bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct cadherin-activated cell signaling
Authors: Yap Alpha S. , Kovacs Eva M.
Published: January 2003

Classical cadherin adhesion molecules are key determinants of cell recognition and tissue morphogenesis, with diverse effects on cell behavior. Recent developments indicate that classical cadherins are adhesion-activated signaling receptors. In particular, early–immediate Rac signaling is emerging as a mechanism to coordinate cadherin–actin integration at the plasma membrane.
Natural Killer Cell Inhibitory Receptors Block Actin Cytoskeleton-dependent Recruitment of 2B4 (CD244) to Lipid Rafts
Authors: Watzl Carsten , Long Eric O.
Published: January 2003

A dynamic balance of positive and negative signals regulates target cell lysis by natural killer (NK) cells upon engagement of a variety of different activation receptors and of inhibitory receptors that recruit the tyrosine phosphatase SHP-1. However, the step at which activation signals are blocked by SHP-1 is not known. We have been using activation receptor 2B4 (CD244) to study the influence of inhibitory receptors on NK cell activation. Engagement of inhibitory receptors by HLA class I on target cells blocks phosphorylation of 2B4, placing the inhibitory step at the level, or upstream of 2B4 phosphorylation. Here we show that phosphorylated 2B4, after engagement with either antibodies or target cells that express the 2B4 ligand, is found exclusively in a detergent-resistant membrane fraction that contains lipid rafts. Integrity of lipid rafts was essential for phosphorylation and activating function of 2B4. Coengagement of inhibitory receptors blocked 2B4 phosphorylation and 2B4 association with detergent-resistant membranes, indicating that inhibitory receptors function upstream of raft-dependent signals. Recruitment of 2B4 into detergent-resistant membrane fractions and 2B4 phosphorylation were dependent on actin polymerization. Blocking actin cytoskeleton-dependent raft recruitment of different receptors may be a general mechanism by which inhibitory receptors control NK cell activation.
Enhanced B Cell Expansion, Survival, and Humoral Responses by Targeting Death Receptor 6
Authors: Schmidt Clint S. , Liu Jinqi , Zhang Tonghai , Song Ho Yeong , Sandusky George , Mintze Karen , Benschop Robert J. , Glasebrook Andrew , Yang Derek D. , Na Songqing
Published: January 2003

Targeted disruption of death receptor (DR)6 results in enhanced CD4+ T cell expansion and T helper cell type 2 differentiation after stimulation. Similar to T cells, DR6 is expressed on resting B cells but is down-regulated upon activation. We examined DR6−/− B cell responses both in vitro and in vivo. In vitro, DR6−/− B cells undergo increased proliferation in response to anti–immunoglobulin M, anti-CD40, and lipopolysaccharide. This hyperproliferative response was due, at least in part, to both increased cell division and reduced cell apoptosis when compared with wild-type B cells. Consistent with these observations, increased nuclear levels and activity of nuclear factor κB transcription factor, c-Rel, and elevated Bcl-xl expression were observed in DR6−/− B cells upon stimulation. In addition, DR6−/− B cells exhibited higher surface levels of CD86 upon activation and were more effective as antigen-presenting cells in an allogeneic T cell proliferation response. DR6−/− mice exhibited enhanced germinal center formation and increased titers of immunoglobulins to T-dependent as well as T-independent type I and II antigens. This is the first demonstration of a regulatory role of DR6 in the activation and function of B cells.
Secondary Heavy Chain Rearrangement
Authors: Sekiguchi Debora R. , Eisenberg Robert A. , Weigert Martin
Published: January 2003

The chronic graft-versus-host (cGVH) reaction results in a syndrome that closely resembles systemic lupus erythematosus (SLE). It is induced in nonautoimmune mice by the transfer of alloreactive T cells. The availability of anti-DNA transgenes allows us to study the genetic origins of autoantibodies in this model. We induced cGVH in two anti-DNA H chain site-directed transgenic mouse strains. This resulted in clonal expansion and selection of specific mutations in the anti–double-stranded (ds) DNA B cell population. These data, together with a high frequency of anti-dsDNA B cell clones recovered as hybridomas, suggested that anti-dsDNAs are the product of an antigen-driven immune response. Genetic analysis associated this response with the generation of anti-dsDNA B cells through secondary rearrangements that replaced the site-directed transgene (sd-tg) with endogenous VH genes.
Mycobacteria Target DC-SIGN to Suppress Dendritic Cell Function
Authors: Geijtenbeek Teunis B.H. , van Vliet Sandra J. , Koppel Estella A. , Sanchez-Hernandez Marta , Vandenbroucke-Grauls Christine M.J.E. , Appelmelk Ben , van Kooyk Yvette
Published: January 2003

Mycobacterium tuberculosis represents a world-wide health risk and immunosuppression is a particular problem in M. tuberculosis infections. Although macrophages are primarily infected, dendritic cells (DCs) are important in inducing cellular immune responses against M. tuberculosis. We hypothesized that DCs represent a target for M. tuberculosis and that the observed immuno-suppression results from modulation of DC functions. We demonstrate that the DC-specific C-type lectin DC-SIGN is an important receptor on DCs that captures and internalizes intact Mycobacterium bovis bacillus Calmette-Guérin (BCG) through the mycobacterial cell wall component ManLAM. Antibodies against DC-SIGN block M. bovis BCG infection of DCs. ManLAM is also secreted by M. tuberculosis–infected macrophages and has been implicated as a virulence factor. Strikingly, ManLAM binding to DC-SIGN prevents mycobacteria- or LPS-induced DC maturation. Both mycobacteria and LPS induce DC maturation through Toll-like receptor (TLR) signaling, suggesting that DC-SIGN, upon binding of ManLAM, interferes with TLR-mediated signals. Blocking antibodies against DC-SIGN reverse the ManLAM-mediated immunosuppressive effects. Our results suggest that M. tuberculosis targets DC-SIGN both to infect DCs and to down-regulate DC-mediated immune responses. Moreover, we demonstrate that DC-SIGN has a broader pathogen recognition profile than previously shown, suggesting that DC-SIGN may represent a molecular target for clinical intervention in infections other than HIV-1.
CD4+CD25+ TR Cells Suppress Innate Immune Pathology Through Cytokine-dependent Mechanisms
Authors: Maloy Kevin J. , Salaun Laurence , Cahill Rachel , Dougan Gordon , Saunders Nigel J. , Powrie Fiona
Published: January 2003

CD4+CD25+ regulatory T (TR) cells can inhibit a variety of autoimmune and inflammatory diseases, but the precise mechanisms by which they suppress immune responses in vivo remain unresolved. Here, we have used Helicobacter hepaticus infection of T cell–reconstituted recombination-activating gene (RAG)−/− mice as a model to study the ability of CD4+CD25+ TR cells to inhibit bacterially triggered intestinal inflammation. H. hepaticus infection elicited both T cell-mediated and T cell–independent intestinal inflammation, both of which were inhibited by adoptively transferred CD4+CD25+ TR cells. T cell–independent pathology was accompanied by activation of the innate immune system that was also inhibited by CD4+CD25+ TR cells. Suppression of innate immune pathology was dependent on T cell–derived interleukin 10 and also on the production of transforming growth factor β. Thus, CD4+CD25+ TR cells do not only suppress adaptive T cell responses, but are also able to control pathology mediated by innate immune mechanisms.
CD28 Costimulation Is Required for In Vivo Induction of Peripheral Tolerance in CD8 T Cells
Authors: Vacchio Melanie S. , Hodes Richard J.
Published: January 2003

Whereas ligation of CD28 is known to provide a critical costimulatory signal for activation of CD4 T cells, the requirement for CD28 as a costimulatory signal during activation of CD8 cells is less well defined. Even less is known about the involvement of CD28 signals during peripheral tolerance induction in CD8 T cells. In this study, comparison of T cell responses from CD28-deficient and CD28 wild-type H-Y–specific T cell receptor transgenic mice reveals that CD8 cells can proliferate, secrete cytokines, and generate cytotoxic T lymphocytes efficiently in the absence of CD28 costimulation in vitro. Surprisingly, using pregnancy as a model to study the H-Y–specific response of maternal T cells in the presence or absence of CD28 costimulation in vivo, it was found that peripheral tolerance does not occur in CD28KO pregnants in contrast to the partial clonal deletion and hyporesponsiveness of remaining T cells observed in CD28WT pregnants. These data demonstrate for the first time that CD28 is critical for tolerance induction of CD8 T cells, contrasting markedly with CD28 independence of in vitro activation, and suggest that the role of CD28/B7 interactions in peripheral tolerance of CD8 T cells may differ significantly from that of CD4 T cells.
THE MULTI-VARIABLE ALEXANDER POLYNOMIAL OF LENS BRAIDS
Authors: CHBILI NAFAA
Published: January 2003

Let n ≥ 2 be an integer and ℬn the n-braid group. A braid β ∈ ℬn is said to be a (p,s)-lens braid if there exists α ∈ ℬn such that β = αp(σ1 σ2 … σn-1)ns. In this paper we use the multi-variable Alexander polynomial to find a necessary condition for a braid to be a (p,s)-lens braid, for p prime. Our main tool here is the multi-variable Burau representation of the n-braid group.
CLASSES OF WIRING DIAGRAMS AND THEIR INVARIANTS
Authors: GARBER DAVID , TEICHER MINA , VISHNE UZI
Published: January 2003

Wiring diagrams usually serve as a tool in the study of arrangements of lines and pseudolines. Here we go in the opposite direction, using known properties of line arrangements to motivate certain equivalence relations and actions on sets of wiring diagrams, which preserve the incidence lattice and the fundamental groups of the affine and projective complements of the diagrams.

These actions are used in [GTV] to classify real arrangements of up to 8 lines and show that in this case, the incidence lattice determines both the affine and the projective fundamental groups.
ON THE RECOGNITION OF BRAIDS
Authors: GAIFULLIN ALEXANDER A. , MANTUROV VASSILY O.
Published: January 2003

A simple complete combinatorial invariant for elements of the braid group is found. It admits some generalizations, e.g. a complete invariant of spherical braids and a complete invariant of cylindrical braids. Values of the invariants are well recognizable, i.e., they provide the complete algorithmic classification of elements in the named braid groups.
THE CANONICAL GENUS OF WHITEHEAD DOUBLES OF A FAMILY TORUS KNOTS
Authors: TRIPP JAMES J.
Published: January 2003

In this paper, we show that gc(Km, n) - g(Km, n) = 2mn for m, n ∈ N, where Km, n is the connected sum of m copies of any Whitehead double of the (2n + 1, 2) torus knot.
AN ELEMENTARY SET FOR θn-CURVE PROJECTIONS
Authors: HUH YOUNGSIK , JIN GYO TAEK , OH SEUNGSANG
Published: January 2003

A finite set of nontrivial θn-curves is shown to be minimal among those which produce all projections of nontrivial θn-curves.
THE CULLER-SHALEN SEMINORMS OF THE (-2, 3, n) PRETZEL KNOT
Authors: MATTMAN THOMAS W.
Published: January 2003

We show that the [Formula: see text]-character variety of the (-2, 3, n) pretzel knot consists of two (respectively three) algebraic curves when 3 ∤ n (respectively 3 | n) and given an explicit calculation of the Culler-Shalem seminorms of these curves. Using this calculation, we describe the fundamental polygon and Newton polygon for these knots and give a list of Dehn surgerise yielding a manifold with finite or cyclic fundamental group. This constitutes a new proof of property P for these knots.
AN INTRODUCTION TO QUANTUM COIN TOSSING
Authors: DÖSCHER C. , KEYL M.
Published: January 2003

We review the quantum version of a well known problem of cryptography called coin tossing ("flipping a coin via telephone"). It can be regarded as a game where two remote players (who distrust each other) try to generate a uniformly distributed random bit which is common to both parties. The only resource they can use to perform this task is a classical or quantum communication channel. In this paper we provide a general overview over such coin tossing protocols, concerning in particular their security.
MINOR MARRIAGES AND KHIYĀR AL-BULŪGH IN OTTOMAN PALESTINE: A NOTE ON WOMEN'S STRATEGIES IN A PATRIARCHAL SOCIETY
Authors: Yazbak Mahmoud
Published: January 2003

Sharī'a court records (sijills) are legal documents that summarize discussions that took place in the courtroom. They also contain a wealth of detail on various aspects of Muslim society. Drawing on different sijills from nineteenth-century Palestine and fatwās of Khayr al-Dīn al-Ramlī, I examine the phenomenon of child marriage and the practice of khiyār al-bulūgh, literally "option of puberty". If a natural guardian contracts a marriage for a minor child, male or female, the child may not subsequently have the contract annulled. Whereas a boy enjoys the right to divorce his wife through the mechanism of talāq as soon as he reaches his majority, a girl who reaches her majority must approach the court if she wants to dissolve a marriage (faskh), and she may do so only if she was married while a minor by a non-natural guardian. In this case, she may exercise her right of khiyār al-bulūgh immediately upon reaching her legal majority, i.e., at the onset of her first menstruation. But she must make a public declaration of the occurrence of menstruation so that the persons who hear the declaration may serve as witnesses on her behalf.
WOMEN IN DAMASCENE FAMILIES AROUND 1700
Authors: Pascual Jean-Paul , Establet Colette
Published: January 2003

449 inventories of deceased Damascenes around 1700 help us to approach a subject which is related to gender studies, since it allows us to compare the economic, social and even cultural domains of feminine and masculine worlds. In this society, the social differences were still signi cant, and women received a patrimony which was clearly inferior to that of men. It consisted of certain items: some real estate, but primarily jewelry and domestic goods. There are few objects that indicate public activities by women and which match men's inventories of this period. Women ruled, with more or less variety and fantasy, the furniture of the house which was used not only for rest and sleep, but also as a venue for receiving guests. 449 inventaires après décès damascènes, vers 1700, aident à aborder un sujet qui s'inscrit dans les gender studies, en permettant la comparaison entre le monde féminin et le monde masculin, dans le domaine économique, social, voire culturel. Dans cette société, où les différences sociales restent déterminantes, les femmes possèdent un patrimoine nettement inférieur à celui des hommes et dont les éléments sont bien particuliers: quelques biens immobiliers, mais avant tout des bijoux et des biens domestiques. Peu d'objets qui ouvrent vers le monde et le temps: les femmes dominent, avec plus ou moins de variété et de fantaisie, l'intérieur textile de la maison destiné aux fonctions du repos, du sommeil, mais aussi de la réception.
LE CONTRAT D'AFFRÈTEMENT MARITIME EN MÉDITERRANÉE: DROIT MARITIME ET PRATIQUE COMMERCIALE ENTRE ISLAM ET CHRÉTIENTÉ (XVIIe-XVIIIe SIÈCLES)
Authors: Panzac Daniel
Published: January 2003

From the end of the 17th to the beginning of the 19th century, the domestic Ottoman seaborne trade was largely ensured by European merchantmen chartered by Muslims traders. This practice suggests that the written contracts, signed by both partners, were consistent with the islamic law. This study will analyse these contracts and confront them with the principles and rules of the Islamic maritime law, elaborated since the upper Middle Ages, in order to evaluate the influence of the Islamic law upon the Christian maritime law which made it acceptable by Muslims. De la fin du XVIIe au début du XIXe siècle, le commerce maritime à l'intérieur de l'Empire ottoman a principalement été assuré par des navires européens affrétés par des négociants musulmans. Cette pratique suggère que les contrats écrits, signés par les deux parties, étaient compatibles avec le droit musulman. Cette étude se propose d'analyser ces contrats et de les comparer avec les principes et les règles du droit maritime musulman, élaboré depuis le haut Moyen-Age. L'importance de son influence sur le droit maritime chrétien explique pourquoi celui-ci est devenu acceptable par des musulmans.
The Speed of Fright: Temporal Dramas in Dante's Inferno
Authors: Costa Dennis
Published: January 2003

This article is in two parts. It opens with a synoptic view of how Dante-poet connects the particular purview of his fictive character (whom critics typically name 'Dante-pilgrim') with a worldview - a philosophical theology, a cosmology and an ethics - shared fairly commonly among Christian intellectuals in the late Middle Ages. This worldview includes certain general assumptions about the nature of time and some detailed ideas about how a human person, an individual psyche, is contextualized by time. Included are some reflections on the medieval figure of the cosmos as God's "book" and of divine creativity and providence as a 'narrative' art. Dante, particularly in the Paradiso, is perhaps the greatest elaborator of that figure. The article's second part is a detailed textual analysis of the episode of the barrators (those who illicitly offer or receive political favors) in Inferno XXII-XXIII. A psychology of uncertainty and terror is dramatized poetically in these cantos in terms of the differences (and some likenesses) between one trapped sinner's experience of time and the pilgrim's participation in it. Virgil's guidance, fidelity and extraordinary discernment are also figured by Dante in temporal terms.
CANIS LUPUS COSMOPOLIS: WOLVES IN A COSMOPOLITAN WORLDVIEW
Authors: Lynn William
Published: January 2003

The subject of wolf recovery in North America sparks heated controversy, both for and against. This paper explores how this subject is informed by cosmopolitan worldviews. These worldviews pull nature and culture into a common orbit of ethical meaning, with implications for the normative relationships that ought to pertain in landscapes shared by people and wolves. This theoretical outlook is illustrated using the controversy over wolves in the northeastern region of the United States. I conclude with a set of reflections on theorizing the cosmopolis, the interpretation of cosmopolitan landscapes, and living with cosmopolitan wolves.
Uniformity and representation of taxonomic and other characters and semi-automatic extraction using computer tools
Authors: Fortuner Renaud
Published: January 2003

A uniform decomposition of morphological-anatomical characters is proposed, based on results from the GENISYS project. Each character is decomposed into a 'structure' (organs and organ parts), a basic property of this structure, and possible states or values of the character. This decomposition can be applied to any character without enforcing any limitations to data entry by biologists. It is shown that a tool ('Terminator') based on this decomposition can be used for semi-automatic extraction of characters from published descriptions or from new data entry. If built, such a tool can be used to populate a database with the decomposed characters. This database could be used with existing computer identification or systematics tools. The same approach can be applied to the decomposition of other kinds of data, including molecular and physiological data. This would create sets of interrelated databases housing various types of knowledge on biodiversity.
Species delimitation and nematode biodiversity: phylogenies rule
Authors: Nadler Steven
Published: January 2003

Practitioners of nematode taxonomy have rarely been explicit about what species represent or how data are being used to delimit species prior to their description. This lack of explicitness reflects the broader species problem common to all biology: there is no universally accepted idea of what species are and, as a consequence, scientists disagree on how to go about finding species in nature. However, like other biologists, nematologists seem to agree that species are real and discrete units in nature, and that they result from descent with modification. This evolutionary perspective provides a conceptual framework for nematologists to view species as independent evolutionary lineages, and provides approaches for their delimitation. Specifically, species may be delimited scientifically by methods that can test the hypothesis of lineage independence. For sequence data, such hypothesis testing should be based on sampling many individual organisms for multiple loci to avoid mistaking tokogeny and gene trees as evidence of species. Evolutionary approaches to analysing data and delimiting species avoid the inherent pitfalls in approaches that use all observed sequence differences to define species through calculation of a genetic distance. To illustrate evolutionary species delimitation, molecular data are used to test the hypothesis that hookworms parasitic in northern fur seals and in California sea lions represent separate species. The advantages and potential caveats of employing nucleotide sequence data for species delimitation are discussed, and the merits of evolutionary approaches are contrasted to inherent problems in similarity-based methods.
Tbx5is essential for forelimb bud initiation following patterning of the limb field in the mouse embryo
Authors: Agarwal Pooja , Wylie John N. , Galceran Juan , Arkhitko Oksana , Li Cuiling , Deng Chuxia , Grosschedl Rudolf , Bruneau Benoit G.
Published: January 2003

Transcriptional cascades responsible for initiating the formation of vertebrate embryonic structures such as limbs are not well established. Limb formation occurs as a result of interplay between fibroblast growth factor(FGF) and Wnt signaling. What initiates these signaling cascades and thus limb bud outgrowth at defined locations along the anteroposterior axis of the embryo is not known. The T-box transcription factor TBX5 is important for normal heart and limb formation, but its role in early limb development is not well defined. We report that mouse embryos lacking Tbx5 do not form forelimb buds, although the patterning of the lateral plate mesoderm into the limb field is intact. Tbx5 is not essential for an early establishment of forelimb versus hindlimb identity. In the absence ofTbx5, the FGF and Wnt regulatory loops required for limb bud outgrowth are not established, including initiation of Fgf10expression. Tbx5 directly activates the Fgf10 gene via a conserved binding site, providing a simple and direct mechanism for limb bud initiation. Lef1/Tcf1-dependent Wnt signaling is not essential for initiation ofTbx5 or Fgf10 transcription, but is required in concert withTbx5 for maintenance of normal levels of Fgf10 expression. We conclude that Tbx5 is not essential for the early establishment of the limb field in the lateral plate mesoderm but is a primary and direct initiator of forelimb bud formation. These data suggest common pathways for the differentiation and growth of embryonic structures downstream of T-box genes.
Cell autonomous requirement for PDGFRα in populations of cranial and cardiac neural crest cells
Authors: Tallquist Michelle D. , Soriano Philippe
Published: January 2003

Cardiac and cephalic neural crest cells (NCCs) are essential components of the craniofacial and aortic arch mesenchyme. Genetic disruption of the platelet-derived growth factor receptor α (PDGFRα) results in defects in multiple tissues in the mouse, including neural crest derivatives contributing to the frontonasal process and the aortic arch. Using chimeric analysis, we show that loss of the receptor in NCCs renders them inefficient at contributing to the cranial mesenchyme. Conditional gene ablation in NCCs results in neonatal lethality because of aortic arch defects and a severely cleft palate. The conotruncal defects are first observed at E11.5 and are consistent with aberrant NCC development in the third, fourth and sixth branchial arches, while the bone malformations present in the frontonasal process and skull coincide with defects of NCCs from the first to third branchial arches. Changes in cell proliferation, migration, or survival were not observed in PDGFRα NCC conditional embryos, suggesting that the PDGFRα may play a role in a later stage of NCC development. Our results demonstrate that the PDGFRα plays an essential, cell-autonomous role in the development of cardiac and cephalic NCCs and provides a model for the study of aberrant NCC development.
Functional subdivision of trunk visceral mesoderm parasegments inDrosophilais required for gut and trachea development
Authors: Hosono Chie , Takaira Katsumi , Matsuda Ryo , Saigo Kaoru
Published: January 2003

In Drosophila, trunk visceral mesoderm, a derivative of dorsal mesoderm, gives rise to circular visceral muscles. It has been demonstrated that the trunk visceral mesoderm parasegment is subdivided into at least two domains by connectin expression, which is regulated by Hedgehog and Wingless emanating from the ectoderm. We now extend these findings by examining a greater number of visceral mesodermal genes, includinghedgehog and branchless. Each visceral mesodermal parasegment appears to be divided into five or six regions, based on differences in expression patterns of these genes. Ectodermal Hedgehog and Wingless differentially regulate the expression of these metameric targets in trunk visceral mesoderm. hedgehog expression in trunk visceral mesoderm is responsible for maintaining its own expression and conexpression. hedgehog expressed in visceral mesoderm parasegment 3 may also be required for normal decapentaplegic expression in this region and normal gastric caecum development. branchless expressed in each trunk visceral mesodermal parasegment serves as a guide for the initial budding of tracheal visceral branches. The metameric pattern of trunk visceral mesoderm, organized in response to ectodermal instructive signals, is thus maintained at a later time via autoregulation, is required for midgut morphogenesis and exerts feedback effect on trachea, ectodermal derivatives.
Wnt2b controls retinal cell differentiation at the ciliary marginal zone
Authors: Kubo Fumi , Takeichi Masatoshi , Nakagawa Shinichi
Published: January 2003

The ciliary marginal zone of the vertebrate retina contains undifferentiated progenitor cells that continue to proliferate and add new neurons and glia peripherally during the embryonic stages — even after the formation of a functional retina. To understand the molecular mechanism that controls the prolonged progenitor cell proliferation in the ciliary marginal zone, we employed a candidate molecule approach, focusing on Wnt2b(formerly know as Wnt13), which is expressed in the marginal most tip of the retina. Frizzled 4 and 5, seven-pass transmembrane Wnt receptors, were expressed in the peripheral and central part of the retina, respectively. LEF1, a downstream Wnt signaling component, was expressed at high levels in the ciliary marginal zone with expression gradually decreasing towards the central retina. The LEF1-expressing region, which is where Wnt signaling is supposedly activated, expressed a set of molecular markers that are characteristic of the progenitor cells in the ciliary marginal zone. Overexpression of Wnt2b by use of in ovo electroporation in the central retina inhibited neuronal differentiation and induced the progenitor cell markers. Blocking of the Wnt downstream signaling pathway by a dominant-negative LEF1 inhibited proliferation of the cells in the marginal area, which resulted in their premature neuronal differentiation. The progenitor cells in the ciliary marginal zone differentiated into all the neuronal and glial cell types when cultured in vitro, and they proliferated for a longer period than did centrally located progenitor cells that underwent a limited number of cell divisions. In addition, the proliferation of these progenitor cells was promoted in the presence of Wnt2b. These results suggest that Wnt2b functions to maintain undifferentiated progenitor cells in the ciliary marginal zone,and thus serves as a putative stem cell factor in the retina.
Identification of spatial and temporal cues that regulate postembryonic expression of axon maintenance factors in theC. elegansventral nerve cord
Authors: Aurelio Oscar , Boulin Thomas , Hobert Oliver
Published: January 2003

Patterns of gene expression are under precise spatial and temporal control. A particularly striking example is represented by several members of thezig gene family, which code for secreted immunoglobulin domain proteins required for maintaining ventral nerve cord organization inCaenorhabditis elegans. These genes are coordinately expressed in a single interneuron in the ventral nerve cord, known as PVT. Their expression is initiated at a precise postembryonic stage, long after PVT has been generated in mid-embryogenesis. We define spatial and temporal cues that are required for the precise regulation of zig gene expression. We find that two LIM homeobox genes, the Lhx3-class gene ceh-14 and the Lmx-class gene lim-6 are coordinately required for ziggene expression in PVT. Temporal control of zig gene expression is conferred by the heterochronic gene lin-14, a nuclear factor previously implicated in developmental timing in various contexts. Loss of thelim-6 and ceh-14 transcription factors and the developmental timer lin-14 cause not only a loss of zig gene expression but also lead to defects in the maintenance of ventral nerve cord architecture. Overriding the normal spatiotemporal control of ziggene expression through expression of one of the zig genes under control of heterologous promoters also causes axon patterning defects in the ventral nerve cord. Our findings illustrate the importance of spatial and temporal control of gene expression in the nervous system and, furthermore,implicate heterochronic genes in postmitotic neural patterning events.
Requirements for transcriptional repression and activation by Engrailed inDrosophilaembryos
Authors: Alexandre Cyrille , Vincent Jean-Paul
Published: January 2003

Genetic analysis shows that Engrailed (En), a homeodomain-containing transcription factor, has both negative and positive targets. Negative regulation is expected from a factor that has a well-defined repressor domain but activation is harder to comprehend. We used VP16En, a form of En that had its repressor domain replaced by the activation domain of VP16, to show that En activates targets using two parallel routes, by repressing a repressor and by being a bona fide activator. We identified the intermediate repressor activity as being encoded by sloppy paired 1 and 2 and showed that bona fide activation is dramatically enhanced by Wingless signaling. Thus, En is a bifunctional transcription factor and the recruitment of additional cofactors presumably specifies which function prevails on an individual promoter. Extradenticle (Exd) is a cofactor thought to be required for activation by Hox proteins. However, in thoracic segments, Exd is required for repression (as well as activation) by En. This is consistent with in vitro results showing that Exd is involved in recognition of positive and negative targets. Moreover, we provide genetic evidence that, in abdominal segments,Ubx and Abd-A, two homeotic proteins not previously thought to participate in the segmentation cascade, are also involved in the repression of target genes by En. We suggest that, like Exd, Ubx and Abd-A could help En recognize target genes or activate the expression of factors that do so.
Engrailed cooperates withextradenticleandhomothoraxto repress target genes inDrosophila
Authors: Kobayashi Masatomo , Fujioka Miki , Tolkunova Elena N. , Deka Deepali , Abu-Shaar Muna , Mann Richard S. , Jaynes James B.
Published: January 2003

Engrailed is a key transcriptional regulator in the nervous system and in the maintenance of developmental boundaries in Drosophila, and its vertebrate homologs regulate brain and limb development. Here, we show that the functions of both of the Hox cofactors Extradenticle and Homothorax play essential roles in repression by Engrailed. Mutations that remove either of them abrogate the ability of Engrailed to repress its target genes in embryos,both cofactors interact directly with Engrailed, and both stimulate repression by Engrailed in cultured cells. We suggest a model in which Engrailed,Extradenticle and Homothorax function as a complex to repress Engrailed target genes. These studies expand the functional requirements forextradenticle and homothorax beyond the Hox proteins to a larger family of non-Hox homeodomain proteins.
Regulation of shoot epidermal cell differentiation by a pair of homeodomain proteins inArabidopsis
Authors: Abe Mitsutomo , Katsumata Hiroshi , Komeda Yoshibumi , Takahashi Taku
Published: January 2003

In higher plants, the outermost cell layer (L1) of the shoot apex gives rise to the epidermis of shoot organs. Our previous study demonstrated that an 8-bp motif named the L1 box functions as a cis-regulatory element for L1-specific gene expression in the shoot system of Arabidopsis. We show here that PROTODERMAL FACTOR2 (PDF2), a member of the HD-GL2 class of homeobox genes, is expressed exclusively in the L1 of shoot meristems and that recombinant PDF2 protein specifically binds to the L1 box in vitro. Although knockout mutants of PDF2 and ATML1,another L1-specific HD-GL2 class gene sharing the highest homology withPDF2, display normal shoot development, the double mutant results in severe defects in shoot epidermal cell differentiation. This suggests thatPDF2 and ATML1 are functionally interchangeable and play a critical role in maintaining the identity of L1 cells, possibly by interacting with their L1 box and those of downstream target-gene promoters.
Separable roles ofUFOduring floral development revealed by conditional restoration of gene function
Authors: Laufs Patrick , Coen Enrico , Kronenberger Jocelyne , Traas Jan , Doonan John
Published: January 2003

The UNUSUAL FLORAL ORGANS (UFO) gene is required for several aspects of floral development in Arabidopsis including specification of organ identity in the second and third whorls and the proper pattern of primordium initiation in the inner three whorls. UFO is expressed in a dynamic pattern during the early phases of flower development. Here we dissect the role of UFO by ubiquitously expressing it inufo loss-of-function flowers at different developmental stages and for various durations using an ethanol-inducible expression system. The previously known functions of UFO could be separated and related to its expression at specific stages of development. We show that a 24- to 48-hour period of UFO expression from floral stage 2, before any floral organs are visible, is sufficient to restore normal petal and stamen development. The earliest requirement for UFO is during stage 2, when the endogenous UFO gene is transiently expressed in the centre of the wild-type flower and is required to specify the initiation patterns of petal,stamen and carpel primordia. Petal and stamen identity is determined during stages 2 or 3, when UFO is normally expressed in the presumptive second and third whorl. Although endogenous UFO expression is absent from the stamen whorl from stage 4 onwards, stamen identity can be restored byUFO activation up to stage 6. We also observed floral phenotypes not observed in loss-of-function or constitutive gain-of-function backgrounds,revealing additional roles of UFO in outgrowth of petal primordia.
DrosophilaMBF1 is a co-activator for Tracheae Defective and contributes to the formation of tracheal and nervous systems
Authors: Liu Qing-Xin , Jindra Marek , Ueda Hitoshi , Hiromi Yasushi , Hirose Susumu
Published: January 2003

During gene activation, the effect of binding of transcription factors to cis-acting DNA sequences is transmitted to RNA polymerase by means of co-activators. Although co-activators contribute to the efficiency of transcription, their developmental roles are poorly understood. We usedDrosophila to conduct molecular and genetic dissection of an evolutionarily conserved but unique co-activator, Multiprotein Bridging Factor 1 (MBF1), in a multicellular organism. Through immunoprecipitation, MBF1 was found to form a ternary complex including MBF1, TATA-binding protein (TBP) and the bZIP protein Tracheae Defective (TDF)/Apontic. We have isolated aDrosophila mutant that lacks the mbf1 gene in which no stable association between TBP and TDF is detectable, and transcription of a TDF-dependent reporter gene is reduced by 80%. Although the null mutants ofmbf1 are viable, tdf becomes haploinsufficient inmbf1-deficient background, causing severe lesions in tracheae and the central nervous system, similar to those resulting from a complete loss oftdf function. These data demonstrate a crucial role of MBF1 in the development of tracheae and central nervous system.
The secreted Frizzled-related protein Sizzled functions as a negative feedback regulator of extreme ventral mesoderm
Authors: Collavin Licio , Kirschner Marc W.
Published: January 2003

The prevailing model of dorsal ventral patterning of the amphibian embryo predicts that the prospective mesoderm is regionalized at gastrulation in response to a gradient of signals. This gradient is established by diffusible BMP and Wnt inhibitors secreted dorsally in the Spemann organizer. An interesting question is whether ventrolateral tissue passively reads graded levels of ventralizing signals, or whether local self-organizing regulatory circuits may exist on the ventral side to control cell behavior and differentiation at a distance from the Organizer. We provide evidence thatsizzled, a secreted Frizzled-related protein expressed ventrally during and after gastrulation, functions in a negative feedback loop that limits allocation of mesodermal cells to the extreme ventral fate, with direct consequences for morphogenesis and formation of the blood islands. Morpholino-mediated knockdown of Sizzled protein results in expansion of ventral posterior mesoderm and the ventral blood islands, indicating that this negative regulation is required for proper patterning of the ventral mesoderm. The biochemical activity of sizzled is apparently very different from that of other secreted Frizzled-related proteins, and does not involve inhibition of Wnt8. Our data are consistent with the existence of some limited self-organizing properties of the extreme ventral mesoderm.
Inhibitory motor neurones supply body wall muscles in the locust abdomen
Authors: Schmäh Michael , Wolf Harald
Published: January 2003

Inhibitory motor neurones in the abdominal ganglia of the locust Locusta migratoria were identified by combining extra- and intracellular electrophysiology, labelling of motor neurones by peripheral nerve backfills, and immunocytochemistry directed against the inhibitory transmitter γ-aminobutyric acid. The fifth and sixth abdominal ganglia were studied in particular detail, although general findings were verified in all other abdominal segments.

In each abdominal ganglion half, there are two inhibitory motor neurones,CIa and CIb, which supply dorsal (CIa) and ventral (CIb) longitudinal muscles. Their cell bodies are located in the next anterior ganglion to where the axons leave the ventral nerve cord via nerve 1. Both inhibitors have contralateral somata in the posterior ventral soma cortex, looping primary neurites and bilateral dorsal arborisations. There are homonomous (segmentally homologous) motor neurones in the fused abdominal neuromeres, the thoracic ganglia, and at least the third subesophageal neuromere.

These body wall inhibitors are distinctly different from the limb muscle inhibitors, CI1-3, described previously. This is signified, for example, by the fact that both types of inhibitory motor neurones coexist in the prothoracic segment and innervate leg and body wall muscles,respectively.
Localization of the vacuolar-type ATPase in swimbladder gas gland cells of the European eel (Anguilla anguilla)
Authors: Boesch S. T. , Niederstätter H. , Pelster B.
Published: January 2003

The vacuolar ATPase is a multifunctional enzyme that consists of several subunits. Subunit B is part of the catalytic domain of the enzyme and is present in two isoforms in fish as well as in mammals. Possibly, these two isoforms — vatB1 (kidney isoform) and vatB2 (brain isoform) —serve different functions. A localization of the two isoforms was attempted in swimbladder gas gland cells of the European eel Anguilla anguilla by immunohistochemistry. Two antibodies were produced by immunization of rabbits with synthetic peptides. Specificity of the antibodies, on the one hand, an isoform-specific antibody for vatB1 and, on the other hand, an antibody that recognizes both isoforms (vatB1 and vatB2), was confirmed by western blot analysis using recombinant proteins produced in a bacterial expression system. The immunohistochemical localization with the antibody directed against both isoforms of the B subunit revealed a positive staining in apical membranes of swimbladder gas gland cells as well as in the basolateral membranes. Significant staining was observed in vesicles located near the apical membrane. Staining with the vatB1-specific antibody resulted in a similar picture in the apical region of the cells. In contrast to the staining with the first antibody, only a poor signal was observed in the basal region. The nature of the vesicles in the apical region of the gas gland cells was determined by using an antibody directed against surfactant protein D.
PPNDS is an agonist, not an antagonist, for the ATP receptor of Paramecium
Authors: Wood Christopher R. , Hennessey Todd M.
Published: January 2003

Paramecium represents a simple, eukaryotic model system to study the cellular effects of some neuroactive drugs. They respond to the agonistβ,γ-methylene ATP with a transient depolarizing receptor potential,Ca2+-based action potentials and repetitive bouts of forward and backward swimming called `avoiding reactions' (AR). In vivo[32P]ATP binding assays showed saturable [32P]ATP binding with an apparent Kd of approximately 23 nmol l-1. Prolonged (15 min) exposure to 25 μmol l-1β,γ-methylene ATP caused behavioral adaptation and losses of AR,ATP receptor potentials and [32P]ATP binding. While screening various ATP receptor inhibitors, we found that the P2X1 `antagonist'pyridoxal-phosphate naphthylazo-nitro-disulfate (PPNDS) is actually an agonist, producing the same responses as β,γ-methylene ATP.[32P]ATP binding assays suggest that both agonists may bind to the same site as [32P]ATP. Cross-adaptation is also seen between PPNDS and β,γ-methylene ATP in terms of losses in AR, depolarizing receptor potentials and [32P]ATP binding. We conclude that the inhibition caused by PPNDS in Paramecium is due to agonist-induced desensitization. Either this represents a unique new class of ATP receptors,in which PPNDS is an agonist instead of an antagonist, or PPNDS (and other drugs like it) may actually be an agonist in many other cell types in which prolonged exposure is necessary for inhibition.
Transcriptional initiation under conditions of anoxia-induced quiescence in mitochondria fromArtemia franciscanaembryos
Authors: Eads Brian D. , Hand Steven C.
Published: January 2003

In response to anoxia, embryos of the brine shrimp Artemia franciscana are able coordinately to downregulate metabolism to levels low enough to permit survival for several years at room temperature. In addition to dramatic decreases in free ATP levels and heat production,intracellular pH drops from 7.8 to 6.3 overnight. Use of isolated mitochondria to study transcriptional responses to anoxia offers several advantages: (1)the localized nature of transcript initiation, processing and degradation, all of which may be followed in organello; (2) the relatively simple cis-and trans-machinery involved and (3) the ability to provide relevant physiological treatments in vitro. In response to anoxic incubation of embryos in vivo for 4 h followed by anoxic mitochondrial isolation and anoxic transcription assay at pH 6.4, a significant decrease in overall UTP incorporation (77%) was seen after 30 min relative to normoxic, pH 7.9 controls. A less severe inhibition of transcription under anoxia (52%) was observed compared with controls when pH was raised to 7.9. Similarly, under normoxia, the incubation at low pH (6.4) reduced transcription by 59%. Ribonuclease protection assays showed that the contribution of in vitro initiation during the assay fell from 78% at pH 7.9 to approximately 32% at pH 6.4 under either normoxic or anoxic conditions. DNA footprinting of putative transcriptional promoters revealed proteins at regular intervals upstream of the 12S rRNA in the control region, which previously had been indirectly inferred to contain promoters for H-strand transcription. The area between 12 030 and 12 065 contains a sequence in the tRNAleu gene believed to bind the transcription termination factor mTERF or TERM, and we provide the first evidence that this sequence is protein-bound in A. franciscana. However, our hypothesis that initiation is reduced at low pH because of a change in DNA binding by mitochondrial transcription factors was not confirmed. We propose that regulation of initiation may be mediated by covalent modification or by protein—protein interactions not detected by footprinting.
The influence of beacon-aiming on the routes of wood ants
Authors: Graham Paul , Fauria Karine , Collett Thomas S.
Published: January 2003

Many insects have an innate propensity to approach conspicuous objects. We explore how such beacon aiming determines the shape of a wood ant's habitual route. We find that a single large black cylinder within an arena biases the route taken by ants as they run from a start position at one end of the arena to reach a feeder at the other. Ants learn a stable route with the first segment of their trajectory aimed at the cylinder, which becomes an intermediate goal on the way to the feeder. When in occasional tests the cylinder is removed or displaced, ants head for the usual site of the cylinder. They also aim for the same site when the cylinder is removed and the ant's normal start position is changed. This behaviour suggests that visual features of the arena are learnt from the vantage point of the cylinder and that this stored snapshot guides the ant to that site. Ants thus reinforce their ability to reach the cylinder by learning other visual features in their surroundings that can also steer them to its location. The use of beacon aiming in fixing routes has several benefits. Because the same path will be traversed on every trial, beacon aiming facilitates the acquisition of routes. Beacon aiming also increases the robustness of learnt routes: ants straying from the route will be attracted to the closest beacon and so regain their habitual paths.
Formation of Novel Phosphide Dichloride Zr Complex from Trichloride Zr Complex with a Secondary Phosphine-pendant Cyclopentadienyl Ligand: Structure of [{η5-C5H4(CH2)2PMes-κP}ZrCl2(N-methylimidazole)2] (Mes = 2,4,6-Trimethylphenyl)
Authors: Ishiyama Takeshi , Mizuta Tsutomu , Miyoshi Katsuhiko , Nakazawa Hiroshi
Published: January 2003

The reaction of [{η5-C5H4(CH2)2P(H)Mes-κP}ZrCl3(tht)] (1; Mes = 2,4,6-trimethylphenyl; tht = tetrahydrothiophene) with 1 equiv of NaCPh3, followed by treatment with N-methylimidazole gave a novel phosphide-pendant dichloride complex [{η5-C5H4(CH2)2PMes-κP}ZrCl2(N-methylimidazole)2] (4) with liberation of HCPh3. The product (4) is the first dichloride terminal phosphide Zr complex characterized by X-ray crystallographic analysis.