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At least 811 records · Page 45Linked to original sources
PubMed1996

Differential expression of integrin alpha subunits supports distinct roles during lung branching morphogenesis.

Epithelial branching morphogenesis is a process by which a continuous epithelium, embedded in mesenchyme, forms tubules that extend and branch into the surrounding mesenchyme. The morphogenetic process is responsible for the architecture of many organs including the lung. Proper expression and function of extracellular matrix (ECM) molecules, such as collagens and laminins, are necessary for branching to occur normally. However, little is known about the role of epithelial cell surface molecules that mediate epithelial-matrix interactions during this process. We have studied the expression patterns of cell surface collagen and laminin integrin receptor alpha subunits, alpha 1, alpha 2, alpha 3, and alpha 6, in relation to that of collagen and laminin during lung branching morphogenesis. The alpha 1 integrin subunit was present on endothelia and smooth muscles around airways and large blood vessels. The mesenchyme expressed high levels of alpha 2 and alpha 6 but not alpha 3, whereas the epithelium expressed all three integrin subunits. In contrast to the widespread epithelial expression of alpha 3 and alpha 6, the epithelial expression of alpha 2 was restricted to branch tips. By performing in situ hybridization and immunofluorescence on serial sections, we found that alpha 2 protein expression on the epithelium correlated spatially and temporally with high level expression of collagen IV and laminin-1 mRNAs, suggesting that the alpha 2-expressing epithelial cells were in the process of producing and assembling their collagen and laminin matrices. While the expression of alpha 3 and alpha 6 on all lung epithelia suggests that these integrins may be important to lung epithelial development, the unique expression pattern of the alpha 2 subunit suggests that the alpha 2 beta 1 integrin may be important at branch tips either in the process of collagen/laminin synthesis and assembly or extension of the epithelial tubules into the mesenchyme.

Animals↗
PubMed1984

Prenatal development of the rat dorsal root ganglia. A scanning electron-microscopic study.

This study describes three-dimensional aspects of the development and pseudo-unipolarization of neuroblasts and the maturation of satellite cells in prenatal rat dorsal root ganglia, using scanning electron microscopy, after removal of extracellular connective tissue components by trypsin digestion and HC1 hydrolysis. At 14 days of gestation, the vast majority of neurons are spindle-shaped or bipolar and only 3% are unipolar, while at 16 and 18 days this percentage has increased to 30% and 91%, respectively. The initial portions of the central and peripheral neuronal processes gradually approach each other and form a common initial portion. Finally, the cytoplasm of this common initial portion becomes thinner and elongates to form the stem process of the mature cell. Satellite cells are present from the beginning of the period studied, but intricate networks of branching satellite cell processes only develop after about day 17.

Animals↗
PubMed2006

Developmental morphology of branching flowers in Nymphaea prolifera.

Nymphaea and Nuphar (Nymphaeaceae) share an extra-axillary mode of floral inception in the shoot apical meristem (SAM). Some leaf sites along the ontogenetic spiral are occupied by floral primordia lacking a subtending bract. This pattern of flower initiation in leaf sites is repeated inside branching flowers of Nymphaea prolifera (Central and South America). Instead of fertile flowers this species usually produces sterile tuberiferous flowers that act as vegetative propagules. N. prolifera changes the meristem identity from reproductive to vegetative or vice versa repeatedly. Each branching flower first produces some perianth-like leaves, then it switches back to the vegetative meristem identity of the SAM with the formation of foliage leaves and another set of branching flowers. This process is repeated up to three times giving rise to more than 100 vegetative propagules. The developmental morphology of the branching flowers of N. prolifera is described using both microtome sections and scanning electron microscopy.

Flowers↗
PubMed2005

A deoxyribozyme that synthesizes 2',5'-branched RNA with any branch-site nucleotide.

RNA molecules with internal 2',5'-branches are intermediates in RNA splicing, and branched RNAs have recently been proposed as retrotransposition intermediates. A broadly applicable in vitro synthetic route to branched RNA that does not require self-splicing introns or spliceosomes would substantially improve our ability to study biochemical processes that involve branched RNA. We recently described 7S11, a deoxyribozyme that was identified by in vitro selection and has general RNA branch-forming ability. However, an important restriction for 7S11 is that the branch-site RNA nucleotide must be a purine (A or G), because a pyrimidine (U or C) is not tolerated. Here, we describe the compact 6CE8 deoxyribozyme (selected using a 20 nt random region) that synthesizes 2',5'-branched RNA with any nucleotide at the branch site. The Mn2+-dependent branch-forming ligation reaction is between an internal branch-site 2'-hydroxyl nucleophile on one RNA substrate with a 5'-triphosphate on another RNA substrate. The preference for the branch-site nucleotide is U > C congruent with A > G, although all four nucleotides are tolerated with useful ligation rates. Nearly all other nucleotides elsewhere in both RNA substrates allow ligation activity, except that the sequence requirement for the RNA strand with the 5'-triphosphate is 5'-pppGA, with 5'-pppGAR (R = purine) preferred. These characteristics permit 6CE8 to prepare branched RNAs of immediate practical interest, such as the proposed branched intermediate of Ty1 retrotransposition. Because this branched RNA has two strands with identical sequence that emerge from the branch site, we developed strategies to control which of the two strands bind with the deoxyribozyme during the branch-forming reaction. The ability to synthesize the proposed branched RNA of Ty1 retrotransposition will allow us to explore this important biochemical pathway in greater detail.

Catalysis↗
PubMed1984

Morphology, distribution, and synaptic relations of somatostatin- and neuropeptide Y-immunoreactive neurons in rat and monkey neocortex.

Neurons in the monkey and rat cerebral cortex immunoreactive for somatostatin tetradecapeptide (SRIF) and for neuropeptide Y (NPY) were examined in the light and electron microscope. Neurons immunoreactive for either peptide are found in all areas of monkey cortex examined as well as throughout the rat cerebral cortex and in the subcortical white matter of both species. In monkey and rat cortex, SRIF-positive neurons are morphologically very similar to NPY-positive neurons. Of the total population of SRIF-positive and NPY-positive neurons in sensory-motor and parietal cortex of monkeys, a minimum of 24% was immunoreactive for both peptides. Most cell bodies are small (8 to 10 micron in diameter) and are present through the depth of the cortex but are densest in layers II-III, in layer VI, and in the subjacent white matter. From the cell bodies several processes commonly emerge, branch two or three times, become beaded, and extend for long distances through the cortex. The fields formed by these processes vary from cell to cell; therefore, the usual morphological terms bipolar, multipolar, and so on do not adequately characterize the full population of neurons. Virtually every cell, however, has at least one long vertically oriented process, and most processes of white matter cells ascent into the cortex. No processes could be positively identified with the light microscope as axons. The processes of the peptide-positive neurons form dense plexuses in the cortex. In each area of monkey cortex, SRIF-positive and NPY-positive processes form a superficial plexus in layers I and II and a deep plexus in layer VI. These plexuses vary in density from area to area. All appear to arise from cortical or white matter cells rather than from extrinsic afferents. In some areas such as SI and areas 5 and 7, the superficial plexus extends deeply into layers III and IV; and in area 17, two very prominent middle plexuses occur in layers IIIB through IVB and in the upper one-third of layer V; these are separated by layer IVC, a major zone of thalamic terminations, which contains very few SRIF- or NPY-positive processes. The density of the plexuses is greater for NPY-positive processes than for SRIF-positive processes in all areas. In the rat, the plexuses do not display a strict laminar organization but generally are densest in the supragranular layers (I to III) and decline steadily in the deeper layers.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

The ratio of dorsal root ganglion cells to dorsal root axons in sacral segments of the cat.

Processes of dorsal root ganglion cells are depicted as being unbranched until they reach the spinal cord or periphery. This is an important concept because, for example, branching of these processes might be a basis for referred pain. Recently several studies indicate that axons of rat dorsal root ganglion cells branch in or near the ganglion. The present study extends this work by showing that there are approximately 1.4 dorsal root axons for each dorsal root ganglion cell in sacral segments of the adult cat, and these data are interpreted as indicating that many dorsal root axons in this animal also branch. Thus this study provides further evidence to indicate that a revision of our ideas about the organization of primary sensory cells is desirable. In addition, this study provides data to indicate that the numbers of both dorsal root ganglion cells and dorsal root axons differ on the right as compared to the left side of the same segment.

Animals↗
PubMed1994

Juvenile visual callosal axons in kittens display origin- and fate-related morphology and distribution of arbors.

In kittens, callosal axons originating either from medial area 17 (transient axons) or near the 17/18 border (mostly permanent axons) were labelled with anterogradely transported biocytin; they were reconstructed by computer from serial sections, and their morphologies compared at different ages. During the first and second postnatal weeks both sets of axons branched profusely in the white matter of the lateral gyrus and the number of branches increased with age. The most common type of axon ending was the growth cone; others may have been collapsing growth cones, branches in the process of elimination or early synaptic boutons. Axons from medial area 17 distributed over a broad territory, including the 17/18 border where callosal axons terminate in the adult cat, but without aiming specifically at any one area. The majority of axons and their branches terminated in the white matter or at the bottom of layer VI; exceptionally they extended further into the cortex. Most of the axons originating near the 17/18 border were different from those described above, and the difference increased with age. Although they also terminated profusely in the white matter of the lateral gyrus, most of the branches terminated near the contralateral 17/18 border; they frequently entered the grey matter up to the superficial layers and branched into it. During the third week, axons from medial area 17 were rarely found to extend beyond the corpus callosum, probably because they were in the process of being eliminated. In contrast, axons originating near the 17/18 border had increased their number of branches in the grey matter. In conclusion, during the first and second postnatal weeks axons grew and differentiated according to their origin, and this anticipated whether they would be maintained or eliminated. Neurotrophic signals, possibly from the white matter or the subplate, and growth-inhibiting signals from area 17 may be involved in this process.

Aging↗
PubMed1980

Sorogen elongation and side branching during fruiting body development in Polysphondylium pallidum.

We report a cinematographic analysis of culmination in fruiting bodies of Polysphondylium pallidum. During the final stages of aggregation, sorogen elongation is slow. An increase in the rate of sorogen elongation occurs when the growing stalk contacts the substratum, lifting the cell mass into the air. The elongation process slows and finally stops as differentation of the terminal spore mass occurs. During the rapid elongation phase, variations in the rate of elongation of the main cell mass are correlated with the process of side branching. Side-branch elongation resembles elongation of the main sorogen with the rate of elongation increasing as the side-branch stalk contacts the main stalk and slowing as spore differentiation occurs. The morphological events of branching have been studied in detail and models to explain this process are discussed.

Morphogenesis↗
PubMed1986

[Neurons of the central nervous system innervating the lips and oral area of the pond snail].

By means of retrograde transport methods, CoCl2 and horseradish peroxidase, localization and morphological peculiarities of the CNS neurons, that innervate lips and oral area, have been studied in the pond snail (Gastropoda). The neurons, sending their processes into the anterior and middle labial nerves, are found nearly in all ganglia of the parapharyngeal nervous ring on the distal and ventral surface. In the cerebral ganglia they situate as several symmetrical groups. Among the neurons revealed, there are cells with rather local distribution of the terminal branches of the processes in the CNS neuropil and neurons with vast branching areas in the neuropil not only of its own ganglion, but also of the neighbouring ones. The problem concerning the zones of possible intersensory interaction in the cerebral ganglia is discussed and presence in them, together with complex reflectory arches, of bisegmental reflectory arches is considered.

Animals↗
PubMed2006

Cell and fibronectin dynamics during branching morphogenesis.

Branching morphogenesis is a dynamic developmental process shared by many organs, but the mechanisms that reorganize cells during branching morphogenesis are not well understood. We hypothesized that extensive cell rearrangements are involved, and investigated cell migration using two-color confocal time-lapse microscopy to image cell and extracellular-matrix dynamics in developing salivary glands. We labeled submandibular salivary gland (SMG) epithelial cells with green fluorescent protein and matrix with fluorescent fibronectin. Surprisingly, we observed substantial, rapid and relatively random migration of individual epithelial cells during branching morphogenesis. We predicted that cell migration would decrease after formation of acini and, indeed, found that rapid cell movements do not occur in SMG from newborn mice. However, in embryonic SMG epithelial cells, we observed an absence of choreographed cell migration, indicating that patterned cell migration alone cannot explain the highly ordered process of branching morphogenesis. We therefore hypothesized a role for directional fibronection assembly in branching. Washout and pulse-chase experiments revealed that older fibronectin accumulates at the base of the clefts and translocates inwards as a wedge, with newer fibronectin assembling behind it. These findings identify a new mechanism for branching morphogenesis involving directional fibronectin translocation superimposed on individual cell dynamics.

Animals↗
PubMed1991

Radial glia give rise to perinodal processes.

Nodes of Ranvier in the central nervous system in mammals are characterized by the presence of perinodal astrocytic processes. This study examines the association between processes of radial glia and the axolemma at nodes of Ranvier in the spinal cord of the mature axolotl, an animal in which radial glia represent a large portion of the total glial population. The radial glial cells have their cell bodies located close to the central canal. Those situated dorsal to the canal send long processes to the dorsal surface of the spinal cord. Along this trajectory these processes coalesce into large fascicles in the midline and form the dorsal median septum. Slender branches rise from the processes in these fascicles and extend into the adjacent white matter to terminate in close apposition to the axolemma at nodes of Ranvier. This arrangement provides an intracellular pathway extending from the perinodal region to the surface of the spinal cord. Radial glia ventral to the central canal give rise to processes that project to the glia limitans adjacent to the ventral spinal artery. These ventrally projecting processes appear to be more irregular in their branching pattern than their dorsal counterparts. Multiple slender processes are seen in close apposition to the nodal axolemma of myelinated axons in the ventral white commissure, again providing an intracellular pathway that runs from the perinodal region to the cord surface. In one instance a radial glial process was observed to occupy a pocket formed by the invagination of the nodal axolemma. The axonal cytoplasm adjacent to the invagination contained a variety of organelles, e.g. multivesicular bodies, vesicles and endoplasmic reticulum, suggesting that this relationship between the radial glial process and the axon is more than a passive interaction. These observations are consistent with the view that processes of radial glial cells may regulate the extracellular environment adjacent to the nodal axolemma, and/or play an active role in the maintenance of the nodal membrane. The existence of perinodally-directed processes of radial glial cells in the salamander indicates that this axo-glial specialization reflects an important functional interaction preserved across a large segment of the phylogenetic scale.

Ambystoma mexicanum↗
PubMed2000

Theoretical analysis of DNA branch migration in the presence of a slow reversible initiation step.

Branched DNA structures include several DNA regions connected by three- or four-way DNA junctions. Branched DNAs can be intermediates in DNA replication and recombination in living organisms and in sequence-specific DNA targeting in vitro. Branched DNA structures are usually metastable and irreversibly dissociate to non-branched products via a DNA strand exchange process commonly known as DNA branch migration. The key parameter in the DNA dissociation process is its characteristic time, which depends on the length of the dissociating DNA structure. Here, we predict that the presence of a slow reversible initiation step, which precedes DNA branch migration, can alter, to almost linear dependence, the "classic" quadratic dependence of the dissociation time on the length of the dissociating DNA structure. This prediction can be applied to dissociation of Y-like DNA structures and double D-loop DNA hybrids, which are DNA structures similar to replication bubbles. In addition, the slow initiation step can increase the effect of DNA sequence heterologies within the structure on its kinetic stability. Applications of our analysis for genetic manipulations with branched DNA structures are discussed.

Algorithms↗
PubMed1993

Formation of a single base mismatch impedes spontaneous DNA branch migration.

DNA branch migration, a process whereby two homologous DNA duplexes exchange strands, is an essential component of genetic recombination. Models for homologous recombination have invoked spontaneous branch migration as one mechanism for the generation of large regions of heteroduplex DNA. During recombination, two homologous parental duplexes that contain similar, but not identical, sequences are paired and undergo strand exchange. An important issue is whether spontaneous branch migration is capable of traversing sequence heterology such as mismatches, insertions and deletions. We use a model four-strand system to examine the effect of mispaired or unpaired bases on branch migration. The assay consists of annealing two short duplexes having defined sequence heterologies. Following annealing, a Holliday junction is formed that is free to branch migrate. Our results demonstrate that a single base mismatch, insertion or deletion is sufficient to pose a substantial barrier to spontaneous branch migration. In the presence of magnesium, branch migration through such sequence heterologies is almost completely blocked. Others have shown that non-mobile four-way junctions undergo a dramatic shift in conformation in the presence of magnesium. Our data suggest that a similar transition occurs for the mobile Holliday junction. We also discuss how proteins may facilitate branch migration through sequence heterologies in vivo.

Base Composition↗
PubMed1979

Lafora-like bodies in a cat. Case report suggestive of glycogen metabolism disturbances.

Lafora-like bodies in an 8-year-old cat were studied light and electron microscopically and histochemically. In addition ot Lafora-like bodies composed of branching filaments, glycogen granules and electron-dense materaisl, abnormal accumulations of glycogen granules attracted attention. The most remarkable features were the developmental processes of the branching filaments originating directly from glycogen granules. Lafora-like bodies in the present study showed ultrastructural, histochemical, and enzymatic similarities to those described in the previous reports in Lafora's disease, glycogenosm is considered to be probably related to the productive mechanism of Lafora-like bodies.

Animals↗
PubMed1998

Distribution of the vesicular transporter for acetylcholine in the rat central nervous system.

In order to develop another selective marker for cholinergic cell bodies and fibres, we have raised a highly specific polyclonal antibody against a peptide derived from the C-terminus of a recently cloned putative vesicular acetylcholine transporter. This antibody recognizes the vesicular acetylcholine transporter protein on western blots of membranes from transfected monkey fibroblast COS cells as well as from various rat brain regions but not from untransfected COS cells or rat liver. In separate mapping studies, the antibody was found to stain cell bodies and fibres in all of the regions of the nervous system known to be cholinergic, including (i) the various nuclei of the basal nuclear complex and their projections to the hippocampus, amygdala, and cerebral cortex, (ii) the caudate-putamen nucleus, accumbens nucleus, olfactory tubercle, and islands of Calleja complex, (iii) the medial habenula, (iv) the mesopontine cholinergic complex and its projections to the thalamus, extrapyramidal motor nuclei, basal forebrain, cingulate cortex, raphe and reticular nuclei, and some cranial nerve nuclei, and (v) the somatic motor and autonomic nuclei of the cranial and spinal nerves. In many of these cholinergic neurons, it is possible to detect immunoreactivity for the vesicular acetylcholine transporter in proximal portions of processes and their branches, as well as in numerous puncta in close association with them. Some of these puncta are large and surround cell bodies and processes of neurons in several regions, including the somatic motor neurons of cranial nerve nuclei in the brainstem and in the ventral horn of the spinal cord. Double immunofluorescence studies indicated that neurons positive for the vesicular acetylcholine transporter also stained for the biosynthetic enzyme of acetylcholine, choline acetyltransferase. We conclude that antibody against the C-terminus of the putative vesicular acetylcholine transporter provides another marker for cholinergic neurons that, unlike in situ hybridization procedures, labels terminals as well as cell bodies. Therefore this antibody has the potential to reveal changes in number and morphology of cholinergic cell bodies and their terminal varicosities that occur in both physiologic and pathologic conditions.

Acetylcholine↗
PubMed2006

Genetic regulation of patterned tubular branching in Drosophila.

A common theme in organogenesis is the branching of epithelial tubes, for example in the lung, liver, or kidney. The later morphogenesis of these branched epithelia dictates the final form and function of the mature tissue. Epithelial branching requires the specification of branch cells, the eversion process itself, and, frequently, patterned morphogenesis to produce branches of specific shape and orientation. Using the branching of renal tubule primordia from the hindgut in Drosophila, we show that these aspects are coordinately regulated. Cell specification depends on Wnt signaling along the tubular gut and results in the spatially restricted coexpression of two transcription factors, Krüppel and Cut, in the hindgut, whose activity drives cells toward renal tubule fate. Significantly, these transcription factors also confer the competence to respond to a second signal; TGF-beta induces branching to form the four renal tubule buds. Differential activation of the TGF-beta pathway also patterns the tubules, resulting in the asymmetry in size and positioning that is characteristic of the two tubule pairs. High levels of TGF-beta promote the expression of Dorsocross1-3 and anterior tubule growth, whereas low levels allow the expression of the transcriptional repressor, Brinker, and thus promote posterior tubule identity. We show that patterning of the tubule primordium into two distinct pairs is critical for the eversion of tubule branches, as well as for their asymmetric morphogenesis.

Animals↗
PubMed1994

The effects of NGF and glucocorticoid on the cytological features of rat chromaffin cells in vitro.

We investigated the effects of nerve growth factor (NGF) and glucocorticoid on the differentiation of rat chromaffin cells during development (postnatal day 0, 5, 10, 15, 25) in vitro, by evaluating four parameters of cytological alterations; the percentage of process-bearing cells, the number of primary processes, the number of branches per cell and the total length of processes. Cultures of dissociated chromaffin cells from each developmental stage were maintained in medium containing a combination of NGF and/or the synthetic glucocorticoid, dexamethasone (DEX). All parameters for neuronal differentiation were highest in chromaffin cells from P0 animals when incubated in NGF(+)/DEX(-), but lowest in those from animals at P25 incubated in NGF(-)/DEX(+). In addition, chromaffin cells became progressively insensitive to the effects of NGF on cytological differentiation from P0 to P25. These results suggest that as development proceeds locally-derived factors become less potent on chromaffin cell differentiation.

Animals↗