We are grateful to R. Guti&#233;rrez and A. Morales for their excellent technical assistance and to L. A. Weiss for editing. C.G.B. is funded by the Spanish Ministerio de Ciencia e Innovaci&#243;n (MICINN), FPI-BES-2012-056011. This work was funded by a grant from BBVA Foundation and SAF2014-58598-JIN (MINECO) to M. Navarrete and by a grant from the Ram&#243;n Areces Foundation and grants SAF2014-52119-R and BFU2014-55738-REDT (from MINECO) to M. Nieto.

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The authors declare no conflicts of interest.

This protocol describes in detail how to label neurons of the somatosensory cortex of C75BL/6 mice in order to analyze their connectivity and their excitability. With respect to existing methods, it visualizes discriminating aspects of connectivity, such as the number of axonal branches per neuron, their precise topography, and their anatomical location. By altering the position of the electrodes, it is possible to target other neuron populations, such as the cingulate cortex (keep the same angle between the electrodes a...

The development of dendritic and axonal structures is an important facet of circuit regulation in the nervous system, including in the cerebral cortex. It plays a critical role during the selective wiring of the diverse neuronal subpopulations. A number of recent reports have shown that, in addition to connectivity, the molecular diversity of neurons is reflected by the acquisition of highly specific modes of firing. However, the mechanisms determining the excitability and connectivity of the distinct neuronal subtypes during development, as well as their degree of coordination, are still poorly understood1,2.
In vivo loss- and gain-of-function analyses allow for the study of the relationship between the expression level of specific genes and their influence in the development of the circuit. In utero electroporation (IUE) is a technique widely used to study the function of a gene of interest in specific neuronal populations and to study the overall patterns of their connectivity. However, to determine the morphological characteristics of axons and dendrites in cortical layers in living mice, it is essential to label neurons sparsely. A Cre recombination system combined with IUE can be used to mark a sparse population of neurons at a sufficiently low density to resolve the projections emitted by individual cells of the identified cortical laminas. This method labels a sufficient number of neurons per cortex to obtain quantitative data after the analysis of reasonable numbers of electroporated brains (Figure 1). This manuscript presents a method for such fine analysis of connectivity. It also presents a similar strategy to analyze, in separate experiments, the electrical properties of neurons by performing current-clamp recordings on green fluorescence protein (GFP)-electroporated cells from acute cortical slices. These protocols are versatile and can be applied to the study of the excitability and connectivity of neurons of WT and transgenic animals, and also of neurons in which losses and gains of function are introduced by additional plasmids during IUE.
Although this protocol describes the electroporation of mice at embryonic day (E)15.5, this technique can be performed at any age between E9.53 and postnatal day (P)24. While electroporation at early stages targets neurons and precursors of the thalamus and deep layers of the cortex, later-stage electroporation marks more superficial layers (e.g., E15.5 IUE targets layer II-III neurons). In summary, the combination of IUE with single-cell morphological analysis and electrophysiology is a useful tool to elucidate the molecular mechanisms underlying the enormous structural and functional diversity of neurons in the nervous system.

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in utero electroporation approaches to study the excitability of neuronal subpopulations and single-cell connectivity

The nervous system is composed of an enormous range of distinct neuronal types. These neuronal subpopulations are characterized by, among other features, their distinct dendritic morphologies, their specific patterns of axonal connectivity, and their selective firing responses. The molecular and cellular mechanisms responsible for these aspects of differentiation during development are still poorly understood.
Here, we describe combined protocols for labeling and characterizing the structural connectivity and excitability of cortical neurons. Modification of the in utero electroporation (IUE) protocol allows the labeling of a sparse population of neurons. This, in turn, enables the identification and tracking of the dendrites and axons of individual neurons, the precise characterization of the laminar location of axonal projections, and morphometric analysis. IUE can also be used to investigate changes in the excitability of wild-type (WT) or genetically modified neurons by combining it with whole-cell recording from acute slices of electroporated brains. These two techniques contribute to a better understanding of the coupling of structural and functional connectivity and of the molecular mechanisms controlling neuronal diversity during development. These developmental processes have important implications on axonal wiring, the functional diversity of neurons, and the biology of cognitive disorders.

To characterize the morphological changes of neurons in detail and throughout development, it is essential to label neurons sparsely. A Cre-recombinase diluted system allows for the expression of a gene of interest in a sparse population of neurons, so that only those neurons that incorporate this enzyme express GFP (Figure 1A). Using this strategy, layer II-III is targeted and labeled by IUE at E15.5. CAG-DsRed2 at 1 &#181;g/&#181;L, is co-electroporated as a control and...

Watch this Scientific Journal Video about In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity at JoVE.com

In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

This manuscript provides protocols that use in utero electroporation (IUE) to describe the structural connectivity of neurons at the single-cell level and the excitability of fluorescently labeled neurons. Histology is used to characterize dendritic and axonal projections. Whole-cell recording in acute slices is used to investigate excitability.

In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

The nervous system is composed of an enormous range of distinct neuronal types. These neuronal subpopulations are characterized by, among other features, ...

in-utero-electroporation-approaches-to-study-excitability-neuronal

Research

JoVE Journal

Neuroscience

9.6K Views.  Centro Nacional de Biotecnología (CNB-CSIC).  Dit manuscript biedt protocollen die gebruik maken van in de baarmoeder elektroporatie (IUE) om de structurele connectiviteit van neuronen te beschrijven op het single-cell niveau en de prikkelbaarheid van fluorescent gelabelde neuronen. Histologie wordt gebruikt dendritische en axonale uitsteeksels karakteriseren. Whole-cell opname in acute plakjes wordt gebruikt om prikkelbaarheid te onderzoeken. 

Video: In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

In utero Electroporation followed by Primary Neuronal Culture for Studying Gene Function in Subset of Cortical Neurons

In vitro study of primary neuronal cultures allows for quantitative analyses of neurite outgrowth. In order to study how genetic alterations affect neuronal process outgrowth, shRNA or cDNA constructs can be introduced into primary neurons via chemical transfection or viral transduction. However, with primary cortical cells, a heterogeneous pool of cell types (glutamatergic neurons from different layers, inhibitory neurons, glial cells) are transfected using these methods. The use of in utero electroporation to introduce DNA constructs in the embryonic rodent cortex allows for certain subsets of cells to be targeted: while electroporation of early embryonic cortex targets deep layers of the cortex, electroporation at late embryonic timepoints targets more superficial layers. Further, differential placement of electrodes across the heads of individual embryos results in the targeting of dorsal-medial versus ventral-lateral regions of the cortex. Following electroporation, transfected cells can be dissected out, dissociated, and plated in vitro for quantitative analysis of neurite outgrowth. Here, we provide a step-by-step method to quantitatively measure neuronal process outgrowth in subsets of cortical cells.
The basic protocol for in utero electroporation has been described in detail in two other JoVE articles from the Kriegstein lab 1, 2. We will provide an overview of our protocol for in utero electroporation, focusing on the most important details, followed by a description of our protocol that applies in utero electroporation to the study of gene function in neuronal process outgrowth.

In utero Electroporation followed by Primary Neuronal Culture for Studying Gene Function in Subset of Cortical Neurons

In utero electroporation is a valuable method for transfecting neuronal progenitor cells in vivo. Depending upon the placement of the electrodes and the developmental timepoint of electroporation, certain subsets of cortical cells can be targeted. Targeted cells can then be analyzed in vivo or in vitro for effects of genetic alteration.

In vitro study of primary neuronal cultures allows for quantitative analyses of neurite outgrowth. In order to study how genetic alterations affect ...

Efficient Gene Delivery into Multiple CNS Territories Using In Utero Electroporation

The ability to manipulate gene expression is the cornerstone of modern day experimental embryology, leading to the elucidation of multiple developmental pathways. Several powerful and well established transgenic technologies are available to manipulate gene expression levels in mouse, allowing for the generation of both loss- and gain-of-function models. However, the generation of mouse transgenics is both costly and time consuming. Alternative methods of gene manipulation have therefore been widely sought. In utero electroporation is a method of gene delivery into live mouse embryos1,2 that we have successfully adapted3,4. It is largely based on the success of in ovo electroporation technologies that are commonly used in chick5. Briefly, DNA is injected into the open ventricles of the developing brain and the application of an electrical current causes the formation of transient pores in cell membranes, allowing for the uptake of DNA into the cell. In our hands, embryos can be efficiently electroporated as early as embryonic day (E) 11.5, while the targeting of younger embryos would require an ultrasound-guided microinjection protocol, as previously described6. Conversely, E15.5 is the latest stage we can easily electroporate, due to the onset of parietal and frontal bone differentiation, which hampers microinjection into the brain. In contrast, the retina is accessible through the end of embryogenesis. Embryos can be collected at any time point throughout the embryonic or early postnatal period. Injection of a reporter construct facilitates the identification of transfected cells.
To date, in utero electroporation has been most widely used for the analysis of neocortical development1,2,3,4. More recent studies have targeted the embryonic retina7,8,9 and thalamus10,11,12. Here, we present a modified in utero electroporation protocol that can be easily adapted to target different domains of the embryonic CNS. We provide evidence that by using this technique, we can target the embryonic telencephalon, diencephalon and retina. Representative results are presented, first showing the use of this technique to introduce DNA expression constructs into the lateral ventricles, allowing us to monitor progenitor maturation, differentiation and migration in the embryonic telencephalon. We also show that this technique can be used to target DNA to the diencephalic territories surrounding the 3rd ventricle, allowing the migratory routes of differentiating neurons into diencephalic nuclei to be monitored. Finally, we show that the use of micromanipulators allows us to accurately introduce DNA constructs into small target areas, including the subretinal space, allowing us to analyse the effects of manipulating gene expression on retinal development.

Efficient Gene Delivery into Multiple CNS Territories Using In Utero Electroporation

In utero electroporation allows for rapid gene delivery in a spatially- and temporally-controlled manner in the developing central nervous system (CNS). Here we describe a highly adaptable in utero electroporation protocol that can be used to deliver expression constructs into multiple embryonic CNS domains, including the telencephalon, diencephalon and retina.

The ability to manipulate gene expression is the cornerstone of modern day experimental embryology, leading to the elucidation of multiple developmental ...

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date this tool has been widely used to study the regulation of cellular proliferation, differentiation and neuronal migration especially in the developing cerebral cortex 6-8. Here we detail our protocol to electroporate in utero the cerebral cortex and the hippocampus and provide evidence that this approach can be used to study dendrites and spines in these two cerebral regions.
Visualization and manipulation of neurons in primary cultures have contributed to a better understanding of the processes involved in dendrite, spine and synapse development. However neurons growing in vitro are not exposed to all the physiological cues that can affect dendrite and/or spine formation and maintenance during normal development. Our knowledge of dendrite and spine structures in vivo in wild-type or mutant mice comes mostly from observations using the Golgi-Cox method 9. However, Golgi staining is considered to be unpredictable. Indeed, groups of nerve cells and fiber tracts are labeled randomly, with particular areas often appearing completely stained while adjacent areas are devoid of staining. Recent studies have shown that IUE of fluorescent constructs represents an attractive alternative method to study dendrites, spines as well as synapses in mutant / wild-type mice 10-11 (Figure 1A). Moreover in comparison to the generation of mouse knockouts, IUE represents a rapid approach to perform gain and loss of function studies in specific population of cells during a specific time window. In addition, IUE has been successfully used with inducible gene expression or inducible RNAi approaches to refine the temporal control over the expression of a gene or shRNA 12. These advantages of IUE have thus opened new dimensions to study the effect of gene expression/suppression on dendrites and spines not only in specific cerebral structures (Figure 1B) but also at a specific time point of development (Figure 1C).
Finally, IUE provides a useful tool to identify functional interactions between genes involved in dendrite, spine and/or synapse development. Indeed, in contrast to other gene transfer methods such as virus, it is straightforward to combine multiple RNAi or transgenes in the same population of cells. 
In summary, IUE is a powerful method that has already contributed to the characterization of molecular mechanisms underlying brain function and disease and it should also be useful in the study of dendrites and spines.

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

This article describes in detail a protocol to electroporate in utero the cerebral cortex and the hippocampus at E14.5 in mice. We also show that this is a valuable method to study dendrites and spines in these two cerebral regions.

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date ...

In utero and ex vivo Electroporation for Gene Expression in Mouse Retinal Ganglion Cells

The retina and its sole output neuron, the retinal ganglion cell (RGC), comprise an excellent model in which to examine biological questions such as cell differentiation, axon guidance, retinotopic organization and synapse formation[1]. One drawback is the inability to efficiently and reliably manipulate gene expression in RGCs in vivo, especially in the otherwise accessible murine visual pathways. Transgenic mice can be used to manipulate gene expression, but this approach is often expensive, time consuming, and can produce unwanted side effects. In chick, in ovo electroporation is used to manipulate gene expression in RGCs for examining retina and RGC development. Although similar electroporation techniques have been developed in neonatal mouse pups[2], adult rats[3], and embryonic murine retinae in vitro[4], none of these strategies allow full characterization of RGC development and axon projections in vivo. To this end, we have developed two applications of electroporation, one in utero and the other ex vivo, to specifically target embryonic murine RGCs[5, 6]. 
With in utero retinal electroporation, we can misexpress or downregulate specific genes in RGCs and follow their axon projections through the visual pathways in vivo, allowing examination of guidance decisions at intermediate targets, such as the optic chiasm, or at target regions, such as the lateral geniculate nucleus. Perturbing gene expression in a subset of RGCs in an otherwise wild-type background facilitates an understanding of gene function throughout the retinal pathway. Additionally, we have developed a companion technique for analyzing RGC axon growth in vitro. We electroporate embryonic heads ex vivo, collect and incubate the whole retina, then prepare explants from these retinae several days later. Retinal explants can be used in a variety of in vitro assays in order to examine the response of electroporated RGC axons to guidance cues or other factors. In sum, this set of techniques enhances our ability to misexpress or downregulate genes in RGCs and should greatly aid studies examining RGC development and axon projections.

In utero and ex vivo Electroporation for Gene Expression in Mouse Retinal Ganglion Cells

Here we present two techniques for manipulating gene expression in murine retinal ganglion cells (RGCs) by in utero and ex vivo electroporation. These techniques enable one to examine how alterations in gene expression affect RGC development, axon guidance, and functional properties.

The retina and its sole output neuron, the retinal ganglion cell (RGC), comprise an excellent model in which to examine biological questions such as cell ...

Biology

Ex utero Electroporation and Whole Hemisphere Explants: A Simple Experimental Method for Studies of Early Cortical Development

Cortical development involves complex interactions between neurons and non-neuronal elements including precursor cells, blood vessels, meninges and associated extracellular matrix. Because they provide a suitable organotypic environment, cortical slice explants are often used to investigate those interactions that control neuronal differentiation and development. Although beneficial, the slice explant model can suffer from drawbacks including aberrant cellular lamination and migration. Here we report a whole cerebral hemisphere explant system for studies of early cortical development that is easier to prepare than cortical slices and shows consistent organotypic migration and lamination. In this model system, early lamination and migration patterns proceed normally for a period of two days in vitro, including the period of preplate splitting, during which prospective cortical layer six forms. We then developed an ex utero electroporation (EUEP) approach that achieves ~80% success in targeting GFP expression to neurons developing in the dorsal medial cortex.
The whole hemisphere explant model makes early cortical development accessible for electroporation, pharmacological intervention and live imaging approaches. This method avoids the survival surgery required of in utero electroporation (IUEP) approaches while improving both transfection and areal targeting consistency. This method will facilitate experimental studies of neuronal proliferation, migration and differentiation.

Ex utero Electroporation and Whole Hemisphere Explants: A Simple Experimental Method for Studies of Early Cortical Development

This protocol describes an improved explant procedure that involves ex utero electroporation, dissection and culture of entire cerebral hemispheres from the embryonic mouse. The preparation facilitates pharmacological studies and assays of gene function during early cortical development.

Cortical development involves complex interactions between neurons and non-neuronal elements including precursor cells, blood vessels, meninges and ...

Subtype-selective Electroporation of Cortical Interneurons

The study of central nervous system (CNS) maturation relies on genetic targeting of neuronal populations. However, the task of restricting the expression of genes of interest to specific neuronal subtypes has proven remarkably challenging due to the relative scarcity of specific promoter elements. GABAergic interneurons constitute a neuronal population with extensive genetic and morphological diversity. Indeed, more than 11 different subtypes of GABAergic interneurons have been characterized in the mouse cortex1. Here we present an adapted protocol for selective targeting of GABAergic populations. We achieved subtype selective targeting of GABAergic interneurons by using the enhancer element of the homeobox transcription factors Dlx5 and Dlx6, homologues of the Drosophila distal-less (Dll) gene2,3, to drive the expression of specific genes through in utero electroporation.

This procedure shows how to target interneurons in the developing mouse forebrain by means of in utero electroporation. This technique was particularly efficient to achieve selective gene expression in interneuron subtypes destined to the superficial layers of the cortex.

The study of central nervous system (CNS) maturation relies on genetic targeting of neuronal populations. However, the task of restricting the expression ...

Ex Utero Electroporation and Organotypic Slice Cultures of Embryonic Mouse Brains for Live-Imaging of Migrating GABAergic Interneurons

GABAergic interneurons (INs) are critical components of neuronal networks that drive cognition and behavior. INs destined to populate the cortex migrate tangentially from their place of origin in the ventral telencephalon (including from the medial and caudal ganglionic eminences (MGE, CGE)) to the dorsal cortical plate in response to a variety of intrinsic and extrinsic cues. Different methodologies have been developed over the years to genetically manipulate specific pathways and investigate how they regulate the dynamic cytoskeletal changes required for proper IN migration. In utero electroporation has been extensively used to study the effect of gene repression or overexpression in specific IN subtypes while assessing the impact on morphology and final position. However, while this approach is readily used to modify radially migrating pyramidal cells, it is more technically challenging when targeting INs. In utero electroporation generates a low yield given the decreased survival rates of pups when electroporation is conducted before e14.5, as is customary when studying MGE-derived INs. In an alternative approach, MGE explants provide easy access to the MGE and facilitate the imaging of genetically modified INs. However, in these explants, INs migrate into an artificial matrix, devoid of endogenous guidance cues and thalamic inputs. This prompted us to optimize a method where INs can migrate in a more naturalistic environment, while circumventing the technical challenges of in utero approaches. In this paper, we describe the combination of ex utero electroporation of embryonic mouse brains followed by organotypic slice cultures to readily track, image and reconstruct genetically modified INs migrating along their natural paths in response to endogenous cues. This approach allows for both the quantification of the dynamic aspects of IN migration with time-lapse confocal imaging, as well as the detailed analysis of various morphological parameters using neuronal reconstructions on fixed immunolabeled tissue.

Ex Utero Electroporation and Organotypic Slice Cultures of Embryonic Mouse Brains for Live-Imaging of Migrating GABAergic Interneurons

Here, we provide a low-cost and reliable method to generate electroporated brain organotypic slice cultures from mouse embryos suitable for confocal microscopy and live-imaging techniques.

GABAergic interneurons (INs) are critical components of neuronal networks that drive cognition and behavior. INs destined to populate the cortex migrate ...

Double In Utero Electroporation to Target Temporally and Spatially Separated Cell Populations

In utero electroporation is an in vivo DNA transfer technique extensively used to study the molecular and cellular mechanisms underlying mammalian corticogenesis. This procedure takes advantage of the brain ventricles to allow the introduction of DNA of interest and uses a pair of electrodes to direct the entrance of the genetic material into the cells lining the ventricle, the neural stem cells. This method allows researchers to label the desired cells and/or manipulate the expression of genes of interest in those cells. It has multiple applications, including assays targeting neuronal migration, lineage tracing, and axonal pathfinding. An important feature of this method is its temporal and regional control, allowing circumvention of potential problems related with embryonic lethality or the lack of specific CRE driver mice. Another relevant aspect of this technique is that it helps to considerably reduce the economic and temporal limitations that involve the generation of new mouse lines, which become particularly important in the study of interactions between cell types that originate in distant areas of the brain at different developmental ages. Here we describe a double electroporation strategy that enables targeting of cell populations that are spatially and temporally separated. With this approach we can label different subtypes of cells in different locations with selected fluorescent proteins to visualize them, and/or we can manipulate genes of interest expressed by these different cells at the appropriate times. This strategy enhances the potential of in utero electroporation and provides a powerful tool to study the behavior of temporally and spatially separated cell populations that migrate to establish close contacts, as well as long-range interactions through axonal projections, reducing temporal and economic costs.

Double in utero electroporation allows targeting cell populations that are spatially and temporally separated. This technique is useful to visualize interactions between those cell populations using fluorescent proteins in normal conditions but also after functional experiments to perturb genes of interest.

In utero electroporation is an in vivo DNA transfer technique extensively used to study the molecular and cellular mechanisms underlying mammalian ...

In Vivo Targeting of Neural Progenitor Cells in Ferret Neocortex by In Utero Electroporation

Manipulation of gene expression in vivo during embryonic development is the method of choice when analyzing the role of individual genes during mammalian development. In utero electroporation is a key technique for the manipulation of gene expression in the embryonic mammalian brain in vivo. A protocol for in utero electroporation of the embryonic neocortex of ferrets, a small carnivore, is presented here. The ferret is increasingly being used as a model for neocortex development, because its neocortex exhibits a series of anatomical, histological, cellular, and molecular features that are also present in human and nonhuman primates, but absent in rodent models, such as mouse or rat. In utero electroporation was performed at embryonic day (E) 33, a midneurogenesis stage in ferret. In utero electroporation targets neural progenitor cells lining the lateral ventricles of the brain. During neurogenesis, these progenitor cells give rise to all other neural cell types. This work shows representative results and analyses at E37, postnatal day (P) 1, and P16, corresponding to 4, 9, and 24 days after in utero electroporation, respectively. At earlier stages, the progeny of targeted cells consists mainly of various neural progenitor subtypes, whereas at later stages most labeled cells are postmitotic neurons. Thus, in utero electroporation enables the study of the effect of genetic manipulation on the cellular and molecular features of various types of neural cells. Through its effect on various cell populations, in utero electroporation can also be used for the manipulation of histological and anatomical features of the ferret neocortex. Importantly, all these effects are acute and are performed with a spatiotemporal specificity determined by the user.

Presented here is a protocol to perform genetic manipulation in the embryonic ferret brain using in utero electroporation. This method allows for targeting of neural progenitor cells in the neocortex in vivo.

Manipulation of gene expression in vivo during embryonic development is the method of choice when analyzing the role of individual genes during mammalian ...

Murine In Utero Electroporation

In utero electroporation is an important technique for studying the molecular mechanisms that guide the proliferation, differentiation, migration, and maturation of cells during neural development. Electroporation enables the rapid and targeted delivery of material into cells by utilizing electrical pulses to create transient pores in cell membranes. Although electroporation has traditionally been used in in vitro studies, scientific advancements have now broadened its utilization to intact organs, such as those found in mouse embryos developing in utero. This video will introduce the key principles behind in utero electroporation in addition to reviewing the basic surgical techniques required to access developing embryos within a pregnant rodent. Details of the injection and electroporation steps are provided along with important considerations for directing gene delivery to specific brain regions. Finally, neurobiological applications of in utero electroporation are presented, such as investigating how specific genes contribute to neural development and how connections form between developing neurons.

Murine In Utero Electroporation

In utero electroporation is an important technique for studying the molecular mechanisms that guide the proliferation, differentiation, migration, and ...

In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

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