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Results for “Spatial pattern formation”

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PubMed1989

Tyrosine phosphorylation in the postnatal rat brain: a developmental, immunohistochemical study.

We have used antibodies against phosphotyrosine to probe 50-microns cerebellar sections from rats of various ages as well as sections of adult brainstem, cerebrum, and olfactory bulb to investigate the developmental appearance of this phosphorylation system as revealed by light microscopy. While the overall intensity of staining in the cerebellum was highest at 7 days, the pattern of staining in the adult is quite disparate from that seen in younger animals. From 10 to 21 days postnatal, staining is associated primarily with the white matter and/or the lower premigratory zone of the external granular layer and adjacent formative molecular layer. While the temporal and spatial appearance of phosphotyrosine immunoreactivity corresponds well to the established patterns of axonal growth in these areas, we cannot at the light level ascertain whether the immunoreactivity is intrinsic or extrinsic to the growing fibers. In animals 28 days and older, however, staining is restricted to a subpopulation of multipolar cells distributed throughout the cerebellum, as well as the olfactory bulb, cerebrum, and brainstem. The phosphotyrosine-positive cells in the adult cerebellum are not comparable to glial-fibrillary-acidic-protein-immunoreactive elements with regard to morphology or distribution, and they fail to colocalize with neuronal somata stained with anti-microtubule-protein-2 antibodies. While it appears that the radial fibers of the Bergmann glia in the external granular layer stain at 7 days, there is no staining detected in the mitotically active neuroblasts of this layer at any age. We conclude that in the immature cerebellum, the majority of tyrosine phosphorylation detectable by this method may be involved in the formation and growth of axonal processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed2001

Evidence for two distinct mechanisms of neurogenesis and cellular pattern formation in regenerated goldfish retinas.

After its destruction by intraocular injection of ouabain, the goldfish retina regenerates, but little is known about the histogenesis of the new tissue, including the structure and formation of regenerated cell mosaic patterns. In an effort to determine how retinal cells are generated and spatially organized within retina regenerated after ouabain injection, in situ hybridization and immunocytochemical techniques were combined with computational analyses of two-dimensional spatial patterns of identified neurons. Labeling with specific opsin riboprobes revealed two distinct cone patterns in the ouabain-injected eyes, each of which was different from the relatively orderly cone patterns of native retina. Central, regenerated regions had sparse aggregates of cones, and a relatively lower density of each cone type. Peripheral regions of experimental retina, likely derived from the circumferential germinal zone, had high densities of all cone types, each of which tended to be distributed randomly. The spatial patterns of inner retinal neurons in experimental eyes were also disorganized with respect to native retina. These results indicate that although some aspects of retinal regeneration resemble normal retinal development and growth, ouabain-induced regeneration does not produce well-organized mosaics of neurons, indicating a failure of the developmental interactions needed for proper pattern formation, which in turn could compromise visual recovery. Furthermore, the distinct cone patterns in different regions of experimental retina support the hypothesis that new goldfish retina arises via two spatially and cellularly distinct mechanisms after exposure to ouabain.

Animals↗

PubMed1983

A morphometric analysis of craniofacial growth and changes in spatial relations during secondary palatal development in human embryos and fetuses.

Staged human embryos and fetuses in the Carnegie Embryological Collection were morphometrically analyzed to show craniofacial dimensions and changes in spatial relations, and to identify patterns that would reflect normal developmental events during palatal formation. Normal embryos aged 7-8 weeks postconception (Streeter-O'Rahilly stages 19-23) and fetuses aged 9-10 weeks postconception, in eight groups with mean crown-rump (CR) lengths of 18-49 mm, were studied with cephalometric methods developed for histologic sections. In the 4-week period studied, facial dimensions increased predominantly in the sagittal plane with extensive changes in length (depth) and height, but limited changes in width. Growth of the mandible was more rapid than the nasomaxillary complex, and the length of Meckel's cartilage exceeded the length of the oronasal cavity at the time of horizontal movement of the shelves during stage 23. Simultaneously with shelf elevation, the upper craniofacial complex lifted, and the tongue and Meckel's cartilage extended forward beneath the primary palate. Analysis of spatial relations in the oronasal cavity showed that the palatomaxillary processes became separated from the tongue--mandibular complex as the head extended, and the tongue became positioned forward with growth of Meckel's cartilage. As the head position extended by 35 degrees, the cranial base angulation was unchanged and the primary palate maintained a 90 degrees position to the posterior cranial base. However, the sagittal position of the maxilla relative to the anterior cranial base increased by 20 degrees between stages 19 and 23. In the late embryonic and early fetal periods, the mean cranial base angulation of approximately 128 degrees and the mean maxillary position angulation of approximately 84 degrees were similar to the angulations previously shown to be present later prenatally and post-natally. The results suggest that human patterns of cranial base angulation and maxillary position to the cranial base develop during the late embryonic period when the chondrocranium and Meckel's cartilage form the primary skeleton.

Cephalometry↗

PubMed2004

Pattern formation driven by nematic ordering of assembling biopolymers.

The biopolymers actin and microtubules are often in an ongoing assembling-disassembling state far from thermal equilibrium. Above a critical density this leads to spatially periodic patterns, as shown by a scaling argument and in terms of a phenomenological continuum model, which meets also Onsager's statistical theory of the nematic-to-isotropic transition in the absence of reaction kinetics. This pattern forming process depends much on nonlinear effects and a common linear stability analysis of the isotropic distribution of the filaments is often misleading. The wave number of the pattern decreases with the assembling-disassembling rate and there is an uncommon discontinuous transition between the nematic and periodic states.

Actins↗

PubMed2002

Modeling and computational analysis of EGF receptor-mediated cell communication in Drosophila oogenesis.

Autocrine signaling through the Epidermal Growth Factor Receptor (EGFR) operates at various stages of development across species. A recent hypothesis suggested that a distributed network of EGFR autocrine loops was capable of spatially modulating a simple single-peaked input into a more complex two-peaked signaling pattern, specifying the formation of a pair organ in Drosophila oogenesis (two respiratory appendages on the eggshell). To test this hypothesis, we have integrated genetic and biochemical information about the EGFR network into a mechanistic model of transport and signaling. The model allows us to estimate the relative spatial ranges and time scales of the relevant feedback loops, to interpret the phenotypic transitions in eggshell morphology and to predict the effects of new genetic manipulations. We have found that the proposed mechanism with a single diffusing inhibitor is sufficient to convert a single-peaked extracellular input into a two-peaked pattern of intracellular signaling. Based on extensive computational analysis, we predict that the same mechanism is capable of generating more complex patterns. At least indirectly, this can be used to account for more complex eggshell morphologies observed in related fly species. We propose that versatility in signaling mediated by autocrine loops can be systematically explored using experiment-based mechanistic models and their analysis.

Animals↗

PubMed1998

Retardation of skeletal development and cervical abnormalities in transgenic mice expressing a dominant-negative retinoic acid receptor in chondrogenic cells.

Skeletal formation is a fundamental element of body patterning and is strictly regulated both temporally and spatially by a variety of molecules. Among these, retinoic acid (RA) has been shown to be involved in normal skeletal development. However, its pleiotropic effects have caused difficulty in identifying its crucial target cells and molecular mechanisms for each effect. Development of cartilage primordia is an important process in defining the skeletal structures. To address the role of RA in skeletal formation, we have generated mice expressing a dominant-negative retinoic acid receptor (RAR) in chondrogenic cells by using the type II collagen alpha1 promoter, and we have analyzed their phenotypes. These mice exhibited small cartilage primordia during development and retarded skeletal formation in both embryonic and postnatal periods. They also showed selective degeneration in their cervical vertebrae combined with homeotic transformations, but not in their extremities. The cervical phenotypes are reminiscent of phenotypes involving homeobox genes. We found that the expression of Hoxa-4 was indeed reduced in the cartilage primordia of cervical vertebrae of embryonic day 12.5 embryos. These observations demonstrate that endogenous RA acts directly on chondrogenic cells to promote skeletal growth in both embryonic and growing periods, and it regulates the proper formation of cervical vertebrae. Furthermore, RA apparently specifies the identities of the cervical vertebrae through the regulation of homeobox genes in the chondrogenic cells. Great similarities of the phenotypes between our mice and reported RAR knockout mice revealed that chondrogenic cells are a principal RA target during complex cascades of skeletal development.

Animals↗

PubMed1991

Yeast BUD5, encoding a putative GDP-GTP exchange factor, is necessary for bud site selection and interacts with bud formation gene BEM1.

Cells of the yeast S. cerevisiae choose bud sites in an axial or bipolar spatial pattern depending on their cell type. We have identified a gene, BUD5, that resembles BUD1 and BUD2 in being required for both patterns; bud5- mutants also exhibit random budding in all cell types. The BUD5 nucleotide sequence predicts a protein of 538 amino acids that has similarity to the S. cerevisiae CDC25 product, an activator of RAS proteins that catalyzes GDP-GTP exchange. Two potential targets of BUD5 are known: BUD1 (RSR1) and CDC42, proteins involved in bud site selection and bud formation, respectively, that have extensive similarity to RAS. We also show that BUD5 interacts functionally with a gene, BEM1, that is required for bud formation. This interaction provides further support for the view that products involved in bud site selection guide the positioning of a complex necessary for bud formation.

Amino Acid Sequence↗

PubMed1986

Stable patterns generated by activator-inhibitor systems.

The paper is concerned with a discrete morphogenetic model of activator-inhibitor type. The aim is to give a theoretical explanation for what we understand as the first step in pattern formation for a growing object: as long as the object remains small enough, its shape is spatially homogeneous, while passing a critical length results in a spontaneous establishment of a non-homogeneous configuration. We show that, for parameters suitably chosen, there are many stable patterns that can be formed. This fact implies, in particular, a sensitive dependence of the established pattern from the perturbation that causes the object to leave the homogeneous state.

Cells↗

PubMed1986

Transient expression of collagen type II at epitheliomesenchymal interfaces during morphogenesis of the cartilaginous neurocranium.

In the avian embryo a matrix-mediated tissue interaction between retinal pigmented epithelium and neural crest-derived periocular mesenchyme leads to the differentiation of (scleral) cartilage. The composition of the extracellular matrix at the interface between these two tissues has been examined immunohistochemically, both during and after the interaction has taken place. Of the matrix components studied (fibronectin, laminin, and collagen types I, II, IV, and V) only collagen type II displayed a dramatic change in distribution between the two stages. During the interaction, at stage 15, type II was present in the extracellular compartment basal to the epithelium. After completion of the interaction, collagen type II was no longer detectable at the interface even though it was readily detectable in the vitreous humor, cornea, and perinotochordal sheath, and subsequently will be expressed by the chondrogenic tissue itself as overt differentiation commences. These results suggest that collagen type II might be causally involved in this particular epitheliomesenchymal interaction. Examination of the spatial and temporal patterns of collagen type II expression elsewhere in the developing craniofacial complex revealed a hitherto unreported pattern of distribution. In addition to its predictable locations (i.e., cornea, vitreous, and perinotochordal sheath) it was found to be present at certain other sites, for example, at the basal surfaces of some neuroepithelia. These additional locations are all known to be sites of chondrogenesis-promoting tissue interactions which result in the formation of the elements of the cartilaginous neurocranium (e.g., otic vesicle). Furthermore this spatial distribution exhibits a changing temporal pattern in that it is detectable at the time that the interactions are known to be taking place, but subsequently is no longer detectable by the immunohistochemical means employed. This definable pattern of transient collagen type II expression, occurring at very early stages of craniofacial development, is interpreted as reflecting one level of morphogenetic specification of chondrocranial/skull form in the developing vertebrate head.

Age Factors↗

PubMed2001

Pattern formation in a tunable medium: the Belousov-Zhabotinsky reaction in an aerosol OT microemulsion.

Turing structures, standing waves, oscillatory clusters, and accelerating waves have been found in the spatially extended Belousov-Zhabotinsky system dispersed in water droplets of a reverse AOT microemulsion. The variety of patterns is determined by the tunable microstructure of the medium, i.e., by the concentration and size of water droplets. We propose a simple model to describe this system.

Aerosols↗

PubMed1994

Specification and segmentation of the paraxial mesoderm.

Somite formation in the mouse embryo begins with the recruitment of mesenchymal cells into the paraxial mesoderm. Cells destined for the paraxial mesoderm are recruited from a progenitor population found first in the embryonic ectoderm and later in the primitive streak and the tail bud. Experimental evidence suggests that the allocation of precursor cells to different mesodermal lineages may be related to the site at which the cells ingress through the primitive streak. An increasing number of genes, such as those encoding growth factor and transcription factors, are now known to be expressed in the primitive streak. It is not known whether the specification of mesodermal cell fate has any relationship with the activity of genes that are expressed in the restricted cell populations of the primitive streak. Somitomeres, which are spherical clusters of mesenchymal cells in the presomitic mesoderm, presage the segmentation of somites in the paraxial mesoderm. The somitomeric organization denotes a pre-pattern of segmentation that defines the physical boundary and the bilateral symmetry of the mesodermal segments in the body axis. The establishment of new somitomeres seems to require the interaction of a resident cell population in the presomitic mesoderm and the incoming primitive streak cells. Cell mixing, which occurs in the somitomeres prior to somite segmentation, poses problems in understanding the developmental role of the somitomere and the real significance of the partitioning of the node-derived and primitive streak-derived cells in the mesodermal segments. In the presomitic mesoderm, the expression of some genes that encode transcription factors, growth factors or tyrosine kinase receptor, and the localization of certain cell adhesion molecules are closely associated with distinct morphogenetic events, such as cell clustering in the presomitic mesoderm and the formation of epithelial somites. There is, however, very little direct relationship between the spatial pattern of gene expression and the somitomeric organization in the presomitic mesoderm. Results of somite transplantation experiments suggest that both the segmental address and the morphogenetic characteristics of the somite may be determined during somite segmentation. Regional identity of the paraxial mesodermal segment is conferred by the expression of a combination of Hox genes in the sclerotome and probably other lineage-specific genes that are subject to imprinting. Superimposed on the global metameric pattern, two orthogonal polarities of cell differentiation are endowed in each mesodermal segment. The rostro-caudal polarity is established prior to somite segmentation. This polarity is later manifested by the subdivision of the sclerotome and the alliance of the neural crest cells and motor axons with the rostral half-somite.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2006

Generation and weak beam control of two-dimensional multicolored arrays in a quadratic nonlinear medium.

We report on the first experimental observation of 2D multicolored transverse arrays in a quadratic nonlinear medium under the pump of two crossly overlapped femtosecond beams. The 2D reproducible patterns are caused by cascaded noncollinear quadratic nonlinear couplings between the input pulses and quadratic spatial solitons originated from spatial breakup of one of the input beams with spatial ellipticity. A seed supercontinuum pulse is then diffracted and amplified with phase preservation, resulting in the formation of up-converted multicolor 2D transverse arrays. By seeding with weak second harmonic pulses, the 2D multicolored transverse patterns are suppressed due to weak beam control of the induced quadratic spatial solitons.

Journal Article↗

PubMed2004

Differential expression patterns of the dentin matrix proteins during mineralized tissue formation.

Sequential and reciprocal interactions between the oral ectoderm and neural crest-derived mesenchyme are responsible for tooth development. During dentin formation, there are three components that are necessary for proper mineralization, namely, collagen which forms a scaffold, noncollagenous proteins that can specifically bind to the collagen template and function as a mineral nucleator and crystalline calcium phosphate deposited in an ordered manner. It is well established that noncollagenous proteins play an important role during mineralized tissue formation. Here we demonstrate by in situ hybridization techniques that the noncollagenous dentin matrix proteins 1, 2 (DMP1, 2) and dentin sialoprotein (DSP) have characteristic temporal and spatial expression patterns within odontogenic tissues during dentin mineralization. DMP1, DMP2 and DSP mRNA are expressed in the odontoblasts at specific and overlapping time points and are thus presumably used for different functions during dentin formation. In developing rat incisors and molars, high levels of expression of DMP2 mRNA were seen in polarized odontoblasts and preameloblasts, while DSP mRNA was expressed at significantly lower levels and was expressed by highly differentiated odontoblasts. However, their expression was continuously maintained during the mineralization of the organic matrix. In the adult rats, DMP2 and DSP mRNA was also detected in the osteoblasts. The expression of DMP1 mRNA was found to coincide with the start of the mineral nucleation process and gradually decreased during the maturation of the mineralized matrix during odontogenesis. In this study, we have also correlated the expression of these proteins relative to the presence of type I collagen and calcium phosphate crystals. Thus, the temporal and spatial differences between DMP1, DMP2 and DSP might implicate a direct demonstration of the functional difference between these three genes during calcified tissue formation.

Animals↗

PubMed1985

Development of cholinergic markers in mouse forebrain. I. Choline acetyltransferase enzyme activity and acetylcholinesterase histochemistry.

Measurements of choline acetyltransferase (ChAT) activity were made during the development of the neocortical cholinergic innervation, and correlated with the development of the acetylcholinesterase (AChE) staining pattern in mouse cerebral cortex and several other areas of the forebrain between the time of initial onset and maturity ChAT activity can first be measured on postnatal day 6 (P6). The enzyme reaches 40% of adult activity by P18 and adult values by 7 weeks postnatal. The onset of AChE staining varies for different regions of the forebrain and for various areas within the cerebral cortex. The earliest appearance of AChE is seen in several basal forebrain nuclei including the striatum, the ventromedial region of the globus pallidus and the hypothalamus on embryonic day 18 (E18). In neocortex and olfactory cortex, AChE-stained axons are seen in the white matter before birth, but do not enter cingulate cortex and hippocampus until P2. By P2. almost all areas of the basal forebrain and diencephalon have acquired some AChE staining pattern. The adult distribution of AChE staining is reached by 3 weeks postnatal in all areas of the forebrain. Adult cerebral cortex shows a characteristic pattern of alternating AChE dense and AChE sparse bands which vary in depth depending on the cortical area. The cortical banding pattern develops in an 'inside-out' fashion, starting in layer VI and gradually entering more superficial layers. In parallel with the AChE pattern of development in cortex, transient AChE staining can be observed in some thalamic nuclei and in some forebrain fiber systems. In the neostriatum patches of intense AChE staining first develop along the ventrolateral border, then spread throughout the whole nucleus and finally coalesce to a uniform high density over the entire neostriatum. We discuss the close spatial and temporal correspondence between AChE pattern development and reported data on synapse formation, and speculate on the role of the cortical cholinergic system in development.

Acetylcholinesterase↗

PubMed2003

Pattern formation in thin liquid films with charged surfactants.

The dynamic evolution of positively charged surfactants at the interface of a thin film resting atop a negatively charged base is investigated. The lubrication approximation is used to develop coupled equations governing the dynamic evolution of such a system in the presence of charge effects coupled with van der Waals forces. The equations are investigated numerically and analytically, and, for certain parameter ranges, pattern formation is observed reminiscent of that accompanying thermocapillary-driven thin films. Spatial nonuniformities in the charge of the underlying substrate are also studied as a possible tool for film rupture wavelength selection.

Journal Article↗

PubMed2005

Model for the robust establishment of precise proportions in the early Drosophila embryo.

During embryonic development, a spatial pattern is formed in which proportions are established precisely. As an early pattern formation step in Drosophila embryos, an anterior-posterior gradient of Bicoid (Bcd) induces hunchback (hb) expression (Nature 337 (1989) 138; Nature 332 (1988) 281). In contrast to the Bcd gradient, the Hb profile includes information about the scale of the embryo. Furthermore, the resulting hb expression pattern shows a much lower embryo-to-embryo variability than the Bcd gradient (Nature 415 (2002) 798). An additional graded posterior repressing activity could theoretically account for the observed scaling. However, we show that such a model cannot produce the observed precision in the Hb boundary, such that a fundamentally different mechanism must be at work. We describe and simulate a model that can account for the observed precise generation of the scaled Hb profile in a highly robust manner. The proposed mechanism includes Staufen (Stau), an RNA binding protein that appears essential to precision scaling (Nature 415 (2002) 798). In the model, Stau is released from both ends of the embryo and relocalizes hb RNA by increasing its mobility. This leads to an effective transport of hb away from the respective Stau sources. The balance between these opposing effects then gives rise to scaling and precision. Considering the biological importance of robust precision scaling and the simplicity of the model, the same principle may be employed more often during development.

Animals↗

PubMed2006

Cyclic di-GMP as a second messenger.

In many bacteria bis-(3',5')-cyclic dimeric guanosine monophosphate (c-di-GMP) signaling determines the timing and amplitude of complex biological processes from biofilm formation and virulence to photosynthesis. Thereby, the tightly regulated temporal and spatial activity patterns of GGDEF and EAL domain proteins, which synthesize and degrade c-di-GMP, respectively, are currently being resolved. Although details of the mechanisms of c-di-GMP signaling are not yet determined, the recent presentation of PilZ as a candidate c-di-GMP binding-domain opens the field for experimental investigations. Besides its role as an intracellular signaling molecule in bacteria, c-di-GMP also acts as an intercellular signaling molecule between prokaryotes and also has effects in eukaryotes that could provide a perspective in cancer treatment.

Animals↗

PubMed2006

Strain-induced self organization of metal-insulator domains in single-crystalline VO2 nanobeams.

We investigated the effect of substrate-induced strain on the metal-insulator transition (MIT) in single-crystalline VO(2) nanobeams. A simple nanobeam-substrate adhesion leads to uniaxial strain along the nanobeam length because of the nanobeam's unique morphology. The strain changes the relative stability of the metal (M) and insulator (I) phases and leads to spontaneous formation of periodic, alternating M-I domain patterns during the MIT. The spatial periodicity of the M-I domains can be modified by changing the nanobeam thickness and the Young's modulus of the substrate.

Crystallization↗