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Results for “Spatial pattern formation”

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PubMed2001

Novel marker genes for early leaf development indicate spatial regulation of carbohydrate metabolism within the apical meristem.

To identify genes expressed at the earliest stages of leaf development, we have performed a differential display analysis using portions of meristems destined to form leaves. Our analysis led to the identification of five genes showing an asymmetric pattern of gene expression within the meristem associated with leaf formation. Surprisingly, three of these genes encoded enzymes involved in carbohydrate metabolism (ADPglucose pyrophosphorylase, sucrose synthase and an SNF1-like kinase). Furthermore, specific transcript patterns were responsive to specific sugar and hormonal treatments. The other two genes identified encoded a Phantastica-like myb transcription factor (associated with the acquisition of leaf dorsiventrality) and CYP85 (a cytochrome P450, which plays a pivotal role in brassinolide metabolism). These data, firstly, identify a novel set of marker genes for the analysis of the earliest stages of leaf formation. Secondly, the function of the proteins encoded by these genes and their expression patterns within the meristem indicate that carbohydrate metabolism is spatially regulated within a tissue involved in key developmental processes. Finally, our data provide the first indication of an asymmetry in gene expression related to hormone biosynthesis in the meristem.

Amino Acid Sequence↗

PubMed1999

Molecular and genetic analysis of the Tribolium Ultrabithorax ortholog, Ultrathorax.

Ultrabithorax (Ubx) is essential for the proper patterning of the posterior thorax and anterior abdomen in Drosophila. The Coleoptera and Diptera differ in the organization and structure of their thorax and anterior abdomen. Changes in the regulation of Ubx and/or its downstream target genes are predicted to underlie these altered morphologies. We exploited the feasibility of genetic analysis in the red flour beetle, Tribolium castaneum, to examine the role of its Ubx ortholog in development. We analyzed genomic and cDNA clones that predict a polypeptide with nearly 100% identity with the Drosophila Ubx gene in the homeodomain and flanking sequences. Southern blot analysis indicates that these clones represent DNA sequences within the Homeotic complex (HOM-C) of Tribolium. Phenotypic analysis of mutant variants of the Ultrathorax (Utx) gene, and its location within the beetle HOM-C, strongly supports Utx being the Tribolium ortholog of Ubx. The embryonic expression pattern of Ubx-homologous transcripts coincides with the phenotypes associated with Utx mutations, providing support that the Ubx-homologous cloned DNA represents the Utx locus. By mid-germband extension Utx transcripts are expressed in a pattern similar to Ubx in Drosophila. However, during early germband formation Utx transcripts differ in both spatial and temporal progression. Utx expression is initially detected in parasegments 4 and 5 (T1p-T3a) as they are established during early germband formation. This is the first report of the wild-type parasegmental expression of an insect Ubx ortholog extending through parasegment 4. The earlier and more anterior expression in the thorax may underlie the modification of the Coleopteran thorax.

Amino Acid Sequence↗

PubMed1977

Temporo-spatial pattern of subcortical spike activity in kindling epilepsy. A statistical approach.

Recording electrodes were implanted stereotaxically in limbic and thalamic structures and the mesencephalic reticular formation in twelve cats. The animals were submitted to daily stimulation of the left amygdaloid nucleus following the technique for the kindling procedure, always combined with 5 h 30 min post-stimulation monitoring. After about 18 days, generalized convulsive activity was established. The following results concerning the quantitative evolution of spontaneously occurring interictal spikes were obtained. Amygdaloid nuclei, the hippocampus and the thalamic nucleus ventralis lateralis (VL) demonstrated an increase of discharge activity during the kindling procedure, following by a significant decrease after convulsions had been elicited. Thalamic nucleus centrum medianum (CM) was the only recording site investigated where the amount of interictal discharge increased and remained at a high level even after generalized convulsions had been established. Fourier analysis of slow oscillations in discharge generation yielded two main types of significant periodicity. A 165 min oscillation could be detected in all structures tested except reticular formation, which developed a 110 min cycle shared only with the thalamic CM. Significant correlations in spike activity were obtained from various structures. Stimulated amygdala seemed to have alternating relations with thalamic CM and VL, whereas stimultaneous oscillations excisted between MRF and CM. The occurrence of high voltage spikes in both contralateral and ipsilateral amygdalae was shown to be significantly correlated.

Action Potentials↗

PubMed1997

Expression of contact, a new zebrafish DVR member, marks mesenchymal cell lineages in the developing pectoral fins and head and is regulated by retinoic acid.

Contact, a new zebrafish transforming growth factor-beta (TGF-beta) member is most closely related to mouse GDF5 and to human CDMP-1 responsible, when mutated, for limb brachypodism phenotype and Hunter-Thompson syndrome, respectively. Contact exhibits a dynamic spatial expression pattern in the pharyngeal arches and the pectoral fin buds that much prefigures cartilage formation. Within the fin buds, contact expression is detected in the proximal mesenchyme from which the endoskeleton will develop. Exogeneously applied retinoic acid (RA) induces duplication of the pectoral fin rudiment in zebrafish embryos as well as contact expression along the proximal margin of the fin mesenchyme showing that both endoskeleton and exoskeleton can be duplicated.

Amino Acid Sequence↗

PubMed1999

Dishevelled: at the crossroads of divergent intracellular signaling pathways.

During the development of multicellular organisms the formation of complex patterns relies on specific cell-cell signaling events. For tissues to become spatially organized and cells to become committed to specialized fates it is absolutely crucial for proper development that the underlying signaling systems receive and route information correctly. Recently, a wealth of genetic and biochemical experimental data has been collected about prevalent evolutionary conserved signaling families, such as the Wnts, Dpp/BMPs, and Hedgehogs, in flies, worms, and vertebrates. Paradoxically, members of a particular signaling family often have receptors with similar biochemical binding properties, though they activate different intracellular pathways in vivo and can be phenotypically distinguished. How are their specific biological responses then generated? With respect to signaling specificity in Wnt pathways, Dishevelled is an intriguing protein; in Drosophila melanogaster it is required in two distinct signaling pathways, that share Frizzled receptors of similar structure, but have distinct intracellular signaling routes. Recent results suggest that Dishevelled is a multifunctional protein at the crossroads of divergent Wnt/Fz pathways. Dishevelled appears to be a key factor in Wnt signaling to read' signals coming from the plasma membrane and route them into the correct intracellular pathways.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Noise-sustained structures in differential-flow reactors with autocatalytic kinetics.

We have studied the formation of noise-sustained structures in a differential-flow reactor with cubic autocatalytic kinetics (the Gray-Scott model). In this system the interplay between advection, diffusion, reaction, and noise fluctuations leads to the formation of noise-sustained patterns in the key species. Numerical integration in one and two spatial dimensions shows that the structures are nonlocally cross correlated. Near threshold, the observed correlation is related to the properties of the convectively unstable critical modes.

Journal Article↗

PubMed2005

Counterpropagating beams in biased photorefractive crystals: anisotropic theory.

We formulate an anisotropic nonlocal theory of the space charge field induced by the coherent counterpropagating beams in biased photorefractive crystals. We establish that the competition between the drift and diffusion terms has to be taken into account when the crystal ĉ axis is tilted with respect to the propagation direction of the beams. We demonstrate that this configuration combines the features of both spatial soliton formation without energy exchange and two-wave mixing with energy exchange leading to pattern formation.

Journal Article↗

PubMed1995

Transcription factors and pattern formation in the developing lung.

During development of the respiratory tract embryonic cells are instructed to organize themselves along an axis and differentiate, such that proximal structures (trachea) greatly differ from those in distal alveoli. Pattern formation relates to this process of organization, and it is believed to be transcriptionally regulated in many developmental systems. Although the lung is the site of expression of many transcription factors, such as Hox, retinoid receptors, hepatocyte nuclear factors, and myc, among others, little information is available on how they influence lung pattern. Functional studies so far have directly implicated the product of the protooncogene N-myc and the retinoic acid receptors as transcriptional regulators of lung patterning, and it is likely that tissue-specific homeobox genes, such as the thyroid transcription factor-1, play an important role in distal lung formation. This review describes several aspects of transcription factors possibly involved in lung patterning, including structure, spatial distribution, and their putative functions.

Aging↗

PubMed2000

The involvement of recurrent connections in area CA3 in establishing the properties of place fields: a model.

Strong constraints on the neural mechanisms underlying the formation of place fields in the rodent hippocampus come from the systematic changes in spatial activity patterns that are consequent on systematic environmental manipulations. We describe an attractor network model of area CA3 in which local, recurrent, excitatory, and inhibitory interactions generate appropriate place cell representations from location- and direction-specific activity in the entorhinal cortex. In the model, familiarity with the environment, as reflected by activity in neuromodulatory systems, influences the efficacy and plasticity of the recurrent and feedforward inputs to CA3. In unfamiliar, novel, environments, mossy fiber inputs impose activity patterns on CA3, and the recurrent collaterals and the perforant path inputs are subject to graded Hebbian plasticity. This sculpts CA3 attractors and associates them with activity patterns in the entorhinal cortex. In familiar environments, place fields are controlled by the way that perforant path inputs select among the attractors. Depending on the training experience provided, the model generates place fields that are either directional or nondirectional and whose changes when the environment undergoes simple geometric transformations are in accordance with experimental data. Representations of multiple environments can be stored and recalled with little interference, and these have the appropriate degrees of similarity in visually similar environments.

Animals↗

PubMed1988

Ontogeny of architectural complexity in embryonic quail visceral arch muscles.

Understanding the mechanisms of muscle pattern formation requires that the complete sequence of ontogenetic events be defined, particularly in the emergence of architectural complexity and in the spatial relations between muscles and skeletal elements. This analysis of visceral arch myogenesis in quail (Coturnix coturnix japonica) embryos identifies the location of premuscle condensations and subsequent segregation of individual muscles, documents the initial orientation of myofibers and changes in alignment associated with maturation, and describes the spatial and temporal relations between muscle development and the formation of connective tissues. Premuscle condensations form within the visceral arches on embryonic days 2-4, before skeletal elements make their appearance. Discrete muscles may form from the subdivision of a muscle mass after fiber orientations have been established (e.g., jaw adductor and hyobranchial muscles) or by the segregation of a mesenchymal cluster from the condensation prior to the appearance of oriented fibers (e.g., protractor, muscle of the columella). The rate and pattern of subsequent muscle maturation are closely associated with the development of the hard tissues. Myogenesis in 4-9-day embryos centers around the quadrate cartilage, the retroarticular process of the mandibular (Meckel's) cartilage, and the epibranchial cartilage. Muscles form attachments on these elements and remain without additional attachments until the appropriate elements (e.g., otic capsule, pterygoid bone) develop. No single description of myogenic events applies to all visceral arch muscles, nor is there an arch-specific pattern of ontogeny. Rather, each muscle has distinctive characteristics based on its spatial relations within the developing head.

Animals↗

PubMed1994

Morphogenetic differences between fore and hind limb precartilage mesenchyme: relation to mechanisms of skeletal pattern formation.

Using a serum-free culture system, we have investigated morphogenetic differences between fore and hind limb precartilage mesenchymal cells derived from stages 21-26 chicken embryos. Across all stages, wing and leg cultures were intrinsically different in the amount and spatial organization of cartilage that they produced. By stage 24, leg cells began to produce a nodular pattern of cartilage while wing cells continued to produce sheets of cartilage. This pattern difference persisted throughout the later stages and was not due to differences in cell survival as judged by DNA content or to the presence of distinctive cell subpopulations in either tissue, as determined by flow cytometry. Chondrogenesis in wing and leg precartilage cell cultures was affected differently by 10% fetal bovine serum, TGF-beta 1 (1 ng/ml for 5 hr on the day after plating), and retinoic acid (5 ng/ml). In wing cultures, the extent of chondrogenesis was significantly enhanced by serum or by a combination of TGF-beta 1 and retinoic acid, but the cartilage pattern was not altered with any treatment. In leg cultures, the extent of chondrogenesis was enhanced by TGF-beta 1 alone, inhibited by retinoic acid alone, and the cartilage pattern was changed from nodular to sheet-like by treatment with TGF-beta 1. Wing and leg cultures also differed from each other in relative cohesivity and in condensation morphology and organization of fibronectin during the early phase of differentiation. Wing cells produced broad, flat condensations containing diffusely organized fibronectin, whereas leg cells elaborated an extensive network of long fibronectin-rich fibrils connecting very compact, fibronectin-rich condensations. These intrinsic and induced differences in fore and hind limb mesenchyme provide insight into the mechanisms that are common to the formation of all limb skeletal elements and those that distinguish skeletal elements from different limb regions and limb types.

Animals↗

PubMed2002

Roles of PIN-FORMED1 and MONOPTEROS in pattern formation of the apical region of the Arabidopsis embryo.

In dicotyledonous plants, the apical region of the embryo shifts from radial to bilateral symmetry as the two cotyledon primordia develop on opposite sides of the shoot meristem. To further elucidate the mechanisms regulating this patterning process, we analyzed functions of two Arabidopsis genes, PIN-FORMED1 (PIN1) and MONOPTEROS (MP), encoding a putative auxin efflux carrier and a transcription factor thought to mediate auxin signaling, respectively. The corresponding mutants show similar defects in apical patterning, including cotyledon fusion and dissymmetric organ positioning. Both mutations perturb the spatial expression patterns of CUP-SHAPED COTYLEDON1 (CUC1) and CUC2, which are redundantly required for cotyledon separation and meristem formation. During early embryogenesis, both CUC genes are affected differently: the area of CUC1 expression is expanded while that of CUC2 expression is reduced. In addition, genetic analysis indicates that PIN1 and MP are required for the activity of CUC2 while CUC1 activity is only slightly affected by both mutations. These results suggest a differential regulation of the CUC genes by PIN1 and MP. Furthermore, genetic analysis suggests that SHOOT MERISTEMLESS (STM), another regulator for cotyledon separation and meristem formation, promotes CUC1 activity in parallel with PIN1. Our results suggest a model where PIN1 and MP regulate apical patterning partially through the control of CUC gene expression.

Arabidopsis↗

PubMed2006

Transcriptional regulation of Dictyostelium pattern formation.

On starvation, Dictyostelium cells form a terminally differentiated structure, known as the fruiting body, which comprises stalk and spore cells. Their precursors--prestalk and prespore cells--are spatially separated and accessible in a migratory structure known as the slug. This simplicity and manipulability has made Dictyostelium attractive to both experimental and theoretical developmental biologists. However, this outward simplicity conceals a surprising degree of developmental sophistication. Multiple prestalk subtypes are formed and undertake a co-ordinated series of morphogenetic cell movements to generate the fruiting body. This review describes recent advances in understanding the signalling pathways that generate prestalk-cell heterogeneity, focusing on the roles of the prestalk-cell inducer differentiation-inducing factor-1 (DIF-1), the tip inducer cAMP and the transcription factors that mediate their actions; these include signal transducer and activator of transcription (STAT) proteins, basic leucine zipper (bZIP) proteins and a Myb protein of a class previously described only in plants.

Animals↗

PubMed1996

Sensitivity of proneural genes to lateral inhibition affects the pattern of primary neurons in Xenopus embryos.

We have compared the roles of XASH-3 and NeuroD, two basic helix-loop-helix transcription factors, in the formation of primary neurons in early Xenopus embryos. When ectopically expressed in Xenopus embryos, XASH-3 and NeuroD induce ectopic primary neurons in very different spatial patterns. We show that the pattern of primary neurons induced by XASH-3 and NeuroD can be accounted for by a difference in their sensitivity to inhibitory interactions mediated by the neurogenic genes, X-Delta-1 and X-Notch-1. Both NeuroD and XASH-3 promote the expression of the inhibitory ligand, X-Delta-1. However, XASH-3 appears to be sensitive to the inhibitory effects of X-Delta-1 while NeuroD is much less so. Consequently only a subset of cells that ectopically express XASH-3 eventually form neurons, giving a scattered pattern, while the ectopic expression of NeuroD leads to a relatively dense pattern of ectopic neurons. We propose that differences in the sensitivity of XASH-3 and NeuroD to lateral inhibition play an important role during their respective roles in neuronal determination and differentiation.

Animals↗

PubMed2002

Transcriptional integration of competence modulated by mutual repression generates cell-type specificity within the cardiogenic mesoderm.

The way in which spatially patterned cellular identities are generated is a central question of organogenesis. In the case of Drosophila heart formation, the cardiac progenitors are specified in precise mesodermal positions, giving rise to multiple cell types in a highly ordered arrangement. Here, we study the mechanisms by which positional information conveyed by signaling pathways and a combinatorial code of activating and repressing transcription factors work together to confine the expression of the homeobox gene even-skipped (eve) to a small region of the dorsal mesoderm. By manipulating both expression patterns and binding sites for transcription factors, we show that a complex combination of regulatory activities converge on a single enhancer of eve to generate precisely targeted gene expression within the cardiac mesoderm. In particular, ladybird early (lbe), a homeobox gene expressed adjacent to eve, restricts the positive actions of factors downstream of wingless, decapentaplegic, and ras to generate the eve pattern. Mutation of a Lbe binding site causes dramatic expansion of expression and abolishes the responsiveness to repression by lbe. Conversely, eliminating eve in the mesoderm expands lbe expression into the normal eve-expressing territory, suggesting that mutual repression between eve and lbe is essential for delineating the spatial patterns of gene expression that specify cell types within the cardiac mesoderm.

Animals↗

PubMed2002

Dentin matrix protein 1, a target molecule for Cbfa1 in bone, is a unique bone marker gene.

Dentin matrix protein 1 (Dmp1), a phosphoprotein highly linked to dentin formation, has also been reported to be expressed in the skeleton. However, the role of Dmp1 in skeletal tissues remains unclear. To clarify the role of Dmp1 in bone formation, we characterized the expression profile of Dmp1 in bone and cartilage and examined whether Dmp1 expression was regulated by core-binding factor a1 (Cbfa1). Studies of fetal rat calvarial (FRC) cell cultures showed that the expression of Dmp1 was associated closely with "bone nodule" formation and mineralization in vitro. In situ hybridization studies were performed to examine the spatial and temporal expression patterns of Dmp1 during development in mouse embryos from 12.5 day postcoitus (dpc) to 8 weeks postnatal; these studies showed that Dmp1 first appeared in hypertrophic cartilage cells, followed by osteoblasts, and later was expressed strongly in osteocytes. The expression profiles of Cbfa1 and Dmp1 overlapped in both cartilage and bone during development, with Cbfa1 preceding Dmp1. Examination of Dmp1 expression in Cbfa1-/- mice revealed that Dmp1 was absent in the developing bones of Cbfa1-null mice, whereas there was essentially no change in Dmp1 expression in the arrested tooth bud. Transient transfection studies showed forced expression of Dmp1 under the control of Cbfa1 and gel shift data indicated the presence of a functional osteocalcin-specific element (OSE)-2 response element in the Dmp1 proximal promoter region. However, in vitro promoter studies suggested that regulation of Dmp1 by Cbfa1 was not mediated by direct binding of Cbfa1 to this site and may be through indirect mechanisms. These studies highlight Dmp1 as a unique marker gene for osteoblastic differentiation. The close association of Dmp1 and Cbfa1 in the developing skeleton suggests that Dmp1 may play an important role in bone formation.

Animals↗

PubMed1997

The biomimetics of enamel: a paradigm for organized biomaterials synthesis.

The formation of enamel takes place through a sequence of processes that can be mimicked in inorganic materials chemistry. This chapter describes the generic features of enamel biomineralization in terms of a house-building analogy. Four stages are identified: supramolecular preorganization and spatial patterning; interfacial molecular recognition in inorganic nucleation; vectorial crystallization; and pattern evolution and hierarchy. Each of these concepts can be translated into synthetic approaches to the formation of inorganic materials with organized architectures. An example of applying this biomimetic paradigm is described. Supersaturated water-in-oil microemulsions have been used to synthesize microskeletal calcium phosphates by controlled nucleation and vectorial growth in constrained reaction environments. The results of these preliminary studies suggest that biomimetic concepts could be useful in the fabrication of biomaterial implants with controlled porosity and microstructure.

Amelogenesis↗

PubMed1993

Distribution of noncollagenous proteins in the matrix of adult human bone: evidence of anatomic and functional heterogeneity.

The microanatomic distribution of several noncollagenous proteins (NCPs) in bone matrix was examined by immunohistochemical analysis of glycol-methyl methacrylate-embedded normal adult human bone biopsies. Osteopontin and bone sialoprotein stained throughout the lamellae of both trabecular and cortical bone. Cement lines (cortical and trabecular) and the mineralized matrix immediately adjacent to each Haversian canal were intensely stained. Osteocalcin was detected in cement lines; however, lamellar staining varied depending on the location within the individual unit of bone. In cortical bone, the inner concentric lamellae of osteons were often unstained but the outer lamellae were heavily stained for osteocalcin. Osteonectin was not detected in cement lines and in most specimens revealed a pattern similar to that of osteocalcin with respect to the absence of immunostaining within the inner concentric lamellae. Decorin was prominent in the perilacunar matrix, the canaliculi of osteocytes, and the matrix immediately adjacent to quiescent Haversian canals. Biglycan appeared evenly distributed throughout cortical and trabecular bone matrix. These results suggest that the incorporation of NCPs into matrix may vary depending on the stage of formation of individual bone units. The specific distribution and spatial relationship of these NCPs may be related to the function of each protein during bone resorption and formation. The distinct patterns of NCP localization in bone support the hypothesis that in addition to their structural and mineral-inducing properties, these proteins may influence the events associated with bone remodeling, such as recruitment, attachment, differentiation, and activity of bone cells.

Adult↗