas A. , Sellars Dwight D. , Bock Cheryl B. , Snyderman Ralph
Published: July 2002

Leukotrienes are derived from arachidonic acid and serve as mediators of inflammation and immediate hypersensitivity. Leukotriene B4 (LTB4) and leukotriene C4 (LTC4) act through G protein–coupled receptors LTB4 receptor (BLTR) and Cys-LTR, respectively. To investigate the physiological role of BLTR, we produced mice with a targeted disruption of the BLTR gene. Mice deficient for BLTR (BLTR−/−) developed normally and had no apparent hematopoietic abnormalities. Peritoneal neutrophils from BLTR−/− mice displayed normal responses to the inflammatory mediators C5a and platelet-activating factor (PAF) but did not respond to LTB4 for calcium mobilization or chemotaxis. Additionally, LTB4 elicited peritoneal neutrophil influx in control but not in BLTR−/− mice. Thus, BLTR is the sole receptor for LTB4-induced inflammation in mice. Neutrophil influx in a peritonitis model and acute ear inflammation in response to arachidonic acid was significantly reduced in BLTR−/− mice. In mice, intravenous administration of PAF induces immediate lethal anaphylaxis. Surprisingly, female BLTR−/− mice displayed selective survival (6 of 9; P = 0.002) relative to male (1 of 11) mice of PAF-induced anaphylaxis. These results demonstrate the role of BLTR in leukotriene-mediated acute inflammation and an unexpected sex-related involvement in PAF-induced anaphylaxis.
Identification of a Crucial Energetic Footprint on the α1 Helix of Human Histocompatibility Leukocyte Antigen (Hla)-A2 That Provides Functional Interactions for Recognition by Tax Peptide/Hla-A2–Specific T Cell Receptors
Authors: Baker Brian M. , Turner Richard V. , Gagnon Susan J. , Wiley Don C. , Biddison William E.
Published: July 2002

Structural studies have shown that class I major histocompatibility complex (MHC)-restricted peptide-specific T cell receptor (TCR)-α/βs make multiple contacts with the α1 and α2 helices of the MHC, but it is unclear which or how many of these interactions contribute to functional binding. We have addressed this question by performing single amino acid mutagenesis of the 15 TCR contact sites on the human histocompatibility leukocyte antigen (HLA)-A2 molecule recognized by the A6 TCR specific for the Tax peptide presented by HLA-A2. The results demonstrate that mutagenesis of only three amino acids (R65, K66, and A69) that are clustered on the α1 helix affected T cell recognition of the Tax/HLA-A2 complex. At least one of these three mutants affected T cell recognition by every member of a large panel of Tax/HLA-A2–specific T cell lines. Biacore measurements showed that these three HLA-A2 mutations also altered A6 TCR binding kinetics, reducing binding affinity. These results show that for Tax/HLA-A2–specific TCRs, there is a location on the central portion of the α1 helix that provides interactions crucial to their function with the MHC molecule.
Structural Comparison of Allogeneic and Syngeneic T Cell Receptor–Peptide-Major Histocompatibility Complex Complexes
Authors: Luz John G. , Huang Mingdong , Garcia K. Christopher , Rudolph Markus G. , Apostolopoulos Vasso , Teyton Luc , Wilson Ian A.
Published: July 2002

The crystal structures of the 2C/H-2Kbm3–dEV8 allogeneic complex at 2.4 Å and H-2Kbm3–dEV8 at 2.15 Å, when compared with their syngeneic counterparts, elucidate structural changes that induce an alloresponse. The Asp77Ser mutation that imbues H-2Kbm3–dEV8 with its alloreactive properties is located beneath the peptide and does not directly contact the T cell receptor (TCR). However, the buried mutation induces local rearrangement of the peptide itself to preserve hydrogen bonding interactions between the peptide and the α1 77 residue. The COOH terminus of the peptide main chain is tugged toward the α1-helix such that its presentation to the TCR is altered. These changes increase the stability of the allogeneic peptide-major histocompatibility complex (pMHC) complex and increase complementarity in the TCR–pMHC interface, placing greater emphasis on recognition of the pMHC by the TCR β-chain, evinced by an increase in shape complementarity, buried surface area, and number of TCR–pMHC contacting residues. A nearly fourfold increase in the number of β-chain–pMHC contacts is accompanied by a concomitant 64% increase in β-chain–pMHC shape complementarity. Thus, the allogeneic mutation causes the same peptide to be presented differently, temporally and spatially, by the allogeneic and syngeneic MHCs.
Escaping High Viral Load Exhaustion
Authors: Reignat Stephanie , Webster George J.M. , Brown David , Ogg Graham S. , King Abigail , Seneviratne Suranjith L. , Dusheiko Geoff , Williams Roger , Maini Mala K. , Bertoletti Antonio
Published: July 2002

Deletion, anergy, and a spectrum of functional impairments can affect virus-specific CD8 cells in chronic viral infections. Here we characterize a low frequency population of CD8 cells present in chronic hepatitis B virus (HBV) infection which survive in the face of a high quantity of viral antigen. Although they do not appear to exert immunological pressure in vivo, these CD8 cells are not classically “tolerant” since they proliferate, lyse, and produce antiviral cytokines in vitro. They are characterized by altered HLA/peptide tetramer reactivity, which is not explained by TCR down-regulation or reduced functional avidity and which can be reversed with repetitive stimulation. CD8 cells with altered tetramer binding appear to have a specificity restricted to envelope antigen and not to other HBV antigens, suggesting that mechanisms of CD8 cell dysfunction are differentially regulated according to the antigenic form and presentation of individual viral antigens.
Sialic Acid Binding Domains of CD22 Are Required For Negative Regulation of B Cell Receptor Signaling
Authors: Jin Lei , McLean Paul A. , Neel Benjamin G. , Wortis Henry H.
Published: July 2002

CD22, a negative regulator of B cell antigen receptor signaling, binds glycoconjugates terminating in α2, 6 sialic acid. The physiological ligand(s) for CD22 remain unknown. We asked whether the sialic acid binding domains are necessary for CD22 to function as a negative regulator. We generated two mutants that lack sialic acid binding activity and expressed them in a novel CD22−/− murine B cell line. Anti-IgM activated B cells expressing either CD22 mutant had greater Ca2+ responses than cells expressing wild-type CD22. Each variant also had reduced CD22 tyrosine phosphorylation and Src homology 2 domain–containing protein tyrosine phosphatase-1 association. These data suggest that the α2, 6 sialic acid ligand binding activity of CD22 is critical for its negative regulatory functions.
Light Adaptation in Pecten Hyperpolarizing Photoreceptors
Authors: Gomez Maria del Pilar , Nasi Enrico
Published: July 2002

The ability of scallop hyperpolarizing photoreceptors to respond without attenuation to repetitive flashes, together with their low light sensitivity, lack of resolvable quantum bumps and fast photoresponse kinetics, had prompted the suggestion that these cells may be constitutively in a state akin to light adaptation. We here demonstrate that their photocurrent displays all manifestations of sensory adaptation: (a) The response amplitude to a test flash is decreased in a graded way by background or conditioning lights. This attenuation of the response develops with a time constant of 200–800 ms, inversely related to background intensity. (b) Adapting stimuli shift the stimulus-response curve and reduce the size of the saturating photocurrent. (c) The fall kinetics of the photoresponse are accelerated by light adaptation, and the roll-off of the modulation transfer function is displaced to higher frequencies. This light-induced desensitization exhibits a rapid recovery, on the order of a few seconds. Based on the notion that Ca mediates light adaptation in other cells, we examined the consequences of manipulating this ion. Removal of external Ca reversibly increased the photocurrent amplitude, without affecting light sensitivity, photoresponse kinetics, or susceptibility to background adaptation; the effect, therefore, concerns ion permeation, rather than the regulation of the visual response. Intracellular dialysis with 10 mM BAPTA did not reduce the peak-to-plateau decay of the photocurrent elicited by prolonged light steps, not the background-induced compression of the response amplitude range and the acceleration of its kinetics. Conversely, high levels of buffered free [Ca]i (10 μM) only marginally shifted the sensitivity curve (Δσ = 0.3 log) and spared all manifestations of light adaptation. These results indicate that hyperpolarizing invertebrate photoreceptors adapt to light, but the underlying mechanisms must utilize pathways that are largely independent of changes in cytosolic Ca. The results are discussed in terms of aspects of commonalty to other ciliary sensory receptor cells.
Separation for kernels of Hankel operators
Authors: Gu Caixing
Published: July 2002

We prove that for two Hankel operators

H

a

1

H_{a_{1}}

and

H

a

2

H_{a_{2}}

on the Hardy space of the unit disk either the kernel of

H

a

1

∗

H

a

2

H_{a_{1}}^{*}H_{a_{2}}

equals the kernel of

H

a

2

H_{a_{2}}

or the kernel of

H

a

2

∗

H

a

1

H_{a_{2}}^{*}H_{a_{1}}

equals the kernel of

H

a

1

H_{a_{1}}

. In fact we prove a version of the above result for products of an arbitrary finite number of Hankel operators. Some immediate corollaries are generalizations of the result of Brown and Halmos on zero products of two Hankel operators and the result of Axler, Chang and Sarason on finite rank products of two Hankel operators. Simple examples show our results are sharp.
Strassen theorems for a class of iterated processes
Authors: Csáki Endre , Földes Antónia , Révész Pál
Published: July 2002

A general direct Strassen theorem is proved for a class of stochastic processes and applied for iterated processes such as

W
(

L
t

)

W(L_t)

, where

W
(
⋅
)

W(\cdot )

is a standard Wiener process and

L
.

L_.

is a local time of a Lévy process independent from

W
(
⋅
)

W(\cdot )

.
Banach spaces with the Daugavet property
Authors: Kadets Vladimir , Shvidkoy Roman , Sirotkin Gleb , Werner Dirk
Published: July 2002

A Banach space

X
X

is said to have the Daugavet property if every operator

T
:
X
→
X

T: X\to X

of rank 

1
1

satisfies

‖
Id
+
T
‖
=
1
+
‖
T
‖

\|\operatorname {Id}+T\| = 1+\|T\|

. We show that then every weakly compact operator satisfies this equation as well and that

X
X

contains a copy of

ℓ

1

\ell _{1}

. However,

X
X

need not contain a copy of

L

1

L_{1}

. We also study pairs of spaces

X
⊂
Y

X\subset Y

and operators

T
:
X
→
Y

T: X\to Y

satisfying

‖
J
+
T
‖
=
1
+
‖
T
‖

\|J+T\|=1+\|T\|

, where

J
:
X
→
Y

J: X\to Y

is the natural embedding. This leads to the result that a Banach space with the Daugavet property does not embed into a space with an unconditional basis. In another direction, we investigate spaces where the set of operators with

‖
Id
+
T
‖
=
1
+
‖
T
‖

\|\operatorname {Id}+T\|=1+\|T\|

is as small as possible and give characterisations in terms of a smoothness condition.
Approximation of continuous time stochastic processes by a local linearization method
Authors: Shoji Isao
Published: July 2002

This paper investigates the rate of convergence of an alternative approximation method for stochastic differential equations. The rates of convergence of the one-step and multi-step approximation errors are proved to be

O
(
(
Δ
t

)
2

)

O((\Delta t)^2)

and

O
(
Δ
t
)

O(\Delta t)

in the

L
p

L_p

sense respectively, where

Δ
t

\Delta t

is discrete time interval. The rate of convergence of the one-step approximation error is improved as compared with methods assuming the value of Brownian motion to be known only at discrete time. Through numerical experiments, the rate of convergence of the multi-step approximation error is seen to be much faster than in the conventional method.
Approximation of the vibration modes of a plate by Reissner-Mindlin equations
Authors: Durán R. , Hervella-Nieto L. , Liberman E. , Hervella-Nieto L. , Solomin J.
Published: July 2002

This paper deals with the approximation of the vibration modes of a plate modelled by the Reissner-Mindlin equations. It is well known that, in order to avoid locking, some kind of reduced integration or mixed interpolation has to be used when solving these equations by finite element methods. In particular, one of the most widely used procedures is the mixed interpolation tensorial components, based on the family of elements called MITC. We use the lowest order method of this family. Applying a general approximation theory for spectral problems, we obtain optimal order error estimates for the eigenvectors and the eigenvalues. Under mild assumptions, these estimates are valid with constants independent of the plate thickness. The optimal double order for the eigenvalues is derived from a corresponding

L
2

L^2

-estimate for a load problem which is proven here. This optimal order

L
2

L^2

-estimate is of interest in itself. Finally, we present several numerical examples showing the very good behavior of the numerical procedure even in some cases not covered by our theory.
Character formulas for tilting modules over Kac-Moody algebras
Authors: Soergel Wolfgang
Published: July 2002

We show how to express the characters of tilting modules in a (possibly parabolic) category

O

\mathcal {O}

over a Kac-Moody algebra in terms of the characters of simple highest weight modules. This settles, in lots of cases, Conjecture 7.2 of Kazhdan-Lusztig-Polynome and eine Kombinatorik für Kipp-Moduln, Representation Theory (An electronic Journal of the AMS) (1997), by the author, describing the character of tilting modules for quantum groups at roots of unity.
Prediction of eukaryotic mRNA translational properties.
Authors: Kochetov A V , Ponomarenko M P , Frolov A S , Kisselev L L , Kolchanov N A
Published: July 2002

MOTIVATION: It is well known that eukaryotic mRNAs are translated at different levels depending on their sequence characteristics. Evaluation of mRNA translatability is of importance in prediction of the gene expression pattern by computer methods and to improve the recognition of mRNAs within cloned nucleotide sequences. It may also be used in biotechnological experiments to optimize the expression of foreign genes in transgenic organisms. RESULTS: The sets of 5' untranslated region characteristics, significantly different between mRNAs encoding abundant and scarce polypeptides, were determined for mammals, dicot plants and monocot plants, and collected in the LEADER_RNA database. Computer tools for the prediction of mRNA translatability are presented. AVAILABILITY: Programs for mRNA translatability prediction are available at http://wwwmgs.bionet.nsc. ru/programs/acts2/mo_mRNA.htm (for monocots), http://wwwmgs.bionet. nsc.ru/programs/acts2/di_mRNA.htm (for dicots) and http://wwwmgs. bionet.nsc.ru/programs/acts2/ma_mRNA.htm (for mammals). The LEADER_RNA database may be accessed at: http://wwwmgs.bionet.nsc. ru/systems/LeaderRNA/.
Analysis of conservation and substitutions of secondary

structure elements within protein superfamilies
Authors: Mizuguchi Kenji , Blundell Tom L.
Published: July 2002

Motivation: Structural alignments of superfamily members often exhibit insertions and deletions of secondary structure elements (SSEs), yet conserved subsets of SSEs appear to be important for maintaining the fold and facilitating common functionalities.

Results: A database of aligned SSEs was constructed from the structure-based alignments of protein superfamily members in the CAMPASS database. SSEs were classified into several types on the basis of their length and solvent accessibility and counts were made for the replacements of SSEs in different types at structurally aligned positions. The results, summarized as log-odds substitution matrices, can be used for two types of comparisons: (1) structure against structure, both with secondary structure assignments; and (2) structure against sequence with predicted secondary structures. The conservation of SSEs at each alignment position was defined as the deviation of observed SSE frequencies from the uniform distribution. This offers a useful resource to define and examine the core of superfamily folds. Even when the structure of only a single member of a superfamily is known, the extended method can be used to predict the conservation of SSEs. Such information will be useful when modelling the structure of other members of a superfamily or identifying structurally and functionally important positions in the fold.

Availability: The database is available on the world wide web at http://www-cryst.bioc.cam.ac.uk/~kenji/ssdb/. The conservation of SSEs was translated into colour values and can be visualized through the web interface.

Contact: kenji@cryst.bioc.cam.ac.uk

* To whom correspondence should be addressed.
Mini‐ and microsatellite expansions: the recombination connection
Authors: Richard Guy‐Franck , Pâques Frédéric
Published: July 2002

It is widely accepted that the large trinucleotide repeat expansions observed in many neurological diseases occur during replication. However, genetic recombination has emerged as a major source of instability for tandem repeats, including minisatellites, and recent studies raise the possibility that it may also be responsible for trinucleotide repeat expansions. We will review data connecting tandem repeat rearrangements and recombination in humans and in eukaryotic model organisms, and discuss the possible role of recombination in trinucleotide repeat expansions in human neurological disorders.
Spatial heterogeneity in three species, plant–parasite–hyperparasite, systems
Authors: White K. A. J. , Gilligan C. A.
Published: July 2002

This paper addresses the question of how heterogeneity may evolve due to interactions between the dynamics and movement of three–species systems involving hosts, parasites and hyperparasites in homogeneous environments. The models are motivated by the spread of soil–borne parasites within plant populations, where the hyperparasite is used as a biological control agent but where patchiness in the distribution of the parasite occurs, even when environmental conditions are apparently homogeneous. However, the models are introduced in generic form as three–species reaction–diffusion systems so that they have broad applicability to a range of ecological systems. We establish necessary criteria for the occurrence of population–driven patterning via diffusion–driven instability. Sufficient conditions are obtained for restricted cases with no host movement. The criteria are similar to those for the well–documented two–species reaction–diffusion system, although more possibilities arise for spatial patterning with three species. In particular, temporally varying patterns, that may be responsible for the apparent drifting of hot–spots of disease and periodic occurrence of disease at a given location, are possible when three species interact. We propose that the criteria can be used to screen population interactions, to distinguish those that cannot cause patterning from those that may give rise to population–driven patterning. This establishes a basic dynamical ‘landscape’ against which other perturbations, including environmentally driven variations, can be analysed and distinguished from population–driven patterns. By applying the theory to a specific model example for host–parasite–hyperparasite interactions both with and without host movement, we show directly how the evolution of spatial pattern is related to biologically meaningful parameters. In particular, we demonstrate that when there is strong density dependence limiting host growth, the pattern is stable over time, whereas with less stable underlying host growth, the pattern varies with time.