Ex ovo electroporation for gene transfer into older chicken embryos

A Multifunctional Scaffold for Bone Infection Treatment by Delivery of microRNA Therapeutics Combined With Antimicrobial Nanoparticles

Treating bone infections and ensuring bone repair is one of the greatest global challenges of modern orthopedics, made complex by antimicrobial resistance (AMR) risks due to long-term antibiotic treatment and debilitating large bone defects following infected tissue removal. An ideal multi-faceted solution would will eradicate bacterial infection without long-term antibiotic use, simultaneously stimulating osteogenesis and angiogenesis. Here, a multifunctional collagen-based scaffold that addresses these needs by leveraging the potential of antibiotic-free antimicrobial nanoparticles (copper-doped bioactive glass, CuBG) to combat infection without contributing to AMR in conjunction with microRNA-based gene therapy (utilizing an inhibitor of microRNA-138) to stimulate both osteogenesis and angiogenesis, is developed. CuBG scaffolds reduce the attachment of gram-positive bacteria by over 80%, showcasing antimicrobial functionality. The antagomiR-138 nanoparticles induce osteogenesis of human mesenchymal stem cells in vitro and heal a large load-bearing defect in a rat femur when delivered on the scaffold. Combining both promising technologies results in a multifunctional antagomiR-138-activated CuBG scaffold inducing hMSC-mediated osteogenesis and stimulating vasculogenesis in an in vivo chick chorioallantoic membrane model. Overall, this multifunctional scaffold catalyzes killing mechanisms in bacteria while inducing bone repair through osteogenic and angiogenic coupling, making this platform a promising multi-functional strategy for treating and repairing complex bone infections.

In Ovo Gain- and Loss-of-Function Approaches to Study Gut Morphogenesis

The polarity of cellular components is essential for cellular shape changes, oriented cell migration, and modulating intra- and intercellular mechanical forces. However, many aspects of polarized cell behavior-especially dynamic cell shape changes during the process of morphogenesis-are almost impossible to study in cells cultured in plastic dishes. Avian embryos have always been a treasured model system to study vertebrate morphogenesis for developmental biologists. Avian embryos recapitulate human biology particularly well in the early stages due to their flat disc gastruloids. Since avian embryos can be manipulated in ovo they present paramount opportunities for highly localized targeting of genetic mechanisms during cellular and developmental processes. Here, we review the application of these methods for both gain of function and loss of function of a gene of interest at a specific developmental stage during left-right (LR) asymmetric gut morphogenesis. These tools present a powerful premise to investigate various polarized cellular activities and molecular processes in vivo in a reproducible manner.

Avian Embryos as a Model to Study Vascular Development

The use of live imaging is indispensable for advancing our understanding of vascular morphogenesis. Imaging fixed embryos at a series of distinct developmental time points, although valuable, does not reveal the dynamic behavior of cells, as well as their interactions with the underlying ECM. Due to the easy access of chicken embryos to manipulation and high-resolution imaging, this model has been at the origin of key discoveries. In parallel, known through its extensive use in quail-chick chimera studies, the quail embryo is equally poised to genetic manipulations and paramount to direct imaging of transgenic reporter quails. Here we describe ex ovo time-lapse confocal microscopy of transgenic quail embryo slices to image vascular development during gut morphogenesis. This technique is powerful as it allows direct observation of the dynamic endothelial cell behaviors along the left-right (LR) axis of the dorsal mesentery (DM), the major conduit for blood and lymphatic vessels that serve the gut. In combination with in ovo plasmid electroporation and quail-chick transplantation, these methods have allowed us to study the molecular mechanisms underlying blood vessel assembly during the formation of the intestine. Below we describe our protocols for the generation of embryo slices, ex ovo time-lapse imaging of fluorescently labeled cells, and quail-chick chimeras to study the early stages of gut vascular development.

Translational Studies on the Potential of a VEGF Nanoparticle-Loaded Hyaluronic Acid Hydrogel

Heart failure has a five-year mortality rate approaching 50%. Inducing angiogenesis following a myocardial infarction is hypothesized to reduce cardiomyocyte death and tissue damage, thereby preventing heart failure. Herein, a novel nano-in-gel delivery system for vascular endothelial growth factor (VEGF), composed of star-shaped polyglutamic acid-VEGF nanoparticles in a tyramine-modified hyaluronic acid hydrogel (nano-VEGF-HA-TA), is investigated. The ability of the nano-VEGF-HA-TA system to induce angiogenesis is assessed in vivo using a chick chorioallantoic membrane model (CAM). The formulation is then integrated with a custom-made, clinically relevant catheter suitable for minimally invasive endocardial delivery and the effect of injection on hydrogel properties is examined. Nano-VEGF-HA-TA is biocompatible on a CAM assay and significantly improves blood vessel branching (p < 0.05) and number (p < 0.05) compared to a HA-TA hydrogel without VEGF. Nano-VEGF-HA-TA is successfully injected through a 1.2 m catheter, without blocking or breaking the catheter and releases VEGF for 42 days following injection in vitro. The released VEGF retains its bioactivity, significantly improving total tubule length on a Matrigel^® assay and human umbilical vein endothelial cell migration on a Transwell^® migration assay. This VEGF-nano in a HA-TA hydrogel delivery system is successfully integrated with an appropriate device for clinical use, demonstrates promising angiogenic properties in vivo and is suitable for further clinical translation.

Gene Silencing in Chicken Brain Development

Despite the development of brain organoids and neural cultures derived from iPSCs (induced pluripotent stem cells), brain development can only be studied in an animal. The mouse is the most commonly used vertebrate model for the analysis of gene function because of the well-established genetic tools that are available for loss-of-function studies. However, studies of gene function during development can be problematic in mammals. Many genes are active during different stages of development. Absence of gene function during early development may cause aberrant neurogenesis or even embryonic lethality and thus prevent analysis of later stages of development. To avoid these problems, precise temporal control of gene silencing is required.In contrast to mammals, oviparous animals are accessible for experimental manipulations during embryonic development. The combination of accessibility and RNAi- or Crispr/Cas9-based gene silencing makes the chicken embryo a powerful model for developmental studies. Depending on the time window during which gene silencing is attempted, chicken embryos can be used in ovo or ex ovo in a domed dish for easier access during later stages of development. Both techniques allow for precise temporal control of gene silencing during embryonic development.

Collagen scaffolds functionalised with copper-eluting bioactive glass reduce infection and enhance osteogenesis and angiogenesis both in vitro and in vivo

The bone infection osteomyelitis (typically by Staphylococcus aureus) usually requires a multistep procedure of surgical debridement, long-term systemic high-dose antibiotics, and - for larger defects - bone grafting. This, combined with the alarming rise in antibiotic resistance, necessitates development of alternative approaches. Herein, we describe a one-step treatment for osteomyelitis that combines local, controlled release of non-antibiotic antibacterials with a regenerative collagen-based scaffold. To maximise efficacy, we utilised bioactive glass, an established osteoconductive material with immense capacity for bone repair, as a delivery platform for copper ions (proven antibacterial, angiogenic, and osteogenic properties). Multifunctional collagen-copper-doped bioactive glass scaffolds (CuBG-CS) were fabricated with favourable microarchitectural and mechanical properties (up to 1.9-fold increase in compressive modulus over CS) within the ideal range for bone tissue engineering. Scaffolds demonstrated antibacterial activity against Staphylococcus aureus (up to 66% inhibition) whilst also enhancing osteogenesis (up to 3.6-fold increase in calcium deposition) and angiogenesis in vitro. Most significantly, when assessed in a chick embryo in vivo model, CuBG-CS not only demonstrated biocompatibility, but also a significant angiogenic and osteogenic response, consistent with in vitro studies. Collectively, these results indicate that the CuBG-CS developed here show potential as a one-step osteomyelitis treatment: reducing infection, whilst enhancing bone healing.

Sonic Hedgehog Regulation of the Neural Precursor Cell Fate During Chicken Optic Tectum Development

During nervous system development, neurons project axons over long distances to reach the appropriate targets for correct neural circuit formation. Sonic hedgehog (Shh) is a secreted protein and plays a key role in regulating vertebrate embryogenesis, especially in central nervous system (CNS) patterning, including neuronal migration and axonal projection in the brain and spinal cord. In the developing ventral midbrain, Shh is sufficient to specify a striped pattern of cell fates. Little is known about the molecular mechanisms underlying the Shh regulation of the neural precursor cell fate during the optic tectum development. Here, we aimed at studying how Shh might regulate chicken optic tectum patterning. In the present study, in ovo electroporation methods were employed to achieve the overexpression of Shh in the optic tectum during chicken embryo development. Besides, the study combined in ovo electroporation and neuron isolation culturing to study the function of Shh in vivo and in vitro. The fluorescent immunohistochemistry methods were used to check the related indicators. The results showed that Shh overexpression caused 87.8% of cells to be distributed to the stratum griseum central (SGC) layer, while only 39.3% of the GFP-transfected cells resided in the SGC layer in the control group. Shh overexpression also reduced the axon length in vivo and in vitro. In conclusion, we provide evidence that Shh regulates the neural precursor cell fate during chicken optic tectum development. Shh overexpression impairs neuronal migration and may affect the fate determination of transfected neurons.

In Ovo Electroporation Methods in Chick Embryos

To elucidate a gene function, in vivo analysis is indispensable. We can carry out gain and loss of function experiment of a gene of interest by electroporation in ovo and ex ovo culture system on early-stage and advanced-stage chick embryos, respectively. In this section, we introduce in/ex ovo electroporation methods for the development of the chick central nervous system and visual system investigation.

Glipizide suppresses embryonic vasculogenesis and angiogenesis through targeting natriuretic peptide receptor A

Glipizide, a second-generation sulfonylurea, has been widely used for the treatment of type 2 diabetes. However, it is controversial whether or not glipizide would affect angiogenesis or vasculogenesis. In the present study, we used early chick embryo model to investigate the effect of glipizide on angiogenesis and vasculogenesis, which are the two major processes for embryonic vasculature formation as well as tumor neovascularization. We found that Glipizide suppressed both angiogenesis in yolk-sac membrane (YSM) and blood island formation during developmental vasculogenesis. Glipizide did not affect either the process of epithelial to mesenchymal transition (EMT) or mesoderm cell migration. In addition, it did not interfere with separation of smooth muscle cell progenitors from hemangioblasts. Moreover, natriuretic peptide receptor A (NPRA) has been identified as the putative target for glipizide׳s inhibitory effect on vasculogenesis. When NPRA was overexpressed or activated, blood island formation was reduced. NPRA signaling may play a crucial role in the effect of glipizide on vasculogenesis during early embryonic development.

NRP1-mediated Sema3A signals coordinate laminar formation in the developing chick optic tectum

The optic tectum comprises multiple layers, which are formed by radial and tangential migration during development. Here, we report that Neuropilin 1 (NRP1)-mediated Sema3A signals are involved in the process of tectal laminar formation, which is elaborated by tangential migration. In the developing chick tectum, NRP1, a receptor for Sema3A, is expressed in microtubule-associated protein 2 (MAP2)-positive intermediate layers IV and V. Sema3A itself is a diffusible guidance factor and is expressed in the overlying layer VI. Using stable fluorescent labeling of tectal cells, we show that MAP2-positive intermediate layers are formed by the neurons that have been dispersed by tangential migration along the tectal efferent axons. When Sema3A was mis-expressed during laminar formation, local Sema3A repelled the tangential migrants, thus eliminating MAP2-positive neurons that expressed NRP1. Furthermore, in the absence of the MAP2-positive neurons, tectal layers were disorganized into an undulated form, indicating that MAP2-positive intermediate layers are required for proper laminar formation. These results suggest that NRP1-mediated Sema3A signals provide repulsive signals for MAP2-positive neurons to segregate tectal layers, which is important in order to coordinate laminar organization of the optic tectum.

Role of En2 in the tectal laminar formation of chick embryos

The chick optic tectum consists of 16 laminae. Here, we report contribution of En2 to laminar formation in chick optic tecta. En2 is specifically expressed in laminae g-j of stratum griseum et fibrosum superficiale (SGFS). Misexpression of En2 resulted in disappearance of En2-expressing cells from the superficial layers (laminae a-f of SGFS), where endogenous En2 is not expressed. Misexpression of En2 before postmitotic cells had left the ventricular layer indicated that En2-misexpressing cells stopped at the laminae of endogenous En2 expression and that they did not migrate into the superficial layers. Induction of En2 misexpression using a tetracycline-inducible system after the postmitotic cells had reached superficial layers also resulted in disappearance of En2-expressing cells from the superficial layers. Time-lapse analysis showed that En2-misexpressing cells migrated back from the superficial layers towards the middle layers, where En2 is strongly expressed endogenously. Our results suggest a potential role of En2 in regulating cell migration and positioning in the tectal laminar formation.

Developmental imaging: the avian embryo hatches to the challenge

The avian embryo provides a multifaceted model to study developmental mechanisms because of its accessibility to microsurgery, fluorescence cell labeling, in vivo imaging, and molecular manipulation. Early two-dimensional planar growth of the avian embryo mimics human development and provides unique access to complex cell migration patterns using light microscopy. Later developmental events continue to permit access to both light and other imaging modalities, making the avian embryo an excellent model for developmental imaging. For example, significant insights into cell and tissue behaviors within the primitive streak, craniofacial region, and cardiovascular and peripheral nervous systems have come from avian embryo studies. In this review, we provide an update to recent advances in embryo and tissue slice culture and imaging, fluorescence cell labeling, and gene profiling. We focus on how technical advances in the chick and quail provide a clearer understanding of how embryonic cell dynamics are beautifully choreographed in space and time to sculpt cells into functioning structures. We summarize how these technical advances help us to better understand basic developmental mechanisms that may lead to clinical research into human birth defects and tissue repair.

ADAM10 negatively regulates neuronal differentiation during spinal cord development

Members of the ADAM (a disintegrin and metalloprotease) family are involved in embryogenesis and tissue formation via their proteolytic function, cell-cell and cell-matrix interactions. ADAM10 is expressed temporally and spatially in the developing chicken spinal cord, but its function remains elusive. In the present study, we address this question by electroporating ADAM10 specific morpholino antisense oligonucleotides (ADAM10-mo) or dominant-negative ADAM10 (dn-ADAM10) plasmid into the developing chicken spinal cord as well as by in vitro cell culture investigation. Our results show that downregulation of ADAM10 drives precocious differentiation of neural progenitor cells and radial glial cells, resulting in an increase of neurons in the developing spinal cord, even in the prospective ventricular zone. Remarkably, overexpression of the dn-ADAM10 plasmid mutated in the metalloprotease domain (dn-ADAM10-me) mimics the phenotype as found by the ADAM10-mo transfection. Furthermore, in vitro experiments on cultured cells demonstrate that downregulation of ADAM10 decreases the amount of the cleaved intracellular part of Notch1 receptor and its target, and increases the number of βIII-tubulin-positive cells during neural progenitor cell differentiation. Taken together, our data suggest that ADAM10 negatively regulates neuronal differentiation, possibly via its proteolytic effect on the Notch signaling during development of the spinal cord.

RNAi-based gene silencing in chicken brain development

The mouse is the most commonly used vertebrate model for the analysis of gene function because of the well-established genetic tools that are available for loss-of-function studies. However, studies of gene function during development can be problematic in mammals. Many genes are active during different stages of development. Absence of gene function during early development may cause embryonic lethality and thus prevent analysis of later stages of development. To avoid these problems, precise temporal control of gene silencing is required. In contrast to mammals, oviparous animals are accessible for experimental manipulations during embryonic development. The combination of accessibility and RNAi-based gene silencing makes the chicken embryo a powerful model for developmental studies. Depending on the time window during which gene silencing is attempted, chicken embryos can be used for RNAi in ovo or cultured in a domed dish for easier access during ex ovo RNAi. Both techniques allow for precise temporal control of gene silencing during embryonic development.

Morpholinos: studying gene function in the chick

The use of morpholinos for perturbing gene function in the chick, Gallus gallus, has led to many important discoveries in developmental biology. This technology makes use of in vivo electroporation, which allows gain and loss of function in a temporally, and spatially controlled manner. Using this method, morpholinos can be transfected into embryonic tissues from early to late developmental stages. In this article, we describe the methods currently used in our laboratory to knock down gene function using morpholinos in vivo. We also detail how morpholinos are used to provide consistency of the results, and describe two protocols to visualise the morpholino after electroporation. In addition, we provide guidance on avoiding potential pitfalls, and suggestions for troubleshooting solutions. These revised techniques provide a practical starting point for investigating gene function in the chick.

A technique to increase accessibility to late-stage chick embryos for in ovo manipulations

BACKGROUND

During early development, avian embryos are easily accessible in ovo for transplantations and experimental perturbations. However, these qualities of the avian embryonic model rapidly wane shortly after embryonic day (E)4 when the embryo is obscured by extraembryonic membranes, making it difficult to study developmental events that occur at later stages in vivo.

RESULTS

In this study, we describe a multistep method that involves initially windowing eggs at E3, followed by dissecting away extraembryonic membranes at E5 to facilitate embryo accessibility in ovo until later stages of development. The majority of the embryos subjected to this technique remain exposed between E5 and E8, then become gradually displaced by the growing allantois from posterior to anterior regions.

CONCLUSIONS

Exposed embryos are viable and compatible with embryological and modern developmental biology techniques including tissue grafting and ablation, gene manipulation by electroporation, and protein expression. This technique opens up new avenues for studying complex cellular interactions during organogenesis and can be further extrapolated to regeneration and stem cell studies.

Different gene transfer methods at the very early, early, late and whole embryonic stages in chicken

New technologies in gene transfer combined with experimental embryology make the chicken embryo an excellent model system for gene function studies. The techniques of in ovo electroporation, in vitro culture for ex ovo electroporation and retrovirus-mediated gene transfer have already been fully developed in chicken. Yet to our knowledge, there are no definite descriptions on the features and application scopes of these techniques. The survival rates of different in vitro culture methods were compared and the EGFP expression areas of different gene transfer techniques were explored. It was that the optimal timings of removing embryo for EC culture and Petri dish system was at E1.5 and E2.5, respectively; and optimal timing of injecting retrovirus is at E0. Results indicated that the EC culture, in ovo electroporation, the Petri dish system and retrovirus-mediated method are, respectively, suitable for the very early, early, late and whole embryonic stages in chicken. Comparison of different gene transfer methods and establishment of optimal timings are expected to provide a better choice of the efficient method for a particular experiment.

Gene transfer into older chicken embryos by ex ovo electroporation

The chicken embryo provides an excellent model system for studying gene function and regulation during embryonic development. In ovo electroporation is a powerful method to over-express exogenous genes or down-regulate endogenous genes in vivo in chicken embryos(1). Different structures such as DNA plasmids encoding genes(2-4), small interfering RNA (siRNA) plasmids(5), small synthetic RNA oligos(6), and morpholino antisense oligonucleotides(7) can be easily transfected into chicken embryos by electroporation. However, the application of in ovo electroporation is limited to embryos at early incubation stages (younger than stage HH20--according to Hamburg and Hamilton)(8) and there are some disadvantages for its application in embryos at later stages (older than stage HH22--approximately 3.5 days of development). For example, the vitelline membrane at later stages is usually stuck to the shall membrane and opening a window in the shell causes rupture of the vessels, resulting in death of the embryos; older embryos are covered by vitelline and allantoic vessels, where it is difficult to access and manipulate the embryos; older embryos move vigorously and is difficult to control the orientation through a relatively small window in the shell. In this protocol we demonstrate an ex ovo electroporation method for gene transfer into chicken embryos at late stages (older than stage HH22). For ex ovo electroporation, embryos are cultured in Petri dishes(9) and the vitelline and allantoic vessels are widely spread. Under these conditions, the older chicken embryos are easily accessed and manipulated. Therefore, this method overcomes the disadvantages of in ovo electroporation applied to the older chicken embryos. Using this method, plasmids can be easily transfected into different parts of the older chicken embryos(10-12).

In ovo eye electroporation

Electroporation has been used successfully to introduce macromolecules such as DNA into the chick embryo for at least 15 years. Purified plasmid DNA is microinjected into embryo and then a series of low voltage electrical pulses are applied to the embryo which allows naked DNA to enter cells. Following entrance into the cytoplasm, the DNA is transported to the nucleus where it is transiently expressed. This powerful technique is useful for studies involving overexpression, misexpression, and knockdown of genes of interest at a variety of developmental timepoints.

Development of high-concentration lipoplexes for in vivo gene function studies in vertebrate embryos

Here we report that highly concentrated cationic lipid/helper lipid-nucleic acid complexes (lipoplexes) can facilitate reproducible delivery of a variety of oligonucleotides and plasmids to chicken embryos or to mouse embryonic mesenchyme. Specifically, liposomes composed of N,N-dioleyl-N,N-dimethylammonium chloride (DODAC)/1,2 dioleoyl glycero-3-phosphorylethanolamine (DOPE) prepared at 18-mM concentrations produced high levels of transfection of exogenous genes in vivo and in vitro. Furthermore, we report sufficient uptake of plasmids expressing interference RNA to decrease expression of both exogenous and endogenous genes. The simplicity of preparation, implementation, and relatively low toxicity of this transfection reagent make it an attractive alternative for developmental studies in post-gastrulation vertebrate embryos.

Versican knock-down compromises chondrogenesis in the embryonic chick limb

Mesenchymal cell aggregation is critical for cartilage formation in the vertebrate limb. The extracellular matrix (ECM) plays a critical role in governing cell behavior and cell phenotype in this tissue, and the hyalectin versican is highly expressed in the ECM of precartilage mesenchymal cells and developing synovial joints. Although several in vitro studies have been conducted in an attempt to address versican's role during limb mesenchymal condensation, factors such as differences in cell density in culture, variations between chondrogenic cell lines, and the inability to prolong the viability of limb explants have led to conflicting data, mandating an in vivo analysis. By using a morpholino directed strategy in ovo, we performed knock-down of versican expression in the presumptive ulnar region of the developing chick wing at time points critical to skeletogenesis. These data indicate that in ovo misexpression of versican compromised mesenchymal condensation with resulting ulnar cartilages reduced in length distally by an average of 53% relative to contralateral control limbs. In select versican morphants the olecranon process was also reduced in size proximally and failed to cup the humerus, likely impairing joint morphogenesis. This study represents the first report assessing the role of versican in the developing chick limb in ovo, further demonstrating the importance of versican proteoglycan expression during chondrogenesis and extending previous findings to suggest a role for versican during synovial joint development.

Axonin-1/TAG-1 is required for pathfinding of granule cell axons in the developing cerebellum

BACKGROUND

Neural development consists of a series of steps, including neurogenesis, patterning, cell migration, axon guidance, and finally, synaptogenesis. Because all these steps proceed in a constantly changing environment, functional gene analyses during development have to take time into account. This is quite challenging, however, as loss-of-function approaches based on classic genetic tools do not allow for the precise temporal control that is required for developmental studies. Gene silencing by RNA interference (RNAi) in combination with the chicken embryo or with cultured embryos opens new possibilities for functional gene analysis in vivo. Axonin-1/TAG-1 is a cell adhesion molecule of the immunoglobulin superfamily with a well defined temporal and spatial expression pattern in the developing vertebrate nervous system. Axonin-1/TAG-1 was shown to promote neurite outgrowth in vitro and to be required for commissural and sensory axon pathfinding in vivo.

RESULTS

To knock down axonin-1 in a temporally and spatially controlled manner during development of the nervous system, we have combined RNAi with the accessibility of the chicken embryo even at late stages of development. Using ex ovo RNAi, we analyzed the function of axonin-1/TAG-1 in cerebellar development. Axonin-1 is expressed in postmitotic granule cells while they extend their processes, the parallel fibers. In the absence of axonin-1 these processes still extend but no longer in a parallel manner to each other or to the pial surface of the cerebellum.

CONCLUSION

Axonin-1/TAG-1 is required for the navigation, but not for the elongation, of granule cell processes in the developing cerebellum in vivo.

Gain- and loss-of-function approaches in the chick embryo

The chicken embryo has been used as a classical embryological model for studying developmental events because of its ready availability, similarity to the human embryos, and amenability to embryological and surgical manipulations. With the arrival of the molecular era, however, avian embryos presented distinct experimental limitations, largely because of the difficulty of performing targeted mutagenesis or transgenic studies. However, in the last decade and a half, a number of new methods for transient transgenesis have been developed that allow efficient alteration of gene function during early embryonic development. These techniques have made it possible to study the effects of gene inactivation or overexpression on downstream transcriptional regulation as well as on embryonic derivatives. This, together with sequencing of the chicken genome, has allowed the chicken embryo to enter the genomic era. While attempts to establish germ line transgenesis are ongoing, methods for rapid, transient spatiotemporally targeted gene alterations have thus again re-established the chick embryo as an important experimental niche by making it possible to apply genetics in concert with classical embryological techniques. This provides a unique tool to explore the role of developmentally important genes (Ishii and Mikawa, 2005; Itasaki et al., 1999; Krull, 2004; Ogura, 2002; Swartz et al., 2001). Transient transfection methods have allowed for efficient mis- and overexpression of transgenes. For long-term analyses, retrovirally mediated gene transfer has particular advantage. For short-term experiments, electroporation and adenoviral-mediated gene transfer methods provide transient expression, largely because of the short persistence time of the transgene within the cell. More recently, Tol2 transposon-mediated constructs have been employed, allowing for integration into the genome and prolonged expression of the transgene (Sato et al., 2007), see Chapter 14 by Takahashi et al., this volume). These methods today are routinely used for gain-of-function analysis, to overexpress or ectopically express genes of interest (Arber et al., 1999; Barembaum and Bronner-Fraser, 2007; Bel-Vialar et al., 2002). Loss-of-function experiments are also possible using electroporation of dominant-negative constructs that act as competitive inhibitors (Bel-Vialar et al., 2002; Renzi et al., 2000; Suzuki-Hirano et al., 2005), morpholino antisense oligos (Basch et al., 2006; Kos et al., 2001; Sheng et al., 2003) that block translation or splicing, or constructs expressing small interfering or small hairpin RNAs (siRNAs or shRNAs) (Chesnutt and Niswander, 2004; Das et al., 2006; Katahira and Nakamura, 2003). Electroporation as the most popular method of the transient transfection into the chick embryos. Electroporation of chicken embryos involves application of an electric field to the exposed tissue that transiently disrupts the stability of the cell plasma membrane, creating reversible pores through which nucleic acids or their analogues can be readily transported into the cytosol. The use of this method for transfection into the vertebrate embryos has been facilitated by adapting the voltage parameters and the type and the duration of the electric pulse. By applying several successive square pulses at a very low voltage, with long rest periods in between, one can successfully deliver a DNA construct or another small charged particle into the cytoplasm, with minimal cell death, high efficiency of the uptake and good embryonic survival rate. The size limit of the DNA molecule that can be transfected in such a way is not yet known, though it is more likely that the size limitation in this procedure (if any) lies within the practical problems of cloning large fragments into the plasmid. We routinely overexpress constructs containing 3-4 kb inserts and coharboring a GFP or RFP reporter whose translation is initiated from an internal ribosomal entry site (IRES), thus allowing easy detection of the electroporated cells.

Electroporation of cDNA/Morpholinos to targeted areas of embryonic CNS in Xenopus

Background

Blastomere injection of mRNA or antisense oligonucleotides has proven effective in analyzing early gene function in Xenopus. However, functional analysis of genes involved in neuronal differentiation and axon pathfinding by this method is often hampered by earlier function of these genes during development. Therefore, fine spatio-temporal control of over-expression or knock-down approaches is required to specifically address the role of a given gene in these processes.

Results

We describe here an electroporation procedure that can be used with high efficiency and low toxicity for targeting DNA and antisense morpholino oligonucleotides (MOs) into spatially restricted regions of the Xenopus CNS at a critical time-window of development (22–50 hour post-fertilization) when axonal tracts are first forming. The approach relies on the design of "electroporation chambers" that enable reproducible positioning of fixed-spaced electrodes coupled with accurate DNA/MO injection. Simple adjustments can be made to the electroporation chamber to suit the shape of different aged embryos and to alter the size and location of the targeted region. This procedure can be used to electroporate separate regions of the CNS in the same embryo allowing separate manipulation of growing axons and their intermediate and final targets in the brain.

Conclusion

Our study demonstrates that electroporation can be used as a versatile tool to investigate molecular pathways involved in axon extension during Xenopus embryogenesis. Electroporation enables gain or loss of function studies to be performed with easy monitoring of electroporated cells. Double-targeted transfection provides a unique opportunity to monitor axon-target interaction in vivo. Finally, electroporated embryos represent a valuable source of MO-loaded or DNA transfected cells for in vitro analysis. The technique has broad applications as it can be tailored easily to other developing organ systems and to other organisms by making simple adjustments to the electroporation chamber.

Electroporation: an arsenal of application

Electroporation is a way to induce nanometersized membrane pore for exogenous substances delivery into cytoplasm using an artificial electric field. Now it was widely used for molecules transfer especially in molecular experiments and genetic aspects. In recent years, modern electroporation on the embryo was developed, whose most important point is that it adopts low energy and rectangular pulse that could obtain high transfection efficiency and low damage to the embryo. This paper reviewed on the pool of application: from lab works to human clinical treatments.

Regionalized cadherin-7 expression by radial glia is regulated by Shh and Pax7 during chicken spinal cord development

During development, several genes that specify neuronal subtype identity are expressed in distinct dorsoventral domains of the spinal cord and hindbrain. Cadherin-7 (Cad7), a member of the cadherin family of adhesion molecules, is expressed by radial glia in a dorsal domain of the spinal cord basal plate in chicken. To study the regulation of the Cad7 gene, we ectopically expressed two known dorsoventral patterning genes, Shh and Pax7, in the caudal neural tube and in two brain regions at different stages of development by in vivo electroporation. Results showed that Shh regulated the expression of Cad7 by radial glia in a concentration-dependent manner. Shh induced or repressed the expression of Cad7, at low and high concentrations, respectively. Furthermore, Pax7 inhibited the expression of Cad7. These results are compatible with a role of Shh and Pax7 in regulating endogenous Cad7 expression during spinal cord and hindbrain development. Our data show, for the first time, that Shh can regulate the expression not only of other gene regulatory factors, but also of Cad7, a morphoregulatory molecule that plays a role in axon elongation and neural circuit formation.