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1.
PLoS Biol ; 22(1): e3002450, 2024 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-38289899

RESUMO

Biological processes are intrinsically noisy, and yet, the result of development-like the species-specific size and shape of organs-is usually remarkably precise. This precision suggests the existence of mechanisms of feedback control that ensure that deviations from a target size are minimized. Still, we have very limited understanding of how these mechanisms operate. Here, we investigate the problem of organ size precision using the Drosophila eye. The size of the adult eye depends on the rates at which eye progenitor cells grow and differentiate. We first find that the progenitor net growth rate results from the balance between their proliferation and apoptosis, with this latter contributing to determining both final eye size and its variability. In turn, apoptosis of progenitor cells is hampered by Dpp, a BMP2/4 signaling molecule transiently produced by early differentiating retinal cells. Our genetic and computational experiments show how the status of retinal differentiation is communicated to progenitors through the differentiation-dependent production of Dpp, which, by adjusting the rate of apoptosis, exerts a feedback control over the net growth of progenitors to reduce final eye size variability.


Assuntos
Proteínas de Drosophila , Drosophila , Animais , Drosophila/genética , Drosophila melanogaster , Proteínas de Drosophila/genética , Tamanho do Órgão , Retroalimentação , Olho , Retina , Apoptose/genética
2.
PLoS Comput Biol ; 18(8): e1010359, 2022 08.
Artigo em Inglês | MEDLINE | ID: mdl-35969646

RESUMO

The Anabaena genus is a model organism of filamentous cyanobacteria whose vegetative cells can differentiate under nitrogen-limited conditions into a type of cell called heterocyst. These heterocysts lose the possibility to divide and are necessary for the colony because they can fix and share environmental nitrogen. In order to distribute the nitrogen efficiently, heterocysts are arranged to form a quasi-regular pattern whose features are maintained as the filament grows. Recent efforts have allowed advances in the understanding of the interactions and genetic mechanisms underlying this dynamic pattern. However, the main role of the patA and hetF genes are yet to be clarified; in particular, the patA mutant forms heterocysts almost exclusively in the terminal cells of the filament. In this work, we investigate the function of these genes and provide a theoretical model that explains how they interact within the broader genetic network, reproducing their knock-out phenotypes in several genetic backgrounds, including a nearly uniform concentration of HetR along the filament for the patA mutant. Our results suggest a role of hetF and patA in a post-transcriptional modification of HetR which is essential for its regulatory function. In addition, the existence of molecular leakage out of the filament in its boundary cells is enough to explain the preferential appearance of terminal heterocysts, without any need for a distinct regulatory pathway.


Assuntos
Anabaena , Regulação Bacteriana da Expressão Gênica , Anabaena/genética , Anabaena/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Regulação Bacteriana da Expressão Gênica/genética , Redes Reguladoras de Genes , Nitrogênio/metabolismo
3.
Proc Natl Acad Sci U S A ; 117(42): 26190-26196, 2020 10 20.
Artigo em Inglês | MEDLINE | ID: mdl-33004629

RESUMO

Epidemic spread is characterized by exponentially growing dynamics, which are intrinsically unpredictable. The time at which the growth in the number of infected individuals halts and starts decreasing cannot be calculated with certainty before the turning point is actually attained; neither can the end of the epidemic after the turning point. A susceptible-infected-removed (SIR) model with confinement (SCIR) illustrates how lockdown measures inhibit infection spread only above a threshold that we calculate. The existence of that threshold has major effects in predictability: A Bayesian fit to the COVID-19 pandemic in Spain shows that a slowdown in the number of newly infected individuals during the expansion phase allows one to infer neither the precise position of the maximum nor whether the measures taken will bring the propagation to the inhibition regime. There is a short horizon for reliable prediction, followed by a dispersion of the possible trajectories that grows extremely fast. The impossibility to predict in the midterm is not due to wrong or incomplete data, since it persists in error-free, synthetically produced datasets and does not necessarily improve by using larger datasets. Our study warns against precise forecasts of the evolution of epidemics based on mean-field, effective, or phenomenological models and supports that only probabilities of different outcomes can be confidently given.


Assuntos
Infecções por Coronavirus/epidemiologia , Previsões , Pneumonia Viral/epidemiologia , Betacoronavirus , COVID-19 , Infecções por Coronavirus/prevenção & controle , Infecções por Coronavirus/transmissão , Previsões/métodos , Humanos , Modelos Biológicos , Pandemias/prevenção & controle , Pneumonia Viral/prevenção & controle , Pneumonia Viral/transmissão , SARS-CoV-2 , Espanha/epidemiologia , Incerteza
5.
Nucleic Acids Res ; 46(22): 11910-11926, 2018 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-30380104

RESUMO

The principal route for dissemination of antibiotic resistance genes is conjugation by which a conjugative DNA element is transferred from a donor to a recipient cell. Conjugative elements contain genes that are important for their establishment in the new host, for instance by counteracting the host defense mechanisms acting against incoming foreign DNA. Little is known about these establishment genes and how they are regulated. Here, we deciphered the regulation mechanism of possible establishment genes of plasmid p576 from the Gram-positive bacterium Bacillus pumilus. Unlike the ssDNA promoters described for some conjugative plasmids, the four promoters of these p576 genes are repressed by a repressor protein, which we named Reg576. Reg576 also regulates its own expression. After transfer of the DNA, these genes are de-repressed for a period of time until sufficient Reg576 is synthesized to repress the promoters again. Complementary in vivo and in vitro analyses showed that different operator configurations in the promoter regions of these genes lead to different responses to Reg576. Each operator is bound with extreme cooperativity by two Reg576-dimers. The X-ray structure revealed that Reg576 has a Ribbon-Helix-Helix core and provided important insights into the high cooperativity of DNA recognition.


Assuntos
Bacillus pumilus/genética , Proteínas de Bactérias/química , DNA/química , Transferência Genética Horizontal , Plasmídeos/química , Proteínas Repressoras/química , Bacillus pumilus/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Sequência de Bases , Sítios de Ligação , Clonagem Molecular , Conjugação Genética , DNA/genética , DNA/metabolismo , Farmacorresistência Bacteriana Múltipla/genética , Escherichia coli/genética , Escherichia coli/metabolismo , Expressão Gênica , Regulação Bacteriana da Expressão Gênica , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Conformação de Ácido Nucleico , Plasmídeos/metabolismo , Regiões Promotoras Genéticas , Ligação Proteica , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre Proteínas , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Shigella flexneri/genética , Shigella flexneri/metabolismo
6.
Proc Natl Acad Sci U S A ; 113(22): 6218-23, 2016 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-27162328

RESUMO

Cyanobacteria forming one-dimensional filaments are paradigmatic model organisms of the transition between unicellular and multicellular living forms. Under nitrogen-limiting conditions, in filaments of the genus Anabaena, some cells differentiate into heterocysts, which lose the possibility to divide but are able to fix environmental nitrogen for the colony. These heterocysts form a quasiregular pattern in the filament, representing a prototype of patterning and morphogenesis in prokaryotes. Recent years have seen advances in the identification of the molecular mechanism regulating this pattern. We use these data to build a theory on heterocyst pattern formation, for which both genetic regulation and the effects of cell division and filament growth are key components. The theory is based on the interplay of three generic mechanisms: local autoactivation, early long-range inhibition, and late long-range inhibition. These mechanisms can be identified with the dynamics of hetR, patS, and hetN expression. Our theory reproduces quantitatively the experimental dynamics of pattern formation and maintenance for wild type and mutants. We find that hetN alone is not enough to play the role as the late inhibitory mechanism: a second mechanism, hypothetically the products of nitrogen fixation supplied by heterocysts, must also play a role in late long-range inhibition. The preponderance of even intervals between heterocysts arises naturally as a result of the interplay between the timescales of genetic regulation and cell division. We also find that a purely stochastic initiation of the pattern, without a two-stage process, is enough to reproduce experimental observations.


Assuntos
Proteínas de Bactérias/metabolismo , Cianobactérias/citologia , Cianobactérias/fisiologia , Regulação Bacteriana da Expressão Gênica , Fixação de Nitrogênio/fisiologia , Proteínas de Bactérias/genética , Redes Reguladoras de Genes , Modelos Teóricos
7.
Development ; 141(6): 1381-91, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24595291

RESUMO

How signaling gradients supply positional information in a field of moving cells is an unsolved question in patterning and morphogenesis. Here, we ask how a Wnt signaling gradient regulates the dynamics of a wavefront of cellular change in a flow of cells during somitogenesis. Using time-controlled perturbations of Wnt signaling in the zebrafish embryo, we changed segment length without altering the rate of somite formation or embryonic elongation. This result implies specific Wnt regulation of the wavefront velocity. The observed Wnt signaling gradient dynamics and timing of downstream events support a model for wavefront regulation in which cell flow plays a dominant role in transporting positional information.


Assuntos
Somitos/embriologia , Somitos/metabolismo , Via de Sinalização Wnt/fisiologia , Proteínas de Peixe-Zebra/fisiologia , Peixe-Zebra/embriologia , Peixe-Zebra/metabolismo , Animais , Animais Geneticamente Modificados , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/fisiologia , Padronização Corporal/genética , Padronização Corporal/fisiologia , Fatores de Crescimento de Fibroblastos/genética , Fatores de Crescimento de Fibroblastos/fisiologia , Regulação da Expressão Gênica no Desenvolvimento , Resposta ao Choque Térmico/genética , Resposta ao Choque Térmico/fisiologia , Peptídeos e Proteínas de Sinalização Intercelular/genética , Peptídeos e Proteínas de Sinalização Intercelular/fisiologia , Modelos Biológicos , Proteínas com Domínio T/genética , Proteínas com Domínio T/fisiologia , Proteínas Wnt/antagonistas & inibidores , Proteínas Wnt/genética , Proteínas Wnt/fisiologia , Via de Sinalização Wnt/genética , Peixe-Zebra/genética , Proteínas de Peixe-Zebra/antagonistas & inibidores , Proteínas de Peixe-Zebra/genética
8.
Development ; 139(4): 625-39, 2012 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-22274695

RESUMO

The segmentation clock is an oscillating genetic network thought to govern the rhythmic and sequential subdivision of the elongating body axis of the vertebrate embryo into somites: the precursors of the segmented vertebral column. Understanding how the rhythmic signal arises, how it achieves precision and how it patterns the embryo remain challenging issues. Recent work has provided evidence of how the period of the segmentation clock is regulated and how this affects the anatomy of the embryo. The ongoing development of real-time clock reporters and mathematical models promise novel insight into the dynamic behavior of the clock.


Assuntos
Relógios Biológicos/fisiologia , Padronização Corporal/fisiologia , Desenvolvimento Embrionário/fisiologia , Somitos/embriologia , Vertebrados/anatomia & histologia , Vertebrados/embriologia , Animais , Evolução Biológica , Proteínas CLOCK/genética , Proteínas CLOCK/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Modelos Teóricos , Receptores Notch/metabolismo , Receptores Opioides delta/metabolismo , Transdução de Sinais/fisiologia , Somitos/anatomia & histologia , Proteínas Wnt/metabolismo
9.
Development ; 139(13): 2321-9, 2012 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-22669822

RESUMO

Signaling mediated by the Delta/Notch system controls the process of lateral inhibition, known to regulate neurogenesis in metazoans. Lateral inhibition takes place in equivalence groups formed by cells having equal capacity to differentiate, and it results in the singling out of precursors, which subsequently become neurons. During normal development, areas of active neurogenesis spread through non-neurogenic regions in response to specific morphogens, giving rise to neurogenic wavefronts. Close contact of these wavefronts with non-neurogenic cells is expected to affect lateral inhibition. Therefore, a mechanism should exist in these regions to prevent disturbances of the lateral inhibitory process. Focusing on the developing chick retina, we show that Dll1 is widely expressed by non-neurogenic precursors located at the periphery of this tissue, a region lacking Notch1, lFng, and differentiation-related gene expression. We investigated the role of this Dll1 expression through mathematical modeling. Our analysis predicts that the absence of Dll1 ahead of the neurogenic wavefront results in reduced robustness of the lateral inhibition process, often linked to enhanced neurogenesis and the presence of morphological alterations of the wavefront itself. These predictions are consistent with previous observations in the retina of mice in which Dll1 is conditionally mutated. The predictive capacity of our mathematical model was confirmed further by mimicking published results on the perturbation of morphogenetic furrow progression in the eye imaginal disc of Drosophila. Altogether, we propose that Notch-independent Delta expression ahead of the neurogenic wavefront is required to avoid perturbations in lateral inhibition and wavefront progression, thus optimizing the neurogenic process.


Assuntos
Neurogênese , Neurônios/citologia , Retina/crescimento & desenvolvimento , Animais , Embrião de Galinha , Simulação por Computador , Drosophila/crescimento & desenvolvimento , Desenvolvimento Embrionário , Peptídeos e Proteínas de Sinalização Intracelular/análise , Proteínas de Membrana/análise , Camundongos , Modelos Biológicos , Retina/citologia
10.
PLoS Biol ; 10(7): e1001364, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22911291

RESUMO

During vertebrate embryogenesis, the rhythmic and sequential segmentation of the body axis is regulated by an oscillating genetic network termed the segmentation clock. We describe a new dynamic model for the core pace-making circuit of the zebrafish segmentation clock based on a systematic biochemical investigation of the network's topology and precise measurements of somitogenesis dynamics in novel genetic mutants. We show that the core pace-making circuit consists of two distinct negative feedback loops, one with Her1 homodimers and the other with Her7:Hes6 heterodimers, operating in parallel. To explain the observed single and double mutant phenotypes of her1, her7, and hes6 mutant embryos in our dynamic model, we postulate that the availability and effective stability of the dimers with DNA binding activity is controlled in a "dimer cloud" that contains all possible dimeric combinations between the three factors. This feature of our model predicts that Hes6 protein levels should oscillate despite constant hes6 mRNA production, which we confirm experimentally using novel Hes6 antibodies. The control of the circuit's dynamics by a population of dimers with and without DNA binding activity is a new principle for the segmentation clock and may be relevant to other biological clocks and transcriptional regulatory networks.


Assuntos
Relógios Biológicos/genética , Regulação da Expressão Gênica no Desenvolvimento , Peixe-Zebra/genética , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Padronização Corporal , Dimerização , Retroalimentação Fisiológica , Modelos Biológicos , Fenótipo , Regiões Promotoras Genéticas , Mapeamento de Interação de Proteínas , Mapas de Interação de Proteínas , Estabilidade Proteica , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Somitos/citologia , Somitos/embriologia , Somitos/metabolismo , Especificidade por Substrato , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Transcrição Gênica , Técnicas do Sistema de Duplo-Híbrido , Peixe-Zebra/embriologia , Peixe-Zebra/metabolismo , Proteínas de Peixe-Zebra/genética , Proteínas de Peixe-Zebra/metabolismo
11.
Phys Rev Lett ; 112(17): 174101, 2014 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-24836248

RESUMO

In systems of coupled oscillators, the effects of complex signaling can be captured by time delays and phase shifts. Here, we show how time delays and phase shifts lead to different oscillator dynamics and how synchronization rates can be regulated by substituting time delays by phase shifts at a constant collective frequency. For spatially extended systems with time delays, we show that the fastest synchronization can occur for intermediate wavelengths, giving rise to novel synchronization scenarios.


Assuntos
Modelos Teóricos , Transição de Fase , Transdução de Sinais
12.
Methods Mol Biol ; 2795: 247-261, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38594544

RESUMO

Increased day lengths and warm conditions inversely affect plant growth by directly modulating nuclear phyB, ELF3, and COP1 levels. Quantitative measures of the hypocotyl length have been key to gaining a deeper understanding of this complex regulatory network, while similar quantitative data are the foundation for many studies in plant biology. Here, we explore the application of mathematical modeling, specifically ordinary differential equations (ODEs), to understand plant responses to these environmental cues. We provide a comprehensive guide to constructing, simulating, and fitting these models to data, using the law of mass action to study the evolution of molecular species. The fundamental principles of these models are introduced, highlighting their utility in deciphering complex plant physiological interactions and testing hypotheses. This brief introduction will not allow experimentalists without a mathematical background to run their own simulations overnight, but it will help them grasp modeling principles and communicate with more theory-inclined colleagues.


Assuntos
Modelos Teóricos , Vernalização , Plantas , Hipocótilo/fisiologia
13.
Phys Biol ; 9(3): 036006, 2012 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-22562967

RESUMO

Cell movement and intercellular signaling occur simultaneously during the development of tissues, but little is known about how movement affects signaling. Previous theoretical studies have shown that faster moving cells favor synchronization across a population of locally coupled genetic oscillators. An important assumption in these studies is that cells can immediately interact with their new neighbors after arriving at a new location. However, intercellular interactions in cellular systems may need some time to become fully established. How movement affects synchronization in this situation has not been examined. Here, we develop a coupled phase oscillator model in which we consider cell movement and the gradual recovery of intercellular coupling experienced by a cell after movement, characterized by a moving rate and a coupling recovery rate, respectively. We find (1) an optimal moving rate for synchronization and (2) a critical moving rate above which achieving synchronization is not possible. These results indicate that the extent to which movement enhances synchrony is limited by a gradual recovery of coupling. These findings suggest that the ratio of time scales of movement and signaling recovery is critical for information transfer between moving cells.


Assuntos
Comunicação Celular , Movimento Celular , Modelos Biológicos , Animais , Relógios Biológicos , Simulação por Computador , Humanos , Morfogênese , Transdução de Sinais
14.
Phys Rev Lett ; 108(20): 204101, 2012 May 18.
Artigo em Inglês | MEDLINE | ID: mdl-23003147

RESUMO

We study the effects of delayed coupling on timing and pattern formation in spatially extended systems of dynamic oscillators. Starting from a discrete lattice of coupled oscillators, we derive a generic continuum theory for collective modes of long wavelengths. We use this approach to study spatial phase profiles of cellular oscillators in the segmentation clock, a dynamic patterning system of vertebrate embryos. Collective wave patterns result from the interplay of coupling delays and moving boundary conditions. We show that the phase profiles of collective modes depend on coupling delays.

15.
Front Cell Dev Biol ; 10: 959468, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36187490

RESUMO

The Anabaena genus is a model organism of filamentous cyanobacteria whose vegetative cells can differentiate under nitrogen-limited conditions into a type of cell called a heterocyst. These heterocysts lose the possibility to divide and are necessary for the filament because they can fix and share environmental nitrogen. In order to distribute the nitrogen efficiently, heterocysts are arranged to form a quasi-regular pattern whose features are maintained as the filament grows. Recent efforts have allowed advances in the understanding of the interactions and genetic mechanisms underlying this dynamic pattern. Here, we present a systematic review of the existing theoretical models of nitrogen-fixing cell differentiation in filamentous cyanobacteria. These filaments constitute one of the simplest forms of multicellular organization, and this allows for several modeling scales of this emergent pattern. The system has been approached at three different levels. From bigger to smaller scale, the system has been considered as follows: at the population level, by defining a mean-field simplified system to study the ratio of heterocysts and vegetative cells; at the filament level, with a continuous simplification as a reaction-diffusion system; and at the cellular level, by studying the genetic regulation that produces the patterning for each cell. In this review, we compare these different approaches noting both the virtues and shortcomings of each one of them.

16.
Sci Adv ; 8(33): eabp8412, 2022 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-35984876

RESUMO

As the summer approaches, plants experience enhanced light inputs and warm temperatures, two environmental cues with an opposite morphogenic impact. Key components of this response are PHYTOCHROME B (phyB), EARLY FLOWERING 3 (ELF3), and CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1). Here, we used single and double mutant/overexpression lines to fit a mathematical model incorporating known interactions of these regulators. The fitted model recapitulates thermal growth of all lines used and correctly predicts thermal behavior of others not used in the fit. While thermal COP1 function is accepted to be independent of diurnal timing, our model shows that it acts at temperature signaling only during daytime. Defective response of cop1-4 mutants is epistatic to phyB-9 and elf3-8, indicating that COP1 activity is essential to transduce phyB and ELF3 thermosensory function. Our thermal model provides a unique toolbox to identify best allelic combinations enhancing climate change resilience of crops adapted to different latitudes.

17.
Front Mol Biosci ; 8: 648468, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33816561

RESUMO

Bacterial conjugation is the main horizontal gene transfer route responsible for the spread of antibiotic resistance, virulence and toxin genes. During conjugation, DNA is transferred from a donor to a recipient cell via a sophisticated channel connecting the two cells. Conjugation not only affects many different aspects of the plasmid and the host, ranging from the properties of the membrane and the cell surface of the donor, to other developmental processes such as competence, it probably also poses a burden on the donor cell due to the expression of the large number of genes involved in the conjugation process. Therefore, expression of the conjugation genes must be strictly controlled. Over the past decade, the regulation of the conjugation genes present on the conjugative Bacillus subtilis plasmid pLS20 has been studied using a variety of methods including genetic, biochemical, biophysical and structural approaches. This review focuses on the interplay between RcopLS20, RappLS20 and Phr*pLS20, the proteins that control the activity of the main conjugation promoter P c located upstream of the conjugation operon. Proper expression of the conjugation genes requires the following two fundamental elements. First, conjugation is repressed by default and an intercellular quorum-signaling system is used to sense conditions favorable for conjugation. Second, different layers of regulation act together to repress the P c promoter in a strict manner but allowing rapid activation. During conjugation, ssDNA is exported from the cell by a membrane-embedded DNA translocation machine. Another membrane-embedded DNA translocation machine imports ssDNA in competent cells. Evidences are reviewed indicating that conjugation and competence are probably mutually exclusive processes. Some of the questions that remain unanswered are discussed.

18.
Neuron ; 89(3): 494-506, 2016 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-26804994

RESUMO

Neuronal subtype-specific transcription factors (TFs) instruct key features of neuronal function and connectivity. Activity-dependent mechanisms also contribute to wiring and circuit assembly, but whether and how they relate to TF-directed neuronal differentiation is poorly investigated. Here we demonstrate that the TF Cux1 controls the formation of the layer II/III corpus callosum (CC) projections through the developmental transcriptional regulation of Kv1 voltage-dependent potassium channels and the resulting postnatal switch to a Kv1-dependent firing mode. Loss of Cux1 function led to a decrease in the expression of Kv1 transcripts, aberrant firing responses, and selective loss of CC contralateral innervation. Firing and innervation were rescued by re-expression of Kv1 or postnatal reactivation of Cux1. Knocking down Kv1 mimicked Cux1-mediated CC axonal loss. These findings reveal that activity-dependent processes are central bona fide components of neuronal TF-differentiation programs and establish the importance of intrinsic firing modes in circuit assembly within the neocortex.


Assuntos
Potenciais de Ação/fisiologia , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/metabolismo , Neurônios/fisiologia , Proteínas Nucleares/metabolismo , Proteínas Repressoras/metabolismo , Superfamília Shaker de Canais de Potássio/fisiologia , Animais , Corpo Caloso/citologia , Corpo Caloso/crescimento & desenvolvimento , Corpo Caloso/fisiologia , Técnicas de Silenciamento de Genes , Camundongos , Camundongos Transgênicos , Cultura Primária de Células , Superfamília Shaker de Canais de Potássio/biossíntese , Superfamília Shaker de Canais de Potássio/genética
19.
Phys Rev E Stat Nonlin Soft Matter Phys ; 70(6 Pt 1): 061607, 2004 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-15697381

RESUMO

We present a modified version of the one-dimensional sine-Gordon model that exhibits a thermodynamic, roughening phase transition, in analogy with the two-dimensional usual sine-Gordon model. The model is suited to study the crystalline growth over an impenetrable substrate and to describe the wetting transition of a liquid that forms layers. We use the transfer integral technique to write down the pseudo-Schro dinger equation for the model, which allows us to obtain some analytical insight, and to compute numerically the free energy from the exact transfer operator. We compare the results with Monte Carlo simulations of the model, finding a perfect agreement between both procedures. We thus establish that the model shows a phase transition between a low-temperature flat phase with intriguing nontrivial properties and a high-temperature rough one. The fact that the model is one-dimensional and that it has a true phase transition makes it an ideal framework for further studies of roughening phase transitions.

20.
Phys Rev E Stat Nonlin Soft Matter Phys ; 67(4 Pt 2): 046108, 2003 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-12786437

RESUMO

We study the one-dimensional sine-Gordon model as a prototype of roughening phenomena. In spite of the fact that it has been recently proven that this model cannot have any phase transition [J. A. Cuesta and A. Sánchez, J. Phys. A 35, 2373 (2002)], Langevin as well as Monte Carlo simulations strongly suggest the existence of a finite temperature separating a flat from a rough phase. We explain this result by means of the transfer operator formalism and show as a consequence that sine-Gordon lattices of any practically achievable size will exhibit this apparent phase transition at unexpectedly large temperatures.

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