Gene Transfer into Neurons from Hippocampal Slices: Comparison of Recombinant Semliki Forest Virus, Adenovirus, Adeno-Associated Virus, Lentivirus, and Measles Virus

Subunit-selective PI3-kinase control of action strategies in the medial prefrontal cortex

PI3-kinase (PI3K) is an intracellular signaling complex that is stimulated upon cocaine exposure and linked with the behavioral consequences of cocaine. We recently genetically silenced the PI3K p110β subunit in the medial prefrontal cortex following repeated cocaine in mice, reinstating the capacity of these mice to engage in prospective goal-seeking behavior. In the present short report, we address two follow-up hypotheses: 1) The control of decision-making behavior by PI3K p110β is attributable to neuronal signaling, and 2) PI3K p110β in the healthy (i.e., drug-naïve) medial prefrontal cortex has functional consequences in the control of reward-related decision-making strategies. In Experiment 1, we found that silencing neuronal p110β improved action flexibility following cocaine. In Experiment 2, we reduced PI3K p110β in drug-naïve mice that were extensively trained to respond for food reinforcers. Gene silencing caused mice to abandon goal-seeking strategies, unmasking habit-based behaviors that were propelled by interactions with the nucleus accumbens. Thus, PI3K control of goal-directed action strategies appears to act in accordance with an inverted U-shaped function, with "too much" (following cocaine) or "too little" (following p110β subunit silencing) obstructing goal seeking and causing mice to defer to habit-like response sequences.

Medial orbitofrontal neurotrophin systems integrate hippocampal input into outcome-specific value representations

In everyday life, we mentally represent possible consequences of our behaviors and integrate specific outcome values into existing knowledge to inform decisions. The medial orbitofrontal cortex (MO) is necessary to adapt behaviors when outcomes are not immediately available-when they and their values need to be envisioned. Nevertheless, neurobiological mechanisms remain unclear. We find that the neuroplasticity-associated neurotrophin receptor tropomyosin receptor kinase B (TrkB) is necessary for mice to integrate outcome-specific value information into choice behavior. This function appears attributable to memory updating (and not retrieval) and the stabilization of dendritic spines on excitatory MO neurons, which led us to investigate inputs to the MO. Ventral hippocampal (vHC)-to-MO projections appear conditionally necessary for value updating, involved in long-term aversion-based value memory updating. Furthermore, vHC-MO-mediated control of choice is TrkB dependent. Altogether, we reveal a vHC-MO connection by which specific value memories are updated, and we position TrkB within this functional circuit.

FAK-Mediated Signaling Controls Amyloid Beta Overload, Learning and Memory Deficits in a Mouse Model of Alzheimer's Disease

The non-receptor focal adhesion kinase (FAK) is highly expressed in the central nervous system during development, where it regulates neurite outgrowth and axon guidance, but its role in the adult healthy and diseased brain, specifically in Alzheimer's disease (AD), is largely unknown. Using the 3xTg-AD mouse model, which carries three mutations associated with familial Alzheimer's disease (APP KM670/671NL Swedish, PSEN1 M146V, MAPT P301L) and develops age-related progressive neuropathology including amyloid plaques and Tau tangles, we describe here, for the first time, the in vivo role of FAK in AD pathology. Our data demonstrate that while site-specific knockdown in the hippocampi of 3xTg-AD mice has no effect on learning and memory, hippocampal overexpression of the protein leads to a significant decrease in learning and memory capabilities, which is accompanied by a significant increase in amyloid β (Aβ) load. Furthermore, neuronal morphology is altered following hippocampal overexpression of FAK in these mice. High-throughput proteomics analysis of total and phosphorylated proteins in the hippocampi of FAK overexpressing mice indicates that FAK controls AD-like phenotypes by inhibiting cytoskeletal remodeling in neurons which results in morphological changes, by increasing Tau hyperphosphorylation, and by blocking astrocyte differentiation. FAK activates cell cycle re-entry and consequent cell death while downregulating insulin signaling, thereby increasing insulin resistance and leading to oxidative stress. Our data provide an overview of the signaling networks by which FAK regulates AD pathology and identify FAK as a novel therapeutic target for treating AD.

All-optical interrogation of neural circuits in behaving mice

Recent advances combining two-photon calcium imaging and two-photon optogenetics with computer-generated holography now allow us to read and write the activity of large populations of neurons in vivo at cellular resolution and with high temporal resolution. Such 'all-optical' techniques enable experimenters to probe the effects of functionally defined neurons on neural circuit function and behavioral output with new levels of precision. This greatly increases flexibility, resolution, targeting specificity and throughput compared with alternative approaches based on electrophysiology and/or one-photon optogenetics and can interrogate larger and more densely labeled populations of neurons than current voltage imaging-based implementations. This protocol describes the experimental workflow for all-optical interrogation experiments in awake, behaving head-fixed mice. We describe modular procedures for the setup and calibration of an all-optical system (~3 h), the preparation of an indicator and opsin-expressing and task-performing animal (~3-6 weeks), the characterization of functional and photostimulation responses (~2 h per field of view) and the design and implementation of an all-optical experiment (achievable within the timescale of a normal behavioral experiment; ~3-5 h per field of view). We discuss optimizations for efficiently selecting and targeting neuronal ensembles for photostimulation sequences, as well as generating photostimulation response maps from the imaging data that can be used to examine the impact of photostimulation on the local circuit. We demonstrate the utility of this strategy in three brain areas by using different experimental setups. This approach can in principle be adapted to any brain area to probe functional connectivity in neural circuits and investigate the relationship between neural circuit activity and behavior.

Knockdown of rno_circRNA_009194 Improves Outcomes in Traumatic Brain Injury Rats through Inhibiting Voltage-Gated Sodium Channel Nav1.3

Excessive activation of voltage-gated sodium channel Nav1.3 has been recently reported in secondary traumatic brain injury (TBI). However, the molecular mechanisms underlying regulating voltage-gated sodium channel (Nav1.3) have not been well understood. The present study used a TBI rat model induced by a fluid percussion device and performed a circular RNA (circRNA) microarray (n = 3) to profile the altered circRNAs in the hippocampus after TBI. After polymerase chain reaction (PCR) validation, certain circRNAs were selected to investigate the function and mechanism in regulating Nav1.3 in the TBI rat model by intracerebroventricular injection with lentivirus. The neurological outcome was evaluated by Morris water maze test, modified Neurological Severity Score (mNSS), brain water content measurement, and hematoxylin and eosin staining. The related molecular mechanisms were explored with PCR, Western blotting, luciferase reporter, chromatin immunoprecipitation assay, and electrophoretic mobility shift assay (EMSA). A total of 347 circRNAs were observed to be differentially expressed (fold change [FC] ≥ 1.2 and p < 0.05) after TBI, including 234 up-regulated and 113 down-regulated circRNAs. Among 10 validated circRNAs, we selected circRNA_009194 with the maximized up-regulated fold change (n = 5, FC = 4.45, p < 0.001) for the in vivo functional experiments. Down-regulation of circRNA_009194 resulted in a 27.5% reduced mNSS in rat brain (n = 6, p < 0.01) after TBI and regulated the expression levels of miR-145-3p, Sp1, and Nav1.3, which was reversed by sh-miR-145-3p or Sp1/Nav1.3 overexpression (n = 5, p < 0.05). Mechanistically, circRNA_009194 might act as a sponge for miR-145-3p to regulate Sp1-mediated Nav1.3. This study demonstrated that circRNA_009194 knockdown could improve neurological outcomes in TBI in vivo by inhibiting Nav1.3, directly or indirectly.

Pyk2 Stabilizes Striatal Medium Spiny Neuron Structure and Striatal-Dependent Action

In day-to-day life, we often choose between pursuing familiar behaviors that have been rewarded in the past or adjusting behaviors when new strategies might be more fruitful. The dorsomedial striatum (DMS) is indispensable for flexibly arbitrating between old and new behavioral strategies. The way in which DMS neurons host stable connections necessary for sustained flexibility is still being defined. An entry point to addressing this question may be the structural scaffolds on DMS neurons that house synaptic connections. We find that the non-receptor tyrosine kinase Proline-rich tyrosine kinase 2 (Pyk2) stabilizes both dendrites and spines on striatal medium spiny neurons, such that Pyk2 loss causes dendrite arbor and spine loss. Viral-mediated Pyk2 silencing in the DMS obstructs the ability of mice to arbitrate between rewarded and non-rewarded behaviors. Meanwhile, the overexpression of Pyk2 or the closely related focal adhesion kinase (FAK) enhances this ability. Finally, experiments using combinatorial viral vector strategies suggest that flexible, Pyk2-dependent action involves inputs from the medial prefrontal cortex (mPFC), but not the ventrolateral orbitofrontal cortex (OFC). Thus, Pyk2 stabilizes the striatal medium spiny neuron structure, likely providing substrates for inputs, and supports the capacity of mice to arbitrate between novel and familiar behaviors, including via interactions with the medial-prefrontal cortex.

The PI3-Kinase p110β Isoform Controls Severity of Cocaine-Induced Sequelae and Alters the Striatal Transcriptome

BACKGROUND

The PI3-kinase (PI3K) complex is a well-validated target for mitigating cocaine-elicited sequelae, but pan-PI3K inhibitors are not viable long-term treatment options. The PI3K complex is composed of p110 catalytic and regulatory subunits, which can be individually manipulated for therapeutic purposes. However, this possibility has largely not been explored in behavioral contexts.

METHODS

Here, we inhibited PI3K p110β in the medial prefrontal cortex (mPFC) of cocaine-exposed mice. Behavioral models for studying relapse, sensitization, and decision-making biases were paired with protein quantification, RNA sequencing, and cell type-specific chemogenetic manipulation and RNA quantification to determine whether and how inhibiting PI3K p110β confers resilience to cocaine.

RESULTS

Viral-mediated PI3K p110β silencing reduced cue-induced reinstatement of cocaine seeking by half, blocked locomotor sensitization, and restored mPFC synaptic marker content after exposure to cocaine. Cocaine blocked the ability of mice to select actions based on their consequences, and p110β inhibition restored this ability. Silencing dopamine D₂ receptor-expressing excitatory mPFC neurons mimicked cocaine, impairing goal-seeking behavior, and again, p110β inhibition restored goal-oriented action. We verified the presence of p110β in mPFC neurons projecting to the dorsal striatum and orbitofrontal cortex and found that inhibiting p110β in the mPFC altered the expression of functionally defined gene clusters within the dorsal striatum and not orbitofrontal cortex.

CONCLUSIONS

Subunit-selective PI3K silencing potently mitigates drug seeking, sensitization, and decision-making biases after exposure to cocaine. We suggest that inhibiting PI3K p110β provides neuroprotection against cocaine by triggering coordinated corticostriatal adaptations.

Efficient infection of organotypic hippocampal slice cultures with adenovirus carrying the transgene REST/NRSF

Organotypic hippocampal slice cultures provide a useful platform maintaining hippocampal structure and synaptic connections of the brain over weeks in culture with ease of in vitro manipulations. Gene transfer is a particularly desirable tool for using with them but current difficulties with transformation of transgenes into these cultures is a barrier to their use in research. Previous quantifications of viral infections have shown low transformation rates and have relied upon invasive microinjections. In this paper we present an efficient way of infecting organotypic cultures with adenovirus at the acute slice stage that does not require injection. We use the adenoviral delivery system to introduce the transcription factor REST and a GFP marker, providing around 41 % cellular infection spread throughout the entire slice culture and promoting transgene expression for weeks in vitro. GFP expression was observed most intensely in the slices when they were infected just a few hours after plating and was shown to infect neurons and microglia. We decided to use the transcription factor REST/NRSF as an example transgene which was delivered into cells via the adenoviral construct, conferring overexpression of REST in addition to the GFP marker. This outlines a technique whereby adenoviral infection of organotypic cultures can infect neurons with good efficiency and confer successful manipulation of genetic factors within the cell.

β1-Integrins in the Developing Orbitofrontal Cortex Are Necessary for Expectancy Updating in Mice

Navigating a changing environment requires associating stimuli and actions with their likely outcomes and modifying these associations when they change. These processes involve the orbitofrontal cortex (OFC). Although some molecular mediators have been identified, developmental factors are virtually unknown. We hypothesized that the cell adhesion factor β1-integrin is essential to OFC function, anticipating developmental windows during which β1-integrins might be more influential than others. We discovered that OFC-selective β1-integrin silencing before adolescence, but not later, impaired the ability of mice to extinguish conditioned fear and select actions based on their likely outcomes. Early-life knock-down also reduced the densities of dendritic spines, the primary sites of excitatory plasticity in the brain, and weakened sensitivity to cortical inputs. Notwithstanding these defects in male mice, females were resilient to OFC (but not hippocampal) β1-integrin loss. Existing literature suggests that resilience may be explained by estradiol-mediated transactivation of β1-integrins and tropomyosin receptor kinase B (trkB). Accordingly, we discovered that a trkB agonist administered during adolescence corrected reward-related decision making in β1-integrin-deficient males. In sum, developmental β1-integrins are indispensable for OFC function later in life.SIGNIFICANCE STATEMENT The orbitofrontal cortex (OFC) is a subregion of the frontal cortex that allows organisms to link behaviors and stimuli with anticipated outcomes, and to make predictions about the consequences of one's behavior. Aspects of OFC development are particularly prolonged, extending well into adolescence, likely optimizing organisms' abilities to prospectively calculate the consequences of their actions and select behaviors appropriately; these decision making strategies improve as young individuals mature into adulthood. Molecular factors are not, however, well understood. Our experiments reveal that a cell adhesion protein termed "β1-integrin" is necessary for OFC neuronal maturation and function. Importantly, β1-integrins operate during a critical period equivalent to early adolescence in humans to optimize the ability of organisms to update expectancies later in life.

The Effects of Sindbis Viral Vectors on Neuronal Function

Viral vectors are attractive tools to express genes in neurons. Transduction of neurons with a recombinant, replication-deficient Sindbis viral vector is a method of choice for studying the effects of short-term protein overexpression on neuronal function. However, to which extent Sindbis by itself may affect neurons is not fully understood. We assessed effects of neuronal transduction with a Sindbis viral vector on the transcriptome and proteome in organotypic hippocampal slice cultures, and analyzed the electrophysiological properties of individual CA1 neurons, at 24 h and 72 h after viral vector injection. Whereas Sindbis caused substantial gene expression alterations, changes at the protein level were less pronounced. Alterations in transcriptome and proteome were predominantly limited to proteins involved in mediating anti-viral innate immune responses. Sindbis transduction did not affect the intrinsic electrophysiological properties of individual neurons: the membrane potential and neuronal excitability were similar between transduced and non-transduced CA1 neurons up to 72 h after Sindbis injection. Synaptic currents also remained unchanged upon Sindbis transduction, unless slices were massively infected for 72 h. We conclude that Sindbis viral vectors at low transduction rates are suitable for studying short-term effects of a protein of interest on electrophysiological properties of neurons, but not for studies on the regulation of gene expression.

Reward-Related Expectations Trigger Dendritic Spine Plasticity in the Mouse Ventrolateral Orbitofrontal Cortex

An essential aspect of goal-directed decision-making is selecting actions based on anticipated consequences, a process that involves the orbitofrontal cortex (OFC) and potentially, the plasticity of dendritic spines in this region. To investigate this possibility, we trained male and female mice to nose poke for food reinforcers, or we delivered the same number of food reinforcers non-contingently to separate mice. We then decreased the likelihood of reinforcement for trained mice, requiring them to modify action-outcome expectations. In a separate experiment, we blocked action-outcome updating via chemogenetic inactivation of the OFC. In both cases, successfully selecting actions based on their likely consequences was associated with fewer immature, thin-shaped dendritic spines and a greater proportion of mature, mushroom-shaped spines in the ventrolateral OFC. This pattern was distinct from spine loss associated with aging, and we identified no effects on hippocampal CA1 neurons. Given that the OFC is involved in prospective calculations of likely outcomes, even when they are not observable, constraining spinogenesis while preserving mature spines may be important for solidifying durable expectations. To investigate causal relationships, we inhibited the RNA-binding protein fragile X mental retardation protein (encoded by Fmr1), which constrains dendritic spine turnover. Ventrolateral OFC-selective Fmr1 knockdown recapitulated the behavioral effects of inducible OFC inactivation (and lesions; also shown here), impairing action-outcome conditioning, and caused dendritic spine excess. Our findings suggest that a proper balance of dendritic spine plasticity within the OFC is necessary for one's ability to select actions based on anticipated consequences.SIGNIFICANCE STATEMENT Navigating a changing environment requires associating actions with their likely outcomes and updating these associations when they change. Dendritic spine plasticity is likely involved, yet relationships are unconfirmed. Using behavioral, chemogenetic, and viral-mediated gene silencing strategies and high-resolution microscopy, we find that modifying action-outcome expectations is associated with fewer immature spines and a greater proportion of mature spines in the ventrolateral orbitofrontal cortex (OFC). Given that the OFC is involved in prospectively calculating the likely outcomes of one's behavior, even when they are not observable, constraining spinogenesis while preserving mature spines may be important for maintaining durable expectations.

Rapid and Sparse Labeling of Neurons Based on the Mutant Virus-Like Particle of Semliki Forest Virus

Sparse labeling of neurons contributes to uncovering their morphology, and rapid expression of a fluorescent protein reduces the experiment range. To achieve the goal of rapid and sparse labeling of neurons in vivo, we established a rapid method for depicting the fine structure of neurons at 24 h post-infection based on a mutant virus-like particle of Semliki Forest virus. Approximately 0.014 fluorescent focus-forming units of the mutant virus-like particle transferred enhanced green fluorescent protein into neurons in vivo, and its affinity for neurons in vivo was stronger than for neurons in vitro and BHK21 (baby hamster kidney) cells. Collectively, the mutant virus-like particle provides a robust and convenient way to reveal the fine structure of neurons and is expected to be a helper virus for combining with other tools to determine their connectivity. Our work adds a new tool to the approaches for rapid and sparse labeling of neurons in vivo.

Nanoinjection system for precise direct delivery of biomolecules into single cells

Intracellular delivery of functional molecules such as proteins, transcription factors and DNA is effective and promising in cell biology. However, existing transfection methods are often unsuitable to deliver big molecules into cells or require carriers such as viruses and peptides specific to the target molecules. In addition, the nature of bulk processing does not generally provide accurate dose control of individual cells. The concept of single-cell-based material injection based on electrokinetic pumping through nanocapillaries could overcome these problems, yet the fabrication and operation of nanoscale 3-dimensional structures have remained unsolved. In this research, a hybrid (PDMS/glass) microfluidic chip with a true 3-dimensional nanoinjection structure (called "nanoinjection system") is presented. The nanoinjection structure was fabricated by femtosecond-laser (fs-laser) ablation in a single solid glass, which showed very successful delivery of red fluorescent protein (RFP) and expression of plasmid DNA in several different types of cells. This system is promising in that the amount of molecules to be delivered is controllable and the processed cells are systematically separated into a harvesting chamber, which can radically improve the purity of the processed cells. In addition, it was confirmed that the cells were healthy even after the molecule injection for a few seconds, indicating that the injection time can be significantly elongated, further improving the delivery efficiency of biomolecules without affecting the cell viability. We envision that the nanoinjection system having the major features of being carrier-free and dose-controllable, having an unlimited injection period, and ease of harvesting will greatly contribute to the next-generation research studies in the fields of cell biology and cell therapeutics.

Regulation of actions and habits by ventral hippocampal trkB and adolescent corticosteroid exposure

In humans and rodents, stress promotes habit-based behaviors that can interfere with action-outcome decision-making. Further, developmental stressor exposure confers long-term habit biases across rodent-primate species. Despite these homologies, mechanisms remain unclear. We first report that exposure to the primary glucocorticoid corticosterone (CORT) in adolescent mice recapitulates multiple neurobehavioral consequences of stressor exposure, including long-lasting biases towards habit-based responding in a food-reinforced operant conditioning task. In both adolescents and adults, CORT also caused a shift in the balance between full-length tyrosine kinase receptor B (trkB) and a truncated form of this neurotrophin receptor, favoring the inactive form throughout multiple corticolimbic brain regions. In adolescents, phosphorylation of the trkB substrate extracellular signal-regulated kinase 42/44 (ERK42/44) in the ventral hippocampus was also diminished, a long-term effect that persisted for at least 12 wk. Administration of the trkB agonist 7,8-dihydroxyflavone (7,8-DHF) during adolescence at doses that stimulated ERK42/44 corrected long-lasting corticosterone-induced behavioral abnormalities. Meanwhile, viral-mediated overexpression of truncated trkB in the ventral hippocampus reduced local ERK42/44 phosphorylation and was sufficient to induce habit-based and depression-like behaviors. Together, our findings indicate that ventral hippocampal trkB is essential to goal-directed action selection, countering habit-based behavior otherwise facilitated by developmental stress hormone exposure. They also reveal an early-life sensitive period during which trkB-ERK42/44 tone determines long-term behavioral outcomes.

Viral vectors for therapy of neurologic diseases

Neurological disorders - disorders of the brain, spine and associated nerves - are a leading contributor to global disease burden with a shockingly large associated economic cost. Various treatment approaches - pharmaceutical medication, device-based therapy, physiotherapy, surgical intervention, among others - have been explored to alleviate the resulting extent of human suffering. In recent years, gene therapy using viral vectors - encoding a therapeutic gene or inhibitory RNA into a "gutted" viral capsid and supplying it to the nervous system - has emerged as a clinically viable option for therapy of brain disorders. In this Review, we provide an overview of the current state and advances in the field of viral vector-mediated gene therapy for neurological disorders. Vector tools and delivery methods have evolved considerably over recent years, with the goal of providing greater and safer genetic access to the central nervous system. Better etiological understanding of brain disorders has concurrently led to identification of improved therapeutic targets. We focus on the vector technology, as well as preclinical and clinical progress made thus far for brain cancer and various neurodegenerative and neurometabolic disorders, and point out the challenges and limitations that accompany this new medical modality. Finally, we explore the directions that neurological gene therapy is likely to evolve towards in the future. This article is part of the Special Issue entitled "Beyond small molecules for neurological disorders".

Photomarking Relocalization Technique for Correlated Two-Photon and Electron Microcopy Imaging of Single Stimulated Synapses

Synapses learn and remember by persistent modifications of their internal structures and composition but, due to their small size, it is difficult to observe these changes at the ultrastructural level in real time. Two-photon fluorescence microscopy (2PM) allows time-course live imaging of individual synapses but lacks ultrastructural resolution. Electron microscopy (EM) allows the ultrastructural imaging of subcellular components but cannot detect fluorescence and lacks temporal resolution. Here, we describe a combination of procedures designed to achieve the correlated imaging of the same individual synapse under both 2PM and EM. This technique permits the selective stimulation and live imaging of a single dendritic spine and the subsequent localization of the same spine in EM ultrathin serial sections. Landmarks created through a photomarking method based on the 2-photon-induced precipitation of an electrodense compound are used to unequivocally localize the stimulated synapse. This technique was developed to image, for the first time, the ultrastructure of the postsynaptic density in which long-term potentiation was selectively induced just seconds or minutes before, but it can be applied for the study of any biological process that requires the precise relocalization of micron-wide structures for their correlated imaging with 2PM and EM.

Supernova: A Versatile Vector System for Single-Cell Labeling and Gene Function Studies in vivo

Here we describe “Supernova” series of vector systems that enable single-cell labeling and labeled cell-specific gene manipulation, when introduced by in utero electroporation (IUE) or adeno-associated virus (AAV)-mediated gene delivery. In Supernova, sparse labeling relies on low TRE leakage. In a small population of cells with over-threshold leakage, initial tTA-independent weak expression is enhanced by tTA/TRE-positive feedback along with a site-specific recombination system (e.g., Cre/loxP, Flpe/FRT). Sparse and bright labeling by Supernova with little background enables the visualization of the morphological details of individual neurons in densely packed brain areas such as the cortex and hippocampus, both during development and in adulthood. Sparseness levels are adjustable. Labeled cell-specific gene knockout was accomplished by introducing Cre/loxP-based Supernova vectors into floxed mice. Furthermore, by combining with RNAi, TALEN, and CRISPR/Cas9 technologies, IUE-based Supernova achieved labeled cell-specific gene knockdown and editing/knockout without requiring genetically altered mice. Thus, Supernova system is highly extensible and widely applicable for single-cell analyses in complex organs, such as the mammalian brain.

Semliki forest virus-based expression of recombinant GPCRs

Due to their importance as targets for drug development, rapid and consistent high-level production of G protein-coupled receptors (GPCRs) has become an essential part of drug discovery. Alphaviruses, particularly recombinant Semliki Forest virus (SFV) particles, have provided the means for expression of a number of GPCRs in a broad range of mammalian host cell lines for pharmacological characterization by determination of receptor binding activity and functional coupling to G proteins. The rapid high-titer virus particle production has made it possible to study a large number of GPCRs in parallel. Moreover, large-scale production in adherent and suspension cultures of mammalian cells has provided sufficient amounts of GPCRs for purification and subsequent structural studies. Furthermore, the high preference for neuronal delivery of SFV particles has allowed functional and localization studies of recombinant proteins in hippocampal slice cultures, in primary neurons, and in vivo.

Measles virus

Measles was an inevitable infection during the human development with substantial degree of morbidity and mortality. The severity of measles virus (MV) infection was largely contained by the development of a live attenuated vaccine that was introduced into the vaccination programs. However, all efforts to eradicate the disease failed and continued to annually result in significant deaths. The development of molecular biology techniques allowed the rescue of MV from cDNA that enabled important insights into a variety of aspects of the biology of the virus and its pathogenesis. Subsequently these technologies facilitated the development of novel vaccine candidates that induce immunity against measles and other pathogens. Based on the promising prospective, the use of MV as a recombinant vaccine and a therapeutic vector is addressed.

ATP-P2X7 Receptor Modulates Axon Initial Segment Composition and Function in Physiological Conditions and Brain Injury

Axon properties, including action potential initiation and modulation, depend on both AIS integrity and the regulation of ion channel expression in the AIS. Alteration of the axon initial segment (AIS) has been implicated in neurodegenerative, psychiatric, and brain trauma diseases, thus identification of the physiological mechanisms that regulate the AIS is required to understand and circumvent AIS alterations in pathological conditions. Here, we show that the purinergic P2X7 receptor and its agonist, adenosine triphosphate (ATP), modulate both structural proteins and ion channel density at the AIS in cultured neurons and brain slices. In cultured hippocampal neurons, an increment of extracellular ATP concentration or P2X7-green fluorescent protein (GFP) expression reduced the density of ankyrin G and voltage-gated sodium channels at the AIS. This effect is mediated by P2X7-regulated calcium influx and calpain activation, and impaired by P2X7 inhibition with Brilliant Blue G (BBG), or P2X7 suppression. Electrophysiological studies in brain slices showed that P2X7-GFP transfection decreased both sodium current amplitude and intrinsic neuronal excitability, while P2X7 inhibition had the opposite effect. Finally, inhibition of P2X7 with BBG prevented AIS disruption after ischemia/reperfusion in rats. In conclusion, our study demonstrates an involvement of P2X7 receptors in the regulation of AIS mediated neuronal excitability in physiological and pathological conditions.

Dual myxovirus screen identifies a small-molecule agonist of the host antiviral response

As we are confronted with an increasing number of emerging and reemerging viral pathogens, the identification of novel pathogen-specific and broad-spectrum antivirals has become a major developmental objective. Targeting of host factors required for virus replication presents a tangible approach toward obtaining novel hits with a broadened indication range. However, the identification of developable host-directed antiviral candidates remains challenging. We describe a novel screening protocol that interrogates the myxovirus host-pathogen interactome for broad-spectrum drug candidates and simultaneously probes for conventional, pathogen-directed hits. With resource efficiency and pan-myxovirus activity as the central developmental parameters, we explored coscreening against two distinct, independently traceable myxoviruses in a single-well setting. Having identified a pair of unrelated pathogenic myxoviruses (influenza A virus and measles virus) with comparable replication kinetics, we observed unimpaired coreplication of both viruses, generated suitable firefly and Renilla luciferase reporter constructs, respectively, and validated the protocol for up to a 384-well plate format. Combined with an independent counterscreen using a recombinant respiratory syncytial virus luciferase reporter, implementation of the protocol identified candidates with a broadened antimyxovirus profile, in addition to pathogen-specific hits. Mechanistic characterization revealed a newly discovered broad-spectrum lead that does not block viral entry but stimulates effector pathways of the innate cellular antiviral response. In summary, we provide proof of concept for the efficient discovery of broad-spectrum myxovirus inhibitors in parallel to para- and orthomyxovirus-specific hit candidates in a single screening campaign. The newly identified compound provides a basis for the development of a novel broad-spectrum small-molecule antiviral class.

Elevated Expression of Serotonin 5-HT(2A) Receptors in the Rat Ventral Tegmental Area Enhances Vulnerability to the Behavioral Effects of Cocaine

The dopamine mesocorticoaccumbens pathway which originates in the ventral tegmental area (VTA) and projects to the nucleus accumbens and prefrontal cortex is a circuit important in mediating the actions of psychostimulants. The function of this circuit is modulated by the actions of serotonin (5-HT) at 5-HT(2A) receptors (5-HT(2A)R) localized to the VTA. In the present study, we tested the hypothesis that virally mediated overexpression of 5-HT(2A)R in the VTA would increase cocaine-evoked locomotor activity in the absence of alterations in basal locomotor activity. A plasmid containing the gene for the 5-HT(2A)R linked to a synthetic marker peptide (Flag) was created and the construct was packaged in an adeno-associated virus vector (rAAV-5-HT(2A)R-Flag). This viral vector (2 μl; 10(9-10) transducing units/ml) was unilaterally infused into the VTA of male rats, while control animals received an intra-VTA infusion of Ringer's solution. Virus-pretreated rats exhibited normal spontaneous locomotor activity measured in a modified open-field apparatus at 7, 14, and 21 days following infusion. After an injection of cocaine (15 mg/kg, ip), both horizontal hyperactivity and rearing were significantly enhanced in virus-treated rats (p < 0.05). Immunohistochemical analysis confirmed expression of Flag and overexpression of the 5-HT(2A)R protein. These data indicate that the vulnerability of adult male rats to hyperactivity induced by cocaine is enhanced following increased levels of expression of the 5-HT(2A)R in the VTA and suggest that the 5-HT(2A)R receptor in the VTA plays a role in regulation of responsiveness to cocaine.

Safety aspects related to recombinant protein expression from Semliki Forest virus vectors

Semliki Forest virus vectors (SFV) have been developed for efficient transgene expression to result in high receptor yields(50-200 pmol receptor/mg protein) in a variety of mammalian host cells. Transfer of the SFV technology to mammalian cells growing in suspension cultures has made it feasible to produce hundreds of milligrams of receptor proteins in a short time. Large-scale production, however, raises the questions of the safety of handling virally infected cells for down-stream processing. Analysis of cell culture medium and SFV-infected cells revealed that some infectious particles were still present. Replacement of virus-containing medium at 2 h post-infection efficiently removed the majority of infectious replication-deficient SFV particles. Washes with PBS further reduced the number of infectious particles significantly both in the medium and associated with cells to levels that allowed safe handling of SFV-infected cells outside the cell culture facility for biochemical, pharmacological, or electrophysiological assays or down-stream processes in connection to receptor purification. Furthermore, engineering of novel temperature-sensitive mutant SFV vectors resulted in temperature-controlled transgene expression, which completely eliminates the risk of contaminating laboratory personnel.

Ex vivo gene delivery to hepatocytes: techniques, challenges, and underlying mechanisms

Gene delivery to primary hepatocytes is an important tool for a number of applications including the study of liver cell biology and pathology, drug screening, and gene therapy. Robust transfection of primary hepatocytes, however, is significantly more difficult to achieve than in cell lines or readily dividing primary cells. In this report, we investigated in vitro gene delivery to both primary rat hepatocytes and Huh7.5.1 cells (a hepatoma cell line) using a number of viral and non-viral methods, including Lipofectamine 2000, FuGene HD, Nucleofection, Magnetofection, and lentiviruses. Our results showed that Lipofectamine 2000 is the most efficient reagent for green fluorescent protein (GFP) gene delivery to primary rat hepatocytes (33.3 ± 1.8% transfection efficiency) with minimal adverse effect on several hepatic functions, such as urea and albumin secretion. The lentiviral vectors used in this study exhibited undetectable gene delivery to primary rat hepatocytes but significant delivery to Huh7.5.1 cells (>80% transfection efficiency). In addition, we demonstrated lentiviral-based and spatially defined delivery of the GFP gene to Huh7.5.1 cells for use in biological microelectromechanical systems.

Methods of dendritic spine detection: from Golgi to high-resolution optical imaging

Dendritic spines, the bulbous protrusions that form the postsynaptic half of excitatory synapses, are one of the most prominent features of neurons and have been imaged and studied for over a century. In that time, changes in the number and morphology of dendritic spines have been correlated to the developmental process as well as the pathophysiology of a number of neurodegenerative diseases. Due to the sheer scale of synaptic connectivity in the brain, work to date has merely scratched the surface in the study of normal spine function and pathology. This review will highlight traditional approaches to the imaging of dendritic spines and newer approaches made possible by advances in microscopy, protein engineering, and image analysis. The review will also describe recent work that is leading researchers toward the possibility of a systematic and comprehensive study of spine anatomy throughout the brain.

Lentiviral gene transfer into the dorsal root ganglion of adult rats

Background

Lentivector-mediated gene delivery into the dorsal root ganglion (DRG) is a promising method for exploring pain pathophysiology and for genetic treatment of chronic neuropathic pain. In this study, a series of modified lentivector particles with different cellular promoters, envelope glycoproteins, and viral accessory proteins were generated to evaluate the requirements for efficient transduction into neuronal cells in vitro and adult rat DRG in vivo.

Results

In vitro, lentivectors expressing enhanced green fluorescent protein (EGFP) under control of the human elongation factor 1α (EF1α) promoter and pseudotyped with the conventional vesicular stomatitis virus G protein (VSV-G) envelope exhibited the best performance in the transfer of EGFP into an immortalized DRG sensory neuron cell line at low multiplicities of infection (MOIs), and into primary cultured DRG neurons at higher MOIs. In vivo, injection of either first or second-generation EF1α-EGFP lentivectors directly into adult rat DRGs led to transduction rates of 19 ± 9% and 20 ± 8% EGFP-positive DRG neurons, respectively, detected at 4 weeks post injection. Transduced cells included a full range of neuronal phenotypes, including myelinated neurons as well as both non-peptidergic and peptidergic nociceptive unmyelinated neurons.

Conclusion

VSV-G pseudotyped lentivectors containing the human elongation factor 1α (EF1α)-EGFP expression cassette demonstrated relatively efficient transduction to sensory neurons following direct injection into the DRG. These results clearly show the potential of lentivectors as a viable system for delivering target genes into DRGs to explore basic mechanisms of neuropathic pain, with the potential for future clinical use in treating chronic pain.

A Simple, Highly Efficient Method for Heterologous Expression in Mammalian Primary Neurons Using Cationic Lipid-mediated mRNA Transfection

Expression of heterologous proteins in adult mammalian neurons is a valuable technique for the study of neuronal function. The post-mitotic nature of mature neurons prevents effective DNA transfection using simple, cationic lipid-based methods. Adequate heterologous protein expression is often only achievable using complex techniques that, in many cases, are associated with substantial toxicity. Here, a simple method for high efficiency transfection of mammalian primary neurons using in vitro transcribed mRNA and the cationic lipid transfection reagent Lipofectamine™ 2000 is described. Optimal transfection conditions were established in adult mouse dissociated dorsal root ganglion (DRG) neurons using a 96-well based luciferase activity assay. Using these conditions, a transfection efficiency of 25% was achieved in DRG neurons transfected with EGFP mRNA. High transfection efficiencies were also obtained in dissociated rat superior cervical ganglion (SCG) neurons and mouse cortical and hippocampal cultures. Endogenous Ca²⁺ currents in EGFP mRNA-transfected SCG neurons were not significantly different from untransfected neurons, which suggested that this technique is well suited for heterologous expression in patch clamp recording experiments. Functional expression of a cannabinoid receptor (CB1R), a G protein inwardly rectifying K⁺ channel (GIRK4) and a dominant-negative G protein α-subunit mutant (G_oA G203T) indicate that the levels of heterologous protein expression attainable using mRNA transfection are suitable for most functional protein studies. This study demonstrates that mRNA transfection is a straightforward and effective method for heterologous expression in neurons and is likely to have many applications in neuroscience research.

An adeno-associated viral vector transduces the rat hypothalamus and amygdala more efficient than a lentiviral vector

Background

This study compared the transduction efficiencies of an adeno-associated viral (AAV) vector, which was pseudotyped with an AAV1 capsid and encoded the green fluorescent protein (GFP), with a lentiviral (LV) vector, which was pseudotyped with a VSV-G envelop and encoded the discosoma red fluorescent protein (dsRed), to investigate which viral vector transduced the lateral hypothalamus or the amygdala more efficiently. The LV-dsRed and AAV1-GFP vector were mixed and injected into the lateral hypothalamus or into the amygdala of adult rats. The titers that were injected were 1 × 10⁸ or 1 × 10⁹ genomic copies of AAV1-GFP and 1 × 10⁵ transducing units of LV-dsRed.

Results

Immunostaining for GFP and dsRed showed that AAV1-GFP transduced significantly more cells than LV-dsRed in both the lateral hypothalamus and the amygdala. In addition, the number of LV particles that were injected can not easily be increased, while the number of AAV1 particles can be increased easily with a factor 100 to 1000. Both viral vectors appear to predominantly transduce neurons.

Conclusions

This study showed that AAV1 vectors are better tools to overexpress or knockdown genes in the lateral hypothalamus and amygdala of adult rats, since more cells can be transduced with AAV1 than with LV vectors and the titer of AAV1 vectors can easily be increased to transduce the area of interest.

Sonoporation-mediated gene transfer into adult rat dorsal root ganglion cells

Background

Gene transfer into many cell types has been successfully used to develop alternative and adjunct approaches to conventional medical treatment. However, effective transfection of postmitotic neurons remains a challenge. The aim of this study was to develop a method for gene transfer into rat primary dorsal root ganglion neurons using sonoporation.

Methods

Dissociated cells from adult rat dorsal root ganglion (DRG) cells were sonicated for 1-8 s at 2.5-10 W to determine the optimal ultrasound duration and power for gene transfection and cell survival. Transfection efficiency was compared between sonoporation, liposome and lentiviral vector gene transfer techniques.

Results

The optimum ultrasound intensity was 5 W for 2 s and yielded an efficiency of gene transfection of 31% and a survival rate of 35%.

Conclusions

Sonoporation can be optimized to minimize cell death and yield a high percentage of transfected neurons and that this technique can be easily applied to primary cultures of rat dorsal root ganglion neurons.

Corpus callosum: a favorable target for rSFV-mediated gene transfer to rat brain with broad and efficient expression

Recombinant Semliki Forest virus (rSFV), as a new kind of neurotropic vector system, has great potential of gene therapy for stroke. However, very little is known about its transduction characteristics in cerebral cortex or corpus callosum (CC) in vivo, which are common targets for gene transfer in experimental stroke therapy. Here, we investigate and compare rSFV-mediated gene expression at above two brain regions in rat; 2.0 x 10(7) IU of rSFV encoding green fluorescent protein (rSFV-GFP) was locally injected into CC or cerebral cortex in two groups. At 36 h following injection, the number of GFP-positive cells, GFP distribution volume, and GFP expression level were examined in the rat brain of each group using continuous frozen sections and enzyme-linked immunosorbent assay. rSFV vector displayed noticeably different transduction patterns in CC and cerebral cortex in vivo. CC injection of vector increased GFP-positive cell number by 802%, GFP transduction volume by 958%, and GFP expression level by 508% compared with cortical injection (all P < 0.01). We concluded that rSFV CC delivery significantly enhances transduction efficiency in rat brain with its ability to achieve transgene extensive transduction and abundant expression, and CC may be a favorable target for improving rSFV-based gene delivery efficiency to brain.

Viral strategies for studying the brain, including a replication-restricted self-amplifying delta-G vesicular stomatis virus that rapidly expresses transgenes in brain and can generate a multicolor golgi-like expression

Viruses have substantial value as vehicles for transporting transgenes into neurons. Each virus has its own set of attributes for addressing neuroscience-related questions. Here we review some of the advantages and limitations of herpes, pseudorabies, rabies, adeno-associated, lentivirus, and others to study the brain. We then explore a novel recombinant vesicular stomatitis virus (dG-VSV) with the G-gene deleted and transgenes engineered into the first position of the RNA genome, which replicates only in the first brain cell infected, as corroborated with ultrastructural analysis, eliminating spread of virus. Because of its ability to replicate rapidly and to express multiple mRNA copies and additional templates for more copies, reporter gene expression is amplified substantially, over 500-fold in 6 hours, allowing detailed imaging of dendrites, dendritic spines, axons, and axon terminal fields within a few hours to a few days after inoculation. Green fluorescent protein (GFP) expression is first detected within 1 hour of inoculation. The virus generates a Golgi-like appearance in all neurons or glia of regions of the brain tested. Whole-cell patch-clamp electrophysiology, calcium digital imaging with fura-2, and time-lapse digital imaging showed that neurons appeared physiologically normal after expressing viral transgenes. The virus has a wide range of species applicability, including mouse, rat, hamster, human, and Drosophila cells. By using dG-VSV, we show efferent projections from the suprachiasmatic nucleus terminating in the periventricular region immediately dorsal to the nucleus. DG-VSVs with genes coding for different color reporters allow multicolor visualization of neurons wherever applied.

Viral vector approaches to modify gene expression in the brain

The use of viral vectors as gene transfer tools for the central nervous system has seen a significant growth in the last decade. Improvements in the safety, efficiency and specificity of vectors for clinical applications have proven to be beneficial also for basic neuroscience research. This review will discuss the viral systems currently available to neuroscientists and some of the recent achievements in the study of synaptic function, memory and drug addiction.

Progress in transduction of cerebellar Purkinje cells in vivo using viral vectors

Expression of a foreign gene in cerebellar Purkinje cells in vivo is a powerful method for exploring the pathophysiology of the cerebellum. Although using developmental engineering many gene-modified mice have been generated, this approach is time-consuming and requires a lot of effort for crossing different lines of mice, genotyping and maintenance of animals. If a gene of interest can be transferred to and efficiently expressed in Purkinje cells of developing and mature animals, it saves much time, effort and money. Recent advances in viral vectors have markedly contributed to selective and efficient gene transfer to Purkinje cells in vivo. There are two approaches for selective gene expression in Purkinje cells: one is to take advantage of the viral tropism for Purkinje cells, which includes the tropism of adeno-associated virus and the vesicular stomatitis virus glycoprotein (VSV-G)-pseudotyped lentivirus. Another method, which might be used in combination with the first one, is utilization of a Purkinje-cell-specific promoter. Focusing mainly on these points, recent progress in viral-vector-mediated transduction of Purkinje cells in vivo is reviewed.

Lentivirus-mediated transgene delivery to the hippocampus reveals sub-field specific differences in expression

Background

In the adult hippocampus, the granule cell layer of the dentate gyrus is a heterogeneous structure formed by neurons of different ages, morphologies and electrophysiological properties. Retroviral vectors have been extensively used to transduce cells of the granule cell layer and study their inherent properties in an intact brain environment. In addition, lentivirus-based vectors have been used to deliver transgenes to replicative and non-replicative cells as well, such as post mitotic neurons of the CNS. However, only few studies have been dedicated to address the applicability of these widespread used vectors to hippocampal cells in vivo. Therefore, the aim of this study was to extensively characterize the cell types that are effectively transduced in vivo by VSVg-pseudotyped lentivirus-based vectors in the hippocampus dentate gyrus.

Results

In the present study we used Vesicular Stomatitis Virus G glycoprotein-pseudotyped lentivirual vectors to express EGFP from three different promoters in the mouse hippocampus. In contrast to lentiviral transduction of pyramidal cells in CA1, we identified sub-region specific differences in transgene expression in the granule cell layer of the dentate gyrus. Furthermore, we characterized the cell types transduced by these lentiviral vectors, showing that they target primarily neuronal progenitor cells and immature neurons present in the sub-granular zone and more immature layers of the granule cell layer.

Conclusion

Our observations suggest the existence of intrinsic differences in the permissiveness to lentiviral transduction among various hippocampal cell types. In particular, we show for the first time that mature neurons of the granule cell layer do not express lentivirus-delivered transgenes, despite successful expression in other hippocampal cell types. Therefore, amongst hippocampal granule cells, only adult-generated neurons are target for lentivirus-mediated transgene delivery. These properties make lentiviral vectors excellent systems for overexpression or knockdown of genes in neuronal progenitor cells, immature neurons and adult-generated neurons of the mouse hippocampus in vivo.

Functional protein delivery into neurons using polymeric nanoparticles

An efficient route for delivering specific proteins and peptides into neurons could greatly accelerate the development of therapies for various diseases, especially those involving intracellular defects such as Parkinson disease. Here we report the novel use of polybutylcyanoacrylate nanoparticles for delivery of intact, functional proteins into neurons and neuronal cell lines. Uptake of these particles is primarily dependent on endocytosis via the low density lipoprotein receptor. The nanoparticles are rapidly turned over and display minimal toxicity to cultured neurons. Delivery of three different functional cargo proteins is demonstrated. When primary neuronal cultures are treated with recombinant Escherichia coli beta-galactosidase as nanoparticle cargo, persistent enzyme activity is measured beyond the period of nanoparticle degradation. Delivery of the small GTPase rhoG induces neurite outgrowth and differentiation in PC12 cells. Finally, a monoclonal antibody directed against synuclein is capable of interacting with endogenous alpha-synuclein in cultured neurons following delivery via nanoparticles. Polybutylcyanoacrylate nanoparticles are thus useful for intracellular protein delivery in vitro and have potential as carriers of therapeutic proteins for treatment of neuronal disorders in vivo.

Construction of cell-type specific promoter lentiviruses for optically guiding electrophysiological recordings and for targeted gene delivery

It is often advantageous to identify and alter gene expression of specific cell populations within the brain. Currently, it is not possible to a priori identify specific cell types within the brain of rats for electrophysiological recordings, nor is it possible to routinely alter gene expression in specific cell types within the CNS of a variety of species. Here, we describe a general method for the relatively rapid screening of specific promoter activity in cell culture, in acute brain slice preparations, and in vivo. As an example, we describe the examination of an approximately 3 kb promoter region of the neuroactive peptide cholecystokinin (CCK) compared to the ubiquitous cytomegalovirus (CMV) promoter. We find a high degree of cell-type specificity in vivo using lentiviral approaches in rats and mice.

Mitochondrial imaging in dorsal root ganglion neurons following the application of inducible adenoviral vector expressing two fluorescent proteins

Mitochondrial morphology and dynamics are known to vary considerably depending on the cell type and organism studied. The objective of this study was to assess the potential application of adenoviral-fluorescent protein constructs for long-term tracking of mitochondria in neurons. An adenoviral vector containing two fluorescent proteins, the enhanced green fluorescent protein (eGFP) targeted to the cytoplasm to highlight the neuronal processes, and the red fluorescent protein (RFP) directed to mitochondria under the control of an inducible promoter, facilitated an efficient and accurate method to study mitochondrial dynamics in long-term studies. Dorsal root ganglion neurons from rat embryos were cultured and infected. The infected neurons exhibited green fluorescence after 24h, while 16 h following induction with doxycycline, red fluorescence protein began to localize within mitochondria. The red fluorescent protein was transported into mitochondria at the cell body followed by distribution within processes. As the neurons aged, the expression of red fluorescent protein was confined to cytoplasmic vacuoles and not mitochondria. Further analysis suggested that the cytoplasmic vacuoles were likely of lysosomal origin. Taken together, the current study presents novel strategies to study the life history of cellular organelles such as mitochondria in long-term studies.

High-throughput screening-based identification of paramyxovirus inhibitors

Several members of the paramyxovirus family constitute major human pathogens that, collectively, are responsible for major morbidity and mortality worldwide. In an effort to develop novel therapeutics against measles virus (MV), a prominent member of the paramyxovirus family, the authors report a high-throughput screening protocol that uses a nonrecombinant primary MV strain as targets. Implementation of the assay has yielded 60 hit candidates from a 137,500-entry library. Counterscreening and generation of dose-response curves narrows this pool to 35 compounds with active concentrations < or =15.3 microM against the MV-Alaska strain and specificity indices ranging from 36 to >500. Library mining for structural analogs of several confirmed hits combined with retesting of identified candidates reveals a high accuracy of primary hit identification. Eleven of the confirmed hits interfere with viral entry, whereas the remaining 24 compounds target postentry steps of the viral life cycle. Activity testing against selected members of the paramyxovirus family reveals 3 patterns of activity: 1) exclusively MV-specific blockers, 2) inhibitors of MV and related viruses of the same genus, and 3) broader range inhibitors with activity against a different Paramyxovirinae genus. Representatives of the last class may open avenues for the development of broad-range paramyxovirus inhibitors through hit-to-lead chemistry.

Alphaviruses: Semliki Forest virus and Sindbis virus vectors for gene transfer into neurons

Alphaviral vectors based on Semliki Forest virus and Sindbis virus infect many host cell types, causing rapid and high-level transgene expression. Compared to other viruses used to infect CNS cell and tissue preparations, Semliki Forest virus and Sindbis virus exhibit an outstanding preference for neurons rather than glial cells. High-titer vector generation typically requires biosafety level 1 or 2 containment and occurs in less than 2 days. Wild-type vectors are cytotoxic, permitting short-term transgene expression. However, mutant vectors with decreased cytotoxicity, to prolong host cell survival, have been developed. They also increase transgene expression and cellular coinfection, permitting heteromeric protein expression in individual cells. Other mutants with temperature-dependent control of transgene expression and altered host cell preference to target interneurons and astrocytes rather than principal neurons are available. Because of these advantages, alphaviral vectors are increasingly used in neurobiological and other studies, including structural biology, vaccine development, and cancer treatment.

Single cell electroporation method for axon tracing in cultured slices

Axon tracing is an essential method to reveal neuronal connection patterns and characteristics of growing axons during development. Here we introduce an electroporation-based gene transfer technique with a fluorescent protein (FP), which enables us to observe a small number of axons. The result also demonstrates that dynamics of axon behavior can be followed for more than a week. Thus, such labeling with FP is a powerful tool for axon tracing.

Characterization of oligophrenin-1, a RhoGAP lost in patients affected with mental retardation: lentiviral injection in organotypic brain slice cultures

Mutations in regulators and effectors of the Rho GTPases underlie various forms of mental retardation (MR). Among them, oligophrenin-1 (OPHN1), which encodes a Rho-GTPase activating protein, was one of the first Rho-linked MR genes identified. Upon characterization of OPHN1 in hippocampal brain slices, we obtained evidence for the requirement of OPHN1 in dendritic spine morphogenesis and neuronal function of CA1 pyramidal neurons. Organotypic hippocampal brain slice cultures are commonly used as a model system to investigate the morphology and synaptic function of neurons, mainly because they allow for the long-term examination of neurons in a preparation where the gross cellular architecture of the hippocampus is retained. In addition, maintenance of the trisynaptic circuitry in hippocampal slices enables the study of synaptic connections. Today, a multitude of gene transfer methods for postmitotic neurons in brain slices are available to easily manipulate and scrutinize the involvement of signaling molecules, such as Rho GTPases, in specific cellular processes in this system. This chapter covers techniques detailing the preparation and culturing of organotypic hippocampal brain slices, as well as the production and injection of lentivirus into brain slices.

Semliki Forest virus vectors with mutations in the nonstructural protein 2 gene permit extended superinfection of neuronal and non-neuronal cells

Semliki Forest virus (SFV) vectors are widely used in neurobiological studies because they efficiently infect neurons. As with any viral vector, they possess a limited cloning capacity, so infection with different SFV vectors may be required to introduce multiple transgenes into individual cells. However, this approach is limited by superinfection exclusion. The authors examined marker expression in baby hamster kidney cells, mouse cortical neurons, and rat hippocampal neurons using different fluorophore-encoding vectors that are based on the wild-type SFV4 strain and on the less cytopathic SFV4(PD) mutant, which carries two point mutations in nonstructural protein 2. For every fluorophore tested, SFV4(PD) gave higher (up to 22-fold) expression compared to SFV4. In infections using two and three different vectors, SFV4 caused relatively few multifluorescent baby hamster kidney cells when applied at 0-s, 15-min, or 2-h intervals. In contrast, SFV4(PD) permitted significantly enhanced marker coexpression, resulting in 46% doubly and 21% triply fluorescent baby hamster kidney cells, and 67% to 8% doubly fluorescent cortical and hippocampal neurons. At 15-min or 2-h addition intervals, SFV4(PD) still permitted 23% to 36% doubly fluorescent baby hamster kidney cells. The increased efficiency of SFV4(PD) in coexpressing separate markers from different viral particles suggests that mutations in nonstructural protein 2 affect alphaviral superinfection exclusion. The results demonstrate that SFV4(PD) is well-suited to coexpress multiple proteins in neuronal and non-neuronal cells. This capability is particularly valuable to express the various components of heteromeric protein complexes, especially when the individual cDNAs cannot be combined into single SFV particles.

In vivo single-cell electroporation for transfer of DNA and macromolecules

Single-cell electroporation allows transfection of plasmid DNA or macromolecules into individual living cells using modified patch electrodes and common electrophysiological equipment. This protocol is optimized for rapid in vivo electroporation of Xenopus laevis tadpole brains with DNA, dextrans, morpholinos and combinations thereof. Experienced users can electroporate roughly 40 tadpoles per hour. The technique can be adapted for use with other charged transfer materials and in other systems and tissues where cells can be targeted with a micropipette. Under visual guidance, an electrode filled with transfer material is placed in a cell body-rich area of the tadpole brain and a train of voltage pulses applied, which electroporates a nearby cell. We show examples of successfully electroporated single cells, instances of common problems and troubleshooting suggestions. Single-cell electroporation is an affordable method to fluorescently label and genetically manipulate individual cells. This powerful technique enables observation of single cells in an otherwise normal environment.