Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “branching process”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,441 records · Page 80Linked to original sources
PubMed1996

Insulin increases the processing efficiency of messenger ribonucleic acid-S14 nuclear precursor.

Feeding a lipogenic diet increases transcription and enhances processing of the rat hepatic messenger RNA (mRNA)-S14 gene. To determine the separate roles of insulin and increased glucose in these processes, we used the streptozotocin-induced diabetic rat model. Diabetes caused a reduction in mature mRNA-S14 in chow- and lipogenic diet-fed animals (P < 0.006 and P < 0.001, respectively). Insulin restored these levels to normal. Despite the known effects of insulin and carbohydrate on the transcription of this gene, we were unable to demonstrate significant changes in the nuclear proteins that bind to carbohydrate response regions. Yet, insulin restored the content of the mRNA by increasing the ratio of mature to precursor mRNA-S14. Insulin significantly increased this ratio (P < 0.0001) independent of diet and diabetes, further supporting the action of insulin on increasing processing from precursor to mature mRNA. The mechanism of the enhanced processing was studied by ribonuclease mapping and primer extension analysis. Ribonuclease mapping showed that lipogenic diet feeding increases the efficiency of processing at a step before formation of the branched form of the precursor mRNA. Taken together, our data demonstrate for the first time that insulin significantly enhances the efficiency of processing of a pre-mRNA.

Animals↗
PubMed1989

New growth elicited in adult leech mechanosensory neurones by peripheral axon damage.

1. New growth in cutaneous mechanosensory neurones elicited by axotomy or axon crush was studied using intracellular injection of horseradish peroxidase at different times after the lesion, ranging from a few days to over a year. 2. Cutting or crushing major, large-calibre axon branches of mechanosensory neurones elicits sprouting of new processes, either centrally within the ganglion neuropile or at the site of the lesion in the peripheral nerve. In contrast, cutting or crushing fine-calibre axon branches supplying accessory parts of the receptive field does not elicit sprouting of the main arbor or main axon branches. 3. Different modalities of mechanosensory neurone respond differently to lesions of their axons. Cutting the axons of high-threshold units responding to noxious stimulation of the skin elicits sprouting of additional processes from the axon hillock region within the central nervous system (CNS), whereas cutting or crushing the axons of low-threshold cells responding to light touch of the skin elicits sprouting at the site of the lesion only, and not within the CNS. 4. In addition to the new growth directed into the peripheral nerve, damaged nociceptive neurones also form new processes that wrap the somata of particular cells within the ganglion. 5. Sprouted processes of axotomized neurones are retained for long periods after the lesion (up to 425 days). 6. The electrical properties of touch and nociceptive cells were studied between 1 and 60 days after axotomy, by intracellular recording from the centrally located cell bodies. The amplitude, width and maximum dV/dt of the action potential and after-hyperpolarization, as well as the resting potential and input resistance, did not change significantly after axotomy, despite the considerable process sprouting known to occur during this time.

Action Potentials↗
PubMed1996

Dual function of the region-specific homeotic gene spalt during Drosophila tracheal system development.

We report that the region-specific homeotic gene spalt affects the Drosophila tracheal system at two different stages of embryonic development. Both lack-of-function and gain-of-function experiments show that blastodermal spalt activity restricts tracheal development to 10 bilaterally positioned pairs of tracheal placodes in the trunk region by repressing placode formation in parasegments 2, 3 and 14. The results suggest that the activity of the zinc-finger type transcription factor encoded by spalt suppresses the molecular pathway that establishes tracheal development. spalt function is also necessary for the directed migration of the dorsal trunk cells, a distinct subset of tracheal cells. This process is a prerequisite for the formation of the dorsal trunk generated by fusion of adjacent tracheal metameres into a common tubular structure. The directed cell migration, in which spalt gene function participates, seems to be independent of branch fusion and general tracheal cell migration processes.

Animals↗
PubMed2006

Asymmetric allylic substitution catalyzed by C1-symmetrical complexes of molybdenum: structural requirements of the ligand and the stereochemical course of the reaction.

Application of new chiral ligands (R)-(-)-12 a and (S)-(+)-12 c (VALDY), derived from amino acids, to the title reaction, involving cinnamyl (linear) and isocinnamyl (branched) type substrates (4 and 5 --> 6), led to excellent regio- and enantioselectivities (>30:1, < or =98 % ee), showing that ligands with a single chiral center are capable of high asymmetric induction. The structural requirements of the ligand and the mechanism are discussed. The application of single enantiomers of deuterium-labeled substrates (both linear 38 c and branched 37 c) and analysis of the products (41-43) by (2)H{(1)H} NMR spectroscopy in a chiral liquid crystal matrix allowed the stereochemical pathways of the reaction to be distinguished. With ligand (S)-(+)-12 c, the matched enantiomer of branched substrate was found to be (S)-5, which was converted into (R)-6 with very high regio- and stereoselectivity via a process that involves net retention of stereochemistry. The mismatched enantiomer of the branched substrate was found to be (R)-5, which was also converted into (R)-6, that is, with apparent net inversion, but at a lower rate and with lower overall enantioselectivity. This latter feature, which may be termed a "memory effect", reduced the global enantioselectivity in the reaction of the racemic substrate (+/-)-5. The stereochemical pathway of the mismatched manifold has been shown also to be one of net retention, the apparent inversion occurring through equilibration via an Mo-allyl intermediate prior to nucleophilic attack. Incomplete equilibration leads to the memory effect and thus to lower enantioselectivity. Analysis of the mismatched manifold over the course of the reaction revealed that the memory effect is progressively attenuated with the nascent global selectivity increasing substantially as the reaction proceeds. The origin of this effect is suggested to be the depletion of CO sources in the reaction mixture, which attenuates turnover rate and thus facilitates greater equilibrium. The linear substrate was also converted into the branched product with net syn stereochemistry, as shown by isotopic labeling. An analogous process operates in the generation of small quantities of linear product from branched substrate.

Allyl Compounds↗
PubMed1998

Reconstitution of mammary gland development in vitro: requirement of c-met and c-erbB2 signaling for branching and alveolar morphogenesis.

We have established a cell culture system that reproduces morphogenic processes in the developing mammary gland. EpH4 mouse mammary epithelial cells cultured in matrigel form branched tubules in the presence of hepatocyte growth factor/scatter factor (HGF/SF), the ligand of the c-met tyrosine kinase receptor. In contrast, alveolar structures are formed in the presence of neuregulin, a ligand of c-erbB tyrosine kinase receptors. These distinct morphogenic responses can also be observed with selected human mammary carcinoma tissue in explant culture. HGF/SF-induced branching was abrogated by the PI3 kinase inhibitors wortmannin and LY294002. In contrast, neuregulin- induced alveolar morphogenesis was inhibited by the MAPK kinase inhibitor PD98059. The c-met-mediated response could also be evoked by transfection of a c-met specific substrate, Gab1, which can activate the PI3 kinase pathway. An activated hybrid receptor that contained the intracellular domain of c-erbB2 receptor suffices to induce alveolar morphogenesis, and was observed in the presence of tyrosine residues Y1028, Y1144, Y1201, and Y1226/27 in the substrate-binding domain of c-erbB2. Our data demonstrate that c-met and c-erbB2 signaling elicit distinct morphogenic programs in mammary epithelial cells: formation of branched tubules relies on a pathway involving PI3 kinase, whereas alveolar morphogenesis requires MAPK kinase.

Androstadienes↗
PubMed1991

Direct binding of a synthetic multichain polypeptide to class II major histocompatibility complex molecules on antigen-presenting cells and stimulation of a specific T-cell line require processing of the polypeptide.

T-cell activation involves the recognition of foreign antigens as a complex with self-major histocompatibility complex (MHC) proteins on the surface of antigen-presenting cells (APC). Protein antigens usually require uptake by the APC and processing that results in the generation of peptide fragments. The branched synthetic polypeptide (Tyr, Glu)-Ala--Lys was chosen as a model antigen to follow the processing requirements, leading to T-cell activation. It has been demonstrated, by using fixed APC and various inhibitors of proteases, that (Tyr, Glu)-Ala--Lys has to be processed to stimulate a (Tyr, Glu)-Ala--Lys-specific T-cell line of C3H.SW (H-2b) origin to proliferate. To determine whether processing of (Tyr,Glu)-Ala--Lys is required to allow its association with the MHC class II molecules, biotin was covalently attached to it. Binding of the biotinylated (Tyr,Glu)-Ala--Lys to MHC class II gene products on the surface of intact normal APC was directly detected by phycoerythrin-streptavidin. The specificity of the binding was confirmed by its inhibition with anti-I-Ab antibodies as well as with excess of nonlabeled (Tyr,Glu)-Ala--Lys. Furthermore, introducing several inhibitors of proteases to the binding assay, we could substantiate that the proteolysis of (Tyr,Glu)-Ala--Lys is required to allow association of the resulting peptidyl T-cell epitopes with the MHC class II molecules themselves. The presence of the biotin moiety in the resulting peptides suggests that the T-cell epitopes of (Tyr,Glu)-Ala--Lys contain the N-terminal portion of the side chains of the branched polypeptide. An apparent Kd of 8.05 x 10(-8) M was determined, and optimal binding was detected after 10 hr of incubation with the antigen. The latter phenomenon is not due to slow uptake, since uptake of (Tyr,Glu)-Ala--Lys occurs mainly during the first 30 min of incubation, but rather reflects the events of processing that precede MHC interaction.

Animals↗
PubMed2005

Identification of RecQL1 as a Holliday junction processing enzyme in human cell lines.

Homologous recombination provides an effective way to repair DNA double-strand breaks (DSBs) and is required for genetic recombination. During the process of homologous recombination, a heteroduplex DNA structure, or a 'Holliday junction' (HJ), is formed. The movement, or branch migration, of this junction is necessary for recombination to proceed correctly. In prokaryotes, the RecQ protein or the RuvA/RuvB protein complex can promote ATP-dependent branch migration of Holliday junctions. Much less is known about the processing of Holliday junctions in eukaryotes. Here, we identify RecQL1 as a predominant ATP-dependent, HJ branch migrator present in human nuclear extracts. A reduction in the level of RecQL1 induced by RNA interference in HeLa cells leads to an increase in sister chromatid exchange. We propose that RecQL1 is involved in the processing of Holliday junctions in human cells.

Adenosine Triphosphatases↗
PubMed2003

Tube or not tube: remodeling epithelial tissues by branching morphogenesis.

Branching morphogenesis involves the restructuring of epithelial tissues into complex and organized ramified tubular networks. Early rounds of branching are controlled genetically in a hardwired fashion in many organs, whereas later, branching is stochastic, responding to environmental cues. We discuss this sequential process from formation of an organ anlage and invagination of the epithelium to branch initiation and outgrowth in several model systems including Drosophila trachea and mammalian lung, mammary gland, and kidney.

Animals↗
PubMed1985

[Electrophysiologic and histochemical characteristics of the fiber composition of the subdiaphragmatic portion of the vagus nerves].

The fibre composition of subphrenic branches of the vagus nerves was studied electrophysiologically and histochemically. In anaesthetized cats, the presence of multicomponent electrical responses was found during stimulation of preganglionic fibres of splanchnic nerves in the splanchnic branch of the dorsal vagus trunk; the presence of synaptically interrupted fibres was shown. Histochemically, adrenergic fibres were found both in the central and in the peripheral stumps of subphrenic branches of the vagus nerves. Most strongly fluorescent fibres were regularly found in the peripheral stump of the splanchnic branch of the dorsal vagus trunk. The data obtained suggest that processes of ganglionic neurons of the celiac plexus ascend within splanchnic and other branches of the vagus nerves.

Adrenergic Fibers↗
PubMed2006

Dendrites contain a spacing pattern.

The distinctive branching patterns of dendritic arbors are essential for neuronal information processing. The final shape of an arbor is the result of intrinsic and extrinsic factors. However, the cellular mechanisms that underlie branch patterning are unknown. In many biological systems, locally acting factors are intrinsically organized into spacing patterns that guide patterned morphogenesis. Here, we show that neurons contain two types of periodic and regular elements (PADREN1s and PADREN2s) that are arranged into a spacing pattern. The wavelength of the pattern is approximately 20 microm. Dendritic branches occur preferentially within PADREN1s, and specific PADREN lengths correspond to specific arbor types. The lengths of the PADRENs also change over time and can be modified by activity. However, PADRENs are intrinsically organized, possibly by a reaction-diffusion process. PADRENs reveal a previously unrecognized level of neuronal organization that may provide insight into how the distinct branching patterns of the dendrites are intrinsically organized.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1978

The effects of various hormones on the surface morphology of testicular cells in culture.

The purpose of this investigation was to study the effects of various hormones on the surface morphology of 20-day-old rat testicular cells in culture. Aggregates containing primarily Sertoli cells and germinal cells were obtained by enzymatic digestion. The surface morphology of the cells composing these aggregates was characterized under various culture conditions using light microscopy and scanning electron microscopy. The cytoplasmic processes of Sertoli cells became highly branched and filamentous after being cultured in the presence of rat, human or ovine FSH. Identical branching and filamentation was observed when Sertoli cells were cultured in rat TSH. Finally, numerous large blebs were observed on the surfaces of germinal cells cultured in the presence of insulin. These results suggest that the branching and filamentation of Sertoli cell cytoplasm observed after FSH stimulation are not specific for that hormone.

Animals↗
PubMed1979

Ultrastructure of the renal corpuscle of the garter snake Thamnophis sirtalis.

The renal corpuscle of the garter snake was examined using scanning and transmission electron microscopy, freeze-fracture and tracer experiments. The renal corpuscle was small and glomerular architecture simple. The visceral epithelium was composed of irregular, highly branched podocytes with broad, interdigitating foot processes. Numerous cell junctions, including fasciae occludentes and adhaerentes, occurred between podocytes. The podocytes bore numerous microvilli which projected into the urinary space and contained large bundles of microfilaments. The podocytes lay on a basal lamina which appeared to act as a primary filtration barrier.

Animals↗
PubMed1989

Starburst amacrine cells of the primate retina.

A group of readily recognized amacrine cells were observed in Golgi-impregnated and flat-mounted macaque, baboon, and human retinas. These cells had roughly-circular or oval dendritic fields that were narrowly stratified within the inner plexiform layer (IPL). Most of these cells stratified in the inner half (sublamina b) of the IPL, and they had their somata in the ganglion-cell layer; a few stratified in the outer half (sublamina a) of the IPL and had their somata in the amacrine-cell layer. Typically, a single dendrite issued from the soma, and, after passing for 10 microns or so, gave rise to five or more radiate processes. As these processes neared the edge of the dendritic field they branched, turned, and became varicose. Most showed no evidence of an axon, although a few had a short process extending inward, toward the optic-fiber layer. Dendritic-field diameters were about 100 microns near the fovea and increased to about 350 microns in the peripheral retina. Mean somal diameter also increased slightly from near the fovea (7.8 microns) to the periphery (8.7 microns). Although the primate cells are smaller, and there are some minor differences in the form of the dendritic fields, these cells appear to be morphologically equivalent to the starburst amacrines of the rabbit retina, whose counterparts have also been observed in the retinas of rats and cats. Presuming that these cells correspond to the choline acetyltransferase immunoreactive primate cells described by Mariani and Hersh (J. Comp. Neurol. 267:269-280, '87), their overlap factor is about ten for the type whose somata lay in the ganglion-cell layer and about 0.25 for those whose somata lay in the amacrine-cell layer.

Animals↗
PubMed2004

Quantum dynamics study of the excited-state double-proton transfer in 2,2'-bipyridyl-3,3'-diol.

Density functional theory and quantum dynamics simulations have been used to study the double-proton transfer reaction in 2,2'-bipyridyl-3,3'-diol in the first singlet excited electronic state. This process is experimentally known to be branched: It consists of a fast, concerted reaction mechanism (tau approximately 100 fs) and a stepwise reaction mechanism [with a fast initial step (tau approximately 100 fs) and a slower final step (tau approximately 10 ps)]. Quantum dynamics simulations on a two-dimensional model reveal that the concerted reaction occurs despite the nonexistence of a concerted reaction path, but they fail to explain the relative slowness of the stepwise mechanism. A qualitative simulation using a three-dimensional model suggests that internal vibrational relaxation (IVR) might be the reason why the second stage of the stepwise mechanism is so slow.

2,2'-Dipyridyl↗
PubMed2003

Gabaergic signaling mediates the morphological organization of astrocytes in the adult rat forebrain.

Previous studies have provided evidence that the morphological organization of immature astrocytes is influenced by the inhibitory neuronal transmitter gamma amino-butyric acid (GABA). The present study was designed to determine whether the occurrence of differential organization of mature astrocytes throughout various regions of the adult brain is related to differential GABAergic signaling. For this we first used Western blotting and high-performance liquid chromatography to quantify the levels of the astrocytic protein glial fibrillary acidic protein (GFAP) and GABA, respectively, within the same tissue punches taken from different forebrain regions of the adult rat, as well as immunocytochemistry for GFAP, GABA, or glutamate decarboxylase to visualize the morphological organization of astrocytes and of GABAergic axons in these regions. These data indicate that GFAP and GABA contents are correlated throughout the different forebrain regions analyzed, and that the regions containing the highest densities in GABAergic terminals are those that contain astrocytes exhibiting the highest degree of stellation. Secondly, we chronically increased GABAergic signaling in vivo by the systemic administration of an inhibitor of GABA transaminase or by the intracerebroventricular infusion of muscimol, a potent agonist of GABA(A) receptors. Our data show that in both cases, the GFAP content of the different forebrain regions is significantly augmented, in close association with a marked increase in the number of astrocytic processes and with their degree of branching. Taken together, these data strongly suggest that GABAergic signaling mediates the morphological organization of astrocytes and their expression of GFAP in the adult brain.

4-Aminobutyrate Transaminase↗
PubMed2005

Theoretical study and rate constant calculation for the reactions of SH (SD) with Cl2, Br2, and BrCl.

The mechanisms of the SH (SD) radicals with Cl2 (R1), Br2 (R2), and BrCl (R3) are investigated theoretically, and the rate constants are calculated using a dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the MP2/6-311G(d,p) and MPW1K/6-311G(d,p) levels. Higher-level energies are obtained at the approximate QCISD(T)/6-311++G(3df, 2pd) level using the MP2 geometries as well as by the multicoefficient correlation method based on QCISD (MC-QCISD) using the MPW1K geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of these reactions, which indicate that the reactions may proceed via an indirect mechanism. The enthalpies of formation for the species XSH/XSD (X = Cl and Br) are evaluated using hydrogenation working reactions method. By canonical variational transition-state theory (CVT), the rate constants of SH and SD radicals with Cl2, Br2, and BrCl are calculated over a wide temperature range of 200-2000 K at the a-QCISD(T)/6-311++G(3df, 2pd)//MP2/6-311G(d, p) level. Good agreement between the calculated and experimental rate constants is obtained in the measured temperature range. Our calculations show that for SH (SD) + BrCl reaction bromine abstraction (R3a or R3a') leading to the formation of BrSH (BrSD) + Cl in a barrierless process dominants the reaction with the branching ratios for channels 3a and 3a' of 99% at 298 K, which is quite different from the experimental result of k3a'/k3' = 54 +/- 10%. Negative activation energies are found at the higher level for the SH + Br2 and SH + BrCl (Br-abstraction) reactions; as a result, the rate constants show a slightly negative temperature dependence, which is consistent with the determination in the literature. The kinetic isotope effects for the three reactions are "inverse". The values of kH/kD are 0.88, 0.91, and 0.69 at room temperature, respectively, and they increase as the temperature increases.

Journal Article↗
PubMed1995

Growth factors as mediators of androgen action during the development of the male urogenital tract.

Studies on the developing prostate and SV suggest that androgens act via mesenchymal AR to elicit synthesis and secretion of various autocrine and paracrine factors that regulate epithelial and stromal growth and differentiation. Clearly, the global regulation of epithelial growth and ductal branching morphogenesis is a complex multifactorial process involving the interplay of many diffusible factors (both positive and negative regulators), extracellular matrix molecules, cell-surface receptors for growth factors, receptors for extracellular matrix molecules, and matrix-degrading enzymes. Future progress will certainly be dependent upon the utilization of appropriate, biologically relevant models to examine the respective roles of various growth factors in the growth and development of androgen target organs.

Androgens↗
PubMed1996

Macrophages during avian optic nerve development: relationship to cell death and differentiation into microglia.

Cell death is frequent during the development of the nervous system. In the developing optic nerve of chicks and quails, neuroepithelial cell death was first observable on the third day of incubation, slightly after the first cell ganglion axons appeared in the stalk. Specialized phagocytes were observed within the stalk in chronological and topographical coincidence with cell death. These cells were identified as macrophages because of their morphological features, intense acid phosphatase activity and, in quail embryos, labeling with QH1, a monoclonal antibody recognizing quail hemangioblastic cells. Macrophages in areas of cell death were round and actively phagocytosed cell debris. We used electron microscopy and histochemical and immunocytochemical labeling to study macrophagic cells of the optic nerve in avian embryos of 3-6.5 days of incubation. As development proceeded, phagocytosing, round macrophages became ameboid macrophages that migrated from areas of cell death toward regions occupied by optic axonal fascicles. Macrophages in these locations were thin and elongated, with a few processes. To elucidate the final fate of macrophagic cells in the optic nerve, sections taken from older embryonic and hatched quails were stained with the QH1 antibody. On the 8th day of incubation some slightly ramified QH1+ cells were present among axonal fascicles. In subsequent stages these cells increased in number and acquired more complex ramifications. In adult optic nerves, QH1+ cells had a small body and sent out slender processes, sometimes with secondary and tertiary branches, which were frequently orientated parallel to the course of the optic axons. These cells were considered to be microglial cells. The appearance of macrophages within the developing optic nerve at the same time as neuroepithelial cell death suggests that cell death influences the recruitment of macrophages into the nerve. When macrophages reach the areas invaded by optic axonal fascicles, they undergo structural and probably also physiological changes that appear to signal differentiation into microglia.

Animals↗