Name: in ovo and ex ovo methods to study avian inner ear development
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Description: Watch this Scientific Journal Video about In Ovo and Ex Ovo Methods to Study Avian Inner Ear Development at JoVE.com

We gratefully acknowledge support from NCBS, TIFR, Infosys-TIFR Leading Edge Research Grant, DST-SERB, and the Royal National Institute for the Deaf. We would like to thank Central Poultry Development Organization and Training Institute, Hesaraghatta, Bengaluru. We are grateful to CIFF and EM facility and lab support at NCBS. We thank Yoshiko Takahashi and Koichi Kawakami for the Tol2-eGFP and T2TP constructs, and Guy Richardson for HCA and G19 Pcdh15 antibody. We are grateful to Earlab members for their constant support and valuable feedback on the protocol.

Protocols involving the procurement, culture, and use of fertilized chicken eggs and unhatched embryos were approved by the Institutional Animal Ethics Committee of the National Centre for Biological Sciences, Bengaluru, Karnataka.
1. In ovo electroporation of chick auditory precursors
<ol>
	<li>sgRNA design and cloning for CRISPR/Cas9 gene knockout
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		<li>For creating gene knockouts, design guide RNAs to disrupt the exon regions of the gene, preferably closer ...

<ol>
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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymmetric+distribution+of+cadherin+23+and+protocadherin+15+in+the+kinocilial+links+of+avian+sensory+hair+cells.">Asymmetric distribution of cadherin 23 and protocadherin 15 in the kinocilial links of avian sensory hair cells.</a> The Journal of Comparative Neurology. 518 (21), 4288-4297 (2010).</li><li>Bartolami, S., Goodyear, R., Richardson, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Appearance+and+distribution+of+the+275+kD+hair-cell+antigen+during+development+of+the+avian+inner+ear.">Appearance and distribution of the 275 kD hair-cell antigen during development of the avian inner ear.</a> The Journal of Comparative Neurology. 314 (4), 777-788 (1991).</li><li>Funahashi, J., Nakamura, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation+in+avian+embryos.">Electroporation in avian embryos.</a> Methods in Molecular Biology. 461, 377-382 (2008).</li><li>Nakamura, H., Funahashi, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation:+past,+present+and+future.">Electroporation: past, present and future.</a> Development, Growth &amp; Differentiation. 55 (1), 15-19 (2013).</li><li>Olaya-Sanchez, D., 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=Fgf3+and+Fgf16+expression+patterns+define+spatial+and+temporal+domains+in+the+developing+chick+inner+ear.">Fgf3 and Fgf16 expression patterns define spatial and temporal domains in the developing chick inner ear.</a> Brain Structure &amp; Function. 222 (1), 131-149 (2017).</li><li>Jones, J. 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The chick is a cost-effective and convenient addition to the model organisms that a lab may use to research the inner ear. The methods described here are routinely used in our lab and complement ongoing research in the mammalian inner ear. In ovo electroporation is used to introduce genetic manipulations into the chick genome. Electroporation can also be used to introduce constructs that encode fluorescent proteins targeted to particular organelles or subcellular structures35,<...

The inner ear of all vertebrates is derived from a simple epithelium known as the otic placode1,2. This will give rise to all the structural elements and the cell types necessary to transduce the mechanosensory information associated with hearing and balance perception. Hair cells (HCs), the ciliated sensor of the inner ear, are surrounded by supporting cells (SCs). HCs relay information to the auditory hindbrain through the neurons of the eighth cranial nerve. These are also generated from the otic placode3. The primary transduction of sound is achieved at the apical surface of the auditory HC, through a mechanically sensitive hair bundle4. This is mediated through modified actin-based protrusions called stereocilia, which are arranged in a graded, staircase pattern5. In addition, a modified primary cilium, called the kinocilium, organizes hair bundle formation and is adjacent to the tallest row of stereocilia6,7,8. The architecture of stereocilia is critical for this role in converting mechanical stimuli derived from acoustic energy to electrical neural signals9. Damage to the auditory HC through ageing, infection, otoacoustic trauma, or ototoxic shock can result in partial or complete hearing loss that, in mammals, is irreversible10.
Cellular replacement therapies have been proposed that might repair such damage11,12. The approach of this research has been to understand the normal development of the mammalian hair cell and ask if development programs can be reinitiated in progenitor-like cells that may exist within the inner ear13. A second approach has been to look outside of mammals, to non-mammalian vertebrates in which robust regeneration of auditory hair cells takes place, such as birds14,15. In birds, hair cell regeneration occurs predominantly through the de-differentiation of a supporting cell to a progenitor-like state, followed by asymmetric&#160;mitotic division to generate a hair cell and supporting cell16. In addition, direct differentiation of a supporting cell to generate a hair cell has also been observed17.
While the mechanisms of avian auditory development do show significant similarities with that of mammals, there are differences18. HC and SC differentiation in the chick BP is apparent from embryonic day (E) 7, becoming more distinct over time. By E12, a well-patterned and well-polarized basilar papilla (BP) can be visualized, and by E17 well-developed hair cells can be seen19. These time points provide windows into the mechanisms of differentiation, patterning, and polarity, as well as hair cell maturation. Understanding whether such mechanisms are conserved or divergent is important, as they provide insights into the deep homology of the origins of mechanosensory hair cells.
Here, we demonstrate an array of techniques performed at early and late embryonic stages to study cellular processes such as proliferation, fate specification, differentiation, patterning, and maintenance throughout the development of the inner ear organ. This complements other protocols on understanding inner ear development in explant culture20,21,22. We first discuss the introduction of exogenous DNA or RNA into BP precursors within the E3.5 otocyst using in ovo electroporation. Although genetic manipulations can provide valuable insights, the phenotypes thus generated can be pleiotropic and consequently confounding. This is particularly true during later inner ear development, where fundamental processes such as cytoskeletal remodeling play multiple roles in cell division, tissue morphogenesis, and cellular specialization. We present protocols for pharmacological inhibition in cultured explants, which offer advantages in controlling dosage and treatment timing and duration, offering precise spatiotemporal manipulation of developmental mechanisms.
Different organ culture methods can be utilized depending on the treatment duration of small inhibitors. Here we demonstrate two methods of organ culture that allow insights into epithelial morphogenesis and cellular specialization. A method for 3D culture using collagen as a matrix to culture the cochlear duct enables robust culturing and live visualization of the developing BP. For understanding the formation of stereocilia, we present a membrane culture method such that epithelial tissue is cultured on a stiff matrix enabling actin protrusions to grow freely. Both methods allow downstream processing such as live-cell imaging, immunohistochemistry, scanning electron microscopy (SEM), cell recording, etc. These techniques provide a roadmap for the effective use of the chick as a model system to understand and manipulate the development, maturation, and regeneration of the avian auditory epithelium.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Alexa Fluor 488 Phalloidin</td>
			<td>Thermo Fisher Scientific</td>
			<td>A12379</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 647 Phalloidin</td>
			<td>Thermo Fisher Scientific</td>
			<td>A22287</td>
			<td></td>
		</tr>
		<tr>
			<td>Alt-R S.p. HiFi Cas9 Nuclease V3</td>
			<td>Integrated DNA Technologies</td>
			<td>1081061</td>
			<td>High fidelity Cas9 protein</td>
		</tr>
		<tr>
			<td>Anti-GFP antibody</td>
			<td>Abcam</td>
			<td>ab290</td>
			<td>Rabbit polyclonal to GFP</td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>Sigma-Aldrich</td>
			<td>A9647</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride Dihydrate</td>
			<td>Thermo Fisher Scientific</td>
			<td>Q12135</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagen I, rat tail</td>
			<td>Thermo Fisher Scientific</td>
			<td>A1048301</td>
			<td></td>
		</tr>
		<tr>
			<td>Critical Point Dryer Leica EM CPD300</td>
			<td>Leica</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>CUY-21 Electroporator</td>
			<td>Nepagene</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide (DMSO)</td>
			<td>Sigma-Aldrich</td>
			<td>D8418</td>
			<td></td>
		</tr>
		<tr>
			<td>DM5000B Widefield Microscope</td>
			<td>Leica</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM, high glucose, GlutaMAX Supplement, pyruvate</td>
			<td>Thermo Fisher Scientific</td>
			<td>10569010</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #5 Forceps</td>
			<td>Fine Science Tools</td>
			<td>11251-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #55 Forceps</td>
			<td>Fine Science Tools</td>
			<td>11255-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Fast Green FCF</td>
			<td>Sigma-Aldrich</td>
			<td>F7252</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluoroshield</td>
			<td>Sigma-Aldrich</td>
			<td>F6182</td>
			<td></td>
		</tr>
		<tr>
			<td>FLUOVIEW 3000 Laser Scanning Microscope</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glutaraldehyde (25 %)</td>
			<td>Sigma-Aldrich</td>
			<td>340855</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Mouse IgG Secondary Antibody, Alexa Fluor 488</td>
			<td>Thermo Fisher Scientific</td>
			<td>A-11001</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Mouse IgG Secondary Antibody, Alexa Fluor 594</td>
			<td>Thermo Fisher Scientific</td>
			<td>A-11032</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Rabbit IgG Secondary Antibody, Alexa Fluor 488</td>
			<td>Thermo Fisher Scientific</td>
			<td>A-11008</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat Serum Sterile filtered</td>
			<td>HiMedia</td>
			<td>RM10701</td>
			<td>Heat inactivated</td>
		</tr>
		<tr>
			<td>Hanks&#39; Balanced Salt Solution (HBSS)</td>
			<td>Thermo Fisher Scientific</td>
			<td>14025092</td>
			<td></td>
		</tr>
		<tr>
			<td>LSM980 Airyscan Microscope</td>
			<td>Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Millicell Cell Culture Insert, 30 mm, hydrophilic PTFE, 0.4 &#181;m</td>
			<td>Sigma-Aldrich</td>
			<td>PICM03050</td>
			<td></td>
		</tr>
		<tr>
			<td>MVX10 Stereo Microscope</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MYO7A antibody</td>
			<td>DSHB</td>
			<td>138-1</td>
			<td>Mouse monoclonal to Unconventional myosin-VIIa</td>
		</tr>
		<tr>
			<td>MZ16 Dissecting microscope</td>
			<td>Leica</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>N-2 Supplement (100X)</td>
			<td>Thermo Fisher Scientific</td>
			<td>17502048</td>
			<td></td>
		</tr>
		<tr>
			<td>Noyes Scissors, 14cm (5.5&#39;&#39;)</td>
			<td>World Precision Instruments</td>
			<td>501237</td>
			<td></td>
		</tr>
		<tr>
			<td>Osmium tetroxide (4%)</td>
			<td>Sigma-Aldrich</td>
			<td>75632</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>158127</td>
			<td></td>
		</tr>
		<tr>
			<td>PC-10 Puller</td>
			<td>Narishige</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pcU6_1sgRNA</td>
			<td>Addgene</td>
			<td>92395</td>
			<td>Mini vector with modified chicken U6 promoter</td>
		</tr>
		<tr>
			<td>Penicillin G sodium salt</td>
			<td>Sigma-Aldrich</td>
			<td>P3032</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (PBS)</td>
			<td>Thermo Fisher Scientific</td>
			<td>10010023</td>
			<td></td>
		</tr>
		<tr>
			<td>ProLong Gold Antifade Mountant</td>
			<td>Thermo Fisher Scientific</td>
			<td>P36934</td>
			<td></td>
		</tr>
		<tr>
			<td>SMZ1500 Dissecting microscope</td>
			<td>Nikon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Cacodylate Buffer, 0.2M</td>
			<td>Electron Microscopy Sciences</td>
			<td>11652</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>HiMedia</td>
			<td>GRM853</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputtre Coater K550X</td>
			<td>Emitech</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Standard Glass Capillaries 3 in, OD 1.0 mm, No Filament</td>
			<td>World Precision Instruments</td>
			<td>1B100-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma-Aldrich</td>
			<td>84097</td>
			<td></td>
		</tr>
		<tr>
			<td>The MERLIN Compact VP</td>
			<td>Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Thiocarbohydrazide</td>
			<td>Alfa Aesar</td>
			<td>L01205</td>
			<td></td>
		</tr>
		<tr>
			<td>TWEEN 20</td>
			<td>Sigma-Aldrich</td>
			<td>P1379</td>
			<td></td>
		</tr>
	</tbody>
</table>

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 the electroporation setup, electrode positioning can play a role in the domain of transfection. The positive electrode is placed under the yolk, and the negative above the embryo (Figure 1A). This results in higher GFP expression in much of the inner ear and both vestibular organs (Figure 1B), and auditory basilar papilla (Figure 1C,D), confirming transfection.
In assessing the phenoty...

Watch this Scientific Journal Video about In Ovo and Ex Ovo Methods to Study Avian Inner Ear Development at JoVE.com

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.

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 ...

Age, infection, and ototoxic drugs can cause degeneration of hair cells of the inner ear, which in us leads to hearing loss. In non-mammalian vertebrates, such as chick, hair cells can be regenerated. The techniques described here make use of the cost effectiveness of working on chick embryos, the ease of obtaining embryos, and good exo development of tissue explants.Understanding avian inner ear hairs development and regeneration can provide important insights into hearing loss and potential therapies, and explant culture can be important for evaluating the ototoxic effects of various drugs. Before starting the experiment, procure freshly laid eggs, and clean them with 70%ethanol to prevent contamination. Incubate the eggs for 3.5 to 4 days, at 37 to 38 degrees Celsius with 45%humidity.After incubation, reposition the embryo to the top of the yolk, by placing an egg on its side for five minutes. Then, use forceps to make a small hole at the top and blunt end of the egg for a 21 gauge needle to pass through. Using a five milliliter syringe and a 21 gauge needle, remove two milliliters of the albumin from a hole at the blunt end of the egg.Cover the hole at the blunt end using clear tape. To make the egg window affix the clear tape to the top of the egg shell. Hold the needles from microinjection from standard glass capillaries using a vertical pipette puller.After pulling, break off the capillary tip using fine forceps to obtain a tip diameter of approximately 50 micrometers with a tapered end. For the gene knockout experiment, mix the three constructs, namely the guide plasmid, pcU6.1sgRNA, T2KeGFP, T2TP in a one-to-one-to-one ratio with one microgram of SP Cas9 protein, 30%sucrose, and 0.1%fast green dye, and a final volume of 10 microliters. While electroporating multiple plasmids, ensure the final concentration of DNA is at least four micrograms per microliter.With the help of springbow scissors cut open around a two centimeter long and 1.5 centimeter wide window, and expose the embryo. Then use forceps to open the chorionic membranes overlying the embryo, allowing access to the embryo. Inject around 200 nanoliter volume of DNA solution mix to fill the otic vesicle.To determine the guide RNA efficiency perform a T7 endonuclease assay. Add 0.719%saline drops to the embryo to lower the electric resistance, and prevent overheating. Next, place the positive electrode through the hole made at the blunt side of the egg, and maneuver the electrode so that it is under the yolk.Place the negative electrode over the filled otocyst. To transfect the plasmid into the otic vesicle with electroporation, use a square pulse generator, and apply five pulses of 25 volts for 100 milliseconds each, 50 milliseconds apart. Determine the conditions empirically based on an individual electroporation set up.After electroporation, hydrate the embryo by adding a few drops of 0.719%saline. Reseal the egg with clear tape, and return to the humidified incubator at 37 to 38 degrees Celsius for further incubation. Disinfect the surgical table, microscope stage, and surrounding area using 70%ethanol and heat, or alcohol sterilize the micro dissection equipment, including minimally springbow scissors, micro curet, and two pairs of fine forceps.Prepare the dissection plates including a glass Petri dish with a black silicone base, a 90 millimeter plastic Petri dish, and a 60 millimeter Petri dish. Keep chilled PBS or Hanks'balanced salt solution also known as HBSS ready for dissections. Gently crack the egg into the 90 millimeter Petri dish.Then identify the outer ear of the chick, and transfer the head to a 60 millimeter Petri dish filled with ice cold PBS. Next, orient the embryo with the top of the beak facing inside, and hold the beak using one of the number five forceps. Scoop out the eyes using the second number five forceps.Then, from rostral to caudal, cut along the skull along its midline, and scoop out the brain. Add more ice cold PBS, or HBSS, and locate the two otoliths of the lagena as shiny structures at the end of the cochlear duct, and close to the midline. To isolate two inner ears, cut between the two lagenas, and well above and below the region.Then under oblique lighting visualize the outline of the inner ear, and remove extraneous tissue and the vestibule. Transfer the isolated cochlea to a black silicone base plate with ice cold PBS. Peel away the cartilaginous cochlear capsule using number five forceps to obtain the cochlear duct.Then locate the undulated layer or tegmentum of the cochlear duct, and remove it using number 55 forceps to expose the basilar papilla or BP.Next, remove the tectorial membrane to expose hair cells and supporting cells using number 55 forceps. For membrane culture of the basilar papilla, take a six well tissue culture plate, and arrange one culture membrane insert per well. Draw up some media in a 200 microliter pipette, and then aspirate the dissected basilar papilla explant with one X HBSS buffer.Transfer the explant onto a membrane, and orient it so that the basilar papilla faces upward, and the hair and support cells are visible from the top. Once the explant is positioned aspirate the HBSS buffer slowly from the culture membrane surface. In this process the explant will attach to the culture membrane.Fill up the well of the six well plate by adding 1.2 milliliters of dulbecco's modified eagle medium, or DMEM culture media, between the membrane insert and the well wall. To prepare the collagen culture of the cochlear duct add three drops of freshly prepared collagen mixture into each well of a four well plate, and transfer dissected cochlear duct to each collagen drop. Incubate the plate for 10 minutes at 37 degrees Celsius, and 5%carbon dioxide to cure the collagen matrix.For a small molecule treatment of the cultures, replace the culture media with 700 microliters of media supplemented with the pharmacological modulator, such as penicillin, and incubate the plates as demonstrated before. Replace 50%of the culture media every day. After appropriate incubation time, remove the culture media, and use the explants for downstream assays.In the electroporation setup the correct electrode positioning resulted in higher GFP expression in the inner ear in both vestibular organs, and auditory basilar papilla confirming transfection. CRISPR Cas9 mediated Atoh1 gene knockout in inner ear, resulted in loss of hair cells. Atoh1 gene knockout via an ovo-electroporation followed by incubation until E10 showed reduced hair cell development compared to empty plasmid control.Although electroporation is mosaic, control electroporated cells were able to form hair cells. In Atoh1 gRNA electroporated samples, green fluorescent protein positive cells never showed the markers of hair cell development. The organ culture of the basilar papilla in a 3D matrix, such as, collagen and stain with antibodies against hair cell antigen provided the excellent preservation of tissue morphology for up to five days.The organization of hair cells and supporting cells were maintained in these culture conditions. The organ cultures on a membrane can be maintained for up to five days while maintaining the hair bundle integrity. This can be seen in the representative image by the localization of the tip link protein, protocadherin 15.For investigating the development of the hair bundle, higher resolution imaging, such as, super resolution microscopy, or scanning electron microscopy can provide more information. Sterile conditions should be maintained throughout the procedure. While electroporating, ensure that the embryos do not dry out.When titrating pharmacological inhibitors, one may reduce the concentration to overcome any lethality. Both embryos and explants can be taken for imaging experiments. Either by performing realtime video microscoping, or static light confocal electron microscoping, as shown in the protocol.Given the ease and accessibility of using chick inner ear explants, we can use medium through proof screening to identify new molecules essential for hair cell regeneration.

in-ovo-and-ex-ovo-methods-to-study-avian-inner-ear-development

Research

JoVE Journal

Developmental Biology

Efficient Gene Transfer in Chick Retinas for Primary Cell Culture Studies: An Ex-ovo Electroporation Approach

The cone photoreceptor-enriched cultures derived from embryonic chick retinas have become an indispensable tool for researchers around the world studying the biology of retinal neurons, particularly photoreceptors. The applications of this system go beyond basic research, as they can easily be adapted to high throughput technologies for drug development. However, genetic manipulation of retinal photoreceptors in these cultures has proven to be very challenging, posing an important limitation to the usefulness of the system. We have recently developed and validated an ex&#160;ovo plasmid electroporation technique that increases the rate of transfection of retinal cells in these cultures by five-fold compared to other currently available protocols1. In this method embryonic chick eyes are enucleated at stage 27, the RPE is removed, and the retinal cup is placed in a plasmid-containing solution and electroporated using easily constructed custom-made electrodes. The retinas are then dissociated and cultured using standard procedures. This technique can be applied to overexpression studies as well as to the downregulation of gene expression, for example via the use of plasmid-driven RNAi technology, commonly achieving transgene expression in 25% of the photoreceptor population. The video format of the present publication will make this technology easily accessible to researchers in the field, enabling the study of gene function in primary retinal cultures. We have also included detailed explanations of the critical steps of this procedure for a successful outcome and reproducibility.

Efficient Gene Transfer in Chick Retinas for Primary Cell Culture Studies: An Ex-ovo Electroporation Approach

Embryonic chick retinal cell cultures constitute valuable tools for the study of photoreceptor biology. We have developed an efficient gene transfer technique based on ex&#160;ovo plasmid electroporation of the retinas prior to culture. This technique considerably increases transfection efficiencies over currently available protocols, making genetic manipulation feasible for this system.

The cone photoreceptor-enriched cultures derived from embryonic chick retinas have become an indispensable tool for researchers around the world studying ...

Optimized Ex-ovo Culturing of Chick Embryos to Advanced Stages of Development

Research in anatomy, embryology, and developmental biology has largely relied on the use of model organisms. In order to study development in live embryos model organisms, such as the chicken, are often used. The chicken is an excellent model organism due to its low cost and minimal maintenance, however they present observational challenges because they are enclosed in an opaque eggshell. In order to properly view the embryo as it develops, the shell must be windowed or removed. Both windowing and ex ovo techniques have been developed to assist researchers in the study of embryonic development. However, each of the methods has limitations and challenges. Here, we present a simple, optimized ex ovo culture technique for chicken embryos that enables the observation of embryonic development from stage HH 19 into late stages of development (HH 40), when many organs have developed. This technique is easy to adopt in both undergraduate classes and more advanced research laboratories where embryo manipulations are conducted.

Optimized Ex-ovo Culturing of Chick Embryos to Advanced Stages of Development

Viewing and accessing the chicken embryo during development can be challenging. We have developed an ex ovo method that is simple, cost effective, and can easily be used in a classroom or research setting. This method provides access to the embryo into late stages of embryonic development (HH 40).

Research in anatomy, embryology, and developmental biology has largely relied on the use of model organisms. In order to study development in live embryos ...

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.

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.

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

A Novel Ex Ovo Banding Technique to Alter Intracardiac Hemodynamics in an Embryonic Chicken System

The new model presented here can be used to understand the influence of hemodynamics on specific cardiac developmental processes, at the cellular and molecular level. To alter intracardiac hemodynamics, fertilized chicken eggs are incubated in a humidified chamber to obtain embryos of the desired stage (HH17). Once this developmental stage is achieved, the embryo is maintained ex ovo and hemodynamics in the embryonic heart are altered by partially constricting the outflow tract (OFT) with a surgical suture at the junction of the OFT and ventricle (OVJ). Control embryos are also cultured ex ovo but are not subjected to the surgical intervention. Banded and control embryos are then incubated in a humidified incubator for the desired period of time, after which 2D ultrasound is employed to analyze the change in blood flow velocity at the OVJ as a result of OFT banding. Once embryos are maintained ex ovo, it is important to ensure adequate hydration in the incubation chamber so as to prevent drying and eventually embryo death. Using this new banded model, it is now possible to perform analyses of changes in the expression of key players involved in valve development and to understand the role of hemodynamics on cellular responses in vivo, which could not be achieved previously.

A Novel Ex Ovo Banding Technique to Alter Intracardiac Hemodynamics in an Embryonic Chicken System

For the first time we present here a reproducible banding procedure to alter hemodynamics in the developing heart ex ovo. This is achieved by partially constricting the outflow tract (OFT).

The new model presented here can be used to understand the influence of hemodynamics on specific cardiac developmental processes, at the cellular and ...

A Submerged Filter Paper Sandwich for Long-term Ex Ovo Time-lapse Imaging of Early Chick Embryos

Due to its availability, low cost, flat geometry, and transparency, the ex ovo chick embryo has become a major vertebrate animal model for the study of morphogenetic events, such as gastrulation2, neurulation3-5, somitogenesis6, heart bending7,8, and brain formation9-13, during early embryogenesis. Key to understanding morphogenetic processes is to follow them dynamically by time-lapse imaging. The acquisition of time-lapse movies of chick embryogenesis ex ovo has been limited either to short time windows or to the need for an incubator to control temperature and humidity around the embryo14. Here, we present a new technique to culture chick embryos ex ovo for high-resolution time-lapse imaging using transmitted light microscopy. The submerged filter paper sandwich is a variant of the well-established filter paper carrier technique (EC-culture)1 and allows for the culturing of chick embryos without the need for a climate chamber. The embryo is sandwiched between two identical filter paper carriers and is kept fully submerged in a simple, temperature-controlled medium covered by a layer of light mineral oil. Starting from the primitive streak stage (Hamburger-Hamilton stage 5, HH5)15 up to at least the 28-somite stage (HH16)15, embryos can be cultured with either their ventral or dorsal side up. This allows the acquisition of time-lapse movies covering about 30 hr of embryonic development. Representative time-lapse frames and movies are shown. Embryos are compared morphologically to an embryo cultured in the standard EC-culture.
The submerged filter paper sandwich provides a stable environment to study early dorsal and ventral morphogenetic processes. It also allows for live fluorescence imaging and micromanipulations, such as microsurgery, bead implantation, microinjection, gene silencing, and electroporation, and has a strong potential to be combined with immersion objectives for laser-based imaging (including light-sheet microscopy).

A Submerged Filter Paper Sandwich for Long-term Ex Ovo Time-lapse Imaging of Early Chick Embryos

Here, we present a new technique to culture chick embryos ex ovo for time-lapse imaging using transmitted light and fluorescence microscopy. The submerged filter paper sandwich is a variant of the well-established filter paper carrier technique1 that allows for the culturing of chick embryos fully-submerged in a liquid culture medium.

Due to its availability, low cost, flat geometry, and transparency, the ex ovo chick embryo has become a major vertebrate animal model for the study of ...

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 ...

Methods for the Study of Regeneration in Stentor

Cells need to be able to regenerate their parts to recover from external perturbations. The unicellular ciliate Stentor coeruleus is an excellent model organism to study wound healing and subsequent cell regeneration. The Stentor genome became available recently, along with modern molecular biology methods, such as RNAi. These tools make it possible to study single-cell regeneration at the molecular level. The first section of the protocol covers establishing Stentor cell cultures from single cells or cell fragments, along with general guidelines for maintaining Stentor cultures. Culturing Stentor in large quantities allows for the use of valuable tools like biochemistry, sequencing, and mass spectrometry. Subsequent sections of the protocol cover different approaches to inducing regeneration in Stentor. Manually cutting cells with a glass needle allows studying the regeneration of large cell parts, while treating cells with either sucrose or urea allows studying the regeneration of specific structures located at the anterior end of the cell. A method for imaging individual regenerating cells is provided, along with a rubric for staging and analyzing the dynamics of regeneration. The entire process of regeneration is divided in three stages. By visualizing the dynamics of the progression of a population of cells through the stages, the heterogeneity in regeneration timing is demonstrated.

Methods for the Study of Regeneration in Stentor

The giant ciliate, Stentor coeruleus, is an excellent system to study regeneration and wound healing. We present procedures for establishing Stentor cell cultures from single cells or cell fragments, inducing regeneration by cutting cells, chemically inducing the regeneration of membranellar band and oral apparatus, imaging, and analysis of cell regeneration.

Cells need to be able to regenerate their parts to recover from external perturbations. The unicellular ciliate Stentor coeruleus is an excellent model ...

Whole-Mount In Situ Hybridization in Zebrafish Embryos and Tube Formation Assay in iPSC-ECs to Study the Role of Endoglin in Vascular Development

Vascular development is determined by the sequential expression of specific genes, which can be studied by performing in situ hybridization assays in zebrafish during different developmental stages. To investigate the role of endoglin(eng) in vessel formation during the development of hereditary hemorrhagic telangiectasia&#160;(HHT), morpholino-mediated targeted knockdown of eng in zebrafish are used to study its temporal expression and associated functions. Here, whole-mount in situ RNA hybridization (WISH) is employed for the analysis of eng and its downstream genes in zebrafish embryos. Also, tube formation assays are performed in HHT patient-derived induced pluripotent stem cell-differentiated&#160;endothelial cells (iPSC-ECs; with eng mutations). A specific signal amplifying system using the whole amount In Situ Hybridization &#8211; WISH provides higher resolution and lower background results compared to traditional methods. To obtain a better signal, the post-fixation time is adjusted to 30 min after probe hybridization. Because fluorescence staining is not sensitive in zebrafish embryos, it is replaced with diaminobezidine (DAB) staining here. In this protocol, HHT&#160;patient-derived iPSC lines containing an eng mutation are differentiated into endothelial cells. After coating a plate with basement membrane matrix for 30 min at 37 &#176;C, iPSC-ECs are seeded as a monolayer into wells and kept at 37 &#176;C for 3 h. Then, the tube length and number of branches are calculated using microscopic images. Thus, with this improved WISH protocol, it is shown that reduced eng expression affects endothelial progenitor formation in zebrafish embryos. This is further confirmed by tube formation assays using iPSC-ECs derived from a patient with HHT. These assays confirm the role for eng in early vascular development.

Presented here is a protocol for whole-mount in situ RNA hybridization analysis in zebrafish and tube formation assay in patient-derived induced pluripotent stem cell-derived endothelial cells to study the role of endoglin in vascular formation.

Vascular development is determined by the sequential expression of specific genes, which can be studied by performing in situ hybridization assays in ...

Creating Avian Forebrain Chimeras to Assess Facial Development

The avian embryo has been used as a model system for more than a century and has led to fundamental understanding of vertebrate development. One of the strengths of this model system is that the effect of, and interaction among, tissues can be directly assessed in chimeric embryos. We have previously shown that signals from the forebrain contribute to facial morphogenesis by regulating the shape of the expression domain of Sonic hedgehog (SHH) in the Frontonasal Ectodermal Zone (FEZ). In this article, the method of generating the forebrain chimeras and provide illustrations of the outcomes of these experiments is described.

This article describes a tissue transplantation technique that was designed to test the signaling and patterning properties of basal forebrain&#160;during craniofacial development.

The avian embryo has been used as a model system for more than a century and has led to fundamental understanding of vertebrate development. One of the ...

In Ovo Feeding of Commercial Broiler Eggs: An Accurate and Reproducible Method to Affect Muscle Development and Growth

Within the past three decades, red meat and poultry scientists focused on developing strategies and technologies to manipulate muscle development during embryonic and fetal development. This area continues to be an area of focus because muscle fiber number is established during this time and determines the basis for all future growth. In poultry, numerous studies demonstrated in ovo feeding of growth factors, vitamins, or other nutrients improved chick embryonic muscle and intestinal development. Improving in ovo muscle development could benefit the poultry industry by possibly influencing meat yield, growth rate, or myopathy conditions. During the past five years, the Gonzalez Laboratory at the University of Georgia developed a nicotinamide riboside in ovo feeding methodology for broiler-chicken embryos, which altered&#160;muscle development. When injected into a developing embryo&#39;s yolk sac, nicotinamide riboside increased pectoralis major muscle weight and muscle fiber density at hatch. This protocol will demonstrate a methodology to accurately and reproducibly conduct in ovo feeding studies utilizing commercial standard- and high-yielding broiler embryos. These data and methods will allow other research groups to perform in ovo feeding studies with much success and reproducibility.

In Ovo Feeding of Commercial Broiler Eggs: An Accurate and Reproducible Method to Affect Muscle Development and Growth

A robust methodology has been developed for conducting in ovo feeding research trials utilizing unincubated commercial broiler eggs to test the ability of natural and synthetic compounds, in this case, nicotinamide riboside, to influence muscle development and growth.

Within the past three decades, red meat and poultry scientists focused on developing strategies and technologies to manipulate muscle development during ...