The authors would like to thank Joseph LoTurco and Dennis Selkoe for helpful discussions on this technique. The authors thank the donors of the American Health Assistance Foundation, for support of this research.

The basic protocol for in utero electroporation has been described in detail in another JoVE article from the Kriegstein lab 1, 2. This technique was originally described in the Osumi lab 3 and our protocol is based upon one developed in the LoTurco lab 4. We will provide an overview of the our protocol for in utero electroporation of rat embryos, 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.
1. In utero Electroporation
<ol>
<li>Preparing DNA and loading needles 
The first step for in utero electroporations is to design your experiment to determine what DNA constructs you want to inject. This method is useful for both misexpressing or knocking down genes of interest. If you are planning on misexpressing or overexpressing a gene, be sure to use a promoter that is active in neuronal precursor cells. We recommend the CAGGS promoter, which consists of the chicken beta-actin promoter and the CMV enhancer 5. Since only a small subset of cells are transfected using in utero electroporation, it is critical to include a plasmid encoding a fluorescent protein such as GFP so that you can follow those cells that were successfully electroporated. For the plasmid encoding GFP, we recommend preparing the DNA at a concentration of 0.5 &mu;g per microliter. For shRNA constructs, we have found that 0.5-1.0 &mu;G per &mu;L results in efficient knock down of your gene of interest. For overexpression or misexpression, we use between 1.0 and 3.0 &mu;G per microliter, depending upon the size of the gene and the level of expression that the experiment calls for. DNAs are prepared using a Qiagen endotoxin-free prep kit, and diluted in 1 x PBS. We inject approximately 0.5-1.0 &mu;L per embryonic brain, so, for a litter of animals we prepare 10 &mu;L of DNA mixture for injection. We add 1 &mu;L of Fast Green to the DNA so that we can follow the injected DNA. 
Pulling needles to the correct shape is a critical step. Walantus et al. uses a different system for delivering the DNA and so their needle prep is also slighly different then ours1,2. The settings that you use to pull your needles will depend upon the brand of needle puller that you have. We use Model 750 from David Kopf. The settings we use are : Heat 1: 9.0, Heat 2: 0, Soleniod: 0, Filament size 3.0 mm, Heater Proximity: 3 mm, Time: 10 sec. Once pulled, we cut our needles with a razor blade at a ~45 degree angle such that the distance from the largest part of the opening to the tip is 11 mm. We then load the DNA from the back end of the needle. We then fill the remaining space in the needle with corn oil. For DNA injection, we use a Picospritzer III. Depending upon the exact bevel that is cut for each needle, we set the Picospritzer from 4.0 to 6.0. We use a foot pedal to deliver the pressurized air that expels the DNA from the needle.</li>
<li> Preparing animals for surgery 
We use pathogen-free Sprague Dawley rats exclusively for these surgeries. Several other labs use mice of varying genotypes as well. Here, we describe show our protocol for electroporation of E15 rat embryos, but in utero electroporation is routinely performed in rats between the ages of E13 and E18. While early stage electroporation targets deep layers of the cortex, later stage electroporations target more superficial layers. 
Animals are given a pre-operative dose of buprenorphine (0.05-0.1 mg/kg) before the surgery starts. There are multiple options for anesthetizing the animal. Walantus et al. utilizes isofuorane inhalation, while we routinely use intraperitoneal injection of ketamine (40-80 mg/kg) and xylazine (5-10 mg/kg)1,2. A toe pinch should always be performed to ensure that animals are fully anesthetized and unresponsive. Animals are kept on a heated pad throughout the surgical procedure. 
The animal's fur is shaved in the region of incision, and washed three times with ethanol followed by three times with iodine. An incision is made in the skin just lateral to the midline, followed by an incision in the muscle. The uterine horns are exposed very carefully. They are gently teased out of the body cavity using your fingertips. Keep embryos hydrated with sterile PBS while they are outside of the body cavity.</li>
<li>Injecting DNA and electroporation 
When you first start performing these surgeries, the hardest part is becoming familiar with where you need to inject the DNA so that you fill the lateral ventricles, and getting used to how deep you inject your needle in order to hit the correct region. Embryos are gently manipulated with your fingertips so that you can identify where the head is, and if you look closely you will be able to see the midline suture. This serves as a general landmark that you can use to determine where the lateral ventricle is located. We inject the DNA through the uterine wall and into the lateral ventricle. We use a footpedal to control the injection of the DNA - multiple pulses of DNA are performed until the lateral ventricle is filled with the DNA/dye mixture. We then place paddle electrodes on either side of the head of the embryo and use another footpedal to deliver the pulse across the head of the embryo. The placement of the electrodes is critical in determining which region of the cortex is electroporated. Since DNA is negatively charged, the DNA will travel toward the positive electrode when a charge is dispelled across the paddles. Depending on the exact placement of the electrodes, different subsets of cells will be targeted. We routinely place the positive electrode near the dorsal-medial positions across the cerebrum. However, the LoTurco lab beautifully showed that if you place the electrodes in more ventral lateral regions of the cerebrum you can target the cells of the cortical-striatal boundary and hit cells of the lateral cortical stream 6. Each embryo can be electroporated, and different combinations of DNA constructs can be used in each embryo.</li>
<li>Suturing and post-operative care 
Following electroporation of all embryos, the uterine horns are carefully returned to the body cavity, and both the muscle layer and the skin are sutured. The technique for this is outlined in Walantus et al1,2. Animals are monitored continuously until they recover from anesthesia, and the analgesic buprenorphine (0.05-0.1 mg/kg) is administered every 8-12 hours.</li>
</ol>
2. Culturing Electroporated Cortical Neurons
<ol>
<li> Harvesting electroporated brains and dissecting electroporated region 
For in vivo analyses following in utero electroporation, animals can be harvested at any time point from 24 hours following electroporation to early after birth to adulthood. However, when culturing primary neurons we harvest 24 hours following electroporation at E16. At this time, the electroporated embryos are expressing detectable levels of GFP. 
Animals are euthanized using carbon dioxide inhalation and rapid decapitation. Embryos are dissected out of the uterus and placed in HBSS with divalent cations, keeping track of which embryos were electroporated with which DNA plasmids. It is critical to use filtered HBSS, sterile tubes and plates, and autoclaved tools for dissection. The cortices are dissected out and the meninges removed using a microscope in a hood. These cortices are then observed under a dissecting microscope with the capacity to visualize GFP. GFP positive regions of the cortex are identified, and we ue a pair of vanna scissors to cut out the GFP positive regions from the cortex. These pieces are placed in HBSS without divalent cations in a 15 ml conical tube.</li>
<li>Dissociating and plating neurons 
Once all GFP positive regions are dissected, HBSS is replaced with 0.25% trypsin, and incubated at 37 degrees for 5 minutes. Trypsin is removed, replaced with plating media (DMEM + 5% FBS + Penn/strep + glutamine), and triturated 5-7 times to dissociate the cells. Volumes used depend upon the amount of tissue present. Dissociated cells are then plated on CC2 coated chamber slides. For two chamber slides, we plate 200,000-350,000 cells per chamber in a volume of 1.5 mL of plating media. After 4 hours, plating media is aspirated and replaced with 1.5 mL Neuronal culture media (Neurobasal media + B27 supplement + glutamax + gentamycin) per chamber.</li>
</ol>
3. Analyzing Neuronal Process Outgrowth
<ol>
<li>Fixing and immunostaining cultures 
In order to measure short term effecs of genetic manipulation of these cells, we harvest the primary neurons after three days in vitro. If primary neurons are to be cultured longer for additional analyses, half of the media should be replaced every three days. For fixing cultures, we aspirate the media from the chambers, and fix the neurons in 4% paraformaldhyde for 15 minutes. Following fixation, cells are washed two times in PBS and then put in blocking solution (2% donkey serum with 0.1% Triton X-100 in PBS) for one hour. Cells are then incubated in primary antibody for 1 hour. For analyses of neuronal process outgrowth, we use anti-beta tubululin antibody to identify neurons - beta II tubulin immunostaining labels the neruonal cell body, dendrites and axons. Cells are then washed three times in PBS for five minutes, and then incubated in Cy3-anti mouse for 1 hour, followed by three more PBS washes, counterstaining nuclei with DAPI and mounting.</li>
<li>Measuring neurite length 
Images of GFP positive, beta-III tubulin positive neurons are acquired on a Zeiss Axioskop with a MC100 camera system. Several variables can be examined in these GFP positive cells including length of all neurites, length of the longest neurite, branching of neurites, size of cell soma, etc. We have used this method to analyze neuronal process outgrowth upon knock down or overexpression of genes relating to neurodevelopment and neurodegeneration, with a focus on neuronal process length. In order to measure neuronal processes outgrowth, we use Axiovision LE 4.4 software (from Zeiss). Within this software, there is an option to select the "outline" tool. Using this tool, you can use your computer's mouse to trace the length of each neuronal process. It is critical to define the objective that you are using in order to get an accurate measure of your neurites. For these analyses, we usually use a 20x objective.</li>
</ol>
4. Representative Results
We have found that Sprague Dawley litter size ranges between 6 and 14 embryos. We usually electroporate all of the embryos. Each embryo can be electroporated with a different combination of DNAs. However, we usually electroporate at least four brains with the same condition and pool these brains before dissociating and plating.
We have found that with this technique approximately 75% of electroporated brains are targeted to the desired region of the cortex, whether that be dorsal medial or ventral lateral cortex (Figure 1). In addition, we have found early electroporations at E13-14 target deep layer neurons such as Tbr1 positive layer VI neurons, while later electroporations target CTIP2 positive, TBR1 negative layer V cells, and still later electroporations target Brn2 positive layer II/III cells. An excellent description of different markers and explanation of neuronal subtype specification in the cortex in found an article by Moleneaux et al 7. Figure 2 shows coronal sections of brains electroporated at either embryonic day 15.5 or 17.5 and harvested at postnatal day 5. Shown in red is immunostaining for Oct6. You can immunostain for markers in culture to confirm what cell layer populations you have targeted. We have found that you can expect to target the same cell layer population of cells in every embryo of the same litter (in other words, the targeting depends upon the embryonic timepoint rather then on other technical variations).
In culture, the percent of cells that are GFP positive can range widely depending on how conservative you are when dissecting out the GFP positive region (Figure 3). However, even when we are very conservative and dissect out only the GFP positive patch of cells, the highest percentage that we observe is 5-10% - although you are dissecting the region of the cortex that was electroporated, cells in only one layer will be targeted. This low transfection effciency is helpful in identifying which processes belong to the electoporated cell that you are analyzing. Plating cells at this higher density contributes to having heathier cultures, however, it is difficult to discern which process belongs to which cell body in the GFP negative cells (Figure 3).
If you have trouble seeing all of the fine processes of the electroporated cells, you can either increase the concentration of GFP DNA that you are electroporating to increase expression of GFP, or you can immunostain the dissociated cells using an anti-GFP antibody (from Invitrogen) along with a Cy2 secondary antibody.
<img src="/files/ftp_upload/2103/2103fig1.jpg" alt="Figure 1" /> Figure 1. E15.5 Sprague-Dawley rats were electroporated with GFP plasmid and harvested three days later. Based upon the placement of the electrodes, different regions of the cortex will be targeted. A-F show GFP fluorescence in whole brains.
<img src="/files/ftp_upload/2103/2103fig2.jpg" alt="Figure 2" /> Figure 2. E15.5 (A) or E17.5 (B) Sprague-Dawley rats were electroporated with GFP plasmid and harvest at postnatal day 5. Brains were fixed, sectioned coronally using a vibratome (100 micron sections), and immunostained for Oct6 (red). A and B show confocal images of immunostained sections.
<img src="/files/ftp_upload/2103/2103fig3.jpg" alt="Figure 3" /> Figure 3. E15.5 Sprague-Dawley rats were electroporated with GFP plasmid. 24 hours following electroporation, brains were harvested and GFP-positive, electroporated regions were dissected and dissociated, as described in the video. After 3 days in vitro, cells were fixed and immunostained for bIII-tubulin (red) and staining nuclei with DAPI (blue) (A,C). The length of the longest neurite was measured using Axiovision software (B,D).

<ol>
	<li>Walantus, W., Castaneda, D., Elias, L., Kriegstein, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+utero+intraventricular+injection+and+electroporation+of+E15+mouse+embryos.">In utero intraventricular injection and electroporation of E15 mouse embryos.</a> J Vis Exp. , (2007).</li><li>Walantus, W., Elias, L., Kriegstein, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+utero+intraventricular+injection+and+electroporation+of+E16+rat+embryos.">In utero intraventricular injection and electroporation of E16 rat embryos.</a> J Vis Exp. , (2007).</li><li>Takahashi, M., Sato, K., Nomura, T., Osumi, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Manipulating+gene+expressions+by+electroporation+in+the+developing+brain+of+mammalian+embryos.">Manipulating gene expressions by electroporation in the developing brain of mammalian embryos.</a> Differentiation. 70 (4-5), 155-1562 (2002).</li><li>Bai, J., Ramos, R. L., Ackman, J. B., Thomas, A. M., Lee, R. V., LoTurco, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNAi+reveals+doublecortin+is+required+for+radial+migration+in+rat+neocortex.">RNAi reveals doublecortin is required for radial migration in rat neocortex.</a> Nat Neurosci. , 1277-1283 (2003).</li><li>Okada, A., Lansford, R., Weimann, J. M., Fraser, S. E., McConnell, S. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+cells+in+the+developing+nervous+system+with+retrovirus+expressing+modified+green+fluorescent+protein.">Imaging cells in the developing nervous system with retrovirus expressing modified green fluorescent protein.</a> Exp Neurol. 156 (2), 394-406 (1999).</li><li>Bai, J., Ramos, R. L., Paramasivam, M., Siddiqi, F., Ackman, J. B., LoTurco, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+DCX+and+LIS1+in+migration+through+the+lateral+cortical+stream+of+developing+forebrain.">The role of DCX and LIS1 in migration through the lateral cortical stream of developing forebrain.</a> Dev Neurosci. , 144-156 (2008).</li><li>Molyneaux, B. J., Arlotta, P., Menezes, J. R., Macklis, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuronal+subtype+specification+in+the+cerebral+cortex.">Neuronal subtype specification in the cerebral cortex.</a> Nat Rev Neurosci. , 427-437 (2007).</li><li>Young-Pearse, T. L., Bai, J., Chang, R., Zheng, J. B., Loturco, J. J., Selkoe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Critical+Function+for+-Amyloid+Precursor+Protein+in+Neuronal+Migration+Revealed+by+In+Utero+RNA+Interference.">A Critical Function for -Amyloid Precursor Protein in Neuronal Migration Revealed by In Utero RNA Interference.</a> J Neurosci. 27, 14459-14469 (2007).</li><li>Young-Pearse, T. L., Chen, A. C., Chang, R., Marquez, C., Selkoe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Secreted+APP+regulates+the+function+of+full-length+APP+in+neurite+outgrowth+through+interaction+with+integrin+beta1.">Secreted APP regulates the function of full-length APP in neurite outgrowth through interaction with integrin beta1.</a> Neural Develop. 3, 15-15 (2008).</li></ol>

No conflicts of interest declared.

In vitro study of primary neuronal cultures allow for quantitative analyses of neurite outgrowth. In order to study how genetic alterations affect neuronal process outgrowth, shRNA or misexpression 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 e...

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>Cortical Neuron Preparation</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Dissection Media:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>10X Hanks' Balanced Salt Solution (HBSS) (Ca+2 /Mg +2 free)</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>14185-052</td>
<td>&nbsp;</td>
<tr>
<td>10X Hanks' Balanced Salt Solution (HBSS) (with Ca+2 /Mg +2 )</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>14065-056</td>
<td>&nbsp;</td>
<tr>
<td>1M HEPES pH 7.4</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>15630-080</td>
<td>&nbsp;</td>
<tr>
<td>Dishes and Vials:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>100 x 15 mm Petri Dishes</td>
<td>
</td>
<td>Fisherbrand</td>
<td>08-757-12</td>
<td>&nbsp;</td>
<tr>
<td>60 x 15 mm Petri Dishes</td>
<td>&nbsp;</td>
<td>BD Falcon</td>
<td>351007</td>
<td>&nbsp;</td>
<tr>
<td>15 mL conical vial</td>
<td>&nbsp;</td>
<td>Sarstedt</td>
<td>62-547-205</td>
<td>&nbsp;</td>
<tr>
<td>50 mL conical vial</td>
<td>&nbsp;</td>
<td>Sarstedt</td>
<td>62-554-205</td>
<td>&nbsp;</td>
<tr>
<td>Dissection Tools:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Scissors </td>
<td>&nbsp;</td>
<td>Fine Science Tools</td>
<td>91402-12</td>
<td>&nbsp;</td>
<tr>
<td>Standard Forceps</td>
<td>
</td>
<td>Fine Science Tools</td>
<td>11000-12</td>
<td>&nbsp;</td>
<tr>
<td>Curved Forceps</td>
<td>&nbsp;</td>
<td>Fine Science Tools</td>
<td>11273-20</td>
<td>&nbsp;</td>
<tr>
<td>Fine Forceps</td>
<td>&nbsp;</td>
<td>Fine Science Tools</td>
<td>11255-20</td>
<td>&nbsp;</td>
<tr>
<td>Vannas spring scissors </td>
<td>&nbsp;</td>
<td>Fine Science Tools</td>
<td>15000-00</td>
<td>&nbsp;</td>
<tr>
<td>Miscellaneous:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>.25% Trypsin-EDTA</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>25200</td>
<td>&nbsp;</td>
<tr>
<td>Reichert Bright-Line Hemacytometer</td>
<td>&nbsp;</td>
<td>Hausser Scientific</td>
<td>1490</td>
<td>&nbsp;</td>
<tr>
<td>Hand-Held Tally Counter</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>Z169021</td>
<td>&nbsp;</td>
<tr>
<td>Plating Medium:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Dulbecco's Modified Eagle Medium (D-MEM)</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>11960-051</td>
<td>&nbsp;</td>
<tr>
<td>Fetal Bovine Serum</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>F4135</td>
<td>&nbsp;</td>
<tr>
<td>Penicillin-Streptomycin</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>15140</td>
<td>&nbsp;</td>
<tr>
<td>L-glutamine</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>25030</td>
<td>&nbsp;</td>
<tr>
<td>Growth Medium:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>NEUROBASAL Medium </td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>21103-049</td>
<td>&nbsp;</td>
<tr>
<td>B-27 Serum-Free Supplement </td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>17504-044</td>
<td>&nbsp;</td>
<tr>
<td>GlutaMAX -I Supplement</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>35050-061</td>
<td>&nbsp;</td>
<tr>
<td>Gentamicin Reagent Solution </td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>15750-060</td>
<td>&nbsp;</td>
<tr>
<td>Immunostaining:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Fixative, Washes, and Blocking Buffer:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Paraformaldehyde</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>P6148</td>
<td>&nbsp;</td>
<tr>
<td>Phosphate Buffered Saline</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>P4417</td>
<td>&nbsp;</td>
<tr>
<td>Triton X-100</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>T9284</td>
<td>&nbsp;</td>
<tr>
<td>Donkey Serum</td>
<td>&nbsp;</td>
<td>Jackson Immuno</td>
<td>017-000-121 </td>
<td>&nbsp;</td>
<tr>
<td>Antibodies:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>beta-III tubulin antibody</td>
<td>&nbsp;</td>
<td>Chemicon</td>
<td>MAB1637</td>
<td>&nbsp;</td>
<tr>
<td>MAP2 antibody</td>
<td>&nbsp;</td>
<td>Chemicon</td>
<td>AB15452</td>
<td>&nbsp;</td>
<tr>
<td>Donkey Cy3 anti-mouse</td>
<td>&nbsp;</td>
<td>Jackson Immuno</td>
<td>715-166-151</td>
<td>&nbsp;</td>
<tr>
<td>Donkey Cy2 anti-chicken</td>
<td>&nbsp;</td>
<td>Jackson Immuno</td>
<td>703-226-155 </td>
<td>&nbsp;</td>
<tr>
<td>DAPI</td>
<td>&nbsp;</td>
<td>Gibco</td>
<td>D3571</td>
<td>&nbsp;</td>
<tr>
<td>Slide Preparation:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>CC2 Coated Two-Chamber Slides </td>
<td>&nbsp;</td>
<td>Lab-Tek</td>
<td>154852</td>
<td>&nbsp;</td>
<tr>
<td>Fluorescent Mounting Media</td>
<td>&nbsp;</td>
<td>KPL</td>
<td>71-00-16</td>
<td>&nbsp;</td>
<tr>
<td>24 x 60 mm Micro Cover Glasses</td>
<td>&nbsp;</td>
<td>VWR</td>
<td>48393-106 </td>
<td>&nbsp;</td>
<tr>
<td>Clear nail polish</td>
<td>&nbsp;</td>
<td>Electron Microscopy Sciences</td>
<td>72180</td>
<td>&nbsp;</td>
<tr>
<td>Electroporation:</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Ketamine</td>
<td>&nbsp;</td>
<td>Henry Schein</td>
<td>995-2949</td>
<td>&nbsp;</td>
<tr>
<td>Xylazine</td>
<td>&nbsp;</td>
<td>Henry Schein</td>
<td>4015809TV</td>
<td>&nbsp;</td>
<tr>
<td>buprenorphine</td>
<td>&nbsp;</td>
<td>Henry Schein</td>
<td>1118217</td>
<td>&nbsp;</td>
<tr>
<td>Picospritzer III</td>
<td>&nbsp;</td>
<td>Parker</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>BTX square wave electroporator</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>BTXECM830</td>
<td>&nbsp;</td>
<tr>
<td>Tweezertrodes, 7 mm, platinum</td>
<td>&nbsp;</td>
<td>Harvard Apparatus</td>
<td>450488</td>
<td>&nbsp;</td>		</tbody>
		</table>
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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.

Watch this Scientific Journal Video about In utero Electroporation followed by Primary Neuronal Culture for Studying Gene Function in Subset of Cortical Neurons at JoVE.com

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 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 ...

in-utero-electroporation-followed-primary-neuronal-culture-for

Research

JoVE Journal

Neuroscience

17.7K vues.  Brigham and Woman's Hospital and Harvard Medical School. Électroporation in utero est une méthode utile pour transfecter des cellules progénitrices neuronales in vivo. Selon le placement des électrodes et la période de développement de l'électroporation, certains sous-ensembles de cellules corticales peuvent être ciblées. Cellules ciblées peuvent ensuite être analysées in vivo ou in vitro des effets de l'altération génétique.

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

Nucleofection and Primary Culture of Embryonic Mouse Hippocampal and Cortical Neurons

Hippocampal and cortical neurons have been used extensively to study central nervous system (CNS) neuronal polarization, axon/dendrite outgrowth, and synapse formation and function. An advantage of culturing these neurons is that they readily polarize, forming distinctive axons and dendrites, on a two dimensional substrate at very low densities. This property has made them extremely useful for determining many aspects of neuronal development. Furthermore, by providing glial conditioning for these neurons they will continue to develop, forming functional synaptic connections and surviving for several months in culture. In this protocol we outline a technique to dissect, culture and transfect embryonic mouse hippocampal and cortical neurons. Transfection is accomplished by electroporating DNA into the neurons before plating via nucleofection. This protocol has the advantage of expressing fluorescently-tagged fusion proteins early in development (~4-8hrs after plating) to study the dynamics and function of proteins during polarization, axon outgrowth and branching. We have also discovered that this single transfection before plating maintains fluorescently-tagged fusion protein expression at levels appropriate for imaging throughout the lifetime of the neuron (&gt; 2 months in culture). Thus, this methodology is useful for studying protein localization and function throughout CNS development with little or no disruption of neuronal function.

This protocol outlines the steps required to dissect, transfect via electroporation and culture mouse hippocampal and cortical neurons. Short-term cultures may be used for studies of axon outgrowth and guidance, while long-term cultures can be used for studies of synaptogenesis and dendritic spine analysis.

Hippocampal and cortical neurons have been used extensively to study central nervous system (CNS) neuronal polarization, axon/dendrite outgrowth, and ...

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 ...

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 ...

Bilaminar Co-culture of Primary Rat Cortical Neurons and Glia

This video will guide you through the process of culturing rat cortical neurons in the presence of a glial feeder layer, a system known as a bilaminar or co-culture model. This system is suitable for a variety of experimental needs requiring either a glass or plastic growth substrate and can also be used for culture of other types of neurons.
Rat cortical neurons obtained from the late embryonic stage (E17) are plated on glass coverslips or tissue culture dishes facing a feeder layer of glia grown on dishes or plastic coverslips (known as Thermanox), respectively. The choice between the two configurations depends on the specific experimental technique used, which may require, or not, that neurons are grown on glass (e.g. calcium imaging versus Western blot). The glial feeder layer, an astroglia-enriched secondary culture of mixed glia, is separately prepared from the cortices of newborn rat pups (P2-4) prior to the neuronal dissection.
A major advantage of this culture system as compared to a culture of neurons only is the support of neuronal growth, survival, and differentiation provided by trophic factors secreted from the glial feeder layer, which more accurately resembles the brain environment in vivo. Furthermore, the co-culture can be used to study neuronal-glial interactions1.
At the same time, glia contamination in the neuronal layer is prevented by different means (low density culture, addition of mitotic inhibitors, lack of serum and use of optimized culture medium) leading to a virtually pure neuronal layer, comparable to other established methods1-3. Neurons can be easily separated from the glial layer at any time during culture and used for different experimental applications ranging from electrophysiology4, cellular and molecular biology5-8, biochemistry5, imaging and microscopy4,6,7,9,10. The primary neurons extend axons and dendrites to form functional synapses11, a process which is not observed in neuronal cell lines, although some cell lines do extend processes.
A detailed protocol of culturing rat hippocampal neurons using this co-culture system has been described previously4,12,13. Here we detail a modified protocol suited for cortical neurons. As approximately 20x106 cells are recovered from each rat embryo, this method is particularly useful for experiments requiring large numbers of neurons (but not concerned about a highly homogenous neuronal population). The preparation of neurons and glia needs to be planned in a time-specific manner. We will provide the step-by-step protocol for culturing rat cortical neurons as well as culturing glial cells to support the neurons.

Here we provide a protocol for culturing rat cortical neurons in the presence of a glial feeder layer. The cultured neurons establish polarity and create synapses, and can be separated from the glia for use in various applications, such as electrophysiology, calcium imaging, cell survival assays, immunocytochemistry, and RNA/DNA/protein isolation.

This video will guide you through the process of culturing rat cortical neurons in the presence of a glial feeder layer, a system known as a bilaminar or ...

In ovo Electroporation in Chick Midbrain for Studying Gene Function in Dopaminergic Neuron Development

Dopaminergic neurons located in the ventral midbrain control movement, emotional behavior, and reward mechanisms1-3. The dysfunction of ventral midbrain dopaminergic neurons is implicated in Parkinson's disease, Schizophrenia, depression, and dementia1-5. Thus, studying the regulation of midbrain dopaminergic neuron differentiation could not only provide important insight into mechanisms regulating midbrain development and neural progenitor fate specification, but also help develop new therapeutic strategies for treating a variety of human neurological disorders.
Dopaminergic neurons differentiate from neural progenitors lining the ventricular zone of embryonic ventral midbrain. The development of neural progenitors is controlled by gene expression programs6,7. Here we report techniques utilizing electroporation to express genes specifically in the midbrain of Hamburger Hamilton (HH) stage 11 (thirteen somites, 42 hours) chick embryos8,9. The external development of chick embryos allows for convenient experimental manipulations at specific embryonic stages, with the effects determined at later developmental time points10-13. Chick embryonic neural tubes earlier than HH stage 13 (nineteen somites, 48 hours) consist of multipotent neural progenitors that are capable of differentiating into distinct cell types of the nervous system. The pCAG vector, which contains both a CMV promoter and a chick &beta;-actin enhancer, allows for robust expression of Flag or other epitope-tagged constructs in embryonic chick neural tubes14. In this report, we emphasize special measures to achieve regionally restricted gene expression in embryonic midbrain dopaminergic neuron progenitors, including how to inject DNA constructs specifically into the embryonic midbrain region and how to pinpoint electroporation with small custom-made electrodes. Analyzing chick midbrain at later stages provides an excellent in vivo system for plasmid vector-mediated gain-of-function and loss-of-function studies of midbrain development. Modification of the experimental system may extend the assay to other parts of the nervous system for performing fate mapping analysis and for investigating the regulation of gene expression.

In ovo Electroporation in Chick Midbrain for Studying Gene Function in Dopaminergic Neuron Development

To assess the function and the regulation of genes during the development of midbrain dopaminergic neurons, we describe a method that involves in ovo electroporation of plasmid DNA constructs into embryonic chick ventral midbrain dopaminergic neuron progenitors. This technique can be used to achieve efficient expression of genes of interest to study different aspects of midbrain development and dopaminergic neuron differentiation.

Dopaminergic neurons located in the ventral midbrain control movement, emotional behavior, and reward mechanisms1-3. The dysfunction of ventral midbrain ...

Generation of Topically Transgenic Rats by In utero Electroporation and In vivo Bioluminescence Screening

In utero electroporation (IUE) is a technique which allows genetic modification of cells in the brain for investigating neuronal development. So far, the use of IUE for investigating behavior or neuropathology in the adult brain has been limited by insufficient methods for monitoring of IUE transfection success by non-invasive techniques in postnatal animals. 
 For the present study, E16 rats were used for IUE. After intraventricular injection of the nucleic acids into the embryos, positioning of the tweezer electrodes was critical for targeting either the developing cortex or the hippocampus. 
 Ventricular co-injection and electroporation of a luciferase gene allowed monitoring of the transfected cells postnatally after intraperitoneal luciferin injection in the anesthetized live P7 pup by in vivo bioluminescence, using an IVIS Spectrum device with 3D quantification software. 
 Area definition by bioluminescence could clearly differentiate between cortical and hippocampal electroporations and detect a signal longitudinally over time up to 5 weeks after birth. This imaging technique allowed us to select pups with a sufficient number of transfected cells assumed necessary for triggering biological effects and, subsequently, to perform behavioral investigations at 3 month of age. As an example, this study demonstrates that IUE with the human full length DISC1 gene into the rat cortex led to amphetamine hypersensitivity. Co-transfected GFP could be detected in neurons by post mortem fluorescence microscopy in cryosections indicating gene expression present at &ge;6 months after birth.
 We conclude that postnatal bioluminescence imaging allows evaluating the success of transient transfections with IUE in rats. Investigations on the influence of topical gene manipulations during neurodevelopment on the adult brain and its connectivity are greatly facilitated. For many scientific questions, this technique can supplement or even replace the use of transgenic rats and provide a novel technology for behavioral neuroscience.

Generation of Topically Transgenic Rats by In utero Electroporation and In vivo Bioluminescence Screening

Genes can be manipulated during development of the cortex or the hippocampus of the rat via in utero electroporation (IUE) at E16, to enable fast and targeted modifications in neuronal connectivity for later studies of behavior or neuropathology in adult animals. Postnatal in vivo imaging for control of IUE success is performed by bioluminescence of activating co-transfected luciferase.

 In utero electroporation (IUE) is a technique which allows genetic modification of cells in the brain for investigating neuronal development. So far, the ...

Rapid Genotyping of Animals Followed by Establishing Primary Cultures of Brain Neurons

High-resolution analysis of the morphology and function of mammalian neurons often requires the genotyping of individual animals followed by the analysis of primary cultures of neurons. We describe a set of procedures for: labeling newborn mice to be genotyped, rapid genotyping, and establishing low-density cultures of brain neurons from these mice. Individual mice are labeled by tattooing, which allows for long-term identification lasting into adulthood. Genotyping by the described protocol is fast and efficient, and allows for automated extraction of nucleic acid with good reliability. This is useful under circumstances where sufficient time for conventional genotyping is not available, e.g., in mice that suffer from neonatal lethality. Primary neuronal cultures are generated at low density, which enables imaging experiments at high spatial resolution. This culture method requires the preparation of glial feeder layers prior to neuronal plating. The protocol is applied in its entirety to a mouse model of the movement disorder DYT1 dystonia (&#916;E-torsinA knock-in mice), and neuronal cultures are prepared from the hippocampus, cerebral cortex and striatum of these mice. This protocol can be applied to mice with other genetic mutations, as well as to animals of other species. Furthermore, individual components of the protocol can be used for isolated sub-projects. Thus this protocol will have wide applications, not only in neuroscience but also in other fields of biological and medical sciences.

We describe procedures for labeling and genotyping newborn mice and generating primary neuronal cultures from them. The genotyping is rapid, efficient and reliable, and allows for automated nucleic-acid extraction. This is especially useful for neonatally lethal mice and their cultures that require prior completion of genotyping.

High-resolution analysis of the morphology and function of mammalian neurons often requires the genotyping of individual animals followed by the analysis ...

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, ...

Modeling Neuronal Death and Degeneration in Mouse Primary Cerebellar Granule Neurons

Cerebellar granule neurons (CGNs) are a commonly used neuronal model, forming an abundant homogeneous population in the cerebellum. In light of their post-natal development, abundance, and accessibility, CGNs are an ideal model to study neuronal processes, including neuronal development, neuronal migration, and physiological neuronal activity stimulation. In addition, CGN cultures provide an excellent model for studying different modes of cell death including excitotoxicity and apoptosis. Within a week in culture, CGNs express N-methyl-D-aspartate (NMDA) receptors, a specific ionotropic glutamate receptor with many critical functions in neuronal health and disease. The addition of low concentrations of NMDA in conjunction with membrane depolarization to rodent primary CGN cultures has been used to model physiological neuronal activity stimulation while the addition of high concentrations of NMDA can be employed to model excitotoxic neuronal injury. Here, a method of isolation and culturing of CGNs from 6 day old pups as well as genetic manipulation of CGNs by adenoviruses and lentiviruses are described. We also present optimized protocols on how to stimulate NMDA-induced excitotoxicity, low-potassium-induced apoptosis, oxidative stress and DNA damage following transduction of these neurons.

This protocol describes a simple method for isolating and culturing primary mouse cerebral granule neurons (CGNs) from 6-7 day old pups, efficient transduction of CGNs for loss and gain of function studies, and modelling NMDA-induced neuronal excitotoxicity, low-potassium-induced cell death, DNA-damage, and oxidative stress using the same culture model.

Cerebellar granule neurons (CGNs) are a commonly used neuronal model, forming an abundant homogeneous population in the cerebellum. In light of their ...

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 ...