hedgehog and engrailed: pattern formation and polarity in the Drosophila abdomen

Development ◽  
1999 ◽  
Vol 126 (11) ◽  
pp. 2431-2439 ◽  
Author(s):  
P.A. Lawrence ◽  
J. Casal ◽  
G. Struhl
Keyword(s):  
Pattern Formation ◽  
Narrow Band ◽  
The State ◽  
Drosophila Embryo ◽  
Hedgehog Signalling ◽  
Working Hypothesis ◽  
A Cells ◽  
A Cell ◽  
P Type ◽  
P Cells

Like the Drosophila embryo, the abdomen of the adult consists of alternating anterior (A) and posterior (P) compartments. However the wing is made by only part of one A and part of one P compartment. The abdomen therefore offers an opportunity to compare two compartment borders (A/P is within the segment and P/A intervenes between two segments), and ask if they act differently in pattern formation. In the embryo, abdomen and wing P compartment cells express the selector gene engrailed and secrete Hedgehog protein whilst A compartment cells need the patched and smoothened genes in order to respond to Hedgehog. We made clones of cells with altered activities of the engrailed, patched and smoothened genes. Our results confirm (1) that the state of engrailed, whether ‘off’ or ‘on’, determines whether a cell is of A or P type and (2) that Hedgehog signalling, coming from the adjacent P compartments across both A/P and P/A boundaries, organises the pattern of all the A cells. We have uncovered four new aspects of compartments and engrailed in the abdomen. First, we show that engrailed acts in the A compartment: Hedgehog leaves the P cells and crosses the A/P boundary where it induces engrailed in a narrow band of A cells. engrailed causes these cells to form a special type of cuticle. No similar effect occurs when Hedgehog crosses the P/A border. Second, we look at the polarity changes induced by the clones, and build a working hypothesis that polarity is organised, in both compartments, by molecule(s) emanating from the A/P but not the P/A boundaries. Third, we show that both the A and P compartments are each divided into anterior and posterior subdomains. This additional stratification makes the A/P and the P/A boundaries fundamentally distinct from each other. Finally, we find that when engrailed is removed from P cells (of, say, segment A5) they transform not into A cells of the same segment, but into A cells of the same parasegment (segment A6).

frizzled regulates mirror-symmetric pattern formation in the Drosophila eye

Development ◽  
1995 ◽  
Vol 121 (9) ◽  
pp. 3045-3055 ◽  
Author(s):  
L. Zheng ◽  
J. Zhang ◽  
R.W. Carthew
Keyword(s):  
Pattern Formation ◽  
Cell Surface ◽  
Transmembrane Protein ◽  
Photoreceptor Cells ◽  
Mirror Image ◽  
Morphogenetic Furrow ◽  
Symmetric Pattern ◽  
Mosaic Analysis ◽  
Drosophila Eye ◽  
A Cell

Coordinated morphogenesis of ommatidia during Drosophila eye development establishes a mirror-image symmetric pattern across the entire eye bisected by an anteroposterior equator. We have investigated the mechanisms by which this pattern formation occurs and our results suggest that morphogenesis is coordinated by a graded signal transmitted bidirectionally from the presumptive equator to the dorsal and ventral poles. This signal is mediated by frizzled, which encodes a cell surface transmembrane protein. Mosaic analysis indicates that frizzled acts non-autonomously in an equatorial to polar direction. It also indicates that relative levels of frizzled in photoreceptor cells R3 and R4 of each ommatidium affect their positional fate choices such that the cell with greater frizzled activity becomes an R3 cell and the cell with less frizzled activity becomes an R4 cell. Moreover, this bias affects the choice an ommatidium makes as to which direction to rotate. Equator-outwards progression of elav expression and expression of the nemo gene in the morphogenetic furrow are regulated by frizzled, which itself is dynamically expressed about the morphogenetic furrow. We propose that frizzled mediates a bidirectional signal emanating from the equator.

scholarly journals armadillo, bazooka, and stardust are critical for early stages in formation of the zonula adherens and maintenance of the polarized blastoderm epithelium in Drosophila.

1996 ◽  
Vol 134 (1) ◽  
pp. 149-163 ◽  
Author(s):  
H A Müller ◽  
E Wieschaus
Keyword(s):  
Plasma Membranes ◽  
Basolateral Membrane ◽  
Cell Sheet ◽  
Cell Monolayer ◽  
Test System ◽  
Sem Analysis ◽  
Drosophila Embryo ◽  
Early Stages ◽  
A Cell ◽  
The Stability

Cellularization of the Drosophila embryo results in the formation of a cell monolayer with many characteristics of a polarized epithelium. We have used antibodies specific to cellular junctions and nascent plasma membranes to study the formation of the zonula adherens (ZA) in relation to the establishment of basolateral membrane polarity. The same approach was then used as a test system to identify X-linked zygotically active genes required for ZA formation. We show that ZA formation begins during cellularization and that the basolateral membrane domain is established at mid-gastrulation. By creating deficiencies for defined regions of the X chromosome, we have identified genes that are required for the formation of the ZA and the generation of basolateral membrane polarity. We show that embryos mutant for both stardust (sdt) and bazooka (baz) fail to form a ZA. In addition to the failure to establish the ZA, the formation of the monolayered epithelium is disrupted after cellularization, resulting in formation of a multilayered cell sheet by mid-gastrulation. SEM analysis of mutant embryos revealed a conversion of cells exhibiting epithelial characteristics into cells exhibiting mesenchymal characteristics. To investigate how mutations that affect an integral component of the ZA itself influence ZA formation, we examined embryos with reduced maternal and zygotic supply of wild-type Arm protein. These embryos, like embryos mutant for both sdt and baz, exhibit an early disruption of ZA formation. These results suggest that early stages in the assembly of the ZA are critical for the stability of the polarized blastoderm epithelium.

scholarly journals Reversal of developmental competence in inverted amphibian eggs

Development ◽  
1983 ◽  
Vol 73 (1) ◽  
pp. 207-220
Author(s):  
Hae Moon Chung ◽  
George M. Malacinski
Keyword(s):  
Pattern Formation ◽  
Early Embryogenesis ◽  
The State ◽  
Developmental Competence ◽  
Cleavage Division ◽  
Developmental Arrest ◽  
Amphibian Embryos

Inverted amphibian embryos were employed for an analysis of pattern formation in early embryogenesis. Axolotl (Ambystoma) and Xenopus eggs were inverted prior to the first cleavage division and permitted to develop upside down to the early gastrulation stage. In both cases the cleavage patterns of the animal and vegetal hemispheres were reversed. By gastrulation, however, developmental arrest began, and no inverted embryos developed beyond neurulation. The state of competence of the animal and vegetal hemisphere cells of inverted embryos was examined in a series of tissue transplantations, usually into genetically marked (albino) hosts. In all cases the developmental competence of the original animal and vegetal hemisphere cells of inverted embryos had been reversed. For example, the egg's original vegetal hemisphere developed into various neural structures. Those observations should eventually be useful in formulating models to account for the mannerin which various regions of the amphibian egg cytoplasm generate early embryonic patterns.

scholarly journals The asymmetric chemical structures of two mating pheromones reflect their differential roles in conjugation of Schizosaccharomyces pombe

2019 ◽  
Author(s):  
Taisuke Seike ◽  
Hiromi Maekawa ◽  
Taro Nakamura ◽  
Chikashi Shimoda
Keyword(s):  
Schizosaccharomyces Pombe ◽  
M Cells ◽  
Opposite Mating Type ◽  
Chemical Structures ◽  
Mating Pheromones ◽  
Fusion Site ◽  
Summary Statement ◽  
P Factor ◽  
P Type ◽  
P Cells

AbstractIn the fission yeast Schizosaccharomyces pombe, the mating reaction is controlled by two mating pheromones, M-factor and P-factor, secreted by M- and P-type cells, respectively. M-factor is a C-terminally farnesylated lipid peptide, whereas P-factor is a simple peptide. To examine whether this chemical asymmetry in the two pheromones is essential for conjugation, we constructed a mating system in which either pheromone can stimulate both M- and P-cells, and examined whether the resulting autocrine strains can mate. Autocrine M-cells responding to M-factor successfully mated with P-factor-less P-cells, indicating that P-factor is not essential for conjugation; by contrast, autocrine P-cells responding to P-factor were unable to mate with M-factor-less M-cells. The sterility of the autocrine P-cells was completely recovered by expressing the M-factor receptor. These observations indicate that the different chemical characteristics of the two types of pheromone, a lipid and a simple peptide, are not essential; however, a lipid peptide is absolutely required for successful mating. Our findings allow us to propose a model of the differential roles of M-factor and P-factor in conjugation of S. pombe.Summary statementLipid pheromone peptides secreted locally from one cell may be concentrated at the fusion site with an opposite mating-type cell, which then polarizes to enable successful conjugation in S. pombe.

First-principles study of the structural and thermoelectric properties of Y-doped α-SrSi2

2022 ◽  
Author(s):  
Masato Yamaguchi ◽  
Daishi Shiojiri ◽  
Tsutomu Iida ◽  
Naomi Hirayama ◽  
Yoji IMAI
Keyword(s):  
Thermoelectric Properties ◽  
First Principles ◽  
Electronic Structures ◽  
Narrow Band ◽  
Hybrid Functional ◽  
Promising Candidate ◽  
Functional Theory ◽  
Seebeck Coefficients ◽  
Increasing Temperature ◽  
P Type

Abstract The narrow-gap semiconductor α-SrSi2 is a promising candidate for low-temperature thermoelectric applications with low environmental load. The only experimental report in which α-SrSi2 is reported to have n-type conductivity is one where it had been doped with yttrium. To further clarify the effects of impurities, theoretical studies are needed. The α-SrSi2 has a very narrow band gap (~13–35 meV), causing difficulties in the accurate calculation of the electronic and thermoelectric properties. In our previous study, we overcame this problem for undoped α-SrSi2 using hybrid functional theory. We used this method in this study to investigate the structures, energetic stabilities, electronic structures, and thermoelectric properties of Y-doped α-SrSi2. The results indicate that substitution at Sr-sites is energetically about two times more stable than that at Si-sites. Furthermore, negative Seebeck coefficients were obtained at low temperatures and reverted to p-type with increasing temperature, which is consistent with the experimental results.

Evolution of the Cell

2021 ◽  
pp. 64-81
Author(s):  
Franklin M. Harold
Keyword(s):  
Genetic Information ◽  
Metabolic Networks ◽  
Building Blocks ◽  
Eukaryotic Cells ◽  
Evolutionary Relationships ◽  
Last Universal Common Ancestor ◽  
Living Things ◽  
Universal Common Ancestor ◽  
A Cell ◽  
P Cells

Cells are life’s basic building blocks, and there is no more profound question than how they came to be. What made this murky subject accessible is the invention of methods to sequence nucleic acids and proteins, and to infer evolutionary relationships from those sequences. It seems that all living things share a common ancestry in LUCA (the Last Universal Common Ancestor), a shadowy entity thought to have lived nearly 4 billion years ago. LUCA’s nature has been much debated, but she appears to have been a cell of sorts endowed with membranes, metabolic networks, a usable energy source and the machinery to express and reproduce genetic information. The earliest known event in cell history was the divergence of Archaea from Bacteria, about 3.5 billion years ago. Eukaryotic cells, more closely allied with Archaea than with Bacteria, appear much later, some 2 billion years ago. Their origin remains one of life’s mysteries, but the evidence currently favors a fusion or merger of an early archaeon with a bacterium; the latter became the ancestor of mitochondria, and played a major role in cell evolution. Eukaryotic cells of the contemporary kind emerged over hundreds of million years. Prominent events included a second instance of intracellular symbiosis, this time with a cyanobacterium, that introduced photosynthesis into the eukaryotic universe and initiated the plant lineage. Eukaryotic cells are the building blocks of all higher organisms. Just what has given the eukaryotic order an edge is yet another of life’s stubborn mysteries.

Early determination in the C. elegans embryo: a gene, cib-1, required to specify a set of stem-cell-like blastomeres

Development ◽  
1990 ◽  
Vol 108 (1) ◽  
pp. 107-119 ◽  
Author(s):  
R. Schnabel ◽  
H. Schnabel
Keyword(s):  
Cell Cycle ◽  
Decision Making ◽  
Stem Cell ◽  
Early Embryo ◽  
Cell Cycles ◽  
C Elegans ◽  
Lethal Mutations ◽  
A Cell ◽  
Early Decision ◽  
P Cells

The early somatic blastomeres founding the tissues in the C. elegans embryo are derived in a stem-cell-like lineage from the P cells. We have isolated maternal effect lethal mutations defining the gene cib-1 in which the P cells, P1-P3, skip a cell cycle and acquire the fates of only their somatic daughters. Therefore, the cib-1 gene is required for the specification of the stem-cell-like fate of these cells. The analysis of the development of these mutants suggests that the clock controlling the cell cycles in the early embryo is directly coupled to the fate of a cell and that there must be another developmental clock that activates the determinative inventory for the early decision-making.

Enhanced thermoelectric performance of InTe through Pb doping

2021 ◽  
Author(s):  
Shantanu Misra ◽  
Adèle Léon ◽  
Petr Levinsky ◽  
Jiří Hejtmánek ◽  
Bertrand Lenoir ◽  
...  
Keyword(s):  
Energy Conversion ◽  
Band Gap ◽  
Narrow Band ◽  
Thermoelectric Performance ◽  
Chalcogenide Semiconductors ◽  
Type Semiconductor ◽  
P Type ◽  
Pb Doping

Chalcogenide semiconductors continue to be of prime interest for designing novel efficient materials for energy-conversion applications. Among them, the narrow-band-gap p-type semiconductor InTe exhibits high thermoelectric performance that mostly stems...

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