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Results for “Spatial pattern formation”

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At least 991 records · Page 55Linked to original sources

PubMed1994

Transcriptional regulation of string (cdc25): a link between developmental programming and the cell cycle.

During postblastoderm embryogenesis in Drosophila, cell cycles progress in an invariant spatiotemporal pattern. Most of these cycles are differentially timed by bursts of transcription of string (cdc25), a gene encoding a phosphatase that triggers mitosis by activating the Cdc2 kinase. An analysis of string expression in 36 pattern-formation mutants shows that known patterning genes act locally to influence string transcription. Embryonic expression of string gene fragments shows that the complete pattern of string transcription requires extensive cis-acting regulatory sequences (> 15.3 kb), but that smaller segments of this regulatory region can drive proper temporal expression in defined spatial domains. We infer that string upstream sequences integrate many local signals to direct string's transcriptional program. Finally, we show that the spatiotemporal progression of string transcription is largely unaffected in mutant embryos specifically arrested in G2 of cycles 14, 15, or 16, or G1 of cycle 17. Thus, there is a regulatory hierarchy in which developmental inputs, not cell cycle inputs, control the timing of string transcription and hence cell cycle progression.

Animals↗

PubMed2004

Capicua integrates input from two maternal systems in Drosophila terminal patterning.

In Drosophila, the maternal terminal system specifies cell fates at the embryonic poles via the localised stimulation of the Torso receptor tyrosine kinase (RTK). Signalling by the Torso pathway relieves repression mediated by the Capicua and Groucho repressors, allowing the restricted expression of the zygotic terminal gap genes tailless and huckebein. Here we report a novel positive input into tailless and huckebein transcription by maternal posterior group genes, previously implicated in abdomen and pole cell formation. We show that absence of a subset of posterior group genes, or their overactivation, leads to the spatial reduction or expansion of the tailless and huckebein posterior expression domains, respectively. We demonstrate that the terminal and posterior systems converge, and that exclusion of Capicua from the termini of posterior group mutants is ineffective, accounting for reduced terminal gap gene expression in these embryos. We propose that the terminal and posterior systems function coordinately to alleviate transcriptional silencing by Capicua, and that the posterior system fine-tunes Torso RTK signalling output, ensuring precise spatial domains of tailless and huckebein expression.

Animals↗

PubMed2004

Three-dimensional, quantitative analysis of desmin and smooth muscle alpha actin expression during angiogenesis.

Angiogenic therapies have been designed for many pathological conditions, but when used as a single therapy, the clinical results have fallen short of expectations. In addition, strategies for vascularizing engineered tissues have been unsuccessful in promoting the formation of an extensive, stable vasculature. Recent evidence suggests that mural cells play a critical role in the success of these approaches, but our current understanding of the function of mural cells in the microvasculature is incomplete. We studied the three-dimensional spatial and temporal kinetics of the mural cell markers desmin and smooth muscle alpha actin during angiogenesis in an in vivo fibrin gel model. The results led to the following conclusions: (1) desmin and smooth muscle alpha actin positive cells are present during the initial development of vessel sprouts; (2) the presence of these cells in the microvasculature is not always an indicator of vessel stability; and (3) the mural cell markers desmin and smooth muscle alpha actin exhibit differential staining patterns during vessel formation. These findings shed new light on the complexity of the relationship between mural cells and the formation of a mature, stable microcirculation.

Actins↗

PubMed2006

Maternal gametophytic baseless1 is required for development of the central cell and early endosperm patterning in maize (Zea mays).

In angiosperms, double fertilization of an egg cell and a central cell with two sperm cells results in the formation of a seed containing a diploid embryo and a triploid endosperm. The extent to which the embryo sac controls postfertilization events in the seed is unknown. The novel gametophytic maternal-effect maize mutation, baseless1 (bsl1) affects central cell development within the embryo sac, frequently by altering the position of the two polar nuclei. Despite this irregularity, fertilization is as efficient as in wild type. The spatial expression of basal endosperm-specific transcripts is altered in free-nuclear and cellular mutant endosperms. At later stages of seed development, bsl1 predominantly affects development of the basal endosperm transfer layer (BETL). When bsl1/+ diploid plants were pollinated by wild-type tetraploid plants, the BETL abnormalities observed in bsl1/bsl1/+/+ tetraploid endosperms were diverse and of variable severity. Moreover, the frequency of kernels with severely perturbed BETL development correlated with the percentage of severely affected bsl1 central cells. Therefore, BSL1 is likely required in the central cell before fertilization for correct BETL patterning to occur. These findings provide new genetic evidence that a maternal gametophytic component is necessary for correct endosperm patterning.

Gametogenesis↗

PubMed1998

Spatial regulation of trichome formation in Arabidopsis thaliana.

Trichomes in Arabidopsis are single-celled hairs that develop from epidermal cells regularly distributed on leaves, sepals and stems. Trichome formation in Arabidopsis is emerging as a genetic and molecular model system for the analysis of the spatial regulation of cell type specification in plants. In this review we focus on two aspects of trichome initiation: the regulation of organ and tissue layer specificity and the establishment of an epidermal spacing pattern.

Arabidopsis↗

PubMed1985

A subset of cells in the nerve net of Hydra oligactis defined by a monoclonal antibody: its arrangement and development.

A monoclonal antibody, termed JD1, was generated that bound to a subset of the nerve cells in the hypostome and tentacles of Hydra oligactis. Using a whole-mount technique the spatial pattern of the subset of nerve cells and their processes could be clearly visualized using indirect immunofluorescence. The subset largely corresponds to the epidermal sensory cells. Using the same technique the development of the pattern during head regeneration and budding was examined. The appearance of the nerve cells coincides with the formation of both the tentacles and hypostome. When head regeneration does not occur, JD1+ cells do not appear suggesting the differentiation of JD1+ cells is an integral event in head formation dependent on antecedent patterning processes.

Animals↗

PubMed2002

Differential segregation in a cell-cell contact interface: the dynamics of the immunological synapse.

Receptor-ligand couples in the cell-cell contact interface between a T cell and an antigen-presenting cell form distinct geometric patterns and undergo spatial rearrangement within the contact interface. Spatial segregation of the antigen and adhesion receptors occurs within seconds of contact, central aggregation of the antigen receptor then occurring over 1-5 min. This structure, called the immunological synapse, is becoming a paradigm for localized signaling. However, the mechanisms driving its formation, in particular spatial segregation, are currently not understood. With a reaction diffusion model incorporating thermodynamics, elasticity, and reaction kinetics, we examine the hypothesis that differing bond lengths (extracellular domain size) is the driving force behind molecular segregation. We derive two key conditions necessary for segregation: a thermodynamic criterion on the effective bond elasticity and a requirement for the seeding/nucleation of domains. Domains have a minimum length scale and will only spontaneously coalesce/aggregate if the contact area is small or the membrane relaxation distance large. Otherwise, differential attachment of receptors to the cytoskeleton is required for central aggregation. Our analysis indicates that differential bond lengths have a significant effect on synapse dynamics, i.e., there is a significant contribution to the free energy of the interaction, suggesting that segregation by differential bond length is important in cell-cell contact interfaces and the immunological synapse.

Animals↗

PubMed1998

Spatially restricted expression of pipe in the Drosophila egg chamber defines embryonic dorsal-ventral polarity.

Expression of pipe in the somatic tissue of the Drosophila ovary is required for the formation of embryonic dorsal-ventral polarity. pipe, which encodes an enzyme similar to the glycosaminoglycan-modifying enzyme heparan sulfate 2-O-sulfotransferase, is expressed in a spatially restricted domain of follicle cells on the ventral side of the egg chamber. Mutations that affect follicular polarity correspondingly alter the spatial pattern of pipe expression. Directed expression of pipe in otherwise pipe mutant females restores embryonic lateral and ventral pattern elements and can orient the dorsal-ventral axis of the embryo. Thus, the localized expression of pipe and the spatially restricted modification of carbohydrate chains play pivotal roles in the mechanisms that establish embryonic pattern and integrate follicular and embryonic polarity.

5' Untranslated Regions↗

PubMed2004

The influence of stimulus properties on category construction.

It has been demonstrated that when people free classify stimuli presented simultaneously in an array, they have a preference to categorize by a single dimension. However, when people are encouraged to categorize items sequentially, they sort by "family resemblance," grouping by overall similarity. The present studies extended this research, producing 3 main findings. First, the sequential procedure introduced by G. Regehr and L. R. Brooks (1995) does not always produce a preference for family resemblance sorts. Second, sort strategy in a sequential procedure is sensitive to subtle variations in stimulus properties. Third, spatially separable stimuli evoked more family resemblance sons than stimuli of greater spatial integration. It is suggested that the family resemblance sorting observed is due to an analytic strategy.

Association Learning↗

PubMed1995

On the possibility of coherently stimulated recombination and cosmological structure generation: recombination instability.

Possible instabilities during cosmological recombination may produce an epoch of nonlinear density growth and fractal-like structural patterns out to the horizon scale at that epoch (approximately 200 Mpc today). With this motivation, we examine the consequences of the change in effective radiative recombination reaction rate coefficients produced by intense stimulated emission. The proton-electron recombination is considered as a natural laser, leading to the formation of spatially nonuniform distributions of neutral matter earlier than the recombination epoch.

Journal Article↗

PubMed2003

Monte Carlo simulation of the image formation process in portal imaging.

We have written Monte Carlo programs to simulate the formation of radiological images. Our code is used to propagate a simulated x-ray fluence through each component of an existing video-based portal imaging system. This simulated fluence consists of a 512 x 512 pixel image containing both contrast-detail patterns as well as checker patterns to assess spatial resolution of the simulated portal imager. All of the components of the portal imaging system were modeled as a cascade of eight linear stages. Using this code, one can assess the visual impact of changing components in the imaging chain by changing the appropriate probability density function. Virtual experiments were performed to assess the visual impact of replacing the lens and TV camera by an amorphous silicon array, and the effect of scattered radiation on portal images.

Computer Simulation↗

PubMed1998

Small intestinal submucosa: a substrate for in vitro cell growth.

The extracellular matrix (ECM) of the small intestinal submucosa (SIS) was harvested by removing the superficial layers of the mucosa and the external muscular layers. The remaining 80 microns thick sheet was disinfected and sterilized by methods which removed all cellular components. The SIS-ECM, retaining its native 3-dimensional microarchitecture and composition, was evaluated for its ability to support in vitro cell growth. Six separate cell types were seeded either alone or in coculture with other cells upon this matrix, grown in selected media, a examined daily for time periods ranging from 48 h to 2 weeks. The six cell types tested were NIH Swiss mouse 3T3 fibroblast, NIH 3T3/j2 fibroblasts, primary human fibroblasts, primary human keratinocytes, human microvascular endothelial cells (HMECs), and an established rat osteosarcoma (ROS) cell line. All cell types showed the ability to attach a proliferate. All fibroblast cell line and the keratinocytes proliferated and/or migrated into the 3-dimensional scaffold of the SIS matrix. The ROS cells and the HMECs were confined in their growth pattern to the surface of the matrix. Coculturing of NIH 3T3/J2 fibroblasts and primary human keratinocytes resulted in a distinctive spatial orientation of the two cell types. The fibroblast populated the mid-substance of the 3-dimensional matrix and the keratinocytes formed an epidermal structure with rete ridge-like formation and stratification when the composite was lifted to an air liquid interface in culture. In summary, SIS provides a substratum with a 3-dimensional scaffold that allows for cell migration and spatial organization. The substratum is suitable for in vitro studies of the interaction between epithelial or mesenchymal cells and a naturally occurring extracellular matrix.

3T3 Cells↗

PubMed1997

Some functions of primary auditory cortex in learning and memory formation.

In the primary auditory field AI of gerbil auditory cortex, aversive tone conditioning paradigms reshaped frequency receptive fields of single units and also changed the spatial representation of tones in fluoro-2-deoxyglucose (FDG) experiments. As another aspect of learning-induced plasticity in gerbil AI, antibodies against the immediate early gene product c-Fos identified an unusual spatial pattern of neurons in terms of a "macrocolumn." The pattern resulted from repeated short exposure of the animals to a tone in a new environment. The search for transmitters that may mediate this gene activation is carried out by microdialysis through chronically implanted probes in auditory cortex. So far, dopamine transmission was found to reflect specific aspects of auditory learning in cortex. The results suggest that spectral features of sounds as well as aspects of learned behavioral meaning of the sounds may be represented in AI.

Animals↗

PubMed1996

Neuronal loss and cytoskeletal disruption following intrahippocampal administration of the metabolic inhibitor malonate: lack of protection by MK-801.

Impaired energy metabolism may contribute to the pathogenesis of late-onset neurodegenerative disorders such as Alzheimer's disease by increasing neuronal vulnerability to excitotoxic damage through the NMDA receptor. The effects of metabolic impairment on the striatum have been extensively examined, but relatively little is known regarding the vulnerability of the hippocampus. To examine the effect of metabolic impairment on the hippocampal formation, malonate (0.25-2.5 mumol), a reversible inhibitor of succinate dehydrogenase, was administered by stereotaxic injection into the hippocampus of male Sprague-Dawley rats. Neuronal loss was assessed by Nissl stain, and immunocytochemistry was used to examine cytoskeletal disruption. Malonate produced a dose-dependent lesion in which CA1 pyramidal neurons were most vulnerable, followed by CA3 and dentate gyrus. Cytoskeletal alterations included the loss of microtubule-associated protein 2 (MAP2) and dendritic MAP1B immunoreactivity, whereas axonal MAP1B and tau proteins were relatively spared. Spatially and temporally correlated with the loss of MAP2 was an increase in the immunoreactivity of calpain-cleaved spectrin. A similar pattern of neuronal damage and cytoskeletal disruption was produced by intrahippocampal injection of quinolinate (0.1 mumol), an NMDA agonist. Although these results are consistent with the hypothesis that metabolic impairment results in excitotoxic death, MK-801 (dizocilipine maleate), a noncompetitive NMDA receptor antagonist, did not attenuate the lesions produced by malonate but was effective against quinolinate. The results suggest that NMDA receptor activation is not required for malonate-induced damage in the hippocampal formation.

Animals↗

PubMed1999

The structural and mechanical complexity of cell-growth control.

Tight control of cell proliferation is required to ensure normal tissue patterning and prevent cancer formation. The analysis of cultured cells has led to an explosion in our understanding of the molecules that trigger growth and mediate cell-cycle progression. However, the mechanism by which the local growth differentials that drive morphogenesis are established and maintained still remains unknown. Here we review recent work that reveals the importance of cell binding to the extracellular matrix, and associated changes in cell shape and cytoskeletal tension, to the spatial control of cell-cycle progression. These findings change the paradigm of cell-growth control, by placing our understanding of molecular signalling cascades in the context of the structural and mechanical complexity of living tissues.

Animals↗

PubMed1993

Differential, temporal and spatial expression of genes involved in storage oil and oleosin accumulation in developing rapeseed embryos: implications for the role of oleosins and the mechanisms of oil-body formation.

The temporal and spatial expression of oleosin and delta 9-stearoyl-ACP desaturase genes and their products has been examined in developing embryos of rapeseed, Brassica napus L. var. Topas. Expression of oleosin and stearate desaturase genes was measured by in situ hybridisation at five different stages of development ranging from the torpedo stage to a mature-desiccating embryo. The temporal pattern of gene expression varied dramatically between the two classes of gene. Stearate desaturase gene expression was relatively high, even at the torpedo stage, whereas oleosin gene expression was barely detectable at this stage. By the stage of maximum embryo fresh weight, stearate desaturase gene expression had declined considerably while oleosin gene expression was at its height. In contrast to their differential temporal expression, the in situ labelling of both classes of embryo-specific gene showed similar, relatively uniform patterns of spatial expression throughout the embryo sections. Immunogold labelling of ultra-thin sections from radicle tissue with anti-oleosin antibodies showed similar patterns to sections from cotyledon tissue. However, whereas at least three oleosin isoforms were detectable on western blots of homogenates from cotyledons, only one isoform was found in radicles. This suggests that some of the oleosin isoforms may be expressed differentially in the various types of embryo tissue. The differential timing of stearate desaturase and oleosin gene expression was mirrored by similar differences in the timing of the accumulation of their ultimate products, i.e. storage oil and oleosin proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Brassica↗

PubMed1994

A role for cytoplasmic determinants in mesoderm patterning: cell-autonomous activation of the goosecoid and Xwnt-8 genes along the dorsoventral axis of early Xenopus embryos.

Although an induction event is required for the formation of mesoderm in Xenopus embryos, it is not clear that this induction is wholly sufficient to give rise to a correctly patterned mesodermal layer. We have studied the expression of the two genes, goosecoid and Xwnt-8, in Xenopus gastrulae in which cell-cell communication, and therefore mesoderm induction, has been prevented by frequent cell dispersion. Although neither the early panmesodermal marker Xbra nor the muscle-specific alpha-actin gene were activated under these conditions, goosecoid and Xwnt-8 were activated in cells of dorsal and ventrolateral origin respectively, thus correctly reflecting their distribution during normal development. We also show that the spatial pattern of expression of these two genes along the animal-vegetal axis is similar in normal and in dissociated early gastrulae: goosecoid is mainly expressed in future mesoderm while the domain of expression of Xwnt-8 spans the mesoderm-endoderm boundary. These results show that, during the blastula and early gastrula stages, gene activation can be controlled cell-autonomously along both the animal-vegetal and dorsoventral embryo axes. This suggests that the inheritance of localised maternal cytoplasmic determinants is a key event for the patterning of mesoderm. We present a modified model of mesoderm formation in which the different mesoderm cell types are produced as a result of cooperation between induction-dependent and induction-independent immediate-early genes.

Animals↗

PubMed1991

A hypothetical mechanism for fetal alcohol syndrome involving ethanol inhibition of retinoic acid synthesis at the alcohol dehydrogenase step.

Ethanol acts as a teratogen causing brain, craniofacial, and limb abnormalities in those suffering from fetal alcohol syndrome. Normal embryonic development of the vertebrate nervous system and limbs has recently been shown to be governed by retinoic acid, the active form of vitamin A. Retinol dehydrogenase is an enzyme needed to convert vitamin A (retinol) to retinoic acid, a molecule that specifies embryonic pattern formation by controlling gene expression. Ethanol acts as a competitive inhibitor of the retinol dehydrogenase activity attributed to mammalian alcohol dehydrogenase (ADH), an enzyme that uses both retinol and ethanol as substrates. An hypothesis is presented in which many of the abnormalities observed in fetal alcohol syndrome may be caused by high levels of ethanol acting as a competitive inhibitor of ADH-catalyzed retinol oxidation in the embryo or fetus. This would presumably result in a reduction of retinoic acid synthesis in embryonic tissues such as the nervous system and limbs that require critical levels of this molecule to specify spatial patterns.

Alcohol Dehydrogenase↗