Induction Of Branching Research Articles

Induction of ureter branching as a response to Wnt-2b signaling during early kidney organogenesis.

Epithelial-mesenchymal tissue interactions play a central role in vertebrate organogenesis, but the molecular mediators and mechanisms of these morphogenetic interactions are still not well characterized. We report here on the expression pattern of Wnt-2b during mouse organogenesis and on tests of its function in epithelial- mesenchymal interactions during kidney development. Wnt-2b is expressed in numerous developing organs in the mouse embryo, including the kidney, lung, salivary gland, gut, pancreas, adrenal gland, and genital tubercle. Additional sites of expression include the branchial arches and craniofacial placodes such as the eye and ear. The data suggest that the expression of Wnt-2b is associated with organs regulated by epithelial-mesenchymal interactions. It is typically localized in the capsular epithelium or peripheral mesenchymal cells of organ rudiments, e.g., the perinephric mesenchymal cells in the region of the presumptive renal stroma in the developing kidney at E11.5. Functional studies of the kidney demonstrate that cells expressing Wnt-2b are not capable of inducing tubule formation but instead stimulate ureter development. Incubation of isolated ureteric buds on such cells supports bud growth and branching. In addition, recombination of Wnt-2b-pretreated ureteric bud tissue with isolated nephrogenic mesenchyme results in a recovery of organogenesis and the expression of epithelial genes within the reconstituted organ explant. Lithium, a known activator of Wnt signaling (Hedgepeth et al. [1997] Dev Biol 185:82-91), is also sufficient to promote ureter branching in the reconstituted kidney in a comparable manner to Wnt-2b signaling, whereas Wnt-4, which induces tubules, neither supports the growth of a ureteric bud nor leads to reconstitution of the ureteric bud with the kidney mesenchyme. We conclude that Wnt-2b may act in the mouse kidney as an early mesenchymal signal controlling morphogenesis of epithelial tissue, and that the Wnt pathway may regulate ureter branching directly. In addition, Wnt signals in the kidney differ qualitatively and are specific to either the epithelial ureteric bud or the kidney mesenchyme.

Estrogen receptor transcription and transactivation: Novel morphoregulatory functions for the adhesion receptor Ep-CAM in the mammary epithelium

Ep-CAM, an epithelial cell-cell adhesion receptor, is often over-expressed in association with proliferation and remodeling in epithelial tissues. Development of the mouse mammary gland during pregnancy is associated with a progressive upregulation of Ep-CAM expression, eventually reaching very high levels at day 16 of pregnancy. This phenomenon is paralleled by a concomitant branching of the mammary ductal tree and a sustained epithelial cell proliferation. Using a MMTV-LTR/Ep-CAM transgenic mouse model, we demonstrate that forced expression of Ep-CAM in the mammary epithelium leads to an induction of budding and secondary branching of the glandular tree in virgin females. Interestingly, a complete cycle of gestation in the Ep-CAM transgenic mice results in extreme ductal hyperplasia/ductectasia and lobular hypoplasia, in combination with partially decreased differentiation of both ductal and alveolar (lobular) epithelial cells. Surprisingly, mammary gland involution is affected because of a decreased frequency of apoptotic figures and increased rate of cell proliferation. These results support novel morphoregulatory functions for the adhesion receptor Ep-CAM in epithelial tissue development and homeostasis.

Delta N89 beta-catenin induces precocious development, differentiation, and neoplasia in mammary gland.

To investigate the role of beta-catenin in mammary gland development and neoplasia, we expressed a stabilized, transcriptionally active form of beta-catenin lacking the NH(2)-terminal 89 amino acids (Delta N 89 beta-catenin) under the control of the mouse mammary tumor virus long terminal repeat. Our results show that Delta N 89 beta-catenin induces precocious lobuloalveolar development and differentiation in the mammary glands of both male and female mice. Virgin Delta N 89 beta-catenin mammary glands resemble those found in wild-type (wt) pregnant mice and inappropriately express cyclin D1 mRNA. In contrast to wt mammary glands, which resume a virgin appearance after cessation of lactation, transgenic mammary glands involute to a midpregnant status. All transgenic females develop multiple aggressive adenocarcinomas early in life. Surprisingly, the Delta N89 beta-catenin phenotype differs from those elicited by overexpression of Wnt genes in this gland. In particular, Delta N 89 beta-catenin has no effect on ductal side branching. This suggests that Wnt induction of ductal branching involves additional downstream effectors or modulators.

Blue light-induced branching in Vaucheria. Requirement of nuclear accumulation in the irradiated region.

When a narrow region of the fresh water coenocytic alga, Vaucheria terrestris sensu Götz is irradiated with moderately intense blue light, a branch is induced from the center of the irradiated region after 4-5 h. Movement of organelles and microtubule bundles during the photocytomorphogenetic response were investigated. Chloroplasts in the cortical layer immediately started to accumulate in the blue light-irradiated region and their accumulation almost completely finished 30-40 min after the onset of light when the nuclei residing in endoplasm started to accumulate. Accumulation of nuclei was synchronized with disorientation and shortening of microtubule bundles, which originally run parallel to the cell axis. Not only amiprophos-methyl, a potent microtubule-decomposing reagent, but also cytochalasin A strongly inhibited the branch induction. Amiprophos-methyl completely and cytochalasin A mostly destroyed microtubules and completely inhibited nuclear accumulation, but both drugs allowed the accumulation of chloroplasts in the cortical layer of irradiated region. These indicate that the accumulation of nuclei is indispensable for branch induction while the chloroplast accumulation is insufficient by itself for branch induction. The ineffectiveness of cytochalasin A on chloroplast movement brings the conventional view of sliding movement of chloroplast on a long actin cable into question. The morphological and functional relationship between a nucleus and a microtubular bundle are discussed.

Neural and Angiogenic Defects in Eyes of Transgenic Mice Expressing a Dominant-Negative FGF Receptor in the Pigmented Cells

Fibroblast growth factors (FGF) are multipotent cytokines with demonstrated mitogenic, neurotrophic and angiogenic properties. There is evidence that they have multiple functions during and after development of the vertebrate eye. Amongst these, the role of FGF receptor mediated signaling in the retinal pigmented epithelium (RPE) is not yet well understood. FGF-2 is produced in RPE cells and may play a role in photoreceptor development and/or survival in vivo. It may also stimulate growth of melanocytes and angiogenesis in the choroid. To address these questions, we have specifically disrupted FGF signaling by generating lines of transgenic mice expressing dominant-negative FGF receptor 1 (FGFR-1) in the pigmented cells. Histological analysis of the eyes were conducted on hemizygous and homozygous mice at different ages. In homozygotes, eye growth is strongly impaired during embryogenesis leading to massive eye degeneration seen in the early post-natal stages. In hemizygotes, the choroid is thinned and the finger-like junctions between RPE cells and photoreceptors are disrupted. Scanning electron microscopy of the choroid vasculature showed that choriocapillary density, diameter and branching are strongly affected. As mice age, they develop progressive retinal degeneration as evidenced by photoreceptor cell loss. Our results are in agreement with the hypothesis that FGF signaling in the RPE participates in photoreceptor survival in vivo. Our model provides evidence that FGF signaling is also involved in choroidal angiogenesis by a process that could relate to induction of terminal branching.

Representations of the symmetric group are reducible over simply transitive subgroups

If the characteristic of F is zero, this problem has been solved by Saxl [16]. An important feature of Saxl’s result is that a groupG as in the problem above is either 2-transitive or fixes a point, i.e. is contained in some Σn−1. The caseG ≤ Σn−1 can then be settled using the branching rule and induction. On the other hand, an explicit list of k-transitive groups (for k ≥ 2) is available, which can be used to complete the proof in characteristic zero, see [16] for more details. From now on we assume that p > 0. In this case the problem is important for determining maximal subgroups of finite classical groups [1],[13]. However, the situation is nowmore complicated. For example, to determine the pairs (G,D) as above withG = An one needs the Mullineux conjecture [7], [2]. IfG is intransitive then, up to a conjugation, it is contained in a standard Young subgroup of the form Σn−k ×Σk. The irreducible restrictions from Σn toΣn−1 have been described in [14], see also [11], [6]. In [11] it is also

Microtubule stabilization leads to growth reorientation in Arabidopsis trichomes.

The single-cell trichomes in wild-type Arabidopsis are either unbranched or have two to five branches. Using transgenic Arabidopsis plants expressing a green fluorescent protein-microtubule-associated protein4 fusion protein, which decorates the microtubular cytoskeleton, we observed that during trichome branching, microtubules reorient with respect to the longitudinal growth axis. Considering branching to be a localized microtubule-dependent growth reorientation event, we investigated the effects of microtubule-interacting drugs on branch induction in trichomes. In unbranched trichomes of the mutant stichel, a change in growth directionality, closely simulating branch initiation, could be elicited by a short treatment with paclitaxel, a microtubule-stabilizing drug, but not with microtubule-disrupting drugs. The growth reorientation appeared to be linked to increased microtubule stabilization and to aster formation in the treated trichomes. Taxol-induced microtubule stabilization also led to the initiation of new branch points in the zwichel mutant of Arabidopsis, which is defective in a kinesin-like microtubule motor protein and possesses trichomes that are less branched. Our observations suggest that trichome cell branching in Arabidopsis might be mediated by transiently stabilized microtubular structures, which may form a component of a multiprotein complex required to reorient freshly polymerizing microtubules into new growth directions.

The chemical-gas dynamic mechanisms of pulsating detonation wave instability

The chemical–gas dynamic mechanisms behind the instability and failure of a one–dimensional pulsating detonation wave driven by a three–step chain–branching reaction are revealed by direct numerical simulation. Two types of pulsating instability observed experimentally are explained. The first involves regular oscillations of the detonation front, where the instability is driven by low–frequency finite–amplitude compression and expansion waves in the chain–branching induction zone between the main reaction layer and the detonation shock. For irregular oscillations of the front, the instability mechanism first involves a decoupling between the shock and main reaction layer. Subsequently, the main reaction layer accelerates, drives a compression wave ahead of it, and undergoes a transition to detonation. This internal detonation wave overtakes the lead detonation shock, generating a new high–pressure detonation, which rapidly decays. A smaller–amplitude pressure oscillation occurs during the decay with a mechanism reminiscent of that observed for the previous regular oscillation, before the detonation and main reaction layer once again decouple and the instability cycle is repeated. For failure scenarios, the shock temperature is observed to drop to the cross–over temperature for the chain–branching reaction, causing the main reaction layer to decouple and retreat indefinitely from the detonation shock.

Thermally induced changes in shoot morphology of Hancornia speciosa microcultures: evidence of mediation by ethylene.

A shoot microculture protocol for the tropical fruit tree Hancornia speciosa Gom. was developed based on high temperature stimulation of axillary branching. An increase in the culture temperature from 25 to 31 degrees C (continuous over a 4-week period) stimulated the elongation of newly subcultured micro-shoots. Increases in culture temperature from 31 to 35 degrees C suppressed elongation but induced branching of all shoots. Increasing temperature to 37 degrees C reduced both shoot elongation and branching severely. Thermoperiodic regimes involving daily exposure for 8 or 16 h at 35 degrees C followed by 31 degrees C for the remainder of the day were only moderately effective in stimulating branching. However, maintaining cultures at 35 degrees C for 2 weeks followed by growth at a constant temperature of 31 degrees C led to vigorous branching. We hypothesize that thermally induced branching is mediated by a reduction in ethylene biosynthesis. In cultures of nodal segments grown at 31 degrees C, ethylene evolution peaked 12 to 16 days after subculture, and then gradually decreased until the end of the culture cycle. Compared with cultures held at 31 degrees C, those grown at 35 degrees C showed an earlier peak and a reduced rate of ethylene evolution throughout most of the culture cycle, and less 1-aminocyclopropane-1-carboxylate (ACC) synthase mRNA transcript and ACC oxidase activity. An inhibitor of ethylene biosynthesis (L-(2-aminoethoxyvinyl)-glycine) at 4.5 &mgr;M mimicked the effect of elevated temperature (35 degrees C) in stimulating lateral branching. The branching pattern of shoots grown at 35 degrees C in the presence of 1 &mgr;l l(-1) ethylene gas resembled that of shoots grown at 31 degrees C. We conclude that a reduction in ethylene evolution has a role in thermal induction of branching in H. speciosa. Heat induced release of axillary buds may be useful in the microculture of trees with strong apical dominance that cannot be overcome by cytokinin treatment.

Induction of isoflavonoid and retrochalcone branches of the flavonoid pathway in cultured Glycyrrhiza echinata cells treated with yeast extract.

Yeast extract-treated suspension cultures of a new cell line, AK-1, of Glycyrrhiza echinata were induced to produce an isoflavonoid phytoalexin (medicarpin) and metabolites of retrochalcone/flavone pathway (echinatin, licodione, and 7,4'-dihydroxyflavone). From these cells, putative full-length cDNAs encoding cytochrome P450s, (2S)-flavanone 2-hydroxylase and isoflavone 2'-hydroxylase, were cloned.

Direct Evidence for Ca2+Regulation of Hyphal Branch Induction

Grinberg, A., and Heath, I. B. 1997. Direct evidence for Ca2+regulation of hyphal branch induction.22,127–139. Irradiation of growing hyphae ofSaprolegnia feraxwith microbeams of UV (300–380 and 385–450 nm) light induced an increase in cytoplasmic [Ca2+] followed by precocious formation of one or more branches within about 4 min. The distribution of branches was strongly skewed toward the subapical side of the irradiation site, but otherwise was apparantly random. Apical (10-μm) irradiations were more effective than subapical (50-μm) ones in that they induced branches at comparable frequencies but with lower doses, consistent with higher concentrations of putative target intracellular Ca2+storage structures in this region. Once formed, induced adjacent branches seem to compete for “resources,” with those closer than ≈50 μm inhibiting each other. The results are most consistent with Ca2+-induced accumulation of branch initiating factors being the cause, not the consequence, of branch formation, thus supporting a primary role for Ca2+in regulation of hyphal tip growth.

Afferent Innervation Influences the Development of Dendritic Branches and Spines via Both Activity-Dependent and Non-Activity-Dependent Mechanisms

The present investigation uses an in vitro co-culture system to study the role of afferent innervation in early development and differentiation of hippocampal neurons. Our experiments indicate that the formation of two key morphological features, dendritic branches and dendritic spines, is induced by afferent innervation. Hippocampal neurons develop multiple dendritic branches and spines only when extensively innervated by living axonal afferents. No morphological changes occurred when hippocampal neurons were plated on other cell surfaces such as fixed axons or astrocytes. Furthermore, afferents exerted their effect locally on individual dendrites that they contacted. When one portion of the dendritic arbor of a neuron was contacted by afferents and the other portion was not, morphological effects were restricted to the innervated dendrites. Innervation of some of the dendrites on a neuron did not produce global effects throughout the neuron. Afferent-induced dendritic branching is independent of activity, since branch induction was unaffected by chronic application of TTX or glutamate receptor blockers. In contrast, the formation of dendritic spines is influenced by activity. The number of developing spines was reduced when TTX or a cocktail of three glutamate receptor blockers was applied. Blockade of individual AMPA, NMDA, or metabotropic glutamate receptors did not affect the number of spines. These results, taken together, demonstrate that afferents can have a prominent influence on the development of postsynaptic target cells via both activity-dependent and non-activity-dependent mechanisms, indicating the presence of multiple signals. Accordingly, this suggests an important interplay between pre- and postsynaptic elements early in development.

Residual Effects of Chemical Induction of Branching of Apple Trees in the Nursery on Their Performance after Transplanting

One-year-old trees of three apple selections [NY73334-35 (A), NY75414-1 (B), and NY75413-30 (C)] from the Geneva Breeding Program were transplanted into an orchard. While at the nursery, the trees were treated with Promalin and Accel, by themselves or in combination, to promote lateral branch formation (feathering). After trees were transplanted, no growth regulators were applied to the trees. One year after transplanting, treated trees of B and C had produced more feathers than the controls. This was particularly pronounced with the very difficult-to-branch selection C. No differences between chemical treatments were found. Regardless of selection, each chemical treatment significantly influenced increase in total extension growth compared to the control and contributed to rapid build up of tree structure. There were no differences between the treatments in tree height, tree caliper, or the number of spurs.

Electrophoretic characterization of endo-(1,4)-β-glucanases secreted during assimilative growth and antheridiol-induced branching inAchlya ambisexualis

Secreted endo-(1,4)-β-glucanases ("cellulases") of Achlya ambisexualis were analyzed by a technique that permits visualization of enzyme activity in situ after electrophoresis in gels containing sodium dodecyl sulfate. Catalytic polypeptides with molecular masses of about 97, 74, 36, 29, and 25 kDa were observed in media from young cultures, though progressively fewer bands were observed as cultures aged. Based on size estimations of native enzymes with gel exclusion chromatography, the 97- and 36-kDa polypeptides were concluded to be subunits of a 245-kDa holoenzyme and the 25-kDa polypeptides were concluded to be subunits of a second holoenzyme of about 92 kDa. The data were insufficient to allow similar assignments for the more ephemeral 74- and 29-kDa polypeptides. The endoglucanases secreted during branch induction by antheridiol or 0.2% peptone comigrated in electrophoretic gels with enzymes secreted during normal assimilative growth. No endoglucanases specific to induced branching were observed.Key words: oomycetes, cell walls, endoglucanases, cellulases, antheridiol.

Action of a diffusible target-derived chemoattractant on cortical axon branch induction and directed growth

Cortical axons innervate their brainstem target, the basilar pons, by the initiation and extension of collateral branches interstitially along their length. To address whether a diffusible pons-derived chemoattractant controls these events, we used cocultures in collagen matrices and time-lapse microscopy. Pontine explants enhanced by 5-fold the de novo initiation of transient branches along cortical axons; most branches were directed toward pons. Of the branches extended toward pons, 2%–3% were stabilized; those extended away were not. Pontine explants also enhanced the stable bifurcation of growth cones and prompted directional changes by growth cone turning and collateral extension. These effects were distance dependent and mimicked by pons-conditioned medium. This evidence indicates that the pons activity promotes branch initiation interstitially along cortical axons, a novel property for a chemoattractant, and provides a directional cue for their growth. These findings suggest that the pons chemoattractant serves as a diffusible target-recognition molecule.

Branch induction on apple nursery trees: Effects of growth regulators and defoliation

Abstract One‐year‐old apple (Malus domestica Borkh.) nursery trees of several cultivars on MM 106 and M 9a rootstock were sprayed once in early summer with benzyladenine (B A) followed by one, two, or three applications of gibberellin (GA4+7) either in 1989 or in 1990. In both years GA4+7applied at the same time or 2 weeks after a B A spray produced more branches and more total growth than controls. In 1990, but not 1989, GA4+7 applied 2 weeks after BA stimulated more branches and more total branch length than when these chemicals were applied together. In 1990 multiple applications of GA4+7 beginning 18 days after B A sprays induced the longest branches, most total branch growth, and greatest branch crotch angles than applications involving a single GA4+7 plus B A spray. In addition in 1989, immature leaves were removed immediately beneath the growing tip on the main stem (LR) once in early summer and sprayed with or without GA4+72 weeks later. Leaf removal treatments did not affect branching.

1115 Action of diffusible target-derived chemoattractant on cortical axon branch induction and directed growth

1115 Action of diffusible target-derived chemoattractant on cortical axon branch induction and directed growth

Induction of lateral branching in young cherry trees

Induction of lateral branching in young cherry trees

Induction of Adventitious Branches from Cultured Citrus Juice Vesicles -- A Potential Means of Proliferation

The noncallusing morphogenetic properties of Citrus juice vesicles cultured in vitro are unknown and were herein studied. Juice vesicles isolated from 120–180-day-old fruits are capable of proliferation via adventitious vesicle branching in vitro. Gibberellic acid levels of 1–100 mg/L greatly enhanced adventitious vesicle branching while delaying vesicle senescence as evidenced by the vesicles' ability to retain its green color for up to 4 to 6 mo in culture. Vesicles grown on media without gibberellic acid readily matured, turning opaque within 2 mo in culture and rarely produced adventitious branches. Additions of 0.1 mg/L α-naphthaleneacetic acid or 1.0 mg/L benzylaminopurine to media containing 10 mg/L gibberellic acid further enhanced vesicle branching in some species and cultivars. Adventitious juice vesicles have been induced from a variety of citrus species, including Citrus grandis (L.) Osb., C. hystrix DC., C. limon (L.) Burm. f., C. medica L., C. paradisi Macf., C. reticulata Blanco, and C. sinensis (L.) Osb. Adventitious vesicle branches originate from primordia initiated on the surface of the cultured vesicle. These primordia commonly occurred on the terminal meristem region of the vesicle. However, some species (e.g., C. grandis and C. paradisi) produced adventitious vesicle branches from their bodies and stalks as well. Distinct vesicle branches begin to appear on preformed vesicles after 30–60 days in culture. A survey to determine the natural occurrence of vesicle branching in various Citrus species was also conducted. Natural vesicle branching commonly occurred in C. grandis, C. paradisi, and in some cultivars of C. reticulata, but was absent in most citrus species and cultivars (e.g., C. aurantifolia (Christm.) Swing., C. canaliculata Hort. ex Y. Tan., C. hystrix, C. limon, C. medica, C. sinensis). It was found that some species which failed to exhibit the adventitious branching phenomenon in nature did so in vitro (e.g., C. hystrix, C. medica, and C. sinensis).

Branch Induction by Growth Regulators and Leaf Removal in ‘Delicious’ Apple Nursery Stock

Abstract Spur-type ‘Delicious’ apple nursery trees do not naturally branch in the nursery. In several experiments during 2 years, combinations of immature leaf removal (LR), BA, and gibberellins 4 + 7 (GA4+7) at 750 and 1000 mg·liter–1 induced lateral shoot formation of Campbell and Mercier strains of ‘Redchief Delicious’ trees in a commercial nursery. Split applications of BA and GA4+7 at 1000 mg·liter–1 induced more and longer branches than simultaneous applications. GA3 did not substitute for GA4+7 in this response. Removing young shoot tip leaves increased branching only when very young leaves were removed during a period of 2 weeks. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine (BA), gibberellin (GA).