RESUMO
Oxytocin is a nonapeptide hormone involved in numerous physiological functions. Real-time electrochemical measurements of oxytocin in living tissue are challenging due to electrode fouling and the large potentials needed to oxidize the tyrosine residue. Here, we used fast-scan cyclic voltammetry at carbon-fiber microelectrodes and flow injection analysis to optimize a waveform for the measurement of oxytocin. This optimized waveform employed an accumulation potential of -0.6 V, multiple scan rates, and a 3 ms holding potential at a positive, oxidizing potential of +1.4 V before linearly scanning the potential back to -0.6 V (versus Ag/AgCl). We obtained a limit of quantitation of 0.34 ± 0.02 µM, and our electrodes did not foul upon multiple injections. Moreover, to demonstrate the utility of our method, we measured the release of oxytocin, evoked by light application and mechanical perturbation, in whole brains from genetically engineered adult zebrafish that express channelrhodopsin-2 selectively on oxytocinergic neurons. Collectively, this work expands the toolkit for the measurement of peptides in living tissue preparations.
Assuntos
Ocitocina , Peixe-Zebra , Animais , Fibra de Carbono , Microeletrodos , NeurôniosRESUMO
The vertebrate hypothalamus contains persistent radial glia that have been proposed to function as neural progenitors. In zebrafish, a high level of postembryonic hypothalamic neurogenesis has been observed, but the role of radial glia in generating these new neurons is unclear. We have used inducible Cre-mediated lineage labeling to show that a population of hypothalamic radial glia undergoes self-renewal and generates multiple neuronal subtypes at larval stages. Whereas Wnt/ß-catenin signaling has been demonstrated to promote the expansion of other stem and progenitor cell populations, we find that Wnt/ß-catenin pathway activity inhibits this process in hypothalamic radial glia and is not required for their self-renewal. By contrast, Wnt/ß-catenin signaling is required for the differentiation of a specific subset of radial glial neuronal progeny residing along the ventricular surface. We also show that partial genetic ablation of hypothalamic radial glia or their progeny causes a net increase in their proliferation, which is also independent of Wnt/ß-catenin signaling. Hypothalamic radial glia in the zebrafish larva thus exhibit several key characteristics of a neural stem cell population, and our data support the idea that Wnt pathway function may not be homogeneous in all stem or progenitor cells.
Assuntos
Autorrenovação Celular/fisiologia , Células Ependimogliais/citologia , Hipotálamo/citologia , Células-Tronco Neurais/citologia , Neurogênese/fisiologia , Via de Sinalização Wnt/genética , Animais , Animais Geneticamente Modificados , Proliferação de Células , Hipotálamo/embriologia , Imuno-Histoquímica , Hibridização In Situ , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Proteínas Wnt/genética , Peixe-Zebra/embriologia , Proteínas de Peixe-Zebra/metabolismo , beta Catenina/genéticaRESUMO
Within reflex circuits, specific anatomical projections allow central neurons to relay sensations to effectors that generate movements. A major challenge is to relate anatomical features of central neural populations, such as asymmetric connectivity, to the computations the populations perform. To address this problem, we mapped the anatomy, modeled the function, and discovered a new behavioral role for a genetically defined population of central vestibular neurons in rhombomeres 5-7 of larval zebrafish. First, we found that neurons within this central population project preferentially to motoneurons that move the eyes downward. Concordantly, when the entire population of asymmetrically projecting neurons was stimulated collectively, only downward eye rotations were observed, demonstrating a functional correlate of the anatomical bias. When these neurons are ablated, fish failed to rotate their eyes following either nose-up or nose-down body tilts. This asymmetrically projecting central population thus participates in both upward and downward gaze stabilization. In addition to projecting to motoneurons, central vestibular neurons also receive direct sensory input from peripheral afferents. To infer whether asymmetric projections can facilitate sensory encoding or motor output, we modeled differentially projecting sets of central vestibular neurons. Whereas motor command strength was independent of projection allocation, asymmetric projections enabled more accurate representation of nose-up stimuli. The model shows how asymmetric connectivity could enhance the representation of imbalance during nose-up postures while preserving gaze stabilization performance. Finally, we found that central vestibular neurons were necessary for a vital behavior requiring maintenance of a nose-up posture: swim bladder inflation. These observations suggest that asymmetric connectivity in the vestibular system facilitates representation of ethologically relevant stimuli without compromising reflexive behavior.SIGNIFICANCE STATEMENT Interneuron populations use specific anatomical projections to transform sensations into reflexive actions. Here we examined how the anatomical composition of a genetically defined population of balance interneurons in the larval zebrafish relates to the computations it performs. First, we found that the population of interneurons that stabilize gaze preferentially project to motoneurons that move the eyes downward. Next, we discovered through modeling that such projection patterns can enhance the encoding of nose-up sensations without compromising gaze stabilization. Finally, we found that loss of these interneurons impairs a vital behavior, swim bladder inflation, that relies on maintaining a nose-up posture. These observations suggest that anatomical specialization permits neural circuits to represent relevant features of the environment without compromising behavior.
Assuntos
Encéfalo/fisiologia , Movimentos Oculares , Neurônios Motores/fisiologia , Células Receptoras Sensoriais/fisiologia , Nervo Vestibular/fisiologia , Animais , Encéfalo/citologia , Reflexo , Nervo Vestibular/citologia , Peixe-ZebraRESUMO
Down syndrome cell adhesion molecules (DSCAMs) are broadly expressed in nervous systems and play conserved roles in programmed cell death, neuronal migration, axon guidance, neurite branching and spacing, and synaptic targeting. However, DSCAMs appear to have distinct functions in different vertebrate animals, and little is known about their functions outside the retina. We leveraged the genetic tractability and optical accessibility of larval zebrafish to investigate the expression and function of a DSCAM family member, dscamb. Using targeted genome editing to create transgenic reporters and loss-of-function mutant alleles, we discovered that dscamb is expressed broadly throughout the brain, spinal cord, and peripheral nervous system, but is not required for overall structural organization of the brain. Despite the absence of obvious anatomical defects, homozygous dscamb mutants were deficient in their ability to ingest food and rarely survived to adulthood. Thus, we have discovered a novel function for dscamb in feeding behavior. The mutant and transgenic lines generated in these studies will provide valuable tools for identifying the molecular and cellular bases of these behaviors.
Assuntos
Moléculas de Adesão Celular/metabolismo , Comportamento Alimentar/fisiologia , Proteínas de Peixe-Zebra/metabolismo , Animais , Animais Geneticamente Modificados , Peixe-ZebraRESUMO
More than 100 species of venomous cone snails (genus Conus) are highly effective predators of fish. The vast majority of venom components identified and functionally characterized to date are neurotoxins specifically targeted to receptors, ion channels, and transporters in the nervous system of prey, predators, or competitors. Here we describe a venom component targeting energy metabolism, a radically different mechanism. Two fish-hunting cone snails, Conus geographus and Conus tulipa, have evolved specialized insulins that are expressed as major components of their venoms. These insulins are distinctive in having much greater similarity to fish insulins than to the molluscan hormone and are unique in that posttranslational modifications characteristic of conotoxins (hydroxyproline, γ-carboxyglutamate) are present. When injected into fish, the venom insulin elicits hypoglycemic shock, a condition characterized by dangerously low blood glucose. Our evidence suggests that insulin is specifically used as a weapon for prey capture by a subset of fish-hunting cone snails that use a net strategy to capture prey. Insulin appears to be a component of the nirvana cabal, a toxin combination in these venoms that is released into the water to disorient schools of small fish, making them easier to engulf with the snail's distended false mouth, which functions as a net. If an entire school of fish simultaneously experiences hypoglycemic shock, this should directly facilitate capture by the predatory snail.
Assuntos
Caramujo Conus/química , Caramujo Conus/fisiologia , Insulina/genética , Toxinas Marinhas/química , Comportamento Predatório/fisiologia , Peixe-Zebra/metabolismo , Sequência de Aminoácidos , Animais , Insulina/análise , Insulina/síntese química , Insulina/metabolismo , Toxinas Marinhas/metabolismo , Espectrometria de Massas , Dados de Sequência Molecular , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Alinhamento de Sequência , Análise de Sequência de DNA , Especificidade da EspécieRESUMO
Reliable optical detection of single action potentials in mammalian neurons has been one of the longest-standing challenges in neuroscience. Here we achieved this goal by using the endogenous fluorescence of a microbial rhodopsin protein, Archaerhodopsin 3 (Arch) from Halorubrum sodomense, expressed in cultured rat hippocampal neurons. This genetically encoded voltage indicator exhibited an approximately tenfold improvement in sensitivity and speed over existing protein-based voltage indicators, with a roughly linear twofold increase in brightness between -150 mV and +150 mV and a sub-millisecond response time. Arch detected single electrically triggered action potentials with an optical signal-to-noise ratio >10. Arch(D95N) lacked endogenous proton pumping and had 50% greater sensitivity than wild type but had a slower response (41 ms). Nonetheless, Arch(D95N) also resolved individual action potentials. Microbial rhodopsin-based voltage indicators promise to enable optical interrogation of complex neural circuits and electrophysiology in systems for which electrode-based techniques are challenging.
Assuntos
Potenciais de Ação/fisiologia , Halorrodopsinas/metabolismo , Neurônios/fisiologia , Animais , Membrana Celular/metabolismo , Corantes Fluorescentes/metabolismo , Células HEK293 , Halorrodopsinas/genética , Halorubrum/química , Hipocampo/citologia , Humanos , Óptica e Fotônica , RatosRESUMO
Somatosensory neurons in teleosts and amphibians are sensitive to thermal, mechanical, or nociceptive stimuli [1, 2]. The two main types of such cells in zebrafish--Rohon-Beard and trigeminal neurons--have served as models for neural development [3-6], but little is known about how they encode tactile stimuli. The hindbrain networks that transduce somatosensory stimuli into a motor output encode information by using very few spikes in a small number of cells [7], but it is unclear whether activity in the primary receptor neurons is similarly efficient. To address this question, we manipulated the activity of zebrafish neurons with the light-activated cation channel, Channelrhodopsin-2 (ChR2) [8, 9]. We found that photoactivation of ChR2 in genetically defined populations of somatosensory neurons triggered escape behaviors in 24-hr-old zebrafish. Electrophysiological recordings from ChR2-positive trigeminal neurons in intact fish revealed that these cells have extremely low rates of spontaneous activity and can be induced to fire by brief pulses of blue light. Using this technique, we find that even a single action potential in a single sensory neuron was at times sufficient to evoke an escape behavior. These results establish ChR2 as a powerful tool for the manipulation of neural activity in zebrafish and reveal a degree of efficiency in coding that has not been found in primary sensory neurons.
Assuntos
Reação de Fuga , Potenciais Somatossensoriais Evocados , Canais Iônicos/fisiologia , Neurônios Aferentes/fisiologia , Proteínas de Peixe-Zebra/fisiologia , Peixe-Zebra/fisiologia , Animais , Eletrofisiologia , Embrião não Mamífero/metabolismo , Embrião não Mamífero/fisiologia , Canais Iônicos/metabolismo , Luz , Neurônios Aferentes/química , Neurônios Aferentes/metabolismo , Estimulação Luminosa , Nervo Trigêmeo/química , Peixe-Zebra/embriologia , Peixe-Zebra/metabolismo , Proteínas de Peixe-Zebra/metabolismoRESUMO
Whereas humans and other adult mammals lack the ability to regain locomotor function after spinal cord injury, zebrafish are able to recover swimming behavior even after complete spinal cord transection. We have previously shown that zebrafish larvae regenerate lost spinal cord neurons within 9 days post-injury (dpi), but it is unknown whether these neurons are physiologically active or integrate into functional circuitry. Here we show that genetically defined premotor interneurons are regenerated in injured spinal cord segments as functional recovery begins. Further, we show that these newly-generated interneurons receive excitatory input and fire synchronously with motor output by 9 dpi. Taken together, our data indicate that regenerative neurogenesis in the zebrafish spinal cord produces interneurons with the ability to integrate into existing locomotor circuitry.
Assuntos
Interneurônios/fisiologia , Locomoção/fisiologia , Rede Nervosa/fisiologia , Regeneração Nervosa/fisiologia , Recuperação de Função Fisiológica/fisiologia , Traumatismos da Medula Espinal/fisiopatologia , Animais , Animais Geneticamente Modificados , Plasticidade Neuronal/fisiologia , Traumatismos da Medula Espinal/genética , Peixe-ZebraRESUMO
T cells interacting with antigen-presenting cells (APCs) form an "immunological synapse" (IS), a bull's-eye pattern composed of a central supramolecular activation cluster enriched with T cell receptors (TCRs) surrounded by a ring of adhesion molecules (a peripheral supramolecular activation cluster). The mechanism responsible for segregating TCR and adhesion molecules remains poorly understood. Here, we show that immortalized Jurkat T cells interacting with a planar lipid bilayer (mimicking an APC) will form an IS, thereby providing an accessible model system for studying the cell biological processes underlying IS formation. We found that an actin-dependent process caused TCR and adhesion proteins to cluster at the cell periphery, but these molecules appeared to segregate from one another at the earliest stages of microdomain formation. The TCR and adhesion microdomains attached to actin and were carried centripetally by retrograde flow. However, only the TCR microdomains penetrated into the actin-depleted cell center, whereas the adhesion microdomains appeared to be unstable without an underlying actin cytoskeleton. Our results reveal that TCR and adhesion molecules spatially partition from one another well before the formation of a mature IS and that differential actin interactions help to shape and maintain the final bull's-eye pattern of the IS.
Assuntos
Células Apresentadoras de Antígenos/imunologia , Moléculas de Adesão Celular/metabolismo , Receptores de Antígenos de Linfócitos T/metabolismo , Linfócitos T/imunologia , Actinas/química , Humanos , Células Jurkat , Bicamadas Lipídicas/química , Microdomínios da Membrana/químicaRESUMO
Dopamine (DA)-producing neurons are critically involved in the production of motor behaviors in multiple circuits that are conserved from basal vertebrates to mammals. Although there is increasing evidence that DA neurons in the hypothalamus play a locomotor role, their precise contributions to behavior and the circuit mechanisms by which they are achieved remain unclear. Here, we demonstrate that tyrosine-hydroxylase-2-expressing (th2+) DA neurons in the zebrafish hypothalamus fire phasic bursts of activity to acutely promote swimming and modulate audiomotor behaviors on fast timescales. Their anatomy and physiology reveal two distinct functional DA modules within the hypothalamus. The first comprises an interconnected set of cerebrospinal-fluid-contacting DA nuclei surrounding the 3rd ventricle, which lack distal projections outside of the hypothalamus and influence locomotion through unknown means. The second includes neurons in the preoptic nucleus, which send long-range projections to targets throughout the brain, including the mid- and hindbrain, where they activate premotor circuits involved in swimming and sensorimotor integration. These data suggest a broad regulation of motor behavior by DA neurons within multiple hypothalamic nuclei and elucidate a novel functional mechanism for the preoptic DA neurons in the initiation of movement.
Assuntos
Tronco Encefálico/fisiologia , Neurônios Dopaminérgicos/metabolismo , Área Pré-Óptica/fisiologia , Natação/fisiologia , Animais , Tronco Encefálico/citologia , Potencial Evocado Motor/fisiologia , Genes Reporter/genética , Proteínas de Fluorescência Verde/genética , Microscopia Intravital/métodos , Masculino , Microscopia de Fluorescência por Excitação Multifotônica , Modelos Animais , Rede Nervosa/fisiologia , Optogenética , Área Pré-Óptica/citologia , Tirosina 3-Mono-Oxigenase/genética , Tirosina 3-Mono-Oxigenase/metabolismo , Gravação em Vídeo , Peixe-Zebra , Proteínas de Peixe-Zebra/genética , Proteínas de Peixe-Zebra/metabolismoRESUMO
Centrosomes are considered to be the major sites of microtubule nucleation in mitotic cells (reviewed in ), yet mitotic spindles can still form after laser ablation or disruption of centrosome function . Although kinetochores have been shown to nucleate microtubules, mechanisms for acentrosomal spindle formation remain unclear. Here, we performed live-cell microscopy of GFP-tubulin to examine spindle formation in Drosophila S2 cells after RNAi depletion of either gamma-tubulin, a microtubule nucleating protein, or centrosomin, a protein that recruits gamma-tubulin to the centrosome. In these RNAi-treated cells, we show that poorly focused bipolar spindles form through the self-organization of microtubules nucleated from chromosomes (a process involving gamma-tubulin), as well as from other potential sites, and through the incorporation of microtubules from the preceding interphase network. By tracking EB1-GFP (a microtubule-plus-end binding protein) in acentrosomal spindles, we also demonstrate that the spindle itself represents a source of new microtubule formation, as suggested by observations of numerous microtubule plus ends growing from acentrosomal poles toward the metaphase plate. We propose that the bipolar spindle propagates its own architecture by stimulating microtubule growth, thereby augmenting the well-described microtubule nucleation pathways that take place at centrosomes and chromosomes.
Assuntos
Microtúbulos/metabolismo , Fuso Acromático/metabolismo , Animais , Núcleo Celular/ultraestrutura , Células Cultivadas , Centrossomo/fisiologia , Cromatina/metabolismo , Drosophila/citologia , Proteínas de Fluorescência Verde/análise , Metáfase , Modelos Biológicos , Interferência de RNA , Proteínas Recombinantes de Fusão/análise , Proteínas Recombinantes de Fusão/metabolismo , Fuso Acromático/ultraestrutura , Tubulina (Proteína)/análise , Tubulina (Proteína)/fisiologiaRESUMO
Animals have evolved specialized neural circuits to defend themselves from pain- and injury-causing stimuli. Using a combination of optical, behavioral and genetic approaches in the larval zebrafish, we describe a novel role for hypothalamic oxytocin (OXT) neurons in the processing of noxious stimuli. In vivo imaging revealed that a large and distributed fraction of zebrafish OXT neurons respond strongly to noxious inputs, including the activation of damage-sensing TRPA1 receptors. OXT population activity reflects the sensorimotor transformation of the noxious stimulus, with some neurons encoding sensory information and others correlating more strongly with large-angle swims. Notably, OXT neuron activation is sufficient to generate this defensive behavior via the recruitment of brainstem premotor targets, whereas ablation of OXT neurons or loss of the peptide attenuates behavioral responses to TRPA1 activation. These data highlight a crucial role for OXT neurons in the generation of appropriate defensive responses to noxious input.
Assuntos
Tronco Encefálico/fisiologia , Vias Neurais/fisiologia , Nociceptividade/fisiologia , Nociceptores/fisiologia , Animais , Tronco Encefálico/citologia , Hipotálamo/citologia , Hipotálamo/fisiologia , Vias Neurais/citologia , Nociceptores/citologia , Ocitocina , Peixe-ZebraRESUMO
Axon guidance in vertebrates is controlled by genetic cascades as well as by intrinsic activity-dependent refinement of connections. Midline axon crossing is one of the best studied pathfinding models and is fundamental to the establishment of bilaterally symmetric nervous systems. However, it is not known whether crossing requires intrinsic activity in axons, and what controls that activity. Further, a mechanism linking neuronal activity and gene expression has not been identified for axon pathfinding. Using embryonic zebrafish, we found that the NMDA receptor (NMDAR) NR1.1 subunit (grin1a) is expressed in commissural axons. Pharmacological inhibition of grin1a, hypoxia exposure reduction of grin1a expression, or CRISPR knock-down of grin1a leads to defects in midline crossing. Inhibition of neuronal activity phenocopies the effects of grin1a loss on midline crossing. By combining pharmacological inhibition of the NMDAR with optogenetic stimulation to precisely restore neuronal activity, we observed rescue of midline crossing. This suggests that the NMDAR controls pathfinding by an activity-dependent mechanism. We further show that the NMDAR may act, via modulating activity, on the transcription factor arxa (mammalian Arx), a known regulator of midline pathfinding. These findings uncover a novel role for the NMDAR in controlling activity to regulate commissural pathfinding and identify arxa as a key link between the genetic and activity-dependent regulation of midline axon guidance.
Assuntos
Axônios/fisiologia , Sistema Nervoso Central/embriologia , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Receptores de N-Metil-D-Aspartato/fisiologia , Animais , Animais Geneticamente Modificados , Embrião não Mamífero , Hipóxia/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Peixe-Zebra , Proteínas de Peixe-ZebraRESUMO
Abundant nonfibrillar oligomeric intermediates are a common feature of amyloid formation, and these oligomers, rather than the final fibers, have been suggested to be the toxic species in some amyloid diseases. Whether such oligomers are critical intermediates for fiber assembly or form in an alternate, potentially separable pathway, however, remains unclear. Here we study the polymerization of the amyloidogenic yeast prion protein Sup35. Rapid polymerization occurs in the absence of observable intermediates, and both targeted kinetic and direct single-molecule fluorescence measurements indicate that fibers grow by monomer addition. A three-step model (nucleation, monomer addition, and fiber fragmentation) accurately accounts for the distinctive kinetic features of amyloid formation, including weak concentration dependence, acceleration by agitation, and sigmoidal shape of the polymerization time course. Thus, amyloid growth can occur by monomer addition in a reaction distinct from and competitive with formation of potentially toxic oligomeric intermediates.
Assuntos
Amiloide/química , Príons/química , Benzotiazóis , Proliferação de Células , Biologia Computacional/métodos , Simulação por Computador , Proteínas Fúngicas/química , Cinética , Microscopia de Força Atômica , Microscopia de Fluorescência , Modelos Estatísticos , Dados de Sequência Molecular , Fatores de Terminação de Peptídeos , Peptídeos/química , Polímeros/química , Príons/metabolismo , Proteínas de Saccharomyces cerevisiae/química , Tiazóis/química , Fatores de Tempo , UltracentrifugaçãoRESUMO
Postembryonic neurogenesis has been observed in several regions of the vertebrate brain, including the dentate gyrus and rostral migratory stream in mammals, and is required for normal behavior [1-3]. Recently, the hypothalamus has also been shown to undergo continuous neurogenesis as a way to mediate energy balance [4-10]. As the hypothalamus regulates multiple functional outputs, it is likely that additional behaviors may be affected by postembryonic neurogenesis in this brain structure. Here, we have identified a progenitor population in the zebrafish hypothalamus that continuously generates neurons that express tyrosine hydroxylase 2 (th2). We develop and use novel transgenic tools to characterize the lineage of th2(+) cells and demonstrate that they are dopaminergic. Through genetic ablation and optogenetic activation, we then show that th2(+) neurons modulate the initiation of swimming behavior in zebrafish larvae. Finally, we find that the generation of new th2(+) neurons following ablation correlates with restoration of normal behavior. This work thus identifies for the first time a population of dopaminergic neurons that regulates motor behavior capable of functional recovery.
Assuntos
Neurônios Dopaminérgicos/metabolismo , Hipotálamo/metabolismo , Atividade Motora/fisiologia , Neurogênese/fisiologia , Proteínas de Peixe-Zebra/metabolismo , Peixe-Zebra/metabolismo , Animais , Animais Geneticamente Modificados , Comportamento Animal/fisiologia , Dopamina/metabolismo , Peixe-Zebra/genéticaRESUMO
Tools for genetically-determined visualization of synaptic circuits and interactions are necessary to build connectomics of the vertebrate brain and to screen synaptic properties in neurological disease models. Here we develop a transgenic FingR (fibronectin intrabodies generated by mRNA display) technology for monitoring synapses in live zebrafish. We demonstrate FingR labeling of defined excitatory and inhibitory synapses, and show FingR applicability for dissecting synapse dynamics in normal and disease states. Using our system we show that chronic hypoxia, associated with neurological defects in preterm birth, affects dopaminergic neuron synapse number depending on the developmental timing of hypoxia.
Assuntos
Neurônios/metabolismo , Sinapses/metabolismo , Animais , Animais Geneticamente Modificados , Rastreamento de Células , Fibronectinas/genética , Imunofluorescência , Expressão Gênica , Ordem dos Genes , Genes Reporter , Vetores Genéticos/genética , Hipóxia/metabolismo , Imuno-Histoquímica , Peixe-ZebraRESUMO
The cardiac action potential (AP) and the consequent cytosolic Ca(2+) transient are key indicators of cardiac function. Natural developmental processes, as well as many drugs and pathologies change the waveform, propagation, or variability (between cells or over time) of these parameters. Here we apply a genetically encoded dual-function calcium and voltage reporter (CaViar) to study the development of the zebrafish heart in vivo between 1.5 and 4 days post fertilization (dpf). We developed a high-sensitivity spinning disk confocal microscope and associated software for simultaneous three-dimensional optical mapping of voltage and calcium. We produced a transgenic zebrafish line expressing CaViar under control of the heart-specific cmlc2 promoter, and applied ion channel blockers at a series of developmental stages to map the maturation of the action potential in vivo. Early in development, the AP initiated via a calcium current through L-type calcium channels. Between 90 and 102 h post fertilization (hpf), the ventricular AP switched to a sodium-driven upswing, while the atrial AP remained calcium driven. In the adult zebrafish heart, a sodium current drives the AP in both the atrium and ventricle. Simultaneous voltage and calcium imaging with genetically encoded reporters provides a new approach for monitoring cardiac development, and the effects of drugs on cardiac function.
RESUMO
Genetically encoded fluorescent reporters of membrane potential promise to reveal aspects of neural function not detectable by other means. We present a palette of multicoloured brightly fluorescent genetically encoded voltage indicators with sensitivities from 8-13% ΔF/F per 100 mV, and half-maximal response times from 4-7 ms. A fluorescent protein is fused to an archaerhodopsin-derived voltage sensor. Voltage-induced shifts in the absorption spectrum of the rhodopsin lead to voltage-dependent nonradiative quenching of the appended fluorescent protein. Through a library screen, we identify linkers and fluorescent protein combinations that report neuronal action potentials in cultured rat hippocampal neurons with a single-trial signal-to-noise ratio from 7 to 9 in a 1 kHz imaging bandwidth at modest illumination intensity. The freedom to choose a voltage indicator from an array of colours facilitates multicolour voltage imaging, as well as combination with other optical reporters and optogenetic actuators.
Assuntos
Potenciais de Ação/fisiologia , Cor , Transferência Ressonante de Energia de Fluorescência/métodos , Proteínas Luminescentes/fisiologia , Neurônios/fisiologia , Sequência de Aminoácidos , Animais , Células Cultivadas , Células HEK293 , Hipocampo/citologia , Humanos , Rim/citologia , Rim/fisiologia , Proteínas Luminescentes/análise , Proteínas Luminescentes/química , Dados de Sequência Molecular , Neurônios/citologia , Ratos , RodopsinaRESUMO
Bacteria have many voltage- and ligand-gated ion channels, and population-level measurements indicate that membrane potential is important for bacterial survival. However, it has not been possible to probe voltage dynamics in an intact bacterium. Here we developed a method to reveal electrical spiking in Escherichia coli. To probe bacterial membrane potential, we engineered a voltage-sensitive fluorescent protein based on green-absorbing proteorhodopsin. Expression of the proteorhodopsin optical proton sensor (PROPS) in E. coli revealed electrical spiking at up to 1 hertz. Spiking was sensitive to chemical and physical perturbations and coincided with rapid efflux of a small-molecule fluorophore, suggesting that bacterial efflux machinery may be electrically regulated.
Assuntos
Escherichia coli/fisiologia , Potenciais da Membrana , Rodopsina/metabolismo , Potenciais de Ação , Escherichia coli/genética , Fluorescência , Corantes Fluorescentes , Concentração de Íons de Hidrogênio , Canais Iônicos/metabolismo , Transporte de Íons , Luz , Prótons , Rodaminas/metabolismo , Rodopsina/química , Rodopsina/genética , Rodopsinas Microbianas , Espectrometria de Fluorescência , Estresse FisiológicoRESUMO
The interaction between a T cell and an antigen-presenting cell (APC) can trigger a signaling response that leads to T cell activation. Prior studies have shown that ligation of the T cell receptor (TCR) triggers a signaling cascade that proceeds through the coalescence of TCR and various signaling molecules (e.g., the kinase Lck and adaptor protein LAT [linker for T cell activation]) into microdomains on the plasma membrane. In this study, we investigated another ligand-receptor interaction (CD58-CD2) that facilities T cell activation using a model system consisting of Jurkat T cells interacting with a planar lipid bilayer that mimics an APC. We show that the binding of CD58 to CD2, in the absence of TCR activation, also induces signaling through the actin-dependent coalescence of signaling molecules (including TCR-zeta chain, Lck, and LAT) into microdomains. When simultaneously activated, TCR and CD2 initially colocalize in small microdomains but then partition into separate zones; this spatial segregation may enable the two receptors to enhance signaling synergistically. Our results show that two structurally distinct receptors both induce a rapid spatial reorganization of molecules in the plasma membrane, suggesting a model for how local increases in the concentration of signaling molecules can trigger T cell signaling.