The work was supported by Barncancerfonden (PR2013-0104), Swedish Research Council (12187-18-3), &#246;gonfonden, Kronprinsessan Margaretas arbetsn&#228;mnd f&#246;r synskadade, Synfr&#228;mjandets forskningsfond and St Eriks &#246;gonsjukhus forskningsstipendier.

This protocol is performed in accordance with the recommendations in the &#8220;Guide for the Care and Use of Laboratory Animals of the Association for research in vision and ophthalmology&#8221;.
1. Egg Handling and Eye collection
<ol>
	<li>Store white Leghorn eggs at 12-14 &#176;C for no longer than 1 week. If available, use a refrigerated wine cooler to store the fertilized eggs. 
	Note: Higher store temperatures lead to abnormal development of embryos, while lower temperatures increases mortality. Extended storage time increases both mortality and abnormal development.</li>
	<li>Incubate the eggs in a 37.5 &#176;C and 60% humidified egg incubator with gentle rocking at a frequency of 5 times per 24 hr.</li>
	<li>Remove the incubated eggs from the egg incubator at the desired embryonic age. 
	Note: The age of the chicken embryo is determined as the time of incubation and is denoted as embryonic days (E) or as stages (st), according to the series of developmental stages described by Hamburger and Hamilton12.</li>
	<li>Place the selected eggs in the laminar flow hood. Wipe the eggshell with 70% ethanol to avoid contamination of the embryo. 
	Note: Conduct all procedures under aseptic conditions with sterile&#160;solutions&#160;<url>https://www.jove.com/science-education/5030/making-solutions-in-the-laboratory&#34;lutions </url> and instruments.</li>
	<li>Tap the side of the egg firmly against a hard surface to crack open the egg. Place the content in a 100 mm Petri dish. Use a small spoon to transfer the embryo to a 35 mm Petri dish containing pre-warmed (37 &#176;C) 1x PBS to prevent the tissue from drying.</li>
	<li>Place the 35 mm Petri dish containing the embryonic tissue onto a binocular stereovision dissecting microscope in the laminar flow hood.&#160;Decapitate the embryo by pinching the neck with fine forceps and discard the body.</li>
	<li>Use fine forceps to make an incision through the mouth, ventral to the eye. Starting at the site of incision, tear open the tissue surrounding the entire eye. Pinch off the optic nerve and remove the intact eye from the eye socket. Collect both the left and right eye from the same embryo for use as either the control or the treated eye.</li>
	<li>Use a small spoon to transfer the eyes to a new 35 mm Petri dish containing pre-warmed (37 &#176;C) 1x PBS.</li>
</ol>
2. Preparation of Whole Retinal Explants
<ol>
	<li>Use fine forceps to remove all tissue around the eye including the scleral anlage. 
	Note: The tissue will detach easily leaving the retina on the vitreous body and lens with the pigment epithelium intact (Figure 1A-B).</li>
	<li>Use fine forceps to pinch a small incision into the pigment epithelium at the dorsal part of the eye without damaging the neural retina (Figure 1C).</li>
	<li>Use fine forceps to gently tear open the pigment epithelium starting at the site of incision, leaving the lens and the entire retina attached to the vitreous body (Figure 1D). Keep the eye in warm (37 &#176;C) 1x PBS to facilitate the removal of the pigment epithelium. 
	Note: The pigment epithelium may be difficult to remove, in particular along the ciliary body around the pupil, in the anterior region of the eye, and along the choroid fissure. Therefore, some of the pigment epithelium may be left on the neural retina (Figure 1E-F).</li>
</ol>
3. Treatment of Whole Retinal Explants
<ol start="1">
	<li>Electroporation of whole retinal explants 
	Note: Electroporation of whole retinal explants can be performed directly after step 2.
	<ol>
		<li>Prepare culture medium containing 1:1 DMEM:F12 Nutrient mix, 10% FBS, 10 U/ml&#160;penicillin streptomycin, 5 &#181;g/ml&#160;Insulin, and 2 mM L-glutamine.</li>
		<li>Cut off a 1.5 ml&#160;disposable plastic cuvette (12.5 mm x 12.5 mm x 45 mm) (or any small container capable of holding 300-400 &#181;l&#160;solution) approximately 8 mm from the bottom using a fine-bladed saw.</li>
		<li>Dilute the DNA plasmid of choice in 1xDPBS to a final concentration of 0.1 &#181;g/&#181;l.</li>
		<li>Turn on the electroporator and set parameters to 15 V&#160;for st20 &#8211; st25 (E3-E4) retina and 20 V&#160;for st26 &#8211; st27 (E5) retina. Set the pulse-repeats to 5 pulses of 50 msec pulse-length with 1 sec intervals. Use a pulse generator that can be controlled by a foot-pedal on the floor as both hands will be needed to hold the electrodes in place.</li>
		<li>Connect two paddle shaped (flat, circular diam. 4 mm) platinum electrodes (Figure 2A) to the output socket on the pulse generator. 
		Note: The platinum electrodes used in this protocol were made by the university workshop. The electrodes were made from 0.1 mm platinum plate &#8220;rondelles&#8221; (platinum grade: 950 Pt/5 Cu). The connecting 0.8 mm wire was insulated using plastic tubing.</li>
		<li>Carefully transfer the whole retinal explant from step 2.3 to the cuvette (or equivalent small container) using a polyethylene Pasteur pipette with the tip cut off to acquire the right tip-opening size for the retinal explant. Avoid using pipette tips as the retina tends to attach to the plastic and tear apart.</li>
		<li>Use a 100 &#181;l pipette to gently remove the entire 1x PBS surrounding the retinal explant taking care not to touch the retina to avoid tearing.</li>
		<li>Add 100 &#181;l plasmid solution to the cuvette to cover the whole retinal explant. Gently push down the retinal explant with forceps if it floats to the top. Use forceps or electrodes to position the lens to face any one side of the cuvette and the optic nerve to the bottom of the cuvette.</li>
		<li>Place the positive electrode in front of the lens and the negative electrode behind the retina (Figure 2A), without touching the tissue.</li>
		<li>Apply the current by pressing down the foot-pedal. Check for bubbles at the electrodes indicating successful discharge.</li>
		<li>Use a 100 &#181;l pipette to remove all the plasmid mix from the cuvette without damaging the retina. The plasmid mix can be reused three to five times.</li>
		<li>Fill up the cuvette with pre-warmed (37 &#176;C) 1x PBS. Use forceps to gently detach the retinal explant from the wall of the cuvette. After electroporation the retina is sometimes covered with bubbles, which makes it adhere to the wall of the cuvette.</li>
		<li>Use the polyethylene Pasteur pipette to transfer the whole retinal explant into a 24-well plate containing 1 ml&#160;pre-warmed (37 &#176;C) culture medium per well. Incubate one retinal explant per well.</li>
		<li>Incubate the retinal explant at 37 &#176;C on a rotator shaker, with a constant speed of 50 rpm, inside a cell incubator with 5% CO2 for 24 hr. The rotation is to ensure maximum exposure to the medium and to prevent adhesion of the retina to the bottom of the 24-well plate.</li>
		<li>Proceed to step 4.</li>
	</ol>
	</li>
	<li>Treatment of whole retinal explants with chemical reagents 
	Note: Chemical treatment of whole retinal explants can be performed directly after step 2.
	<ol>
		<li>Prepare culture medium containing 1:1 DMEM:F12 Nutrient mix, 10% FBS, 10 U/ml&#160;penicillin streptomycin, 5 &#181;g/ml&#160;Insulin, and 2 mM L-glutamine.</li>
		<li>Use a small spoon to transfer the retinal explant from step 2.3 into a 24-well plate containing 1 ml&#160;pre-warmed (37 &#176;C) culture medium per well. Incubate one retinal explant per well.</li>
		<li>Incubate the whole retinal explant for 60 min at 37 &#176;C on a rotator shaker, with a constant speed of 50 rpm, inside a cell incubator with 5% CO2 before adding a chemical reagent or vehicle.</li>
		<li>Prepare the chemical solution, for example Cdk1/2 inhibitor III, an inhibitor of M-phase progression13, at a final concentration of 30 &#181;M in DMSO.</li>
		<li>Remove the 24-well plate, containing the whole retinal explant, from the cell incubator. Add 10 &#181;l of the chemical reagent or the vehicle (DMSO) directly to the retinal medium, resulting in a final concentration of 300 nM Cdk1/2 inhibitor III in 0.01% DMSO. Manually rotate the 24-well plate to allow for even distribution of the chemical reagent or vehicle in the solution.</li>
		<li>Incubate the retinal explants at 37 &#176;C on a rotator shaker, with a constant speed of 50 rpm, inside an incubator with 5% CO2 for the desired time (up to 24 hr).</li>
		<li>Proceed to step 4.</li>
	</ol>
	</li>
</ol>
4. Fixation and Freezing of Whole Retinal Eexplants
<ol>
	<li>Remove the 24-well plate containing the treated whole retinal explant from the cell incubator.</li>
	<li>Use a small spoon to transfer the retinal explant to a 24-well plate containing 1 ml/well ice cold 4% paraformaldehyde in 1xPBS. Incubate on ice for 15 min.</li>
	<li>Use a small spoon to transfer the whole retinal explant to a 24-well plate containing 1 ml/well ice cold 1xPBS to wash the retina. Incubate on ice for 10 min.</li>
	<li>Use a small spoon to transfer the whole retinal explant to a 24-well plate containing 1 ml/well ice cold 30% sucrose in 1xPBS. Incubate on ice for 1-3 hr&#160;depending on the embryonic day of the retina. For st20 &#8211; st25 (E3) retinas, incubate for 1 hr, older retinas need longer incubation time in sucrose.</li>
	<li>Use a small spoon to transfer the whole retinal explant onto a paraffin film containing approximately 500 &#181;l&#160;cryostat freezing mounting medium. Remove as much sucrose as possible by gently moving the retinal explant in the freezing medium using the small spoon.</li>
	<li>Transfer the retinal explant to an embedding mold containing freezing medium. Position the eye to facilitate future sectioning. Put the embedding mold containing the whole retinal explant on dry ice until the medium is frozen solid. Store at -80 &#176;C.</li>
</ol>

<ol>
	<li>Muramatsu, T., Mizutani, Y., Ohmori, Y., Okumura, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+three+nonviral+transfection+methods+for+foreign+gene+expression+in+early+chicken+embryos+in+ovo.">Comparison of three nonviral transfection methods for foreign gene expression in early chicken embryos in ovo.</a> Biochem Biophys Res Commu. 230, 376-380 (1997).</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=Introduction+of+DNA+into+chick+embryos+by+in+ovo+electroporation.">Introduction of DNA into chick embryos by in ovo electroporation.</a> Method. 24, 43-48 (2001).</li><li>Kohl, A., Hadas, Y., Klar, A., Sela-Donenfeld, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Axonal+patterns+and+targets+of+dA1+interneurons+in+the+chick+hindbrain.">Axonal patterns and targets of dA1 interneurons in the chick hindbrain.</a> J Neurosc. 32, 5757-5771 (2012).</li><li>Islam, M. M., Doh, S. T., Cai, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+ovo+electroporation+in+embryonic+chick+retina.">In ovo electroporation in embryonic chick retina.</a> J Vis Exp. , (2012).</li><li>Sparrow, J. R., Hicks, D., Barnstable, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+commitment+and+differentiation+in+explants+of+embryonic+rat+neural+retina.+Comparison+with+the+developmental+potential+of+dissociated+retina.">Cell commitment and differentiation in explants of embryonic rat neural retina. Comparison with the developmental potential of dissociated retina.</a> Brain res Dev brain re. 51, 69-84 (1990).</li><li>Tomita, K., 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=Mammalian+hairy+and+Enhancer+of+split+homolog+1+regulates+differentiation+of+retinal+neurons+and+is+essential+for+eye+morphogenesis.">Mammalian hairy and Enhancer of split homolog 1 regulates differentiation of retinal neurons and is essential for eye morphogenesis.</a> Neuro. 16, 723-734 (1996).</li><li>Matsuda, T., Cepko, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation+and+RNA+interference+in+the+rodent+retina+in+vivo+and+in+vitro.">Electroporation and RNA interference in the rodent retina in vivo and in vitro.</a> Proc Nat Acad Sci US. 101, 16-22 (2004).</li><li>Donovan, S. L., Dyer, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+square+wave+electroporation+of+retinal+explant+cultures.">Preparation and square wave electroporation of retinal explant cultures.</a> Nature protocol. 1, 2710-2718 (2006).</li><li>Thangaraj, G., Greif, A., Layer, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+explant+culture+of+the+embryonic+chicken+retina+with+long-term+preservation+of+photoreceptors.">Simple explant culture of the embryonic chicken retina with long-term preservation of photoreceptors.</a> Exp eye re. 93, 556-564 (2011).</li><li>Shirazi Fard, S., All-Ericsson, C., Hallbook, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+heterogenic+final+cell+cycle+of+chicken+retinal+Lim1+horizontal+cells+is+not+regulated+by+the+DNA+damage+response+pathway.">The heterogenic final cell cycle of chicken retinal Lim1 horizontal cells is not regulated by the DNA damage response pathway.</a> Cell Cycl. 13, 408-417 (2014).</li><li>Shirazi Fard, S., Thyselius, M., All-Ericsson, C., Hallbook, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+terminal+basal+mitosis+of+chicken+retinal+Lim1+horizontal+cells+is+not+sensitive+to+cisplatin-induced+cell+cycle+arrest.">The terminal basal mitosis of chicken retinal Lim1 horizontal cells is not sensitive to cisplatin-induced cell cycle arrest.</a> Cell Cycl. 13, 3698-3706 (2014).</li><li>Hamburger, V., Hamilton, H. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+series+of+normal+stages+in+the+development+of+the+chick+embryo.">A series of normal stages in the development of the chick embryo.</a> J. Morphol. 88, 49-92 (1951).</li><li>Gavet, O., Pines, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+cyclin+B1-Cdk1+synchronizes+events+in+the+nucleus+and+the+cytoplasm+at+mitosis.">Activation of cyclin B1-Cdk1 synchronizes events in the nucleus and the cytoplasm at mitosis.</a> J Cell Bio. 189, 247-259 (2010).</li><li>Sauer, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitosis+in+the+neural+tube.">Mitosis in the neural tube.</a> J Comp Neurol. 62, 377-405 (1935).</li><li>Baye, L. M., Link, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interkinetic+nuclear+migration+and+the+selection+of+neurogenic+cell+divisions+during+vertebrate+retinogenesis.">Interkinetic nuclear migration and the selection of neurogenic cell divisions during vertebrate retinogenesis.</a> J Neurosc. 27, 10143-10152 (2007).</li></ol>

The authors declare that they have no competing financial interests.

In this work a detailed protocol for dissection, electroporation or chemical treatment, and culturing of whole retinal explants from chicken embryos is presented. This protocol is easy, quick and allows for both a high success rate and reproducible results.
Electroporation of whole retinal explants produces large areas of cells that express the gene construct of interest. It is easy to correctly position the electrodes and to expose a specific portion of the retina to a define...

The retina is part of the central nervous system and it is, with its relative simplicity and well-characterized cellular architecture, a popular model for studying central nervous system development. The eye of the chicken embryo is relatively large in comparison to the rest of the embryo. It is therefore easily accessible in ovo for experimental manipulations, such as injections or electroporation, and serves as an excellent tool to gain knowledge about retinal cell and developmental biology in vivo. Despite these major advantages, survival of the embryos can be low when experiments are invasive such as with electroporations, repeated injections, or combined experimental manipulations.
Electroporation of DNA plasmids into the chicken embryo in ovo is an important and well-established technique1. It allows for labeling of neurons, tracing of cell fate as well as neuronal tracts in the central nervous system and it allows for ectopic gene expression to analyze protein function in vivo. The technique has been used for studies of neural tube2, hindbrain3, and retina4. Electroporation of embryonic retina in ovo has some experimental difficulties that are related to the in vivo situation. The position of the eye, due to the cranial folding of the embryo, is relatively close to the heart. This proximity increases the risk of cardiac arrest following electroporation, and the risk increases with the age of the embryo. Moreover, to access the eye, it is necessary to open the embryonic membranes, thereby increasing the risk for bleeding, malformations and subsequent reduced viability. When testing and optimizing a new DNA plasmid often without a known phenotypic outcome, these limitations may decrease the efficacy and power of the method even for an experienced experimentalist. As presented in this protocol, the culture of the whole retinal explant, defined as the whole neural retina with the pigment epithelium removed, is an efficient method that complements the in ovo approach.
Intraocular injections of chemical reagents are relatively easy to perform in ovo. However, the effective and exact concentration of injected reagents within the neural retina may be difficult to fully control. The injected volume may vary due to leakage and the exact site of injection may affect both the distribution of the reagent within the eye and the diffusion through the vitreous body. The variability will have major implications for the interpretation of the results when i.e., a dose response curve for an enzyme inhibitor is determined; particularly if the effect is small and the temporal window of the effect is narrow. Moreover, only a single eye can be used from each embryo when performing in ovo experiments due to potential systemic effects via the blood stream onto the contralateral eye. Age matching is important when studying development and the individual variability between treated and control embryos may lead to additional experimental variability.
For these reasons, an ex ovo method based on retinal explants from chicken embryos was developed, in which the neural retina can be exposed to a uniform and controlled experimental condition in vitro. The present protocol was developed based on previous protocols5-9. Retinal explants from stage (st) 20 (embryonic days [E] 3) to st31 (E7) chicken embryos were dissected, cultured and electroporated with a defined DNA plasmid concentration or exposed to a medium containing a defined concentration of a chemical reagent. The protocol presented here has been successfully implemented in recent publications, using several different chemical reagents, including regulators of the DNA damage pathway, such as KU55933, SB 218078, and NSC 109555 ditosylate, and the cell cycle, such as Cdk1/2 inhibitor III10,11.

<table border="0" cellpadding="0" cellspacing="0" width="859">
	<tbody>
		<tr>
			<td>1xPBS (tablet)</td>
			<td>Life technologies</td>
			<td>18912-014</td>
			<td></td>
		</tr>
		<tr>
			<td>10xDPBS</td>
			<td>Life technologies</td>
			<td>14080-048</td>
			<td></td>
		</tr>
		<tr>
			<td>100 mm Petri dish</td>
			<td>VWR</td>
			<td>734-0006</td>
			<td></td>
		</tr>
		<tr>
			<td>100 &#956;L pipette tips</td>
			<td>VWR</td>
			<td>613-0798</td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL disposable plastic cuvette</td>
			<td>Thomas Scientific</td>
			<td>8495V01</td>
			<td></td>
		</tr>
		<tr>
			<td>24-well plate</td>
			<td>Sigma Aldrich</td>
			<td>D7039</td>
			<td></td>
		</tr>
		<tr>
			<td>35 mm Petri dish</td>
			<td>VWR</td>
			<td>391-1998</td>
			<td></td>
		</tr>
		<tr>
			<td>70% ethanol</td>
			<td>Solveco</td>
			<td>1054</td>
			<td></td>
		</tr>
		<tr>
			<td>Cdk1/2 inhibitor III</td>
			<td>217714</td>
			<td>Calbiochem</td>
			<td>300nM in 0.01% DMSO</td>
		</tr>
		<tr>
			<td>Cell culture incubator</td>
			<td>Thermo Forma</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dissecting microscope</td>
			<td>Leica</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Life Technologies</td>
			<td>41966-029</td>
			<td></td>
		</tr>
		<tr>
			<td>Electrodes</td>
			<td></td>
			<td></td>
			<td>Platina, custom made</td>
		</tr>
		<tr>
			<td>Electro square porator ECM 830</td>
			<td>Harvard Apparatus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>F12 Nutrient mix</td>
			<td>Life Technologies</td>
			<td>31331-028</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Life Technologies</td>
			<td>16140-071</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>AgnThos</td>
			<td>0108-5-PS</td>
			<td></td>
		</tr>
		<tr>
			<td>Freezing medium NEG50</td>
			<td>Cellab, Sweden</td>
			<td>6502</td>
			<td></td>
		</tr>
		<tr>
			<td>GFP expressing DNA plasmid (pZGs)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Humidified incubator</td>
			<td>Grumbach Brutgeraete GmbH, Asslar, Germany</td>
			<td>8204</td>
			<td></td>
		</tr>
		<tr>
			<td>Insulin</td>
			<td>Sigma Aldrich</td>
			<td>I9278-5ML</td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutamine</td>
			<td>Life Technologies</td>
			<td>25030024</td>
			<td></td>
		</tr>
		<tr>
			<td>Mounting medium ProLong Gold with DAPI</td>
			<td>Life Technologies</td>
			<td>P36935</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin film</td>
			<td>VWR</td>
			<td>291-1214P</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma Aldrich</td>
			<td>16005-1KG-R</td>
			<td></td>
		</tr>
		<tr>
			<td>Peel-A-Way embedding mold&#160;</td>
			<td>Sigma Aldrich</td>
			<td>E6032</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin streptomycin</td>
			<td>Life Technologies</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr>
			<td>PhosphoHistone 3 (PH3)&#160;</td>
			<td>Millipore</td>
			<td>06-570</td>
			<td>Dilution 1/4000</td>
		</tr>
		<tr>
			<td>Platinum electrodes (custom made from &#34;rondelles&#34;)</td>
			<td>Sargenta</td>
			<td>390-R (rondeller)</td>
			<td>Dia: 4mm, 0.1 mm thickness</td>
		</tr>
		<tr>
			<td>Platimun electrodes&#160;</td>
			<td>Sonidel</td>
			<td>CUY700P4L</td>
			<td>Dia: 4 mm</td>
		</tr>
		<tr>
			<td>Polyethylene pasteur pipette</td>
			<td>VWR</td>
			<td>612-2853</td>
			<td></td>
		</tr>
		<tr>
			<td>Rotator shaker</td>
			<td>VWR</td>
			<td>444-2900</td>
			<td></td>
		</tr>
		<tr>
			<td>Small spoon</td>
			<td>VWR</td>
			<td>231-2151</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>VWR</td>
			<td>443815S</td>
			<td></td>
		</tr>
		<tr>
			<td>White Leghorn eggs</td>
			<td></td>
			<td></td>
			<td>Local supplier</td>
		</tr>
		<tr>
			<td>Wine cooler</td>
			<td>WineMaster 24, Caso, Berlin Germany</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
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whole retinal explants from chicken embryos for electroporation and chemical reagent treatments

The retina is a good model for the developing central nervous system. The large size of the eye and most importantly the accessibility for experimental manipulations in ovo/in vivo makes the chicken embryonic retina a versatile and very efficient experimental model. Although the chicken retina is easy to target in ovo by intraocular injections or electroporation, the effective and exact concentration of the reagents within the retina may be difficult to fully control. This may be due to variations of the exact injection site, leakage from the eye or uneven diffusion of the substances. Furthermore, the frequency of malformations and mortality after invasive manipulations such as electroporation is rather high.
This protocol describes an ex ovo technique for culturing whole retinal explants from chicken embryos and provides a method for controlled exposure of the retina to reagents. The protocol describes how to dissect, experimentally manipulate, and culture whole retinal explants from chicken embryos. The explants can be cultured for approximately 24 hr and be subjected to different manipulations such as electroporation. The major advantages are that the experiment is not dependent on the survival of the embryo and that the concentration of the introduced reagent can be varied and controlled in order to determine and optimize the effective concentration. Furthermore, the technique is rapid, cheap and together with its high experimental success rate, it ensures reproducible results. It should be emphasized that it serves as an excellent complement to experiments performed in ovo.

This protocol describes the preparation (Figure 1A-F) and culturing of whole retinal explants from chicken embryos. This protocol has been successfully used for whole retinal explants from embryos of st20 (E3) to st31 (E7).
Electroporation of DNA plasmids into whole retinal explants allows for labeling and tracing of retinal progenitor cells or over-expression of different gene products. For electroporation experiments, the pigment epithelium was carefully removed from the enu...

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Whole Retinal Explants from Chicken Embryos for Electroporation and Chemical Reagent Treatments

This protocol describes a method to dissect, experimentally manipulate and culture whole retinal explants from chicken embryos. The explant cultures are useful when high success rate, efficacy and reproducibility are needed to test the effects of plasmids for electroporation and/or reagent substances, i.e., enzymatic inhibitors.

The retina is a good model for the developing central nervous system. The large size of the eye and most importantly the accessibility for experimental ...

whole-retinal-explants-from-chicken-embryos-for-electroporation

Research

JoVE Journal

Developmental Biology

9.4K Views.  Uppsala University. This protocol describes a method to dissect, experimentally manipulate and culture whole retinal explants from chicken embryos. The explant cultures are useful when high success rate, efficacy and reproducibility are needed to test the effects of plasmids for electroporation and/or reagent substances, i.e., enzymatic inhibitors.

Video: Whole Retinal Explants from Chicken Embryos for Electroporation and Chemical Reagent Treatments

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 ...

Dual Labeling of Neural Crest Cells and Blood Vessels Within Chicken Embryos Using ChickGFP Neural Tube Grafting and Carbocyanine Dye DiI Injection

All developing organs need to be connected to both the nervous system (for sensory and motor control) as well as the vascular system (for gas exchange, fluid and nutrient supply). Consequently both the nervous and vascular systems develop alongside each other and share striking similarities in their branching architecture. Here we report embryonic manipulations that allow us to study the simultaneous development of neural crest-derived nervous tissue (in this case the enteric nervous system), and the vascular system. This is achieved by generating chicken chimeras via transplantation of discrete segments of the neural tube, and associated neural crest, combined with vascular DiI injection in the same embryo. Our method uses transgenic chickGFP embryos for intraspecies grafting, making the transplant technique more powerful than the classical quail-chick interspecies grafting protocol used with great effect since the 1970s. ChickGFP-chick intraspecies grafting facilitates imaging of transplanted cells and their projections in intact tissues, and eliminates any potential bias in cell development linked to species differences. This method takes full advantage of the ease of access of the avian embryo (compared with other vertebrate embryos) to study the co-development of the enteric nervous system and the vascular system.

Dual Labeling of Neural Crest Cells and Blood Vessels Within Chicken Embryos Using ChickGFP Neural Tube Grafting and Carbocyanine Dye DiI Injection

Here we report dual labeling of neural crest cells and blood vessels using chickGFP neural tube intraspecies grafting combined with intra-vascular DiI injection. This experimental technique allows us to simultaneously visualize and study development of the NCC-derived (enteric) nervous system and the vascular system, during organogenesis.

All developing organs need to be connected to both the nervous system (for sensory and motor control) as well as the vascular system (for gas exchange, ...

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. ...

Culture of Adult Transgenic Zebrafish Retinal Explants for Live-cell Imaging by Multiphoton Microscopy

An endogenous regeneration program is initiated by M&#252;ller glia in the adult zebrafish (Danio rerio) retina following neuronal damage and death. The M&#252;ller glia re-enter the cell cycle and produce neuronal progenitor cells that undergo subsequent rounds of cell divisions and differentiate into the lost neuronal cell types. Both M&#252;ller glia and neuronal progenitor cell nuclei replicate their DNA and undergo mitosis in distinct locations of the retina, i.e. they migrate between the basal Inner Nuclear Layer (INL) and the Outer Nuclear Layer (ONL), respectively, in a process described as Interkinetic Nuclear Migration (INM). INM has predominantly been studied in the developing retina. To examine the dynamics of INM in the adult regenerating zebrafish retina in detail, live-cell imaging of fluorescently-labeled M&#252;ller glia/neuronal progenitor cells is required. Here, we provide the conditions to isolate and culture dorsal retinas from Tg[gfap:nGFP]mi2004 zebrafish that were exposed to constant intense light for 35 h. We also show that these retinal cultures are viable to perform live-cell imaging experiments, continuously acquiring z-stack images throughout the thickness of the retinal explant for up to 8 h using multiphoton microscopy to monitor the migratory behavior of gfap:nGFP-positive cells. In addition, we describe the details to perform post-imaging analysis to determine the velocity of apical and basal INM. To summarize, we established conditions to study the dynamics of INM in an adult model of neuronal regeneration. This will advance our understanding of this crucial cellular process and allow us to determine the mechanisms that control INM.

Zebrafish retinal regeneration has mostly been studied using fixed retinas. However, dynamic processes such as interkinetic nuclear migration occur during the regenerative response and require live-cell imaging to investigate the underlying mechanisms. Here, we describe culture and imaging conditions to monitor Interkinetic Nuclear Migration (INM) in real-time using multiphoton microscopy.

An endogenous regeneration program is initiated by M&#252;ller glia in the adult zebrafish (Danio rerio) retina following neuronal damage and death. The ...

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 ...

Visualizing the Node and Notochordal Plate In Gastrulating Mouse Embryos Using Scanning Electron Microscopy and Whole Mount Immunofluorescence

The post-implantation mouse embryo undergoes major shape changes after the initiation of gastrulation and morphogenesis. A hallmark of morphogenesis is the formation of the transient organizers, the node and notochordal plate, from cells that have passed through the primitive streak. The proper formation of these signaling centers is essential for the development of the body plan and techniques to visualize them are of high interest to mouse developmental biologists. The node and notochordal plate lie on the ventral surface of gastrulating mouse embryos around embryonic day (E) 7.5 of development. The node is a cup-shaped structure whose cells possess a single slender cilium each. The proper subcellular localization and rotation of the cilia in the node pit determines left-right asymmetry. The notochordal plate cells also possess single cilia albeit shorter than those of the node cells. The notochordal plate forms the notochord which acts as an important signaling organizer for somitogenesis and neural patterning. Because the cells of the node and notochordal plate are transiently present on the surface and possess cilia, they can be visualized using scanning electron microscopy (SEM). Among other techniques used to visualize these structures at the cellular level is whole mount immunofluorescence (WMIF) using the antibodies against the proteins that are highly expressed in the node and notochordal plate. In this report, we describe our optimized protocols to perform SEM and WMIF of the node and notochordal plate in developing mouse embryos to help in the assessment of tissue shape and cellular organization in wild-type and gastrulation mutant embryos.

The node and notochordal plate are transient signaling organizers in developing mouse embryos that can be visualized using several techniques. Here, we describe in detail how to perform two of the techniques to study their structure and morphogenesis: 1) scanning electron microscopy (SEM); and 2) whole mount immunofluorescence (WMIF).

The post-implantation mouse embryo undergoes major shape changes after the initiation of gastrulation and morphogenesis. A hallmark of morphogenesis is ...

Fast and Efficient Expression of Multiple Proteins in Avian Embryos Using mRNA Electroporation

We report that mRNA electroporation permits fluorescent proteins to label cells in living quail embryos more quickly and broadly than DNA electroporation. The high transfection efficiency permits at least 4 distinct mRNAs to be co-transfected with ~87% efficiency. Most of the electroporated mRNAs are degraded during the first 2 h post-electroporation, permitting time-sensitive experiments to be carried out in the developing embryo. Finally, we describe how to dynamically image live embryos electroporated with mRNAs that encode various subcellular targeted fluorescent proteins.

We report messenger RNA (mRNA) electroporation as a method that permits fast and efficient expression of multiple proteins in the quail embryo model system. This method can be used to fluorescently label cells and record their in vivo movements by time-lapse microscopy shortly after electroporation.

We report that mRNA electroporation permits fluorescent proteins to label cells in living quail embryos more quickly and broadly than DNA electroporation. ...

Isolation and Differentiation of Primary Myoblasts from Mouse Skeletal Muscle Explants

Primary myoblasts are undifferentiated proliferating precursors of skeletal muscle. They can be cultured and studied as muscle precursors or induced to differentiate into later stages of muscle development. The protocol provided here describes a robust method for the isolation and culture of a highly proliferative population of myoblast cells from young adult mouse skeletal muscle explants. These cells are useful for the study of the metabolic properties of skeletal muscle of different mouse models, as well as in other downstream applications such as transfection with exogenous DNA or transduction with viral expression vectors. The level of differentiation and metabolic profile of these cells depends on the length of exposure, and composition of the media used to induce myoblast differentiation. These methods provide a robust system for the study of mouse muscle cell metabolism ex vivo. Importantly, unlike in vivo models, the methods described here provide a cell population that can be expanded and studied with high levels of reproducibility.

Myoblasts are proliferating precursor cells that differentiate to form polynucleated myotubes and eventually skeletal muscle myofibers. Here, we present a protocol for efficient isolation and culture of primary myoblasts from young adult mouse skeletal muscles. The method enables molecular, genetic, and metabolic studies of muscle cells in culture.

Primary myoblasts are undifferentiated proliferating precursors of skeletal muscle. They can be cultured and studied as muscle precursors or induced to ...

A Layered Mounting Method for Extended Time-Lapse Confocal Microscopy of Whole Zebrafish Embryos

Dynamics of development can be followed by confocal time-lapse microscopy of live transgenic zebrafish embryos expressing fluorescence in specific tissues or cells. A difficulty with imaging whole embryo development is that zebrafish embryos grow substantially in length. When mounted as regularly done in 0.3-1% low melt agarose, the agarose imposes growth restriction, leading to distortions in the soft embryo body. Yet, to perform confocal time-lapse microscopy, the embryo must be immobilized. This article describes a layered mounting method for zebrafish embryos that restrict the motility of the embryos while allowing for the unrestricted growth. The mounting is performed in layers of agarose at different concentrations. To demonstrate the usability of this method, whole embryo vascular, neuronal and muscle development was imaged in transgenic fish for 55 consecutive hours. This mounting method can be used for easy, low-cost imaging of whole zebrafish embryos using inverted microscopes without requirements of molds or special equipment.

This article describes a method to mount fragile zebrafish embryos for extended time-lapse confocal microscopy. This low-cost method is easy to perform using regular glass-bottom microscopy dishes for imaging on any inverted microscope. The mounting is performed in layers of agarose at different concentrations.

Dynamics of development can be followed by confocal time-lapse microscopy of live transgenic zebrafish embryos expressing fluorescence in specific tissues ...

Whole Mount Immunohistochemistry in Zebrafish Embryos and Larvae

Immunohistochemistry is a widely used technique to explore protein expression and localization during both normal developmental and disease states. Although many immunohistochemistry protocols have been optimized for mammalian tissue and tissue sections, these protocols often require modification and optimization for non-mammalian model organisms. Zebrafish are increasingly used as a model system in basic, biomedical, and translational research to investigate the molecular, genetic, and cell biological mechanisms of developmental processes. Zebrafish offer many advantages as a model system but also require modified techniques for optimal protein detection. Here, we provide our protocol for whole-mount fluorescence immunohistochemistry in zebrafish embryos and larvae. This protocol additionally describes several different mounting strategies that can be employed and an overview of the advantages and disadvantages each strategy provides. We also describe modifications to this protocol to allow detection of chromogenic substrates in whole mount tissue and fluorescence detection in sectioned larval tissue. This protocol is broadly applicable to the study of many developmental stages and embryonic structures.

Here, we present a protocol for fluorescent antibody-mediated detection of proteins in whole preparations of zebrafish embryos and larvae.

Immunohistochemistry is a widely used technique to explore protein expression and localization during both normal developmental and disease states. ...