This work was funded by the German Research Foundation (Deutsche Forschungsgemeinschaft).

1. Preparation of DNA and Glass Micropipettes for Injection
<ol>
	<li>Good quality glass micropipettes are essential to reduce initial high abortion rate due to loss of amniotic fluid. The procedure to pull glass micropipettes has been well documented13,18,25. Use 1.2 mm diameter capillaries pulled in a conventional Sutter P-97 device with the settings P=500; Heat=300; Pull=40; Velocity=50; Time=50. Fit the puller with 3 mm "trough" filaments (Sutter Instrument FT330B). The 2 mm size filaments have yielded for us less satisfactory results. On the other hand, beveling of the micropipette tips does not seem to improve results for us.</li>
	<li>Dissolve purified, endotoxin-free plasmid DNA in PBS (Cell Culture Grade) containing 0.1% Fast Green to a final concentration of 1 to 2 &mu;g/&mu;l. The Fast Green will make the injected solution visible in the embryonic brain ventricle.</li>
	<li>Load 10 &mu;l of the DNA solution into the glass micropipette.</li>
	<li>Connect the glass micropipette to the injection system (Pico Pump) or mouth pipette.</li>
</ol>
2. Anesthesia
Prepare the surgical table with a heating pad and the surgical instruments. Turn on the cold-light sources to facilitate the visualization of the embryos. Disinfect the surgical tools using for instance a glass bead sterilizer.
Three different anesthesia procedures are possible for this protocol (see Discussion). Here we will describe the one we consider the best, using isoflurane inhalation for anesthesia induction (flow rate 0.5 L/min) as well as maintenance (flow rate 1 L/min).
<ol>
	<li>Introduce the pregnant mouse in a small transparent (so the mouse remains visible) container connected to the Komesaroff Mark 5 Anesthetic Device by a short length of tubing.</li>
	<li>Fill the vaporizer with isoflurane, then open the oxygen bottle attached to the device. Blow one or two pulses of isoflurane/oxygen (0.5 L/min) into the container holding the mouse and watch for narcosis to set in.</li>
	<li>Take the mouse out, cover its eyes with ointment to prevent them from drying and fit the flow anesthesia mask on its head immediately.</li>
</ol>
3. Laparotomy
<ol>
	<li>Place the mouse belly up on the heating pad (otherwise its body temperature will go down very fast, decreasing chances of recovery) and secure its body into place by fixing its four legs to the sides with tape. Assess the depth of anesthesia by checking for loss of response to reflex stimulation (e.g. toe or tail pinch with firm pressure).</li>
	<li>Shave the abdominal surface and disinfect it with the iodophorpovidone-iodine (Braunoderm).</li>
	<li>Make a longitudinal incision (1 to 1.5 cm long) on the abdominal skin. Then cut the peritoneum. Place cotton gauze around the incision. Make one uterine horn visible and pull it out carefully with blunt forceps onto the PBS-rinsed gauze. Rinse the uterus with PBS very often to keep it always moistened (Figures 2A and 2B). During the entire procedure avoid pulling the mesometrium or the uterus tight, since high pressure inside the uterus will transmit to the embryo increasing the chances of loss of fluid upon injection resulting in abortion.</li>
</ol>
4. DNA Injection into the Brain Ventricle
<ol>
	<li>Hold the uterus in such a way that the brain ventricles can be visualized. Do not extensively reposition an embryo that lies in an unfavorable position - this only increases the chances of abortion.</li>
	<li>Looking at the embryo's head from top, localize visually the gap or fissure between the left and right cortical hemispheres. The hemispheres are easy to distinguish and the lateral ventricles inside them (not to be targeted) can usually be perceived as somewhat darker shapes. If an embryo is found to be perfectly oriented for DNA injection (Figures 2C and 2D), it is possible to pierce the uterine wall and enter the third ventricle at once. Hold the glass micropipette at 45&deg; to the uterine wall and puncture it at the rostral end of the gap between cortical hemispheres, penetrating for about 1 mm. In this way the tip of the glass micropipette will enter the third ventricle of the brain (not the lateral ventricle) (Figures 2C and 2D). In embryos less favorably oriented it is useful to first pierce the uterine wall (always at 45&deg;) in the vicinity of the embryonic head, place the micropipette tip in the right position between the cortical hemispheres and only then perforate the brain. Inject about 1 &mu;l of DNA solution into the third ventricle (a good injection fills the ventricle with green fluid). Repeat the same procedure with all embryos of one uterus horn. This allows some time for the DNA solution to mix evenly with the ventricular fluid and reach the entire neuroepithelium.</li>
</ol>
5. Targeting the Hypothalamus for Electroporation
<ol>
	<li>Switch the electroporator on and adjust settings according to the embryonic age (for E12.5 we use 5 square-wave pulses, 50 V, 50 msec ON/950 msec OFF). Use as positive pole the stainless steel needle electrode (CUY550-10) and as negative pole a round flat electrode (CUY700P4L). (It is important that the electrodes are smaller than the embryo, since otherwise the current just flows around the embryo but not through it.)</li>
	<li>Select for electroporation those embryos whose dorsal side is up (i.e. turned towards the experimenter) (as most of them are), and discard those whose orientation is not favorable. It is now safe to touch the uterus with ethanol-disinfected fingers or with gloves. Holding the uterus with forceps, however, would interfere with the flow of current during electroporation.</li>
	<li>Pierce the uterine wall by the embryo's head between the amniotic sac and the placenta by thrusting downwards through it with the tip of the needle electrode. Use the index finger of the other hand as thrust block. About 5 mm of the electrode tip must be now between the amniotic sac and the uterine wall, at about the level of the midbrain (Figures 2E and 2F). Remember that this is the "targeting electrode", so its position will determine which part of the hypothalamic neuroepithelium is most likely to get transfected. The embryo has to be very gently "squeezed" between the electrodes.</li>
	<li>With the other hand, position the round flat electrode outside of the uterus wall on the opposite side of the embryo's head (Figures 2E and 2G).</li>
	<li>Use the pedal switch to apply voltage (50 V, 50 msec ON, 950 msec OFF, 5 square-wave pulses).</li>
	<li>Slowly pull the needle electrode out of the uterus while holding back the uterus with the index finger of the other hand - if amniotic liquid is lost through the punctured wall, usually the embryo will undergo abortion. Repeat the procedure with all the embryos.</li>
	<li>Return the uterus horn into the abdomen and repeat the injection and electroporation in the remnant horn.</li>
</ol>
6. Finishing the Surgery
<ol>
	<li>After injection and electroporation of all embryos, place the uterus back into the abdomen very carefully, positioned exactly as they were before and moist the peritoneal cavity with saline before closing it.</li>
	<li>Suture the peritoneum with surgical catgut (Vicryl Polyglactin 910, 5-0, Ethicon V4914). For the closure of the skin use "interrupted stitch" methodwith a more resistant suture (Supramid Nylon, 6-0, Serag Wiessner TO 07171L).</li>
	<li>Disinfect the abdomen surface with povidone-iodine(Braunoderm) and inject a non-steroid anti-inflammatory subcutaneously (e.g. 100 &mu;l of a 1:10 solution of Rimadyl in 0.9% NaCl) or, even better, an opioid like buprenorphine (Temgesic, 0.05 to 0.1 mg/kg body weight in 0.9% NaCl)to relieve pain.</li>
	<li>Remove the mother from the anesthetic machine and place it in a cage which is heated by a heating pad. Monitor the mouse continually until it is completely recovered from the anesthesia. Later on, check the animals daily to insure they are recovering from the procedure without any sign of infection or pain.</li>
</ol>
7. Analyzing the Results
<ol>
	<li>Harvest the embryos (or postnatals) according to the desired day of analysis. Postnatal mice (1 to 2 day old) are killed by decapitation.</li>
	<li>Separate every embryo according to the previous electroporation annotation. Dissect the brain under a stereomicroscope and check under the microscope for green fluorescent signal (from the GFP reporter) in the appropriate region.</li>
	<li>The selected brain can be analyzed "fresh": fix the tissue for a short time in 4% paraformaldehyde and embed in agarose 4% or in gelatin-albumin, then section on a vibratome-type device (Figure 3). For more detailed immunohistochemical analysis (Figure 4), cryo-protect the brain in 30% saccharose solution, embed in OCT mounting medium (Tissue Tek) then cut 20 &mu;m sections in a cryostat.</li>
</ol>

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L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+promoters+for+driving+efficient+transgene+expression+in+neonatal+porcine+islets.">Evaluation of promoters for driving efficient transgene expression in neonatal porcine islets.</a> Xenotransplantation. 14, 119-125 (2007).</li></ol>

The authors declare that they have no competing financial interests.

About the anesthesia: Since in utero electroporation into the hypothalamus can be technically arduous and require longer narcosis times, we prefer to induce and maintain anesthesia through administration of a mixture of oxygen and isoflurane. In our experience, animals can remain suitably anaesthetized in this way for periods of up to one hour at least, the recovery of the mother is very fast, and embryo survival improved. Other approaches to anesthesia are also available. The most simple procedure consis...

Genetic manipulation of the embryonic mouse brain is a preferred approach to learn about developmental regulation. The generation of mutant mouse lines however is slow and expensive. One powerful method to introduce specific genetic changes in developing neurons of the mammalian brain is in utero electroporation. Essentially, the technique consists of transfecting DNA into the embryonic brain neuroepithelium by means of electric pulses, then allowing the embryo to survive for a certain period of time, collect the brain and examine them for possible novel, informative phenotypes. In this way, the experimenter can test hypotheses almost immediately without the long waiting periods necessary for the production of mouse mutants.	
	Transfection of DNA into developing embryos started with in ovo electroporation on chick embryos1. The essential proof-of-concept for the mouse was performed in culture2. This was soon followed by the first descriptions of the technique on the mouse in utero3,4.	
	The main problem is to transfect the brain of embryos developing in utero without killing them or the mother. Learning to perform the necessary surgery (laparotomy, injection, electroporation) requires a long training period. Once the surgery has been mastered to the point where the embryo survival ratio is acceptable, the next key question is: which brain structures are accessible? Not surprisingly, the first published papers showing results obtained with in utero electroporation focused on cortical development5-9. This is still true for most of the publications using this technique, since the region of the developing mouse brain most accessible to surgical procedures is the cortex (Figure 1). The procedure for in utero electroporation into the cortex has been described in print10 and in video11-14. A modification of the technique can be used to target a ventral part of the telencephalon, the basal ganglia15.	
	Beyond the telencephalon, the diencephalon (classically divided into thalamus and hypothalamus) is a region of the forebrain more difficult to reach. A small number of papers reports targeting of its dorsal and most accessible part, the thalamus16-19.	
	The hypothalamus is the most ventral part of the forebrain, therefore the one localized most deeply from the dorsal surface (cortex) (Figure 1). This region remains a difficult challenge for researchers committed to genetically manipulate the mouse brain in utero. To our knowledge, only very few articles report on results of in utero transfection into the mouse hypothalamus 20,21. However, the functional importance of the hypothalamus cannot be overstated, since it regulates behaviors like eating and drinking, mating, breeding and parenting22. Moreover, alterations in hypothalamic development contribute to originate later in life conditions like obesity, hypertension, diabetes and precocious puberty23. Being able to alter genetically the hypothalamus during development would provide a very powerful tool to understand it.	
	The basic surgical protocol for the laparotomy of pregnant mice that we use here is similar to that used in other protocols11,13,14,24. We will describe them here briefly for completeness. Key to our procedure, on the other hand, are the type of anesthesia, the place of injection, the type of electrodes and the insertion and position of the positive electrode with respect to the embryo's head. We prefer to induce and maintain anesthesia through gas inhalation over simple intraperitoneal anesthesia, since the former allows for the somewhat longer periods of narcosis required for a difficult surgery. Isoflurane inhalation results in faster recovery from anesthesia, since usually the mother demonstrates normal behavior already minutes after the surgery. The easiest point of injection of the DNA solution with the glass micropipette is the lateral ventricle, which however is completely unsuitable for hypothalamus electroporation. Injection directly in the third ventricle is indeed crucial to target deep diencephalic structures. It is possible to transfect the hypothalamus from E12.0 or E12.5 with standard, off-the-shelf electrodes. We have found some of the electrodes manufactured by Nepa Gene (Chiba, Japan) particularly suited to this purpose.	
	With our procedure we obtain transfection of the entire hypothalamic neuroepithelium or partial, regional transfection depending on electrode orientation. Here we demonstrate the technique by transfecting the mammillary body, arguably the deepest and most recessed of all hypothalamic nuclei. Additionally, we show detailed histological analysis of the transfected cells down to the cellular level of resolution.	
	A comparison of in utero electroporation with other approaches to transfecting the mouse developing brain in utero can be found in the Discussion section.

<table border="1">
	<tbody>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>REAGENTS</td>
		</tr>
		<tr>
			<td>Acepromazine</td>
			<td>Sanofi GmbH</td>
			<td>&nbsp;</td>
			<td>anesthetic</td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Baxter</td>
			<td>HDG9623</td>
			<td>anesthetic</td>
		</tr>
		<tr>
			<td>Ketamin</td>
			<td>Pharma GmbH</td>
			<td>&nbsp;</td>
			<td>anesthetic</td>
		</tr>
		<tr>
			<td>Fast Green</td>
			<td>Fluka</td>
			<td>44715</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Rimadyl</td>
			<td>Pfizer</td>
			<td>&nbsp;</td>
			<td>non-steroidal anti-inflammatory</td>
		</tr>
		<tr>
			<td>Braunoderm</td>
			<td>Braun</td>
			<td>3887138</td>
			<td>povidone-iodine</td>
		</tr>
		<tr>
			<td>Phosphate Buffer Saline PBS</td>
			<td>Gibco</td>
			<td>14190</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Temgesic (buprenorphine)</td>
			<td>Essex Pharma</td>
			<td>&nbsp;</td>
			<td>opioid analgesic</td>
		</tr>
		<tr>
			<td>Eye Ointment</td>
			<td>Pan-Ophtal</td>
			<td>7136926</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Xylazine</td>
			<td>Bayer</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>EQUIPMENT</td>
		</tr>
		<tr>
			<td>Anaesthetic Device Komesaroff Mark-5</td>
			<td>Medical Developments Australia</td>
			<td>ACN 004 903 682</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Capillary puller P-97</td>
			<td>Sutter Instrument Co.</td>
			<td>P-97</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Compresstome</td>
			<td>Precisionary Instr.</td>
			<td>VF-300</td>
			<td>Vibratome-type device</td>
		</tr>
		<tr>
			<td>Confocal Microscope</td>
			<td>Zeiss</td>
			<td>LSM700</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Cryostat</td>
			<td>Leica</td>
			<td>CM3050S</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Electroporator</td>
			<td>Nepa Gene Co. Ltd.</td>
			<td>CUY21EDIT</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Electrode 1</td>
			<td>Nepa Gene Co. Ltd.</td>
			<td>CUY550-10</td>
			<td>Stainless Steel Needle Electrode, 10 mm-Tip, 0. 5 mm diam.</td>
		</tr>
		<tr>
			<td>Electrode 2</td>
			<td>Nepa Gene Co. Ltd.</td>
			<td>CUY700P4L</td>
			<td>Cover Round Platinum Plate 4 mm diameter</td>
		</tr>
		<tr>
			<td>Fiberoptic cold light source</td>
			<td>Leica</td>
			<td>KL2500 LCD</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Glass capillaries</td>
			<td>Harvard Apparatus</td>
			<td>GC120T-15</td>
			<td>1. 2 mm O.D. x 0. 94 mm I.D.</td>
		</tr>
		<tr>
			<td>Glass bead sterilizer</td>
			<td>Fine Science Tools</td>
			<td>FST250</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Heating pad</td>
			<td>Harvard Apparatus</td>
			<td>py872-5272</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Injection device</td>
			<td>World Precision Instruments</td>
			<td>Pneumatic Pico Pump PV820</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Suture Thread Coated Vicryl</td>
			<td>Ethicon</td>
			<td>V4914</td>
			<td>Peritoneal Suture</td>
		</tr>
		<tr>
			<td>Suture Thr. Supramid</td>
			<td>Serag Wiessner</td>
			<td>TO07171L</td>
			<td>Skin Suture</td>
		</tr>
	</tbody>
</table>

genetic manipulation of the mouse developing hypothalamus through in utero electroporation

Genetic modification of specific regions of the developing mammalian brain is a very powerful experimental approach. However, generating novel mouse mutants is often frustratingly slow. It has been shown that access to the mouse brain developing in utero with reasonable post-operatory survival is possible. Still, results with this procedure have been reported almost exclusively for the most superficial and easily accessible part of the developing brain, i.e. the cortex. The thalamus, a narrower and more medial region, has proven more difficult to target. Transfection into deeper nuclei, especially those of the hypothalamus, is perhaps the most challenging and therefore very few results have been reported. Here we demonstrate a procedure to target the entire hypothalamic neuroepithelium or part of it (hypothalamic regions) for transfection through electroporation. The keys to our approach are longer narcosis times, injection in the third ventricle, and appropriate kind and positioning of the electrodes. Additionally, we show results of targeting and subsequent histological analysis of the most recessed hypothalamic nucleus, the mammillary body.

Most hypothalamus neurons are born between E11.5 to E15.2, according to birth-dating analysis in the rat26 translated into the somewhat shorter mouse development27,28. The peak of hypothalamic neurogenesis is reached at E12.529-31. Accordingly, at the transfection age chosen for the present study (E12.5), a large proportion of hypothalamic neurons can be labeled at any given rostro-caudal level.
Analysis at E18.5 on thick vibratome-type sections (Figur...

Watch this Scientific Journal Video about Genetic Manipulation of the Mouse Developing Hypothalamus through In utero Electroporation at JoVE.com

Genetic Manipulation of the Mouse Developing Hypothalamus through In utero Electroporation

Despite the functional and medical importance of the hypothalamus, in utero genetic manipulation of its development has rarely been attempted. We show a detailed procedure for in utero electroporation into the mouse hypothalamus and show representative results of total and partial (regional) hypothalamic transfection.

Genetic Manipulation of the Mouse Developing Hypothalamus through In utero Electroporation

Genetic  modification of specific regions of the developing mammalian brain is a very  powerful experimental approach. However, generating novel mouse ...

genetic-manipulation-mouse-developing-hypothalamus-through-utero

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15.7K Views.  University of Heidelberg. Despite the functional and medical importance of the hypothalamus, in utero genetic manipulation of its development has rarely been attempted. We show a detailed procedure for in utero electroporation into the mouse hypothalamus and show representative results of total and partial (regional) hypothalamic transfection.

Video: Genetic Manipulation of the Mouse Developing Hypothalamus through In utero Electroporation

In vivo Electroporation of Developing Mouse Retina

The functional characterization of genes expressed during mammalian retinal development remains a significant challenge. Gene targeting to generate constitutive or conditional loss of function knockouts remains cost and labor intensive, as well as time consuming. Adding to these challenges, retina expressed genes may have essential roles outside the retina leading to unintended confounds when using a knockout approach. Furthermore, the ability to ectopically express a gene in a gain of function experiment can be extremely valuable when attempting to identify a role in cell fate specification and/or terminal differentiation.
We present a method for the rapid and efficient incorporation of DNA plasmids into the neonatal mouse retina by electroporation. The application of short electrical impulses above a certain field strength results in a transient increase in plasma membrane permeability, facilitating the transfer of material across the membrane 1,2,3,4. Groundbreaking work demonstrated that electroporation could be utilized as a method of gene transfer into mammalian cells by inducing the formation of hydrophilic plasma membrane pores allowing the passage of highly charged DNA through the lipid bilayer 5. Continuous technical development has resulted in the viability of electroporation as a method for in vivo gene transfer in multiple mouse tissues including the retina, the method for which is described herein 6, 7, 8, 9, 10. 
DNA solution is injected into the subretinal space so that DNA is placed between the retinal pigmented epithelium and retina of the neonatal (P0) mouse and electrical pulses are applied using a tweezer electrode. The lateral placement of the eyes in the mouse allows for the easy orientation of the tweezer electrode to the necessary negative pole-DNA-retina-positive pole alignment. Extensive incorporation and expression of transferred genes can be identified by postnatal day 2 (P2). Due to the lack of significant lateral migration of cells in the retina, electroporated and non-electroporated regions are generated. Non-electroporated regions may serve as internal histological controls where appropriate. 
Retinal electroporation can be used to express a gene under a ubiquitous promoter, such as CAG, or to disrupt gene function using shRNA constructs or Cre-recombinase. More targeted expression can be achieved by designing constructs with cell specific gene promoters. Visualization of electroporated cells is achieved using bicistronic constructs expressing GFP or by co-electroporating a GFP expression construct. Furthermore, multiple constructs may be electroporated for the study of combinatorial gene effects or simultaneous gain and loss of function of different genes. Retinal electroporation may also be utilized for the analysis of genomic cis-regulatory elements by generating appropriate expression constructs and deletion mutants. Such experiments can be used to identify cis-regulatory regions sufficient or required for cell specific gene expression 11. Potential experiments are limited only by construct availability.

In vivo Electroporation of Developing Mouse Retina

A method for the incorporation of plasmid DNA into murine retinal cells for the purpose of performing either gain- or loss of function studies in vivo is presented. This method capitalizes on the transient increase in permeability of cell plasma membranes induced by the application of an external electrical field.

The functional characterization of genes expressed during mammalian retinal development remains a significant challenge.  Gene targeting to generate ...

Mouse in Utero Electroporation: Controlled Spatiotemporal Gene Transfection

In order to understand the function of genes expressed in specific region of the developing brain, including signaling molecules and axon guidance molecules, local gene transfer or knock- out is required. Gene targeting knock-in or knock-out into local regions is possible to perform with combination with a specific CRE line, which is laborious, costly, and time consuming. Therefore, a simple transfection method, an in utero electroporation technique, which can be performed with short time, will be handy to test the possible function of candidate genes prior to the generation of transgenic animals 1,2. In addition to this, in utero electroporation targets areas of the brain where no specific CRE line exists, and will limit embryonic lethality 3,4. Here, we present a method of in utero electroporation combining two different types of electrodes for simple and convenient gene transfer into target areas of the developing brain. First, a unique holding method of embryos using an optic fiber optic light cable will make small embryos (from E9.5) visible for targeted DNA solution injection into ventricles and needle type electrodes insertion to the targeted brain area 5,6. The patterning of the brain such as cortical area occur at early embryonic stage, therefore, these early electroporation from E9.5 make a big contribution to understand entire area patterning event. Second, the precise shape of a capillary prevents uterine damage by making holes by insertion of the capillary. Furthermore, the precise shape of the needle electrodes are created with tungsten and platinum wire and sharpened using sand paper and insulated with nail polish 7, a method which is described in great detail in this protocol. This unique technique allows transfection of plasmid DNA into restricted areas of the brain and will enable small embryos to be electroporated. This will help to, open a new window for many scientists who are working on cell differentiation, cell migration, axon guidance in very early embryonic stage. Moreover, this technique will allow scientists to transfect plasmid DNA into deep parts of the developing brain such as thalamus and hypothalamus, where not many region-specific CRE lines exist for gain of function (GOF) or loss of function (LOF) analyses.

Mouse in Utero Electroporation: Controlled Spatiotemporal Gene Transfection

A gene transfer method into the developing mouse brain is described by using a unique surgical method and special shape of electrodes. This unique technique allows transfection of plasmid DNA temporally and spatially, which will aid many neuroscientists in studying brain development.

In order to understand the function of genes expressed in specific region of the developing brain, including signaling molecules and axon guidance ...

Gene Transfer to the Developing Mouse Inner Ear by In Vivo Electroporation

The mammalian inner ear has 6 distinct sensory epithelia: 3 cristae in the ampullae of the semicircular canals; maculae in the utricle and saccule; and the organ of Corti in the coiled cochlea. The cristae and maculae contain vestibular hair cells that transduce mechanical stimuli to subserve the special sense of balance, while auditory hair cells in the organ of Corti are the primary transducers for hearing 1. Cell fate specification in these sensory epithelia and morphogenesis of the semicircular canals and cochlea take place during the second week of gestation in the mouse and are largely completed before birth 2,3. Developmental studies of the mouse inner ear are routinely conducted by harvesting transgenic embryos at different embryonic or postnatal stages to gain insight into the molecular basis of cellular and/or morphological phenotypes 4,5. We hypothesize that gene transfer to the developing mouse inner ear in utero in the context of gain- and loss-of-function studies represents a complimentary approach to traditional mouse transgenesis for the interrogation of the genetic mechanisms underlying mammalian inner ear development6.
The experimental paradigm to conduct gene misexpression studies in the developing mouse inner ear demonstrated here resolves into three general steps: 1) ventral laparotomy; 2) transuterine microinjection; and 3) in vivo electroporation. Ventral laparotomy is a mouse survival surgical technique that permits externalization of the uterus to gain experimental access to the implanted embryos7. Transuterine microinjection is the use of beveled, glass capillary micropipettes to introduce expression plasmid into the lumen of the otic vesicle or otocyst. In vivo electroporation is the application of square wave, direct current pulses to drive expression plasmid into progenitor cells8-10. 
We previously described this electroporation-based gene transfer technique and included detailed notes on each step of the protocol11. Mouse experimental embryological techniques can be difficult to learn from prose and still images alone. In the present work, we demonstrate the 3 steps in the gene transfer procedure. Most critically, we deploy digital video microscopy to show precisely how to: 1) identify embryo orientation in utero; 2) reorient embryos for targeting injections to the otocyst; 3) microinject DNA mixed with tracer dye solution into the otocyst at embryonic days 11.5 and 12.5; 4) electroporate the injected otocyst; and 5) label electroporated embryos for postnatal selection at birth. We provide representative examples of successfully transfected inner ears; a pictorial guide to the most common causes of otocyst mistargeting; discuss how to avoid common methodological errors; and present guidelines for writing an in utero gene transfer animal care protocol.

Gene Transfer to the Developing Mouse Inner Ear by In Vivo Electroporation

The mouse inner ear is a placode-derived sensory organ whose developmental program is elaborated during gestation. We define an in utero gene transfer technique consisting of three steps: mouse ventral laparotomy, transuterine microinjection, and in vivo electroporation. We use digital video microscopy to demonstrate the critical experimental embryological techniques.

The mammalian inner ear has 6 distinct sensory epithelia: 3 cristae in the ampullae of the semicircular canals; maculae in the utricle and saccule; and ...

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 ...

Genetic Manipulation of Cerebellar Granule Neurons In Vitro and In Vivo to Study Neuronal Morphology and Migration

Developmental events in the brain including neuronal morphogenesis and migration are highly orchestrated processes. In vitro and in vivo analyses allow for an in-depth characterization to identify pathways involved in these events. Cerebellar granule neurons (CGNs) that are derived from the developing cerebellum are an ideal model system that allows for morphological analyses. Here, we describe a method of how to genetically manipulate CGNs and how to study axono- and dendritogenesis of individual neurons. With this method the effects of RNA interference, overexpression or small molecules can be compared to control neurons. In addition, the rodent cerebellar cortex is an easily accessible in vivo system owing to its predominant postnatal development. We also present an in vivo electroporation technique to genetically manipulate the developing cerebella and describe subsequent cerebellar analyses to assess neuronal morphology and migration.

Genetic Manipulation of Cerebellar Granule Neurons In Vitro and In Vivo to Study Neuronal Morphology and Migration

Neuronal morphogenesis and migration are crucial events underlying proper brain development. Here, we describe methods to genetically manipulate cultured cerebellar granule neurons and the developing cerebellum for the assessment of morphology and migratory characteristics of neurons.

Developmental events in the brain including neuronal morphogenesis and migration are highly orchestrated processes. In vitro and in vivo analyses allow ...

Cortex-, Hippocampus-, Thalamus-, Hypothalamus-, Lateral Septal Nucleus- and Striatum-specific In Utero Electroporation in the C57BL/6 Mouse

In utero electroporation is a widely used technique for fast and efficient spatiotemporal manipulation of various genes in the rodent central nervous system. Overexpression of desired genes is just as possible as shRNA mediated loss-of-function studies. Therefore it offers a wide range of applications. The feasibility to target particular cells in a distinct area further increases the range of potential applications of this very useful method. For efficiently targeting specific regions knowledge about the subtleties, such as the embryonic stage, the voltage to apply and most importantly the position of the electrodes, is indispensable.
Here, we provide a detailed protocol that allows for specific and efficient in utero electroporation of several regions of the C57BL/6 mouse central nervous system. In particular it is shown how to transfect regions the develop into the retrosplenial cortex, the motor cortex, the somatosensory cortex, the piriform cortex, the cornu ammonis 1-3, the dentate gyrus, the striatum, the lateral septal nucleus, the thalamus and the hypothalamus. For this information about the appropriate embryonic stage, the appropriate voltage for the corresponding embryonic stage is provided. Most importantly an angle-map, which indicates the appropriate position of the positive pole, is depicted. This standardized protocol helps to facilitate efficient in utero electroporation, which might also lead to a reduced number of animals.

Cortex-, Hippocampus-, Thalamus-, Hypothalamus-, Lateral Septal Nucleus- and Striatum-specific In Utero Electroporation in the C57BL/6 Mouse

This protocol describes in detail how to specifically transfect different regions in the C57BL/6 central nervous system via in utero electroporation. Included in this protocol are detailed instructions for transfections of regions that develop into the cortex, hippocampus, thalamus, hypothalamus, lateral septal nucleus and striatum.

In utero electroporation is a widely used technique for fast and efficient spatiotemporal manipulation of various genes in the rodent central nervous ...

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.

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.

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

Time-lapse Confocal Imaging of Migrating Neurons in Organotypic Slice Culture of Embryonic Mouse Brain Using In Utero Electroporation

In utero electroporation is a rapid and powerful approach to study the process of radial migration in the cerebral cortex of developing mouse embryos. It has helped to describe the different steps of radial migration and characterize the molecular mechanisms controlling this process. To directly and dynamically analyze migrating neurons they have to be traced over time. This protocol describes a workflow that combines in utero electroporation with organotypic slice culture and time-lapse confocal imaging, which allows for a direct examination and dynamic analysis of radially migrating cortical neurons. Furthermore, detailed characterization of migrating neurons, such as migration speed, speed profiles, as well as radial orientation changes, is possible. The method can easily be adapted to perform functional analyses of genes of interest in radially migrating cortical neurons by loss and gain of function as well as rescue experiments. Time-lapse imaging of migrating neurons is a state-of-the-art technique that once established is a potent tool to study the development of the cerebral cortex in mouse models of neuronal migration disorders.

Time-lapse Confocal Imaging of Migrating Neurons in Organotypic Slice Culture of Embryonic Mouse Brain Using In Utero Electroporation

This protocol provides instructions for direct observation of radially migrating cortical neurons. In utero electroporation, organotypic slice culture, and time-lapse confocal imaging are combined to directly and dynamically study the effects of overexpression or downregulation of genes of interest in migrating neurons and to analyze their differentiation during development.

In utero electroporation is a rapid and powerful approach to study the process of radial migration in the cerebral cortex of developing mouse embryos. It ...

Inducing Cre-lox Recombination in Mouse Cerebral Cortex Through In Utero Electroporation

Cell-autonomous neuronal functions of genes can be revealed by causing loss or gain of function of a gene in a small and sparse population of neurons. To do so requires generating a mosaic in which neurons with loss or gain of function of a gene are surrounded by genetically unperturbed tissue. Here, we combine the Cre-lox recombination system with in utero electroporation in order to generate mosaic brain tissue that can be used to study the cell-autonomous function of genes in neurons. DNA constructs (available through repositories), coding for a fluorescent label and Cre recombinase, are introduced into developing cortical neurons containing genes flanked with loxP sites in the brains of mouse embryos using in utero electroporation. Additionally, we describe various adaptations to the in utero electroporation method that increase survivability and reproducibility. This method also involves establishing a titer for Cre-mediated recombination in a sparse or dense population of neurons. Histological preparations of labeled brain tissue do not require (but can be adapted to) immunohistochemistry. The constructs used guarantee that fluorescently labeled neurons carry the gene for Cre recombinase. Histological preparations allow morphological analysis of neurons through confocal imaging of dendritic and axonal arbors and dendritic spines. Because loss or gain of function is achieved in sparse mosaic tissue, this method permits the study of cell-autonomous necessity and sufficiency of gene products in vivo.

Inducing Cre-lox Recombination in Mouse Cerebral Cortex Through In Utero Electroporation

Cell-autonomous functions of genes in the brain can be studied by inducing loss or gain of function in sparse populations of cells. Here, we describe in utero electroporation to deliver Cre recombinase into sparse populations of developing cortical neurons with floxed genes to cause loss of function in vivo.

Cell-autonomous neuronal functions of genes can be revealed by causing loss or gain of function of a gene in a small and sparse population of neurons. To ...

Stereotaxic Surgery for Genetic Manipulation in Striatal Cells of Neonatal Mouse Brains

Many genes are expressed in embryonic brains, and some of them are continuously expressed in the brain after birth. For such persistently expressed genes, they may function to regulate the developmental process and/or physiological function in neonatal brains. To investigate neurobiological functions of specific genes in the brain, it is essential to inactivate genes in the brain. Here, we describe a simple stereotaxic method to inactivate gene expression in the striatum of transgenic mice at neonatal time windows. AAV-eGFP-Cre viruses were microinjected into the striatum of Ai14 reporter gene mice at postnatal day (P) 2 by stereotaxic brain surgery. The tdTomato reporter gene expression was detected in P14 striatum, suggesting a successful Cre-loxP mediated DNA recombination in AAV-transduced striatal cells. We further validated this technique by microinjecting AAV-eGFP-Cre viruses into P2Foxp2fl/fl mice. Double labeling of GFP and Foxp2 showed that GFP-positive cells lacked Foxp2 immunoreactivity in P9 striatum, suggesting the loss of Foxp2 protein in AAV-eGFP-Cre transduced striatal cells. Taken together, these results demonstrate an effective genetic deletion by stereotaxically microinjected AAV-eGFP-Cre viruses in specific neuronal populations in the neonatal brains of floxed transgenic mice. In conclusion, our stereotaxic technique provides an easy and simple platform for genetic manipulation in neonatal mouse brains. The technique can not only be used to delete genes in specific regions of neonatal brains, but it also can be used to inject pharmacological drugs, neuronal tracers, genetically modified optogenetics and chemogenetics proteins, neuronal activity indicators and other reagents into the striatum of neonatal mouse brains.

We describe a protocol of stereotaxic surgery with a homemade head-fixed device for microinjecting reagents into the striatum of neonatal mouse brains. This technique allows genetic manipulation in neuronal cells of specific regions of neonatal mouse brains.

Many genes are expressed in embryonic brains, and some of them are continuously expressed in the brain after birth. For such persistently expressed genes, ...