The authors thank Dr. James Bamburg and members of his laboratory for collaboration in these studies. This work was funded by NIH grants HD19950, EY07133 and by grants from the Minnesota Medical Foundation.

For rhodamine-actin labeling, neurons are cultured on glass coverslips placed in the bottom of 35 mm plastic dishes, or on coverslips glued into "video" dishes.
1. Preparation of Coverslips or "Video" Dishes
<ol>
<li>Many neuronal types are poorly adhesive to in vitro substrates. Glass coverslips, which are required for this procedure, may not allow sufficient neuron-substrate adhesion unless they are adequately cleaned and prepared. A detailed procedure for acid washing and cleanin...

<ol>
	<li>Lowery, L. A., Van Vactor, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+trip+of+the+tip:+Understanding+the+growth+cone+machinery.">The trip of the tip: Understanding the growth cone machinery.</a> Nat Rev Mol Cell Biol. 10, 332-343 (2009).</li><li>Letourneau, P., Squire, L. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Axonal+Pathfinding:+Extracellular+Matrix+Role.">Axonal Pathfinding: Extracellular Matrix Role.</a> Encyclopedia of Neuroscience. , 1139-1145 (2008).</li><li>Kalil, K., Dent, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Touch+and+go:+Guidance+cues+signal+to+the+growth+cone+cytoskeleton.">Touch and go: Guidance cues signal to the growth cone cytoskeleton.</a> Curr Opin Neurobio. 15, 521-526 (2005).</li><li>Dent, E. W., Gertler, F. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cytoskeletal+dynamics+and+transport+in+growth+cone+motility+and+axon+guidance.">Cytoskeletal dynamics and transport in growth cone motility and axon guidance.</a> Neuron. 40, 209-227 (2003).</li><li>Pak, C. W., Flynn, K. C., Bamburg, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actin-binding+proteins+take+the+reins+in+growth+cones.">Actin-binding proteins take the reins in growth cones.</a> Nat Rev Neurosci. 9, 136-147 (2008).</li><li>Guan, K. L., Rao, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Signaling+mechanisms+mediating+neuronal+responses+to+guidance+cues.">Signaling mechanisms mediating neuronal responses to guidance cues.</a> Nat Rev Neurosci. 4, 941-956 (2003).</li><li>Gallo, G., Letourneau, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+growth+cone+actin+filaments+by+guidance+cues.">Regulation of growth cone actin filaments by guidance cues.</a> J. Neurobiology. 58, 92-102 (2004).</li><li>Fass, J., Gehler, S., Sarmiere, P., Letourneau, P., Bamburg, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulating+filopodial+dynamics+through+actin-depolymerizing+factor/cofilin.">Regulating filopodial dynamics through actin-depolymerizing factor/cofilin.</a> Anat Sci Inter. 79, 173-183 (2004).</li><li>Bernstein, B. W., Bamburg, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ADF/cofilin:+A+functional+node+in+cell+biology.">ADF/cofilin: A functional node in cell biology.</a> Trends Cell Biol. 20, 187-195 (2010).</li><li>Marsick, B. M., Flynn, K. C., Santiago, M., Bamburg, J. R., Letourneau, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+ADF/cofilin+mediates+attractive+growth+cone+turning+toward+nerve+growth+factor+and+netrin-1.">Activation of ADF/cofilin mediates attractive growth cone turning toward nerve growth factor and netrin-1.</a> Dev Neurobiol. 70, 565-588 (2010).</li><li>Symons, M. H., Mitchison, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+actin+polymerization+in+live+and+permeabilized+fibroblasts.">Control of actin polymerization in live and permeabilized fibroblasts.</a> J Cell Biol. 114, 503-513 (1991).</li><li>Chan, A. Y., Raft, S., Bailly, M., Wyckoff, J. B., Segall, J. E., Condeelis, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EGF+stimulates+an+increase+in+actin+nucleation+and+filament+number+at+the+leading+edge+of+the+lamellipod+in+mammary+adenocarcinoma+cells.">EGF stimulates an increase in actin nucleation and filament number at the leading edge of the lamellipod in mammary adenocarcinoma cells.</a> J Cell Sci. 111, 199-211 (1998).</li></ol>

No conflicts of interest declared.

The methods presented here allow temporal and spatial resolution of cellular components that are involved in the dynamic remodeling of the actin cytoskeleton at the leading margin of migrating growth cones. The action of attractant molecules, like NGF or netrin, to rapidly stimulate actin filament polymerization is revealed as a local increase in actin barbed ends, created by actin filament severing by activated ADF/cofilin10, as shown in Figures 1 and 2. The method permits localization of other proteins invol...

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		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
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<tr>
<td>18x18 mm coverslip</td>
<td>&nbsp;</td>
<td>Gold Seal</td>
<td>3305</td>
<td>&nbsp;</td>
<tr>
<td>35mm Petri dishes</td>
<td>&nbsp;</td>
<td>Falcon</td>
<td>351008</td>
<td>&nbsp;</td>
<tr>
<td>Aquarium cement</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>DAP 100% silicone aquarium sealant</td>
<td>Any hardware store</td>
</tr>
<tr>
<td>Poly-D-lysine (mw &gt; 300,000)</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>P1024</td>
<td>&nbsp;</td>
<tr>
<td>Natural mouse laminin</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>23017-015</td>
<td>&nbsp;</td>
<tr>
<td>L1 CAM</td>
<td>&nbsp;</td>
<td>R &amp; D systems</td>
<td>777-NC</td>
<td>&nbsp;</td>
<tr>
<td>Alexa-fluor 350 phalloidin</td>
<td>&nbsp;</td>
<td>Invitrogen (Molecular Probes)</td>
<td>A22281</td>
<td>&nbsp;</td>
<tr>
<td>Rhodamine non-muscle actin</td>
<td>&nbsp;</td>
<td>Cytoskeleton, Inc.</td>
<td>APHR-A</td>
<td>&nbsp;</td>
<tr>
<td>F12 Culture medium</td>
<td>&nbsp;</td>
<td>Invitrogen (Gibco)</td>
<td>21700-075</td>
<td>&nbsp;</td>
<tr>
<td>B27</td>
<td>&nbsp;</td>
<td>Invitrogen (Gibco)</td>
<td>17504-044</td>
<td>&nbsp;</td>
<tr>
<td>Slowfade </td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>536937</td>
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labeling f-actin barbed ends with rhodamine-actin in permeabilized neuronal growth cones

The motile tips of growing axons are called growth cones. Growth cones lead navigating axons through developing tissues by interacting with locally expressed molecular guidance cues that bind growth cone receptors and regulate the dynamics and organization of the growth cone cytoskeleton3-6. The main target of these navigational signals is the actin filament meshwork that fills the growth cone periphery and that drives growth cone motility through continual actin polymerization and dynamic remodeling7. Positive or attractive guidance cues induce growth cone turning by stimulating actin filament (F-actin) polymerization in the region of the growth cone periphery that is nearer the source of the attractant cue. This actin polymerization drives local growth cone protrusion, adhesion of the leading margin and axonal elongation toward the attractant.
Actin filament polymerization depends on the availability of sufficient actin monomer and on polymerization nuclei or actin filament barbed ends for the addition of monomer. Actin monomer is abundantly available in chick retinal and dorsal root ganglion (DRG) growth cones. Consequently, polymerization increases rapidly when free F-actin barbed ends become available for monomer addition. This occurs in chick DRG and retinal growth cones via the local activation of the F-actin severing protein actin depolymerizing factor (ADF/cofilin) in the growth cone region closer to an attractant8-10. This heightened ADF/cofilin activity severs actin filaments to create new F-actin barbed ends for polymerization. The following method demonstrates this mechanism. Total content of F-actin is visualized by staining with fluorescent phalloidin. F-actin barbed ends are visualized by the incorporation of rhodamine-actin within growth cones that are permeabilized with the procedure described in the following, which is adapted from previous studies of other motile cells11, 12. When rhodamine-actin is added at a concentration above the critical concentration for actin monomer addition to barbed ends, rhodamine-actin assembles onto free barbed ends. If the attractive cue is presented in a gradient, such as being released from a micropipette positioned to one side of a growth cone, the incorporation of rhodamine-actin onto F-actin barbed ends will be greater in the growth cone side toward the micropipette10.
Growth cones are small and delicate cell structures. The procedures of permeabilization, rhodamine-actin incorporation, fixation and fluorescence visualization are all carefully done and can be conducted on the stage of an inverted microscope. These methods can be applied to studying local actin polymerization in migrating neurons, other primary tissue cells or cell lines.

Watch this Scientific Journal Video about Labeling F-actin Barbed Ends with Rhodamine-actin in Permeabilized Neuronal Growth Cones at JoVE.com

Labeling F-actin Barbed Ends with Rhodamine-actin in Permeabilized Neuronal Growth Cones

A method to visualize and quantify F-actin barbed ends in neuronal growth cones is described. After culturing neurons on glass coverslips, cells are permeabilized with a saponin-containing solution. Then, a short incubation with the saponin buffer containing rhodamine-actin incorporates fluorescent actin onto free actin barbed ends.

The motile tips of growing axons are called growth cones. Growth cones lead navigating axons through developing tissues by interacting with locally ...

labeling-f-actin-barbed-ends-with-rhodamine-actin-permeabilized

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JoVE Journal

Neuroscience

14.7K Görüntüleme.  University of Minnesota. Nöronal büyüme konileri dikenli biter görselleştirmek ve F-aktin ölçmek için bir yöntem açıklanmıştır. Cam lamelleri kültür nöronlar sonra, hücreler saponin içeren bir çözüm permeabilize. Sonra, rodamin-aktin içeren saponin tamponu ile kısa bir inkübasyon ücretsiz aktin dikenli uçları üzerine floresan aktin içermektedir.