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ChemPlusChem Aug 2023Nanographenes (NGs) have drawn extensive attention as promising candidates for next-generation optoelectronic and nonlinear optical (NLO) materials, owing to its unique... (Review)
Review
Nanographenes (NGs) have drawn extensive attention as promising candidates for next-generation optoelectronic and nonlinear optical (NLO) materials, owing to its unique optoelectronic properties and high thermal stability. However, the weak polarity or even non-polarity of NGs (resulting in weak even order NLO properties) and the high chemical reactivity of zigzag edged NGs hinder their further applications in nonlinear optics, thus stabilization (lowering the chemical reactivity) and polarizing the charge distribution in NGs are necessary for such applications of NGs. The fusion of heptagon and pentagon endows the azulene with the character of donor-acceptor, and the B=N unit is isoelectronic to C=C unit. The introduction of polar azulene and BN are idea to polarize and stabilize the electronic structure of NGs for NLO applications. In the present review, a survey on the functionalization and applications of NGs in nonlinear optics is conducted. The engineering of the electronic structure of NGs by topological defects, doping and edge modulation is summarized. Finally, a summary of challenges and perspectives for carbon-based NLO nanomaterials is presented.
PubMed: 37515505
DOI: 10.1002/cplu.202300279 -
Cold Spring Harbor Perspectives in... Aug 2009During Drosophila development, neuroblasts divide to generate progeny with two different fates. One daughter cell self-renews to maintain the neuroblast pool, whereas... (Review)
Review
During Drosophila development, neuroblasts divide to generate progeny with two different fates. One daughter cell self-renews to maintain the neuroblast pool, whereas the other differentiates to populate the central nervous system. The difference in fate arises from the asymmetric distribution of proteins that specify either self-renewal or differentiation, which is brought about by their polarization into separate apical and basal cortical domains during mitosis. Neuroblast symmetry breaking is regulated by numerous proteins, many of which have only recently been discovered. The atypical protein kinase C (aPKC) is a broad regulator of polarity that localizes to the neuroblast apical cortical region and directs the polarization of the basal domain. Recent work suggests that polarity can be explained in large part by the mechanisms that restrict aPKC activity to the apical domain and those that couple asymmetric aPKC activity to the polarization of downstream factors. Polarized aPKC activity is created by a network of regulatory molecules, including Bazooka/Par-3, Cdc42, and the tumor suppressor Lgl, which represses basal recruitment. Direct phosphorylation by aPKC leads to cortical release of basal domain factors, preventing them from occupying the apical domain. In this framework, neuroblast polarity arises from a complex system that orchestrates robust aPKC polarity, which in turn polarizes substrates by coupling phosphorylation to cortical release.
Topics: Animals; Body Patterning; Cell Differentiation; Cell Division; Drosophila; Models, Biological; Neoplasms; Neurons; Protein Isoforms; Protein Kinase C; Spindle Apparatus; Stem Cells
PubMed: 20066083
DOI: 10.1101/cshperspect.a001388 -
PLoS Biology Nov 2006Cellular polarity is a general feature of animal development. However, the mechanisms that establish and maintain polarity in a field of cells or even in the whole...
Cellular polarity is a general feature of animal development. However, the mechanisms that establish and maintain polarity in a field of cells or even in the whole embryo remain elusive. Here we provide evidence that in the Caenorhabditis elegans embryo, the descendants of P1, the posterior blastomere of the 2-cell stage, constitute a polarising centre that orients the cell divisions of most of the embryo. This polarisation depends on a MOM-2/Wnt signal originating from the P1 descendants. Furthermore, we show that the MOM-2/Wnt signal is transduced from cell to cell by a relay mechanism. Our findings suggest how polarity is first established and then maintained in a field of cells. According to this model, the relay mechanism constantly orients the polarity of all cells towards the polarising centre, thus organising the whole embryo. This model may also apply to other systems such as Drosophila and vertebrates.
Topics: Animals; Blastomeres; Body Patterning; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Cell Division; Cell Lineage; Embryo, Nonmammalian; Intracellular Signaling Peptides and Proteins; Protein Transport; Signal Transduction; Wnt Proteins
PubMed: 17121454
DOI: 10.1371/journal.pbio.0040396 -
The Journal of Cell Biology Sep 2014The receptor deleted in colorectal cancer (DCC) directs dynamic polarizing activities in animals toward its extracellular ligand netrin. How DCC polarizes toward netrin...
The receptor deleted in colorectal cancer (DCC) directs dynamic polarizing activities in animals toward its extracellular ligand netrin. How DCC polarizes toward netrin is poorly understood. By performing live-cell imaging of the DCC orthologue UNC-40 during anchor cell invasion in Caenorhabditis elegans, we have found that UNC-40 clusters, recruits F-actin effectors, and generates F-actin in the absence of UNC-6 (netrin). Time-lapse analyses revealed that UNC-40 clusters assemble, disassemble, and reform at periodic intervals in different regions of the cell membrane. This oscillatory behavior indicates that UNC-40 clusters through a mechanism involving interlinked positive (formation) and negative (disassembly) feedback. We show that endogenous UNC-6 and ectopically provided UNC-6 orient and stabilize UNC-40 clustering. Furthermore, the UNC-40-binding protein MADD-2 (a TRIM family protein) promotes ligand-independent clustering and robust UNC-40 polarization toward UNC-6. Together, our data suggest that UNC-6 (netrin) directs polarized responses by stabilizing UNC-40 clustering. We propose that ligand-independent UNC-40 clustering provides a robust and adaptable mechanism to polarize toward netrin.
Topics: Actins; Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Cell Adhesion Molecules; Cell Polarity; Female; Intracellular Signaling Peptides and Proteins; Nerve Tissue Proteins; Netrins; Protein Multimerization; Protein Stability; Protein Transport; Uterus
PubMed: 25154398
DOI: 10.1083/jcb.201405026 -
Current Biology : CB Feb 2009Asymmetric intracellular signals enable cells to migrate in response to external cues. The multiprotein WAVE (also known as SCAR or WASF) complex activates the...
Asymmetric intracellular signals enable cells to migrate in response to external cues. The multiprotein WAVE (also known as SCAR or WASF) complex activates the actin-nucleating Arp2/3 complex [1-4] and localizes to propagating "waves," which direct actin assembly during neutrophil migration [5, 6]. Here, we observe similar WAVE complex dynamics in other mammalian cells and analyze WAVE complex dynamics during establishment of neutrophil polarity. Earlier models proposed that spatially biased generation [7] or selection of protrusions [8] enables chemotaxis. These models require existing morphological polarity to control protrusions. We show that spatially biased generation and selection of WAVE complex recruitment also occur in morphologically unpolarized neutrophils during development of their first protrusions. Additionally, several mechanisms limit WAVE complex recruitment during polarization and movement: Intrinsic cues restrict WAVE complex distribution during establishment of polarity, and asymmetric intracellular signals constrain it in morphologically polarized cells. External gradients can overcome both intrinsic biases and control WAVE complex localization. After latrunculin-mediated inhibition of actin polymerization, addition and removal of agonist gradients globally recruits and releases the WAVE complex from the membrane. Under these conditions, the WAVE complex no longer polarizes, despite the presence of strong external gradients. Thus, actin polymer and the WAVE complex reciprocally interact during polarization.
Topics: Actins; Animals; Blotting, Western; Bridged Bicyclo Compounds, Heterocyclic; Cell Fractionation; Cell Line; Cell Polarity; Mice; Micromanipulation; Microscopy, Video; Multiprotein Complexes; Neutrophils; Thiazolidines; Wiskott-Aldrich Syndrome Protein Family
PubMed: 19200726
DOI: 10.1016/j.cub.2008.12.044 -
Seminars in Cell & Developmental Biology Oct 2004The early events of mouse embryogenesis lead to the formation of three distinct cell lineages by the blastocyst: the pluripotent epiblast and the two extraembryonic... (Review)
Review
The early events of mouse embryogenesis lead to the formation of three distinct cell lineages by the blastocyst: the pluripotent epiblast and the two extraembryonic lineages, the trophoblast and primitive endoderm. Segregation of the lineages depends on the relative levels of expression of key transcription factors, whose localized expression must be controlled by the earlier events of compaction and polarization of the morula. Soon after lineage specification, the two extraembryonic lineages show evidence of early polarities that may relate to the polarity of the postimplantation embryo at gastrulation. The exact relationship between lineage segregation, preimplantation polarities and the postimplantation axes remain to be determined but are now open to molecular and cellular investigation.
Topics: Animals; Blastocyst; Body Patterning; Cell Differentiation; Cell Lineage; Ectoderm; Endoderm; Mice; Pluripotent Stem Cells
PubMed: 15271303
DOI: 10.1016/j.semcdb.2004.04.003 -
Development (Cambridge, England) May 2010Polarization of the C. elegans zygote is initiated by ECT-2-dependent cortical flows, which mobilize the anterior PAR proteins (PAR-3, PAR-6 and PKC-3) away from the...
Polarization of the C. elegans zygote is initiated by ECT-2-dependent cortical flows, which mobilize the anterior PAR proteins (PAR-3, PAR-6 and PKC-3) away from the future posterior end of the embryo marked by the sperm centrosome. Here, we demonstrate the existence of a second, parallel and redundant pathway that can polarize the zygote in the absence of ECT-2-dependent cortical flows. This second pathway depends on the polarity protein PAR-2. We show that PAR-2 localizes to the cortex nearest the sperm centrosome even in the absence of cortical flows. Once on the cortex, PAR-2 antagonizes PAR-3-dependent recruitment of myosin, creating myosin flows that transport the anterior PAR complex away from PAR-2 in a positive-feedback loop. We propose that polarity in the C. elegans zygote is initiated by redundant ECT-2- and PAR-2-dependent mechanisms that lower PAR-3 levels locally, triggering a positive-feedback loop that polarizes the entire cortex.
Topics: Alleles; Amino Acid Sequence; Animals; Animals, Genetically Modified; Body Patterning; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Cell Polarity; Embryo, Nonmammalian; Genes, Helminth; Green Fluorescent Proteins; Guanine Nucleotide Exchange Factors; Molecular Sequence Data; Sequence Homology, Amino Acid; Signal Transduction; Zygote
PubMed: 20392744
DOI: 10.1242/dev.045823 -
Developmental Cell Feb 2011In most flowering plants, the apical-basal body axis is established by an asymmetric division of the polarized zygote. In Arabidopsis, early embryo patterning is...
In most flowering plants, the apical-basal body axis is established by an asymmetric division of the polarized zygote. In Arabidopsis, early embryo patterning is regulated by WOX homeobox genes, which are coexpressed in the zygote but become restricted to apical (WOX2) and basal (WOX8/9) cells. How the asymmetry of zygote division is regulated and connected to the daughter cell fates is largely unknown. Here, we show that expression of WOX8 is independent of the axis patterning signal auxin, but, together with the redundant gene WOX9, is activated in the zygote, its basal daughter cell, and the hypophysis by the zinc-finger transcription factor WRKY2. In wrky2 mutants, egg cells polarize normally but zygotes fail to reestablish polar organelle positioning from a transient symmetric state, resulting in equal cell division and distorted embryo development. Both defects are rescued by overexpressing WOX8, indicating that WRKY2-dependent WOX8 transcription links zygote polarization with embryo patterning.
Topics: Arabidopsis; Arabidopsis Proteins; Cell Division; Cell Polarity; Gene Expression Regulation, Developmental; Gene Expression Regulation, Plant; Genes, Plant; Homeodomain Proteins; Promoter Regions, Genetic; Transcription Factors; Transcription, Genetic; Transcriptional Activation; Zygote
PubMed: 21316593
DOI: 10.1016/j.devcel.2011.01.009 -
Science (New York, N.Y.) Apr 1993A thin ferromagnetic film can be used to polarize the spin axes of the electrons carrying an electric current in a manner loosely analogous with a light polarizer. When...
A thin ferromagnetic film can be used to polarize the spin axes of the electrons carrying an electric current in a manner loosely analogous with a light polarizer. When such a film is fabricated on a gold film, a nonequilibrium population of spin-polarized electrons is built up in the gold causing a "spin bottleneck" effect. The addition of a second ferromagnetic film results in a device whose output voltage depends on the orientation of the spins.
PubMed: 17838246
DOI: 10.1126/science.260.5106.320 -
Optics Letters Nov 1980A technique is presented for the fabrication of high-quality single-mode fiber-optic polarizers. Properties of polarizers made using this technique include extinction...
A technique is presented for the fabrication of high-quality single-mode fiber-optic polarizers. Properties of polarizers made using this technique include extinction ratios in excess of 60 dB as well as low loss for the desired polarization.
PubMed: 19701278
DOI: 10.1364/ol.5.000479