SEARCH · PubMed Health

Results for “Spatial pattern formation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 703 records · Page 39Linked to original sources

PubMed1996

Reorganization of membrane contacts prior to apoptosis in the Drosophila retina: the role of the IrreC-rst protein.

The final step of pattern formation in the developing retina of Drosophila is the elimination of excess cells between ommatidia and the differentiation of the remaining cells into secondary and tertiary pigment cells. Temporally and spatially highly regulated expression of the irregular chiasmC-roughest protein, an adhesion molecule of the immunoglobulin superfamily known to be involved in axonal pathfinding, is essential for correct sorting of cell-cell contacts in the pupal retina without which the ensuing wave of apoptosis does not occur. Irregular chiasmC-roughest accumulates strongly at the borders between primary pigment and interommatidial cells. Mutant and misexpression analysis show that this accumulation of the irregular chiasmC-roughest protein is necessary for aligning interommatidial cells in a single row. This reorganisation is a prerequisite for the identification of death candidates. Irregular chiasmC-roughest function in retinal development demonstrates the importance of specific cell contacts for assignment of the apoptotic fate.

Animals↗

PubMedDate not supplied

Homoeobox gene expression in mouse embryos varies with position by the primitive streak stage.

Pattern formation in animal development requires that genes be expressed differentially according to position in the sheets of cells that make up the early embryo. The homoeobox-containing genes of Drosophila are control genes active both in the establishment of a segmentation pattern and in the specification of segment identity. In situ hybridization experiments confirm that these genes are expressed in a segmentally-restricted manner and that their expression presages morphological differentiation of segmental structures. Homoeobox genes have recently been isolated from the mouse and have been shown to be expressed during mouse development. Using in situ hybridization, we show here that expression of the mouse homoeobox gene Mo-10 (ref. 7) is spatially restricted in the developing embryo and that localization of expression is already evident within the germ layers before their morphological differentiation. These findings support the suggestion that the homoeobox genes of mammals, like those of Drosophila, may be important in pattern formation.

Animals↗

PubMed2002

Transcriptional heterochrony of scute and changes in bristle pattern between two closely related species of blowfly.

Temporal shifts in the expression of regulatory genes, relative to other events taking place during development, can result in changes in morphology. Such transcriptional heterochrony can introduce dramatic morphological changes that involve rather few genetic events and so has the potential to cause rapid changes during evolution. We have shown previously that stereotyped species-specific bristle patterns on the notum of higher Diptera correlate with changes in the spatial regulation of scute expression. scute encodes a proneural gene required for the development of sensory bristle precursors and is expressed before pupation in discrete domains on the presumptive notum at sites where the macrochaete precursors arise. Thus, for Ceratitis capitata and Calliphora vicina, species separated from Drosophila melanogaster by about 80 and 100 million years respectively, the domains of sc expression differ. In all three species, a second phase of ubiquitous sc expression, after pupation, precedes formation of the microchaete precursors. Here, we describe sc expression in Phormia terranovae, a species belonging to the family Calliphoridae that is closely related to C. vicina. We find that spatial regulation is almost identical between P. terranovae and C. vicina, in spite of their different bristle patterns. The timing of sc expression differs, however, between the two. The first spatially restricted phase of expression is slightly delayed and the second ubiquitous phase remarkably accelerated, such that there is a period of overlap. As a result, the last precursors from the first phase of expression arise at the same time as the first precursors from the second phase of expression and are morphologically indistinguishable from the late-arising microchaetes. These observations illustrate the power of developmental heterochrony in bringing about rapid morphological change.

Animals↗

PubMed1998

3D reconstruction of the mouse's mesonephros.

The present work reports on the three-dimensional reconstruction of the segmented mesonephros during the embryonic development of the mouse. With a light microscope and an automatic reconstruction of surfaces, aspects of the mesonephros are described. These surfaces are obtained by using digitized contour lines. A new interpolation method called DSI (Discrete Smooth Interpolation) enables correction of the distortion induced by microtomy in paraffin sections. After a triangulation step, this method uses a smoothing algorithm, which implies a spatial redistribution of the vertices of the triangles to correct the rotational and translational misalignment. The use of this 3D program improves the understanding of the development patterns and helps us to appreciate changes in the rebuilt mesonephros. By 10.5 embryonic days, tubules emerge from the Wolffian body and begin their formation, then between 11.5 and 13.5 embryonic days, tortuous mesonephric tubules bound to the Wolffian duct form small curls, which grow and finally unwind. At the same time, mesonephric tubules unbound to the Wolffian duct appear, and on 13.5 embryonic days, the Müllerian duct is visible. After 14.5 embryonic days, the segmented mesonephros keeps its general aspect but decreases in size. At this time, each gonad is provided with both Wolffian and Müllerian ducts. Later, the Wolffian duct differentiates into the definitive male duct system, whilst the Müllerian duct regresses. Conversely, the paramesonephric duct differentiates into the definitive female duct system, whilst the mesonephric duct in turn degenerates. By this time degeneration has begun in the cranial portion of the mesonephros and this process progresses caudally. The spatial organization of the mesonephric tubules and the precise organization of all connections between these elements and the ducts may be well defined. Such approach can allow for a high definition of the normal pattern of mesonephros differentiation.

Animals↗

PubMed1986

Afterimage-like effects in the motion-sensitive neuron H1.

A powerful effect resembling an afterimage is demonstrated on the pathway to the motion-sensitive neuron H1. This effect is independent of the locally generated gain control described in an earlier paper (Maddess & Laughlin 1985, Proc. R. Soc. Lond. B 225, 251). The afterimage, produced across the eye by a stationary pattern, causes the sensitivity to movement to be different according to the local stimulus history, and the effects of low-contrast (0.1) patterns, presented for as little as a few hundred milliseconds, remain for up to 2 s. Moving patterns interact with the afterimage to modulate the spike rate of H1. The afterimage increases with contrast but saturates at contrasts above 0.5. Low spatial frequencies generate afterimages less effectively than moderate ones; this result indicates that the afterimage process could lie at, or after, lateral inhibition between tonic units. This is supported by the fact that the altered sensitivity profiles generated by single bright and dark vertical bars initially resemble Mach bands. However, this character alters as the afterimage decays, and the depression of H1's response to moving bright stimuli, produced by the afterimage of a dark bar, continues to grow for up to 1 s after the adapting bar is removed. A short-lived (0.5 s) reduction of H1's directional selectivity accompanies strong afterimage formation. All these factors, especially the saturation at low contrasts and the spatial frequency tuning, rule out light adaptation by photoreceptors as the afterimage source. Luminances used were also low enough to exclude influence by the pupil mechanism. Lastly, responses to patterns that are occasionally jumped by large or small distances are broadened by stimuli that produce an afterimage. Responses to small displacements have previously been described as 'velocity impulse responses' (Srinivasan 1983, Vision Res. 23, 659; Zaagman et al. 1983, IEEE Trans. SMC 13, 900) and so the response broadening (stimulus blurring) can be taken as a reduction of the fly's temporal resolution of moving objects. Previously reported work shows that afterimages seen in humans and the effect reported here act over the same range of temporal frequencies rather than retinal drift speeds. This may suggest an important role for afterimage-like effects in the processing of the low temporal frequency components of moving images. Certainly, the fly's afterimage system reduces the visibility of moving objects within patches of an image that, have on average, contained slowly varying motion signals.(ABSTRACT TRUNCATED AT 400 WORDS)

Afterimage↗

PubMed1999

The actin cytoskeleton is required to elaborate and maintain spatial patterning during trichome cell morphogenesis in Arabidopsis thaliana.

Arabidopsis thaliana trichomes provide an attractive model system to dissect molecular processes involved in the generation of shape and form in single cell morphogenesis in plants. We have used transgenic Arabidopsis plants carrying a GFP-talin chimeric gene to analyze the role of the actin cytoskeleton in trichome cell morphogenesis. We found that during trichome cell development the actin microfilaments assumed an increasing degree of complexity from fine filaments to thick, longitudinally stretched cables. Disruption of the F-actin cytoskeleton by actin antagonists produced distorted but branched trichomes which phenocopied trichomes of mutants belonging to the 'distorted' class. Subsequent analysis of the actin cytoskeleton in trichomes of the distorted mutants, alien, crooked, distorted1, gnarled, klunker and wurm uncovered actin organization defects in each case. Treatments of wild-type seedlings with microtubule-interacting drugs elicited a radically different trichome phenotype characterized by isotropic growth and a severe inhibition of branch formation; these trichomes did not show defects in actin cytoskeleton organization. A normal actin cytoskeleton was also observed in trichomes of the zwichel mutant which have reduced branching. ZWICHEL, which was previously shown to encode a kinesin-like protein is thought to be involved in microtubule-linked processes. Based on our results we propose that microtubules establish the spatial patterning of trichome branches whilst actin microfilaments elaborate and maintain the overall trichome pattern during development.

Actins↗

PubMed1978

Hippocampal connections and spatial discrimination.

Rats were tested in a new spatial discrimination procedure which measured working memory. Following preoperative testing, lesions were placed to disrupt each of the major extrinsic fiber connections of the hippocampal formation. Destruction of the entorhinal area, body of the fimbria-fornix anterior to hippocampus, septum, or postcommisural fornix produced a severe and consistent impairment in performance. Analysis of error patterns indicated that when animals with limbic lesions made errors, they were likely to make these errors in the same sequence as the original choices. These data support the hypothesis that the hippocampus has an important role in the processing of information about spatial location, and that normal performance on this task requires an intact hippocampal circuitry.

Acetylcholinesterase↗

PubMed1993

Interaction between dorsal and ventral cells in the imaginal disc directs wing development in Drosophila.

The adult appendages of Drosophila develop from imaginal discs. An early step in disc patterning involves the formation of developmental boundaries that subdivide the discs into compartments. Anterior and posterior compartments are established in the embryo. Later in development a new boundary originates to subdivide the wing disc into dorsal and ventral compartments, which correspond to the dorsal and ventral surfaces of the adult wing. We report here that spatially localized expression of the homeobox gene apterous (ap) specifies the identity of dorsal cells in the wing. The boundary of cell lineage restriction between dorsal and ventral compartments coincides with the limit of the domain of ap expression. Using genetic mosaics, we show that juxtaposition of dorsal and ventral cells induces formation of the wing margin. We present evidence that the dorsal-ventral boundary promotes growth and serves as a pattern-organizing center in the wing disc.

Animals↗

PubMed1984

The appearance of alpha, beta and gamma crystallins in an anophthalmic strain of mice.

A certain percentage of congenitally anophthalmic mouse embryos have the ability to generate small lens vesicles that have previously been shown to produce alpha crystallin at 13-day gestation. Further immunohistological analysis of 13- and 15-day-gestation anophthalmia embryos indicates that beta crystallin is present in those 13-day embryos which have lens vesicles with lens-fiber formation. Also, 15-day embryos with lenses demonstrating fiber elongation can produce both beta and gamma crystallins. The conclusion is drawn that the genetic potential to produce at least three characteristic biochemical markers of normal lens differentiation is present in the anophthalmia mutant. The spatial distribution patterns of the crystallins in normal and anophthalmia embryos were similar. However, there appeared to be a transposition in the temporal appearance of beta and gamma crystallins in the anophthalmia mutant. Optic cups and associated lenses in 15-day anophthalmia specimens were much smaller than those in controls. The optic and lens rudiments in these anophthalmia embryos were fairly proportional in size, which indicates that some degree of allometric growth compensation had occurred during the course of development. This ability for differential growth compensation in the mouse eye appears to be restricted to the predifferentiative stages of eye formation.

Animals↗

PubMed1995

Developmental alteration and neuron-specific expression of bone morphogenetic protein-6 (BMP-6) mRNA in rodent brain.

Bone morphogenetic proteins (BMPs) are a group of proteins which induce bone formation from mesenchymal cells. The existence of BMPs in the nervous system as well as in bone tissue has recently been reported. In this study, we show that BMP-6 is neuron-specific, and describe the temporal and spatial expression patterns of BMP-6 mRNA in the developing rat and gerbil brain. Northern blot analysis showed that the BMP-6 transcript level was specifically high from newborn to 3 weeks after birth compared with those in fetal and adult rats. In situ hybridization showed that most of the neurons possessed high levels of BMP-6 mRNA in the neonatal brain, while in the adult brain, BMP-6 mRNA level was significantly decreased in most of the neurons except those in hippocampus which retained high levels. Furthermore, to show that the BMP-6 expression was specific to neurons, we induced delayed neuronal cell death and compensative glial cell proliferation in the gerbil hippocampus by transient ischemia. Our findings collectively suggest that BMP-6 is neuron-specific and may play important roles in neuronal maturation and synapse formation.

Animals↗

PubMed1997

A dynamic model for the morphogenesis of the late vertebrate lens.

A mathematical model is presented for the morphogenesis of the post-vesicular vertebrate lens with an umbilical suture. The lens is modeled as having four compartments: anterior epithelium (germinative and central anterior zones), recruitment zone (transitional zone), cortex (discrete concentric cohorts of secondary cortex fiber cells, each cohort treated individually), and nucleus. Equations are written to describe the time evolution of the cohorts; their shapes collectively determine the shape of the lens. The growth of cell volume is exponential, with different rates in the cortex and epithelium; recruitment of epithelium cells into the cortex is described as resulting from an overproduction of epithelial basal (capsular) surface in the anterior epithelium. The equations contain three dimensionless numbers determined by the physiology of the epithelium and cortex cells. Solutions are stable attractors in a morphological space. All solutions entail exponential growth of the lens diameter; a portion of parameter space corresponds to exponential growth superimposed on large amplitude oscillations in lens shape. Emergent time-scales for increase in lens size and oscillation period are an order of magnitude longer than the cellular growth time-scales. The lens shapes tend to a family of stable scaling solutions, the shapes of which remain unchanged as the lens grows. The model is applied to morphological data for the chick and lamprey lenses. The dynamics described are seen as exemplifying an auto-regulatory morphogenesis process wherein a system passes through a sequence of developmental stages. Each stage is characterized by its own fixed informing geometry (a set of defining spatial relationships), within which a growth process unfolds autonomously, generating a dynamically stable structure. The developing system invokes a means of forgetting dated structural information; this dissipation is necessary to the pattern formation process.

Animals↗

PubMed1990

Experimental analysis of the role of ECM in the patterning of the distal tendons of the developing limb bud.

We have shown previously that from stage 27 the distal growing region of the limb exhibits a tenascin-rich sheet of extracellular matrix termed the "mesenchyme lamina" (ML), which runs from the ectodermal basement membrane in a proximal direction until it contacts the distal tip of the muscle blocks. This study reports experimental evidence that the mesenchyme lamina is a pretendinous structure that controls the spatial organization of the flexor and extensor tendons of the distal part of the chick leg. Two sets of experiments were designed to alter the ML position and examine subsequent tendon pattern formation. In a first series of experiments limbs with digits lacking phalangeal elements were induced by AER removal at stages 26 and 27. This procedure induced an abnormal arrangement of the ML around the distal tip of each terminal phalange of the truncated digit, which was followed by the development of a precisely similar pattern of abnormal extensor and flexor tendons. In the second set of experiments, an extradigit was induced to form in the interdigital mesenchyme through surgical removal of the marginal ectoderm of the third interdigit of stage 29 leg buds. By day 4 post-operation, a chondrogenic extradigit had formed, together with a ML that ran from the cartilage to the normal ventral flexor and dorsal extensor tendons. By day 6 post-operation, the experimentally induced ML had transformed into a tendinous structure connecting with the adjacent normal tendon. Both experiments show that the position of the ML defines the position of subsequent tendon development, thus supporting its role as a pretendinous structure which might be responsible for the alignment of the pretendinous condensing cells.

Animals↗

PubMed1993

Transforming growth factor-alpha immunoreactivity in a variety of epithelial tissues.

The immunohistochemical expression of transforming growth factor-alpha (TGF alpha) has been examined in a range of normal adult epithelial tissues from both man and rat using an anti-hTGF alpha monoclonal antibody (GF10). No differences in distribution were apparent between man and rat. In the continually renewing epithelium of the gastrointestinal tract, no staining was seen within the proliferative compartments, but strong immunoexpression was noted in various differentiated populations. In the testis, the spermatogonia were unstained, but the more luminally orientated germ cells were strongly positive. In the gastrointestinal tract, at least, any mitogenic action of TGF alpha must be mediated through a relatively long paracrine loop. In contrast, the differentiated parenchyma of kidney, salivary gland and liver remained unstained apart from collecting ducts in the kidney, striated ducts in salivary glands and bile ducts in the liver. The association of TGF alpha with tubule formation was reinforced by the very strong staining of newly forming bile ducts in a model of liver oval cell proliferation. Thus, in all the epithelia studied there was a distinct spatial pattern of TGF alpha immunoreactivity.

Adult↗

PubMed2006

Incomplete cryptic speciation between intertidal and subtidal morphs of Acrocnida brachiata (Echinodermata: Ophiuroidea) in the Northeast Atlantic.

The brittle-star Acrocnida brachiata (Montagu) lives in sandy-bottom habitat of both intertidal and subtidal zones along the coasts of the northwestern Europe. An allozyme frequency-based survey (five enzyme loci) was combined with a mitochondrial (mt) COI haplotype analysis (598-bp sequences) on 17 populations to trace back past colonization pathways from the actual population structure of the species. Both genetic markers display a sharp genetic break between intertidal (clade I) and subtidal populations (clade S). This break corresponds to an allele frequency inversion at three enzyme loci (Hk, Pgm and Pgi) and a deep divergence of about 20% in mtCOI sequences between most of the intertidal populations and other samples. The geographic distribution of clade I seems to be more restricted than clade S as it is absent from the intertidal of the eastern English Channel and North Sea and may be replaced by clade S in south Brittany. Applying previously published rates of mutation, divergence between the two clades is estimated to pre-date 5 million years ago and may be due to allopatric speciation processes at the Mio-Pliocene transition. The occurrence of putative hybrids in a few localities, however, suggests incomplete cryptic speciation with secondary contact zones. The relative importance of colonization history vs. habitat specialization are discussed in the light of neutral evolution as tested from mtCOI gene sequences. While differential selection seems to have contributed little to the separation of the lineages, it may have played a role in the emergence of adaptive polymorphisms in the hybrid zone. Furthermore, congruent spatial patterns of differentiation were observed in both clades suggesting a recent increase in population size. These findings are in agreement with a recent expansion of the populations during or after the formation of the English Channel, from a southern refuge for the subtidal clade whereas the intertidal clade may have persisted further north. As previously suspected for a species with a very short pelagic larval phase, contemporary gene flow between distant or adjacent populations appears to be extremely reduced or even absent.

Animals↗

PubMedDate not supplied

Spatial patterns of the vacuolation in subcortical white matter in sporadic Creutzfeldt-Jakob disease (sCJD).

OBJECTIVE: To study the spatial patterns of the vacuolation ("spongiform change") in the subcortical white matter in the "classical" form of sporadic Creutzfeldt-Jakob disease (sCJD). MATERIAL: Frontal, parietal, occipital and temporal lobes of 11 cases of sCJD. METHOD: Spatial patterns were studied across the white matter at the base of the gyri using spatial pattern analysis. RESULTS: In the white matter of all gyri studied, vacuoles were aggregated into clusters, 50 to > 800 microm in diameter and in 22/37 (59%) of gyri, the clusters of vacuoles exhibited a regular distribution across the base of the gyri. In the remaining gyri, the vacuoles were aggregated into large clusters, at least 400 microm or 800 microm in diameter, but without evidence of a regular distribution. In a significant proportion of gyri, the spatial patterns of the vacuolation were similar to those reported previously for spongiform change and prion protein (PrP) deposits in the corresponding grey matter. CONCLUSIONS: Degeneration of the white matter and the formation of clusters of vacuoles may occur before the degeneration of the grey matter or could be a consequence of pathology affecting the cortico-cortical pathways.

Aged↗

PubMed2003

Adaptive walks in a gene network model of morphogenesis: insights into the Cambrian explosion.

The emergence of complex patterns of organization close to the Cambrian boundary is known to have happened over a (geologically) short period of time. It involved the rapid diversification of body plans and stands as one of the major transitions in evolution. How it took place is a controversial issue. Here we explore this problem by considering a simple model of pattern formation in multicellular organisms. By modeling gene network-based morphogenesis and its evolution through adaptive walks, we explore the question of how combinatorial explosions might have been actually involved in the Cambrian event. Here we show that a small amount of genetic complexity including both gene regulation and cell-cell signaling allows one to generate an extraordinary repertoire of stable spatial patterns of gene expression compatible with observed anteroposterior patterns in early development of metazoans. The consequences for the understanding of the tempo and mode of the Cambrian event are outlined.

Adaptation, Physiological↗

PubMed1995

Identification of a spatially specific enhancer element in the chicken Msx-2 gene that regulates its expression in the apical ectodermal ridge of the developing limb buds of transgenic mice.

Msx-2 is a member of the Msx family of homeobox-containing genes expressed in a variety of embryonic tissues involved in epithelial-mesenchymal interactions and pattern formation. In the developing chick limb bud, Msx-2 is expressed in the apical ectodermal ridge, which plays a crucial role in directing the growth and patterning of limb mesoderm. In addition, Msx-2 is expressed in the anterior nonskeletal-forming mesoderm of the limb bud, in the posterior necrotic zone, and in the interdigital mesenchyme. Studies of the altered expression patterns of Msx-2 in amelic and polydactylous mutant chick limbs have suggested that the apical ectodermal ridge and mesodermal domains of Msx-2 expression are independently regulated and that there might be separate cis-regulatory elements in the Msx-2 gene controlling its spatially distinct domains of expression. To test this hypothesis, we have isolated the chicken Msx-2 gene and have tested the ability of various regions of the gene to target expression of LacZ reporter gene to specific regions of the limbs of transgenic mice. A variety of these constructs are consistently expressed only in the apical ectodermal ridge and the ectoderm of the genital tubercle and are not expressed in the mesoderm of the limb bud or in other regions of the embryo where the endogenous Msx-2 gene is expressed. These results suggest the presence of spatially specific cis-regulatory elements in the Msx-2 gene. We identified a 348-bp region in the 5' flanking region of the Msx-2 gene which can act as an apical ectodermal ridge enhancer element when placed in reverse orientation in front of the reporter gene with transcription initiation directed by the minimal hsp68 promoter.

Animals↗

PubMed1997

Self-organization of trajectory formation. II. Theoretical model.

Most studies of movement coordination deal with temporal patterns of synchronization between components, often without regard to the actual amplitudes the components make. When such a system is required to produce a composite action that is spatially constrained, coordination persists, but its stability is modulated by spatial requirements effected, we hypothesize, through the component amplitudes. As shown experimentally in part I, when a redundant three-joint system (wrist, elbow, and shoulder) is required to trace a specified arc in space, the joint angles may be frequency- and phased-locked even as the curvature of the trajectory is manipulated. Transitions between joint coordination patterns occur at a critical curvature, accompanied by a significant reduction in wrist amplitude. Such amplitude reduction is viewed as destabilizing the existing coordinative pattern under current task constraints, thereby forcing the joints into a more stable phase relationship. This paper presents a theoretical analysis of these multijoint patterns and proposes an amplitude mechanism for the transition process. Our model uses three linearly coupled, nonlinear oscillators for the joint angles and reproduces both the observed interjoint coordination and component amplitude effects as well as the resulting trajectories of the end effector.

Arm↗