bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of neural crest competence territory: Role of Wnt signaling
Authors: Bastidas Francisco , De Calisto Jaime , Mayor Roberto 
Published: December 2003

AbstractIn recent years, research on neural crest induction has allowed the identification of several molecules as candidates for neural crest inducers. Although many of these molecules have the ability to induce neural crest in different assays, a general mechanism of neural crest induction that includes a description of the tissues that produce the inductive signals and the time and steps in which this process takes place remains elusive. To better understand the mechanism of neural crest induction, we developed an assay that has been used previously by Nieuwkoop to study anterior–posterior pattern of the neural plate. Folds of competent ectoderm were implanted in different positions of a young neurula embryo, and the induction of neural crest was analyzed using the expression of the neural crest marker Xslug. We identified a very localized region of the early neurula where it is possible to get neural crest induction, whereas all of the regions tested showed a clear induction of the neural plate marker Xsox2. These results indicate that there is a region in the embryo with the appropriate combination of signals needed to induce neural crest cells; we called this region the neural crest competence territory. In addition, our results show that neural crest induction is always accompanied by neural plate induction, but there are many cases where neural plate was induced without neural crest. These results support the model in which the neural crest is induced by an interaction between neural plate and epidermis, but they also suggest that additional signals are required. By making grafts of different sizes and implanting them in the epidermis or the neural plate, we concluded that one of the inductive signals is produced in the dorsal region of the embryo and travels into the ectoderm. Finally, by performing gain‐ and loss‐of‐function of Wnt signaling experiments, we show that this pathway plays an important role not only in neural crest induction but also in the specification of the neural crest competence territory. Developmental Dynamics 229:109–117, 2004. © 2003 Wiley‐Liss, Inc.
Slow degeneration of zebrafish Rohon‐Beard neurons during programmed cell death
Authors: Reyes Rosario , Haendel Melissa , Grant Deanna , Melancon Ellie , Eisen Judith S. 
Published: December 2003

AbstractRohon‐Beard cells are large, mechanosensory neurons located in the dorsal spinal cord of anamniote vertebrates. In most species studied to date, these cells die during development. We followed labeled Rohon‐Beard cells in living zebrafish embryos and found that they degenerate slowly, over many days. During degeneration, the soma shrinks and finally disappears, and the processes become beady in appearance and finally break apart, but they do not retract. Zebrafish Rohon‐Beard cells apparently fragment their DNA, as revealed by terminal deoxynucleotidyl transferase‐mediated dUTP nick end‐labeling (TUNEL) labeling, before undergoing degenerative morphologic changes. We also followed the development of labeled dorsal root ganglion neurons, as they are developing at the same stages that Rohon‐Beard cells are degenerating. We found that, although axons of both cell types extend into similar regions, Rohon‐Beard cells degenerate normally in mutants lacking dorsal root ganglia, providing evidence that interactions between the two cell types are not responsible for Rohon‐Beard cell degeneration. Developmental Dynamics 229:30–41,2004. © 2003 Wiley‐Liss, Inc.
Long‐distance cue from emerging dermis stimulates neural crest melanoblast migration
Authors: Tosney Kathryn W. 
Published: December 2003

AbstractNeural crest melanoblasts display unique navigational abilities enabling them to colonize the dorsal path between ectoderm and somite. One signal shown here to elicit melanoblast migration is a chemotactic cue supplied by the emerging dermis. Until dermis emerges, melanoblasts fail to enter the dorsal path. The dermis emerges from a site that is too distant to stimulate migration by cell contact. Instead, surgeries show that dermis elicits migration from a distance. When dermis is grafted distally, neural crest cells enter the path precociously. Moreover, large grafts recruit melanoblasts from the control sides (without increasing crest cell numbers) as well as a few crest cells from ventral somite. Because other grafted tissues fail to stimulate migration, the dermis stimulus is specific. This report is the first documentation that trunk neural crest cells can be guided chemotactically. It also extends evidence that migration is exquisitely sensitive to temporal–spatial patterns of somite morphogenesis. Developmental Dynamics 229:99–108, 2004. © 2003 Wiley‐Liss, Inc.
Skeletal and pigment cell defects in the lockjaw mutant reveal multiple roles for zebrafish tfap2a in neural crest development
Authors: Knight Robert D. , Javidan Yashar , Nelson Sarah , Zhang Tailin , Schilling Thomas 
Published: December 2003

AbstractMembers of the AP‐2 transcription factor family have critical roles in many aspects of embryonic development. The zebrafish tfap2a mutant lockjaw (low) displays defects in skeletal and pigment cell derivatives of the neural crest. Here we show essential roles for tfap2a in subsets of embryonic cartilages and pigment cells. Defects in cartilage of the hyoid arch in low correlate with a loss of Hox group 2 gene expression and are suggestive of a transformation to a mandibular fate. In contrast, loss of joints in the mandibular arch and defects in certain types of pigment cells suggest a requirement for tfap2a independent of Hox regulation. Early melanophores do not develop in low mutants, and we propose that this results in part from a loss of kit function, leading to defects in migration, as well as kit‐independent defects in melanophore specification. Iridophores are also reduced in low, in contrast to xanthophores, revealing a role for tfap2a in the development of pigment subpopulations. We propose a model of tfap2a function in the neural crest in which there are independent functions for tfap2a in specification of subpopulations of pigment cells and segmental patterning of the pharyngeal skeleton through the regulation of Hox genes. Developmental Dynamics 229:87–98, 2004. © 2003 Wiley‐Liss, Inc.
Multiple roles of Sox2, an HMG‐box transcription factor in avian neural crest development
Authors: Wakamatsu Yoshio , Endo Yukinori , Osumi Noriko , Weston James A. 
Published: December 2003

AbstractExpression of Sox2, which encodes an HMG‐box–type transcription factor, is down‐regulated in the neural plate when neural crest segregates from dorsal neural tube and remains low during crest cell migration. Sox2 expression is subsequently up‐regulated in some crest‐derived cells in the developing peripheral nervous system and is later restricted to glial sublineages. Misexpression of Sox2 and mutant forms of Sox2 both in neural plate explants and in embryonic ectoderm reveals that Sox2 inhibits neural crest formation as a transcriptional activator. Similar manipulation of Sox2 function in migratory and postmigratory neural crest‐derived cells indicates that Sox2 regulates proliferation and differentiation in developing peripheral nervous system. Developmental Dynamics 229:74–86, 2004. © 2003 Wiley‐Liss, Inc.
Weathering and biokarst development on marine terraces, northwest Morocco
Authors: Duane Michael J. , AL‐Mishwat Ali T. , Rafique Mohammed 
Published: December 2003

AbstractWeathering features are described from an arid coastal area in northern Morocco which are indicative of invasive chasmolithic and endolithic microbial communities. Active weathering of marine terraces and karst development is associated with endolithic and epilithic algae responsible for boring, disintegration of matrix and mineral fabrics, solution and biomineralization that undermines the marine carbonate platform. Evidence of a range of biological weathering agents remains preserved, speciﬁcally calciﬁed ﬁlaments and sporangial material. An abundance of ﬁlaments and spores representative of a consortium of algae, fungi, cyanobacteria and lichens is associated with the most denuded outcrops. The array of microbes contributes to the formation of the stromatolites to depths of 0·5 m within the limestone substrate. The preservation of stromatolites is supported by calciﬁcation of spores and ﬁlaments, with trapping and binding of carbonate held in suspension by vadose waters. The pervasive weathering on this sector of coastline has important practical implications for coastal planning and development authorities in Morocco. Copyright © 2003 John Wiley & Sons, Ltd.
Processes of tidal channel development in salt and freshwater marshes
Authors: Perillo Gerardo M. E. , Iribarne Oscar O. 
Published: December 2003

AbstractMechanisms for the formation of creeks in tidal ﬂats are rarely discussed in literature. There are some general theories about their formation but there are no data to support the evidence. It is generally believed that marshes inherit creeks from previous tidal ﬂats that their plants colonize and further modify them. The aim of this paper is to present three mutually exclusive cases from marshes in Argentina where creeks are formed by either purely physical or biological–physical interactions. Except for Loyola Bay, this is the ﬁrst discussion of these mechanisms. They may represent special cases, but the fact that all three of them occur along the coast of Argentina, could indicate that similar cases may be found somewhere else. Copyright © 2003 John Wiley & Sons, Ltd.
Surface particle sizes on armoured gravel streambeds: effects of supply and hydraulics
Authors: Whiting Peter J. , King John G. 
Published: December 2003

AbstractMost gravel‐bed streams exhibit a surface armour in which the median grain size of the surface particles is coarser than that of the subsurface particles. This armour has been interpreted to result when the supply of sediment is less than the ability of the stream to move sediment. While there may be certain sizes in the bed for which the supply is less than the ability of the stream to transport these sizes, for other sizes of particles the supply may match or even exceed the ability of the channel to transport these particles. These sizes of particles are called ‘supply‐limited’ and ‘hydraulically limited’ in their transport, respectively, and can be differentiated in dimensionless sediment transport rating curves by size fractions. The supply‐ and hydraulically limited sizes can be distinguished also by comparing the size of particles of the surface and subsurface. Those sizes that are supply‐limited are winnowed from the bed and are under‐represented in the surface layer. Progressive truncation of the surface and subsurface size distributions from the ﬁne end and recalculation until the size distributions are similar (collapse), establishes the break between supply‐ and hydraulically limited sizes. At sites along 12 streams in Idaho ranging in drainage area from about 100 to 4900 km2, sediment transport rating curves by size class and surface and subsurface size distributions were examined. The break between sizes that were supply‐ and hydraulically limited as determined by examination of the transport rate and surface and subsurface size distributions was similar. The collapse size as described by its percentile in the cumulative size distribution averaged D36 of the surface and D73 of the subsurface. The discharge at which the collapse size began to move averaged 88 per cent of bankfull discharge. The collapse size decreased as bed load yield increased and increased with the degree of selective transport. Copyright © 2003 John Wiley & Sons, Ltd.
The influence of parent material on topsoil geochemistry in eastern England
Authors: Rawlins B. G. , Webster R. , Lister T. R. 
Published: December 2003

AbstractThe topsoil of around 10 000 km2 in eastern England has recently been sampled intensely at 4609 sites to characterize its geochemistry. The parent materials, which include both solid geology and Quaternary sediments, range in age from Permian to Holocene. The distributions of the concentrations of major and trace elements have been characterized geostatistically, and the role of parent material on their spatial structure (anisotropy) and their spatial relationships (coregionalization) have been investigated.Analysis of variance with the sites grouped by major parent material type showed that this classiﬁcation accounted for 14 to 48 per cent of the variance for the various elements. Global variograms of 13 elements (Al, As, Ca, Cr, Cu, Fe, Mg, Mo, Ni, P, Pb, Ti, and U) have been computed and modelled. Eleven of the variograms seem to comprise two structures, both of which we modelled with spherical functions, one of short range, 3·5 to 9 km, and the other with a range of 15 to 23 km. The models included a nugget variance, which varied from 27 per cent (for As, Fe, and Mg) to 63 per cent (for P) of the total. The long‐range structures are related to the separations of the major parent materials.The variograms of several elements showed appreciable anisotropy, most notably that of Mg. Anisotropy is evident at short ranges of less than 5 km. This accords with the geological structure of the beds which dip from west to east so that their outcrops are elongated from north to south. A linear model of coregionalization ﬁtted to the data emphasized several important geochemical associations, which we interpret. Elements commonly associated with clay minerals (Mg, Al) and the clay size fraction (Ti) are dominated by the long‐range structure of the coregionalization, whilst several trace elements (As, Cr, Ni and U) are spatially correlated with Fe over short distances, through adsorption of the former on the surfaces of Fe oxyhydroxides.The topsoil around large urban areas is enriched in lead, but it is not clear whether anthropogenic sources are responsible for this metal's anomalous spatial relationships with other elements. Crown copyright © 2003. Reproduced with the permission of Her Majesty's Stationery Ofﬁce. Published by John Wiley & Sons, Ltd.
Sphenopteris coemansiAndrae – neue, aussagefähige Funde
Authors: Daber R. 
Published: December 2003

AbstractIm Ergebnis paläobotanischer Geländearbeit im Saarbecken wurden zwei Stücke von Sphenopteris coemansi Andrae entdeckt, die nunmehr Spheno‐pteris coemansi und Sphenopteris lanceolata besser vergleichen lassen. Diese beiden nahestehenden Arten unterscheiden sich in der Form und in der Anzahl der Blättchen (der Fiedern letzter Ordnung) im Wedel, was meine Abbildungen dokumentieren. Wenn jemand über Sphenopteris coemansi Genaueres erfahren möchte, so sollte er die Abbildung, die Andrae 1865 veröffentlichte, und ergänzend dazu diese beiden im Saarbecken gemachten Funde betrachten.
Notes on South American Valerianaceae I
Authors: Weberling F. 
Published: December 2003

AbstractA new species of Belonanthus, Belonanthus theodorici sp. nova, is described. It is characterized by spathulate foliage leaves, the ovate blades of which are rather distinctly contracted into a long and narrow sheathing petiole and bear a dense covering with long hairs, giving the surface of the rosette a silvery sheen. In the monothyrsoid inflorescence the peduncles (hypopodia) of the lower partial inflorescences are considerably elongated. – Valeriana micropterina Wedd., V. poterioides Graebn., V. thalictroides Graebn. and V. aspleniifolia Killip are included into Valeriana microptera. – For Valeriana fonkii Phil. and V. radicalis Clos reliable distinctive characters are named. – For Valeriana decussata Ruiz & Pav. virescent calices with green sepals are described and illustrated.
Vergleichende Untersuchungen zur Sprossvariation bei PlectranthusL'Herit. (Lamiaceae)
Authors: Pohlheim F. 
Published: December 2003

AbstractDrei Periklinalchimären von Plectranthus forsteri Benth. wurden analysiert. Typ 1 und Typ 2 sind Trichimären. Typ 3 ist eine Monektochimäre. Konstitutionen in L1, L2, L3: Typ 1: weiß/normalwüchsig – hellgrün/normalwüchsig – grün/normalwüchsig; Typ 2: weiß/normalwüchsig – weiß/wachstumsgehemmt – grün/normalwüchsig, Typ 3: weiß/normalwüchsig – grün/normalwüchsig – grün/normalwüchsig. Es wird gezeigt, dass perikline Teilungen in sich entwickelnden Epidermen gehäuft auftreten, wenn L1 von einer wachstumsgehemmten L2‐Komponente unterlagert ist.
On the occurrence of non‐axillary ovules in Tetraclinis articulata (Vahl) Mast. (Cupressaceae s.str.)
Authors: Jagel A. , Stützel Th. 
Published: December 2003

AbstractThe cone morphology in Tetraclinis was studied to elucidate the taxonomic position of the genus. A careful analysis of the cone development shows that the characters used as arguments for an affiliation within Callitroideae are superficial and of little taxonomic significance. The developmental patterns indicate a position of Tetraclinis within Cupressoideae. Tetraclinis displays ovules inserted directly at the distal end of the cone axis and not born in the axil of a seed scale as recently shown for Juniperus (Schulz et al. 2003) and Microbiota (Jagel & Stützel 2001b). The close relationship between Tetraclinis, Juniperus and Cupressus as suggested by Saxton (1913) based on embryological data, by Gadek & Quinn (1985) based on biflavones and by Gadek et al. (2000) based on DNS‐sequences is supported by the morphological data presented here. Conflicting morphological concepts or morphological trees (e.g. Gadek et al. 2000) are in parts weakly supported and suffer either from ambiguous coding of morphological data or are based on historical morphological errors. To calculate reliable morphological trees, however, requires data of similar quality and cannot be achieved by using data which are tailed to the use in effective diagnostic keys.
The distribution of the vegetation in the Uvs‐nuur basin and its surrounding mountain ranges
Authors: Hilbig W. 
Published: December 2003

AbstractThe paper informs on the distribution and the ecological and altitudinal conditions of the plant communities which characterize the vegetation in the Uvs‐nuur basin and the surrounding mountain ranges. This is shown by means of three vegetation profiles extending from North to South in the western, middle and eastern part of the territory belonging to the Uvs Aymak (Mongolia) and – in the North – to the Republic of Tuva (Russian Federation).The manifold vegetation is represented in the center of the basin at 760 m above sea level by water, reed, salt, and meadow communities. The semi desert vegetation (800–1000 m) turns to steppe vegetation (900–1400 m), which occurs from the inner part of the basin till the sand areas in the East and the foothills of the mountain ranges. Plant communities of the ruderal and weed vegetation can be met in the settlements and on arable fields. Larch forests together with meadow steppes characterize the landscape from 1600 till 2300 m, the first predominant in northern, the latter in southern exposition. The alpine belt above 2300 m is represented by stands of Dryas oxyodonta and alpine Kobresia meadows, which are followed from 2600 m by high alpine cushion vegetation.
Stability and slightly supercritical oscillatory regimes of natural convection in a 8:1 cavity: solution of the benchmark problem by a global Galerkin method
Authors: Gelfgat Alexander Yu. 
Published: December 2003

AbstractThe global Galerkin method is applied to the benchmark problem that considers an oscillatory regime of convection of air in a tall two‐dimensional rectangular cavity. The three most unstable modes of the linearized system of the Boussinesq equations are studied. The converged values of the critical Rayleigh numbers together with the corresponding oscillation frequencies are calculated for each mode. The oscillatory flow regimes corresponding to each of the three modes are approximated asymptotically. No direct time integration is applied. Good agreement with the previously published results obtained by solution of the time‐dependent Boussinesq equations is reported. Copyright © 2004 John Wiley & Sons, Ltd.
Wenn kleine Organismen große Wirkung zeigen
Authors: Lange Otto L. 
Published: December 2003

AbstractIn allen warmen und kalten Trockengebieten der Erde gibt es lebende Bodenkrusten. Sie bilden nicht nur bemerkenswert ausdauernde Lebensgemeinschaften, sondern schützen den Boden effektiv vor Erosion durch Wind oder Wasser
Der Rhesusaffe und die Vermehrungsstrategie
Authors: Schmidtke Jörg , Nürnberg Peter , Krawczak Michael 
Published: December 2003

AbstractDas Rhesusaffenmännchen verlässt seine Geburtsgruppe, um sich fortzupflanzen. Auf der „Affeninsel”︁ Cayo Santiago bei Puerto Rico machten sich Forscher auf die Suche nach dem Gen, das das Wanderverhalten von Primaten steuert
Der Griff in die Computerwelt
Authors: Schmidt Günther 
Published: December 2003

AbstractBei Computerspielen oder anderen multimedialen Anwendungen erhält der Nutzer ausschließlich visuelle und akustische Sinneseindrücke. Neuartige Tastdisplays helfen, auch Berührungsreize zu vermitteln, was die Grundlage für ein wirklichkeitsnahes „Begreifen”︁ am Computer legt
Eine Hand voll Technik mit Fingerspitzengefühl
Authors: Meuser Marcell , Murrenhoff Hubertus 
Published: December 2003

AbstractOb als Prothese oder Roboterhand — Künstliche Hände werden für eine Vielzahl von Anwendungen benötigt. Eine neue, mit Druckluft betriebene Roboterhand zeichnet sich durch besondere Greif‐ und Haltemöglichkeiten aus
Precursor‐Directed Biosynthesis: Stereospecificity for Branched‐Chain Diketides of the β‐Ketoacyl‐ACP Synthase Domain 2 of 6‐Deoxyerythronolide B Synthase
Authors: Kinoshita Kenji , Khosla Chaitan , Cane David E. 
Published: December 2003

AbstractModular polyketide synthases such as 6‐deoxyerythronolide B synthase (DEBS) catalyze the biosynthesis of structurally complex natural products. Streptomyces coelicolor CH999/pJRJ2 harbors a plasmid encoding DEBS(KS10), a mutant form of 6‐deoxyerythronolide B synthase that is blocked in the formation of 6‐deoxyerythronolide B (1, 6‐dEB) due to a mutation in the active site of the ketosynthase (KS1) domain that normally catalyzes the first polyketide chain‐elongation step of 6‐dEB biosynthesis. Administration of (2S,3R,4S)‐ and (2S,3R,4R)‐3‐hydroxy‐2,4‐dimethylhexanoic acid N‐acetylcysteamine (SNAC) thioesters (= S‐[2‐(acetylamino)ethyl] (2S,3R,4S)‐ and (2S,3R,4R)‐3‐hydroxy‐2,4‐dimethylhexanethioates) 3 and 4 in separate experiments to cultures of Streptomyces coelicolor CH999/pJRJ2 led to production of the corresponding (14S)‐ and (14R)‐14‐methyl analogues of 6‐dEB, 10 and 11, respectively. Unexpectedly, when a 3 : 2 mixture of 4 and 3 was fed under the same conditions, exclusively branched‐chain macrolactone 11 was isolated. In similar experiments, feeding of 3 and 4 to S. coelicolor CH999/pCK16, an engineered strain harboring DEBS1+TE(KS10), resulted in formation of the branched‐chain triketide lactones 13 and 14, while feeding of the 3 : 2 mixture of 4 and 3 gave exclusively 14. The biochemical basis for this stereochemical discrimination was established by using purified DEBS module 2+TE to determine the steady‐state kinetic parameters for 3 and 4, with the kcat/KM for 4 shown to be sevenfold greater than that of 3.