The prostate cell lines are kindly provided by Dr. Ling-Yu Wang and Dr. Hsing-Jien Kung at Cancer Center, UC Davis. This project is supported by NIH galvanotaxis grant 4R33AI080604.

1. Culturing Prostate Cells
<ol>
	<li>Culture the pRNS-1-1 and PNT2 prostate cells on 100 mm culture dishes in RPMI 1640 medium supplemented with 10% FBS and Antibiotic-Antimycotic at 37 &#176;C with 5% CO2. Refresh the culture medium every day until the cells reach 80% confluency for the galvanotaxis experiments.</li>
</ol>
2. Assembling Galvanotaxis Chambers
<ol>
	<li>Assembling bottom chambers
	<ol>
		<li>Wipe a plastic galvanotaxis chamber with 2-propanol. Apply the marine grade silicon sealer around the circular openings on the bottom side of a chamber with a syringe and attach a large coverglass (Figure 1). Use the back side of a cotton applicator to push down the coverglass and wipe off the excess glue with cotton swabs. The circular openings allow the medium and electric current to flow over the cells located between the two inner medium reservoirs.</li>
		<li>Cut a small coverglass to make 6 mm x 25 mm spacers with a diamond point marker.</li>
		<li>Flip the chamber. Apply 2 stripes of the silicon glue with a syringe and/or a metal spatula to create a 10 mm x 25 mm channel surface for cell attachment between the 2 circular openings on the bottom glass. Glue 2 pieces of glass spacer between the 2 circular openings. Use the back side of the cotton applicators to push down the spacers and wipe off the excess glue with cotton swabs and/or toothpicks.</li>
		<li>Dry the chamber for 24 hr until the silicon glue is cured. Soak the chamber in distilled water overnight to remove the acetic acid residue from the glue. Dry the chamber for immediate use, or store the chamber for later use in a clean container. 
		<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51973/51973fig1highres.jpg" width="500" /> 
	Figure 1: Assembly of the bottom galvanotaxis chamber. A) A large coverglass is attached to the bottom of a clean chamber. B) Two pieces of glass spacers are glued between the 2 circular openings to create a 10 mm x 25 mm channel for cells to attach.</li>
	</ol>
	</li>
	<li>Seeding cells on the galvanotaxis chambers
	<ol>
		<li>Prepare the require number of galvanotaxis chambers needed for the experiment. Each cell line or treatment requires a single galvanotaxis chamber. Wipe the galvanotaxis chambers with 2-propanol. Wash the chambers with sterile PBS 3 times and check the liquid flow between the 2 circular openings in the chambers.</li>
		<li>Enclose the chambers in sterile cell culture dishes and allow them to equilibrate at 37 &#176;C for 15 min. Detach the prostate cells from their culture dish using 5 ml 0.25% Trypsin-EDTA at 37 &#176;C for 5 min. Neutralize the trypsin-EDTA with 5 ml 10% FBS in PBS.</li>
		<li>Transfer the cells to 15 ml tubes and centrifuge the cells for 5 min at 200 x g, 37 &#176;C. Aspirate the supernatant and re-suspend the cells in 1 ml of culture medium.</li>
		<li>Take 20 &#181;l of cell solution to load to a counting chamber and calculate the cell number. Adjust the cell concentration to 8 x 104 cell/ml with culture medium.</li>
		<li>Take the galvanotaxis chambers out of the 37 &#176;C incubator. Seed 350 &#181;l of the cell suspension onto each chamber.</li>
		<li>Incubate the cells in the chambers overnight in the culture dish with wet Kimwipe or in a humidity chamber in the incubator at 37 &#176;C with 5% CO2.</li>
	</ol>
	</li>
</ol>
	<img alt="Figure 2" fo:content-width="5in" src="/files/ftp_upload/51973/51973fig2highres.jpg" width="500" /> 
	Figure 2: Seeding the cells to the chamber. The bottom chamber is dried and cleaned. A) Prostate cells are trypsinized, counted and transferred to the chamber and incubated overnight. B) A top coverglass is attached to seal the chamber before filming.
<ol start="3">
	<li>Assembling the top chambers
	<ol>
		<li>Assemble the top chamber prior to filming. The microscope can only accommodate imaging a single galvanotaxis chamber at one time. Warm up 10 ml of culture medium at 37 &#176;C for each galvanotaxis chamber. Transfer a galvanotaxis chamber from the incubators to a 37 &#176;C warming plate.</li>
		<li>Rinse the cells with culture medium to remove the unattached cells. Leave 400 &#181;l of medium in the chamber. Use a syringe to apply high vacuum grease on top of both glass spacers.</li>
		<li>Add a small coverglass to seal the chamber. Gently press down the coverglass with the back side of a cotton applicator. Wipe off the excess medium with cotton swabs.</li>
		<li>Dry the glass surface and apply high vacuum grease to seal the gap between the coverglass and the chamber. Use a metal spatula to spread the grease. Add 4 ml of the culture medium to the inner reservoirs and check the liquid flow between the reservoirs.</li>
	</ol>
	</li>
	<li>Make agar bridges
	<ol>
		<li>Cut a pair of 2 inch long PVC tubing (503/16 ID x 5/16 OD x 1/16 Wall), flip and insert them into a 100 ml beaker.</li>
		<li>Measure 200 mg Bacto-Agar and add it in a 50 ml flask with 10 ml culture medium to make 2% agar gel. Microwave for 30 sec. Load the agar gel to the plastic tubing with a transfer pipet. Leave the agar bridges at room temperature for 10 min to solidify the agar.</li>
		<li>Add 2 ml culture medium to the outer reservoirs of the galvanotaxis chamber. Insert the agar bridges to the inner and outer medium reservoirs to conduct the current.</li>
	</ol>
	</li>
</ol>
	<img alt="Figure 3" fo:content-width="3.5in" src="/files/ftp_upload/51973/51973fig3highres.jpg" width="350" /> 
	Figure 3: Filming the cells on the chamber. A diagram to demonstrate the final assembly of the galvanotaxis chamber. The chamber is completely sealed with high vacuum grease. Medium is added to fill the reservoirs, and two agar bridges are inserted into the chamber. Then the galvanotaxis chamber is transferred to the microscope stage and the electrodes are attached to apply the electric field. Side-view of the assembled galvanotaxis chamber is shown to demonstrate that the electric current flows over the cells through the agar bridges and the space between the cover glass.
3. Time-lapse Imaging
<ol>
	<li>Switch on the environmental chamber to 37 &#176;C with 5% CO2 in the circulating air 2 hr prior to imaging.</li>
	<li>Switch on the microscope and initiate the image-acquiring software. Calibrate the microscope stage and select the 10X objective.</li>
	<li>Transfer the galvanotaxis chambers to the microscope stage, secure the chamber with tape and focus on the cells. Insert the galvanotaxis electrodes to the outer reservoirs with cathode on the right side. Secure the wire and the electrodes with tape.</li>
	<li>Switch on the power box to apply an electric field to the chamber. Measure the output voltage with the voltmeter across the chamber to reach 2.5 volts for the 25 mm long chamber (100 mV/mm). Maintain the field strength during the experiment by adjusting the output current.</li>
	<li>Select 10 points across the chamber to film in the software to generate ten time-lapse movies. Set up the acquisition conditions at 10-min intervals for 2 hr.</li>
	<li>Start filming and adjust the output current as needed.</li>
	<li>At the end of the experiment, remove the chamber from the stage and fix the cells with 95% alcohol. Break open the chamber with a razor blade to clean and re-use it.</li>
</ol>
4. Quantification of Galvanotaxis
<ol>
	<li>Rotate the time-lapse movies and re-orient the cathode to the top of the images. Export the movies to the cell tracking software.</li>
	<li>Manually track the (x,y) position of 10-20 cells at each time-point from each movie (Figure 4 A, B). The migration distances and the angles relative to the north-south direction, the same orientation of the electric field, will be calculated in the cell tracking software (Figure 4C). 
	NOTE: The average migration speed is converted from the total migration distance and total filming time. The directionality is converted from the angles to the cosine value. If cells migrate with random directionality, the average of net cosine will be close to zero. If the cells migrate directly toward the cathode, the cosine value will be +1. If the cells migrate directly toward the anode, the cosine value will be -1.</li>
</ol>
<img alt="Figure 4" fo:content-width="4in" src="/files/ftp_upload/51973/51973fig4highres.jpg" width="400" /> 
Figure 4: Cell tracking to measure directionality. A) Overlay of the tracking lines with cell images. The (x, y) positions of the cells are manually tracked in the time-lapse movies. If the cells migrate randomly, the average cosine is close to zero. B) However, if the cells migrate toward the cathode or the anode, the value of the average cosine is close to + (cathode) or &#8211; (anode) 1.0. C) The directionality is presented by the cosine value, which is converted from the migration angles (&#952;). The cosine (&#952;) equals the ratio of the distance a (the migration distance) to distance b (the distance projected to the direction of the electric field).
<ol start="3">
	<li>Save the measurements. Import the data to a database application to calculate the combined results.</li>
	<li>Export the combined data of average migration speed and average cosine value to a spreadsheet to plot the bar graphs (Figure 5).</li>
</ol>

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The authors have nothing to disclose.

The analysis of a cell&#8217;s galvanotaxis response has been an important functional indicator for many cellular migratory or growth processes 27, 28. Here we use a custom-made chamber with glass surface to film two prostate cell lines. These cell lines demonstrated different degrees of galvanotaxis, and we speculate that the intracellular localization or the activation of the galvanotaxis-mediating proteins might be interfered during the process of generating the immortal cell lines, resulting in the observed difference in the galvanotaxis response.
Compared to other galvanotaxis chamber designs made in culture dishes27, 28, there are several benefits to the current design. First, the glass surface is suitable for imaging and the coverglass with cells can be retrieved after galvanotaxis for immunostaining. In this study we used a low magnification of 10X objective to monitor a group of cells. However, with these improved glass optics, it is possible to film a single cell at higher magnification with a 60X oil objective, for tracking the fast extension and retraction of lamellipodial at the leading edge of the cells 17, or tracking cells labeled with fluorescent proteins. Second, the glass surface could be modified with matrix protein coatings 10, 12 or patterned with micro-channels. Chemical treatments are also possible to pre- treat the cells before filming 29. Matrix coating is not required for the prostate cell lines used here, and the matrix coating is cell type-dependent. For example, collagen I coating is required for the galvanotaxis of human keratinocytes 30, but laminin coating is required for the galvanotaxis of human neural stem cells 31. We tested human keratinocyte galvanotaxis on collagen I, collagen IV, fibronectin, and laminin. Different matrix proteins altered cell migration speed, but did not change the cathodal migration in galvanotaxis 29. Third, the modified platinum electrodes are inert in the electric field. Compared to the silver electrodes as used in other galvanotaxis methods 27, they do not break down or release metal ions to the medium, which reduces the cytotoxicity in galvanotaxis. Fourth, we may change the intervals of frame capturing, which helps us to monitor either fast or slow cell migration. The motorized microscope also provides the opportunity to acquire multiple movies from different areas in one chamber. A control experiment without the applied electric field is important for determining whether the electric field alters the migratory speed of the cells.
However, the current galvanotaxis chambers are limited to filming cell migration for up to 4 hours due to the small volume of medium in the reservoirs. With an enlarged version of the chamber design, it would be possible to film cells for a longer period of time.
Some potential problems in the method include: 1) the cells might die during the chamber assembly if they become desiccated. Since there is a very small volume of medium in the chamber (400 &#181;l), it is important to avoid trapping air bubbles in the chamber and to keep some liquid covering the cells during the cell rinse step. 2) The chamber could leak during imaging, which would decrease the current passing through the chamber. The liquid flow in the chamber should be carefully checked before it is transferred to the microscope stage and more high vacuum grease applied if needed. 3) Smudged high vacuum grease may interfere with filming. The glass surface can be cleaned with 95% alcohol to remove grease. 4) Stage drift or any displacement of the chambers on a motorized microscope stage could bias the measurements of the directional migration. Therefore, it is important to secure the galvanotaxis chambers with adequate stage holder and labeling tape.
Overall, the galvanotaxis method is useful to reveal the intrinsic directionality of motile cells in an applied electric field, which will help us to further understand the directional migration in organisms.

Endogenous electric fields are detected in various tissues, such as skin 1, 32, 33 and brain 2. The physiological electric field serves specific biological functions, including directing embryo development 3, 4, guiding the outgrowth of neuronal processes 5, 6 and promoting epithelial and corneal wound closure 1, 7. In vitro, application of a direct current electric field to cultured cells mimics the physiological electric field and induces directional cell migration, or galvanotaxis. Galvanotaxis has been studied in fibroblasts 8, fish keratinocytes 9, human epithelial and corneal keratinocytes 10-12, lymphocytes 13, neuroblasts 2, and neuronal progenitor cells 14. When exposed to the applied field, the majority of studied cells migrate directionally toward the cathodal (-) pole. Yet, several cancer cells, including highly metastatic human breast cancer cells and the human prostate cancer cell line PC-3M, move to the anodal (+) pole 15, 16. Several mechanisms are proposed to mediate galvanotaxis or to explain the ability of the cells to sense the electric field, including activation of EGF receptors 12, the epithelial sodium channel 17, PI3K and PTEN 18, and release of calcium ions 15, 19. The mechanism is not yet fully understood and it is possible that multiple signaling pathways are involved in galvanotaxis.
The 2-dimensional galvanotaxis method we demonstrate here is useful to characterize the directional migration of adherent, motile cells, either to monitor individual cell migration 10, 12, 17 or migration of a sheet of confluent cells 18, 20. This technique is modified from Peng and Jaffe21, and Nishimura et al.10 with custom-made, clear PVC chambers, with removable coverslips allowing for easy cell retrieval after galvanotaxis for secondary analysis, such as immuno-fluorescence imaging. The glass surface of the galvanotaxis chambers is optical-compatible, which allows the filming at high magnification and with fluorescently-labeled cells. It also allows the experimental design with modification of the glass surface, such as changing the surface coating or charges. Spacers made of No. 1 coverglass are used in the chambers to minimize the current flow over the cells; therefore the joule heating, which is proportional to the square of the current flow, would not overheat the cells during the experiment. The connecting agar bridges prevent direct contact of the electrodes with the cells and prevent change of the medium pH or ion concentration during galvanotaxis.
Two non-tumorigenic human prostate cell lines were examined for their galvanotaxis response in this study. The pRNS-1-1 22 and PNT2 23 are both SV40-immortalized, growth factor-dependent cell lines expressing the epithelial markers cytokeratin 5, 8, 18 and 19 with low or no expression of the prostate specific-antigen (PSA). Both cell lines maintain the polygonal morphology of normal epithelial cells, but chromosome abnormality was observed in karyotyping 22, 24. Although pRNS-1-1 and PNT2 share similar behaviors in most experiments, they do show differences in the formation of acinar structure and in galvanotaxis. On a 3-D matrix, Matrigel, the pRNS-1-1 cells form hollow acinar structures with lumens resembling the normal prostate gland tissue 25. However, the PNT2 cells form solid spheroids without a lumen or polarized epithelium 26. The pRNS-1-1 cells also demonstrate a higher galvanotactic response than the PNT2 in the current study. The correlation between the formation of acinar structure and galvanotaxis in pRNS-1-1 suggests that the galvanotactic signals may play a role in organizing the prostate gland tissue movements in response to endogenous electric fields, and provides further characteristics to discriminate between these 2 cell lines.

<table><tbody><tr><td colspan="4">&lt;strong&gt;Cells&lt;/strong&gt;</td></tr><tr><td>pRNS-1-1 prostate cells</td><td></td><td></td><td>Lee, &lt;em&gt;et al.&lt;/em&gt; (1994)</td></tr><tr><td>PNT2 prostate cells</td><td>Sigma-Aldrich</td><td>95012613-1VL</td><td>Berthon, &lt;em&gt;et al.&lt;/em&gt; (1995)</td></tr><tr><td colspan="4">&lt;strong&gt;Medium and solutions&lt;/strong&gt;</td></tr><tr><td>RPMI 1640 medium&amp;nbsp;</td><td>Invitrogen</td><td>11875-093</td><td>warm up to 37 &amp;deg;C before use</td></tr><tr><td>Fetal Bovine Serum - Premium</td><td>Atlanta Biologicals</td><td>S11150</td><td>10% in PBS, warm up to 37 &amp;deg;C before use</td></tr><tr><td>Antibiotic-Antimycotic (100x)</td><td>Life Technologies</td><td>15240</td><td>add 5 ml to 500 ml medium</td></tr><tr><td>2-propanol</td><td>VWR</td><td>BDH1133-5GL</td><td></td></tr><tr><td>PBS</td><td>-</td><td>-</td><td>137 mM NaCl, 2.7 mM KCl, 4.3 mM Na&lt;sub&gt;2&lt;/sub&gt;HPO&lt;sub&gt;4&lt;/sub&gt; and 1.5 mM KH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt; in 1,000 ml of H&lt;sub&gt;2&lt;/sub&gt;O, pH to 7.4 and autoclaved, warm up to 37 &amp;deg;C before use</td></tr><tr><td>0.25% Trypsin-EDTA&amp;nbsp;</td><td>Invitrogen</td><td>25200-056</td><td>warm up to 37 &amp;deg;C before use, treat cells for 3-5 min at 37 &amp;deg;C</td></tr><tr><td colspan="4">&lt;strong&gt;Galvanotaxis device&lt;/strong&gt;</td></tr><tr><td>Galvanotaxis chambers</td><td>Precision Plastics Inc, CA</td><td></td><td>Custom-designed (1/4&quot; x 2&quot; x 3.5&quot;), non-toxic, clear PVC chambers. Please contact the authors for the design specs.</td></tr><tr><td>Galvanotaxis electrodes</td><td>UCD electric shop</td><td></td><td>platinum coiled electrodes with flexable cords</td></tr><tr><td>Galvanotaxis power box</td><td>Substrate Engineering, CA</td><td></td><td>custom-designed DC power output with voltmeter</td></tr><tr><td>Microscope Cover Glass, Large, 45 x 50 mm, No. 1.5</td><td>Fisher</td><td>12-544-F</td><td></td></tr><tr><td>Microscope Cover Glass, small, 25 x 25 mm, No. 1</td><td>ThermoScientific</td><td>3307</td><td></td></tr><tr><td>Diamond point marker</td><td>ThermoScientific</td><td>750</td><td></td></tr><tr><td>Marine grade silicon sealer, clear</td><td>3M</td><td>051135-08019</td><td></td></tr><tr><td>High vacuum grease</td><td>Dow Corning</td><td>2021846-0807</td><td></td></tr><tr><td>6 ml syringe</td><td>Fisher Scientific</td><td>05-561-64</td><td></td></tr><tr><td>Nichiryo Syringe, 1.5 ml</td><td>Nichiryo</td><td>SG-M</td><td></td></tr><tr><td>Cotton applicators</td><td>Purtian Medical Products</td><td>806-WC</td><td></td></tr><tr><td>Qtips</td><td>Johnson &amp;amp; Johnson</td><td>729389</td><td></td></tr><tr><td>Nalgene 180 PVC tubing&amp;nbsp;</td><td>Nalgene</td><td>8000-9030</td><td>503/16 ID x 5/16 OD x 1/16 Wall</td></tr><tr><td>Bacto-Agar</td><td>Difco</td><td>0140-01</td><td>make 2% agar solution</td></tr><tr><td>Razor Blade</td><td>Personna</td><td>74-0001</td><td></td></tr><tr><td colspan="4">&lt;strong&gt;Equipments and Software&lt;/strong&gt;</td></tr><tr><td>Benchtop Centrifuge</td><td>Eppendorf</td><td>5810R</td><td>operated with an A-4-62 rotor</td></tr><tr><td>Cellometer Auto T4</td><td>Nexcelom</td><td>Auto T4</td><td></td></tr><tr><td>Cellometer counting chambers</td><td>Nexcelom</td><td>CHT4-SD100-002</td><td>load 20 &amp;#956;l cell solutions to count</td></tr><tr><td>Culture Temp Warming plate</td><td>Bel-Art Scienceware</td><td>370150000</td><td>to keep the galvanotaxis chambers at 37 &amp;deg;C&amp;nbsp;</td></tr><tr><td>Eclipse TE-2000 microscope with motorized stage and environmental chamber</td><td>Nikon</td><td></td><td></td></tr><tr><td>Plan Fluor 10X/0.30 objective len</td><td>Nikon</td><td></td><td></td></tr><tr><td>Retiga EX CCD camera&amp;nbsp;</td><td>Qimaging</td><td></td><td>Cooled CCD camara, mono-color, 12-bit</td></tr><tr><td>Compressed air with 5% CO&lt;sub&gt;2&lt;/sub&gt;</td><td>Airgas</td><td></td><td>special order</td></tr><tr><td>Volocity 6.3</td><td>PerkinElmer</td><td></td><td>Image acquiring software</td></tr><tr><td>Improvision OpenLab 5.5.2</td><td>PerkinElmer</td><td></td><td>Cell tracking software and customized to measure migration angles</td></tr><tr><td>FileMaker Pro Advanced, 8.0</td><td>FileMaker</td><td></td><td></td></tr><tr><td>Microsoft Excel 2008 for Mac</td><td>Microsoft</td><td></td><td></td></tr></tbody></table>

utilizing custom-designed galvanotaxis chambers to study directional migration of prostate cells

The physiological electric field serves specific biological functions, such as directing cell migration in embryo development, neuronal outgrowth and epithelial wound healing. Applying a direct current electric field to cultured cells in vitro induces directional cell migration, or galvanotaxis. The 2-dimensional galvanotaxis method we demonstrate here is modified with custom-made poly(vinyl chloride) (PVC) chambers, glass surface, platinum electrodes and the use of a motorized stage on which the cells are imaged. The PVC chambers and platinum electrodes exhibit low cytotoxicity and are affordable and re-useable. The glass surface and the motorized microscope stage improve quality of images and allow possible modifications to the glass surface and treatments to the cells. We filmed the galvanotaxis of two non-tumorigenic, SV40-immortalized prostate cell lines, pRNS-1-1 and PNT2. These two cell lines show similar migration speeds and both migrate toward the cathode, but they do show a different degree of directionality in galvanotaxis. The results obtained via this protocol suggest that the pRNS-1-1 and the PNT2 cell lines may have different intrinsic features that govern their directional migratory responses.

Two lines of prostate cells (pRNS-1-1 and PNT2) were investigated with this method. Cells in both lines migrate at similar speeds of 1.0 +/- 0.3 microns/min over the course of 2-hours (Figure 5A). However, the directionality to the electric field is 0.7 +/- 0.3 for the pRNS-1-1 line, and 0.2 +/- 0.8 for the PNT2 line (Figure 5B). The results show a significant difference in the galvanotaxis of these two cell lines (p&#60;0.01, 100 cells were tracked), suggesting that they have different cellular signaling mechanisms that result in different directional responses to positional cues.
<img alt="Figure 5" fo:content-width="5in" src="/files/ftp_upload/51973/51973fig5highres.jpg" width="500" /> 
Figure 5: Galvanotaxis of prostate cells. A) The migration speeds of pRNS-1-1 and PNT2 lines are similar when the cells are exposed to the electric field. B) However, the pRNS-1-1 line showed a high directionality toward cathode (cosine = 0.7), while the PNT2 line showed a low directionality (cosine = 0.2) in the electric field.

Watch this Scientific Journal Video about Utilizing Custom-designed Galvanotaxis Chambers to Study Directional Migration of Prostate Cells at JoVE.com

Utilizing Custom-designed Galvanotaxis Chambers to Study Directional Migration of Prostate Cells

We present a method to apply a physiological electric field to migrating, immortalized prostate cells in a custom-made galvanotaxis chamber. Using this method, we demonstrate that 2 lines of non-tumorigenic prostate cells demonstrate different degrees of migration directionality in the field.

The physiological electric field serves specific biological functions, such as directing cell migration in embryo development, neuronal outgrowth and ...

utilizing-custom-designed-galvanotaxis-chambers-to-study-directional

Universidad San Sebastian

Research

JoVE Journal

Biology

9.1K Views.  University of California, Davis. We present a method to apply a physiological electric field to migrating, immortalized prostate cells in a custom-made galvanotaxis chamber. Using this method, we demonstrate that 2 lines of non-tumorigenic prostate cells demonstrate different degrees of migration directionality in the field.

Video: Utilizing Custom-designed Galvanotaxis Chambers to Study Directional Migration of Prostate Cells

Electric Field-controlled Directed Migration of Neural Progenitor Cells in 2D and 3D Environments

Endogenous electric fields (EFs) occur naturally in vivo and play a critical role during tissue/organ development and regeneration, including that of the central nervous system1,2. These endogenous EFs are generated by cellular regulation of ionic transport combined with the electrical resistance of cells and tissues. It has been reported that applied EF treatment can promote functional repair of spinal cord injuries in animals and humans3,4. In particular, EF-directed cell migration has been demonstrated in a wide variety of cell types5,6, including neural progenitor cells (NPCs)7,8. Application of direct current (DC) EFs is not a commonly available technique in most laboratories. We have described detailed protocols for the application of DC EFs to cell and tissue cultures previously5,11. Here we present a video demonstration of standard methods based on a calculated field strength to set up 2D and 3D environments for NPCs, and to investigate cellular responses to EF stimulation in both single cell growth conditions in 2D, and the organotypic spinal cord slice in 3D. The spinal cordslice is an ideal recipient tissue for studying NPC ex vivo behaviours, post-transplantation, because the cytoarchitectonic tissue organization is well preserved within these cultures9,10. Additionally, this ex vivo model also allows procedures that are not technically feasible to track cells in vivo using time-lapse recording at the single cell level. It is critically essential to evaluate cell behaviours in not only a 2D environment, but also in a 3D organotypic condition which mimicks the in vivo environment. This system will allow high-resolution imaging using cover glass-based dishes in tissue or organ culture with 3D tracking of single cell migration in vitro and ex vivo and can be an intermediate step before moving onto in vivo paradigms.

This protocol demonstrates methods used to establish 2D and 3D environments in custom-designed electrotactic chambers, which can track cells in vivo/ex vivo using time-lapse recording at the single cell level, in order to investigate galvanotaxis/electrotaxis and other cellular responses to direct current (DC) electric fields (EFs).

Endogenous electric fields (EFs) occur naturally in vivo and play a critical role during tissue/organ development and regeneration, including that of the ...

Bioengineering

Evaluation of Cancer Stem Cell Migration Using Compartmentalizing Microfluidic Devices and Live Cell Imaging

In the last 40 years, the United States invested over 200 billion dollars on cancer research, resulting in only a 5% decrease in death rate. A major obstacle for improving patient outcomes is the poor understanding of mechanisms underlying cellular migration associated with aggressive cancer cell invasion, metastasis and therapeutic resistance1. Glioblastoma Multiforme (GBM), the most prevalent primary malignant adult brain tumor2, exemplifies this difficulty. Despite standard surgery, radiation and chemotherapies, patient median survival is only fifteen months, due to aggressive GBM infiltration into adjacent brain and rapid cancer recurrence2. The interactions of aberrant cell migratory mechanisms and the tumor microenvironment likely differentiate cancer from normal cells3. Therefore, improving therapeutic approaches for GBM require a better understanding of cancer cell migration mechanisms. Recent work suggests that a small subpopulation of cells within GBM, the brain tumor stem cell (BTSC), may be responsible for therapeutic resistance and recurrence. Mechanisms underlying BTSC migratory capacity are only starting to be characterized1,4.
Due to a limitation in visual inspection and geometrical manipulation, conventional migration assays5 are restricted to quantifying overall cell populations. In contrast, microfluidic devices permit single cell analysis because of compatibility with modern microscopy and control over micro-environment6-9.
We present a method for detailed characterization of BTSC migration using compartmentalizing microfluidic devices. These PDMS-made devices cast the tissue culture environment into three connected compartments: seeding chamber, receiving chamber and bridging microchannels. We tailored the device such that both chambers hold sufficient media to support viable BTSC for 4-5 days without media exchange. Highly mobile BTSCs initially introduced into the seeding chamber are isolated after migration though bridging microchannels to the parallel receiving chamber. This migration simulates cancer cellular spread through the interstitial spaces of the brain. The phase live images of cell morphology during migration are recorded over several days. Highly migratory BTSC can therefore be isolated, recultured, and analyzed further. 
Compartmentalizing microfluidics can be a versatile platform to study the migratory behavior of BTSCs and other cancer stem cells. By combining gradient generators, fluid handling, micro-electrodes and other microfluidic modules, these devices can also be used for drug screening and disease diagnosis6. Isolation of an aggressive subpopulation of migratory cells will enable studies of underlying molecular mechanisms.

A compartmentalizing microfluidic device for investigating cancer stem cell migration is described. This novel platform creates a viable cellular microenvironment and enables microscopic visualization of live cell locomotion. Highly motile cancer cells are isolated to study molecular mechanisms of aggressive infiltration, potentially leading to more effective future therapies.

In the last 40 years, the United States invested over 200 billion dollars on cancer research, resulting in only a 5% decrease in death rate. A major ...

Medicine

Migratory Behavior of Cells Generated in Ganglionic Eminence Cultures

Migration of cells is a common process that leads to the development and maturation of the vertebrate central nervous system (Hatten, '99). The cerebral cortex consists of two basic neuronal types: excitatory and inhibitory. These cells arise in distinct areas and migrate into the cortex along different routes (Pearlman et al., '98). Inhibitory interneurons migrate tangentially from subcortical sources, mostly from different regions of the ganglionic eminences (Gelman et al., '09; Xu et al., '04). Their movement requires precise spatiotemporal control imposed by environmental cues, to allow for the establishment of proper cytoarchitecture and connectivity in the cerebral cortex (Caviness &amp; Rakic, '78; Hatten, '90; Rakic, '90). To study the migratory behavior of cells generated in proliferative zones of the ganglionic eminences (GE) in newborn ferrets in vitro we used a 3 dimensional culture arrangement in a BD Matrigel Matrix. The culture setup consisted of two GE explants and a source of tested proteins extracted from the cerebral cortex and adsorbed on fluorescent latex Retrobeads IX positioned between the explants (Hasling et al., '03; Riddle et al., '97). After 2-3 days of culture, the cells start to appear at the edge of the explant showing a propensity to leave the tissue in a radial direction. Live imaging allowed observation of migratory patterns without the necessity of labeling or marking the cells. When exposed to fractions of the protein extract obtained from isochronic ferret cortex, the GE cells displayed different behaviors as judged by quantitative kinetic analysis of individual moving cells.

Time lapse imaging of 3D tissue culture allows studying migratory behavior of individual cells originating from ganglionic eminence in reaction to fractionated protein extract from cerebral cortex.

Migration of cells is a common process that leads to the development and maturation of the vertebrate central nervous system (Hatten, '99). The cerebral ...

Neuroscience

Live-Cell Imaging Assays to Study Glioblastoma Brain Tumor Stem Cell Migration and Invasion

Glioblastoma (GBM) is an aggressive brain tumor that is poorly controlled with the currently available treatment options. Key features of GBMs include rapid proliferation and pervasive invasion into the normal brain. Recurrence is thought to result from the presence of radio- and chemo-resistant brain tumor stem cells (BTSCs) that invade away from the initial cancerous mass and, thus, evade surgical resection. Hence, therapies that target BTSCs and their invasive abilities may improve the otherwise poor prognosis of this disease. Our group and others have successfully established and characterized BTSC cultures from GBM patient samples. These BTSC cultures demonstrate fundamental cancer stem cell properties such as clonogenic self-renewal, multi-lineage differentiation, and tumor initiation in immune-deficient mice. In order to improve on the current therapeutic approaches for GBM, a better understanding of the mechanisms of BTSC migration and invasion is necessary. In GBM, the study of migration and invasion is restricted, in part, due to the limitations of existing techniques which do not fully account for the in vitro growth characteristics of BTSCs grown as neurospheres. Here, we describe rapid and quantitative live-cell imaging assays to study both the migration and invasion properties of BTSCs. The first method described is the BTSC migration assay which measures the migration toward a chemoattractant gradient. The second method described is the BTSC invasion assay which images and quantifies a cellular invasion from neurospheres into a matrix. The assays described here are used for the quantification of BTSC migration and invasion over time and under different treatment conditions.

Here, we describe live-cell imaging techniques to quantitatively measure the migration and invasion of glioblastoma brain tumor stem cells over time and under multiple treatment conditions.

Glioblastoma (GBM) is an aggressive brain tumor that is poorly controlled with the currently available treatment options. Key features of GBMs include ...

Cancer Research

Analysis of Trunk Neural Crest Cell Migration using a Modified Zigmond Chamber Assay

Neural crest cells (NCCs) are a transient population of cells present in vertebrate development that emigrate from the dorsal neural tube (NT) after undergoing an epithelial-mesenchymal transition 1,2. Following EMT, NCCs migrate large distances along stereotypic pathways until they reach their targets. NCCs differentiate into a vast array of cell types including neurons, glia, melanocytes, and chromaffin cells 1-3. The ability of NCCs to reach and recognize their proper target locations is foundational for the appropriate formation of all structures containing trunk NCC-derived components 3. Elucidating the mechanisms of guidance for trunk NCC migration has therefore been a matter of great significance. Numerous molecules have been demonstrated to guide NCC migration 4. For instance, trunk NCCs are known to be repelled by negative guidance cues such as Semaphorin, Ephrin, and Slit ligands 5-8. However, not until recently have any chemoattractants of trunk NCCs been identified 9. 
Conventional in vitro approaches to studying the chemotactic behavior of adherent cells work best with immortalized, homogenously distributed cells, but are more challenging to apply to certain primary stem cell cultures that initially lack a homogenous distribution and rapidly differentiate (such as NCCs). One approach to homogenize the distribution of trunk NCCs for chemotaxis studies is to isolate trunk NCCs from primary NT explant cultures, then lift and replate them to be almost 100% confluent. However, this plating approach requires substantial amounts of time and effort to explant enough cells, is harsh, and distributes trunk NCCs in a dissimilar manner to that found in in vivo conditions. 
Here, we report an in vitro approach that is able to evaluate chemotaxis and other migratory responses of trunk NCCs without requiring a homogenous cell distribution. This technique utilizes time-lapse imaging of primary, unperturbed trunk NCCs inside a modified Zigmond chamber (a standard Zigmond chamber is described elsewhere10). By exposing trunk NCCs at the periphery of the culture to a chemotactant gradient that is perpendicular to their predicted natural directionality, alterations in migratory polarity induced by the applied chemotactant gradient can be detected. This technique is inexpensive, requires the culturing of only two NT explants per replicate treatment, avoids harsh cell lifting (such as trypsinization), leaves trunk NCCs in a more similar distribution to in vivo conditions, cuts down the amount of time between explantation and experimentation (which likely reduces the risk of differentiation), and allows time-lapse evaluation of numerous migratory characteristics.

An approach to analyze the migration of explanted cells (trunk neural crest cells) is described. This method is inexpensive, gentle, and capable of distinguishing chemotaxis from both chemokinesis and other influences on migratory polarity such as those derived from cell-cell interactions within the primary trunk neural crest cell culture.

Neural crest cells (NCCs) are a transient population of cells present in vertebrate development that emigrate from the dorsal neural tube (NT) after ...

Study of Cell Migration in Microfabricated Channels

The method described here allows the study of cell migration under confinement in one dimension. It is based on the use of microfabricated channels, which impose a polarized phenotype to cells by physical constraints. Once inside channels, cells have only two possibilities: move forward or backward. This simplified migration in which directionality is restricted facilitates the automatic tracking of cells and the extraction of quantitative parameters to describe cell movement. These parameters include cell velocity, changes in direction, and pauses during motion. Microchannels are also compatible with the use of fluorescent markers and are therefore suitable to study localization of intracellular organelles and structures during cell migration at high resolution. Finally, the surface of the channels can be functionalized with different substrates, allowing the control of the adhesive properties of the channels or the study of haptotaxis. In summary, the system here described is intended to analyze the migration of large cell numbers in conditions in which both the geometry and the biochemical nature of the environment are controlled, facilitating the normalization and reproducibility of independent experiments.

A quantitative method to study spontaneous migration of cells in a one-dimensional confined microenvironment is described. This method takes advantage of microfabricated channels and can be used to study migration of large number of cells under different conditions in single experiments.

The method described here allows the study of cell migration under confinement in one dimension. It is based on the use of microfabricated channels, which ...

A Galvanotaxis Assay for Analysis of Neural Precursor Cell Migration Kinetics in an Externally Applied Direct Current Electric Field

The discovery of neural stem and progenitor cells (collectively termed neural precursor cells) (NPCs) in the adult mammalian brain has led to a body of research aimed at utilizing the multipotent and proliferative properties of these cells for the development of neuroregenerative strategies. A critical step for the success of such strategies is the mobilization of NPCs toward a lesion site following exogenous transplantation or to enhance the response of the endogenous precursors that are found in the periventricular region of the CNS. Accordingly, it is essential to understand the mechanisms that promote, guide, and enhance NPC migration. Our work focuses on the utilization of direct current electric fields (dcEFs) to promote and direct NPC migration - a phenomenon known as galvanotaxis. Endogenous physiological electric fields function as critical cues for cell migration during normal development and wound repair. Pharmacological disruption of the trans-neural tube potential in axolotl embryos causes severe developmental malformations1. In the context of wound healing, the rate of repair of wounded cornea is directly correlated with the magnitude of the epithelial wound potential that arises after injury, as shown by pharmacological enhancement or disruption of this dcEF2-3. We have demonstrated that adult subependymal NPCs undergo rapid and directed cathodal migration in vitro when exposed to an externally applied dcEF. In this protocol we describe our lab's techniques for creating a simple and effective galvanotaxis assay for high-resolution, long-term observation of directed cell body translocation (migration) on a single-cell level. This assay would be suitable for investigating the mechanisms that regulate dcEF transduction into cellular motility through the use of transgenic or knockout mice, short interfering RNA, or specific receptor agonists/antagonists.

In this protocol we demonstrate how to construct custom chambers that permit the application of a direct current electric field to enable time-lapse imaging of adult brain derived neural precursor cell translocation during galvanotaxis.

The discovery of neural stem and progenitor  cells (collectively termed neural precursor cells) (NPCs) in the adult  mammalian brain has led to a body of ...

Planar Gradient Diffusion System to Investigate Chemotaxis in a 3D Collagen Matrix

The importance of cell migration can be seen through the development of human life. When cells migrate, they generate forces and transfer these forces to their surrounding area, leading to cell movement and migration. In order to understand the mechanisms that can alter and/or affect cell migration, one can study these forces. In theory, understanding the fundamental mechanisms and forces underlying cell migration holds the promise of effective approaches for treating diseases and promoting cellular transplantation. Unfortunately, modern chemotaxis chambers that have been developed are usually restricted to two dimensions (2D) and have complex diffusion gradients that make the experiment difficult to interpret. To this end, we have developed, and describe in this paper, a direct-viewing chamber for chemotaxis studies, which allows one to overcome modern chemotaxis chamber obstacles able to measure cell forces and specific concentration within the chamber in a 3D environment to study cell 3D migration. More compelling, this approach allows one to successfully model diffusion through 3D collagen matrices and calculate the coefficient of diffusion of a chemoattractant through multiple different concentrations of collagen, while keeping the system simple and user friendly for traction force microscopy (TFM) and digital volume correlation (DVC) analysis.

Cell migration is an important part of human development and life. In order to understand the mechanisms that can alter cell migration, we present a planar gradient diffusion system to investigate chemotaxis in a 3D collagen matrix, which allows one to overcome modern diffusion chamber limitations of existing assays.

The importance of cell migration can be seen through the development of human life. When cells migrate, they generate forces and transfer these forces to ...

Measurement of Cellular Chemotaxis with ECIS/Taxis

Cellular movement in response to external stimuli is fundamental to many cellular processes including wound healing, inflammation and the response to infection. A common method to measure chemotaxis is the Boyden chamber assay, in which cells and chemoattractant are separated by a porous membrane. As cells migrate through the membrane toward the chemoattractant, they adhere to the underside of the membrane, or fall into the underlying media, and are subsequently stained and visually counted 1. In this method, cells are exposed to a steep and transient chemoattractant gradient, which is thought to be a poor representation of gradients found in tissues 2.
Another assay system, the under-agarose chemotaxis assay, 3, 4 measures cell movement across a solid substrate in a thin aqueous film that forms under the agarose layer. The gradient that develops in the agarose is shallow and is thought to be an appropriate representation of naturally occurring gradients. Chemotaxis can be evaluated by microscopic imaging of the distance traveled. Both the Boyden chamber assay and the under-agarose assay are usually configured as endpoint assays.
The automated ECIS/Taxis system combines the under-agarose approach with Electric Cell-substrate Impedance Sensing (ECIS) 5, 6. In this assay, target electrodes are located in each of 8 chambers. A large counter-electrode runs through each of the 8 chambers (Figure 2). Each chamber is filled with agarose and two small wells are the cut in the agarose on either side of the target electrode. One well is filled with the test cell population, while the other holds the sources of diffusing chemoattractant (Figure 3). Current passed through the system can be used to determine the change in resistance that occurs as cells pass over the target electrode. Cells on the target electrode increase the resistance of the system 6. In addition, rapid fluctuations in the resistance represent changes in the interactions of cells with the electrode surface and are indicative of ongoing cellular shape changes. The ECIS/Taxis system can measure movement of the cell population in real-time over extended periods of time, but is also sensitive enough to detect the arrival of a single cell at the target electrode. 
Dictyostelium discoidium is known to migrate in the presence of a folate gradient 7, 8 and its chemotactic response can be accurately measured by ECIS/Taxis 9. Leukocyte chemotaxis, in response to SDF1&alpha; and to chemotaxis antagonists has also been measured with ECIS/Taxis 10, 11. An example of the leukocyte response to SDF1&alpha; is shown in Figure 1.

The ECIS/Taxis system is an automated, real-time assay that measures cellular chemotaxis. In this assay, cells move beneath a layer of agarose to arrive at a target electrode. Cellular movement is measured by the onset of resistance to AC current 0.

Cellular movement in response to external stimuli is fundamental to many cellular processes including wound healing, inflammation and the response to ...

Imaging G Protein-coupled Receptor-mediated Chemotaxis and its Signaling Events in Neutrophil-like HL60 Cells

Eukaryotic cells sense and move towards a chemoattractant gradient, a cellular process referred as chemotaxis. Chemotaxis plays critical roles in many physiological processes, such as embryogenesis, neuron patterning, metastasis of cancer cells, recruitment of neutrophils to sites of inflammation, and the development of the model organism Dictyostelium discoideum. Eukaryotic cells sense chemo-attractants using G protein-coupled receptors. Visual chemotaxis assays are essential for a better understanding of how eukaryotic cells control chemoattractant-mediated directional cell migration. Here, we describe detailed methods for: 1) real-time, high-resolution monitoring of multiple chemotaxis assays, and 2) simultaneously visualizing the chemoattractant gradient and the spatiotemporal dynamics of signaling events in neutrophil-like HL60 cells.

Visual chemotaxis assays are essential for a better understanding of how eukaryotic cells control chemoattractant-mediated directional cell migration. Here, we describe detailed methods for: 1) real-time, high-resolution monitoring of multiple chemotaxis assays, and 2) simultaneously visualizing the chemoattractant gradient and the spatiotemporal dynamics of signaling events in neutrophil-like HL60 cells.

Eukaryotic cells sense and move towards a chemoattractant gradient, a cellular process referred as chemotaxis. Chemotaxis plays critical roles in many ...