Models for positional signalling with application to the dorsoventral patterning of insects and segregation into different cell types

Development ◽  
1989 ◽  
Vol 107 (Supplement) ◽  
pp. 169-180 ◽  
Author(s):  
Hans Meinhardt
Keyword(s):  
Positional Information ◽  
Cell Types ◽  
Ventral Side ◽  
Homogeneous Distribution ◽  
Dorsoventral Patterning ◽  
High Concentration ◽  
Low Concentrations ◽  
Homogeneous Cell ◽  
Pattern Forming ◽  
Different Cell Types

Models of pattern formation and possible molecular realizations are discussed and compared with recent experimental observations. In application to the dorsoventral patterning of insects, it is shown that a superposition of two pattern-forming reactions is required. The first system generates the overall dorsoventral polarity of the oocyte, the second generates the positional information proper with a stripe-like region of high concentration along the ventral side of the embryo. A single reaction would be insufficient since the two reactions require different parameters. The model accounts for the orientation of the DV axes of the oocytes in the ovary of Musca domestica and Sarcophaga, independent of the DV axis of the mother, for the formation of several ventral furrows in the absence of the primary gurken/torpedo system in Drosophila, as well as for the good size regulation of the dorsoventral axis as observed in some insect species. Segregation of a homogeneous cell population into different cell types requires autocatalytic processes that saturate at relatively low concentrations and nondiffusible substances responsible for the autocatalytic feedback loops. Thus, these loops can be realized directly on the gene level via their gene products, for instance, by the mutual repression of two genes. A balance of the two cell types is achieved by a long-ranging substance interfering with the self-enhancing process. This substance is expected to have a more or less homogeneous distribution. This model accounts for the reestablishment of the correct proportion after an experimental interference and the change of determination after transplantation. Applications to the segregation of prestalk and prespore cells in Dictyostelium and of neuroblast cells from the ventral ectoderm in Drosophila are provided.

scholarly journals Autoradiographic localization of beta-adrenoreceptors in rat uterus.

1988 ◽  
Vol 36 (12) ◽  
pp. 1475-1479 ◽  
Author(s):  
M Tolszczuk ◽  
G Pelletier
Keyword(s):  
Quantitative Estimation ◽  
Cell Types ◽  
Receptor Subtypes ◽  
High Concentration ◽  
Rat Uterus ◽  
Beta Adrenergic ◽  
Adrenergic Antagonist ◽  
Beta 2 ◽  
Different Cell Types

The inhibitory effects of catecholamines on uterine smooth muscle are known to be mediated through beta-adrenergic receptors. To investigate further the distribution of these receptors in the rat uterus, we utilized in vitro autoradiography using [125I]-cyanopindolol [CYP], a specific beta-receptor ligand that has equal activity for both beta 1- and beta 2-receptor subtypes. The specificity of the labeling and the characterization of receptor subtypes in different cell types were achieved by displacement of radioligand with increasing concentrations of zinterol, a beta-adrenergic agonist with preferential affinity for the beta 2-adrenoreceptor subtype, and practolol, a beta-adrenergic antagonist that binds preferentially to the beta 1-subtype. Quantitative estimation of ligand binding was performed by densitometry. It was shown that the vast majority of beta-adrenoreceptors were of the beta 2-subtype and were found in high concentration not only in the myometrium but also in the endometrial and serosal epithelia. Specific labeling was also observed in glandular elements. These results suggest that beta-adrenoreceptors might be involved in different functions in the uterus.

Applications of a Theory of Biological Pattern Formation Based on Lateral Inhibition

1974 ◽  
Vol 15 (2) ◽  
pp. 321-346 ◽  
Author(s):  
H. MEINHARDT ◽  
A. GIERER
Keyword(s):  
Pattern Formation ◽  
Lateral Inhibition ◽  
Molecular Mechanisms ◽  
Positional Information ◽  
Cell Types ◽  
Model Calculations ◽  
Slime Moulds ◽  
Biological Pattern Formation ◽  
Pattern Forming ◽  
Differentiation And Proliferation

Model calculations are presented for various problems of development on the basis of a theory of primary pattern formation which we previously proposed. The theory involves short-range autocatalytic activation and longer-range inhibition (lateral inhibition). When a certain criterion is satisfied, self-regulating patterns are generated. The autocatalytic features of the theory are demonstrated by simulations of the determination of polarity in the Xenopus retina. General conditions for marginal and internal activation, and corresponding effects of symmetry are discussed. Special molecular mechanisms of pattern formation are proposed in which activator is chemically converted into inhibitor, or an activator precursor is depleted by conversion into activator. The (slow) effects of primary patterns on differentiation can be included into the formalism in a straightforward manner. In conjunction with growth, this can lead to asymmetric steady states of cell types, cell differentiation and proliferation as found, for instance, in growing and budding hydra. In 2 dimensions, 2 different types of patterns can be obtained. Under some assumptions, a single pattern-forming system produces a ‘bristle’ type pattern of peaks of activity with rather regular spacings on a surface. Budding of hydra is treated on this basis. If, however, gradients develop under the influence of a weak external or marginal asymmetry, a monotonic gradient can be formed across the entire field, and 2 such gradient-forming systems can specify ‘positional information’ in 2 dimensions. If inhibitor equilibrates slowly, a spatial pattern may oscillate, as observed with regard to the intracellular activation of cellular slime moulds. The applications are intended to demonstrate the ability of the proposed theory to explain properties frequently encountered in developing systems.

The ultrastructure of the dimorphic infection cells of Haptoglossa heteromorpha illustrates the developmental plasticity of infection apparatus structures in a nematode parasite

2000 ◽  
Vol 78 (8) ◽  
pp. 1095-1107 ◽  
Author(s):  
Sally L Glockling ◽  
Gordon W Beakes
Keyword(s):  
Developmental Plasticity ◽  
Biological Significance ◽  
Cell Types ◽  
Ventral Side ◽  
Nematophagous Fungus ◽  
Fibrillar Material ◽  
Host Parasite Interactions ◽  
Host Parasite ◽  
Different Cell Types ◽  
Direct Confirmation

The nematophagous fungus Haptoglossa heteromorpha Glockling & Beakes is unusual in this genus, as it consistently produces two morphologically distinct infection cells that develop respectively from the large and small aplanospores. The large infection cells are typical "gun cells" and are uninucleate with over half the cytoplasmic volume occupied by the basal vacuole. However, the small infection cells are considerably modified in their structure. They have an elongate tapered morphology with a bilobed base. Small infection cells are binucleate and contain both apical and basal vacuolar regions. The inverted injection tube is highly modified and originates at a raised padlike region on the mid ventral side of the cell. This protruding pad is associated with a diffuse covering of fibrillar material. The bore region extends deep into the cell and the highly compressed missile chamber is located beneath the hindmost nucleus, near the base of the cell. Finally, there is a more typical tube tail segment, which winds between the nuclei and eventually terminates beneath the anterior vacuole. The differences with gun cells of previously described Haptoglossa species are documented. The functional and biological significance of these two different infection cells is discussed. Only the large gun cells were observed to discharge to form sporidia. It seems unlikely that the highly modified smaller cells can infect in this way. It may be that the two different cell types have evolved to infect different hosts, but no direct confirmation of this could be obtained.Key words: Haptoglossa, host-parasite interactions, infection (gun) cell, nematophagous fungi, ultrastructure.

The hedgehog morphogen and gradients of cell affinity in the abdomen of Drosophila

Development ◽  
1999 ◽  
Vol 126 (11) ◽  
pp. 2441-2449 ◽  
Author(s):  
P.A. Lawrence ◽  
J. Casal ◽  
G. Struhl
Keyword(s):  
Positional Information ◽  
Cell Types ◽  
Direct Response ◽  
Cell Affinity ◽  
A Chain ◽  
Different Cell Types ◽  
The Relationship ◽  
P Cells ◽  
Adult Abdomen ◽  
As If

The adult abdomen of Drosophila is a chain of anterior (A) and posterior (P) compartments. The engrailed gene is active in all P compartments and selects the P state. Hedgehog enters each A compartment across both its anterior and posterior edges; within A its concentration confers positional information. The A compartments are subdivided into an anterior and a posterior domain that each make different cell types in response to Hedgehog. We have studied the relationship between Hedgehog, engrailed and cell affinity. We made twin clones and measured the shape, size and displacement of the experimental clone, relative to its control twin. We varied the perceived level of Hedgehog in the experimental clone and find that, if this level is different from the surround, the clone fails to grow normally, rounds up and sometimes sorts out completely, becoming separated from the epithelium. Also, clones are displaced towards cells that are more like themselves: for example groups of cells in the middle of the A compartment that are persuaded to differentiate as if they were at the posterior limit of A, move posteriorly. Similarly, clones in the anterior domain of the A compartment that are forced to differentiate as if they were at the anterior limit of A, move anteriorly. Quantitation of these measures and the direction of displacement indicate that there is a U-shaped gradient of affinity in the A compartment that correlates with the U-shaped landscape of Hedgehog concentration. Since affinity changes are autonomous to the clone we believe that, normally, each cell's affinity is a direct response to Hedgehog. By removing engrailed in clones we show that A and P cells also differ in affinity from each other, in a manner that appears independent of Hedgehog. Within the P compartment we found some evidence for a U-shaped gradient of affinity, but this cannot be due to Hedgehog which does not act in the P compartment.

Dispersal of Golgi apparatus in nocodazole-treated fibroblasts is a kinesin-driven process

1997 ◽  
Vol 110 (19) ◽  
pp. 2495-2505 ◽  
Author(s):  
A.A. Minin
Keyword(s):  
Golgi Apparatus ◽  
Human Skin ◽  
Cell Types ◽  
Human Skin Fibroblasts ◽  
Low Concentrations ◽  
Complete Disruption ◽  
Rat Fibroblasts ◽  
Different Cell Types ◽  
Blocking Analysis ◽  
Perinuclear Area

The morphology and location of the Golgi apparatus (GA) has been shown to change upon microtubule (Mt) depolymerization. The GA in different cell types undergoes fragmentation and dispersal throughout the cytoplasm upon treatment with nocodazole. In this study experiments were performed on human skin fibroblasts (HSFs) and rat fibroblasts (REF 52) to determine whether the dispersal of GA in HSFs treated with nocodazole is dependent on Mts that show the higher resistance to this Mt-depolymerizing drug. It is shown here that nocodazole at concentrations as low as 100 nM caused the GA to disperse in treated fibro-blasts that still contained a fairly high amount of Mts. Antibody-blocking analysis of Mts after injection of biotin-tubulin into the HSFs was used to show that nocodazole at low concentrations induced the stabilization of the remaining Mts. The complete disruption of Mts by the incubation of HSFs at 0 degrees C prevented the dispersal of GA from the perinuclear area when the cells were subsequently warmed to 37 degrees C in the presence of nocodazole. Micro-injection of the well-characterized HD antibody against kinesin but not the preimmune IgG caused inhibition of GA dispersal in HSFs by nocodazole. These data demonstrate that the dispersal of GA in the cytoplasm of nocodazole-treated HSFs is a kinesin-driven process with stable Mts serving as tracks.

scholarly journals A minibead method for detection of membrane lectins.

1989 ◽  
Vol 37 (1) ◽  
pp. 91-96 ◽  
Author(s):  
T Matsuoka ◽  
M Tavassoli
Keyword(s):  
Soluble Sugar ◽  
Cell Types ◽  
Cell Populations ◽  
Morphological Identification ◽  
Cell Systems ◽  
Biological Phenomena ◽  
Homogeneous Cell ◽  
Different Cell Types ◽  
Derivatives Of ◽  
Scanning Electron

Membrane lectins are being increasingly implicated in many biological phenomena. Previous methods for detection of these substances are applicable only to homogeneous cell populations. We have now developed a method that permits morphological identification of lectin-bearing cells in heterogeneous cell populations. Amide-modified latex minibeads (0.345 or 0.532 micron) were activated with glutaraldehyde and then covalently bound to p-aminophenyl derivatives of various sugars. When the probe thus constructed was incubated with cell systems known to bear well-defined membrane lectins (galactosyl receptors in hepatocytes, mannosyl receptors in macrophages), binding occurred and could be visualized by scanning electron microscopy. Binding was inhibited in the presence of excess soluble sugar, indicating the specificity of reaction. Incubation of a mixture of two different-sized probes with two different cell types led to segregation of the probes. This method also permits semiquantification of binding.

Study of the Molecular Architecture of Keratin Filaments by Electron Microscopy

1982 ◽  
Vol 40 ◽  
pp. 118-119
Author(s):  
U. Aebi ◽  
P. Rew ◽  
T.-T. Sun
Keyword(s):  
Electron Microscopy ◽  
Structural Organization ◽  
Cell Types ◽  
Structural Features ◽  
Molecular Architecture ◽  
The Past ◽  
Keratin Filaments ◽  
Different Types ◽  
10 Nm Filaments ◽  
Different Cell Types

Various types of intermediate-sized (10-nm) filaments have been found and described in many different cell types during the past few years. Despite the differences in the chemical composition among the different types of filaments, they all yield common structural features: they are usually up to several microns long and have a diameter of 7 to 10 nm; there is evidence that they are made of several 2 to 3.5 nm wide protofilaments which are helically wound around each other; the secondary structure of the polypeptides constituting the filaments is rich in ∞-helix. However a detailed description of their structural organization is lacking to date.

Processing and Characterization of Recombinant von Willebrand Factor Expressed in Different Cell Types Using a Vaccinia Virus Vector

1992 ◽  
Vol 67 (01) ◽  
pp. 154-160 ◽  
Author(s):  
P Meulien ◽  
M Nishino ◽  
C Mazurier ◽  
K Dott ◽  
G Piétu ◽  
...  
Keyword(s):  
Vaccinia Virus ◽  
Von Willebrand Factor ◽  
Human Fibroblasts ◽  
Active Form ◽  
Cell Types ◽  
Biologically Active ◽  
L Cells ◽  
Von Willebrand ◽  
Different Cell Types ◽  
Willebrand Factor

SummaryThe cloning of the cDNA encoding von Willebrand factor (vWF) has revealed that it is synthesized as a large precursor (pre-pro-vWF) molecule and it is now clear that the prosequence or vWAgll is responsible for the intracellular multimerization of vWF. We have cloned the complete vWF cDNA and expressed it using a recombinant vaccinia virus as vector. We have characterized the structure and function of the recombinant vWF (rvWF) secreted from five different cell types: baby hamster kidney (BHK), Chinese hamster ovary (CHO), human fibroblasts (143B), mouse fibroblasts (L) and primary embryonic chicken cells. Forty-eight hours after infection, the quantity of vWF antigen found in the cell supernatant varied from 3 to 12 U/dl depending on the cell type. By SDS-agarose gel electrophoresis, the percentage of high molecular weight forms of vWF varied from 39 to 49% relative to normal plasma for BHK, CHO, 143B and chicken cells but was less than 10% for L cells. In all cell types, the two anodic subbands of each multimer were missing. The two cathodic subbands were easily detected only in BHK and L cells. By SDS-PAGE of reduced samples, pro-vWF was present in similar quantity to the fully processed vWF subunit in L cells, present in moderate amounts in BHK and CHO and in very low amounts in 143B and chicken cells. rvWF from all cells bound to collagen and to platelets in the presence of ristocetin, the latter showing a high correlation between binding efficiency and degree of multimerization. rvWF from all cells was also shown to bind to purified FVIII and in this case binding appeared to be independent of the degree of multimerization. We conclude that whereas vWF is naturally synthesized only by endothelial cells and megakaryocytes, it can be expressed in a biologically active form from various other cell types.

Role of Transcriptional Read-Through in PRE Activity in Drosophila melanogaster

Acta Naturae ◽  
2016 ◽  
Vol 8 (2) ◽  
pp. 79-86 ◽  
Author(s):  
P. V. Elizar’ev ◽  
D. V. Lomaev ◽  
D. A. Chetverina ◽  
P. G. Georgiev ◽  
M. M. Erokhin
Keyword(s):  
Dna Sequences ◽  
Cell Types ◽  
Transcription Terminator ◽  
Response Elements ◽  
Polycomb Response Elements ◽  
The Individual ◽  
Multicellular Organisms ◽  
Different Cell Types ◽  
Main Factor

Maintenance of the individual patterns of gene expression in different cell types is required for the differentiation and development of multicellular organisms. Expression of many genes is controlled by Polycomb (PcG) and Trithorax (TrxG) group proteins that act through association with chromatin. PcG/TrxG are assembled on the DNA sequences termed PREs (Polycomb Response Elements), the activity of which can be modulated and switched from repression to activation. In this study, we analyzed the influence of transcriptional read-through on PRE activity switch mediated by the yeast activator GAL4. We show that a transcription terminator inserted between the promoter and PRE doesnt prevent switching of PRE activity from repression to activation. We demonstrate that, independently of PRE orientation, high levels of transcription fail to dislodge PcG/TrxG proteins from PRE in the absence of a terminator. Thus, transcription is not the main factor required for PRE activity switch.

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