We thank Prof. Elly M. Tanaka for her continuous and long-term support. This work was supported by a National Natural Science Foundation of China (NSFC) Grant (317716), Research Starting Grants from South China Normal University (S82111 and 8S0109), and a China Postdoctoral Science Foundation Grant (2018M633067).

All animal experiments must be carried out in accordance with local and national regulations on animal experimentation and with approval of the relevant institutional review board.
1. Preparing the CAS9-gRNA RNP mix
<ol>
	<li>Design and synthesize gRNAs. 
	NOTE: Refer to other publications for designing and synthesizing gRNAs, including one exclusively concerning axolotls15,20,21,<su...

<ol>
	<li>O'Hara, C. M., Egar, M. W., Chernoff, E. A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reorganization+of+the+ependyma+during+axolotl+spinal+cord+regeneration:+Changes+in+intermediate+filament+and+fibronectin+expression.">Reorganization of the ependyma during axolotl spinal cord regeneration: Changes in intermediate filament and fibronectin expression.</a> Developmental Dynamics. 193 (2), 103-115 (1992).</li><li>Mchedlishvili, L., Mazurov, V., Tanaka, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstitution+of+the+Central+Nervous+System+During+Salamander+Tail+Regeneration+from+the+Implanted+Neurospheres.">Reconstitution of the Central Nervous System During Salamander Tail Regeneration from the Implanted Neurospheres.</a> Plant, Soil and Environment. 916 (8), 197-202 (2012).</li><li>Nordlander, R. H., Singer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+ependyma+in+regeneration+of+the+spinal+cord+in+the+urodele+amphibian+tail.">The role of ependyma in regeneration of the spinal cord in the urodele amphibian tail.</a> Journal of Comparative Neurology. 180 (2), 349-373 (1978).</li><li>Fei, J. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue-+and+time-directed+electroporation+of+CAS9+protein&#8211;gRNA+complexes+in+vivo+yields+efficient+multigene+knock-out+for+studying+gene+function+in+regeneration.">Tissue- and time-directed electroporation of CAS9 protein&#8211;gRNA complexes in vivo yields efficient multigene knock-out for studying gene function in regeneration.</a> npj Regenerative Medicine. 1 (1), 16002 (2016).</li><li>Fei, J. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CRISPR-mediated+genomic+deletion+of+Sox2+in+the+axolotl+shows+a+requirement+in+spinal+cord+neural+stem+cell+amplification+during+tail+regeneration.">CRISPR-mediated genomic deletion of Sox2 in the axolotl shows a requirement in spinal cord neural stem cell amplification during tail regeneration.</a> Stem Cell Reports. 3 (3), 444-459 (2014).</li><li>Flowers, G. P., Timberlake, A. T., McLean, K. C., Monaghan, J. R., Crews, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+efficient+targeted+mutagenesis+in+axolotl+using+Cas9+RNA-guided+nuclease.">Highly efficient targeted mutagenesis in axolotl using Cas9 RNA-guided nuclease.</a> Development. 141 (10), 2165-2171 (2014).</li><li>Flowers, G. P., Sanor, L. D., Crews, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lineage+tracing+of+genome-edited+alleles+reveals+high+fidelity+axolotl+limb+regeneration.">Lineage tracing of genome-edited alleles reveals high fidelity axolotl limb regeneration.</a> eLife. 6, (2017).</li><li>Fei, J. -. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+gene+knockin+in+axolotl+and+its+use+to+test+the+role+of+satellite+cells+in+limb+regeneration.">Efficient gene knockin in axolotl and its use to test the role of satellite cells in limb regeneration.</a> Proceedings of the National Academy of Sciences. 201706855. , (2017).</li><li>Nowoshilow, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+axolotl+genome+and+the+evolution+of+key+tissue+formation+regulators.">The axolotl genome and the evolution of key tissue formation regulators.</a> Nature. 554 (7690), 50-55 (2018).</li><li>Bryant, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Tissue-Mapped+Axolotl+De+Novo+Transcriptome+Enables+Identification+of+Limb+Regeneration+Factors.">A Tissue-Mapped Axolotl De Novo Transcriptome Enables Identification of Limb Regeneration Factors.</a> Cell Reports. 18 (3), 762-776 (2017).</li><li>Smith, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+chromosome-scale+assembly+of+the+axolotl+genome.">A chromosome-scale assembly of the axolotl genome.</a> Genome Research. 373548, (2019).</li><li>Smith, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sal-Site:+Integrating+new+and+existing+ambystomatid+salamander+research+and+informational+resources.">Sal-Site: Integrating new and existing ambystomatid salamander research and informational resources.</a> BMC Genomics. 6, 1-6 (2005).</li><li>Campbell, L. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=et+al+Gene+expression+profile+of+the+regeneration+epithelium+during+axolotl+limb+regeneration.">et al Gene expression profile of the regeneration epithelium during axolotl limb regeneration.</a> Developmental Dynamics. 240 (7), 1826-1840 (2011).</li><li>Stewart, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+RNA-seq+Analysis+in+the+Unsequenced+Axolotl:+The+Oncogene+Burst+Highlights+Early+Gene+Expression+in.">Comparative RNA-seq Analysis in the Unsequenced Axolotl: The Oncogene Burst Highlights Early Gene Expression in.</a> the Blastema. PLoS Computational Biology. 9 (3), (2013).</li><li>Fei, J. -. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+and+optimization+of+CRISPR&#8211;Cas9-mediated+genome+engineering+in+axolotl+(Ambystoma+mexicanum).">Application and optimization of CRISPR&#8211;Cas9-mediated genome engineering in axolotl (Ambystoma mexicanum).</a> Nature Protocols. 13 (12), 2908-2943 (2018).</li><li>Holder, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+growth+of+the+motor+system+in+the+axolotl.">Continuous growth of the motor system in the axolotl.</a> Journal of Comparative Neurology. 303 (4), 534-550 (1991).</li><li>Tazaki, A., Tanaka, E. M., Fei, J. 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The authors declare no conflicts of interest.

The described protocol allows time and space restricted gene knock-out in the NSCs in the axolotl spinal cord. The current protocol allows specific targeting of NSCs at a defined time and location with high penetrance. It avoids potential undesired effects originating from gene knock-out in NSCs in other regions such as the brain that occur when using the Cre-LoxP system. It also avoids developmental effects originating from a persistent knock-out, allowing the study of gene function focused on regeneration. In addition,...

The spinal cord of most vertebrates is unable to regenerate following injury, leading to permanent disability. Several salamanders, such as the axolotl, are notable exceptions. The axolotl can fully regenerate a structurally identical spinal cord and completely restore spinal cord function. Much of the regenerative capability of the axolotl spinal cord is due to ependymal cells. These cells line the central canal, and unlike those in mammals, axolotl ependymal cells remain as neural stem cells (NSCs) post-embryonic development. After spinal cord injury (e.g., from a tail amputation), these NSCs proliferate to regrow the ependymal tube and differentiate to replace lost neurons1,2,3. Uncovering how axolotl spinal cord NSCs remain pluripotent and become activated after injury can provide valuable information on developing new therapeutic strategies for human patients.
Due to advances in the CRISPR-Cas9 gene knock-out technique, performing knock-outs to decipher gene function has become easier and has been shown to have broad applicability in various species, including axolotls4,5,6,7,8. The recent release of the full axolotl genome and transcriptome now allows any genomic locus to be targeted and for better assess to off-target effects9,10,11,12,13,14. Optimized protocols have been developed for knock-out and knock-in in axolotls using the CRISPR-Cas9 system15. Delivery of the CRISPR-Cas9 machinery in the form of CAS9 protein-gRNA ribonucleoprotein (RNP) has been shown to be more efficient than using Cas9 and gRNA-encoding plasmids4. This is likely due to the RNP being smaller in size than plasmid vectors, its ability to create DNA breaks immediately, and protecting of the gRNA from RNA degradation. In addition, using RNPs bypasses transcription and translation; thus, it avoids issues such as promoter strength and optimal codon usage when plasmid elements are derived from a different species.
Loss-of-function studies are one of the general approaches to investigating potential functions of genes of interest. In order to study gene function during regeneration, a knock-out should ideally be performed just before an injury to avoid effects on development. In addition, the knock-out should be restricted to both the NSCs and region of regeneration. A knock-out of the target gene in all NSCs (including those in the brain, which is the case in Cre-LoxP systems), may produce effects not related to regeneration that can confound the interpretation of results. Fortunately, the structure of the axolotl spinal cord provides a unique opportunity for time- and space-restricted knock-out in NSCs. Most of the spinal cord NSCs are in contact with the central canal and constitute the vast majority of the cells in contact with the central canal16,17. Therefore, an injection of the CAS9-gRNA complex into the central canal, followed by electroporation, allows delivery to spinal cord NSCs in a desired region at a specific time4,18,19. This protocol demonstrates how this is performed, leading to highly penetrating knock-out in the targeted spinal cord NSCs. Subsequent analysis are then performed to study the effects on regeneration and NSC behavior.

<table border="0" cellpadding="0" cellspacing="0" style="width:1355px;" width="1354">
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	<tbody>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Agarose</td>
			<td style="width:455px;">Sigma-Aldrich</td>
			<td style="width:241px;">A9539</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">&#65279;Benzocaine</td>
			<td style="width:455px;">Sigma-Aldrich</td>
			<td style="width:241px;">E1501-100G</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="140">
			<td height="140" style="height:140px;width:492px;">&#65279;Benzocaine 0.03 % (wt/vol)</td>
			<td style="width:455px;">Mix 500 ml of 10&#215; TBS, 500 ml of 400% (wt/vol) Holtfreter&#8217;s solution and 30 ml of 10% (wt/vol) benzocaine stock solution. Fill up the volume to 10 L with dH2O. &#65279;The solution can be stored at room temperature for up to 6 months.</td>
			<td style="width:241px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:492px;">&#65279;Benzocaine 10 % (wt/vol)</td>
			<td style="width:455px;">Mix 50 g of benzocaine in 500 ml of 100% (vol/vol) ethanol. The solution can be stored at room temperature for up to 12 months.</td>
			<td style="width:241px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Borosilicate glass capillaries &#65279;1.2 mm O.D., 0.94 mm I.D.</td>
			<td style="width:455px;">Stutter Instrument&#160;</td>
			<td style="width:241px;">BF120-94-8</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;width:492px;">CaCl2&#183;2H2O</td>
			<td style="width:455px;">Merck</td>
			<td style="width:241px;">&#65279;102382</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:492px;">CAS9 buffer, 10x</td>
			<td style="width:455px;">Mix 200 mM HEPES and 1.5 M KCl in RNase-free water. Adjust pH to 7.5. Filter sterilize, aliquot and store at &#8722;20 &#176;C for up to 24 months</td>
			<td style="width:241px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">&#65279;CAS9-NLS protein&#160;&#160;</td>
			<td style="width:455px;">PNA Bio</td>
			<td style="width:241px;">CP03</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Cell culture dishes, 10cm</td>
			<td style="width:455px;">Falcon</td>
			<td style="width:241px;">351029</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Dumont #5 - Fine Forceps</td>
			<td style="width:455px;">Fine Scientific Instruments</td>
			<td style="width:241px;">11254-20</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Electroporator</td>
			<td style="width:455px;">Nepa Gene&#160;</td>
			<td style="width:241px;">NEPA21</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:492px;"></td>
			<td style="width:455px;">BEX</td>
			<td style="width:241px;">Pulse Generator CUY21EDIT II</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Fast Green FCF</td>
			<td style="width:455px;">Sigma-Aldrich</td>
			<td style="width:241px;">F7252-5G</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:492px;">Fast Green FCF Solution, 5x</td>
			<td style="width:455px;">Dissolve 12.5 mg of Fast Green FCF powder in 10 mL of 1&#215; PBS.</td>
			<td style="width:241px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Flaming/Brown Micropipette Puller&#160;</td>
			<td style="width:455px;">Stutter Instrument&#160;</td>
			<td style="width:241px;">P-97</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="105">
			<td height="105" style="height:105px;width:492px;">&#65279;Holtfreter&#8217;s solution 400% (wt/vol)&#160;</td>
			<td style="width:455px;">&#65279;Dissolve 11.125 g of MgSO4&#183;7H2O, 5.36 g of CaCl2&#183;2H2O, 158.4 g of NaCl and 2.875 g of KCl in 10 L of dH2O. The solution can be stored at room temperature for up to 6 months.</td>
			<td style="width:241px;"></td>
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		<tr height="28">
			<td height="28" style="height:28px;width:492px;">KCl</td>
			<td style="width:455px;">Merck</td>
			<td style="width:241px;">&#65279;104936</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;width:492px;">MgSO4&#183;7H2O</td>
			<td style="width:455px;">Merck</td>
			<td style="width:241px;">&#65279;105886</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Microloader pipette tips</td>
			<td style="width:455px;">Eppendorf</td>
			<td style="width:241px;">5242956003</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Micromanipulator&#160;</td>
			<td style="width:455px;">Narishige</td>
			<td style="width:241px;">MN-153&#160;</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">NaCl</td>
			<td style="width:455px;">Merck</td>
			<td style="width:241px;">&#65279;106404</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Pneumatic PicoPump</td>
			<td style="width:455px;">World Precision Instruments&#160;</td>
			<td style="width:241px;">SYS-PV830</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Ring Forceps</td>
			<td style="width:455px;">Fine Scientific Instruments</td>
			<td style="width:241px;">11103-09</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Stereomicroscope</td>
			<td style="width:455px;">Olympus</td>
			<td style="width:241px;">SZX10&#160;</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:492px;">Tris base</td>
			<td style="width:455px;">Sigma-Aldrich</td>
			<td style="width:241px;">&#65279;T6066</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="112">
			<td height="112" style="height:112px;width:492px;">Tris-buffered saline, 10x</td>
			<td style="width:455px;">&#65279;Dissolve 24.2 g of Tris base and 90 g of NaCl in 990 ml of dH2O. Adjust pH to 8.0 by adding 10 ml of 37% (vol/vol) HCl. The solution can be stored at room temperature for up to 6 months.</td>
			<td style="width:241px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:492px;">Tweezers w/Variable Gap 2 Round Platinum Plate Electrode, 10mm diameter</td>
			<td style="width:455px;">Nepa Gene&#160;</td>
			<td style="width:241px;">&#65279;CUY650P10</td>
			<td style="width:167px;"></td>
		</tr>
	</tbody>
</table>

direct gene knock-out of axolotl spinal cord neural stem cells via electroporation of cas9 protein-grna complexes

The axolotl has the unique ability to fully regenerate its spinal cord. This is largely due to the ependymal cells remaining as neural stem cells (NSCs) throughout life, which proliferate to reform the ependymal tube and differentiate into lost neurons after spinal cord injury. Deciphering how these NSCs retain pluripotency post-development and proliferate upon spinal cord injury to reform the exact pre-injury structure can provide valuable insight into how mammalian spinal cords may regenerate as well as potential treatment options. Performing gene knock-outs in specific subsets of NSCs within a restricted time period will allow study of the molecular mechanisms behind these regenerative processes, without being confounded by development perturbing effects. Described here is a method to perform gene knock-out in axolotl spinal cord NSCs using the CRISPR-Cas9 system. By injecting the CAS9-gRNA complex into the spinal cord central canal followed by electroporation, target genes are knocked out in NSCs within specific regions of the spinal cord at a desired timepoint, allowing for molecular studies of spinal cord NSCs during regeneration.

Injection and electroporation of CAS9-gRNA complex against Sox2 into the axolotl spinal cord central canal led to a massive loss of SOX2 immunoreactivity in a majority of spinal cord NSCs, with gRNA against Tyrosinase (Tyr) as a control (Figure 2A). B3-tubulin (stained with TUJ1)&#160;is a marker for neurons and was not expressed in NSCs, and SOX2- TUJ1- cells surrounding the central canal were considered to be cells harboring Sox2 deletions. Quantification...

Watch this Scientific Journal Video about Direct Gene Knock-out of Axolotl Spinal Cord Neural Stem Cells via Electroporation of CAS9 Protein-gRNA Complexes at JoVE.com

Direct Gene Knock-out of Axolotl Spinal Cord Neural Stem Cells via Electroporation of CAS9 Protein-gRNA Complexes

Presented here is a protocol to perform time- and space-restricted gene knock-out in axolotl spinal cords by injecting CAS9-gRNA complex into the spinal cord central canal followed by electroporation.

The axolotl has the unique ability to fully regenerate its spinal cord. This is largely due to the ependymal cells remaining as neural stem cells (NSCs) ...

This protocol allows rapid and highly-penetrating time and space-restricted gene knock-outs in axolotl spinal cord neural stem cells for study of the molecular mechanisms of spinal cord regeneration. This technique allows the study of gene function in neural stem cells, its medical regeneration without being confounded by developmental effects or effects from other cell types. Axolotl neural stem cells contribute largely to their ability to regenerate their spinal cords.Understanding regeneration mechanisms could lead to insights for developing treatments for human spinal cord injury. This method provides insight into how axolotl neural stem cells mount a regenerative response to spinal cord injury. Correctly positioning the injection capillary into the spinal cord central column can be challenging and practicing on test animals helps with the mastering the technique.Viewing the administration can show how to perform the injection and what a successful injection looks like. To prepare the Cas9 guide RNA ribonuclear protein mixture, mix five micrograms of Cas9 nuclear localization sequence protein, four micrograms of guide RNA, and 0.9 microliters of 10X Cas9 buffer. Then bring the total volume to 10 microliters with nuclease-free water and store the Cas9 guide RNA ribonuclear protein mixture at minus 80 degrees Celsius if not used immediately.For agarose electroporation plate preparation, prepare 200 milliliters of 2%agarose in Dulbecco's PBS and dissolve the mixture in a microwave. After slight cooling, pour the liquid agarose into 10-centimeter Petri dishes to a depth of about 10 millimeters and allow the plates to solidify at room temperature. When the agarose is firm to the touch, use a surgical scalpel to cut a slit in the agarose of each dish for holding the tail straight, a well to fit the body of the animal, and two extra wells to hold the electrodes.Then place the plates on ice and fill them to the rim with ice-cold DPBS. To configure the electroporator, set the poring pulse to one bipolar pulse at 70 volts with a duration of five milliseconds, an interval of 50 milliseconds, and no voltage decay. Set the transfer pulse to four bipolar pulses of 40 volts with a duration of 50 milliseconds, an interval of 999 milliseconds, and a 10%voltage decay.Then connect the electrodes to the electroporator and adjust the tweezers so that they are seven millimeters apart before submerging the electrodes in a beaker of PBS. To prepare glass micro-injection capillaries, perform a ramp test on a micropipette puller as per the manufacturer's instructions to determine the heat value. Then pull injection capillaries with tapered ends with the indicated parameters.After pulling, use a stereo microscope and fine forceps to break the capillary at an angle so that it has a slanted tip at a position where the tip is thin enough to target the central canal of the axolotl spine while remaining strong enough to pierce the skin. Before loading the tip, add fast green FCF solution to the ribonuclear protein mixture at a one to 30 ratio and use a gel-loading pipette tip to load about five microliters of the injection mix into the capillary. Then mount the capillary on the pneumatic pump with the slanted tip facing downward.To configure the pneumatic pump, set the hold to 0.5 pounds per square inch, the ejection to two pounds per square inch hold, and the duration to gated. To test the capillary and pump settings, dip the capillary into a drop of water and press the foot pedal to inject. The injection mix should come out in a slow but steady stream.To inject the ribonuclear protein mixture, flip the axolotls to be injected upside down in the water to confirm sedation and use ring forceps to transfer one animal onto a bed of silicone with the left side of the animal facing up and the tail pointing to the right. Position the injection site in the middle of the field of view of the stereo microscope and adjust the micromanipulator so that the capillary will enter the animal at a 60-degree angle from the right side of the field of view. After identifying the spinal cord and central canal, slowly move the capillary toward the central canal of the spinal cord until it gently pierces the skin and muscle.When the capillary is in position, press and hold down the foot pedal to inject the mixture into the central canal. If the capillary has been properly placed, the ribonuclear protein mixture will spread along the central canal as a blue line in both directions. It can be challenging to position the capillary correctly.If the mixture does not spread correctly, adjust the capillary position in small steps while keeping the footpad pressed. Continue to hold down the foot pedal until the mixture reaches the terminal vesicle at the end of the spinal cord and the ventricles in the brain. It might be necessary to adjust the ejection pressure during the injection.Immediately after the injection, use ring forceps to transfer the animal onto the prepared agarose electroporation plate on ice and place the tail inside the slit so that it is sandwiched by the agarose. Place the electrodes into the wells on both sides of the tail, taking care that the entire animal and electrodes are covered by ice-cold PBS and press the foot switch to start the electroporation. Then return the animal to the water with monitoring until full recovery and inject and electroporate the subsequent animals in the same manner.To evaluate the efficiency of the knock-out at the protein level, obtain a cross-section of the tail and perform immunohistochemical analysis according to standard protocols. Alternatively, extract the electroporated spinal cord and lyse the sample to obtain the DNA. Then perform genotyping PCR followed by Sanger sequencing or next-generation sequencing to assess the percentage of edited genetic loci.The injection and electroporation of Cas9 guide RNA complexes against Sox2 into the axolotl spinal cord central canal leads to a massive loss of Sox2 immunoreactivity in the majority of the spinal cord neural stem cells compared the the injection and electroporation of Cas9 guide RNA complexes against tyrosinase as a control. Quantification of Sox2-positive cells in spinal cord tissue section samples reveals a significantly-reduced number of Sox2-expressing cells in Cas9 Sox2 guide RNA electroporation knock-out animals, indicating that this method leads to an efficient and highly-penetrating gene knock-out in spinal cord neural stem cells. After simultaneous injection and electroporation of two Cas9 guide RNA complexes against Sox2 and GFP into transgenic axolotls with ubiquitous GFP expression, a high percentage of double knock-out neural stem cells is observed, indicating that the protocol can be used to flexibly knock out multiple genes.It's helpful to practice targeting the central canal with a capillary and to put on formula with the troubleshooting steps for when the injection does not work as expected. This technique allows researchers to study the functions of genes in neural stem cells that are specific to regeneration. Take care when manipulating the capillary and make sure not to stabs your own fingers.

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Research

JoVE Journal

Genetics

7.9K Görüntüleme.  South China Normal University. Bu protokol, omurilik rejenerasyonunun moleküler mekanizmalarının incelenmesi için axolotl spinal kord sinir kök hücrelerinde hızlı ve yüksek nüfuz lu zaman ve uzay kısıtlamalı gen nakavtları sağlar. Bu teknik, nöral kök hücrelerde gen fonksiyonunun incelenmesini, diğer hücre tiplerinden gelen gelişimsel etkiler veya etkilerle şaşkına girmeden tıbbi yenilenmesine olanak sağlar. Axolotl nöral kök hücreler omuriliklerini yenileme yeteneklerine büyük ölçüde katk...