We thank members of the Evans laboratory for their help in preparing this presentation. The morpholinos used here were originally validated by Dr. Audrey Holtzinger. T.E. is supported by grants from the National Institutes of Health (HL064282 and HL056182). Experiments on animals were performed in accordance with the guidelines and regulations set forth by the Institute for Animal Care and Use Committee, of the Weill Cornell Medical College.

Our goal here is to test the functional redundancy of two transcription factors for specification of cardiomyocyte progenitors. The factors are encoded by the two related genes gata5 and gata6 and we are using the zebrafish model to understand their relative functions1. Our strategy is to block gene function using morpholinos2. We will inject morpholinos for one or the other gene into fertilized eggs, and compare the embryonic phenotype with embryos derived from eggs injected simultaneously with both morpholinos. To simplify the evaluation of phenotypes, we use eggs derived from fish that carry a transgene that expresses GFP in cardiomyocytes.
Step 1. Preparing for microinjection.
A) Setting up breeding pairs of fish
The evening prior to injection, single male and single female adult fish (3-18 months of age) are placed in pairs into breeder tanks separated by a divider until the next morning. We typically set up 10-20 pairs of fish, and these are mated once a week, regardless of whether the eggs will be used, to maintain fecundity. For this experiment we are using a reporter strain, transgenic for cmlc2:egfp, because it provides a simple readout to identify differentiating cardiomyocytes. The next morning, once the lights are turned on, the water is changed, and dividers are pulled from tanks allowing the fish pairs to mate and produce eggs. Egg production can be monitored, and may initiate immediately, or after a period of an hour or more, depending on the fish. Typically, after approximately 20 minutes of uninterrupted mating, eggs are collected using a pipette or strainer and poured into 100 mm Petri dishes containing system water. It is important to monitor egg production in order to assure that embryos are injected between the 1-4 cell stage. By releasing several pairs at a time, it is possible to stagger the egg production and thereby maximize the amount of eggs that can be injected at an early developmental stage. A good pair of fish may generate more than 200 embryos, and it makes no practical sense to collect thousands of eggs at the same time, since a single investigator would not be able to inject them quickly enough before they develop beyond the 4-cell stage. Fish are stimulated to breed on the light cycle, so this is an experiment that requires an early start, and eggs are not usually obtained after noon.
B) Preparing needles
<ol>
 <li> Use a Micropipette Puller and a 3.5" glass capillary tube to generate two needles using the following condition: Heat=626, Pull=60, Velocity=60, and Time=250. We use open core needles that do not contain a filament, because we front-fill them with suction.</li>
 <li> The tip of each needle is then gently broken using a clean razor blade or forceps, and subsequently beveled at a 30 degrees angle for about 20 seconds using an EG-4 micro-grinder. This sharpens the tip and is important if you inject through the chorion.</li>
 <li> It is important to obtain a consistent needle diameter tip size of about 15 micron (calibrated as 4 units using a gridded microscope eyepiece, to be able to calibrate a 1-2 nl injection volume).</li>
 <li> Needles should be prepared in advance, stored safely in a secure location, and each is individually calibrated just prior to starting injections to assure consistent injection volume (see section D for details). If you are fortunate, you may be able to use a single needle for an entire experiment. However, a needle can easily break in the middle of an experiment, and you don't want to use that time to pull new needles.</li>
</ol>
C) Making injection plates
<ol>
 <li> Prepare 100 ml of a 2% agarose solution in system water, by boiling in a microwave oven.</li>
 <li> Cool to the touch, and pour about 12ml into the inverted lid of a 100mm Petri dish.</li>
 <li> Insert 2 microscope slides, slanted at approximately 45-degree angles, into the two sides of the lid. Once the agarose has solidified, gently pull the two slides away from the lid.</li>
 <li> This creates troughs where embryos will be placed and subsequently injected. Multiple plates can be prepared ahead of time. They can be stored indefinitely at 4&deg;C after adding a layer of 70% ethanol, adding the bottom of the original plate, and sealing with parafilm. Remember to wash well before using.</li>
</ol>
D) Microinjection station and needle calibration
<ol>
 <li> Turn on the compressed nitrogen source and PLI-100 microinjector. The injector should be adjusted for a constant flow pressure of 18 PSI.</li>
 <li> Before inserting a needle, assure that the micromanipulator is in a proper position to allow a wide range of movement, and that an inserted needle will not strike the table. Insert one of the needles prepared previously (see section C) into the micromanipulator making sure there is a tight seal. Be careful not to break the needle.</li>
 <li> Observe the needle tip under the microscope to make sure it is not clogged before proceeding to calibration.</li>
 <li> Place a drop (2-3 &mu;l) of injection solution or ddH2O onto a small piece of parafilm and fill about 1.5 &mu;l by pulling it into the needle using the fill button. Be sure that you have the needle tip fully in the solution, and observe the liquid suction through the microscope to avoid drawing in any air bubbles.</li>
 <li> Place a drop of mineral oil onto the grid of a micrometer.</li>
 <li> Adjust empirically the time of injection to ensure that the drop size is approximately 1.5 micron in diameter. This will deliver an injection volume of ~ 1.8 nl. The actual volume can be adjusted to your choice, but in a practical sense it is difficult to accurately calibrate volumes below 1 nl, and the embryos may not tolerate volumes above 2 nl. Regardless of the volume size you choose, keep it the same for all your injections including controls, and adjust your solution concentrations (rather than the injection volume) to titrate the amount of injected morpholino.</li>
 <li> Recalibration is necessary each time a needle is replaced, since the needle tip sizes will vary.</li>
</ol>
Step 2. Validation of morpholinos targeting two distinct genes
Morpholinos are designed to target the translation initiation site or splice sites of a target mRNA thereby blocking protein synthesis or proper mRNA processing. When analyzing a gene for the first time, we use both types of morpholinos to test if they generate the same phenotype, indicating a specific knockdown. An advantage of the splice-blocker is that you can verify the knockdown of the normal transcript by RT-PCR, which is especially useful if antibodies for the target gene are not available. We will illustrate how a consistent cardiac phenotype is achieved for the gata5 and gata6 genes using morpholinos (gata5 5'UTR MO sequence: 5'-AAGATAAAGCCAGGCTCGAATACAT-3'; gata5 Splice Site MO sequence: 5'-TCTTAAGATTTTTACCTATACTGGA-3'; gata6 5'UTR MO sequence: 5'-AGCTGTTATCACCCAGGTCCATCCA-3').
<ol>
 <li> Morpholinos are obtained from Gene Tools, LLC (Philomath, OR). Gene Tools will help you choose the best sequence to target, if you ask their support staff. You only need to send them the accession number, and they will advise. However, there is no guarantee that the morpholino will work, which is why you need to be prepared to validate the activity. You can also check if the morpholino is available from OpenBiosystems. Gene Tools provides stocks of synthesized morpholinos to OpenBiosystems. While there is again no guarantee it will work, they sell smaller quantities at a lower cost, which may help defray costs for testing new targets. Be sure to BLAST your morpholino against the transcriptome; we use the BLAT feature on the UCSC zebrafish genome browser (genome.ucsc.edu). Of course, if a morpholino has been validated (rigorously) in the literature, it is recommended that you purchase that same sequence.</li>
 <li> The morpholino is dissolved in sterile ddH20 to a final concentration of 1 mM and stored at room temperature. DO NOT FREEZE the morpholino solutions, as for some reason low temperatures can sometimes cause them to aggregate and precipitate. Morpholinos are insensitive to proteases or nucleases, so as long as the water you add is sterile, they should be quite safe at room temperature.</li>
 <li> Before injecting, incubate the morpholino at 65&deg;C for 5 minutes to assure it is completely dissolved, and allow to cool to room temperature. Do NOT place the sample on ice. Keep the morpholino at room temperature until injection.</li>
 <li> To titrate a morpholino, we typically prepare serial dilutions of the stock concentration in ddH20 to yield working concentrations of 1 mM, 0.5 mM, 0.25 mM, and 0.125mM. Depending on the sequence, using 1.8 nl of injection volume, this represents approximately 20ng, 10ng, 5ng, and 2.5ng of morpholino per injection. This is just a starting point, since the tolerance and efficacy of each morpholino will vary and cannot be predicted. Most morpholinos will not be tolerated much above 20 ng, but some can be effective at doses well below 1 ng. Our approach is to define the concentration at which a phenotype "plateaus". In other words, if a defined phenotype is not seen using 2.5 ng, but is similar using any amount at or above 5 ng, we would choose 5 ng as a threshold amount. Of course, it might be useful to next titrate between 2.5 ng and 5.0 ng, to ensure that you are working reproducibly beyond the threshold, rather than right "on the border".</li>
 <li> Fill the attached and calibrated needle (see above) with the lowest working concentration (most dilute) morpholino solution. Avoid over-filling the needle, as it will simply waste material. If you fill only 1 &mu;l, there is sufficient solution for 500 injections.</li>
 <li> Using a disposable pipette, transfer fertilized one-cell embryos into the troughs of the microinjection plate. Remove excess water to ensure that the embryos fall to the bottom of the injection troughs. They should not float, but rather adhere to the agarose bed.</li>
 <li> Position the injection plate so that the micromanipulator can descend the needle tip through the chorion and into the yolk for injection. To position individual embryos, manipulate the injection plate such that the tip of the injection needle pushes or pulls the embryos to the proper position. Be careful not to break the needle tip or damage embryos! This takes some practice, but as a rule you use the micromanipulator simply to move the injection needle into the embryo and then after the injection, rather quickly and cleanly out. Embryos are brought into injection position by moving the plate using your free hand (left hand if you inject with your right hand). For a new learner, it is useful to practice using a solution containing 0.25% phenol red in order to visualize the injected solution. Confidence is also gained by injecting a solution containing fluorescent-tagged microspheres (Molecular Probes; F-8794), to confirm that solution was injected into the embryo, rather than the inter-chorion space. However, after a few rounds of practice, these aids are typically no longer required. It is a good idea to occasionally inject into the air, just to confirm that the needle is not clogged and that the volume being injected appears appropriate.</li>
 <li> Injected embryos are transferred back to a 100mm Petri dish with system water and cultured at 28.5C. After injection of the lowest working concentration, any remaining solution can be expelled and the next highest working concentration of morpholino used to fill the needle. Repeat for each concentration of morpholino. Although it is possible to rinse out the needle using water, when testing a distinct morpholino, we prefer to change needles and recalibrate. Be sure to keep a cohort of uninjected embryos to verify whether the specific batch of embryos was healthy and normal.</li>
</ol>
Step 3. Co-injection of morpholinos at individual threshold doses
The goal of the titration carried out above was to define a threshold dose for each morpholino. In the best-case scenario, essentially 100% of the morphants will display a defined phenotype, if the targeted gene has an essential function. However, you can expect some variability due to mis-injection artifacts. With practice, this should not exceed 10%. Some batches of embryos (including the uninjected controls) may not survive well, in which case the experiment may need to be discounted. Meanwhile, there is also biological variability, since individual embryos may be more or less tolerant to the knockdown. Finally, some morpholinos may just not be efficient enough to achieve a robust (penetrant) knockdown. If a phenotype is generated in a low percentage of embryos, but is reproducible, it may be worth testing a distinct morpholino. The goal of this next experiment is to determine if an entirely new phenotype is seen when both genes are targeted simultaneously. We are not simply looking for an increase in the percentage of embryos that have a morphant phenotype, but rather for the generation of a distinct phenotype that is not seen at or above the threshold level when testing either of the individual genes.
<ol>
 <li> Prepare a mixture of the combination of morpholinos tested previously, at the threshold concentration of each individual morpholino that generated a defined phenotype. For example, if the threshold for each gene was 5 ng, prepare a working solution that will contain 5 ng + 5 ng of each (10 ng total). Since embryos may not tolerate much more than 20 ng total morpholino, it is important, based on the previous experiments, to use the minimal amount of each that is sufficient to efficiently target each gene.</li>
 <li> Controls should include sets of embryos injected with each individual morpholino alone at the same concentration that was used for the combination. Volumes of injection solution should be kept constant (e.g. 1.8 nl). A big advantage of using a reporter strain is that you can evaluate the phenotype (for example cardiomyocyte differentiation) at any time, and repeatedly. If embryos are to be evaluated for gene expression by in situ hybridization, stage-matched embryos and controls can be fixed at various times post-injection. For our experiment, we are going to evaluate GFP expression as a surrogate for cardiomyocyte differentiation, at approximately 24 hpf.</li>
</ol>
Step 4. Evaluation of phenotypes
<ol>
 <li> Injected embryos should be monitored, just after the injection, and several times during the day, to remove any dead or dying embryos, since these can compromise the viability of the remaining morphants. To evaluate expression of the reporter gene, embryos are examined using a dissecting microscope outfitted with fluorescence capacity. We use a Nikon SMZ1500 microscope, with a 1X or 1.6X objective and a range of magnification from 0.75x to 11.25x. When using a fluorescent filter, be sure to open the diaphragm to the fully open setting to maximize the light intensity. Also be sure to use the correct filter, depending on the reporter gene (GFP, RFP, etc.).</li>
 <li> Embryos are typically sedated using a 1/20 dilution in system water of 4mg/ml stock of tricaine methanesulfonate. The stocks are stored frozen at -20C. Alternatively, embryos can be euthanized using the 20x tricaine stock. Embryos can usually be screened even if they are still in the chorion. However, particularly if they will be photographed, it is a good idea to remove the chorions using sharp forceps. Embryos can be viewed after placing in depression slides in the tricaine solution, or to better immobilize them for photography placed into a small drop of 3% methylcellulose.</li>
 <li> Observe embryo phenotypes in those injected with the combination of morpholinos compared to single morphants. Here we are looking for the pattern of GFP expression in the primordial heart tube. In this reporter strain GFP is expressed exclusively in cardiomyocytes via the cmlc2 promoter, which allows detailed analysis of cardiac specification and heart tube morphogenesis.</li>
</ol>
Representative Results
In our experiment, both the gata5 and gata6 single morphants show reproducible cardiac phenotypes when injected with threshold levels, although there is considerable biological variability3,4. For example, most of the gata5 morphants generate a bifid heart, with GFP expression located in two regions. This occurs because the cardiac progenitors fail to migrate properly to fuse at the midline during heart tube formation. However, some of the gata5 morphants do generate a defective heart tube, and in a small number (5%) there is a significant decrease in the amount of GFP+ cells. We believe this reflects biological variability, but may also be due to the fact that morpholinos are not equivalent to a "null" mutation.
Likewise, the gata6 morphants all show a cardiac phenotype, but there is a range of phenotypes including a small number of bifid heats, and hearts that are morphological disturbed compared to the uninjected control embryos. This variability is not unusual for a cardiac morphogenetic phenotype, since heart formation is a dynamic process and at least some of the heart phenotype may be due indirectly from embryonic morphogenetic defects. However, importantly, the range of cardiac morphogenetic defects for both gata5 and gata6 morphants is consistent and reproducible, and for the most part the embryos generate substantial GFP+ cardiomyocytes.
In stark contrast to the gata5 and gata6 single morphants, embryos depleted of both factors show a complete loss of GFP expression, consistent with a loss of cardiomyocytes. Thus, gata5 and gata6 each have non-redundant functions for cardiac morphogenesis, but the two genes are functionally redundant in a requirement for generation of differentiated cardiomyocytes. Our previous studies showed also a loss of the earliest cardiomyocyte markers, including nkx2.5, suggesting a requirement for cardiomyocyte specification3.

<ol>
	<li>Heicklen-Klein, A., McReynolds, L. J., Evans, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+the+zebrafish+model+to+study+GATA+transcription+factors.">Using the zebrafish model to study GATA transcription factors.</a> Semin Cell Dev Biol. 16, 95-106 (2005).</li><li>Bill, B. R., Petzold, A. M., Clark, K. J., Schimmenti, L. A., Ekker, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+primer+for+morpholino+use+in+zebrafish.">A primer for morpholino use in zebrafish.</a> Zebrafish. 6, 69-77 (2009).</li><li>Holtzinger, A., Evans, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gata5+and+Gata6+are+functionally+redundant+in+zebrafish+for+specification+of+cardiomyocytes.">Gata5 and Gata6 are functionally redundant in zebrafish for specification of cardiomyocytes.</a> Dev Biol. 312, 613-622 (2007).</li><li>Peterkin, T., Gibson, A., Patient, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Redundancy+and+evolution+of+GATA+factor+requirements+in+development+of+the+myocardium.">Redundancy and evolution of GATA factor requirements in development of the myocardium.</a> Dev Biol. 311, 623-635 (2007).</li><li>Holtzinger, A., Evans, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gata4+regulates+the+formation+of+multiple+organs.">Gata4 regulates the formation of multiple organs.</a> Development. 132, 4005-4014 (2005).</li><li>Sorrentino, R. P., Gajewski, K. M., Schulz, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GATA+factors+in+Drosophila+heart+and+blood+cell+development.">GATA factors in Drosophila heart and blood cell development.</a> Semin Cell Dev Biol. 16, 107-116 (2005).</li></ol>

No conflicts of interest declared.

In the experiment described here, we combined two morpholinos, each of which alone generate a distinct range of phenotypes, and found an entirely different phenotype when they were co-injected together. Of course, we needed a justification for doing this experiment in the first place. We suspected that the two genes might compensate each other for an earlier function, in this case cardiac specification. This is because the genes are highly related (and capable of binding to the same DNA sequences) and are expressed in ov...

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		<th>Comment</th>
		</tr>
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		<tbody>
		
<tr>
<td>Fish breeder tanks and dividers</td>
<td>&nbsp;</td>
<td>Aquatic Habitats</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Fish nets</td>
<td>&nbsp;</td>
<td>Aquatic Habitats</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>System water</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>60mg &#x201C;Instant Ocean&#x201D; per liter dH2O</td>
</tr>
<tr>
<td>100mm Petri dishes</td>
<td>&nbsp;</td>
<td>BD Falcon</td>
<td>351029</td>
<td>&nbsp;</td>
<tr>
<td>Micropipette needle puller</td>
<td>&nbsp;</td>
<td>Sutter instruments, Co.</td>
<td>P-97 Flaming/Brown</td>
<td>&nbsp;</td>
<tr>
<td>3.5" glass capillaries</td>
<td>&nbsp;</td>
<td>Drummond</td>
<td>3-000-203-G/X</td>
<td>&nbsp;</td>
<tr>
<td>Razor blade</td>
<td>&nbsp;</td>
<td>Personna</td>
<td>94-120-71</td>
<td>&nbsp;</td>
<tr>
<td>Micro grinder</td>
<td>&nbsp;</td>
<td>Narishige, Japan</td>
<td>EG-4</td>
<td>&nbsp;</td>
<tr>
<td>Gridded microscope eyepiece</td>
<td>&nbsp;</td>
<td>Premiere</td>
<td>MF-02</td>
<td>&nbsp;</td>
<tr>
<td>Micrometer</td>
<td>&nbsp;</td>
<td>Ward&#x2019;s Natural Science</td>
<td>94 W 9910</td>
<td>&nbsp;</td>
<tr>
<td>Ultrapure agarose</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>15510-027</td>
<td>&nbsp;</td>
<tr>
<td>Spatula</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>14-357Q</td>
<td>&nbsp;</td>
<tr>
<td>Scale</td>
<td>&nbsp;</td>
<td>Mettler Toledo</td>
<td>AB54-S/FACT</td>
<td>&nbsp;</td>
<tr>
<td>Disposable weigh dishes</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>2-202-B</td>
<td>&nbsp;</td>
<tr>
<td>Conventional microwave</td>
<td>&nbsp;</td>
<td>General Electric</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Erlenmeyer flask</td>
<td>&nbsp;</td>
<td>Corning</td>
<td>4980</td>
<td>&nbsp;</td>
<tr>
<td>Microscope slides</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>12-552</td>
<td>&nbsp;</td>
<tr>
<td>Graduated cylinder</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>08-572-6D</td>
<td>&nbsp;</td>
<tr>
<td>Automatic pipette man</td>
<td>&nbsp;</td>
<td>BrandTech</td>
<td>2026333</td>
<td>&nbsp;</td>
<tr>
<td>70% ethanol wash solution</td>
<td>&nbsp;</td>
<td>Tarr</td>
<td>801VWR</td>
<td>&nbsp;</td>
<tr>
<td>N2 tank</td>
<td>&nbsp;</td>
<td>Tech Air</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Microinjector</td>
<td>&nbsp;</td>
<td>Harvard apparatus</td>
<td>PLI-100</td>
<td>&nbsp;</td>
<tr>
<td>Micromanipulator</td>
<td>&nbsp;</td>
<td>Micro Instruments</td>
<td> LTD</td>
<td>&nbsp;</td>
<tr>
<td>Dissecting microscope</td>
<td>&nbsp;</td>
<td>Nikon</td>
<td>SMZ1500</td>
<td>&nbsp;</td>
<tr>
<td>Parafilm</td>
<td>&nbsp;</td>
<td>American National Can</td>
<td>PM-992</td>
<td>&nbsp;</td>
<tr>
<td>Mineral oil</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>M5904</td>
<td>&nbsp;</td>
<tr>
<td>Kimwipes</td>
<td>&nbsp;</td>
<td>Kimberly-Clark</td>
<td>34155</td>
<td>&nbsp;</td>
<tr>
<td>gata5 splice site morpholino</td>
<td>&nbsp;</td>
<td>Genetools, LLC</td>
<td>&nbsp;</td>
<td>5'-TCTTAAGATTTTTACCTATACTGGA-3'</td>
</tr>
<tr>
<td>gata5 ATG Blocker</td>
<td>&nbsp;</td>
<td>Genetools, LLC</td>
<td>&nbsp;</td>
<td>5'-AAGATAAAGCCAGGCTCGAATACAT-3'</td>
</tr>
<tr>
<td>gata6 Long Isoform ATG Blocker</td>
<td>&nbsp;</td>
<td>Genetools, LLC</td>
<td>&nbsp;</td>
<td>5'-AGCTGTTATCACCCAGGTCCATCCA-3'</td>
</tr>
<tr>
<td>Disposable Pasteur Pipette</td>
<td>&nbsp;</td>
<td>Fisher Scientific</td>
<td>13-678-20B</td>
<td>&nbsp;</td>
<tr>
<td>Tricaine Methanesulfonate</td>
<td>&nbsp;</td>
<td>Argent Chemical Laboratories</td>
<td>MS-222</td>
<td>&nbsp;</td>
<tr>
<td>Methycellulose</td>
<td>&nbsp;</td>
<td>ICN Biomedicals</td>
<td>155495</td>
<td>&nbsp;</td>
<tr>
<td>Heat Block</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>11-718-4</td>
<td>&nbsp;</td>
<tr>
<td>Sharp forceps</td>
<td>&nbsp;</td>
<td>Dumont</td>
<td>&nbsp;</td>
<td>Size 55</td>
</tr>
<tr>
<td>Depression Microslides</td>
<td>&nbsp;</td>
<td>VWR</td>
<td>48339-009</td>
<td>&nbsp;</td>		</tbody>
		</table>
		</div>

a reverse genetic approach to test functional redundancy during embryogenesis

Gene function during embryogenesis is typically defined by loss-of-function experiments, for example by targeted mutagenesis (knockout) in the mouse. In the zebrafish model, effective reverse genetic techniques have been developed using microinjection of gene-specific antisense morpholinos. Morpholinos target an mRNA through specific base-pairing and block gene function transiently by inhibiting translation or splicing for several days during embryogenesis (knockdown). However, in vertebrates such as mouse or zebrafish, some gene functions can be obscured by these approaches due to the presence of another gene that compensates for the loss. This is especially true for gene families containing sister genes that are co-expressed in the same developing tissues. In zebrafish, functional compensation can be tested in a relatively high-throughput manner, by co-injection of morpholinos that target knockdown of both genes simultaneously. Likewise, using morpholinos, a genetic interaction between any two genes can be demonstrated by knockdown of both genes together at sub-threshold levels. For example, morpholinos can be titrated such that neither individual knockdown generates a phenotype. If, under these conditions, co-injection of both morpholinos causes a phenotype, a genetic interaction is shown. Here we demonstrate how to show functional redundancy in the context of two related GATA transcription factors. GATA factors are essential for specification of cardiac progenitors, but this is revealed only by the loss of both Gata5 and Gata6. We show how to carry out microinjection experiments, validate the morpholinos, and evaluate the compensated phenotype for cardiogenesis.

Watch this Scientific Journal Video about A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis at JoVE.com

A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis

Gene function can be obscured in loss-of-function experiments if there is compensation by another gene. The zebrafish model provides a relatively high-throughput means to reveal such functional redundancy in living embryos.

Gene function during embryogenesis is typically defined by loss-of-function experiments, for example by targeted mutagenesis (knockout) in the mouse. In ...

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11.9K Views.  Weill Cornell Medical College of Cornell University. Gene function can be obscured in loss-of-function experiments if there is compensation by another gene. The zebrafish model provides a relatively high-throughput means to reveal such functional redundancy in living embryos.

Video: A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis

Light/dark Transition Test for Mice

Although all of the mouse genome sequences have been determined, we do not yet know the functions of most of these genes. Gene-targeting techniques, however, can be used to delete or manipulate a specific gene in mice. The influence of a given gene on a specific behavior can then be determined by conducting behavioral analyses of the mutant mice. As a test for behavioral phenotyping of mutant mice, the light/dark transition test is one of the most widely used tests to measure anxiety-like behavior in mice. The test is based on the natural aversion of mice to brightly illuminated areas and on their spontaneous exploratory behavior in novel environments. The test is sensitive to anxiolytic drug treatment. The apparatus consists of a dark chamber and a brightly illuminated chamber. Mice are allowed to move freely between the two chambers. The number of entries into the bright chamber and the duration of time spent there are indices of bright-space anxiety in mice. To obtain phenotyping results of a strain of mutant mice that can be readily reproduced and compared with those of other mutants, the behavioral test methods should be as identical as possible between laboratories. The procedural differences that exist between laboratories, however, make it difficult to replicate or compare the results among laboratories. Here, we present our protocol for the light/dark transition test as a movie so that the details of the protocol can be demonstrated. In our laboratory, we have assessed more than 60 strains of mutant mice using the protocol shown in the movie. Those data will be disclosed as a part of a public database that we are now constructing.

Visualization of the protocol will facilitate understanding of the details of the entire experimental procedure, allowing for standardization of the protocols used across laboratories and comparisons of the behavioral phenotypes of various strains of mutant mice assessed using this test.

The light/dark transition test is one of the most widely used tests to measure anxiety-like behavior in mice. Here, we present a movie that shows detailed procedures on how we conduct the test.

Although all of the mouse genome sequences have been determined, we do not yet know the functions of most of these genes. Gene-targeting techniques, ...

Method for Culture of Early Chick Embryos ex vivo (New Culture)

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying  the formation and patterning of brain, neural tube, somite and heart primordia. Applications of chick embryo culture include electroporation of DNA or RNA constructs in order to analyze gene function, grafts of growth factor coated beads such as FGFs and BMPs , as well as whole mount in situ hybridization and immunohistochemistry. This video demonstrates the different steps in chick embryo culture; First, the embryo is explanted in saline. Then, the embryo is centered on a glass ring. The membranes surrounding the embryo are lifted along the walls of the ring. The ring is then placed in a culture dish containing a pool of albumine. The culture dish is sealed and placed in a humid chamber, where the embryo is cultured for up to 24 hrs. Finally, the embryo is removed from the ring, fixed and processed for further applications. A troubleshooting guide is also presented.

Method for Culture of Early Chick Embryos ex vivo New Culture

This video demonstrates New culture, a method by which chick embryos are cultured outside the egg for up to 24 hr. This method enables one to study early development (primitive streak to 14 som.), a period corresponding to E7-9 in mouse. Applications of this technique include electroporation, in situ hybridization and immunohistochemistry.

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ...

Double Whole Mount in situ Hybridization of Early Chick Embryos

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying  gene expression in brain, neural tube, somite and heart primordia formation. This video demonstrates the different steps in 2-color whole mount in situ hybridization; First, the embryo is dissected from the egg and fixed in paraformaldehyde. Second, the embryo is processed for prehybridization. The embryo is then hybridized with two different probes, one coupled to DIG, and one coupled to FITC.  Following overnight hybridization, the embryo is incubated with DIG coupled antibody. Color reaction for DIG substrate is performed, and the region of interest appears blue. The embryo is then incubated with FITC coupled antibody. The embryo is processed for color reaction with FITC, and the region of interest appears red. Finally, the embryo is fixed and processed for phtograph and sectioning. A troubleshooting guide is also presented.

This video demonstrates 2-color whole mount in situ hybridization, a method by which the spatial and temporal expression pattern of 2 different genes can be visualized in young chick embryos. This method was originally introduced by David Wilkinson, Domingos Henrique, Phil Ingham and David Ish -Horowicz.

Assay for Neural Induction in the Chick Embryo

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying the formation and initial patterning of the nervous system. This video demonstrates how to graft organizer tissue into a host, a method by which Hensen s node (the organizer in the chick embryo) is grafted to a host competent ectoderm. The organizer graft instructs overlying na ve tissue to adopt a neural fate via neural inducing signals. This mechanism is referred to as neural induction, and constitutes the initial step in the formation of brain and spinal cord in amniotes. This method is essentially used for the characterization of putative neural inducing molecules in chick. This video demonstrates the different steps in the assay for neural induction; First, the donnor embryo is explanted and pinned on a dish. Then, the host embryo is prepared for New culture. The graft is excised and transplanted to the host area pellucida margin. The host is cultured for 18-22 hrs. The assembly is fixed and processed for further applications (e.g. in situ hybridization). This method was originally devised by Waddington 1,2 and Gallera 3,4.

Neural induction is the first step in the formation of the brain. It is a mechanism by which Hensen's node (organizer), instructs adjacent tissue to adopt a neural fate, i.e. to give rise to the nervous system. This video demonstrates an assay for neural induction in chick embryo.

Elevated Plus Maze for Mice

Although the mouse genome is now completely sequenced, the functions of most of the genes expressed in the brain are not known. The influence of a given gene on a specific behavior can be determined by behavioral analysis of mutant mice. If a target gene is expressed in the brain, behavioral phenotype of the mutant mice could elucidate the genetic mechanism of normal behaviors. The elevated plus maze test is one of the most widely used tests for measuring anxiety-like behavior. The test is based on the natural aversion of mice for open and elevated areas, as well as on their natural spontaneous exploratory behavior in novel environments. The apparatus consists of open arms and closed arms, crossed in the middle perpendicularly to each other, and a center area. Mice are given access to all of the arms and are allowed to move freely between them. The number of entries into the open arms and the time spent in the open arms are used as indices of open space-induced anxiety in mice. Unfortunately, the procedural differences that exist between laboratories make it difficult to duplicate and compare results among laboratories. Here, we present a detailed movie demonstrating our protocol for the elevated plus maze test. In our laboratory, we have assessed more than 90 strains of mutant mice using the protocol shown in the movie. These data will be disclosed as a part of a public database that we are now constructing.
Visualization of the protocol will promote better understanding of the details of the entire experimental procedure, allowing for standardization of the protocols used in different laboratories and comparisons of the behavioral phenotypes of various strains of mutant mice assessed using this test. 


The elevated plus maze test is one of the most widely used tests for measuring anxiety-like behavior in mice. Here, we present a movie showing the detailed procedures for conducting the test.

Although the mouse genome is now completely sequenced, the functions of most of the genes expressed in the brain are not known. The influence of a given ...

Dissection of Hippocampal Dentate Gyrus from Adult Mouse

The hippocampus is one of the most widely studied areas in the brain because of its important functional role in memory processing and learning, its remarkable neuronal cell plasticity, and its involvement in epilepsy, neurodegenerative diseases, and psychiatric disorders. The hippocampus is composed of distinct regions; the dentate gyrus, which comprises mainly granule neurons, and Ammon's horn, which comprises mainly pyramidal neurons, and the two regions are connected by both anatomic and functional circuits. Many different mRNAs and proteins are selectively expressed in the dentate gyrus, and the dentate gyrus is a site of adult neurogenesis; that is, new neurons are continually generated in the adult dentate gyrus. To investigate mRNA and protein expression specific to the dentate gyrus, laser capture microdissection is often used. This method has some limitations, however, such as the need for special apparatuses and complicated handling procedures. In this video-recorded protocol, we demonstrate a dissection technique for removing the dentate gyrus from adult mouse under a stereomicroscope. Dentate gyrus samples prepared using this technique are suitable for any assay, including transcriptomic, proteomic, and cell biology analyses. We confirmed that the dissected tissue is dentate gyrus by conducting real-time PCR of dentate gyrus-specific genes, tryptophan 2,3-dioxygenase (TDO2) and desmoplakin (Dsp), and Ammon's horn enriched genes, Meis-related gene 1b (Mrg1b) and TYRO3 protein tyrosine kinase 3 (Tyro3). The mRNA expressions of TDO2 and Dsp in the dentate gyrus samples were detected at obviously higher levels, whereas Mrg1b and Tyro3 were lower levels, than those in the Ammon's horn samples. To demonstrate the advantage of this method, we performed DNA microarray analysis using samples of whole hippocampus and dentate gyrus. The mRNA expression of TDO2 and Dsp, which are expressed selectively in the dentate gyrus, in the whole hippocampus of alpha-CaMKII+/- mice, exhibited 0.037 and 0.10-fold changes compared to that of wild-type mice, respectively. In the isolated dentate gyrus, however, these expressions exhibited 0.011 and 0.021-fold changes compared to that of wild-type mice, demonstrating that gene expression changes in dentate gyrus can be detected with greater sensitivity. Taken together, this convenient and accurate dissection technique can be reliably used for studies focused on the dentate gyrus.

A dissection technique for removal of the dentate gyrus from adult mouse under a stereomicroscope was demonstrated in this video-recorded protocol.

The hippocampus is one of the most widely studied areas in the brain because of its important functional role in memory processing and learning, its ...

A Practical Approach to Genetic Inducible Fate Mapping: A Visual Guide to Mark and Track Cells In Vivo

Fate maps are generated by marking and tracking cells in vivo to determine how progenitors contribute to specific structures and cell types in developing and adult tissue. An advance in this concept is Genetic Inducible Fate Mapping (GIFM), linking gene expression, cell fate, and cell behaviors in vivo, to create fate maps based on genetic lineage.
GIFM exploits X-CreER lines where X is a gene or set of gene regulatory elements that confers spatial expression of a modified bacteriophage protein, Cre recombinase (CreERT). CreERT contains a modified estrogen receptor ligand binding domain which renders CreERT sequestered in the cytoplasm in the absence of the drug tamoxifen. The binding of tamoxifen releases CreERT, which translocates to the nucleus and mediates recombination between DNA sequences flanked by loxP sites. In GIFM, recombination typically occurs between a loxP flanked Stop cassette preceding a reporter gene such as GFP.
Mice are bred to contain either a region- or cell type-specific CreER and a conditional reporter allele. Untreated mice will not have marking because the Stop cassette in the reporter prevents further transcription of the reporter gene. We administer tamoxifen by oral gavage to timed-pregnant females, which provides temporal control of CreERT release and subsequent translocation to the nucleus removing the Stop cassette from the reporter. Following recombination, the reporter allele is constitutively and heritably expressed. This series of events marks cells such that their genetic history is indelibly recorded. The recombined reporter thus serves as a high fidelity genetic lineage tracer that, once on, is uncoupled from the gene expression initially used to drive CreERT.
We apply GIFM in mouse to study normal development and ascertain the contribution of genetic lineages to adult cell types and tissues. We also use GIFM to follow cells on mutant genetic backgrounds to better understand complex phenotypes that mimic salient features of human genetic disorders.
This video article guides researchers through experimental methods to successfully apply GIFM. We demonstrate the method using our well characterized Wnt1-CreERT;mGFP mice by administering tamoxifen at embryonic day (E)8.5 via oral gavage followed by dissection at E12.5 and analysis by epifluorescence stereomicroscopy. We also demonstrate how to micro-dissect fate mapped domains for explant preparation or FACS analysis and dissect adult fate-mapped brains for whole mount fluorescent imaging. Collectively, these procedures allow researchers to address critical questions in developmental biology and disease models.

A Practical Approach to Genetic Inducible Fate Mapping: A Visual Guide to Mark and Track Cells In Vivo

Genetic Inducible Fate Mapping (GIFM) marks and tracks cells with fine spatial and temporal control in vivo and elucidates how cells from a specific genetic lineage contribute to developing and adult tissues. Demonstrated here are the techniques required to fate map E12.5 mouse embryos for epifluorescent and explant analysis.

Fate maps are generated by marking and tracking cells in vivo to determine how progenitors contribute to specific structures and cell types in developing ...

An Allele-specific Gene Expression Assay to Test the Functional Basis of Genetic Associations

The number of significant genetic associations with common complex traits is constantly increasing. However, most of these associations have not been understood at molecular level. One of the mechanisms mediating the effect of DNA variants on phenotypes is gene expression, which has been shown to be particularly relevant for complex traits1.
This method tests in a cellular context the effect of specific DNA sequences on gene expression. The principle is to measure the relative abundance of transcripts arising from the two alleles of a gene, analysing cells which carry one copy of the DNA sequences associated with disease (the risk variants)2,3. Therefore, the cells used for this method should meet two fundamental genotypic requirements: they have to be heterozygous both for DNA risk variants and for DNA markers, typically coding polymorphisms, which can distinguish transcripts based on their chromosomal origin (Figure 1). DNA risk variants and DNA markers do not need to have the same allele frequency but the phase (haplotypic) relationship of the genetic markers needs to be understood. It is also important to choose cell types which express the gene of interest. This protocol refers specifically to the procedure adopted to extract nucleic acids from fibroblasts but the method is equally applicable to other cells types including primary cells.
DNA and RNA are extracted from the selected cell lines and cDNA is generated. DNA and cDNA are analysed with a primer extension assay, designed to target the coding DNA markers4. The primer extension assay is carried out using the MassARRAY (Sequenom)5 platform according to the manufacturer's specifications. Primer extension products are then analysed by matrix-assisted laser desorption/ionization time of-flight mass spectrometry (MALDI-TOF/MS). Because the selected markers are heterozygous they will generate two peaks on the MS profiles. The area of each peak is proportional to the transcript abundance and can be measured with a function of the MassARRAY Typer software to generate an allelic ratio (allele 1: allele 2) calculation. The allelic ratio obtained for cDNA is normalized using that measured from genomic DNA, where the allelic ratio is expected to be 1:1 to correct for technical artifacts. Markers with a normalised allelic ratio significantly different to 1 indicate that the amount of transcript generated from the two chromosomes in the same cell is different, suggesting that the DNA variants associated with the phenotype have an effect on gene expression. Experimental controls should be used to confirm the results.

Genetic associations often remain unexplained at a functional level. This method aims to assess the effect of phenotype-associated genetic markers on gene expression by analyzing cells heterozygous for transcribed SNPs. The technology allows accurate measurement by MALDI-TOF mass spectrometry to quantify allele-specific primer extension products.

The number of significant genetic associations with common complex traits is constantly increasing. However, most of these associations have not been ...

Pharmacological and Functional Genetic Assays to Manipulate Regeneration of the Planarian Dugesia japonica

Free-living planarian flatworms have a long history of experimental usage owing to their remarkable regenerative abilities1. Small fragments excised from these animals reform the original body plan following regeneration of missing body structures. For example if a 'trunk' fragment is cut from an intact worm, a new 'head' will regenerate anteriorly and a 'tail' will regenerate posteriorly restoring the original 'head-to-tail' polarity of body structures prior to amputation (Figure 1A).
Regeneration is driven by planarian stem cells, known as 'neoblasts' which differentiate into ~30 different cell types during normal body homeostasis and enforced tissue regeneration. This regenerative process is robust and easy to demonstrate. Owing to the dedication of several pioneering labs, many tools and functional genetic methods have now been optimized for this model system. Consequently, considerable recent progress has been made in understanding and manipulating the molecular events underpinning planarian developmental plasticity2-9.
The planarian model system will be of interest to a broad range of scientists. For neuroscientists, the model affords the opportunity to study the regeneration of an entire nervous system, rather than simply the regrowth/repair of single nerve cell process that typically are the focus of study in many established models. Planarians express a plethora of neurotransmitters10, represent an important system for studying evolution of the central nervous system11, 12 and have behavioral screening potential13, 14. 
Regenerative outcomes are amenable to manipulation by pharmacological and genetic apparoaches. For example, drugs can be screened for effects on regeneration simply by placing body fragments in drug-containing solutions at different time points after amputation. The role of individual genes can be studied using knockdown methods (in vivo RNAi), which can be achieved either through cycles of microinjection or by feeding bacterially-expressed dsRNA constructs8, 9, 15. Both approaches can produce visually striking phenotypes at high penetrance- for example, regeneration of bipolar animals16-21. To facilitate adoption of this model and implementation of such methods, we showcase in this video article protocols for pharmacological and genetic assays (in vivo RNAi by feeding) using the planarian Dugesia japonica.

Pharmacological and Functional Genetic Assays to Manipulate Regeneration of the Planarian Dugesia japonica

An attractive model for studying stem cell differentiation within a live animal is the planarian flatworm. Regeneration is studied by simple amputation experiments that are easily performed in a basic laboratory and are amenable to pharmacological and genetic (in vivo RNAi) manipulation as detailed by protocols in this article.

Free-living planarian flatworms have a long history of experimental usage owing to their remarkable regenerative abilities1. Small fragments excised from ...

Mapping Bacterial Functional Networks and Pathways in Escherichia Coli using Synthetic Genetic Arrays

Phenotypes are determined by a complex series of physical (e.g. protein-protein) and functional (e.g. gene-gene or genetic) interactions (GI)1. While physical interactions can indicate which bacterial proteins are associated as complexes, they do not necessarily reveal pathway-level functional relationships1. GI screens, in which the growth of double mutants bearing two deleted or inactivated genes is measured and compared to the corresponding single mutants, can illuminate epistatic dependencies between loci and hence provide a means to query and discover novel functional relationships2. Large-scale GI maps have been reported for eukaryotic organisms like yeast3-7, but GI information remains sparse for prokaryotes8, which hinders the functional annotation of bacterial genomes. To this end, we and others have developed high-throughput quantitative bacterial GI screening methods9, 10.
Here, we present the key steps required to perform quantitative E. coli Synthetic Genetic Array (eSGA) screening procedure on a genome-scale9, using natural bacterial conjugation and homologous recombination to systemically generate and measure the fitness of large numbers of double mutants in a colony array format. Briefly, a robot is used to transfer, through conjugation, chloramphenicol (Cm) - marked mutant alleles from engineered Hfr (High frequency of recombination) 'donor strains' into an ordered array of kanamycin (Kan) - marked F- recipient strains. Typically, we use loss-of-function single mutants bearing non-essential gene deletions (e.g. the 'Keio' collection11) and essential gene hypomorphic mutations (i.e. alleles conferring reduced protein expression, stability, or activity9, 12, 13) to query the functional associations of non-essential and essential genes, respectively. After conjugation and ensuing genetic exchange mediated by homologous recombination, the resulting double mutants are selected on solid medium containing both antibiotics. After outgrowth, the plates are digitally imaged and colony sizes are quantitatively scored using an in-house automated image processing system14. GIs are revealed when the growth rate of a double mutant is either significantly better or worse than expected9. Aggravating (or negative) GIs often result between loss-of-function mutations in pairs of genes from compensatory pathways that impinge on the same essential process2. Here, the loss of a single gene is buffered, such that either single mutant is viable. However, the loss of both pathways is deleterious and results in synthetic lethality or sickness (i.e. slow growth). Conversely, alleviating (or positive) interactions can occur between genes in the same pathway or protein complex2 as the deletion of either gene alone is often sufficient to perturb the normal function of the pathway or complex such that additional perturbations do not reduce activity, and hence growth, further. Overall, systematically identifying and analyzing GI networks can provide unbiased, global maps of the functional relationships between large numbers of genes, from which pathway-level information missed by other approaches can be inferred9.

Mapping Bacterial Functional Networks and Pathways in Escherichia Coli using Synthetic Genetic Arrays

Systematic, large-scale synthetic genetic (gene-gene or epistasis) interaction screens can be used to explore genetic redundancy and pathway cross-talk. Here, we describe a high-throughput quantitative synthetic genetic array screening technology, termed eSGA that we developed for elucidating epistatic relationships and exploring genetic interaction networks in Escherichia coli.

Phenotypes  are determined by a complex series of physical (e.g. protein-protein) and  functional (e.g. gene-gene or genetic) interactions (GI)1. While ...