We thank Dr. Doris K. Wu for expression plasmids and in situ probes, the Johns Hopkins University Center for Sensory Biology imaging facility and the Center for Hearing and Balance. This work was supported by NIDCD Grant T32 DC000023 to L.E.

The eggs and unhatched embryos are cared for and treated ethically&#160;and humanely. All protocols for unhatched embryo use were approved by the Animal Care and Use Committee at the Johns Hopkins School of Medicine, Baltimore, Maryland.
1. Eggs and Preparation of Expression Constructs
<ol>
	<li>Eggs:
	<ol>
		<li>Incubate 3 - 4 dozen fertilized chicken eggs (Gallus gallus) lying flat on their sides at 37 &#176;C.
		<ol>
			<li>After 24 hr&#160;of incubation, pull 3 cc of albumen with a syringe from the round back end of the egg and seal the hole with clear tape. This creates an air chamber between the embryo and the eggshell, allowing for ease of access to the embryo without the embryo sticking to the shell when cutting the window for access on top of the egg 19.</li>
			<li>At 117 hr&#160;of incubation time, stage the embryos according to Hamburger and Hamilton 20 developmental stages at E4 (HH24-25) (See Figure 1D).</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Expression Constructs:
	<ol>
		<li>Prepare the plasmid DNA using reagents and the protocol provided by the manufacturer of a commercially available preparation kit. At the final step of preparation, elute the DNA into 500 &#181;l TE (Tris-EDTA) buffer provided in the kit into a 1.5 ml tube.</li>
		<li>Ethanol precipitate the DNA to concentrate it by adding 50 &#181;l of 3 M Sodium Acetate and 1 ml of 100% Ethanol to the tube. Place the tube at -20 &#176;C O/N.</li>
		<li>Centrifuge the tube for 30 min at 14,000 rpm at 4 &#176;C. Remove the supernatant and air-dry the pellet for 10 min at RT. Dissolve the pellet in 15 &#181;l TE buffer, which should yield a concentration of ~4 &#181;g/&#181;l. 
		NOTE: The control expression constructs used here are pMES-IRES-GFP10, which is driven by a chicken &#946;-actin promoter, or pCI-H2B-IRES-RFP10, which is driven by the CMV promoter.</li>
	</ol>
	</li>
</ol>
2. Chicken In Ovo&#160;Micro-electroporation and In Ovo&#160;Cell Proliferation Assay
<ol>
	<li>In Ovo&#160;Micro-injection of Expression Construct and Micro-electroporation:
	<ol>
		<li>Pull the glass capillary tubes into fine needles using a micro-pipette puller with the following optimized parameters for a 2.5 x 2.5 mm Box Platinum Heating Filament: Pressure = 500, Heat = 600 &#176;C, Pull = 64, Velocity = 105, and Time = 150 msec (see Table 1).</li>
		<li>Set up the Left- and Right-handed micro-manipulator stages flanking the microscope (see Figure 1A). The Right-handed micro-manipulator holds the glass capillary needle and the Left-handed micro-manipulator holds the electrodes (Figure 1A).</li>
		<li>Prepare the finely pulled glass capillary needle for micro-injection by cutting the tip of the needle with a forceps while working under the microscope.</li>
		<li>Fill the needle manually by hand using the micro-manipulator with 2.5 &#181;l of plasmid DNA tinted with 0.1% Fast Green while working under the microscope.</li>
		<li>Place the egg lying on its side within a mold/egg holding device (see Figure 1A). Cut a round window on top of the egg using scissors 19 (Figure 1A).</li>
		<li>While working under the microscope, carefully open the two membranes overlaying the embryo using forceps.</li>
		<li>While working under the microscope, deliver approximately ~0.5 &#181;l of plasmid DNA to the right otic vesicle lumen by micro-injection manually using the right hand by using the micro-manipulator and by micro-electroporation.
		<ol>
			<li>To do so, micro-inject the right otic vesicle lumen with the DNA with the Right-hand micro-manipulator (Figure 1B-D) while at the same time using the left hand holding a forcep to steady the head of the embryo, because the head of the embryo dips at stage E4. Do not micro-inject past the otic vesicle lumen, because this will damage the otic vesicle.</li>
			<li>Immediately after micro-injection, while working under the microscope, use the Left-hand micro-manipulator to place the positive (anode) 2 mm platinum electrode anterior-ventral to the right otic vesicle and the negative 2 mm electrode (cathode) in parallel 1 mm apart (see Figure 1 C). Deliver 4 pulses at 12 V with 100 msec duration and 200 msec spacing. The left otic vesicle serves as an internal untreated control. 
			NOTE: Clean the electrodes in between electroporations with a cotton-tipped swab dipped in 1x PBS.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>In Ovo&#160;Cell Proliferation Assay:
	<ol>
		<li>Immediately after electroporation add 50 &#956;l of 0.25 mg/ml EdU in 1x PBS by manually dropping the 50 &#956;l EdU solution onto the whole embryo in ovo using a pipette. Seal the eggs with tape and return to the incubator for 18 -&#160;96 hr.</li>
		<li>Carefully remove the tape and check the embryos for fluorescent GFP or RFP signal within the otic vesicle after 18 - 24 hr&#160;using a standard fluorescent microscope (see Figure 1 E-E&#39;). If fluorescent signal is present, at this point harvest the embryos for analyses or reseal with tape and return it to the incubator for harvesting and analyses at later stages (see Figure 1 F-P&#39;&#39;). 
		NOTE: Expression of GFP signal with the pMES-IRES-GFP construct is evident 6 - 7 hr&#160;after electroporation 10.</li>
	</ol>
	</li>
</ol>
3. Embryo Harvesting and Tissue Processing for RNA In Situ hybridization and Immunohistochemistry
<ol>
	<li>Harvest the embryos using forceps. Rinse the embryo in cold 1x PBS. Remove the heads of the embryos, by cutting the head by its neck using forceps, and place the heads into 4% paraformaldehyde O/N at 4 &#176;C. Puncture the brain using a forcep to allow penetration of the 4% paraformaldehyde inside the head.</li>
	<li>Dehydrate the heads in 30% sucrose (in 1x PBS) O/N at 4 &#176;C.</li>
	<li>Mount the heads in cryoprotective medium by rapid freezing in a slurry of dry ice and methylbutane (2-Methylbutane). Alternatively, rapid freeze the heads in cryoprotective medium with liquid nitrogen. Store the mounted heads at -80 &#176;C.</li>
	<li>Cryosection the heads into 12 &#181;m thick tissue sections and collect all the inner ear-containing tissue sections onto superfrosted microscope glass slides.</li>
	<li>Perform standard RNA in situ hybridization and immunohistochemistry as previously described 4,21, and analyze for EdU cell proliferation following the protocol provided by the manufacturer of the kit. 
	NOTE: Hair cells can be identified using rabbit polyclonal &#945;-MyosinVIIa (Myo7a) antibody (1:1,000, Proteus Biosciences) and fluorescently-labeled secondary antibody (1:250, Goat anti-Rabbit AlexaFluor 488; Invitrogen).</li>
</ol>
4. Image Capture and Processing
<ol>
	<li>Take images with digital imaging equipment. Image immunohistochemistry results with a standard fluorescent microscope and results of the in situ using a standard wide-field microscope (ranging from 5x to 40x in magnification).</li>
	<li>Process the images using image processing software.</li>
</ol>

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T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+the+inner+ear.">Development of the inner ear.</a> Current opinion in genetics &amp; development. 32, 112-118 (2015).</li><li>Raft, S., 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=Cross-regulation+of+Ngn1+and+Math1+coordinates+the+production+of+neurons+and+sensory+hair+cells+during+inner+ear+development.">Cross-regulation of Ngn1 and Math1 coordinates the production of neurons and sensory hair cells during inner ear development.</a> Development. 134, 4405-4415 (2007).</li><li>Satoh, T., Fekete, D. 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The authors have nothing to disclose.

The here described method of in ovo micro-electroporation is optimized for gene transfer into the developing auditory organ. It is compatible with plasmid DNA-based expression vectors typically used to manipulate gene function/expression. The timing of electroporation at E4 is optimal for investigations that focus on HC development in the auditory organ. The most critical steps are micro-injecting the DNA into the otic vesicle lumen without going too deep with the needle and damaging the otic vesicle (see <stron...

Despite differences in morphology and cellular patterning between the mammalian and avian auditory sensory organ, the molecular factors and pathways responsible for sensory HC development are thought to be evolutionarily conserved 1-3. The basilar papilla, which houses the auditory HCs and their surrounding SCs, develops as an outpocketing of the inner ear otocyst. Early on a pool of HC and SC progenitors is specified within the otic placode/otic cup neural-sensory competent domain (NSD). Fate-mapping data provide evidence that neuronal and sensory lineages are linked and arise from the NSD located in the antero-ventral region of the otic cup or otocyst in mice and chicken 4,5. First, neuroblasts delaminate from the NSD to give rise to the neurons of the auditory-vestibular ganglion, which eventually split into auditory and vestibular ganglia. These neurons innervate the sensory HCs of the inner ear and nuclei in the brainstem. The cells that remain in the NSD are thought to give rise to various sensory patches, including the auditory sensory organ, consisting of the mechano-transducing sensory HCs and their associated SCs.
In both the chick and murine, auditory organ sensory progenitor cell-cycle exit and HC differentiation occur in opposing gradients. In chick, auditory progenitor cell-cycle exit starts around ~E5 and progresses from the base to the apex, and from the center to the periphery 6. One day later, HC differentiation starts in the apex and progresses to the base 7. Studying the development of the inner ear in chicken provides many technical advantages as functional mechanisms can be investigated with relative ease in ovo as opposed to manipulating embryos in utero in other model systems, which requires complex surgeries. The method described here uses in ovo micro-electroporation to target genes of interest in the presumptive basilar papilla area anterior-ventrally in the otic vesicle specifically at E4.
Electroporation in ovo is a technique that is well established and commonly used 8-14. The principle of the electroporation technique is based on the fact that nucleotides (e.g., plasmid DNA, synthetic DNA, or RNA oligonucleotides) are negatively charged. The DNA is injected into the tissue of interest. When an electric current is placed across the tissue, the current opens up transient pores in the cell walls and allows for the uptake of the DNA, as the negatively charged DNA flows toward the positive electrode (anode). For gain-of-function experiments, genes of interest are commonly subcloned into expression plasmids that contain appropriate expression cassettes for green fluorescent protein (GFP) or red fluorescent protein (RFP). For loss-of-function experiments plasmid-based dominant negative repressor constructs, or RNAi, or morpholino constructs are commonly used 15,16. To inhibit microRNA (miRNA) function miRNAs sponge constructs, which are typically plasmid based, can be used 17. The here described method allows for investigating the molecular mechanisms that control proliferation and differentiation in the auditory organ, as the in ovo micro-electroporation method can be easily combined with in ovo cell proliferation assay by adding EdU to the whole embryo.
The electroporation and addition of EdU is performed at E4 in the otic vesicle, which is one day before the onset of cell-cycle exit in the auditory organ. Analysis of the auditory organ is typically performed 18 - 96 hr&#160;after electroporation at E5 (onset of sensory progenitor cell-cycle exit), E6 (onset of HC differentiation), and E7 (during HC differentiation); and later up to ~E9 (end of HC differentiation). This electroporation method of gene transfer is transient lasting approximately ~4 days, because the genes of interest do not integrate into the genome, but the method is applicable for use with appropriate plasmid DNA-based expression vectors, which do have the ability to integrate into the genome, such as Tol2-mediated gene transfer 11. With this method robust GFP or RFP expression lasts ~4 days in the cochlea, after which point the signals fade, yet provide an ample time window to study the intricate development of the auditory organ. This in ovo gene transfer method is novel and allows to specifically target the presumptive auditory organ at E4, which is optimal for investigations that focus on HC development in the auditory organ. It is a good addition to alternative methods, which electroporate at much younger developmental stages 11,12 or compared to the use of in vitro basilar papillae explant cultures 18.

<table><tbody><tr><td>Sterile 1x PBS pH 7.4</td><td>gibco</td><td>10010-023</td><td></td></tr><tr><td>Fast Green FCF Powder</td><td>Sigma</td><td>F7252-5G</td><td></td></tr><tr><td>EdU Powder</td><td>Invitrogen</td><td>E10187</td><td></td></tr><tr><td>Click-IT EdU Alexa Fluor 555 Imaging Kit</td><td>Invitrogen</td><td>C10338</td><td></td></tr><tr><td>HiSpeed Plasmid Midi Kit (25)</td><td>Qiagen</td><td>12643</td><td></td></tr><tr><td>ECM 830 ElectroSquarePorator&amp;nbsp;</td><td>BTX Harvard Apparatus</td><td></td><td></td></tr><tr><td>Banana to Micrograbber Cable Kit</td><td>BTX Harvard Apparatus</td><td>45-0216</td><td></td></tr><tr><td>Right Handed &amp;amp; Left Handed Micromanipulators</td><td>World Precision Instruments Inc.&amp;nbsp;</td><td>M3301R &amp;amp; M3301L</td><td></td></tr><tr><td>Two 12 mm Magnetic Holding Device Stages with 7 inch vertical posts</td><td>World Precision Instruments Inc.&amp;nbsp;</td><td>M10</td><td></td></tr><tr><td>Metal Steel Base Plate 12x24 inch</td><td>World Precision Instruments Inc.&amp;nbsp;</td><td>5479</td><td></td></tr><tr><td>Scissors for Eggs 12 cm long curved, 12 mm extrafine blades; Spring Scissors</td><td>World Precision Instruments Inc.&amp;nbsp;</td><td>14120</td><td></td></tr><tr><td>Micropippette Puller for pulling needles</td><td>Sutter Instrument Co.</td><td>P-97</td><td></td></tr><tr><td>2.5x2.5 mm Box Platinum Heating Filament</td><td>Sutter Instrument Co.</td><td></td><td></td></tr><tr><td>Glass Capillary Tubes/Needles/No Fiber/Borosil 1 mm</td><td>FHC</td><td>27-30-0</td><td></td></tr><tr><td>Hamilton Glass Syringe 100 &amp;mu;l</td><td>Hamilton</td><td>80601 Model 710LT</td><td></td></tr><tr><td>Mineral Oil (Heavy) for Hamilton Glass Syringe</td><td>Fisher Scientific</td><td>O122-1</td><td></td></tr><tr><td>Polyethylene Tubing for connecting the Glass Syringe and Glass Cappillary Needles/ Non Toxic</td><td>Becton Dickinson and Company (BD)</td><td>427420 Intramedic Clay Adams Brand</td><td></td></tr><tr><td>3 cc Disposable Syringes</td><td>Becton Dickinson and Company (BD)</td><td>309657</td><td></td></tr><tr><td>Disposable 21 Gauge Needles</td><td>Becton Dickinson and Company (BD)</td><td>305122</td><td></td></tr><tr><td>One pair of 2 mm Platinum Electrodes</td><td>Bulldog Bio. / Nepagene</td><td>CUY611P3-2</td><td></td></tr><tr><td>Electrode Holder</td><td>Bulldog Bio. / Nepagene</td><td>CUY580</td><td></td></tr><tr><td>One pair of Dumont fine forceps number 5</td><td>Fine Science Tools (FST)</td><td></td><td></td></tr><tr><td>Matte finish invisible tape for sealing eggs</td><td>Office Depot</td><td>520-928</td><td></td></tr><tr><td>Cotton-Tipped Swabs</td><td>Fisher Scientific</td><td>23-400-101</td><td></td></tr><tr><td>Sterile filter tips</td><td></td><td></td><td></td></tr></tbody></table>

gene transfer into the chicken auditory organ by in ovo micro-electroporation

Chicken embryos are ideal model systems for studying embryonic development as manipulations of gene function can be conducted with relative ease in ovo. The inner ear auditory sensory organ is critical for our ability to hear. It houses a highly specialized sensory epithelium that consists of mechano-transducing hair cells (HCs) and surrounding glial-like supporting cells (SCs). Despite structural differences in the auditory organs, molecular mechanisms regulating the development of the auditory organ are evolutionarily conserved between mammals and aves. In ovo electroporation is largely limited to early stages at E1 - E3. Due to the relative late development of the auditory organ at E5, manipulations of the auditory organ by in ovo electroporation past E3 are difficult due to the advanced development of the chicken embryo at later stages. The method presented here is a transient gene transfer method for targeting genes of interest at stage E4 - E4.5 in the developing chicken auditory sensory organ via in ovo micro-electroporation. This method is applicable for gain- and loss-of-functions with conventional plasmid DNA-based expression vectors and can be combined with in ovo cell proliferation assay by adding EdU (5-ethynyl-2&#180;-deoxyuridine) to the whole embryo at the time of electroporation. The use of green or red fluorescent protein (GFP or RFP) expression plasmids allows the experimenter to quickly determine whether the electroporation successfully targeted the auditory portion of the developing inner ear. In this method paper, representative examples of GFP electroporated specimens are illustrated; embryos were harvested 18 - 96 hr&#160;after electroporation and targeting of GFP to the pro-sensory area of the auditory organ was confirmed by RNA in situ hybridization. The method paper also provides an optimized protocol for the use of the thymidine analog EdU to analyze cell proliferation; an example of an EdU based cell proliferation assay that combines immuno-labeling and click EdU chemistry is provided.

In this method paper plasmid&#160;DNA consisting of green fluorescent protein (GFP) expression cassettes was targeted into the developing chicken basilar papilla (BP) with optimized parameters of 12 V&#160;and 4 pulses with 100 msec pulse duration and intervals of 200 msec, yielding a ~50% embryo survival rate and efficiency of plasmid-DNA targeting into the BP. Fluorescent imaging of native GFP expression in developing embryos showed this method of electroporation preferentially targets ...

Watch this Scientific Journal Video about Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation at JoVE.com

Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

The auditory organ mediates hearing. Here we present a modified in ovo micro-electroporation method optimized for studying auditory progenitor cell proliferation and differentiation in the developing chicken auditory organ.

Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

Chicken embryos are ideal model systems for studying embryonic development as manipulations of gene function can be conducted with relative ease in ovo. ...

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9.4K Views.  The Johns Hopkins University, School of Medicine. The auditory organ mediates hearing. Here we present a modified in ovo micro-electroporation method optimized for studying auditory progenitor cell proliferation and differentiation in the developing chicken auditory organ. 

Video: Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

Culture of Embryonic Mouse Cochlear Explants and Gene Transfer by Electroporation

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair cells are aligned in one row of inner hair cells and three rows of outer hair cells that extend along the basal to apical axis of the cochlea. The explant culture technique described here provides an efficient method to isolate and maintain cochlear explants from the embryonic mouse inner ear. Also, the morphology and molecular characteristics of sensory hair cells and nonsensory supporting cells within the cochlear explant cultures resemble those observed in vivo and can be studied within its intrinsic cellular environment. The cochlear explants can serve as important experimental tools for the identification and characterization of molecular and genetic pathways that are involved in cellular specification and patterning. Although transgenic mouse models provide an effective approach for gene expression studies, a considerable number of mouse mutants die during embryonic development thereby hindering the analysis and interpretation of developmental phenotypes. The organ of Corti from mutant mice that die before birth can be cultured so that their in vitro development and responses to different factors can be analyzed. Additionally, we describe a technique for electroporating embryonic cochlear explants ex vivo which can be used to downregulate or overexpress specific gene(s) and analyze their potential endogenous function and test whether specific gene product is necessary or sufficient in a given context to influence mammalian cochlear development1-8.

We present a method that describes isolation and culture of cochlear explants from embryonic mouse inner ear. We also demonstrate a method for gene transfer into cochlear explants via square-wave electroporation. The in vitro explant culture coupled with gene transfer technique enables researchers to study the effects of altering gene expression during development.

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair ...

In Ovo Electroporations of HH Stage 10 Chicken Embryos

Large size and external development of the chicken embryo have long made it a valuable tool in the study of developmental biology.  With the advent of molecular biological techniques, the chick has become a useful system in which to study gene regulation and function.  By electroporating DNA or RNA constructs into the developing chicken embryo, genes can be expressed or knocked down in order to analyze in vivo gene function.  Similarly, reporter constructs can be used for fate mapping or to examine putative gene regulatory elements.  Compared to similar experiments in mouse, chick electroporation has the advantages of being quick, easy and inexpensive.  This video demonstrates first how to make a window in the eggshell to manipulate the embryo.  Next, the embryo is visualized with a dilute solution of India ink injected below the embryo.  A glass needle and pipette are used to inject DNA and Fast Green dye into the developing neural tube, then platinum electrodes are placed parallel to the embryo and short electrical pulses are administered with a pulse generator.  Finally, the egg is sealed with tape and placed back into an incubator for further development.  Additionally, the video shows proper egg storage and handling and discusses possible causes of embryo loss following electroporation.

Chick in ovo electroporation is a technique which allows genetic manipulation of the avian embryo. Common applications of this technique include functional analysis of genes and putative enhancer elements. This video demonstrates neural tube electroporation in HH 10 chick embryos. Injection technique and proper egg handling are discussed.

Large size and external development of the chicken embryo have long made it a valuable tool in the study of developmental biology.  With the advent of ...

Biology

In Ovo Electroporation in the Chicken Auditory Brainstem

Electroporation is a method that introduces genes of interest into biologically relevant organisms like the chicken embryo. It is long established that the chicken embryo is an effective research model for studying basic biological functions of auditory system development. More recently, the chicken embryo has become particularly valuable in studying gene expression, regulation and function associated with hearing. In ovo electroporation can be used to target auditory brainstem regions responsible for highly specialized auditory functions. These regions include the chicken nucleus magnocellularis (NM) and nucleus laminaris (NL). NM and NL neurons arise from distinct precursors of rhombomeres 5 and 6 (R5/R6). Here, we present in ovo electroporation of plasmid-encoded genes to study gene-related properties in these regions. We show a method for spatial and temporal control of gene expression that promote either gain or loss of functional phenotypes. By targeting auditory neural progenitor regions associated with R5/R6, we show plasmid transfection in NM and NL. Temporal regulation of gene expression can be achieved by adopting a tet-on vector system. This is a drug inducible procedure that expresses the genes of interest in the presence of doxycycline (Dox). The in ovo electroporation technique &#8211; together with either biochemical, pharmacological, and or in vivo functional assays &#8211; provides an innovative approach to study auditory neuron development and associated pathophysiological phenomena.

In Ovo Electroporation in the Chicken Auditory Brainstem

Auditory brainstem neurons of avians and mammals are specialized for fast neural encoding, a fundamental process for normal hearing functions. These neurons arise from distinct precursors of embryonic hindbrain. We present techniques utilizing electroporation to express genes in the hindbrain of chicken embryos to study gene function during auditory development.

Electroporation is a method that introduces genes of interest into biologically relevant organisms like the chicken embryo. It is long established that ...

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 ...

Neuroscience

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 ...

In ovo Expression of MicroRNA in Ventral Chick Midbrain

Non-coding RNAs are additional players in regulating gene expression. Targeted in ovo electroporation of specific areas provides a unique tool for spatial and temporal control of ectopic microRNA expression. However, ventral brain structures like ventral midbrain are rather difficult to reach for any manipulations. Here, we demonstrate an efficient way to electroporate miRNA into ventral midbrain using thin platinum electrodes. This method offers a reliable way to transfect specific areas of the midbrain and a useful tool for in vivo studies.

In ovo Expression of MicroRNA in Ventral Chick Midbrain

Ectopic expression is one technique to elucidate the microRNAs role in brain development. However, targeting specific areas using in ovo electroporation is challenging. Here, we show an efficient way to selectively electroporate ventral and dorsal midbrain regions.

Non-coding RNAs are additional players in regulating gene expression. Targeted in ovo electroporation of specific areas provides a unique tool for spatial ...

In Ovo and Ex Ovo Methods to Study Avian Inner Ear Development

The inner ear perceives sound and maintains balance using the cochlea and vestibule. It does this by using a dedicated mechanosensory cell type known as the hair cell. Basic research in the inner ear has led to a deep understanding of how the hair cell functions, and how dysregulation can lead to hearing loss and vertigo. For this research, the mouse has been the pre-eminent model system. However, mice, like all mammals, have lost the ability to replace hair cells. Thus, when trying to understand cellular therapies for restoring inner ear function, complementary studies in other vertebrate species could provide further insights. The auditory epithelium of birds, the basilar papilla (BP), is a sheet of epithelium composed of mechanosensory hair cells (HCs) intercalated by supporting cells (SCs). Although the anatomical architecture of the basilar papilla and the mammalian cochlea differ, the molecular mechanisms of inner ear development and hearing are similar. This makes the basilar papilla a useful system for not only comparative studies but also to understand regeneration. Here, we describe dissection and manipulation techniques for the chicken inner ear. The technique shows genetic and small molecule inhibition methods, which offer a potent tool for studying the molecular mechanisms of inner ear development. In this paper, we discuss in ovo electroporation techniques to genetically perturb the basilar papilla using CRIPSR-Cas9 deletions, followed by dissection of the basilar papilla. We also demonstrate the BP organ culture and optimal use of culture matrices, to observe the development of the epithelium and the hair cells.

In Ovo and Ex Ovo Methods to Study Avian Inner Ear Development

The chick is a cost-effective, accessible, and widely available model organism for a variety of studies. Here, a series of protocols is detailed to understand the molecular mechanisms underlying avian inner ear development and regeneration.

The inner ear perceives sound and maintains balance using the cochlea and vestibule. It does this by using a dedicated mechanosensory cell type known as ...

In Ovo Electroporation in Embryonic Chick Retina

Chicken embryonic retina is an excellent tool to study retinal development in higher vertebrates. Because of large size and external development, it is comparatively very easy to manipulate the chick embryonic retina using recombinant DNA/RNA technology. Electroporation of DNA/RNA constructs into the embryonic retina have a great advantage to study gene regulation in retinal stem/progenitor cells during retinal development. Different type of assays such as reporter gene assay, gene over-expression, gene knock down (shRNA) etc. can be performed using the electroporation technique. This video demonstrates targeted retinal injection and in ovo electroporation into the embryonic chick retina at the Hamburger and Hamilton stage 22-23, which is about embryonic day 4 (E4). Here we show a rapid and convenient in ovo electroporation technique whereby a plasmid DNA that expresses green fluorescent protein (GFP) as a marker is directly delivered into the chick embryonic subretinal space and followed by electric pulses to facilitate DNA uptake by retinal stem/progenitor cells. The new method of retinal injection and electroporation at E4 allows the visualization of all retinal cell types, including the late-born neurons1, which has been difficult with the conventional method of injection and electroporation at E1.52.

In Ovo Electroporation in Embryonic Chick Retina

The overall goal of this video is to show how to perform targeted retinal injection and in ovo electroporation of DNA/RNA constructs into the chick embryonic retina at the Hamburger and Hamilton stage 22-23, which is about embryonic day 4 (E4). This technique is very useful to study gene expression, gene regulation, and morphological change in developing chick retina.

Chicken embryonic retina is an excellent tool to study retinal development in higher vertebrates. Because of large size and external development, it is ...

Gene Transfer into Older Chicken Embryos by ex ovo Electroporation

The chicken embryo provides an excellent model system for studying gene function and regulation during embryonic development. In ovo electroporation is a powerful method to over-express exogenous genes or down-regulate endogenous genes in vivo in chicken embryos1. Different structures such as DNA plasmids encoding genes2-4, small interfering RNA (siRNA) plasmids5, small synthetic RNA oligos6, and morpholino antisense oligonucleotides7 can be easily transfected into chicken embryos by electroporation. However, the application of in ovo electroporation is limited to embryos at early incubation stages (younger than stage HH20 - according to Hamburg and Hamilton)8 and there are some disadvantages for its application in embryos at later stages (older than stage HH22 - approximately 3.5 days of development). For example, the vitelline membrane at later stages is usually stuck to the shall membrane and opening a window in the shell causes rupture of the vessels, resulting in death of the embryos; older embryos are covered by vitelline and allantoic vessels, where it is difficult to access and manipulate the embryos; older embryos move vigorously and is difficult to control the orientation through a relatively small window in the shell.
In this protocol we demonstrate an ex ovo electroporation method for gene transfer into chicken embryos at late stages (older than stage HH22). For ex ovo electroporation, embryos are cultured in Petri dishes9 and the vitelline and allantoic vessels are widely spread. Under these conditions, the older chicken embryos are easily accessed and manipulated. Therefore, this method overcomes the disadvantages of in ovo electroporation applied to the older chicken embryos. Using this method, plasmids can be easily transfected into different parts of the older chicken embryos10-12.

Gene Transfer into Older Chicken Embryos by ex ovo Electroporation

A method of gene transfer into chicken embryos at later incubation stages (older than Hamburger and Hamilton stage (HH) 22) is described. This method overcomes disadvantages of in ovo electroporation applied to older chicken embryos and is a useful technique to study gene function and regulation at older developmental stages.

The chicken embryo provides an  excellent model system for studying gene function and regulation during  embryonic development. In ovo electroporation is ...

Dissecting Cell-Autonomous Function of Fragile X Mental Retardation Protein in an Auditory Circuit by In Ovo Electroporation

Fragile X mental retardation protein (FMRP) is an mRNA-binding protein that regulates local protein translation. FMRP loss or dysfunction leads to aberrant neuronal and synaptic activities in fragile X syndrome (FXS), which is characterized by intellectual disability, sensory abnormalities, and social communication problems. Studies of FMRP function and FXS pathogenesis have primarily been conducted with Fmr1 (the gene encoding FMRP) knockout in transgenic animals. Here we report an in vivo method for determining the cell-autonomous function of FMRP during the period of circuit assembly and synaptic formation using chicken embryos. This method employs stage-, site-, and direction-specific electroporation of a drug-inducible vector system containing Fmr1 small hairpin RNA (shRNA) and an EGFP reporter. With this method, we achieved selective FMRP knockdown in the auditory ganglion (AG) and in one of its brainstem targets, the nucleus magnocellularis (NM), thus providing a component-specific manipulation within the AG-NM circuit. Additionally, the mosaic pattern of the transfection allows within-animal controls and neighboring neuron/fiber comparisons for enhanced reliability and sensitivity in data analyzing. The inducible vector system provides temporal control of gene editing onset to minimize accumulating developmental effects. The combination of these strategies provides an innovative tool to dissect the cell-autonomous function of FMRP in synaptic and circuit development.

Dissecting Cell-Autonomous Function of Fragile X Mental Retardation Protein in an Auditory Circuit by In Ovo Electroporation

Using in ovo electroporation, we devised a method to selectively transfect the auditory inner ear and cochlear nucleus in chicken embryos to achieve a cell-group-specific knockdown of fragile X mental retardation protein during discrete periods of circuit assembly.

Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

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