The authors thank Jacques Bellalou, Lorelei Fournier, Emmanuelle Cl&#233;rin, Fr&#233;d&#233;ric Blond and the entreprise agricole &#224; responsabilit&#233; limit&#233;e (EARL Morizeau Dangers, France) for their invaluable help. This work was supported by Inserm, Sorbonne University, the Agence Nationale pour la Recherche (ANR, Labex Lifesenses), Foundation Fighting Blindness (USA) and IHU FOReSIGHT [ANR-18-IAHU-0001] supported by French state funds managed by the ANR within the Investissements d&#39;Avenir program.

The protocol was approved by the Committee on the Ethics of Animal Experiments of the University Pierre and Marie Curie and the French ministry of research (Permit Number: APAFIS#1028 2015070211275177). The animal experiments were performed under the following authorization: &#34;Certificat d&#39;autorisation d&#39;exp&#233;rimenter sur les animaux vert&#233;br&#233;s A-75-1863. Pr&#233;fecture de Police de Paris (November 9th 2011-November 8th 2016)&#34;.
1. Incubation of fertilized eggs
<ol>
	<li>Collect weekly fertilized eggs (strain I 657, red label), obtained naturally, at an industrial hatchery.</li>
	<li>Maintain the fertilized eggs at 17&#176;C (their biological zero) in the laboratory after they are &#34;laid&#34; by the hen.</li>
	<li>For each culture, incubate seven fertilized eggs for 24 hours at 20 &#176;C and then 136 hours at 37 &#176;C with intermittent reversion of the inclination (a progressive movement for 2 hours from one side to its opposite, a 4-hours cycle) of the eggs in a humidified chamber.</li>
</ol>
2. Recovery of the chicken embryos
<ol>
	<li>Wash the surface of the seven eggs with disinfectant (e.g., Pursept A express).</li>
	<li>To break the eggshell, make a hole in the top of the shell with large straight pliers. Then cut the shell to remove the hat from the egg as a soft-boiled egg.</li>
	<li>Gently extract each embryo from the eggshell with curved forceps, and then transfer it to a Petri dish containing sterile phosphate buffer saline (PBS) previously heated to 37 &#176;C. Gently, remove the envelope that surrounds the embryos (the chorion or chorioallantoic membrane).</li>
	<li>Verify the stage of development of each embryo by visual comparison to Hamburger and Hamilton42.</li>
	<li>Select two embryos at the 29th stage of development (Figure 1). The wings bend at the elbows. The collar stands out visibly. The bill is more prominent than at the 28th stage.</li>
	<li>Enucleate the eyes of these selected embryos and transfer them in CO2-independent medium (Life technologies). 
	CAUTION: It is very important that the embryo is at stage 29, and not at stage 28 or 30 (Figure 1); that is why it is necessary to incubate at least 7 eggs, even if only two will be finally used. The chorion is very thin, so hard to distinguish, but it is very close from the embryo, so it has to be removed without touching the embryo.</li>
</ol>
3. Dissection of the retinas
<ol>
	<li>Decapitate and enucleate the selected embryos with curved forceps.</li>
	<li>Transfer the four eyes into CO2-independent medium. This medium contains 0.9 mM CaCl2 and 0.65 mM MgCl2.</li>
	<li>Position the eye with the cornea face down, the optic nerve facing the experimenter. Drill a hole in the optic nerve using two straight forceps.</li>
	<li>Insert a branch of each forceps between the retina and the pigment epithelium (Figure 2). Pull on each forceps and rotate the eye to detach the epithelium from the retina. Remove the cornea followed by the lens and the vitreous.</li>
	<li>Transfer the four retinas in a Petri dish containing Ringer&#39;s medium at pH 7.2. 
	&#8203;CAUTION: Make sure that only the retina remains and remove any traces of vitreous and remaining retinal pigmented epithelium.</li>
</ol>
4. Preparing the retinal cell suspension
<ol>
	<li>Cut the four retinas in very small pieces using two straight pliers.</li>
	<li>Wash the retinal pieces twice with Ringer&#39;s medium.</li>
	<li>After the second wash with Ringer&#39;s medium, let the pieces of retina fall on the bottom of the tube and remove the Ringer&#39;s medium. Treat the retinal pieces for 20 minutes at 37 &#176;C with a solution of trypsin (0.25% w/v).</li>
	<li>Disperse the solution after 10 minutes by successive suction. Discharge using a Pasteur pipette and check for dissociation of the retinal pieces. Stop the reaction by adding culture media supplemented with 10% inactivated foetal calf serum.</li>
	<li>Incubate the cell suspension with 0.05 mg of DNase I. Dissociate the cell clusters and the DNA by successive suction and discharge using a Pasteur pipette immediately after adding the DNase.</li>
	<li>Wash the retinal cell suspension twice with chemical defined culture medium (CDCM): an equal volume of Dulbecco&#39;s Modified Eagle Medium and M199 media supplemented with 100 &#181;g/mL linoleic acid/BSA, 0.86 &#181;M insulin, 0.07 &#181;M transferrin, 2.0 &#181;M progesterone, 0.28 &#181;M prostaglandin, 0.29 &#181;M Na2SeO3, 182 &#181;M putrescine, 3 mM taurine, 4.7 &#181;M cytidine 5&#8242;-diphosphocholin, 2.7 &#181;M cytidine 5&#8242;-diphosphoethanolamine, 0.55 &#181;M hydrocortisone, 0.03 &#181;M triiodothyronine, 1 mM sodium pyruvate and 20 &#181;M gentamycin.</li>
</ol>
5. Retinal cell seeding
<ol>
	<li>Treat two black 96-well culture plates with transparent bottom for 2 hours at 37 &#176;C with poly-L-lysine at 32.25 &#181;g/cm2.</li>
	<li>Rinse these plates twice with M199 culture medium. Resuspend the cell pellet in 1 mL of CDCM.</li>
	<li>Add to an aliquot of 10 &#181;L of the cell suspension trypan blue to stain the living cells. Add the cells suspension specimen to a haemocytometer (cell counting-chamber of Malassez).
	<ol>
		<li>Under a microscope, count the stained cells for four rows of the haemocytometer (i.e., 40 squares), and then calculate the average cell number for one row. Calculate the concentration of cells of the suspension by applying the following method: Number of cells/mL&#160;of suspension = average number of cells in a row (10 squares) x 10 the total number of squares of the haemocytometer x dilution with trypan blue x 1,000 (to express the result as cells/mL).</li>
	</ol>
	</li>
	<li>Bring the cell suspension to two concentrations (5.6 x 104 cells/mL and 1.12 x 105 cells/mL) corresponding to the two plating densities (1 x 105 cells/cm2 and 2 x 105 cells/cm2) using CDCM.</li>
	<li>Seed 50 &#181;L of the two cell suspensions into the two pretreated black 96-well culture plates. Distribute the cells in the plates with a multichannel pipette from the right of the plate to the left, homogenizing between each column, so that the distribution of the cells is homogeneous.</li>
	<li>Add 50 &#181;L of the library of molecules (e.g., the conditioned media from a cDNA library, see below) to be screened using a predefined pattern (Table 1).</li>
	<li>Incubate the plates for seven days at 37&#176;C under 5% CO2 with no change of media.</li>
</ol>
6. Counting viable cells
<ol>
	<li>To each well of the plate, add 2.7 &#181;M of calcein AM and 0.3 mM of ethidium homodimer. 
	NOTE: Calcein penetrates the cells that are impermeable to large molecules as ethidium homodimer. In the cytoplasm of living cells, calcein is hydrolyzed by endogenous esterases, becomes fluorescent by emitting at 520 nm when excited at 485 nm. Ethidium homodimer bind to DNA on dead cells. Ethidium DNA-homodimer binding causes red fluorescence to be emitted at 635 nm after excitation at 520 nm.</li>
	<li>Incubate the plates for 1 hour at room temperature in the absence of light.</li>
	<li>Read the fluorescence on an automated plate reader composed of an inverted microscope equipped with a mercury lamp with two excitation filters at 485 and 520 nm, two filters of emission at 520 and 635 nm, an objective (x10), a motorized stage controlled by a processor and a charge-coupled device camera (CCD). This counting platform is controlled by the Metamorph software19. It makes it possible to acquire fluorescence images of living cells and dead cells simultaneously in each well of the 96-well plate, starting from wells A1 towards well A12, then B12 towards B1, C1 towards C12 and so on (Table I).</li>
	<li>Calculate the average area A of a single cell using the 18 wells of the negative controls (Table I).</li>
	<li>Count the cells in each well of the plate and apply the following empirical formula A x 29 / 20.7 to prevent that cell doublets (grouping of two cells) are counted. Score the protective effect of the cones by molecules as the ratio between the average cell number in the 4 wells where we tested the molecule versus the average cell number in the 18 wells of the negative control (see Table 1 and Supplementary Figure 1).</li>
	<li>Combine the results of the plate seeded at 1 x 105 cells/cm2 with the one seeded at 2 x 105 cells/cm2 to evaluate the potential protection (viability ratio) by each molecule screened.</li>
</ol>

TL, J-AS and VF hold a patent on the use of EdCVF to treat retinal degenerations [WO2009071659 (A1). Jun. 12 2007].

Among the many parameters that might limit the production of a cone-enriched culture from chicken embryos, the first critical step is to accurately identify the stage of development of the embryos in the hatched eggs. It has been observed that culture of cells from the retinas of embryos at ED8 (34th stage) produces only 35% photoreceptors, with the remaining 65% are made of other neurons4. Whatever the logistic applied to get the hatched eggs, it is necessary to fine-tune the temperature and the incubation time, and to examine carefully the embryos as compared to the reference pictures of all stages of development42,45.
Originally, the cone-enriched culture system was developed using the White Leghorn strain4. The white color of the eggs of that strain is not particularly appreciated in France, so we used a strain of chicken that produce brown eggs. We utilized the I 657 strain, which is made by crossing I 66 roosters with JA57 hens5. We were able to reproduce the characteristics of the original cultures. This shows that the genetic background of the chicken is not critical to obtain cone-enriched cultures.
We have not tested the effect of individual removal of the supplements in the culture medium, but have observed that insulin plays a critical role in accordance to the effect of insulin on the survival of cones in the rd1 mouse, a model of autosomal recessive RP46. Triiodothyronine (T3) may also participate in the differentiation of retinal precursor cells of the chicken embryo into cones according to the role of thyroid hormone receptor in retinal cell fate during development40. Consequently, the cone-enriched culture system cannot be used to identify insulin by expression cloning46.
The cone-enriched culture system relies on the culture of primary neurons and is much more appropriate tha methods relying on the use of immortalized cells as the cell line 661W24,25,26.
The method described here can be modified by performing a prior electroporation with plasmid DNA20. Before preparing the retinal cell suspension, the entire retina is placed in the chamber of a custom-made electroporator with 120 &#181;L of 0.5 &#181;g/&#181;L of plasmid DNA in 10 mM Tris-HCl pH 8.0, 1 mM EDTA. Five pulses of 15 V for 50 ms each are applied separated by 950 ms interval22. Attempts to deliver interfering RNA (RNAi) using the replication competent avian splice (RCAS) retroviruses into cone-enriched cultures were unsuccessful47. This is certainly due to the fact that in the absence of serum and in cultures of low density, retinal precursor cells are not replicative, a requisite for the propagation of retroviruses.
We developed the cone-enriched culture system to identify trophic factors that promote cone survival using expression cloning19. In order to make it feasible, we performed a first step of high content screening using conditioned medium from pools of 100 clones. Even if the cDNAs from the library are expressed under the control of a strong CMV promoter after transfection of COS-1 cells, it does not offer a guaranty that all the proteins encoded by individual cDNAs reach a concentration sufficient to be scored positive by the viability assay. This is a major limitation. In that sense, any screening is not really exhaustive. In addition, even if membranous proteins were not removed from the conditioned medium, the configuration of the assay is unfavorable to the identification of non-diffusive factors. An alternative would be to screen individual clones after having obtained the sequence of the cDNAs in order to avoid duplications in assaying many times the same candidate protein. This was initiated by sequencing the retinal cDNA libraries we used43. While rational, this approach has also its limitations. The bioinformatic analysis of the cDNA sequences will irresistibly impose, beside the reduction of the redundancy, the prioritization of screening certain clones based on knowledge. This will not be detrimental if finally, the whole library would be screened even if the time required to do it will be significantly lengthened. But invariably, the identity of the sequence will influence our way of looking at the results. This will not be neutral since the interpretation of the sequence will naturally be in competition with the experimental data.
The identification of EdCVF also show that high content screening entails technical limitations. From the first round of screening, we identified two pools with high activity (Supplementary Figure 1). The pool 0073 led to the successful identification of EdCVF, while pool 0080 did not conduct to such finding. We have not solved the problem that could result from the loss of the active clone during the preparation of sub-pools. Alternatively, it is not excluded, even if not statistically favorable, that among the cDNAs of pool 0080, two proteins were acting synergistically and their activity could not be observed as individual clones.
The identification of molecules protecting cones by screening small molecules is a future application of the cone-enriched culture system. Such molecules will be invaluable for the treatment of retinal pathologies for which gene therapy is not the most appropriate approach as age-related macular degeneration.

The retina of vertebrate species is dual, with rod photoreceptors for dim light vision and cone photoreceptors for daylight, color and acuity vision. Primate visual acuity relies on a region at the center of the retina, called the fovea, that is enriched in cones, but overall, cones represent only 5% of all photoreceptors. Consequently, the analysis of the cones in primate retina and especially the culture of cones are technically difficult. All other mammalian species have no fovea and the percentage of cones is low for rodents that are most commonly used in retinal research. This is not the case for avian species, for which cones dominate the retina of these well seeing bird species. Dinosaurs, which have dominated the ecosystem when the mammals first appeared during evolution, are at the phylogenetic origin of birds1. As a consequence of such competition between dinosaurs and early mammals, the mammals are mostly nocturnal with retinas dominated by rods. Only later during evolution did the diurnal vision of some mammalian species, among which primates belong, became an evolutionary advantage. Nevertheless, the ancestral period remains as an atavism of the nocturnal bottleneck in the evolution of mammalian vision2,3.
While studying retinal cell differentiation, Adler and Hatlee showed that photoreceptors represent&#160;approximately 70% of the retinal differentiated cells in cultures derived from chicken at the embryonic day (ED) 6 or stage 294. Because of the prevalence of cones in the chicken retina, cultures of retinal cells from ED6 chicken embryos have been developed as cone-enriched cultures5.
The importance of cone-mediated visual acuity for human is a truism. People affected by genetic or aging diseases that alter cone function are greatly handicapped. This has promoted a very large body of studies on inherited retinal degenerations (IRD) with the objective of finding treatments for these blinding diseases6,7. The first success, obtained using a recombinant adeno-associated vector (AAV) for the therapy of a severe form of IRD Leber congenital amaurosis (LCA), is a proof of concept for gene therapy8. The identification of the genes whose mutations trigger IRD opens the possibility of curing these diseases using gene therapy. Nevertheless, these diseases are resulting from mutations in more than 200 distinct genes9. Even in the case of autosomal recessive forms of IRD, when the reintroduction of the normal copy of the morbid gene could restore visual function, the economic cost of each individual development favors the most prevalent ones in detriment to the less common ones and to those for which the genetic origin remains unknown. This fact led researchers to think about more general therapies. Apoptotic cell death appeared as a common pathway, and a therapeutic target of these diseases that progress by the degeneration of photoreceptors, including for autosomal dominant forms10,11. However, the successes of such an approach are missing. For the most common form of IRD, retinitis pigmentosa (RP), the common pathway is the secondary loss of function ultimately followed by the degeneration of cones12,13. Preventing the loss of cone function will preserve central vision of the fovea independently of the causative mutations14.
In the early stage of RP, the loss of rods triggers a reduction in the expression of rod-derived cone viability factor (RdCVF), encoded by the nucleoredoxin-like 1 (NXNL1) gene, which interrupts the metabolic and redox signaling between rods and cones15. The administration of a recombinant AAV encoding the two products of the NXNL1 gene, the trophic factor RdCVF and the thioredoxin enzyme RdCVFL, could theoretically prevent cone vision loss in all genetic forms of RP16. We have shown that the NXNL1 gene product, RdCVFL, is expressed in chicken cone-enriched cultures17 and where it plays a protective role18. RdCVF and the NXNL1 gene were identified by high content screening of a retinal cDNA library using the survival of cells from a cone-enriched culture as readout19. We screened the equivalent of 210,000 individual clones of the library using 8 parallel tests for each clone. This represents a very large number of tests requiring easy access to the biological material, the retinas of chicken embryos. We found that it was relatively easy to obtain embryonated chicken eggs on a weekly basis because they are widely produced for the agro-industry for egg-laying hens and meat-producing chickens. After careful standardization of the cone-enriched cultures, the system provides an easy, robust and reproducible way of testing thousands of molecules for their ability to preserve cone viability. These cells are also amenable to genetic manipulations20 that benefit to the study of signal transduction and to biochemical analyses21,22,23.
Retinal researchers have developed alternative methods as the use of the cone cell line 661W24,25,26. Nevertheless, the identity of this cell line remains controversial27,28. The 661W cells were cloned from retinal tumors of a transgenic mouse line that expresses the SV40 large T antigen under control of the human interphotoreceptor retinol-binding protein promoter. SV40 large T antigen mediates cellular transformation and immortalization. As the consequence, signaling pathway identified using 661W cells must be reported into the context of a transformed and immortalized cell line which is distinct in many ways from cones in situ. In that respect, the cone-enriched culture system is composed of primary neurons, the cones that are more physiologically relevant.
While it is possible to obtain a pure culture of photoreceptors using vibratome sectioning of the mouse retina, the very low percentage of cones in the outer retina of rodents makes this approach unsuited for producing cone-enriched cultures29. The pig retina contains no fovea but has a region called area centralis that is very enriched in cones30. The high proportion of cones in the retina diurnal rodents, as Arvicanthis ansorgei and Psammomys obsesus31,32, offers a possible solution but requires the breeding of such exotic species. Adult pig eyes, collected from local slaughterhouses, can be used to produce a mixed culture of rods and cones that have been used to study photoreceptor survival33. An elegant solution is to pre-purify cones from the pig retina using panning with peanut agglutinin (PNA) lectin, which selectively binds to cones34. Nevertheless, this method is difficult to implement on a large scale because of its complexity.
Human induced pluripotent stem cells (iPS) offers the most promising approach to obtain a cone photoreceptor cell population that can be used for retinal transplantation but that can also be adapted to cone-enriched culture35,36. Since the transcription factor NRL is required for rod-photoreceptors37, the Nrl-/- mouse has a retina dominated by short wave cones (S-cones). The inactivation could be used to produce S-cone-enriched preparation by differentiation of human from iPS38,39. Another possible approach is to promote cone differentiation using thyroid hormone signaling40. While novel methods for producing cone-enriched cultures from human iPS are emerging, chicken embryos provide a current proven method19.
The cone-enriched culture was instrumental in the identification of RdCVF by expression cloning19. This system was also used successfully to demonstrate that RdCVF stimulates glucose uptake and its metabolism by aerobic glycolysis22. Furthermore cone-enriched culture was used to validate the protective role of RdCVFL, the second product of the NXNL1 gene23. More recently, this system was used to demonstrate the existence of protecting molecules secreted by retinal pigmented epithelial cells transduced with OTX241.

<table><tbody><tr><td>96 black plates (Clear Button with lid Tissue culture treated)</td><td>Corning</td><td>3603</td><td></td></tr><tr><td>Calcein AM</td><td>Thermo-Fisher scientific</td><td>C1430</td><td></td></tr><tr><td>CCD Camera</td><td>Photometrics</td><td>CoolSnap&amp;nbsp; FX HQ</td><td></td></tr><tr><td>CDPC (Cytidine 5&amp;prime;-diphosphocholine sodium salt dihydrate)</td><td>Sigma-Aldrich</td><td>C0256</td><td></td></tr><tr><td>CO&lt;sub&gt;2&lt;/sub&gt; Independant</td><td>Thermo-Fisher scientific</td><td>18045-054</td><td></td></tr><tr><td>Curved forceps</td><td>Dutscher</td><td>005093</td><td></td></tr><tr><td>DMEM Media</td><td>Thermo-Fisher scientific</td><td>41966-029</td><td></td></tr><tr><td>DNAse</td><td>Sigma-Aldrich</td><td>D4263</td><td></td></tr><tr><td>Eggs incubator</td><td>FarmLine</td><td>M08 01 3100</td><td></td></tr><tr><td>Ethidium Homodimer</td><td>Thermo-Fisher scientific</td><td>E1169</td><td></td></tr><tr><td>F&amp;oelig;tal bovine serum</td><td>Thermo-Fisher scientific</td><td>10270-098</td><td></td></tr><tr><td>Gentamycin</td><td>Thermo-Fisher scientific</td><td>15710-049</td><td></td></tr><tr><td>Hydrocortisone</td><td>Sigma-Aldrich</td><td>H0880</td><td></td></tr><tr><td>ITS (insulin Transferine selenium)</td><td>Sigma-Aldrich</td><td>I1884</td><td></td></tr><tr><td>large straight pliers</td><td>Dutscher</td><td>005074</td><td></td></tr><tr><td>Linoleic acid</td><td>Sigma-Aldrich</td><td>L8384</td><td></td></tr><tr><td>M199 medium</td><td>Thermo-Fisher scientific</td><td>31150-022</td><td></td></tr><tr><td>Metamorph software</td><td>Metamorph</td><td></td><td></td></tr><tr><td>Microscope</td><td>NIKON</td><td>Eclipse TE2000</td><td></td></tr><tr><td>Motorized stage</td><td>Martzauzer</td><td>Mutlicontrol 2000</td><td></td></tr><tr><td>Optical filter switch</td><td>Shutter Instrument company</td><td>Lambda 10-2</td><td></td></tr><tr><td>PBS 1X</td><td>Thermo-Fisher scientific</td><td>14190-086</td><td></td></tr><tr><td>Poly-L-lysine</td><td>Sigma-Aldrich</td><td>P6282</td><td></td></tr><tr><td>Progesterone</td><td>Sigma-Aldrich</td><td>P7556</td><td></td></tr><tr><td>Pursept A express</td><td>Fisher scientific</td><td>11814110</td><td></td></tr><tr><td>Putriscine</td><td>Sigma-Aldrich</td><td>P5780</td><td></td></tr><tr><td>Sodium pyruvate</td><td>Sigma-Aldrich</td><td>S8636</td><td></td></tr><tr><td>straight forceps</td><td>Dutscher</td><td>005092</td><td></td></tr><tr><td>Taurine</td><td>Sigma-Aldrich</td><td>T8691</td><td></td></tr><tr><td>Triiodothyronine</td><td>Sigma-Aldrich</td><td>T6397</td><td></td></tr><tr><td>Trypan blue</td><td>Thermo-Fisher scientific</td><td>15250-061</td><td></td></tr><tr><td>Trypsine 0.25 %</td><td>Thermo-Fisher scientific</td><td>25200-056</td><td></td></tr></tbody></table>

cone-enriched cultures from the retina of chicken embryos to study rod to cone cellular interactions

Human daytime vision relies on the function of cone photoreceptors at the center of the retina, the fovea. Patients suffering from the most prevalent form of inherited retinal degeneration, retinitis pigmentosa, lose night vision because of mutation driven loss of rod photoreceptors, a phenomenon followed by a progressive loss of function and death of cones leading to blindness. Geneticists have identified many genes with mutations causing this disease, but the first mutations identified questioned the mechanisms of secondary cone degeneration and how a dominant mutation in the rhodopsin gene encoding for the visual pigment expressed exclusively in rods can trigger cone degeneration.
This result of transplantations in a genetic model of the disease led to the concept of cell interactions between rods and cones and of non-cell autonomous degeneration of cones in all genetic forms of retinitis pigmentosa.
Cones comprise 5% of all photoreceptors in humans and only 3% in the mouse, so their study is difficult in these species, but cones outnumber rods in bird species. We have adapted 96-well plates to culture retinal precursors from the retina of chicken embryos at stage 29 of their development. In these primary cultures, cones represent 80% of the cells after in vitro differentiation. The cells degenerate over a period of one week in the absence of serum. Here, we describe the methods and its standardization.
This cone-enriched culture system was used to identify the epithelium-derived cone viability factor (EdCVF) by high content screening of a rat retinal pigmented epithelium normalized cDNA library. Recombinant EdCVF prevents the degeneration of the cones.

We describe here how the cone-enriched culture system can be used to identify novel cone protecting proteins. We used this protocol to screen a normalized cDNA library made of choroid and retinal pigmented epithelium from 400 eyes of 8 weeks old Long-Evans rats43.
This library contains 6.0 x 106 independent colonies forming units (CFUs) and has an average cloned insert size of 2.1 kilobase (kb), with greater than 99% of recombinant clones. Pools of 100 clones from that library were transiently transfected (0.1 &#181;g of plasmid DNA) into COS-1 cells and the conditioned medium (CM) of COS-1 were harvested after incubation for 48 hours in DMEM without serum. Membranes or exosomes were not removed by ultracentrifugation. Fifty microliters of each CM were added to 4 wells of two 96-well plates: one seeded at 2 x 105 cells/cm2, the other one at 4 x 105 cells/cm2. CM from COS-1 cells transfected with the empty vector pcDNA3.1 used to construct the library was used as negative control (Table 1). A total of 2,112 sets of 100 clones corresponding to 211,200 individual clones were evaluated in four culture wells and for two seeding conditions of cone-enriched cultures. The two conditions correspond to two slightly different inoculation densities which makes it possible to assess the protective activity more precisely, for a total of 1,689,600 culture wells.
Among the 42 pools of clones with a ratio greater than 2, pools 0080 and 0073 have viability ratio 16 and 14 times higher after 7 days of culture than the negative control, pcDNA3.1 (Supplementary Figure 1). This analysis is essential to identify the pools of interest. Each selected pool of 100 clones was subdivided into 16 sets of 10 clones from their glycerol stock. These sub-pools were prepared and tested according to the same method in a second round of screening (i.e., a total of 3,200 culture wells). The sub-pool 0073-09 gave the strongest viability ratio (Supplementary Figure 2A) and was subdivided to produce 16 individual clones that were tested in a third round of screening on cone-enriched cultures. The clone 0073-09-37 clone clearly stands out from the others with a viability ratio equal to 2.5 (Supplementary Figure 2B). The y axis has a different scale even if the seeding density was the same than in Supplementary figure 2A. We have seen this commonly when the assays are repeated weekly for months. After analysis, these results confirm that clone 0073-09-37 has a robust and reproducible effect on cone survival. The test was repeated independently (Figure 3A), and the insert of 1.8 kb was sequenced (Figure 3B).
A bioinformatic analysis revealed that the clone 0073-09-37, that we named epithelium-derived cone viability factor (EdCVF), contains three open reading frames (ORFs), the one the most upstream (ORF1) encodes for 84 residues of the C-terminal part of the rat protein zinc finger protein-180 (ZFP180, NP_653358) of 727 amino acids44. The other two ORFs (ORF2 and ORF3) are much less well conserved in mice and absent in other mammals. When tested independently, only ORF1 exerts a protective effect on the cones (Supplementary Figure 3). ORF1 was produced as a glutathione S-transferase (GST) fusion protein (Figure 4A). The EdCVF protein was purified and the GST tag removed (Figure 4B). EdCVF is able to prevent cone degeneration in the cone-enriched culture system (Figure 4C).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61998/61998fig01.jpg" /> 
Figure 1: Chicken embryos at stages 28th, 29th and 30th of development. Arrows W: wing, C: collar and B: bill. Scale bar 1 cm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61998/61998fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61998/61998fig02.jpg" /> 
Figure 2: Dissection of the retina of the chicken embryo&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61998/61998fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61998/61998fig03.jpg" /> 
Figure 3: Epithelium-derived cone viability factor (EdCVF), clone 0073-09-37.&#160;A. Increased viability on cone-enriched culture. B. The sequence of the cDNA clone 0073-09-37. The underlined sequence GAATTC is the EcoRI restriction site used to construct the library. The two codons GTG in bold are uncommon translation initiation sites for EdCVF originating from the vector. Statistical analysis by Student&#39;s test. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61998/61998fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61998/61998fig04.jpg" /> 
Figure 4: Recombinant EdCVF activity. A. Sequence of EdCVF in the fusion with glutathione S-transferase (GST). B. The purified recombinant EdCVF protein. C. Trophic activity of GST-EdCVF on cone in culture. Statistical analysis using Tukey&#39;s test. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61998/61998fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplementary Figure 1: Ratio of the average cell number for a cDNA pool and the negative control, the conditioned medium of COS-1 cells transfected with the empty vector pcDNA3.1 during the first round of screening.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61998/Supplemntary_File_1_12_11_2020.pdf" target="_blank">Please click here to download&#160;this file.</a>
Supplementary Figure 2: Number of cells alive.&#160;A. The second round of screening with sub-pools of 0073 pool. B. The third round of screening with isolated clones. CN: the conditioned medium of COS-1 cells transfected with the empty vector, pcDNA3.1.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61998/Supplementary_Figure_2_12_11_2020.pdf" target="_blank">Please click here to download&#160;this file.</a> 
Supplementary Figure 3: Trophic activity of the three open reading frames of the isolated clone 0073-09-37. Statistical analysis using Dunnett&#39;s test.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61998/Supplementary_figure_3.pdf" target="_blank">Please click here to download&#160;this file.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td>1</td>
			<td>2</td>
			<td>3</td>
			<td>4</td>
			<td>5</td>
			<td>6</td>
			<td>7</td>
			<td>8</td>
			<td>9</td>
			<td>10</td>
			<td>11</td>
			<td>12</td>
		</tr>
		<tr>
			<td>A</td>
			<td>1</td>
			<td>1</td>
			<td>1</td>
			<td>1</td>
			<td>2</td>
			<td>NC</td>
			<td>2</td>
			<td>2</td>
			<td>2</td>
			<td>3</td>
			<td>3</td>
			<td>NC</td>
		</tr>
		<tr>
			<td>B</td>
			<td>NC</td>
			<td>3</td>
			<td>3</td>
			<td>4</td>
			<td>4</td>
			<td>4</td>
			<td>NC</td>
			<td>4</td>
			<td>5</td>
			<td>5</td>
			<td>5</td>
			<td>5</td>
		</tr>
		<tr>
			<td>C</td>
			<td>6</td>
			<td>NC</td>
			<td>6</td>
			<td>6</td>
			<td>6</td>
			<td>7</td>
			<td>7</td>
			<td>NC</td>
			<td>7</td>
			<td>7</td>
			<td>8</td>
			<td>8</td>
		</tr>
		<tr>
			<td>D</td>
			<td>8</td>
			<td>8</td>
			<td>NC</td>
			<td>9</td>
			<td>9</td>
			<td>9</td>
			<td>9</td>
			<td>10</td>
			<td>NC</td>
			<td>10</td>
			<td>10</td>
			<td>10</td>
		</tr>
		<tr>
			<td>E</td>
			<td>11</td>
			<td>11</td>
			<td>11</td>
			<td>NC</td>
			<td>11</td>
			<td>12</td>
			<td>12</td>
			<td>12</td>
			<td>12</td>
			<td>NC</td>
			<td>13</td>
			<td>13</td>
		</tr>
		<tr>
			<td>F</td>
			<td>13</td>
			<td>13</td>
			<td>14</td>
			<td>14</td>
			<td>NC</td>
			<td>14</td>
			<td>14</td>
			<td>15</td>
			<td>15</td>
			<td>15</td>
			<td>NC</td>
			<td>15</td>
		</tr>
		<tr>
			<td>G</td>
			<td>16</td>
			<td>16</td>
			<td>16</td>
			<td>16</td>
			<td>17</td>
			<td>NC</td>
			<td>17</td>
			<td>17</td>
			<td>17</td>
			<td>18</td>
			<td>18</td>
			<td>NC</td>
		</tr>
		<tr>
			<td>H</td>
			<td>18</td>
			<td>18</td>
			<td>19</td>
			<td>19</td>
			<td>19</td>
			<td>19</td>
			<td>NC</td>
			<td>20</td>
			<td>20</td>
			<td>20</td>
			<td>NC</td>
			<td>20</td>
		</tr>
		<tr>
			<td colspan="13">NC negative controls</td>
		</tr>
		<tr>
			<td colspan="13">1-20 positions of the pools tested in quadruplicate</td>
		</tr>
	</tbody>
</table>
Table 1: Plan of the 96-well plate for high content screening

Watch this Scientific Journal Video about Cone-Enriched Cultures from the Retina of Chicken Embryos to Study Rod to Cone Cellular Interactions at JoVE.com

Cone-Enriched Cultures from the Retina of Chicken Embryos to Study Rod to Cone Cellular Interactions

We describe a method to obtain primary cultures of cone photoreceptors from the retina of chicken embryos and its use for high content screening.

Human daytime vision relies on the function of cone photoreceptors at the center of the retina, the fovea. Patients suffering from the most prevalent form ...

cone-enriched-cultures-from-retina-chicken-embryos-to-study-rod-to

Nanyang Technological University

Research

JoVE Journal

Neuroscience

3.5K Views.  Institut de la Vision. Deze methode wordt gebruikt om kegelreceptoren te bestuderen die essentieel zijn voor daglichtzicht. Het voordeel van de methoden is dat het bevruchte kippeneieren gebruikt, die gemakkelijk toegankelijk zijn, en een van de enige bron van primaire kegelculturen. Het protocol werd gebruikt om Rod-Derived Cone Viability Factor te identificeren, een toekomstige veelbelovende behandeling voor erfelijke retinale degeneratie.Bovendien werd het protocol gebruikt om het metabolisme van kegelfot...

Video: Cone-Enriched Cultures from the Retina of Chicken Embryos to Study Rod to Cone Cellular Interactions

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 ...

Developmental Biology

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 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 ...

Transretinal ERG Recordings from Mouse Retina: Rod and Cone Photoresponses

There are two distinct classes of image-forming photoreceptors in the vertebrate retina: rods and cones. Rods are able to detect single photons of light whereas cones operate continuously under rapidly changing bright light conditions. Absorption of light by rod- and cone-specific visual pigments in the outer segments of photoreceptors triggers a phototransduction cascade that eventually leads to closure of cyclic nucleotide-gated channels on the plasma membrane and cell hyperpolarization. This light-induced change in membrane current and potential can be registered as a photoresponse, by either classical suction electrode recording technique1,2 or by transretinal electroretinogram recordings (ERG) from isolated retinas with pharmacologically blocked postsynaptic response components3-5. The latter method allows drug-accessible long-lasting recordings from mouse photoreceptors and is particularly useful for obtaining stable photoresponses from the scarce and fragile mouse cones. In the case of cones, such experiments can be performed both in dark-adapted conditions and following intense illumination that bleaches essentially all visual pigment, to monitor the process of cone photosensitivity recovery during dark adaptation6,7. In this video, we will show how to perform rod- and M/L-cone-driven transretinal recordings from dark-adapted mouse retina. Rod recordings will be carried out using retina of wild type (C57Bl/6) mice. For simplicity, cone recordings will be obtained from genetically modified rod transducin &alpha;-subunit knockout (T&alpha;-/-) mice which lack rod signaling8.

We describe a relatively simple method of transretinal electroretinogram (ERG) recordings for obtaining rod and cone photoresponses from intact mouse retina. This approach takes advantage of the block of synaptic transmission from photoreceptors to isolate their light responses and record them using field electrodes placed across the isolated flat-mounted retina.

There are two distinct classes of image-forming photoreceptors in the vertebrate retina: rods and cones. Rods are able to detect single photons of light ...

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 vivo-like Organotypic Murine Retinal Wholemount Culture

Targeted ablations of genes and analysis of animal models is the classical strategy for enrolling specific retinal gene function. However, transgenic, retina-specific or conditional knockout mouse models often display early lethality or suffer from severe malformations, preventing an analysis beyond embryonic or early postnatal stages.
Primary cell culture is an alternative to investigate the effects of exogenously applied recombinant factors, overexpression of genes or siRNA-mediated gene knockdown in a controlled environment. Dissociated cell culture has the advantage that the endogenous signals reaching the target cells are reduced, thereby facilitating the identification of exogenously triggered effects after pharmacological manipulation. However, important cell-cell interactions are initially destroyed by enzymatic digestion or mechanical dissociation, even if re-aggregated retinospheroid cultures1 are used.
By contrast, organotypic retinal wholemount cultures provide a system close to the physiological in vivo situation with neuronal interactions and connections still preserved2-5.
In this video article we provide a step by step demonstration of (1) the establishment of in vivo-like organotypic retinal wholemount cultures including dissection peculiarities of embryonic, postnatal and adult murine eyes and (2) a dissociation and cytospin procedure for analysis of neuronal apoptosis and retinal cell proliferation in organotypic wholemounts, e.g. after culture in the presence of exogenously applied recombinant factors.

In vivo-like Organotypic Murine Retinal Wholemount Culture

This video article demonstrates the establishment of organotypic retinal wholemount cultures and a cytospin procedure for analysis of exogenously induced effects. Organotypic retinal wholemount cultures mimic the in vivo situation and significantly facilitate the accessibility of murine retinas for experimental manipulations while circumventing the disadvantages of classical murine animal models.

Targeted ablations of genes and analysis of animal models is the classical strategy for enrolling specific retinal gene function. However, transgenic, ...

Biology

Single-cell Suction Recordings from Mouse Cone Photoreceptors

Rod and cone photoreceptors in the retina are responsible for light detection. In darkness, cyclic nucleotide-gated (CNG) channels in the outer segment are open and allow cations to flow steadily inwards across the membrane, depolarizing the cell. Light exposure triggers the closure of the CNG channels, blocks the inward cation current flow, and thus results in cell hyperpolarization. Based on the polarity of photoreceptors, a suction recording method was developed in 1970s that, unlike the classic patch-clamp technique, does not require penetrating the plasma membrane 1. Drawing the outer segment into a tightly-fitting glass pipette filled with extracellular solution allows recording the current changes in individual cells upon test-flash exposure. However, this well-established "outer-segment-in (OS-in)" suction recording is not suitable for mouse cone recordings, because of the low percentage of cones in the mouse retina (3%) and the difficulties in identifying the cone outer segments. Recently, an inner-segment-in (IS-in) recording configuration was developed to draw the inner segment/nuclear region of the photoreceptor into the recording pipette 2,3. In this video, we will show how to record from individual mouse cone photoresponses using single-cell suction electrode.

We will show how to record flash responses from single mouse cones using a suction electrode.

Rod and cone photoreceptors in the retina are responsible for light detection. In darkness, cyclic nucleotide-gated (CNG) channels in the outer segment ...

Vibratome Sectioning Mouse Retina to Prepare Photoreceptor Cultures

The retina is a part of the central nervous system that has organized architecture, with neurons in layers from the photoreceptors, both rods and cones in contact with the retinal pigmented epithelium in the most distant part on the retina considering the direction of light, and the ganglion cells in the most proximal distance. This architecture allows the isolation of the photoreceptor layer by vibratome sectioning. The dissected neural retina of a mouse aged 8 days is flat-embedded in 4% gelatin on top of a slice of 20% gelatin photoreceptor layer facing down. Using a vibratome and a double edged razor blade, the 100 &#181;m thick inner retina is sectioned. This section contains the ganglion cells and the inner layer with notably the bipolar cells. An intermediary section of 15 &#181;m is discarded before 200 &#181;m of the outer retina containing the photoreceptors is recovered. The gelatin is removed by heating at 37 &#176;C. Pieces of outer layer are incubated in 500 &#181;l of Ringer&#39;s solution with 2 units of activated papain for 20 min at 37 &#176;C. The reaction is stopped by adding 500 &#181;l 10% fetal calf serum (FCS) in Dulbecco&#39;s Modified Eagle Medium (DMEM), then 25 units of DNAse I is added before centrifugation at RT, washed several times to remove serum and the cells are resuspended in 500 &#181;l of DMEM and seeded at 1 x 105 cells/cm2. The cells are grown to 5 days in vitro and their viability scored using live/dead assay. The purity of the culture is first determined by microscopic observation during the experiment. The purity is then validated by seeding and fixing cells on a histological slide and analyzing using a rabbit polyclonal anti-SAG, a photoreceptor marker and mouse monoclonal anti-RHO, a rod photoreceptor specific marker. Alternatively, the photoreceptor layer (97% rods) can be used for gene or protein expression analysis and for transplantation.

Neural retina of a mouse aged 8 days is on top of a 4% gelatin block. After isolation of the photoreceptor layer (200 &#181;m) by vibratome, the photoreceptors are seeded after mechanical and enzymatic dissociation for culture. The photoreceptor layer can be used for molecular, biochemical analyses or transplantation.

The retina is a part of the central nervous system that has organized architecture, with neurons in layers from the photoreceptors, both rods and cones in ...

Imaging Ca2+ Dynamics in Cone Photoreceptor Axon Terminals of the Mouse Retina

Retinal cone photoreceptors (cones) serve daylight vision and are the basis of color discrimination. They are subject to degeneration, often leading to blindness in many retinal diseases. Calcium (Ca2+), a key second messenger in photoreceptor signaling and metabolism, has been proposed to be indirectly linked with photoreceptor degeneration in various animal models. Systematically studying these aspects of cone physiology and pathophysiology has been hampered by the difficulties of electrically recording from these small cells, in particular in the mouse where the retina is dominated by rod photoreceptors. To circumvent this issue, we established a two-photon Ca2+ imaging protocol using a transgenic mouse line that expresses the genetically encoded Ca2+ biosensor TN-XL exclusively in cones and can be crossbred with mouse models for photoreceptor degeneration. The protocol described here involves preparing vertical sections (&#8220;slices&#8221;) of retinas from mice and optical imaging of light stimulus-evoked changes in cone Ca2+ level. The protocol also allows &#8220;in-slice measurement&#8221; of absolute Ca2+ concentrations; as the recordings can be followed by calibration. This protocol enables studies into functional cone properties and is expected to contribute to the understanding of cone Ca2+ signaling as well as the potential involvement of Ca2+ in photoreceptor death and retinal degeneration.

Imaging Ca2+ Dynamics in Cone Photoreceptor Axon Terminals of the Mouse Retina

We describe a protocol to monitor Ca2+ dynamics in the axon terminals of cone photoreceptors using an ex-vivo&#160;slice preparation of the mouse retina. This protocol allows comprehensive studies of cone Ca2+ signaling in an important mammalian model system, the mouse.

Retinal cone photoreceptors (cones) serve daylight vision and are the basis of color discrimination. They are subject to degeneration, often leading to ...

In Ovo Electroporation in Embryonic Chick Retina

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

In Ovo Electroporation in Embryonic Chick Retina

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

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

Studying Protein Expression During Chicken Lens Development

Microinjection of Recombinant RCAS(A) Retrovirus into Embryonic Chicken Lens

Embryonic chicken (Gallus domesticus) is a well-established animal model for the study of lens development and physiology, given its high degree of similarity with the human lens. RCAS(A) is a replication-competent chicken retrovirus that infects dividing cells, which serves as a powerful tool to study the in situ expression and function of wild-type and mutant proteins during lens development by microinjection into the empty lumen of lens vesicle at early developmental stages, restricting its action to surrounding proliferating lens cells. Compared to other approaches, such as transgenic models and ex vivo cultures, the use of an RCAS(A) replication-competent avian retrovirus provides a highly effective, rapid, and customizable system to express exogenous proteins in chick embryos. Specifically, targeted gene transfer can be confined to proliferative lens fiber cells without the need for tissue-specific promoters. In this article, we will briefly overview the steps needed for recombinant retrovirus RCAS(A) preparation, provide a detailed, comprehensive overview of the microinjection procedure, and provide sample results of the technique.

Author Spotlight: Investigating Lens Development and Function Through Microinjection of RCAS(A) Retrovirus in Embryonic Chicken Lens 

This protocol paper describes the methodology of embryonic chicken lens microinjection of an RCAS(A) retrovirus as a tool for studying in situ function and expression of proteins during lens development.

Embryonic chicken (Gallus domesticus) is a well-established animal model for the study of lens development and physiology, given its high degree of ...

Cone-Enriched Cultures from the Retina of Chicken Embryos to Study Rod to Cone Cellular Interactions

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