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PubMed1995

Ramification of the portal vein at the porta hepatis in humans.

The ramification of the portal vein at the porta hepatis was studied by anatomic dissection performed in 32 formalin fixed human livers. In all the specimens there were branches which ran towards the caudate lobe, arising from the portal vein and either from the left or the right portal branches. Tri- and quadrifurcation of the portal vein was observed. In 5 cases (16%) there were branches arising from left portal branch or portal vein and directed anteriorly to the quadrate lobe or to the region of the gall-bladder sulcus. These branches ranged from 1.0 to 6.0 mm in diameter. The portal caudate branches were divided into 3 groups. Group 1: Branches to the papillary process; 1 or 2 branches in 26 cases (82%), 3 or 5 branches in 3 cases (9%) and no branches in 3 cases (9%); Group 2: Branches to the vena cava region, including the left part of the caudate process; 1 or 2 branches in 30 cases (94%), 3 branches in 1 case (3%) and no branches in 1 case (3%); Group 3: Branches to the right part of the caudate process; 1 or 2 branches in 12 cases (37%), and no branches in 20 cases (63%).

Adult↗
PubMed2001

Activins as regulators of branching morphogenesis.

Development of glandular organs such as the kidney, lung, and prostate involves the process of branching morphogenesis. The developing organ begins as an epithelial bud that invades the surrounding mesenchyme, projecting dividing epithelial cords or tubes away from the site of initiation. This is a tightly regulated process that requires complex epithelial-mesenchymal interactions, resulting in a three-dimensional treelike structure. We propose that activins are key growth and differentiation factors during this process. The purpose of this review is to examine the direct, indirect, and correlative lines of evidence to support this hypothesis. The expression of activins is reviewed together with the effect of activins and follistatins in the development of branched organs. We demonstrate that activin has both negative and positive effects on cell growth during branching morphogenesis, highlighting the complex nature of activin in the regulation of proliferation and differentiation. We propose potential mechanisms for the way in which activins modify branching and address the issue of whether activin is a regulator of branching morphogenesis.

Activins↗
PubMed1983

Distribution and organization of odontoblast processes in human dentin.

The distribution and organization of odontoblast processes in young human dentin was examined with a scanning electron microscope. By applying the HCl-collagenase method, the extracellular matrix of dentin was almost completely removed, thereby exposing the odontoblast processes and their branches to direct observation. The odontoblast processes are located close to the dentinoenamel junction. In the middle and outer zones of dentin the processes bear numerous branches. Some of these appeared to bridge the space between the processes and connect them.

Child↗
PubMed1985

Characterization of GABAergic neurons in cerebellar primary cultures and selective neurotoxic effects of a serum fraction.

The morphological and functional differentiation of GABAergic interneurons present in cerebellar primary cultures has been examined by means of [3H]gamma-aminobutyric acid (GABA) autoradiography and [3H]GABA depolarization-evoked release. At 2 days in vitro these neurons showed scarce accumulation of radioactivity and no Ca2+-dependent K+-evoked or veratridine-induced release of [3H]GABA. At 5 days in vitro GABAergic interneurons appeared more intensely labeled and had grown out long and often branched neuritic processes; a large Ca2+-dependent release of [3H] GABA could be evoked by high K+. At later stages the progressive increase in labeling and branching of the neuritic processes was paralleled by a further increase in the amount and Ca2+ dependence of [3H]GABA release; a tetrodotoxin-sensitive, veratridine-stimulated release was also demonstrated. The [3H]GABA-accumulating stellate astrocytes present in the culture were not responsible for the observed release of the amino acid. GABAergic neurons were also identified by indirect immunofluorescence, using antibodies to the specific marker glutamic acid decarboxylase. Total renewal of the culture medium at 7 days in vitro caused a drastic (90%) reduction in the number of GABAergic neurons and a concomitant decrease in the amount of [3H]GABA uptake and release in the cultures. The disappearance of GABAergic neurons was caused by a low molecular weight (Mr less than 1000) fraction of the serum used to supplement the basal culture medium. This serum component did not significantly influence the survival of the major neuronal population of the culture (the granule cells) and appeared to be selectively toxic for GABAergic neurons only after they had reached a quite advanced degree of morphological and functional differentiation in vitro. The toxic activity was no longer present in neuronal or glial conditioned media.

Animals↗
PubMed1988

[The synthesis of mathematical models of the branched axons and dendrites].

A mathematical apparatus of computer modelling was elaborated reflecting more completely the real morphological and electrophysiological features of axons and dendrites without restrictions and simplifications which were typical of the existing models of these structures. Equivalent electrical circuits of branching axons and dendrites were constructed with in-series and node connections of standard four-terminal networks corresponding to elementary segments with active or passive membrane. Basing on these circuits the equations were obtained describing electrical phenomena in branching neuronal processes. They were generalized for the case of multiple binary branching with arbitrary symmetry and geometry of the branches. A difference scheme common for the whole class of models under consideration was also constructed and an algorithm was elaborated for numerical solution of the obtained system of difference equations. The suggested model allows synthetizing a variety of models of branching axons and dendrites, that promotes the possibilities of model investigation of electrotonus, propagated excitation and their interactions.

Animals↗
PubMed1985

Morphological observations on the mesodermal cells in the 8 day opossum embryo.

Cells of the mesodermal layer of the 8 day opossum were examined by scanning and transmission electron microscopy after removal of the ectoderm. The mesodermal layer is formed by a multilayered network of large somewhat flattened, stellate-shaped cells, whose broad surfaces usually lie parallel to the external surface of the embryo. The mesodermal cells show numerous cytoplasmic processes which often appear as long delicate threads that may branch. The processes may course for considerable distances and establish contact with adjacent mesodermal cells. Contact points between processes, processes and cells, and between adjacent cell bodies showed junctional complexes. Most of the junctional complexes appeared morphologically similar to the nexus (communicating) type. Occasional desmosome-like junctions also were observed. Extracellular fibers were not observed.

Animals↗
PubMed1995

Chick wing innervation. II. Morphology of motor and sensory axons and their growth cones during early development.

The development and distribution of neuronal projections to the developing chick wing was studied using anterograde transport of horseradish peroxidase (HRP). Small injections of HRP were made into motor or sensory neuronal populations in order to visualize individual axons and their associated growth cones. Motor growth cones were observed in different regions of the embryo at different stages, in a proximal-to-distal pattern of distribution which paralleled the process of axon outgrowth and nerve formation. Different growth cone morphologies were associated with differing regions of the developing projection. In the spinal nerves, axons destined for the limb were unbranched and terminated in simply shaped growth cones. As axons approached the developing limb and entered the plexus region, their growth cones became more complex and larger primarily because of widening, and they sometimes branched, producing processes which could extend tens of microns from a tricorne branch point on the parent axon. Both motor and sensory fibers showed similar morphological changes in the plexus region. A distinctively shaped growth cone expanded on its leading edge was observed, sequentially apparent in the distal spinal nerves, in the plexus region, in the loosely organized axonal sheets projecting to the uncleaved dorsal or ventral muscle masses, and where muscle nerves diverged from nerve trunks and within muscle nerves. It is likely that some of these are transitional growth cones preparing to branch, because complex and branched growth cones were also observed in these regions. Branched axons oriented along the anteroposterior axis were similarly observed in the plexus region and distal to the plexus when axons first projected to the limb bud. At somewhat older stages when the basic peripheral nerve branching pattern had formed, motor growth cones were observed in common nerve trunks and in individual muscle nerves, but they were no longer found in the plexus region. Branched axons were likewise restricted to these peripheral locations. Taken together, these observations suggest that one of the ways in which axons navigate is by exploration in the form of growth cone widening, and in some cases terminal bifurcation which may produce axon branches. Selection of the most appropriately directed growth cone process and/or precocious axonal branches may be one of the ways in which axons respond to specific growth cues which guide axons into the limb bud. Alternatively, this precocious branching may be an early neurotrophic response to developing muscle and play no significant role in axon navigation.

Animals↗
PubMed1984

Scanning electron microscopy of Ito's fat-storing cells in the rat liver.

The whole body including extended processes of Ito's fat-storing cells was observed by scanning electron microscopy in rat liver injured with lithocholic acid (LCA). Necrotic foci developed in the midlobular zone 48 h after LCA administration. Demonstration of Ito cell bodies around the foci was probably facilitated by easy detachment of hepatocytes from Ito cells. The body and the processes were located mainly between the sinusoidal endothelium and hepatocytes; sometimes they were between hepatocytes. Ito cells often were proximate to collagen fiber bundles and sometimes were attached to them. The cell body was flatly round or elliptic, 7 to 12 micron in diameter. Its surface was finely undulated with microvillous projections about 0.1 micron in length. Branching patterns of the processes resembled a fern-leaf mantling the sinusoidal endothelium. The trunks of the processes were about 2 micron in diameter and 20-30 micron in length. These processes tapered, branching into thinner processes, with the most peripheral being 0.1 micron in diameter. Ito cells and their branching processes likely strengthen sinusoidal walls and control blood flow in the sinusoids.

Animals↗
PubMed1999

A three-dimensional model of the human airway tree.

A three-dimensional (3D) model of the human airway tree is proposed using a deterministic algorithm that can generate a branching duct system in an organ. The algorithm is based on two principles: 1) the amount of fluid delivery through a branch is proportional to the volume of the region it supplies; and 2) the terminal branches are arranged homogeneously within the organ. These principles define the basic process of branching: generation of the dimensions and directionality of two daughter branches is governed by the properties of the parent branch and the region the parent supplies. The algorithm is composed of nine basic rules and four complementary rules. When the contour of an organ and the position of the trunk are specified, branches are successively generated by the algorithm. Applied to the human lung, the algorithm generates an airway tree that consists of approximately 54,000 branches. Its morphometric characteristics are in good agreement with those reported in the literature. The algorithm and the 3D airway model are useful for studying the structure-function relationship in the lung.

Algorithms↗
PubMed2001

Changing the landscape: a new strategy for estimating large phylogenies.

In this paper we describe a new heuristic strategy designed to find optimal (parsimonious) trees for data sets with large numbers of taxa and characters. This new strategy uses an iterative searching process of branch swapping with equally weighted characters, followed by swapping with reweighted characters. This process increases the efficiency of the search because, after each round of swapping with reweighted characters, the subsequent swapping with equal weights will start from a different group (island) of trees that are only slightly, if at all, less optimal. In contrast, conventional heuristic searching with constant equal weighting can become trapped on islands of suboptimal trees. We test the new strategy against a conventional strategy and a modified conventional strategy and show that, within a given time, the new strategy finds trees that are markedly more parsimonious. We also compare our new strategy with a recent, independently developed strategy known as the Parsimony Ratchet.

Animals↗
PubMed1999

Effects of anticoagulant, processing delay, and assay method (branched DNA versus reverse transcriptase PCR) on measurement of human immunodeficiency virus type 1 RNA levels in plasma.

We conducted two studies to determine the potential influence of delays in blood processing, type of anticoagulant, and assay method on human immunodeficiency virus type 1 (HIV-1) RNA levels in plasma. The first was an experimental study in which heparin- and EDTA-anticoagulated blood samples were collected from 101 HIV-positive individuals and processed to plasma after delays of 2, 6, and 18 h. HIV-1 RNA levels in each sample were then measured by both branched-DNA (bDNA) and reverse transcriptase PCR (RT-PCR) assays. Compared to samples processed within 2 h, the loss (decay) of HIV-1 RNA in heparinized blood was significant (P < 0.05) but small after 6 h (bDNA assay, -0.12 log(10) copies/ml; RT-PCR, -0.05 log(10) copies/ml) and after 18 h (bDNA assay, -0.27 log(10) copies/ml; RT-PCR, -0.15 log(10) copies/ml). Decay in EDTA-anticoagulated blood was not significant after 6 h (bDNA assay, -0.002 log(10) copies/ml; RT-PCR, -0.02 log(10) copies/ml), but it was after 18 h (bDNA assay, -0.09 log(10) copies/ml; RT-PCR, -0.09 log(10) copies/ml). Only 4% of samples processed after 6 h lost more than 50% (>/=0.3 log(10) copies/ml) of the HIV-1 RNA, regardless of the anticoagulant or the assay that was used. The second study compared HIV-1 RNA levels in samples from the Multicenter AIDS Cohort Study (MACS; samples were collected in heparin-containing tubes in 1985, had a 6-h average processing delay, and were assayed by bDNA assay) and the British Columbia Drug Treatment Program (BCDTP) (collected in EDTA- or acid citrate dextrose-containing tubes in 1996 and 1997, had a 2-h maximum processing delay, and were assayed by RT-PCR). HIV-1 RNA levels in samples from the two cohorts were not significantly different after adjusting for CD4(+)-cell count and converting bDNA assay values to those corresponding to the RT-PCR results. In summary, the decay of HIV-1 RNA measured in heparinized blood after 6 h was small (-0.05 to -0.12 log(10) copies/ml), and the minor impact of this decay on HIV-1 RNA concentrations in archived plasma samples of the MACS was confirmed by the similarity of CD4(+)-cell counts and assay-adjusted HIV-1 RNA concentrations in the MACS and BCDTP.

Acquired Immunodeficiency Syndrome↗
PubMed2000

3'-Azidothymidine potently inhibits the biosynthesis of highly branched N-linked oligosaccharides and poly-N-acetyllactosamine chains in cells.

Previous studies in our laboratory have characterized 3'-azido-3'-deoxythymidine (AZT) as a potent inhibitor of glycosphingolipid biosynthesis in cultured cells (Steet, R., Alizadeh, M., Melançon, P., and Kuchta, R. D. (1999) Glycoconj. J. 16, 237-245; Yan, J.-P., Ilsley, D. D., Frohlick, C., Steet, R., Hall, E. T., Kuchta, R. D., and Melançon, P. (1995) J. Biol. Chem. 270, 22836-22841). Here, we report that AZT treatment of K562 cells results in significant alterations in the profile of N-linked oligosaccharides. Fractionation of [(3)H]mannose-labeled oligosaccharides from AZT-treated K562 cells using lectin affinity chromatography revealed striking changes in the branching and processing of N-linked glycoconjugates. AZT treatment resulted in the production of fewer highly branched complex glycans (60% of control at 20 micrometer AZT) and a significant accumulation of core-fucosylated biantennary oligosaccharides. In addition, extension of branched oligosaccharides with multiple poly-N-acetyllactosamine repeats is nearly abolished by AZT concentrations as low as 2 micrometer. A shift from multiantennary to moderately branched oligosaccharides was also apparent in the melanoma cell line SK-MEL-30 upon AZT treatment. N-Linked glycans from both cell lines exhibited increased affinity for the beta-galactoside-binding lectin RCA-I in the presence of AZT, suggesting that the addition of terminal sialic acid is sensitive to the drug. These results demonstrate the ability of AZT to modulate strongly the processing of asparagine-linked glycoconjugates in whole cells and reveal a novel mechanism by which AZT treatment may cause anemia.

Humans↗
PubMed2002

Glycosidases during chick embryo lung development and their colocalization with proteoglycans and growth factors.

During development, the epithelial component of the lung goes through a complex orderly process of branching, following strict patterns of space and time. Proteoglycans, glycosaminoglycans and growth factors are fundamental components of the extracellular matrix and perform a key role in differentiative processes. The embryonic chick lung shows a specific glycosaminoglycan composition at different levels of branching and at different embryonic stages. Proteoglycan and glycosaminoglycan accumulation is the result of secretion, absorption and degradation processes. In this pathway, enzymes, such as glycosidases, growth factors and cytokines are involved. We examined the behaviour of glycosidases, such as beta-hexosaminidases (beta-N-acetyl-D-glucosaminidase, beta-N-acetyl-D-galactosaminidase), beta-glucuronidase and beta-galactosidase, during the development of the lung bud. Our data show that the activity of the enzymes is closely linked to the processes of epithelial proliferation, bronchial tubule lengthening and infiltration of the surrounding mesenchyme. The glycosaminoglycans colocalize with transforming growth factor beta2 and interleukin-1 in the basement membrane and in the mesenchymal areas where the epithelium grows, and are complementary to the presence of the glycosidases. In conclusion, the activity of these glycosidases is spatially and temporally programmed and favors the release of the factors and the events which they influence.

Animals↗
PubMed1991

Potential role of RGD-binding integrins in mammalian lung branching morphogenesis.

Cell-matrix interactions are generally considered critical for normal lung development. This is particularly likely to be true during the glandular stage, when the primitive airways are formed through a process termed branching morphogenesis. Integrins, transmembrane receptors that bind to extracellular matrices, are likely to mediate important interactions between embryonic cells and their matrices during branching morphogenesis. In this report, we examine the role of integrin receptors in this process. Immunohistochemical studies revealed that the integrins VLA 3, VLA 5 and integrin receptors to vitronectin are expressed in the epithelium and/or mesenchyme during the glandular stage of murine lung development. To correlate expression with function, an in vitro model of murine lung branching morphogenesis was utilized to examine branching in the presence of inhibitors of ligand binding to integrin receptors. One such reagent, a hexapeptide containing the RGD (Arg-Gly-Asp) sequence, diminished branching and resulted in an abnormal morphology, whereas a control peptide RGESP (Arg-Gly-Glu-Ser-Pro) had no effect. These findings suggest a critical role for cell-matrix interactions mediated via integrin receptors in early stages of mammalian lung development.

Animals↗
PubMed1993

Vascular dimensions of the cerebral arteries follow the principle of minimum work.

BACKGROUND AND PURPOSE: The principle of minimum work is a parametric optimization model for the growth and adaptation of arterial trees. It establishes a balance between energy dissipation due to frictional resistance of laminar flow (shear stress) and the minimum volume of the vascular system, implying that the radius of the vessel is adjusted to the cube root of the volumetric flow. The purpose of this study is to verify whether the internal carotid artery system obeys the principle of minimum work. METHODS: Measurements of the radius of parent and branch segments of the internal carotid, anterior, and middle cerebral arteries were performed on analog angiographs chosen at random from a set classified as normal. The branch angles were measured from lateral projections in bifurcations of the anterior cerebral artery. The relation of the calibers of parent and branch vessels was analyzed. RESULTS: The area ratio of the bifurcations (N = 174) was 1.2 +/- 0.4 (mean +/- SD). The equation (r0)n = (r1)n + (r2)n was solved for n, resulting in n = 2.9 +/- 0.7 (mean +/- SD, N = 157). Optimum proportions between the radii of parent (r0) and branch (r1 and r2) vessels in the internal carotid artery system were verified in normal carotid angiographs up to four branch generations, according to the theoretical equation r0(3) = r1(3) + r2(3) (r = 0.989, N = 174). No clear correlation was found between the measured branch angles, the relative branch cross-sectional area, and the theoretical optimum angles. CONCLUSIONS: This study demonstrates that the process of branching of the internal carotid artery system obeys the principle of minimum work, as the diameter exponent approximates 3. The principle of minimum work establishes strict functional relations between volumetric flow, flow velocity, and vessel radius. This model was extended to parametric optimization of branch angles, which has proved irrelevant in terms of functional optimization. Our results corroborate this finding. Shear stress-induced endothelial mediation seems to be the regulating mechanism for the maintenance of this optimum vessel design. The magnitude of wall shear stress is the same at every point in a vascular network obeying the principle of minimum work, because the flow rate influences the shear stress proportionally to the third power of the vessel radius. This observation has implications for understanding the remodeling of the cerebral vascular network in the presence of arteriovenous malformations and for the pathogenesis of saccular aneurysms.

Blood Flow Velocity↗
PubMed1982

Branching structure of motoneuron stem dendrites: a study of neck muscle motoneurons intracellularly stained with horseradish peroxidase in the cat.

The branching structure of the stem dendrites of five motoneurons innervating the dorsal neck muscles, biventer cervicis and complexus, was examined in the adult cat using intracellular staining techniques. The dendritic tree of each motoneuron was reconstructed completely and then dissected into several parts, each corresponding to the branches. Twenty-five of the 49 stem dendrites examined had branches which confined to a small region of the territory occupied by the complete dendritic tree. These dendrites were distributed to one of three zones, a ventral zone deep in the ventral horn, a lateral zone dorsolateral to the motor nucleus, and a medial zone dorsomedial to the motor nucleus. The remaining stem dendrites projected to two or more of these zones and occasionally occupied a region almost as large as the territory occupied by the complete dendritic tree. The frequency of each type of stem dendrite, defined according to the number and location of the zones to which they projected, was remarkably consistent from motoneuron to motoneuron. The maximum order of branching reached by stem dendrites of biventer cervicis and complexus motoneurons was variable. Stem dendrites whose maximum order of branching was four or less usually had one major stalk from which emerged simple, unbranched, side processes. The branching structure was not related, in a simple manner, to the dendritic distribution pattern. These results indicate that the distribution and branching structure of motoneuron stem dendrites are organized in a complex, but precise, fashion which could play an important role in the integrative properties of the motoneuron.

Animals↗
PubMed1994

Equilibrium analysis of ethidium binding to DNA containing base mismatches and branches.

In the processes of DNA replication, recombination, and repair, duplex DNA can transiently form branched structures, such as Holliday junctions, as well as base pair mismatches and bulges. These stages have altered ligand and protein binding properties from normal double helical DNA. A variety of ligands have been reported to interact more tightly at branches and bulges than to normal duplex sites. The stoichiometry, structural basis, and thermodynamics of this effect have not been determined. We have investigated the binding of the intercalator, ethidium bromide, to several DNA constructs including base mismatches, bulges, and three- and four-arm branched structures, using chemical footprinting, titration calorimetry, and fluorescence lifetime measurements. Two classes of binding sites are detected in three- and four-arm junctions in our high ionic strength conditions: one class is characterized by a small number of ligands (2-4 per DNA), with high binding affinity (K > 10(5)), and the second by a larger number of sites (10-12 per DNA) with lower affinity (K approximately 10(4)). By use of appropriate control experiments, the former appear to be associated with sites at or near the branch point or mismatch, while the latter are consistent with binding to the normal duplex DNA region(s) of the molecule. Titration calorimetry indicates an enthalpy of -10 to -13 kcal/mol for binding of ethidium to a mismatch or three- and four-arm branch point. The tight binding class is associated with a fluorescence lifetime of 12-16 ns, distinct from that of free ethidium (ca. 2 ns) and the longer lifetime observed for ethidium intercalated in duplex DNA (22-26 ns).

Base Composition↗
PubMed1998

Formation of RuvABC-Holliday junction complexes in vitro.

In Escherichia coli, the RuvA, RuvB and RuvC proteins are required for the late stages of homologous recombination and DNA repair. RuvA and RuvB form a complex that interacts with Holliday junctions--crossed DNA structures that are recombination intermediates--and promotes branch migration; RuvC is a junction-specific endonuclease that resolves Holliday junctions and completes the recombination process. Because genetic and biochemical experiments suggest that the processes of branch migration and resolution are linked, coimmunoprecipitation experiments were carried out to determine whether the three Ruv proteins interact to form a functional complex (RuvABC). Using a synthetic Holliday junction, a multisubunit complex containing the junction and RuvA, RuvB and RuvC was detected. In the absence of RuvB, RuvAC-junction complexes were observed. Complex formation was not facilitated by duplex DNA. The identification of a RuvABC-junction complex provides direct evidence that the RuvABC proteins interact at the Holliday junction.

Bacterial Proteins↗