Transfer of small interfering RNA by single-cell electroporation in cerebellar cell cultures

Effect of Experimental Electrical and Biological Parameters on Gene Transfer by Electroporation: A Systematic Review and Meta-Analysis

The exact mechanisms of nucleic acid (NA) delivery with gene electrotransfer (GET) are still unknown, which represents a limitation for its broader use. Further, not knowing the effects that different experimental electrical and biological parameters have on GET additionally hinders GET optimization, resulting in the majority of research being performed using a trial-and-error approach. To explore the current state of knowledge, we conducted a systematic literature review of GET papers in in vitro conditions and performed meta-analyses of the reported GET efficiency. For now, there is no universal GET strategy that would be appropriate for all experimental aims. Apart from the availability of the required electroporation device and electrodes, the choice of an optimal GET approach depends on parameters such as the electroporation medium; type and origin of cells; and the size, concentration, promoter, and type of the NA to be transfected. Equally important are appropriate controls and the measurement or evaluation of the output pulses to allow a fair and unbiased evaluation of the experimental results. Since many experimental electrical and biological parameters can affect GET, it is important that all used parameters are adequately reported to enable the comparison of results, as well as potentially faster and more efficient experiment planning and optimization.

Non-Pigmented Ciliary Epithelium-Derived Extracellular Vesicles Loaded with SMAD7 siRNA Attenuate Wnt Signaling in Trabecular Meshwork Cells In Vitro

Primary open-angle glaucoma is established by the disruption of trabecular meshwork (TM) function. The disruption leads to increased resistance to the aqueous humor (AH), generated by the non-pigmented ciliary epithelium (NPCE). Extracellular vesicles (EVs) participate in the communication between the NPCE and the TM tissue in the ocular drainage system. The potential use of NPCE-derived EVs to deliver siRNA to TM cells has scarcely been explored. NPCE-derived EVs were isolated and loaded with anti-fibrotic (SMAD7) siRNA. EV’s structural integrity and siRNA loading efficiency were estimated via electron microscopy and fluorescence. Engineered EVs were added to pre-cultured TM cells and qRT-PCR was used to verify the transfer of selected siRNA to the cells. Western blot analysis was used to evaluate the qualitative effects on Wnt-TGFβ2 proteins’ expression. EVs loaded with exogenous siRNA achieved a 53% mRNA knockdown of SMAD7 in TM cells, resulting in a significant elevation in the levels of β-Catenin, pGSK3β, N-Cadherin, K-Cadherin, and TGFβ2 proteins in TM cells. NPCE-derived EVs can be used for efficient siRNA molecule delivery into TM cells, which may prove to be beneficial as a therapeutic target to lower intraocular pressure (IOP).

In situ electroporation of mammalian cells through SiO2 thin film capacitive microelectrodes

Electroporation is a widely used non-viral technique for the delivery of molecules, including nucleic acids, into cells. Recently, electronic microsystems that miniaturize the electroporation machinery have been developed as a new tool for genetic manipulation of cells in vitro, by integrating metal microelectrodes in the culture substrate and enabling electroporation in-situ. We report that non-faradic SiO₂ thin film-insulated microelectrodes can be used for reliable and spatially selective in-situ electroporation of mammalian cells. CHO-K1 and SH-SY5Y cell lines and primary neuronal cultures were electroporated by application of short and low amplitude voltage transients leading to cell electroporation by capacitive currents. We demonstrate reliable delivery of DNA plasmids and exogenous gene expression, accompanied by high spatial selectivity and cell viability, even with differentiated neurons. Finally, we show that SiO₂ thin film-insulated microelectrodes support a double and serial transfection of the targeted cells.

Promotion of Dendritic Differentiation of Cerebellar Purkinje Cells by Ca2+/calmodulin-dependent Protein Kinase IIα, IIβ and IV and Possible Involvement of CREB Phosphorylation

Cerebellar Purkinje cells develop the most elaborate dendritic trees among neurons in the brain. To examine the role of Ca²⁺/calmodulin-dependent protein kinase (CaMK) IIα, IIβ and IV in the dendritic differentiation of Purkinje cells, we introduced siRNA against these CaMKs into Purkinje cells in cerebellar cell cultures using a single-cell electroporation technique. Single-cell electroporation enables us to transfer siRNA into specific cells within a heterogeneous cell population. In addition, we can easily and reliably transfer multiple types of siRNA into a cell simply by loading them together in one micropipette. Any one of the siRNA against CaMKIIα, IIβ and IV (single knockdown) or any combinations of two of the siRNA against these CaMKs (double knockdown) had no significant effects on the dendritic differentiation of Purkinje cells. However, the combination of all three siRNA against these CaMKs (triple knockdown) inhibited the branching of Purkinje cell dendrites. Furthermore, the triple knockdown reduced the phosphorylation of CREB in Purkinje cells. These findings suggest the promotion of dendritic differentiation of Purkinje cells by CaMKIIα, IIβ and IV and the possible involvement of phosphorylation of CREB as a common substrate of these CaMKs.

Myosin 18Aα targets the guanine nucleotide exchange factor β-Pix to the dendritic spines of cerebellar Purkinje neurons and promotes spine maturation

Myosin 18Aα is a myosin 2-like protein containing unique N- and C-terminal protein interaction domains that co-assembles with myosin 2. One protein known to bind to myosin 18Aα is β-Pix, a guanine nucleotide exchange factor (GEF) for Rac1 and Cdc42 that has been shown to promote dendritic spine maturation by activating the assembly of actin and myosin filaments in spines. Here, we show that myosin 18A⍺ concentrates in the spines of cerebellar Purkinje neurons via co-assembly with myosin 2 and through an actin binding site in its N-terminal extension. miRNA-mediated knockdown of myosin 18A⍺ results in a significant defect in spine maturation that is rescued by an RNAi-immune version of myosin 18A⍺. Importantly, β-Pix co-localizes with myosin 18A⍺ in spines, and its spine localization is lost upon myosin 18A⍺ knockdown or when its myosin 18A⍺ binding site is deleted. Finally, we show that the spines of myosin 18A⍺ knockdown Purkinje neurons contain significantly less F-actin and myosin 2. Together, these data argue that mixed filaments of myosin 2 and myosin 18A⍺ form a complex with β-Pix in Purkinje neuron spines that promotes spine maturation by enhancing the assembly of actin and myosin filaments downstream of β-Pix's GEF activity.

A Single-Neuron: Current Trends and Future Prospects

The brain is an intricate network with complex organizational principles facilitating a concerted communication between single-neurons, distinct neuron populations, and remote brain areas. The communication, technically referred to as connectivity, between single-neurons, is the center of many investigations aimed at elucidating pathophysiology, anatomical differences, and structural and functional features. In comparison with bulk analysis, single-neuron analysis can provide precise information about neurons or even sub-neuron level electrophysiology, anatomical differences, pathophysiology, structural and functional features, in addition to their communications with other neurons, and can promote essential information to understand the brain and its activity. This review highlights various single-neuron models and their behaviors, followed by different analysis methods. Again, to elucidate cellular dynamics in terms of electrophysiology at the single-neuron level, we emphasize in detail the role of single-neuron mapping and electrophysiological recording. We also elaborate on the recent development of single-neuron isolation, manipulation, and therapeutic progress using advanced micro/nanofluidic devices, as well as microinjection, electroporation, microelectrode array, optical transfection, optogenetic techniques. Further, the development in the field of artificial intelligence in relation to single-neurons is highlighted. The review concludes with between limitations and future prospects of single-neuron analyses.

A highly efficient method for single-cell electroporation in mouse organotypic hippocampal slice culture

BACKGROUND

Exogenous gene introduction by transfection is one of the most important approaches for understanding the function of specific genes at the cellular level. Electroporation has a long-standing history as a versatile gene delivery technique in vitro and in vivo. However, it has been underutilized in vitro because of technical difficulty and insufficient transfection efficiency.

NEW METHOD

We have developed an electroporation technique that combines the use of large glass electrodes, tetrodotoxin-containing artificial cerebrospinal fluid and mild electrical pulses. Here, we describe the technique and compare it with existing methods.

RESULTS

Our method achieves a high transfection efficiency (∼80 %) in both excitatory and inhibitory neurons with no detectable side effects on their function. We demonstrate this method is capable of transferring at least three different genes into a single neuron. In addition, we demonstrate the ability to transfect different genes into neighboring cells.

COMPARISON WITH EXISTING METHODS

The majority of existing methods use fine-tipped glass electrodes (i.e. > 10 MΩ) and apply high voltage (10 V) pulses with high frequency (100 Hz) for 1 s. These parameters contribute to practical difficulties thus lowering the transfection efficiency. Our unique method minimizes electrode clogging and therefore procedure duration, increasing transfection efficiency and cellular viability.

CONCLUSIONS

Our modifications, relative to current methods, optimize electroporation efficiency and cell survival. Our approach offers distinct research strategies not only in elucidating cell-autonomous functions of genes but also for assessing genes contributing to intercellular functions, such as trans-synaptic interactions.

Large-Scale, High-Resolution Microelectrode Arrays for Interrogation of Neurons and Networks

High-density microelectrode arrays (HD-MEAs) are increasingly being used for the observation and manipulation of neurons and networks in vitro. Large-scale electrode arrays allow for long-term extracellular recording of the electrical activity from thousands of neurons simultaneously. Beyond population activity, it has also become possible to extract information of single neurons at subcellular level (e.g., the propagation of action potentials along axons). In effect, HD-MEAs have become an electrical imaging platform for label-free extraction of the structure and activation of cells in cultures and tissues. The quality of HD-MEA data depends on the resolution of the electrode array and the signal-to-noise ratio. In this chapter, we begin with an introduction to HD-MEA signals. We provide an overview of the developments on complementary metal-oxide-semiconductor or CMOS-based HD-MEA technology. We also discuss the factors affecting the performance of HD-MEAs and the trending application requirements that drive the efforts for future devices. We conclude with an outlook on the potential of HD-MEAs for advancing basic neuroscience and drug discovery.

Accurate signal-source localization in brain slices by means of high-density microelectrode arrays

Extracellular recordings by means of high-density microelectrode arrays (HD-MEAs) have become a powerful tool to resolve subcellular details of single neurons in active networks grown from dissociated cells. To extend the application of this technology to slice preparations, we developed models describing how extracellular signals, produced by neuronal cells in slices, are detected by microelectrode arrays. The models help to analyze and understand the electrical-potential landscape in an in vitro HD-MEA-recording scenario based on point-current sources. We employed two modeling schemes, (i) a simple analytical approach, based on the method of images (MoI), and (ii) an approach, based on finite-element methods (FEM). We compared and validated the models with large-scale, high-spatiotemporal-resolution recordings of slice preparations by means of HD-MEAs. We then developed a model-based localization algorithm and compared the performance of MoI and FEM models. Both models provided accurate localization results and a comparable and negligible systematic error, when the point source was in saline, a condition similar to cell-culture experiments. Moreover, the relative random error in the x-y-z-localization amounted only up to 4.3% for z-distances up to 200 μm from the HD-MEA surface. In tissue, the systematic errors of both, MoI and FEM models were significantly higher, and a pre-calibration was required. Nevertheless, the FEM values proved to be closer to the tissue experimental results, yielding 5.2 μm systematic mean error, compared to 22.0 μm obtained with MoI. These results suggest that the medium volume or "saline height", the brain slice thickness and anisotropy, and the location of the reference electrode, which were included in the FEM model, considerably affect the extracellular signal and localization performance, when the signal source is at larger distance to the array. After pre-calibration, the relative random error of the z-localization in tissue was only 3% for z-distances up to 200 μm. We then applied the model and related detailed understanding of extracellular recordings to achieve an electrically-guided navigation of a stimulating micropipette, solely based on the measured HD-MEA signals, and managed to target spontaneously active neurons in an acute brain slice for electroporation.

Expression of the GluA2 subunit of glutamate receptors is required for the normal dendritic differentiation of cerebellar Purkinje cells

Cerebellar Purkinje cells differentiate the most elaborate dendritic trees among neurons in the brain and constitute the principal part of cerebellar neuronal circuitry. In the present study, we examined the role of the GluA2 subunit of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors in the dendritic differentiation of Purkinje cells. Since mature Purkinje cells express the GluA2 subunit, AMPA receptors on them exhibit a low Ca²⁺ permeability. Does this expression of GluA2, leading to the loss of Ca²⁺ permeability of AMPA receptors, have a positive significance in the dendritic differentiation of Purkinje cells? To answer this question, we introduced GluA2 siRNA into immature Purkinje cells in cerebellar cell cultures using a single-cell electroporation technique. The dendritic elongation and branching, as well as spine formation, were inhibited by GluA2 knockdown in Purkinje cells. GluA2 knockdown augmented the elevation of intracellular Ca²⁺ concentrations and a higher incidence of oscillation of intracellular Ca²⁺ concentrations in response to glutamate. These findings suggest that excessive elevation of intracellular Ca²⁺ concentrations has a negative effect on the dendritic differentiation of Purkinje cells and that the expression of GluA2 inhibits this negative effect in the development of Purkinje cells.

Optimization of cerebellar purkinje neuron cultures and development of a plasmid-based method for purkinje neuron-specific, miRNA-mediated protein knockdown

We present a simple and efficient method to knock down proteins specifically in Purkinje neurons (PN) present in mixed mouse primary cerebellar cultures. This method utilizes the introduction via nucleofection of a plasmid encoding a specific miRNA downstream of the L7/Pcp2 promoter, which drives PN-specific expression. As proof-of-principle, we used this plasmid to knock down the motor protein myosin Va, which is required for the targeting of smooth endoplasmic reticulum (ER) into PN spines. Consistent with effective knockdown, transfected PNs robustly phenocopied PNs from dilute-lethal (myosin Va-null) mice with regard to the ER targeting defect. Importantly, our plasmid-based approach is less challenging technically and more specific to PNs than several alternative methods (e.g., biolistic- and lentiviral-based introduction of siRNAs). We also present a number of improvements for generating mixed cerebellar cultures that shorten the procedure and improve the total yield of PNs, and of transfected PNs, considerably. Finally, we present a method to rescue cerebellar cultures that develop large cell aggregates, a common problem that otherwise precludes the further use of the culture.

Indole and synthetic derivative activate chaperone expression to reduce polyQ aggregation in SCA17 neuronal cell and slice culture models

In spinocerebellar ataxia type 17 (SCA17), the expansion of a translated CAG repeat in the TATA box binding protein (TBP) gene results in a long polyglutamine (polyQ) tract in the TBP protein, leading to intracellular accumulation of aggregated TBP and cell death. The molecular chaperones act in preventing protein aggregation to ameliorate downstream harmful events. In this study, we used Tet-On SH-SY5Y cells with inducible SCA17 TBP/Q₇₉-green fluorescent protein (GFP) expression to test indole and synthetic derivative NC001-8 for neuroprotection. We found that indole and NC001-8 up-regulated chaperone expression to reduce polyQ aggregation in neuronal differentiated TBP/Q₇₉ cells. The effects on promoting neurite outgrowth and on reduction of aggregation on Purkinje cells were also confirmed with cerebellar primary and slice cultures of SCA17 transgenic mice. Our results demonstrate how indole and derivative NC001-8 reduce polyQ aggregation to support their therapeutic potentials in SCA17 treatment.

Optimization of single-cell electroporation protocol for forced gene expression in primary neuronal cultures

The development and function of the central nervous system (CNS) are realized through interactions between many neurons. To investigate cellular and molecular mechanisms of the development and function of the CNS, it is thus crucial to be able to manipulate the gene expression of single neurons in a complex cell population. We recently developed a technique for gene silencing by introducing small interfering RNA into single neurons in primary CNS cultures using single-cell electroporation. However, we had not succeeded in forced gene expression by introducing expression plasmids using single-cell electroporation. In the present study, we optimized the experimental conditions to enable the forced expression of green fluorescent protein (GFP) in cultured cerebellar Purkinje neurons using single-cell electroporation. We succeeded in strong GFP expression in Purkinje neurons by increasing the inside diameter of micropipettes or by making the size of the original plasmid smaller by digestion and cyclizing it by ligation. Strong GFP expression in Purkinje neurons electroporated under the optimal conditions continued to be observed for more than 25 days after electroporation. Thus, this technique could be used for forced gene expression in single neurons to investigate cellular and molecular mechanisms of the development, function, and disease of the CNS.

Transdermal enhancement effect and mechanism of iontophoresis for non-steroidal anti-inflammatory drugs

Iontophoresis is an important approach to improve transdermal drug delivery. However, The transdermal enhancement mechanism of iontophoresis was not well known. The relationship between the physicochemical properties of drugs and the transdermal enhancement effect of iontophoresis was revealed in this study. Non-steroidal anti-inflammatory drugs (NSAIDs) were used as the models, including aspirin, ibuprofen and indomethacin. Their oil-water partition coefficients were measured. The carbomer-based hydrogels of them were prepared. Iontophoresis significantly enhanced in vitro transdermal delivery across the rat skins. Strong lipophilicity could lead to high permeation of drugs. However, the dissociation extent (indicated as pKa) of drugs was the key factor to determine the transdermal enhancement effect of iontophoresis. The more dissociation the drugs were, the higher the transdermal enhancement effect of iontophoresis. The drug-loaded hydrogels combined with iontophoresis improved the treatment of rat raw's inflammatory syndrome. Iontophoresis significantly improved the drugs penetrating into the hypodermis, dermis and epidermis, more deeply than the application of drugs alone according to the experimental result of 5-carboxylfluorescein hydrogels. Iontophoresis led to the unordered arrangement of skin intercellular lipids, the significantly increased flowability and loose stratum corneum structure. Iontophoresis is a promising approach to improve transdermal drug delivery with safety and high efficiency.

siRNA delivery via electropulsation: a review of the basic processes

Due to their capacity for inducing strong and sequence specific gene silencing in cells, small interfering RNAs (siRNAs) are now recognized not only as powerful experimental tools for basic research in Molecular biology but with promising potentials in therapeutic development. Delivery is a bottleneck in many studies. There is a common opinion that full potential of siRNA as therapeutic agent will not be attained until better methodologies for its targeted intracellular delivery to cells and tissues are developed. Electropulsation (EP) is one of the physical methods successfully used to transfer siRNA into living cells in vitro and in vivo. This review will describe how siRNA electrotransfer obeys characterized biophysical processes (cell-size-dependent electropermeabilization, electrophoretic drag) with a strong control of a low loss of viability. Protocols can be easily adjusted by a proper setting of the electrical parameters and pulsing buffers. EP can be easily directly applied on animals. Preclinical studies showed that electropermeabilization brings a direct cytoplasmic distribution of siRNA and an efficient silencing of the targeted protein expression. EP appears as a promising tool for clinical applications of gene silencing. A panel of successful trials will be given.

Dendritic differentiation of cerebellar Purkinje cells is promoted by ryanodine receptors expressed by Purkinje and granule cells

Cerebellar Purkinje cells have the most elaborate dendritic trees among neurons in the brain. We examined the roles of ryanodine receptor (RyR), an intracellular Ca(2+) release channel, in the dendrite formation of Purkinje cells using cerebellar cell cultures. In the cerebellum, Purkinje cells express RyR1 and RyR2, whereas granule cells express RyR2. When ryanodine (10 µM), a blocker of RyR, was added to the culture medium, the elongation and branching of Purkinje cell dendrites were markedly inhibited. When we transferred small interfering RNA (siRNA) against RyR1 into Purkinje cells using single-cell electroporation, dendritic branching but not elongation of the electroporated Purkinje cells was inhibited. On the other hand, transfection of RyR2 siRNA into granule cells also inhibited dendritic branching of Purkinje cells. Furthermore, ryanodine reduced the levels of brain-derived neurotrophic factor (BDNF) in the culture medium. The ryanodine-induced inhibition of dendritic differentiation was partially rescued when BDNF was exogenously added to the culture medium in addition to ryanodine. Overall, these results suggest that RyRs expressed by both Purkinje and granule cells play important roles in promoting the dendritic differentiation of Purkinje cells and that RyR2 expressed by granule cells is involved in the secretion of BDNF from granule cells.

Single-cell juxtacellular transfection and recording technique

Genetic modifications and pharmacological studies enable the analysis of protein function in living cells. While many of these studies investigate the effect of proteins by bulk administration or withdrawal of the protein in complex cellular networks, understanding the more subtle mechanisms of protein function requires fine-tuned changes on a single-cell level without affecting the balance of the system. In order to analyse the consequences of protein modification at the single-cell level, we have developed a single-cell transfection method in the loose patch configuration, which allows juxtacellular recordings of neuronal cells prior to juxtacellular transfection. CA1 pyramidal neurons were selected based on morphological and electrophysiological criteria. Using a patch clamp amplifier which allows sensitive recordings of action currents in the loose seal mode as well as electroporation with high-voltage electrical stimulation the identified neurons were transfected with a combination of specific nucleotides, e.g. siRNA and a plasmid coding for GFP for later cell retrieval. Two days after transfection, whole-cell patch clamp recordings of transfected cells were performed to analyse electrophysiological properties. Action potential firing and synaptic transmission of single electroporated CA1 pyramidal cells were comparable to untransfected cells. Our study presents a method which enables identification of neurons by juxtacellular recording prior to single-cell juxtacellular transfection, allowing subsequent analysis of morphological and electrophysiological parameters several days after the genetic modification.

Functional genomic screening identifies dual leucine zipper kinase as a key mediator of retinal ganglion cell death

Glaucoma, a major cause of blindness worldwide, is a neurodegenerative optic neuropathy in which vision loss is caused by loss of retinal ganglion cells (RGCs). To better define the pathways mediating RGC death and identify targets for the development of neuroprotective drugs, we developed a high-throughput RNA interference screen with primary RGCs and used it to screen the full mouse kinome. The screen identified dual leucine zipper kinase (DLK) as a key neuroprotective target in RGCs. In cultured RGCs, DLK signaling is both necessary and sufficient for cell death. DLK undergoes robust posttranscriptional up-regulation in response to axonal injury in vitro and in vivo. Using a conditional knockout approach, we confirmed that DLK is required for RGC JNK activation and cell death in a rodent model of optic neuropathy. In addition, tozasertib, a small molecule protein kinase inhibitor with activity against DLK, protects RGCs from cell death in rodent glaucoma and traumatic optic neuropathy models. Together, our results establish a previously undescribed drug/drug target combination in glaucoma, identify an early marker of RGC injury, and provide a starting point for the development of more specific neuroprotective DLK inhibitors for the treatment of glaucoma, nonglaucomatous forms of optic neuropathy, and perhaps other CNS neurodegenerations.

Delivery systems and local administration routes for therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.

Single-cell electroporation using a multifunctional pipette

We present here a novel platform combination, using a multifunctional pipette to individually electroporate single-cells and to locally deliver an analyte, while in their culture environment. We demonstrate a method to fabricate low-resistance metallic electrodes into a PDMS pipette, followed by characterization of its effectiveness, benefits and limits in comparison with an external carbon microelectrode.

High-throughput single-cell manipulation in brain tissue

The complexity of neurons and neuronal circuits in brain tissue requires the genetic manipulation, labeling, and tracking of single cells. However, current methods for manipulating cells in brain tissue are limited to either bulk techniques, lacking single-cell accuracy, or manual methods that provide single-cell accuracy but at significantly lower throughputs and repeatability. Here, we demonstrate high-throughput, efficient, reliable, and combinatorial delivery of multiple genetic vectors and reagents into targeted cells within the same tissue sample with single-cell accuracy. Our system automatically loads nanoliter-scale volumes of reagents into a micropipette from multiwell plates, targets and transfects single cells in brain tissues using a robust electroporation technique, and finally preps the micropipette by automated cleaning for repeating the transfection cycle. We demonstrate multi-colored labeling of adjacent cells, both in organotypic and acute slices, and transfection of plasmids encoding different protein isoforms into neurons within the same brain tissue for analysis of their effects on linear dendritic spine density. Our platform could also be used to rapidly deliver, both ex vivo and in vivo, a variety of genetic vectors, including optogenetic and cell-type specific agents, as well as fast-acting reagents such as labeling dyes, calcium sensors, and voltage sensors to manipulate and track neuronal circuit activity at single-cell resolution.

An efficient method for the long-term and specific expression of exogenous cDNAs in cultured Purkinje neurons

We present a simple and efficient method for expressing cDNAs in Purkinje neurons (PNs) present in heterogeneous mouse cerebellar cultures. The method combines the transfection of freshly dissociated cerebellar cells via nucleofection with the use of novel expression plasmids containing a fragment of the L7 (Pcp2) gene that, within the cerebellum, drives PN-specific expression. The efficiency of PN transfection (determined 13 days post nucleofection) is approximately 70%. Double and triple transfections are routinely achieved at slightly lower efficiencies. Expression in PNs is obvious after one week in culture and still strong after three weeks, by which time these neurons are well-developed. Moreover, high-level expression is restricted almost exclusively to the PNs present in these mixed cultures, which greatly facilitates the characterization of PN-specific functions. As proof of principle, we used this method to visualize (1) the morphology of living PNs expressing mGFP, (2) the localization and dynamics of the dendritic spine proteins PSD-93 and Homer-3a tagged with mGFP and (3) the interaction of live PNs expressing mGFP with other cerebellar neurons expressing mCherry from a β-Actin promoter plasmid. Finally, we created a series of L7-plasmids containing different fluorescent protein cDNAs that are suited for the expression of cDNAs of interest as N- and C-terminally tagged fluorescent fusion proteins. In summary, this procedure allows for the highly efficient, long-term, and specific expression of multiple cDNAs in differentiated PNs, and provides a favorable alternative to two procedures (viral transduction, ballistic gene delivery) used previously to express genes in cultured PNs.

Long-term gene-silencing effects of siRNA introduced by single-cell electroporation into postmitotic CNS neurons

To explore how long the gene-silencing effects of siRNA introduced into postmitotic neurons continue, we transferred siRNA against GFP into GFP-expressing Purkinje and Golgi cells in cerebellar cell cultures by single-cell electroporation. The temporal changes in the intensity of GFP fluorescence in the same electroporated cells were monitored in real time using GFP imaging. Under standard conditions, GFP fluorescence was reduced to under one-tenth of the initial levels 4-7 days after electroporation. Such effects continued at least up to 14 days after electroporation. The effects of siRNAs against endogenous genes also continued for the same period. Thus, this method could be an effective tool for silencing gene expression for a long period in postmitotic neurons.

A role for myosin Va in cerebellar plasticity and motor learning: a possible mechanism underlying neurological disorder in myosin Va disease

Mutations of the myosin Va gene cause the neurological diseases Griscelli syndrome type 1 and Elejalde syndrome in humans and dilute phenotypes in rodents. To understand the pathophysiological mechanisms underlying the neurological disorders in myosin Va diseases, we conducted an integrated analysis at the molecular, cellular, electrophysiological, and behavioral levels using the dilute-neurological (d-n) mouse mutant. These mice manifest an ataxic gait and clonic seizures during postnatal development, but the neurological disorders are ameliorated in adulthood. We found that smooth endoplasmic reticulum (SER) rarely extended into the dendritic spines of Purkinje cells (PCs) of young d-n mice, and there were few, if any, IP(3) receptors. Moreover, long-term depression (LTD) at parallel fiber-PC synapses was abolished, consistent with our previous observations in juvenile lethal dilute mutants. Young d-n mice exhibited severe impairment of cerebellum-dependent motor learning. In contrast, adult d-n mice showed restoration of motor learning and LTD, and these neurological changes were associated with accumulation of SER and IP(3) receptors in some PC spines and the expression of myosin Va proteins in the PCs. RNA interference-mediated repression of myosin Va caused a reduction in the number of IP(3) receptor-positive spines in cultured PCs. These findings indicate that myosin Va function is critical for subsequent processes in localization of SER and IP(3) receptors in PC spines, LTD, and motor learning. Interestingly, d-n mice had defects of motor coordination from young to adult ages, suggesting that the role of myosin Va in PC spines is not sufficient for motor coordination.

Single neuron electroporation in manipulating and measuring the central nervous system

The development and application of single neuron electroporation largely advanced the use of traditional genetics in investigations of the central nervous system. This quick and accurate manipulation of the brain at individual neuron level allowed the gain and loss of functional analyses of different genes and/or proteins. This manuscript reviewed the development of the technique and discussed some technical aspects in practical manipulations. Then the manuscript summarized the potential applications with this technique. Last but not least, the technique showed prospective future when combined with other modern methods in neuroscience research.

Single-cell electroporation

Single-cell electroporation (SCEP) is a relatively new technique that has emerged in the last decade or so for single-cell studies. When a large enough electric field is applied to a single cell, transient nano-pores form in the cell membrane allowing molecules to be transported into and out of the cell. Unlike bulk electroporation, in which a homogenous electric field is applied to a suspension of cells, in SCEP an electric field is created locally near a single cell. Today, single-cell-level studies are at the frontier of biochemical research, and SCEP is a promising tool in such studies. In this review, we discuss pore formation based on theoretical and experimental approaches. Current SCEP techniques using microelectrodes, micropipettes, electrolyte-filled capillaries, and microfabricated devices are all thoroughly discussed for adherent and suspended cells. SCEP has been applied in in-vivo and in-vitro studies for delivery of cell-impermeant molecules such as drugs, DNA, and siRNA, and for morphological observations.

Dendrite formation of cerebellar Purkinje cells

During postnatal cerebellar development, Purkinje cells form the most elaborate dendritic trees among neurons in the brain, which have been of great interest to many investigators. This article overviews various examples of cellular and molecular mechanisms of formation of Purkinje cell dendrites as well as the methodological aspects of investigating those mechanisms.

Effects of 1-naphthyl acetyl spermine on dendrite formation by cultured cerebellar Purkinje cells

Cerebellar Purkinje cells have the most elaborate dendritic trees among neurons in the brain. To date, the contributions of calcium-permeable AMPA receptors (CP-AMPARs) in calcium signaling and dendrite formation of Purkinje cells remain to be elucidated. In the present study, therefore, we examined the effects of 1-naphthyl acetyl spermine (NAS), a blocker of CP-AMPARs, on dendrite formation by cultured Purkinje cells. NAS markedly inhibited elongation and branching of Purkinje cell dendrites. Calcium imaging experiments using caged glutamate demonstrated that NAS inhibits the increase of intracellular calcium concentration in Purkinje cells after glutamate release. These results suggest that calcium signaling mediated through CP-AMPARs plays an important role in Purkinje cell dendrite formation.