Here we describe methods for assessing cellular response to acute mechanical stimulation. In the microscopy-based assay, we examine localization of fluorescently-labeled biosensors following brief stimulation with shear flow. We also test activation of various proteins of interest in response to acute mechanical stimulation biochemically.
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Method Article
Assessment of Dictyostelium discoideum Response to Acute Mechanical Stimulation
In This Article
Summary
Abstract
Chemotaxis, or migration up a gradient of a chemoattractant, is the best understood mode of directed migration. Studies using social amoeba Dictyostelium discoideum revealed that a complex signal transduction network of parallel pathways amplifies the response to chemoattractants, and leads to biased actin polymerization and protrusion of a pseudopod in the direction of a gradient. In contrast, molecular mechanisms driving other types of directed migration, for example, due to exposure to shear flow or electric fields, are not known. Many regulators of chemotaxis exhibit localization at the leading or lagging edge of a migrating cell, as well as show transient changes in localization or activation following global stimulation with a chemoattractant. To understand the molecular mechanisms of other types of directed migration we developed a method that allows examination of cellular response to acute mechanical stimulation based on brief (2 - 5 s) exposure to shear flow. This stimulation can be delivered in a channel while imaging cells expressing fluorescently-labeled biosensors to examine individual cell behavior. Additionally, cell population can be stimulated in a plate, lysed, and immunoblotted using antibodies that recognize active versions of proteins of interest. By combining both assays, one can examine a wide array of molecules activated by changes in subcellular localization and/or phosphorylation. Using this method we determined that acute mechanical stimulation triggers activation of the chemotactic signal transduction and actin cytoskeleton networks. The ability to examine cellular responses to acute mechanical stimulation is important for understanding the initiating events necessary for shear flow-induced motility. This approach also provides a tool for studying the chemotactic signal transduction network without the confounding influence of the chemoattractant receptor.
Introduction
Migration of eukaryotic cells is biased by diverse chemical and physical cues in the environment, including gradients of soluble or substrate-bound chemoattractants, variable stiffness of the substrates, electric fields, or shear flow. Although there have been many advances in our understanding of the molecular mechanisms driving chemotaxis, less is known about other types of directed migration and how these diverse signals are integrated at the cellular level to produce a unified migratory response.
Directed migration toward an increasing concentration of a chemoattractant involves three behavioral components: motility, directional sensing....
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Protocol
1. Preparation of Solutions
- Prepare HL-5 media using the following: 10 g/L dextrose, 10 g/L proteose peptone, 5 g/L yeast extract, 0.965 g/L Na2HPO4·7H2O, 0.485 g/L KH2PO4, and, unless otherwise indicated, 0.03 g/L streptomycin in deionized water. Autoclave the medium and store at room temperature.
NOTE: Due to differences between proteose peptone and yeast extract acquired from different suppliers, as well as between individual batches, pH of the media may need to be adjusted to the typical range of 6.4 to 6.7. - Prepare SM plates using the following: 10 g/L dextrose, 10 g/L pepton....
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Results
Temporal response of chemotaxis regulators to acute mechanical stimulation
To assess the response of D. discoideum cells to mechanical stimulation, adherent aggregation-competent cells were exposed to a brief pulse of shear flow. Aggregation-competent D. discoideum cells secrete cAMP, which can be sensed by neighboring cells. To overcome the contribution of cell-cell signaling, cells were treated with caffeine, wh.......
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Discussion
The methods described here offer a convenient way to assess both population and individual cell behavior in response to shear flow. Importantly, while previous studies analyzed localization of leading and lagging edge markers during migration, the current approach allows investigation of immediate effects by applying the shear flow acutely. Using this method we demonstrated that, in fact, the initial response of cells to shear flow does not require cell migration. Instead, the rapid and transient response to the initial .......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by National Institutes of Health grant R35 GM118177 to PND.
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Reagents | |||
| Dextrose | Fisher | D16-1 | Use to prepare HL-5 media and SM plates (steps 1.1, 1.2) |
| Proteose peptone | Fisher | DF0120-17-6 | Use to prepare HL-5 media (step 1.1) |
| Yeast extract | Fisher | 50-550-445 | Use to prepare HL-5 media and SM plates (steps 1.1, 1.2) |
| Na2HPO4·7H2O | Fisher | S373-500 | Use to prepare HL-5 media, and 10X Phosphate Buffer (steps 1.1, 1.3) |
| KH2PO4 | Fisher | P386-500 | Use to prepare HL-5 media, SM plates, and 10X Phosphate Buffer (steps 1.1-1.3) |
| Streptomycin (dihydrostreptomycin sulfate) | Fisher | ICN10040525 | Use to prepare HL-5 media (step 1.1) |
| Peptone (Bacto) | Fisher | DF0118-17-0 | Use to prepare SM plates (step 1.2) |
| K2HPO4 | Fisher | P288-100 | Use to prepare SM plates (step 1.2) |
| Agar | Fisher | BP1423-500 | Use to prepare SM plates (step 1.2) |
| MgSO4 | Fisher | M65-500 | Use to prepare DB Buffer (step 1.4) |
| CaCl2 | Fisher | C79-500 | Use to prepare DB Buffer (step 1.4) |
| Caffeine | Fisher | O1728-500 | Use to prepare caffeine (step 1.5) |
| cAMP (EMD Millipore Calbiochem Adenosine 3 ft.,5 ft.-cyclic Monophosphate, Sodium Salt) | Fisher | 11-680-1100MG | Use to prepare cAMP (step 1.6) |
| Folic acid | Sigma | F7876 | Use to prepare folic acid (step 1.7) |
| Tris base | Fisher | BP152-500 | Use to prepare 3X sample buffer (step 1.8) |
| Sodium dodecyl sulfate (SDS) | Fisher | BP166-500 | Use to prepare 3X sample buffer (step 1.8) |
| Glycerol | Fisher | G33-500 | Use to prepare 3X sample buffer (step 1.8) |
| Dithiothreitol (DTT) | Bio-Rad | 1610610 | Use to prepare 3X sample buffer (step 1.8) |
| Bromophenol blue | Bio-Rad | 1610404 | Use to prepare 3X sample buffer (step 1.8) |
| NaF | Fisher | S299-100 | Use to prepare sample buffer with protease and phosphatase inhibitors (step 1.8) |
| Na3VO4 | Fisher | 50-994-911 | Use to prepare sample buffer with protease and phosphatase inhibitors (step 1.8) |
| Sodium pyrophosphate decahydrate | Fisher | S390-500 | Use to prepare sample buffer with protease and phosphatase inhibitors (step 1.8) |
| Complete EDTA-free protease inhibitor cocktail (Roche) | Sigma | 11873580001 | Use to prepare sample buffer with protease and phosphatase inhibitors (step 1.8) |
| Latrunculin A | Enzo Life Sciences | BML-T119-0100 | Use to prepare Latrunculin A (step 1.9) |
| 4-15% Tris-HCl polyacrylamide gel | Bio-Rad | 3450029 | Use for immunoblotting (step 3.3) |
| Polyvinylidene fluoride membrane | Bio-Rad | 1620177 | Use for immunoblotting (step 3.3) |
| Phospho-PKC (pan) (zeta Thr410) (190D10) Rabbit antibody | Cell Signaling | 2060 | Primary antibody for use in immunoblotting (step 3.3) |
| Phospho-p44/42 MAPK (Erk1/2) (Thr202/Tyr204) (D13.14.4E) XP antibody | Cell Signaling | 4370 | Primary antibody for use in immunoblotting (step 3.3) |
| Rabbit IgG HRP Linked Whole Ab (from Donkey) | GE Healthcare | NA934-100UL | Secondary antibody for use in immunoblotting (step 3.3) |
| Enhanced chemiluminescence substrate (Clarity Western ECL Substrate) | Bio-Rad | 1705060 | Use for immunoblotting (step 3.3) |
| Stripping buffer (Restore Plus Western blot stripping buffer) | Pierce | PI46430 | Use for immunoblotting (step 3.3) |
| Coomassie Brilliant Blue | Fisher | PI20278 | Use for immunoblotting (step 3.3) |
| K. aerogenes strain (non-pathogenic) | Dicty Stock Center (dictybase.org) | ||
| Name | Company | Catalog Number | Comments |
| Materials and Equipment | |||
| Orbital shaker (model G-33, or a comparable alternative) | New Brunswick Scientific | Use to grow K. aerogenes (step 2.1.1), and to basalate and stimulate D. discoideum cells (step 3). The radius of gyration for this shaker is 9.5 mm. | |
| 10 cm Petri dish | Fisher | FB0875712 | Use to prepare SM plates (step 1.2) |
| Hemocytometer | Fisher | 02-671-51B | Use to count D. discoideum cells (step 2.1.2) |
| 35 mm dish (Corning Falcon Easy-Grip Tissue Culture Dish) | Fisher | 08-772A | Use to plate D. discoideumcells for mechanical stimulation followed by cell lysis (step 3.1.1) |
| Polystyrene cup (5 mL) | VWR | 13915-985 | Use to stimulate D. discoideum cell suspension with a chemoattractant (step 3.2.2) |
| Fluidic unit with pump (ibidi Pump System) | Ibidi | 10902 | Use to deliver mechanical stimulation to D. discoideum cells in a channel (steps 4.1, 4.2, and 5) |
| Slide with a channel (μ-Slide III 3in1 ibiTreat: #1.5 polymer coverslip, tissue culture treated, sterilized) | Ibidi | 80316 | Use to plate D. discoideum cells for mechanical stimulation delivered by a fluidic device (steps 4.1, 4.2, and 5) |
| 50 mL reservoirs (Ibidi Reservoir Holder for Fluidic Unit) | Ibidi | 10978 | Use to setup the fluidic device for delivering mechanical stimulation to D. discoideum cells in a channel (steps 4.1, 4.2, and 5) |
| Lines for the fluidic unit (Perfusion Set YELLOW-and-GREEN) | Ibidi | 10964 | Use to setup the fluidic device for delivering mechanical stimulation to D. discoideum cells in a channel (steps 4.1, 4.2, and 5). Note: the two lines can also be cut from the 1.6 mm tubing (catalog number 10842). |
| Line for the drain (1.6 mm ID tubing) | Ibidi | 10842 | Use to setup the fluidic device for delivering mechanical stimulation to D. discoideum cells in a channel (steps 4.1, 4.2, and 5). |
| Zeiss Observer.Z1 inverted microscope equipped with a 40X/1.3 oil objective and a 20X/0.3 air objective (or a comparable alternative) | Zeiss | Used to image D. discoideum cells with phase-contrast or fluorescence illumination (steps 4 and 5) | |
| UltraView spinning disk confocal microscope equipped with a 40×/1.25–0.75 oil objective (or a comparable alternative) | Perkin-Elmer | DM 16000 | An alternative used to image D. discoideum cells (step 4.1.4) |
| FemtoJet Microinjector (Eppendorf; model 5247, or a comparable alternative) with Eppendorf InjectMan | Eppendorf | 5252000021D and 5192000027 | Use to deliver mechanical stimulation to D. discoideum cells by a micropipette (step 4.3). Note: catalog number are for the newest version of the equipment (4i). |
| Micropipette (Femtotip; 1 μm outside diameter, 0.5 μm inside diameter ) | Eppendorf | 930000035 | Use to deliver mechanical stimulation to D. discoideum cells by a micropipette (step 4.3) |
| Microloader tips (Eppendorf Femtotips Microloader Tips for Femtojet Microinjector) | Eppendorf | 5242956.003 | Use to fill the micropipette (femtotip) with buffer (step 4.3.1) |
| 1-well chamber (Thermo Scientific Nunc Lab-Tek Chambered Coverglass) | Fisher | 12-565-472 | Use to plate D. discoideum cells for mechanical stimulation delivered by a micropipette (step 4.3.2) |
| 8-well chamber (Thermo Scientific Nunc Lab-Tek II Chambered Coverglass) | Fisher | 12-565-338 | Use to plate D. discoideum cells for mechanical stimulation delivered by bulk buffer addition (step 4.4.1) |
| Name | Company | Catalog Number | Comments |
| Software | |||
| Image Analysis Software (Fiji) | NIH | https://fiji.sc/ | Use to quantify response to mechanical stimulation (step 4.5) |
| Migration analysis software (Tracking Tool PRO) | Gradientech | http://gradientech.se/tracking-tool-pro/ | Use to quantify cell speed and persistence (step 5.4) |
References
- Swaney, K. F., Huang, C. H., Devreotes, P. N. Eukaryotic chemotaxis: a network of signaling pathways controls motility, directional sensing, and polarity. Annu Rev Biophys. 39, 265-289 (2010).
- Sasaki, A. T., Chun, C., Takeda, K., Firtel, R. A.
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