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1.
Cell ; 165(1): 20-21, 2016 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-27015304

RESUMO

How is the picture of the visual scene that the eye encodes represented by neural circuits in the brain? In this issue of Cell, Morgan et al. address this question by forming an ultrastructural "connectome" of the mouse's visual thalamus that depicts individual retinal afferents and every contact these form with target relay cells.


Assuntos
Conectoma , Tálamo , Animais , Encéfalo , Retina , Vias Visuais
2.
PLoS Pathog ; 20(1): e1011945, 2024 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-38252628

RESUMO

The rice blast fungus Magnaporthe oryzae differentiates specialized cells called appressoria that are required for fungal penetration into host leaves. In this study, we identified the novel basic leucine zipper (bZIP) transcription factor BIP1 (B-ZIP Involved in Pathogenesis-1) that is essential for pathogenicity. BIP1 is required for the infection of plant leaves, even if they are wounded, but not for appressorium-mediated penetration of artificial cellophane membranes. This phenotype suggests that BIP1 is not implicated in the differentiation of the penetration peg but is necessary for the initial establishment of the fungus within plant cells. BIP1 expression was restricted to the appressorium by both transcriptional and post-transcriptional control. Genome-wide transcriptome analysis showed that 40 genes were down regulated in a BIP1 deletion mutant. Most of these genes were specifically expressed in the appressorium. They encode proteins with pathogenesis-related functions such as enzymes involved in secondary metabolism including those encoded by the ACE1 gene cluster, small secreted proteins such as SLP2, BAS2, BAS3, and AVR-Pi9 effectors, as well as plant cuticle and cell wall degrading enzymes. Interestingly, this BIP1 network is different from other known infection-related regulatory networks, highlighting the complexity of gene expression control during plant-fungal interactions. Promoters of BIP1-regulated genes shared a GCN4/bZIP-binding DNA motif (TGACTC) binding in vitro to BIP1. Mutation of this motif in the promoter of MGG_08381.7 from the ACE1 gene cluster abolished its appressorium-specific expression, showing that BIP1 behaves as a transcriptional activator. In summary, our findings demonstrate that BIP1 is critical for the expression of early invasion-related genes in appressoria. These genes are likely needed for biotrophic invasion of the first infected host cell, but not for the penetration process itself. Through these mechanisms, the blast fungus strategically anticipates the host plant environment and responses during appressorium-mediated penetration.


Assuntos
Ascomicetos , Magnaporthe , Oryza , Fatores de Transcrição de Zíper de Leucina Básica/genética , Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Oryza/microbiologia , Magnaporthe/metabolismo , Ascomicetos/genética , Ascomicetos/metabolismo , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Regulação Fúngica da Expressão Gênica
3.
Annu Rev Neurosci ; 38: 309-29, 2015 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-26154979

RESUMO

Inhibitory neurons dominate the intrinsic circuits in the visual thalamus. Interneurons in the lateral geniculate nucleus innervate relay cells and each other densely to provide powerful inhibition. The visual sector of the overlying thalamic reticular nucleus receives input from relay cells and supplies feedback inhibition to them in return. Together, these two inhibitory circuits influence all information transmitted from the retina to the primary visual cortex. By contrast, relay cells make few local connections. This review explores the role of thalamic inhibition from the dual perspectives of feature detection and information theory. For example, we describe how inhibition sharpens tuning for spatial and temporal features of the stimulus and how it might enhance image perception. We also discuss how inhibitory circuits help to reduce redundancy in signals sent downstream and, at the same time, are adapted to maximize the amount of information conveyed to the cortex.


Assuntos
Inibição Neural/fisiologia , Tálamo/fisiologia , Vias Visuais/fisiologia , Percepção Visual/fisiologia , Animais , Corpos Geniculados/fisiologia , Interneurônios/fisiologia , Córtex Visual/fisiologia
4.
J Neurosci ; 40(26): 5019-5032, 2020 06 24.
Artigo em Inglês | MEDLINE | ID: mdl-32350041

RESUMO

Even though the lateral geniculate nucleus of the thalamus (LGN) is associated with form vision, that is not its sole role. Only the dorsal portion of LGN (dLGN) projects to V1. The ventral division (vLGN) connects subcortically, sending inhibitory projections to sensorimotor structures, including the superior colliculus (SC) and regions associated with certain behavioral states, such as fear (Monavarfeshani et al., 2017; Salay et al., 2018). We combined computational, physiological, and anatomical approaches to explore visual processing in vLGN of mice of both sexes, making comparisons to dLGN and SC for perspective. Compatible with past, qualitative descriptions, the receptive fields we quantified in vLGN were larger than those in dLGN, and most cells preferred bright versus dark stimuli (Harrington, 1997). Dendritic arbors spanned the length and/or width of vLGN and were often asymmetric, positioned to collect input from large but discrete territories. By contrast, arbors in dLGN are compact (Krahe et al., 2011). Consistent with spatially coarse receptive fields in vLGN, visually evoked changes in spike timing were less precise than for dLGN and SC. Notably, however, the membrane currents and spikes of some cells in vLGN displayed gamma oscillations whose phase and strength varied with stimulus pattern, as for SC (Stitt et al., 2013). Thus, vLGN can engage its targets using oscillation-based and conventional rate codes. Finally, dark shadows activate SC and drive escape responses, whereas vLGN prefers bright stimuli. Thus, one function of long-range inhibitory projections from vLGN might be to enable movement by releasing motor targets, such as SC, from suppression.SIGNIFICANCE STATEMENT Only the dorsal lateral geniculate nucleus (dLGN) connects to cortex to serve form vision; the ventral division (vLGN) projects subcortically to sensorimotor nuclei, including the superior colliculus (SC), via long-range inhibitory connections. Here, we asked how vLGN processes visual information, making comparisons with dLGN and SC for perspective. Cells in vLGN versus dLGN had wider dendritic arbors, larger receptive fields, and fired with lower temporal precision, consistent with a modulatory role. Like SC, but not dLGN, visual stimuli entrained oscillations in vLGN, perhaps reflecting shared strategies for visuomotor processing. Finally, most neurons in vLGN preferred bright shapes, whereas dark stimuli activate SC and drive escape behaviors, suggesting that vLGN enables rapid movement by releasing target motor structures from inhibition.


Assuntos
Corpos Geniculados/fisiologia , Percepção Visual/fisiologia , Animais , Potenciais Evocados Visuais/fisiologia , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Vias Visuais/fisiologia
5.
J Neurosci ; 36(43): 10949-10963, 2016 10 26.
Artigo em Inglês | MEDLINE | ID: mdl-27798177

RESUMO

Comparative physiological and anatomical studies have greatly advanced our understanding of sensory systems. Many lines of evidence show that the murine lateral geniculate nucleus (LGN) has unique attributes, compared with other species such as cat and monkey. For example, in rodent, thalamic receptive field structure is markedly diverse, and many cells are sensitive to stimulus orientation and direction. To explore shared and different strategies of synaptic integration across species, we made whole-cell recordings in vivo from the murine LGN during the presentation of visual stimuli, analyzed the results with different computational approaches, and compared our findings with those from cat. As for carnivores, murine cells with classical center-surround receptive fields had a "push-pull" structure of excitation and inhibition within a given On or Off subregion. These cells compose the largest single population in the murine LGN (∼40%), indicating that push-pull is key in the form vision pathway across species. For two cell types with overlapping On and Off responses, which recalled either W3 or suppressed-by-contrast ganglion cells in murine retina, inhibition took a different form and was most pronounced for spatially extensive stimuli. Other On-Off cells were selective for stimulus orientation and direction. In these cases, retinal inputs were tuned and, for oriented cells, the second-order subunit of the receptive field predicted the preferred angle. By contrast, suppression was not tuned and appeared to sharpen stimulus selectivity. Together, our results provide new perspectives on the role of excitation and inhibition in retinothalamic processing. SIGNIFICANCE STATEMENT: We explored the murine lateral geniculate nucleus from a comparative physiological perspective. In cat, most retinal cells have center-surround receptive fields and push-pull excitation and inhibition, including neurons with the smallest (highest acuity) receptive fields. The same is true for thalamic relay cells. In mouse retina, the most numerous cell type has the smallest receptive fields but lacks push-pull. The most common receptive field in rodent thalamus, however, is center-surround with push-pull. Thus, receptive field structure supersedes size per se for form vision. Further, for many orientation-selective cells, the second-order component of the receptive field aligned with stimulus preference, whereas suppression was untuned. Thus, inhibition may improve spatial resolution and sharpen other forms of selectivity in rodent lateral geniculate nucleus.


Assuntos
Corpos Geniculados/fisiologia , Rede Nervosa/fisiologia , Sinapses/fisiologia , Campos Visuais/fisiologia , Vias Visuais/fisiopatologia , Percepção Visual/fisiologia , Animais , Mapeamento Encefálico , Gatos , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Modelos Neurológicos , Inibição Neural/fisiologia , Ratos , Ratos Long-Evans , Células Ganglionares da Retina/fisiologia , Especificidade da Espécie , Transmissão Sináptica/fisiologia
6.
bioRxiv ; 2023 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-37609295

RESUMO

By influencing the type and quality of information that relay cells transmit, local interneurons in thalamus have a powerful impact on cortex. To define the sensory features that these inhibitory neurons encode, we mapped receptive fields of optogenetically identified cells in the murine dorsolateral geniculate nucleus. Although few in number, local interneurons had diverse types of receptive fields, like their counterpart relay cells. This result differs markedly from visual cortex, where inhibitory cells are typically less selective than excitatory cells. To explore how thalamic interneurons might converge on relay cells, we took a computational approach. Using an evolutionary algorithm to search through a library of interneuron models generated from our results, we show that aggregated output from different groups of local interneurons can simulate the inhibitory component of the relay cell's receptive field. Thus, our work provides proof-of-concept that groups of diverse interneurons can supply feature-specific inhibition to relay cells.

7.
Viruses ; 15(11)2023 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-38005837

RESUMO

In the past decade, severe epidemics of cucumber mosaic virus (CMV) have caused significant damage to Espelette pepper crops. This virus threatens the production of Espelette pepper, which plays a significant role in the local economy and touristic attractiveness of the French Basque Country, located in southwestern France. In 2021 and 2022, CMV was detected via double-antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISAs) in Gorria pepper seed lots harvested from naturally infected fields scattered throughout the entire Espelette pepper production area. These seed lots were used in greenhouse grow-out tests to determine whether CMV could be transmitted to seedlings from contaminated seeds, using visual symptom assessment, DAS-ELISAs, and reverse transcription-polymerase chain reaction (RT-PCR). Despite the widespread occurrence of CMV in seeds of field samples, the grow-out experiments on a total of over 5000 seedlings yielded no evidence of seed transmission of local CMV isolates in Gorria pepper. Therefore, rather than seeds from infected pepper plants, sources of CMV inoculum in Espelette are more likely to be alternative hosts present in and around pepper fields that can allow for the survival of CMV during the off-season. These results have important epidemiological implications and will guide the choice of effective measures to control current epidemics.


Assuntos
Cucumovirus , Infecções por Citomegalovirus , Cucumovirus/genética , Sementes , Produtos Agrícolas , França/epidemiologia
8.
Mol Plant Pathol ; 23(2): 254-264, 2022 02.
Artigo em Inglês | MEDLINE | ID: mdl-34729890

RESUMO

We performed a genome-wide association study of pepper (Capsicum annuum) tolerance to potato virus Y (PVY). For 254 pepper accessions, we estimated the tolerance to PVY as the coefficient of regression of the fresh weight (or height) of PVY-infected and mock-inoculated plants against within-plant virus load. Small (strongly negative) coefficients of regression indicate low tolerance because plant biomass or growth decreases sharply as virus load increases. The tolerance level varied largely, with some pepper accessions showing no symptoms or fairly mild mosaics, whereas about half (48%) of the accessions showed necrotic symptoms. We found two adjacent single-nucleotide polymorphisms (SNPs) at one extremity of chromosome 9 that were significantly associated with tolerance to PVY. Similarly, in three biparental pepper progenies, we showed that the induction of necrosis on PVY systemic infection segregated as a monogenic trait determined by a locus on chromosome 9. Our results also demonstrate the existence of a negative correlation between resistance and tolerance among the cultivated pepper accessions at both the phenotypic and genetic levels. By comparing the distributions of the tolerance-associated SNP alleles and previously identified PVY resistance-associated SNP alleles, we showed that cultivated pepper accessions possess favourable alleles for both resistance and tolerance less frequently than expected under random associations, while the minority of wild pepper accessions frequently combined resistance and tolerance alleles. This divergent evolution of PVY resistance and tolerance could be related to pepper domestication or farmer's selection.


Assuntos
Capsicum , Potyvirus , Alelos , Capsicum/genética , Estudo de Associação Genômica Ampla , Doenças das Plantas/genética , Potyvirus/genética
9.
Neuron ; 55(3): 465-78, 2007 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-17678858

RESUMO

Thalamic relay cells transmit information from retina to cortex by firing either rapid bursts or tonic trains of spikes. Bursts occur when the membrane voltage is low, as during sleep, because they depend on channels that cannot respond to excitatory input unless they are primed by strong hyperpolarization. Cells fire tonically when depolarized, as during waking. Thus, mode of firing is usually associated with behavioral state. Growing evidence, however, suggests that sensory processing involves both burst and tonic spikes. To ask if visually evoked synaptic responses induce each type of firing, we recorded intracellular responses to natural movies from relay cells and developed methods to map the receptive fields of the excitation and inhibition that the images evoked. In addition to tonic spikes, the movies routinely elicited lasting inhibition from the center of the receptive field that permitted bursts to fire. Therefore, naturally evoked patterns of synaptic input engage dual modes of firing.


Assuntos
Natureza , Inibição Neural/fisiologia , Neurônios/fisiologia , Estimulação Luminosa/métodos , Tálamo/fisiologia , Vias Visuais/fisiologia , Potenciais de Ação , Animais , Gatos , Eletrofisiologia , Filmes Cinematográficos , Sinapses/fisiologia , Tálamo/citologia , Vias Visuais/citologia
10.
J Neurosci ; 30(41): 13567-77, 2010 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-20943898

RESUMO

The neural code that represents the world is transformed at each stage of a sensory pathway. These transformations enable downstream neurons to recode information they receive from earlier stages. Using the retinothalamic synapse as a model system, we developed a theoretical framework to identify stimulus features that are inherited, gained, or lost across stages. Specifically, we observed that thalamic spikes encode novel, emergent, temporal features not conveyed by single retinal spikes. Furthermore, we found that thalamic spikes are not only more informative than retinal ones, as expected, but also more independent. Next, we asked how thalamic spikes gain sensitivity to the emergent features. Explicitly, we found that the emergent features are encoded by retinal spike pairs and then recoded into independent thalamic spikes. Finally, we built a model of synaptic transmission that reproduced our observations. Thus, our results established a link between synaptic mechanisms and the recoding of sensory information.


Assuntos
Potenciais de Ação/fisiologia , Neurônios/fisiologia , Retina/fisiologia , Sinapses/fisiologia , Transmissão Sináptica/fisiologia , Tálamo/fisiologia , Animais , Gatos , Eletrofisiologia , Modelos Neurológicos , Estimulação Luminosa , Vias Visuais/fisiologia
11.
Virus Res ; 286: 198042, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32504705

RESUMO

Plant viral diseases represent a significant burden to plant health, and their highest impact in Mediterranean agriculture is on vegetables grown under intensive horticultural practices. In order to understand better virus evolution and emergence, the most prevalent viruses were mapped in the main cucurbitaceous (melon, squashes) and solanaceous (tomato, pepper) crops and in some wild hosts in the French Mediterranean area, and virus diversity, evolution and population structure were studied through molecular epidemiology approaches. Surveys were performed in summer 2016 and 2017, representing a total of 1530 crop samples and 280 weed samples. The plant samples were analysed using serological and molecular approaches, including high-throughput sequencing (HTS). The viral species and their frequency in crops were quite similar to those of surveys conducted ten years before in the same areas. Contrary to other Mediterranean countries, aphid-transmitted viruses remain the most prevalent in France whereas whitefly-transmitted ones have not yet emerged. However, HTS analysis of viral evolution revealed the appearance of undescribed viral variants, especially for watermelon mosaic virus (WMV) in cucurbits, or variants not present in France before, as for cucumber mosaic virus (CMV) in solanaceous crops. Deep sequencing also revealed complex virus populations within individual plants with frequent recombination or reassortment. The spatial genetic structure of cucurbit aphid-borne yellows virus (CABYV) was related to the landscape structure, whereas in the case of WMV, the recurrence of introduction events and probable human exchanges of plant material resulted in complex spatial pattern of genetic variation.


Assuntos
Cucurbita/virologia , Evolução Molecular , Doenças das Plantas/virologia , Solanum lycopersicum/virologia , Vírus/genética , Animais , Afídeos/virologia , Produtos Agrícolas/virologia , França , Insetos Vetores/virologia , Região do Mediterrâneo , Filogenia , Vírus Reordenados/genética , Recombinação Genética , Vírus/classificação
12.
Cereb Cortex ; 18(1): 13-28, 2008 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-17420172

RESUMO

Time invariant description of synaptic connectivity in cortical circuits may be precluded by the ongoing growth and retraction of dendritic spines accompanied by the formation and elimination of synapses. On the other hand, the spatial arrangement of axonal and dendritic branches appears stable. This suggests that an invariant description of connectivity can be cast in terms of potential synapses, which are locations in the neuropil where an axon branch of one neuron is proximal to a dendritic branch of another neuron. In this paper, we attempt to reconstruct the potential connectivity in local cortical circuits of the cat primary visual cortex (V1). Based on multiple single-neuron reconstructions of axonal and dendritic arbors in 3 dimensions, we evaluate the expected number of potential synapses and the probability of potential connectivity among excitatory (pyramidal and spiny stellate) neurons and inhibitory basket cells. The results provide a quantitative description of structural organization of local cortical circuits. For excitatory neurons from different cortical layers, we compute local domains, which contain their potentially pre- and postsynaptic excitatory partners. These domains have columnar shapes with laminar specific radii and are roughly of the size of the ocular dominance column. Therefore, connections between most excitatory neurons in the ocular dominance column can be implemented by local synaptogenesis. Structural connectivity involving inhibitory basket cells is generally weaker than excitatory connectivity. Here, only nearby neurons are capable of establishing more than one potential synapse, implying that within the ocular dominance column these connections have more limited potential for circuit remodeling.


Assuntos
Rede Nervosa/citologia , Vias Neurais/citologia , Sinapses/ultraestrutura , Córtex Visual/citologia , Animais , Gatos , Células Cultivadas
13.
Nat Neurosci ; 8(3): 372-9, 2005 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-15711543

RESUMO

Here we ask whether visual response pattern varies with position in the cortical microcircuit by comparing the structure of receptive fields recorded from the different layers of the cat's primary visual cortex. We used whole-cell recording in vivo to show the spatial distribution of visually evoked excitatory and inhibitory inputs and to stain individual neurons. We quantified the distribution of 'On' and 'Off' responses and the presence of spatially opponent excitation and inhibition within the receptive field. The thalamorecipient layers (4 and upper 6) were dominated by simple cells, as defined by two criteria: they had separated On and Off subregions, and they had push-pull responses (in a given subregion, stimuli of the opposite contrast evoked responses of the opposite sign). Other types of response profile correlated with laminar location as well. Thus, connections unique to each visual cortical layer are likely to serve distinct functions.


Assuntos
Neurônios/fisiologia , Transmissão Sináptica/fisiologia , Córtex Visual/citologia , Córtex Visual/fisiologia , Campos Visuais/fisiologia , Vias Visuais/fisiologia , Potenciais de Ação/fisiologia , Potenciais de Ação/efeitos da radiação , Animais , Mapeamento Encefálico , Gatos , Eletrofisiologia , Corpos Geniculados/citologia , Corpos Geniculados/fisiologia , Modelos Neurológicos , Inibição Neural/fisiologia , Neurônios/classificação , Estimulação Luminosa/métodos , Tempo de Reação/fisiologia , Tempo de Reação/efeitos da radiação , Tálamo/citologia , Tálamo/fisiologia
14.
Trends Neurosci ; 29(1): 30-9, 2006 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-16309753

RESUMO

Neural sensitivity to basic elements of the visual scene changes dramatically as information is handed from the thalamus to the primary visual cortex in cats. Famously, thalamic neurons are insensitive to stimulus orientation whereas their cortical targets easily resolve small changes in stimulus angle. There are two main types of cells in the visual cortex, simple and complex, defined by the structure of their receptive fields. Simple cells are thought to lay the groundwork for orientation selectivity. This review focuses on approaches that combine anatomy with physiology at the intracellular level, to explore the circuits that build simple receptive fields and that help to maintain neural sensitivity to stimulus features even when luminance contrast changes.


Assuntos
Potenciais Evocados Visuais/fisiologia , Rede Nervosa/fisiologia , Vias Neurais/fisiologia , Neurônios/fisiologia , Córtex Visual/fisiologia , Campos Visuais/fisiologia , Percepção Visual/fisiologia , Animais , Gatos , Humanos , Rede Nervosa/citologia , Vias Neurais/citologia , Neurônios/citologia , Córtex Visual/citologia
15.
BMC Plant Biol ; 8: 123, 2008 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-19055717

RESUMO

BACKGROUND: The plant miRNAs represent an important class of endogenous small RNAs that guide cleavage of an mRNA target or repress its translation to control development and adaptation to stresses. MiRNAs are nuclear-encoded genes transcribed by RNA polymerase II, producing a primary precursor that is subsequently processed by DCL1 an RNase III Dicer-like protein. In rice hundreds of miRNAs have been described or predicted, but little is known on their genes and precursors which are important criteria to distinguish them from siRNAs. Here we develop a combination of experimental approaches to detect novel miRNAs in rice, identify their precursor transcripts and genes and predict or validate their mRNA targets. RESULTS: We produced four cDNA libraries from small RNA fractions extracted from distinct rice tissues. By in silico analysis we selected 6 potential novel miRNAs, and confirmed that their expression requires OsDCL1. We predicted their targets and used 5'RACE to validate cleavage for three of them, targeting a PPR, an SPX domain protein and a GT-like transcription factor respectively. In addition, we identified precursor transcripts for the 6 miRNAs expressed in rice, showing that these precursors can be efficiently processed using a transient expression assay in transfected Nicotiana benthamiana leaves. Most interestingly, we describe two precursors producing tandem miRNAs, but in distinct arrays. We focus on one of them encoding osa-miR159a.2, a novel miRNA produced from the same stem-loop structure encoding the conserved osa-miR159a.1. We show that this dual osa-miR159a.2-osa-miR159a.1 structure is conserved in distant rice species and maize. Finally we show that the predicted mRNA target of osa-miR159a.2 encoding a GT-like transcription factor is cleaved in vivo at the expected site. CONCLUSION: The combination of approaches developed here identified six novel miRNAs expressed in rice which can be clearly distinguished from siRNAs. Importantly, we show that two miRNAs can be produced from a single precursor, either from tandem stem-loops or tandemly arrayed in a single stem-loop. This suggests that processing of these precursors could be an important regulatory step to produce one or more functional miRNAs in plants and perhaps coordinate cleavage of distinct targets in the same plant tissue.


Assuntos
Regulação da Expressão Gênica de Plantas , Variação Genética , Genoma de Planta/genética , MicroRNAs/genética , Oryza/genética , Precursores de RNA/genética , Sequência de Bases , Sequência Conservada , Perfilação da Expressão Gênica , Genes de Plantas , Dados de Sequência Molecular , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Reprodutibilidade dos Testes , Homologia de Sequência do Ácido Nucleico
16.
Curr Opin Neurobiol ; 16(4): 377-84, 2006 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-16842989

RESUMO

Sensory regions of neocortex are organized as arrays of vertical columns composed of cells that share similar response properties, with the orientation columns of the cat's visual cortex being the best known example. Interest in how sensitivity to different stimulus features first emerges in the columns and how this selectivity is refined by subsequent processing has fueled decades of research. A natural starting point in approaching these issues is anatomy. Each column traverses the six cortical layers and each layer has a unique pattern of inputs, intrinsic connections and outputs. Thus, it makes sense to explore the possibility of corresponding laminar differences in sensory function, that is, to examine relationships between morphology and physiology. In addition, to help identify general patterns of cortical organization, it is useful to compare results obtained from different sensory systems and diverse species. The picture that emerges from such comparisons is that each cortical layer serves a distinct role in sensory function. Furthermore, different cortices appear to share some common strategies for processing information but also have specialized mechanisms adapted for the demands of specific sensory tasks.


Assuntos
Rede Nervosa/fisiologia , Neurônios/fisiologia , Córtex Visual/fisiologia , Vias Visuais/fisiologia , Percepção Visual/fisiologia , Animais , Gatos , Humanos , Rede Nervosa/anatomia & histologia , Inibição Neural/fisiologia , Neurônios/citologia , Especificidade da Espécie , Transmissão Sináptica/fisiologia , Córtex Visual/anatomia & histologia , Campos Visuais/fisiologia , Vias Visuais/anatomia & histologia
17.
J Plant Physiol ; 165(1): 114-24, 2008 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-17905473

RESUMO

The interaction between rice and the blast fungus Magnaporthe grisea is the focus of extensive studies on rice disease resistance and fungal infection mechanisms. Here, we review the characteristics of susceptible rice blast infections in terms of physiology, cytology and both host and pathogen transcriptional responses. The success of the infection and the type of disease symptoms strongly depend on environmental and developmental cues. After its penetration into a host cell, the fungus differentiates invasive hyphae that fill up the plant cell lumen and are in direct contact with the membrane of the infected cell. The infected plant cell is alive, displaying considerable vesicle accumulation near the fungus, which is consistent with the establishment of a biotrophic phase at this stage of the infection. Colonization of host tissues by the fungus occurs through the perforation of cell walls from adjacent cells, likely using plasmodesmata as breaking points, or through hyphal growth in the apoplasm. After a few days of biotrophic growth within rice tissues, the fungus switches to a necrotrophic-like phase associated with the onset of sporulation, leading to visible lesions. Genome-wide transcriptomic studies have shown that classical plant defence responses are triggered during a susceptible infection, although the kinetics and amplitude of these responses are slower and lower than in resistant interactions. Infected rice cells are submitted to an intense transcriptional reprogramming, where responses to hormones such as auxins, abscissic acid and jasmonates are likely involved. Consistent with the extensive plant-fungal exchanges during the biotrophic phase, many rice genes expressed during infection encode plasma membrane proteins. At the onset of lesion formation (5 days after the start of infection), M. grisea is actively reprogramming its transcription towards active DNA, RNA and protein syntheses to sustain its rapid growth in infected tissues. A striking characteristic of M. grisea genes expressed at this stage of the infection is the over-representation of genes encoding secreted proteins, mainly of unknown function. However, some of these secreted proteins are enzymes involved in cell wall, protein and lipid degradation, suggesting that the fungus is starting to degrade host polymers and cell walls or is remodelling its own cell wall. The next challenge will be to decipher the role of these induced plant and fungal genes in the susceptible interaction.


Assuntos
Magnaporthe/fisiologia , Oryza/microbiologia , Suscetibilidade a Doenças
18.
Nat Neurosci ; 6(12): 1300-8, 2003 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-14625553

RESUMO

Here we explore inhibitory circuits at the thalamocortical stage of processing in layer 4 of the cat's visual cortex, focusing on the anatomy and physiology of the interneurons themselves. Our immediate aim was to explore the inhibitory mechanisms that contribute to orientation selectivity, perhaps the most dramatic response property to emerge across the thalamocortical synapse. The broader goal was to understand how inhibitory circuits operate. Using whole-cell recording in cats in vivo, we found that layer 4 contains two populations of inhibitory cells defined by receptive field class--simple and complex. The simple cells were selective for stimulus orientation, whereas the complex cells were not. Our observations help to explain how neurons become sensitive to stimulus orientation and maintain that selectivity as stimulus contrast changes. Overall, the work suggests that different sources of inhibition, either selective for specific features or broadly tuned, interact to provide appropriate representations of elements within the environment.


Assuntos
Inibição Neural/fisiologia , Neurônios/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Córtex Visual/fisiologia , Animais , Gatos , Interneurônios/citologia , Interneurônios/fisiologia , Rede Nervosa/citologia , Rede Nervosa/fisiologia , Neurônios/citologia , Estimulação Luminosa/métodos , Córtex Visual/citologia
19.
Nat Commun ; 8(1): 800, 2017 10 06.
Artigo em Inglês | MEDLINE | ID: mdl-28986534

RESUMO

Inhibitory projections from the visual sector of the thalamic reticular nucleus to the lateral geniculate nucleus complete the earliest feedback loop in the mammalian visual pathway and regulate the flow of information from retina to cortex. There are two competing hypotheses about the function of the thalamic reticular nucleus. One regards the structure as a thermostat that uniformly regulates thalamic activity through negative feedback. Alternatively, the searchlight hypothesis argues for a role in focal attentional modulation through positive feedback, consistent with observations that behavioral state influences reticular activity. Here, we address the question of whether cells in the reticular nucleus have receptive fields small enough to provide localized feedback by devising methods to quantify the size of these fields across visual space. Our results show that reticular neurons in the cat operate over discrete spatial scales, at once supporting the searchlight hypothesis and a role in feature selective sensory processing.The searchlight hypothesis proposes that the thalamic reticular nucleus regulates thalamic relay activity through focal attentional modulation. Here the authors show that the receptive field sizes of reticular neurons are small enough to provide localized feedback onto thalamic neurons in the visual pathway.


Assuntos
Potenciais de Ação , Corpos Geniculados/fisiologia , Neurônios/fisiologia , Núcleos Ventrais do Tálamo/fisiologia , Vias Visuais/fisiologia , Animais , Atenção , Gatos , Corpos Geniculados/anatomia & histologia , Neurônios/citologia , Núcleos Ventrais do Tálamo/anatomia & histologia , Vias Visuais/anatomia & histologia
20.
Plant Sci ; 242: 240-249, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26566841

RESUMO

Plants are constantly exposed to a variety of biotic and abiotic stresses that reduce their fitness and performance. At the molecular level, the perception of extracellular stimuli and the subsequent activation of defense responses require a complex interplay of signaling cascades, in which protein phosphorylation plays a central role. Several studies have shown that some members of the Leucine-Rich Repeat Receptor-Like Kinase (LRR-RLK) family are involved in stress and developmental pathways. We report here a systematic analysis of the role of the members of this gene family by mutant phenotyping in the monocotyledon model plant rice, Oryza sativa. We have then targeted 176 of the ∼320 LRR-RLK genes (55.7%) and genotyped 288 mutant lines. Position of the insertion was confirmed in 128 lines corresponding to 100 LRR-RLK genes (31.6% of the entire family). All mutant lines harboring homozygous insertions have been screened for phenotypes under normal conditions and under various abiotic stresses. Mutant plants have been observed at several stages of growth, from seedlings in Petri dishes to flowering and grain filling under greenhouse conditions. Our results show that 37 of the LRR-RLK rice genes are potential targets for improvement especially in the generation of abiotic stress tolerant cereals.


Assuntos
Adaptação Fisiológica/genética , Grão Comestível/genética , Mutação , Oryza/genética , Proteínas de Plantas/genética , Proteínas Serina-Treonina Quinases/genética , Alelos , Análise por Conglomerados , Cotilédone/efeitos dos fármacos , Cotilédone/genética , Cotilédone/crescimento & desenvolvimento , Grão Comestível/efeitos dos fármacos , Grão Comestível/crescimento & desenvolvimento , Genótipo , Manitol/farmacologia , Família Multigênica , Oryza/efeitos dos fármacos , Oryza/crescimento & desenvolvimento , Fenótipo , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/genética , Folhas de Planta/crescimento & desenvolvimento , Proteínas de Plantas/classificação , Proteínas Serina-Treonina Quinases/classificação , Plântula/efeitos dos fármacos , Plântula/genética , Plântula/crescimento & desenvolvimento , Cloreto de Sódio/farmacologia , Estresse Fisiológico/genética
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