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Results for “spatial patterning”

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At least 73 records · Page 4Linked to original sources
PubMed1988

Geometry and spatial patterns in Polysphondylium pallidum.

The formation of secondary sori in whorls of Polysphondylium pallidum provides an attractive model system for the study of symmetry breaking during morphogenesis. Tip-specific antibodies that permit detection of very early stages in this patterning process are available. We have found that the patterns of tip-specific antigen expression vary considerably depending on the size, shape, and developmental stage of the whorl. All of these patterns, however, are well explained by patterning models that rely on short-range autocatalysis and long-range inhibition, as exemplified by reaction-diffusion theories. In the context of reaction-diffusion, we discuss the possible effects of initial conditions, boundary conditions, and nonlinearities on the selection of patterns in P. pallidum whorls.

Models, Theoretical↗
PubMed1990

Developmental regulation and spatial pattern of expression of the structural genes for nitrogenase in the cyanobacterium Anabaena.

Depriving the cyanobacterium Anabaena of fixed nitrogen induces the differentiation of heterocysts at intervals along its filaments. To test whether the oxygen-deficient conditions believed to prevail within mature heterocysts are sufficient, in the absence of fixed nitrogen, to elicit the expression of nitrogenase, PnifHDK was fused transcriptionally to luxAB (encoding luciferase). Expression, monitored from individual cells as light emission, was localized (with a resolution of approximately 1 micron) to differentiated cells, whether or not oxygen was present. Anabaena PCC 7118 is a heterocystless mutant strain that is known to fix nitrogen when deprived of combined nitrogen under anaerobic conditions. Three lines of evidence indicate that the mutant has retained the ability to develop a pattern despite its inability to make heterocysts. First, morphologically distinct cells appear at nonrandom intervals when filaments are starved of nitrogen. Second, these cells, like heterocysts, have little or no phycocyanin-dependent fluorescence. Third, nitrogen-starved filaments fragment, with fragment lengths similar to the spacing normally seen between heterocysts. Expression of PnifHDK-luxAB was largely confined to differentiated cells in the mutant as in the wild-type strain. These results provide evidence for a causal relationship between development and transcriptional events in Anabaena.

Aerobiosis↗
PubMed1989

Spatial patterns of gene expression in preimplantation mouse embryos.

The distribution of total polyadenylated RNA and mRNAs from the beta-actin, fibronectin, and cytokeratin Endo A genes was examined in preimplantation mouse embryos using in situ hybridization of riboprobes to RNA in sections of embryos. Polyadenylated RNA was found in the cytoplasm of all cells of blastocyst-stage embryos, whereas the specific mRNAs displayed three distinct patterns of expression: uniform throughout the embryo (beta-actin), enriched in the inner cell mass (fibronectin), and enriched in the trophectoderm (Endo A). In eight-cell embryos, the polyadenylated RNA was more concentrated in nuclei than in the cytoplasm (as noted previously), although this was not the case in blastocysts, nor was it true for the specific mRNAs that were examined. These experiments demonstrate that there is localized gene expression in the early mouse embryo, which correlates with the formation of the trophectoderm and the inner cell mass.

Actins↗
PubMed1979

Spatial patterns for an interaction-diffusion equation in morphogenesis.

A certain interaction-diffusion equation occurring in morphogenesis is considered. This equation is proposed by Gierer and Meinhardt, which is introduced by Child's gradient theory and Turing's idea about diffusion driven instability. It is shown that slightly asymmetric gradients in the tissue produce stable striking patterns depending on its asymmetry, starting from uniform distribution of morphogens. The tool is the perturbed bifurcation theory. Moreover, from a mathematical point of view, the global existence of steady state solutions with respect to some parameters is discussed.

Cell Differentiation↗
PubMed1990

Temporal and spatial patterns of transforming growth factor-beta 1 expression in developing rat molars.

Regulatory peptides of the TGF-beta family affect various aspects of embryonic development. Recent immunolocalization and in situ hybridization studies have demonstrated a specific time- and tissue-dependent expression of TGF-beta 1 in the developing mouse embryo. The purpose of this study was to evaluate the distribution of TGF-beta 1 within rat molars at different stages of development, using a well-characterized antibody, highly specific for TGF-beta 1, and immunohistochemical methods of detection. TGF-beta 1 was immunolocalized intensely within the ectodermally derived stellate reticulum and the mesenchyme of the dental papilla at the bell stage of development. Marked immunostaining was also evident in the papillary layer and the reduced dental organ subjacent to ameloblasts in the differentiation and secretory phases of amelogenesis. During the formation of coronal tissues and in the pre-eruptive phase, immunoreactive TGF-beta 1 was localized conspicuously within the dental follicle overlying the tooth germ. This temporospatial pattern of expression of TGF-beta 1 appears to correlate with specific events in morphogenesis, histogenesis and cytodifferentiation during tooth development.

Ameloblasts↗
PubMed1985

The spatial pattern and temporal sequence in which feather germs arise in the white Leghorn chick embryo.

Feather germs arise in a specific sequence and spatio-temporal pattern within each of 10 feather areas on the White Leghorn chick embryo. The time of feather germ initiation was determined by histological and gross macroscopic analyses. Protruding feather germs are sequentially visualized in the dorsal, thigh, breast, head, humoral, ventral, wing, eye, and external auditory meatus feather areas, respectively, from stage 31- to stage 39+ [V. Hamburger and H.L. Hamilton (1951) J. Morphol. 88, 49-92]. The rate at which successive feather tracts appear was found to differ for different feather areas and was not simply due to the size of a feather area. Feather germ histogenesis was examined in the dorsal, thigh, breast, ventral, wing, and tail feather areas. The stages of feather germ histogenesis, examined on the wing feather area, are similar to those previously described for the dorsal surface. Gross and histological analyses gave different times and temporal sequences of feather germ visualization. Some feather areas were readily visualized at the time of feather germ initiation, while others showed a lag between the histological appearance of feather germs and their macroscopic visualization. Thus, macroscopic observations do not accurately reflect the pattern of histogenesis.

Animals↗
PubMed1986

Spatial patterns of metallothionein mRNA expression in the sea urchin embryo.

Metallothioneins (MTs) are small, cysteine-rich proteins that bind heavy metals which induce their synthesis. Tissue fractionation of embryos at pluteus stage previously demonstrated that in the absence of added zinc, basal expression of MT mRNA is confined to ectoderm, whereas induction by zinc results in increased expression in the endoderm + mesoderm tissue fraction. Using in situ hybridization we now show that expression in the pluteus larva is restricted almost exclusively to the single cell type comprising the aboral ectoderm. Induction by Zn results in a marked accumulation of MT mRNA in gut and oral ectoderm to levels at least as high as that in aboral ectoderm. MT mRNA is also expressed in presumptive aboral ectoderm at earlier stages of normal development. In addition it is transiently expressed at variable levels in oral ectoderm and, to a lesser extent, in presumptive gut.

Animals↗
PubMed1991

Changes in temporal and spatial patterns of Gi protein expression in postimplantation mouse embryos.

We previously demonstrated the presence of GTP-binding proteins, G proteins, in the preimplantation mouse embryo (Jones and Schultz, 1990. Dev. Biol. 139, 250-262). These studies have been extended to the Day 6.5, 7.5, and 8.5 gestation embryo by employing PT-catalyzed ADP-ribosylation and immunoblotting techniques. We report here that the amount of embryonic alpha i increases from Day 6.5 to Day 7.5 of gestation, and remains at about the same level at Day 8.5. In contrast, the extent of PT-catalyzed ADP-ribosylation of Gi alpha protein(s) decreases between Days 6.5 and 7.5--this decrease is global and not restricted to a particular germ layer of the Day 7.5 embryo--and then dramatically increases by Day 8.5 of gestation. In the Day 8.5 gestation embryo, the extent of PT-catalyzed ADP-ribosylation of Gi alpha proteins increases along the anterior-posterior axis, whereas the amount of immunoreactive alpha i subunit decreases along this axis. By using a combination of PT-catalyzed ADP-ribosylation and immunoprecipitation with antisera specific for alpha i1, alpha i2, or alpha i3, we report that all three alpha i subtypes are present in the Day 8.5 gestation mouse embryo. Results of these experiments suggest that an activation of Gi proteins occurs between Days 6.5 and 7.5 of gestation in the postimplantation embryo, a time during which the embryo is gastrulating, and that a decreasing gradient of activation exists along the anterior to posterior axis in the Day 8.5 gestation embryo. Last, we report that oocytes, eggs, and preimplantation embryos possess all three subtypes of alpha i.

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↗
PubMedDate not supplied

Temporal and spatial pattern of cellular myc oncogene expression during human placental development.

The human placental trophoblast component is of embryonic origin and is developmentally regulated; the tissue is highly proliferative and often described as pseudomalignant. Because cellular oncogenes have been implicated in normal cellular proliferation and differentiation processes, we have studied c-myc oncogene expression in relation to the progression of human placental development. The c-myc transcript shows a 20- to 30-fold variation over the course of placental development, with a peak at four to five weeks after conception. A clear decline in placental c-myc transcription is seen before the end of the first trimester of pregnancy. In situ hybridization to [125I]-labelled myc probes demonstrates an unequal distribution of myc transcripts in placenta, with particularly high expression in the cytotrophoblastic shell of the early placenta. The localization of myc transcripts to cytotrophoblast and the temporal pattern of myc expression support a strong correlation between myc transcript abundance and cytotrophoblastic proliferation. These findings are discussed in the light of a possible role for the c-myc gene in proliferation of normal cells.

Female↗
PubMed1992

Challenges to understanding spatial patterns of disease: philosophical alternatives to logical positivism.

Most studies of disease distribution, in medical geography and other related disciplines, have been empirical in nature and rooted in the assumptions of logical positivism. However, some of the more newly articulated philosophies of the social sciences, and of social theory, have much to add in the understanding of the processes and mechanisms underlying disease distribution. This paper represents a plea for creative synthesis between logical positivism and realism or structuration, and uses specific examples to suggest how disease distribution, as a surface phenomenon, can be explained using deeper analysis.

Cross-Cultural Comparison↗