Common Junctions Research Articles

Lycat and cloche at the Switch Between Blood Vessel Growth and Differentiation?

See related article, pages 1057–1064 The formation of the cardiovascular system starts in the mouse embryo at approximately embryonic day (E)7.0 to E7.5. The first blood vessels in the extraembryonic membranes, the major intraembryonic vessels, and the heart form by vasculogenesis, the in situ differentiation of mesodermal cells that give rise to “blood-islands.” The latter are composed of hemangioblasts, the common precursors of endothelial and blood cells. Hemangioblasts situated in the lumen of the blood islands will further differentiate into hematocytoblasts, the precursors of all 3 lineages of blood cells. In contrast, hemangioblasts lining the walls of the blood islands will give rise to angioblasts that form endothelial cells.1 Migrating angioblasts from the proximal lateral mesoderm assemble symmetrically at the lateral sides of the embryo to establish 2 preendocardial tubes. They fuse to give rise to the primordial heart.2 While vasculogenesis is still proceeding, the uniform blood islands begin to remodel to a network of large and small vessels by the process of angiogenesis, preferentially intussusceptive microvascular growth.3,4 Gene expression and targeting studies have identified vascular endothelial growth factor and its 2 receptors, KDR/flk-1 and flt-1, as critical for the formation and early remodeling of the blood islands. Vascular endothelial growth factor is produced by endodermal and mesodermal cells at the onset of hemangioblast formation, whereas its receptors are expressed in the future endothelial cells lining the blood islands.5 Flk-1−/− embryos lack blood islands throughout the embryo and yolk sac.6 In flt-1−/− embryos, blood islands do not properly remodel but form large blood channels.7 Inactivation of a single vascular endothelial growth factor allele caused multiple embryonic malformations including the heart, rudimentary dorsal aortae, and a reduced number of blood cells.8,9 All deletions were lethal between days E8.5 and E11 to …

Selective Desulfurization of Cysteine in the Presence of Cys(Acm) in Polypeptides Obtained by Native Chemical Ligation

Increased versatility for the synthesis of proteins and peptides by native chemical ligation requires the ability to ligate at positions other than Cys. Here, we report that Raney nickel can be used under standard conditions for the selective desulfurization of Cys in the presence of Cys(Acm). This simple and practical tactic enables the more common Xaa-Ala junctions to be used as ligation sites for the chemical synthesis of Cys-containing peptides and proteins. [reaction: see text].

The interactive online SKY/M‐FISH & CGH Database and the Entrez Cancer Chromosomes search database: Linkage of chromosomal aberrations with the genome sequence

To catalog data on chromosomal aberrations in cancer derived from emerging molecular cytogenetic techniques and to integrate these data with genome maps, we have established two resources, the NCI and NCBI SKY/M-FISH & CGH Database and the Cancer Chromosomes database. The goal of the former is to allow investigators to submit and analyze clinical and research cytogenetic data. It contains a karyotype parser tool, which automatically converts the ISCN short-form karyotype into an internal representation displayed in detailed form and as a colored ideogram with band overlay, and also has a tool to compare CGH profiles from multiple cases. The Cancer Chromosomes database integrates the SKY/M-FISH & CGH Database with the Mitelman Database of Chromosome Aberrations in Cancer and the Recurrent Chromosome Aberrations in Cancer database. These three datasets can now be searched seamlessly by use of the Entrez search and retrieval system for chromosome aberrations, clinical data, and reference citations. Common diagnoses, anatomic sites, chromosome breakpoints, junctions, numerical and structural abnormalities, and bands gained and lost among selected cases can be compared by use of the "similarity" report. Because the model used for CGH data is a subset of the karyotype data, it is now possible to examine the similarities between CGH results and karyotypes directly. All chromosomal bands are directly linked to the Entrez Map Viewer database, providing integration of cytogenetic data with the sequence assembly. These resources, developed as a part of the Cancer Chromosome Aberration Project (CCAP) initiative, aid the search for new cancer-associated genes and foster insights into the causes and consequences of genetic alterations in cancer.

Transplanted bone marrow regenerates liver by cell fusion.

Results from several experimental systems suggest that cells from one tissue type can form other tissue types after transplantation. This could be due to the presence of multipotential or several types of adult stem cells in donor tissues, or alternatively, to fusion of donor and recipient cells. In a model of tyrosinaemia type I, mice with mutations in the fumarylacetoacetate hydrolase gene (Fah-/-) regain normal liver function after transplantation of Fah+/+ bone marrow cells, and form regenerating liver nodules with normal histology that express Fah. Here we show that these hepatic nodules contain more mutant than wild-type Fah alleles, and that their hepatocytes express both donor and host genes, consistent with polyploid genome formation by fusion of host and donor cells. Using bone marrow cells marked with integrated foamy virus vectors that express green fluorescent protein, we identify common proviral junctions in hepatic nodules and haematopoietic cells. We also show that the haematopoietic donor genome adopts a more hepatocyte-specific expression profile after cell fusion, as the wild-type Fah gene was activated and the pan-haematopoietic CD45 marker was no longer expressed.

Folding of branched RNA species.

The global structures of branched RNA species are important to their function. Branched RNA species are defined as molecules in which double-helical segments are interrupted by abrupt discontinuities. These include helical junctions of different orders, and base bulges and loops. Common helical junctions are three- and four-way junctions, often interrupted by mispairs or additional nucleotides. There are many interesting examples of functional RNA junctions, including the hammerhead and hairpin ribozymes, and junctions that serve as binding sites for proteins. The junctions display some common structural properties. These include a tendency to undergo pairwise helical stacking and ion-induced conformational transitions. Helical branchpoints can act as key architectural components and as important sites for interactions with proteins. Copyright 1999 John Wiley & Sons, Inc.

Dihedral angles of septal "bend" structures in lung parenchyma.

Alveolar parenchyma comprises two interacting tensile systems: the cable system (a network of linear condensations of connective tissue) and the membrane system (a network of quasiplanar alveolar septa). Inferences can be drawn about the mechanics of this structure from it configuration. We reported earlier (E.H. Oldmixon, J.P. Butler, and F.G. Hoppin, Jr. J. Appl. Physiol. 64: 299-307, 1988) that the angles between alveolar septa at the common three-way junctions (J) are nearly uniform, indicating that septal tensions are also nearly uniform. We now report on the interseptal angles at the next most common class of septal junction (B), a structure where two septa meet along a segment of the cable system. We find, first, that the distributions of interseptal angles at B junctions have means > 120 degrees, are narrow, and have few, if any, angles < 120 degrees. The findings of uniform 120 degrees angles at J junctions and a cutoff below 120 degrees at B junctions are also characteristic of soap films supported on a frame, which follows the physical principle of surface area minimization. We suggest that this principle may be operative in parenchymal development and remodeling.

Establishing the anatomic hallmarks of congenitally malformed hearts

A detailed knowledge of the precise morphology of the congenitally malformed heart has never been more important. In fields as diverse as clinical genetic counseling, epidemiology, surgery, and development biology, a proper description of morphology is essential to understand the cause and prevention of cardiac malformations. There has been a tendency in the past to categorize malformed hearts on the basis of putative developmental faults that are deduced from abnormal morphology, for example “endocardial cushion” or “looping” defects. We consider that this is potentially misleading. A better approach is exactly to determine cardiac structure so as to identify the “hallmark” (or “prototype”) morphology of a given lesion. The hallmark will constitute those features, among all the changes in a malformed heart, that best define its fundamental character. As an example of the confusion produced by mechanistic extrapolation, consider the cleft in the anterior leaflet of an otherwise normal mitral valve, compared with the space between the leaflets bridging the ventricular septum in hearts with common atrioventricular junctions and deficient atrioventricular septation (“atrioventricular canal malformations”). It is probably correct to presume that both of these entities result from failure of fusion of the atrioventricular endocardial cushions. It is quite inappropriate, in contrast, to group these two lesions together morphologically, given the major anatomical differences seen in the formed hearts (Sigfússon et al. 1995). Therefore it is also important from the stance of developmental biology that the precise morphology of a genetically or chemically induced lesion be recognized if appropriate inferences are to be drawn for consideration of morphogenetic mechanisms and of comparable lesions in humans.

Organisation of the murine 5-HT 3 receptor gene and assignment tohuman chromosome 11

We have isolated the murine gene encoding the 5-HT 3 receptor (5-HT 3R), a member of the ligand-gated ion channels, that mediates a variety of physiological effects in central and peripheral neurons. DNA sequence analysis of the 5-HT 3R gene revealed its organisation in 9 exons distributed over approximately 12 kbp of DNA. Alternative use ofexon 9 splice acceptor sites generated two 5-HT 3R variants. The 5-HT 3R gene, whose structure is closely related to neuronal and muscle AChRα genes, as demonstrated by four common splice junctions, was localised on human chromosome 11.

Effects of field area and configuration on chromatic and border discriminations

Visual discrimination was tested with juxtaposed fields that differed only in luminance, S cone excitation, or the ratio of L to M cone excitation. Observers were asked to make discriminations based upon a criterion of color difference or of the perception of a border between fields. The area of the fields was varied either by increasing the length of their common junction or by increasing their widths at constant junction length. For fields larger than 0.2–0.4 deg 2, area controls sensitivity. For smaller fields, discrimination may be worse for narrow fields with long common junctions than for wide ones with small common junctions, especially for discriminations that depend upon S cones, in which the field components tend to become spatially integrated. Decreasing viewing time reduces the magnitude of this effect. S cone and L-M channel acuities were estimated at about 7 and 32 c/deg, respectively.

Glass-plastic push-pull cannula system for regional perfusion of sites in the brain

A new non-metallic push-pull cannula device is described for the localized perfusion of brain sites in the rat or other animal. Comprised entirely of glass and plastic materials, the cannula is intended for usage in an experiment in which the presence in tissue of metal tubing for delivery of perfusate is methodologically inappropriate. The main features of the cannula include its light weight, a Delrin pedestal base, a micro-glass guide tube, a polyethylene stylet, plastic spacers for adjustment of depth of perfusion, a protective cap for the chronic maintenance of the preparation, low cost and re-usability. The push-pull cannula is of concentric design and is fashioned from glass capillary and polyethylene tubing which are bonded at their common junctions by an epoxy cement. During a push-pull perfusion a special perfusion cap is used not only to hold the cannula firmly in place but also to protect the glass components from external damage. To further coincide with the metal-free requirements of the preparation, bone screws of nylon are used during the surgical implantation of the pedestal base. A prototype experiment illustrating its use in an unrestrained animal also is presented. The special applications for this cannula system are discussed which include its usage in experiments in either the anesthetized or unanesthetized rat exposed to microwave radiation where the presence of metal in the field would result in unwanted ‘hot spots’ in the cerebral tissue.

The use of power flow methods for the assessment of sound transmission in building structures

A description is given of a versatile method of analysis of noise transmission in buildings. This method incorporates power flow techniques and has the advantage that a unified approach is possible to both the direct and indirect transmission paths and is therefore equally applicable to transmission between rooms which are adjacent or several rooms or floors apart. The first configuration only lies within the range of classical theories. In this analysis, the building is regarded as an assembly of plate elements. Vibrational energy flows to and from each plate across common structural junctions in a manner analogous to heat transfer between bodies at different temperatures, and can also flow to and from the enclosed air volume. The solution of sets of simultaneous energy-balance equations gives the steady-state vibrational energy of each plate at their common junction. The pressure wave energy generated within a room by plate (or wall) vibrations is also predicted. The vibrational energies are predicted from the modal density, loss factor, coupling loss factor, and radiation loss factors, which are assessed theoretically and experimentally. Numerical calculations, involving a computer, yield values of the transmission coefficients of bending and longitudinal wave at cross-junctions, T-junctions and corners of reinforced concrete plates. The theory is compared with measurements involving quarter-scale models over a frequency range of measurement of 400 Hz-12·5 kHz.

Compressive buckling analysis and design of stiffened flat plates with multilayered composite reinforcement

This paper describes an analysis and its application in design for compressive buckling of flat stiffened plates considered as an assemblage of linked orthotropic flat plate and beam elements. Plates can be multilayered, with possible coupling between bending and stretching. Structural lips and beads are idealized as beams. The plate and the beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Buckling loads are found as the lowest of all possible general and local failure modes. The mode shape is used to determine whether buckling is a local or general instability and is particularly useful to the designer in identifying the weak elements for redesign purposes. Typical design curves are presented for the initial buckling of a hat stiffened plate locally reinforced with boron fiber composite.

Buckling analysis for structural sections and stiffened plates reinforced with laminated composites

A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked flat plate and beam elements. Plates are idealized as multilayered orthotropic elements; structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections and stiffened plates is investigated. Buckling loads are found as the lowest of all possible general and local failure modes and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections and stiffened plates including boron-reinforced structures are discussed. In general, correlations are reasonably good.

Calcite Rims, Little Falls Formation, Upper Cambrian, New York: A Dedolomitization Fabric?: ABSTRACT

Calcite rims on dolomite crystals have been observed in the Little Falls Formation of east-central New York. Most rims are even, syntaxial, and 5 to 25µ thick. Some, however, are irregular, apparently resembling the envelopes of Goldman. Electron probe microanalysis verifies the dolomitic center and the calcitic border, the latter commonly being very slightly ferroan. Dolomite preceded development of quartz overgrowths, as determined by spatial relations (e.g., enfacial junctions). The rims seem to be along crystal faces of dolomite rather than along compromise boundaries or against detrital quartz cores. Calcite beyond the rims exists as poikilotopic, centimicron-sized, void-filling spar, some of which is optically continuous with adjacent rims and dolomit crystals. Common enfacial junctions of calcite crystals against secondary quartz faces suggest a later development of the calcite. The rims are the same age as the remainder of the calcite. Such syntaxial rims could result either from marginal dedolomitization (calcitization) or from passive precipitation on a nucleus of dolomite. Optical continuity of the rim and nucleus and the presumed post-secondary quartz age of the calcite strongly suggest dedolomitization. Solutions with high Ca++/Mg++ ratios provided by meteoric water passing through overlying Ordovician limestones may have been the dedolomitizing agent. This unusual fabric may constitute another piece of evidence for dedolomitization. End_of_Article - Last_Page 664------------

Trunking of a t.d.m. electronic exchange with subscribers' lines having permanently allocated multiplex channels

A t.d.m.-exchange system is described in which the subscribers' line equipments have permanently allocated channels. If n channel multiplexes are used, the subscribers' lines are effectively divided into n separate space-division exchanges with common registers and junctions. Existing trunking theory still applies, but with the unusual aspects that the division by n results in an aggregation of n small, or even very small, exchanges, and that the relatively high cost of the switching elements justifies greater care in trunking design to minimise the number of switching elements.

Scattering Equivalent Circuits for Common Symmetrical Junctions

A novel form of equivalent circuit is presented for the symmetric two-port, the shunt- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</tex> junction, the hybrid- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</tex> junction, and certain directional couplers. These circuits are derived from symmetry properties of the scattering matrix and represent simplifications in that one and two-ports interconnected by ideal hybrid junctions replace the corresponding multiport junctions. The term "scattering equivalent circuit" is employed principally because it is possible to trace incident and reflected waves through this internal structure. The circuit form is based on symmetry considerations and therefore essentially independent of the frequency. The equivalent circuits are conveniently tabulated, and their properties discussed in sections independent of those dealing with their derivation. Examples of application are given.