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 border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<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&#160; FX HQ</td>
			<td></td>
		</tr>
		<tr>
			<td>CDPC (Cytidine 5&#8242;-diphosphocholine sodium salt dihydrate)</td>
			<td>Sigma-Aldrich</td>
			<td>C0256</td>
			<td></td>
		</tr>
		<tr>
			<td>CO2 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&#339;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/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/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/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/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/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/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/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 ...

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Research

JoVE Journal

Neuroscience

3.4K Views.  Institut de la Vision. We describe a method to obtain primary cultures of cone photoreceptors from the retina of chicken embryos and its use for high content screening. 

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

Derivation of Enriched Oligodendrocyte Cultures and Oligodendrocyte/Neuron Myelinating Co-cultures from Post-natal Murine Tissues

Identifying the molecular mechanisms underlying OL development is not only critical to furthering our knowledge of OL biology, but also has implications for understanding the pathogenesis of demyelinating diseases such as Multiple Sclerosis (MS). Cellular development is commonly studied with primary cell culture models. Primary cell culture facilitates the evaluation of a given cell type by providing a controlled environment, free of the extraneous variables that are present in vivo. While OL cultures derived from rats have provided a vast amount of insight into OL biology, similar efforts at establishing OL cultures from mice has been met with major obstacles. Developing methods to culture murine primary OLs is imperative in order to take advantage of the available transgenic mouse lines. 
Multiple methods for extraction of OPCs from rodent tissue have been described, ranging from neurosphere derivation, differential adhesion purification and immunopurification 1-3. While many methods offer success, most require extensive culture times and/or costly equipment/reagents. To circumvent this, purifying OPCs from murine tissue with an adaptation of the method originally described by McCarthy &amp; 
de Vellis 2 is preferred. This method involves physically separating OPCs from a mixed glial culture derived from neonatal rodent cortices. The result is a purified OPC population that can be differentiated into an OL-enriched culture. This approach is appealing due to its relatively short culture time and the unnecessary requirement for growth factors or immunopanning antibodies. 
While exploring the mechanisms of OL development in a purified culture is informative, it does not provide the most physiologically relevant environment for assessing myelin sheath formation. Co-culturing OLs with neurons would lend insight into the molecular underpinnings regulating OL-mediated myelination of axons. For many OL/neuron co-culture studies, dorsal root ganglion neurons (DRGNs) have proven to be the neuron type of choice. They are ideal for co-culture with OLs due to their ease of extraction, minimal amount of contaminating cells, and formation of dense neurite beds. While studies using rat/mouse myelinating xenocultures have been published 4-6, a method for the derivation of such OL/DRGN myelinating co-cultures from post-natal murine tissue has not been described. Here we present detailed methods on how to effectively produce such cultures, along with examples of expected results. These methods are useful for addressing questions relevant to OL development/myelinating function, and are useful tools in the field of neuroscience.

This article describes methods to derive enriched populations of murine oligodendrocyte precursor cells (OPCs) in primary culture, which differentiate to produce mature oligodendrocytes (OLs). In addition, this report describes techniques to produce murine myelinating co-cultures by seeding mouse OPCs onto a neurite bed of mouse dorsal root ganglion neurons (DRGNs).

Identifying the molecular mechanisms underlying OL development is not only critical to furthering our knowledge of OL biology, but also has implications ...

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 ...

Sex Stratified Neuronal Cultures to Study Ischemic Cell Death Pathways

Sex differences in neuronal susceptibility to ischemic injury and neurodegenerative disease have long been observed, but the signaling mechanisms responsible for those differences remain unclear. Primary disassociated embryonic neuronal culture provides a simplified experimental model with which to investigate the neuronal cell signaling involved in cell death as a result of ischemia or disease; however, most neuronal cultures used in research today are mixed sex. Researchers can and do test the effects of sex steroid treatment in mixed sex neuronal cultures in models of neuronal injury and disease, but accumulating evidence suggests that the female brain responds to androgens, estrogens, and progesterone differently than the male brain. Furthermore, neonate male and female rodents respond differently to ischemic injury, with males experiencing greater injury following cerebral ischemia than females. Thus, mixed sex neuronal cultures might obscure and confound the experimental results; important information might be missed. For this reason, the Herson Lab at the University of Colorado School of Medicine routinely prepares sex-stratified primary disassociated embryonic neuronal cultures from both hippocampus and cortex. Embryos are sexed before harvesting of brain tissue and male and female tissue are disassociated separately, plated separately, and maintained separately. Using this method, the Herson Lab has demonstrated a male-specific role for the ion channel TRPM2 in ischemic cell death. In this manuscript, we share and discuss our protocol for sexing embryonic mice and preparing sex-stratified hippocampal primary disassociated neuron cultures. This method can be adapted to prepare sex-stratified cortical cultures and the method for embryo sexing can be used in conjunction with other protocols for any study in which sex is thought to be an important determinant of outcome.

Primary disassociated embryonic hippocampal neuronal cultures are useful for investigating the signaling mechanisms involved in neuron death. Sexing the embryos before the isolation and dissociation of the hippocampus allows the preparation of separate male and female cultures, which enables the researcher to identify and investigate sex-specific cell signaling.

Sex differences in neuronal susceptibility to ischemic injury and neurodegenerative disease have long been observed, but the signaling mechanisms ...

Genetic Manipulation of Cerebellar Granule Neurons In Vitro and In Vivo to Study Neuronal Morphology and Migration

Developmental events in the brain including neuronal morphogenesis and migration are highly orchestrated processes. In vitro and in vivo analyses allow for an in-depth characterization to identify pathways involved in these events. Cerebellar granule neurons (CGNs) that are derived from the developing cerebellum are an ideal model system that allows for morphological analyses. Here, we describe a method of how to genetically manipulate CGNs and how to study axono- and dendritogenesis of individual neurons. With this method the effects of RNA interference, overexpression or small molecules can be compared to control neurons. In addition, the rodent cerebellar cortex is an easily accessible in vivo system owing to its predominant postnatal development. We also present an in vivo electroporation technique to genetically manipulate the developing cerebella and describe subsequent cerebellar analyses to assess neuronal morphology and migration.

Genetic Manipulation of Cerebellar Granule Neurons In Vitro and In Vivo to Study Neuronal Morphology and Migration

Neuronal morphogenesis and migration are crucial events underlying proper brain development. Here, we describe methods to genetically manipulate cultured cerebellar granule neurons and the developing cerebellum for the assessment of morphology and migratory characteristics of neurons.

Developmental events in the brain including neuronal morphogenesis and migration are highly orchestrated processes. In vitro and in vivo analyses allow ...

Organotypic Slice Cultures to Study Oligodendrocyte Dynamics and Myelination

NG2 expressing cells (polydendrocytes, oligodendrocyte precursor cells) are the fourth major glial cell population in the central nervous system. During embryonic and postnatal development they actively proliferate and generate myelinating oligodendrocytes. These cells have commonly been studied in primary dissociated cultures, neuron cocultures, and in fixed tissue. Using newly available transgenic mouse lines slice culture systems can be used to investigate proliferation and differentiation of oligodendrocyte lineage cells in both gray and white matter regions of the forebrain and cerebellum. Slice cultures are prepared from early postnatal mice and are kept in culture for up to 1 month. These slices can be imaged multiple times over the culture period to investigate cellular behavior and interactions. This method allows visualization of NG2 cell division and the steps leading to oligodendrocyte differentiation while enabling detailed analysis of region-dependent NG2 cell and oligodendrocyte functional heterogeneity. This is a powerful technique that can be used to investigate the intrinsic and extrinsic signals influencing these cells over time in a cellular environment that closely resembles that found in vivo.

A technique to study NG2 cells and oligodendrocytes using a slice culture system of the forebrain and cerebellum is described. This method allows examination of the dynamics of proliferation and differentiation of cells within the oligodendrocyte lineage where the extracellular environment can be easily manipulated while maintaining tissue cytoarchitecture.

NG2 expressing cells (polydendrocytes, oligodendrocyte precursor cells) are the fourth major glial cell population in the central nervous system. During ...

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 ...

The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

The olfactory system has the unusual capacity to generate new neurons throughout the lifetime of an organism. Olfactory stem cells in the basal portion of the olfactory epithelium continuously give rise to new sensory neurons that extend their axons into the olfactory bulb, where they face the challenge to integrate into existing circuitry. Because of this particular feature, the olfactory system represents a unique opportunity to monitor axonal wiring and guidance, and to investigate synapse formation. Here we describe a procedure for in vivo labeling of sensory neurons and subsequent visualization of axons in the olfactory system of larvae of the amphibian Xenopus laevis. To stain sensory neurons in the olfactory organ we adopt the electroporation technique. In vivo electroporation is an established technique for delivering fluorophore-coupled dextrans or other macromolecules into living cells. Stained sensory neurons and their axonal processes can then be monitored in the living animal either using confocal laser-scanning or multiphoton microscopy. By reducing the number of labeled cells to few or single cells per animal, single axons can be tracked into the olfactory bulb and their morphological changes can be monitored over weeks by conducting series of in vivo time lapse imaging experiments. While the described protocol exemplifies the labeling and monitoring of olfactory sensory neurons, it can also be adopted to other cell types within the olfactory and other systems.

The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

We describe a protocol for in vivo labeling of olfactory sensory neurons by electroporation and subsequent confocal laser-scanning or multiphoton microscopy to visualize neuronal morphology and its development over time.

The olfactory system has the unusual capacity to generate new neurons throughout the lifetime of an organism. Olfactory stem cells in the basal portion of ...

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 Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

The nervous system is composed of an enormous range of distinct neuronal types. These neuronal subpopulations are characterized by, among other features, their distinct dendritic morphologies, their specific patterns of axonal connectivity, and their selective firing responses. The molecular and cellular mechanisms responsible for these aspects of differentiation during development are still poorly understood.
Here, we describe combined protocols for labeling and characterizing the structural connectivity and excitability of cortical neurons. Modification of the in utero electroporation (IUE) protocol allows the labeling of a sparse population of neurons. This, in turn, enables the identification and tracking of the dendrites and axons of individual neurons, the precise characterization of the laminar location of axonal projections, and morphometric analysis. IUE can also be used to investigate changes in the excitability of wild-type (WT) or genetically modified neurons by combining it with whole-cell recording from acute slices of electroporated brains. These two techniques contribute to a better understanding of the coupling of structural and functional connectivity and of the molecular mechanisms controlling neuronal diversity during development. These developmental processes have important implications on axonal wiring, the functional diversity of neurons, and the biology of cognitive disorders.

In Utero Electroporation Approaches to Study the Excitability of Neuronal Subpopulations and Single-cell Connectivity

This manuscript provides protocols that use in utero electroporation (IUE) to describe the structural connectivity of neurons at the single-cell level and the excitability of fluorescently labeled neurons. Histology is used to characterize dendritic and axonal projections. Whole-cell recording in acute slices is used to investigate excitability.

The nervous system is composed of an enormous range of distinct neuronal types. These neuronal subpopulations are characterized by, among other features, ...

Time-dependent Increase in the Network Response to the Stimulation of Neuronal Cell Cultures on Micro-electrode Arrays

Micro-electrode arrays (MEAs) can be used to investigate drug toxicity, design paradigms for next-generation personalized medicine, and study network dynamics in neuronal cultures. In contrast with more traditional methods, such as patch-clamping, which can only record activity from a single cell, MEAs can record simultaneously from multiple sites in a network, without requiring the arduous task of placing each electrode individually. Moreover, numerous control and stimulation configurations can be easily applied within the same experimental setup, allowing for a broad range of dynamics to be explored. One of the key dynamics of interest in these in vitro studies has been the extent to which cultured networks display properties indicative of learning. Mouse neuronal cells cultured on MEAs display an increase in response following training induced by electrical stimulation. This protocol demonstrates how to culture neuronal cells on MEAs; successfully record from over 95% of the plated dishes; establish a protocol to train the networks to respond to patterns of stimulation; and sort, plot, and interpret the results from such experiments. The use of a proprietary system for stimulating and recording neuronal cultures is demonstrated. Software packages are also used to sort neuronal units. A custom-designed graphical user interface is used to visualize post-stimulus time histograms, inter-burst intervals, and burst duration, as well as to compare the cellular response to stimulation before and after a training protocol. Finally, representative results and future directions of this research effort are discussed.

Mouse neuronal cells cultured on multi-electrode arrays display an increase in response following electrical stimulation. This protocol demonstrates how to culture neurons, how to record activity, and how to establish a protocol to train the networks to respond to patterns of stimulation.

Micro-electrode arrays (MEAs) can be used to investigate drug toxicity, design paradigms for next-generation personalized medicine, and study network ...