Spatially and temporally controlled electroporation of early chick embryos

The introduction of in ovo electroporation a decade ago has helped the chick embryo to become a powerful system to study gene regulation and function during development. Although this is a simple procedure for embryos of 2-d incubation, earlier stages (from laying to early neurulation, 0-1 d) present special challenges. Here we describe a robust and reproducible protocol for electroporation of expression vectors and morpholino oligonucleotides into the epiblast of embryos from soon after laying (stage XI) to stages 6-7 (early neurulation), with precise spatial and temporal control. Within 3 h, about 12 embryos can be electroporated and set up for culture by the New technique; the effects of morpholinos can be assessed immediately after electroporation, and robust overexpression from plasmid DNA is seen 2-3 h after electroporation. These techniques can be used for time-lapse imaging, gain- and loss-of-function experiments and studying gene regulatory elements in living embryos.     

Enhanced gene transfer into brain capillary endothelial cells using Antp-modified DNA-loaded nanoparticles

Brain capillary endothelial cells (BCECs) have been considered as one of the primary targets for cerebral gene therapy. However, the cells, well-known for their poor function of endocytosis, are difficult to be transfected by general non-viral vectors. The aim of this study was to enhance the efficiency of transfection and expression in BCECs of DNA/polymer nanoparticles with the modification of membrane-penetrating peptide, Antennapedia peptide (Antp) polyethylenimine (PEI) and polyamidoamine (PAMAM) were chosen to prepare Antp-modified DNA-loaded nanoparticles with a complex coacervation technique. After a 20-min transfection, the efficiency, in terms of transfection and expression, of DNA/PEI NP or DNA/PAMAM NP was enhanced significantly with the modification of Antp. After a 3-h transfection of DNA/Antp/PEI NP, there was no difference in cellular uptake but an enhancement in gene expression, compared to DNA/PEI NP alone. However, both the transfection and expression efficiency of DNA/PAMAM NP were enhanced using Antp. These observations suggest that Antp can increase the membrane-penetrating ability of DNA-loaded nanoparticles, which can be employed as novel non-viral gene vectors.     

In situ electroporation of radioactive compounds into adherent cells

We previously developed a technique, termed in situ electroporation, where nonpermeant molecules are introduced through an electrical pulse into adherent cells, while they grow on electrically conductive, optically transparent, indium-tin oxide (ITO). Careful control of the electric field intensity results in essentially 100% of the cells taking up the introduced material, without any detectable effect upon the physiology of the cell, presumably because the pores reseal rapidly so that the cellular interior is restored to its original state. Electroporation of radioactive material is faced with two important considerations: (1) potential for exposure of personnel to irradiation, and (2) the requirement for electroporation of a large number of cells. In this report, we describe a modification in the geometry of the slides and electrodes which permits the use of inexpensive ITO-coated glass of lower conductivity that can be discarded after use, to electroporate large numbers of cells using a minimum volume of radioactive nucleotide solution. The results demonstrate that, using this assembly, the determination of the Ras-bound GTP/GTP+GDP ratios through electroporation of [alpha32P]GTP can be conducted using approximately five times lower amounts of isotope than in previous designs. Moreover, this assembly permits efficient upscaling, which makes the determination of Ras-GTP binding in cells which are deficient in Ras activity possible. In addition, we demonstrate the labeling of two viral phosphoproteins--the Simian Virus 40 Large Tumor antigen, and Adenovirus E1A--through [gamma32P]ATP electroporation using this setup. In both cases, electroporation of the nucleotide can achieve a great increase in the efficiency and specificity of labeling compared to the addition of [32P]-orthophosphate to the culture medium, presumably because the immediate phosphate donor nucleotide itself is introduced, which can directly bind to the target proteins.     

Nucleoporation of dendritic cells: efficient gene transfer by electroporation into human monocyte-derived dendritic cells

Four new members of the ERF (ethylene-response factor) family of plant-specific DNA-binding (GCC box) factors were isolated from tomato fruit (LeERF1–4). Phylogenetic analysis indicated that LeERF2 belongs to a new ERF class, characterized by a conserved N-terminal signature sequence. Expression patterns and cis/trans binding affinities differed between the LeERFs. Combining experimental data and modeled three-dimensional analysis, it was shown that binding affinity of the LeERFs was affected by both the variation of nucleotides surrounding the DNA cis-element sequence and the nature of critical amino acid residues within the ERF domain.     

Delivery of plasmid DNA into intact plant cells by electroporation of plasmolyzed cells

This report describes the delivery of plasmid DNA containing either the β-glucuronidase (GUS) or the green fluorescent protein (GFP) reporter gene into intact plant cells of bamboo callus, lilium scales, and Nicotiana benthamiana suspension culture cells. By first plasmolyzing the tissues or cells with 0.4 m sucrose in the presence of plasmid DNA, electroporation effectively delivers plasmid DNA into the intact plant cells. Transient expression of the GUS gene, as revealed by histochemical assays, showed the presence of blue-staining areas in the electroporated tissues. A short exposure of cells to 2% DMSO (dimethyl sulfoxide) prior to plasmolysis elevated the level of transient GUS activity. When plasmid DNA containing a synthetic GFP gene was used, a strong green fluorescence was observed in N. benthamiana suspension culture cells that were subjected to plasmolysis and electroporation. These results suggest that plasmolysis brings the plasmid DNA into the void space that is in close vicinity to the plasmalemma, allowing electroporation to efficiently deliver the plasmid DNA into intact plant cells. Received: 15 June 1998 / Revision received: 18 August 1998 / Accepted: 28 August 1998     

Gene transfer by electroporation into intact scutellum cells of wheat embryos

Summary Gene transfer into intact cells was achieved by electroporating zygotic wheat embryos without any special pretreatment. Electroporation was tissue specific in so far as scutellum cells were found to be much more susceptible to gene transfer than other cell types of the embryo. The orientation of the embryos in the electroporation chamber also influenced the number of transformed scutellum cells; during electroporation, as in electrophoresis, the negatively charged plasmid DNA molecules seemed to move towards the positive electrode. Therefore, the embryos were arranged so that the scutella faced the negative electrode. The use of plasmids carrying either two chimeric anthocyanin regulatory genes or a chimeric gusA gene allowed clear identification of transformed cells in the scutellum. On some of the embryos, more than 100 transformed scutellum cells were found after electroporation with single electric pulses of 275 V/cm discharged from a 960-F capacitor and with 100 g DNA/ml electroporation buffer. Using the anthocyanin marker system, visibly transformed cells grew to produce red sectors.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - GUS -glucuronidase - MES 2-N-morpholinoethane sulfonic acid     

Co-transfer of restriction endonucleases and plasmid DNA into mammalian cells by electroporation: effects on stable transformation

The antimutagenic principle of the green fruits of Momordica charantia was shown by the micronucleus test to be an intractable mixture of novel acylglucosylsterols. The antimutagens were extracted from the green fruits with ethanol and isolated from the bioactive petroleum ether and carbon tetrachloride extracts by repeated and sequential flash column chromatography. The major component of the mixture is

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and the minor component is the stearyl derivative (Guevara, 1989). At a dosage range in mice of 50–12.5 μg extract/g, the mixture reduced by about 80% the number of micronucleated polychromatic erythrocytes induced by the well-known mutagen mitomycin C. Structure-activity correlation studies suggested that the antimutagenic activity may reside in the peculiar lipid-like structure of the acylglucosylsterols. Ingestion of these compounds may result in their absorption in the plasma membrane lipid bilayer which could adversely affect the membrane permeability towards mitomycin C and disrupt the cellular activity of the latter.     

Retrovirus vector-mediated gene transfer into the chick optic vesicle by in ovo electroporation

Owing to its external position in the embryo, the chick eye has been used as a readily accessible model for studying the molecular mechanisms behind the patterning of the central nervous system. Although methods of genetic analysis have not been established as in the mouse, the chick is convenient for analyzing the functions of genes by in ov o electroporation of retroviral vectors. In this review, we describe the retroviral vector-mediated transfer of genes into the chick optic vesicle by in ovo electroporation. A rapid, efficient, and sustained expression of transgenes is achieved by this approach.     

Gene transfer into cultured mammalian embryos by electroporation

To gain a better understanding of mammalian development at the molecular level, technology is needed that allows the transfer of exogenous genes into desired embryonic regions at defined stages of development. Our strategy has been to use electroporation (EP) of plasmid DNA following whole-embryo culture (WEC). In our gene transfer system, postimplantation rodent embryos are taken out of the uterus and a purified DNA solution of mammalian expression plasmid constructs is injected into the neural tube. A square-pulse current is delivered using an electroporator with an optimizer. Electroporated embryos are allowed to develop in the WEC system for 24--48 h. Within the targeted area, the proportion of transfected cells varied from 10% to approximately 100% depending on the test conditions (e.g., DNA concentration, voltage, duration of EP, and pulse number). The EP--WEC system has several advantages including rapid gene expression, minimal laboratory work, precisely targeted regions, and no risk for human beings. Application of the method is useful in improving our understanding of early neural development (E7--E12 in mice), e.g., alteration of gene function via ectopic expression, interference with dominant negative proteins, and fate mapping with marker genes. In addition, EP can complement genetic approaches such as the generation of knockout and transgenic mice.     

Gene transfer into mouse lyoma cells by electroporation in high electric fields.

Electric impulses (8 kV/cm, 5 microseconds) were found to increase greatly the uptake of DNA into cells. When linear or circular plasmid DNA containing the herpes simplex thymidine kinase (TK) gene is added to a suspension of mouse L cells deficient in the TK gene and the cells are then exposed to electric fields, stable transformants are formed that survive in the HAT selection medium. At 20 degrees C after the application of three successive electric impulses followed by 10 min to allow DNA entry there result 95 (+/- 3) transformants per 10(6) cells and per 1.2 micrograms DNA. Compared with biochemical techniques, the electric field method of gene transfer is very simple, easily applicable, and very efficient. Because the mechanism of DNA transport through cell membranes is not known, a simple physical model for the enhanced DNA penetration into cells in high electric fields is proposed. According to this ' electroporation model' the interaction of the external electric field with the lipid dipoles of a pore configuration induces and stabilizes the permeation sites and thus enhances cross membrane transport.     

Optimization of gene transfer into barley (Hordeum vulgare L.) mature embryos by tissue electroporation

 This study was conducted to detect the optimum conditions for DNA transfer into mature embryos of barley via electroporation. Cultured mature embryos of barley were directly electroporated in the presence of the pBI 121 vector carrying both the β-glucuronidase (GUS) and neomycin phosphotransferase II (npt II) genes. It was found that 500 v/cm and 500 μFd capacitance was the optimum combination for healthy germination of the transformed plants from mature electroporated embryos. Effects of culture duration before electroporation and selection antibiotic concentrations on germination were also examined. Gene transfer performed on 3-day-old cultures resulted in the highest germination frequencies. GUS expression was observed on transversal sections of embryos and mature leaves from 3 month-old regenerants. PCR and Southern blot analyses show the presence of the npt II transgene in the genome of a plant. Received: 15 June 1999 / Revision received: 27 September 1999 / Accepted: 26 October 1999     

Retroviral-mediated gene transfer into mammalian cells

Retroviruses may be used as genetic vectors to transfer genes into mammalian cells with high efficiency. We have shown that the N2 vector will transfer a functional bacterial gene for neomycin resistance (NeoR) into more than 80% of mouse spleen foci. A derivative of the N2 vector was constructed to study transfer and expression of the human gene for adenosine deaminase (ADA) in mammalian lymphoid and hematopoietic stem cells. This vector, termed SAX, contains the human ADA cDNA with an SV40 promoter in addition to the NeoR gene. The SAX vector was found to efficiently transfer and express the ADA gene in an ADA-deficient human T-cell line. Gene transfer by SAX using an autologous nonhuman primate bone marrow transplant model resulted in expression of the human ADA gene in peripheral blood cells of treated animals. Human bone marrow treated with SAX produced 1%-2% of colonies in vitro that were expressing the vector genes. Transfer of genes into circulating hematopoietic stem cells of fetal sheep in utero was most efficient; vector gene expression was evident in 20%-40% of hematopoietic colonies. Therefore, retroviral vectors are capable of transferring functional genes into a wide variety of mammalian lymphoid and hematopoietic cells. Such vectors may be useful for clinical trials of gene therapy, that is, the correction of genetic diseases by insertion of a normal gene into a patient's defective cells.     

Ultrasound-mediated gene transfer into neuronal cells

A new field of gene transfer is emerging as a simple, effective means to drive the expression foreign genes in cells: ultrasound-mediated gene transfer or sonoporation. We report here that sonoporation is an effective means of gene transfer for cultured neurons, a cell type that has been difficult to transfect. Neuronal cell types that are effectively sonoporated include chick retinal neurons, chick dorsal forebrain, chick optic tectum, PC12 cells, rat cerebellar neurons and mouse hippocampal neurons. Depending on the type of cell and conditions of sonoporation the transfection efficacy was as high as 20%. Sonoporation of plasmid DNA was effective for cells adherent to a substrate and for free-floating cells that were freshly dissociated. In the free-floating preparations, between 60 and 95% of the cells that were transfected were neuronal, as much as 90% higher than that observed for other methods of gene transfer including adenovirus and lipid-based transfection methods. We conclude that sonoporation is a simple, effective and inexpensive means by which to preferentially transfect DNA into neuronal cells.     

Development of plasmid vector and electroporation condition for gene transfer in sporogenic lactic acid bacterium, Bacillus coagulans

Bacillus coagulans is a sporogenic lactic acid bacterium that ferments glucose and xylose, major components of plant biomass, a potential feedstock for cellulosic ethanol. The temperature and pH for optimum rate of growth of B. coagulans (50 to 55 degrees C, pH 5.0) are very similar to that of commercially developed fungal cellulases (50 degrees C; pH 4.8). Due to this match, simultaneous saccharification and fermentation (SSF) of cellulose to products by B. coagulans is expected to require less cellulase than needed if the SSF is conducted at a sub-optimal temperature, such as 30 degrees C, the optimum for yeast, the main biocatalyst used by the ethanol industry. To fully exploit B. coagulans as a platform organism, we have developed an electroporation method to transfer plasmid DNA into this genetically recalcitrant bacterium. We also constructed a B. coagulans/E. coli shuttle vector, plasmid pMSR10 that contains the rep region from a native plasmid (pMSR0) present in B. coagulans strain P4-102B. The native plasmid, pMSR0 (6823bp), has 9 ORFs, and replicates by rolling-circle mode of replication. Plasmid pNW33N, developed for Geobacillus stearothermophilus, was also transformed into this host and stably maintained while several other Bacillus/Escherichia coli shuttle vector plasmids were not transformed into B. coagulans. The transformation efficiency of B. coagulans strain P4-102B using the plasmids pNW33N or pMSR10 was about 1.5x10(16) per mole of DNA. The availability of shuttle vectors and an electroporation method is expected to aid in genetic and metabolic engineering of B. coagulans.     

Introduction of deoxyribonucleoside triphosphates into intact cells by electroporation

A simple method, employing high-voltage electric discharge (electroporation), was developed to introduce phosphorylated nucleosides into the cytoplasm of viable cells. HL-60 leukemia cells permeabilized by this technique remained viable and incorporated deoxyribonucleoside triphosphates into nuclear DNA. Furthermore, DNA synthesis was depressed for at least 24 h in HL-60 cells made permeable to 1-beta-D-arabinosylcytosine 5'-triphosphate by this methodology. Electroporation was found to be applicable to the permeabilization of a wide variety of cell lines in culture to nucleotides, suggesting that this methodology may be useful for the introduction into intact cells of a wide variety of molecules that are not normally transported effectively.