Name: a temperature gradient assay to determine thermal preferences of drosophila larvae
Uploaded: 2018-06-25T14:30:00
Description: Watch this Scientific Journal Video about A Temperature Gradient Assay to Determine Thermal Preferences of Drosophila Larvae at JoVE.com

C.M. is supported by funding from the NEI (EY008117, EY010852), NIDCD (DC007864, DC016278) and the NIAID (1DP1AI124453).

1. Equipment Fabrication and Assembling Apparatus for Gradient Assays
<ol>
	<li>Fabricate the aluminum assay plates for the single-directional gradient assay.
	<ol>
		<li>Trim and grind each aluminum assay plate (Figure 1A) out of a single piece of aluminum using a band saw and sharp vertical mill with the following dimensions: the outer size is 140 x 100 x 9 mm and the inner size is 130 x 90 x 8 mm (Figure 1B). Anodize the inside of each assay plate with blac...

<ol>
	<li>Fowler, M. A., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drosophila+TRP+channels+and+animal+behavior.">Drosophila TRP channels and animal behavior.</a> Life Sci. 92, 394-403 (2013).</li><li>Palkar, R., Lippoldt, E. K., McKemy, D. 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+molecular+and+cellular+basis+of+thermosensation+in+mammals.">The molecular and cellular basis of thermosensation in mammals.</a> Curr Opin Neurobiol. 34, 14-19 (2015).</li><li>Vriens, J., Nilius, B., Voets, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Peripheral+thermosensation+in+mammals.">Peripheral thermosensation in mammals.</a> Nat Rev Neurosci. 15 (9), 573-589 (2014).</li><li>Rosenzweig, 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=The+Drosophila+ortholog+of+vertebrate+TRPA1+regulates+thermotaxis.">The Drosophila ortholog of vertebrate TRPA1 regulates thermotaxis.</a> Genes Dev. 19, 419-424 (2005).</li><li>Kwon, Y., Shim, H. S., Wang, X., Montell, C. <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+thermotactic+behavior+via+coupling+of+a+TRP+channel+to+a+phospholipase+C+signaling+cascade.">Control of thermotactic behavior via coupling of a TRP channel to a phospholipase C signaling cascade.</a> Nat Neurosci. 11, 871-873 (2008).</li><li>Kwon, Y., Shen, W. L., Shim, H. S., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fine+thermotactic+discrimination+between+the+optimal+and+slightly+cooler+temperatures+via+a+TRPV+channel+in+chordotonal+neurons.">Fine thermotactic discrimination between the optimal and slightly cooler temperatures via a TRPV channel in chordotonal neurons.</a> J Neurosci. 30 (31), 10465-10471 (2010).</li><li>Shen, W. L., 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=Function+of+rhodopsin+in+temperature+discrimination+in+Drosophila.">Function of rhodopsin in temperature discrimination in Drosophila.</a> Science. 331 (6022), 1333-1336 (2011).</li><li>Sokabe, T., Chen, H. S., Luo, J., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+switch+in+thermal+preference+in+Drosophila+larvae+depends+on+multiple+rhodopsins.">A switch in thermal preference in Drosophila larvae depends on multiple rhodopsins.</a> Cell Rep. 17, 336-344 (2016).</li><li>Ni, L., 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+Ionotropic+Receptors+IR21a+and+IR25a+mediate+cool+sensing+in+Drosophila.">The Ionotropic Receptors IR21a and IR25a mediate cool sensing in Drosophila.</a> Elife. 5, 13254 (2016).</li><li>Luo, L., 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=Navigational+decision+making+in+Drosophila+thermotaxis.">Navigational decision making in Drosophila thermotaxis.</a> J Neurosci. 30 (12), 4261-4272 (2010).</li><li>Ashburner, M., Golic, K. G., Hawley, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Drosophila: a laboratory handbook. , (2005).</li></ol>

To ensure the success of this protocol, it is important to take steps to obtain adequate numbers of larvae to perform the experiments. These include pre-feeding the flies in yeast paste-containing vials for 2-3 d to improve egg laying. The vials need to be placed in a tray containing water vials and enclosed in a clear plastic bag, which maintains the moisture of the food and promotes effective feeding by the larvae while permitting exposure to normal light-dark cycles. However, the yeast paste should not be so soft that...

Thermotaxis is employed by mobile animals to select an environment with the most favorable conditions1,2,3. If the climate is excessively hot or cold, this behavior is vital for the survival. In addition, many animals are sensitive to very small differences in temperature in the comfortable range and seek out surroundings with an ideal temperature. This is of particular importance for poikilothermic organisms such as fruit flies, which equilibrate their body temperature with the environment. Assays to monitor larval thermotaxis have been instrumental in identifying and clarifying the roles of molecular sensors such as Drosophila Transient Receptor Potential (TRP) channels4,5,6, rhodopsins7,8, and ionotropic receptor receptors (IRs)9, which endow these animals with temperature sensitivities over different temperature ranges.
A two-way choice test provides one approach to study thermal preferences in larvae6,7. The assay entails establishing two distinct temperature zones and allows&#160;the animals to select one side over the other. The results from two-way choice tests can be robust, especially if the temperature differences between the two options are&#160;large. In addition, since each assay involves tabulating only two groups, the data can be expressed as a simple preference index. The ease and simplicity of two-way choice assays are also amenable to genetic screens. However, a major limitation is that many experiments are required to establish the preferred temperature of the wild-type or mutant animals.
A gradient assay offers the opportunity to establish the preferred temperature in a single assay8. Moreover, unlike the two-way choice test, it permits the evaluation of the distribution of a group of animals, when confronted with a continuous range of temperatures. One gradient assay uses a Petri dish and single animals and is well-suited for characterizing the detailed behavior of individual animals10. However, since Petri dishes are round, the sizes of the temperature zones vary and are progressively smaller depending on the distance from the center. Therefore, this setup is not ideal for monitoring the temperature selections of populations of animals.
A continuous thermal gradient apparatus that is well-suited to assess the temperature preferences of groups of larvae employs a rectangular arena and is described here. The apparatus is simple to construct and assemble. In addition, the gradient is linear, and is flexible, as it can be used to assess thermotaxis over large temperature ranges from 10 &#176;C to 42 &#176;C. The assay is rapid and straightforward to perform and yields reproducible data. In addition to reporting the favored temperature of larvae, it reveals the preferences of the population of animals over an entire linear range in a single experiment. Due to these advantages, it is an excellent choice for identifying genes required for thermotaxis.

<table>
	<tbody>
		<tr>
			<td>Gradient assay apparatus</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PolyScience 9106, Refrigerated/Heated 6L Circulating Bath</td>
			<td>Thomas Scientific</td>
			<td>9106</td>
			<td>This model is discontinued. Updated replacement models include: 1186R00 and 1197U04 for 120 V, 60 Hz, or 1184L08 and 1197U04 for 240 V, 50 Hz.</td>
		</tr>
		<tr>
			<td>Aluminum assay plate (for single directional gradient)</td>
			<td></td>
			<td></td>
			<td>Outer size: 14 x 10.1 x 0.9 cm, inner size: 12.9 x 8.7 x 0.8 cm, black anodized.</td>
		</tr>
		<tr>
			<td>Aluminum plate (for bidirectional gradient)</td>
			<td></td>
			<td></td>
			<td>25 x 22 x 0.2 cm, black anodized.</td>
		</tr>
		<tr>
			<td>Aluminum block</td>
			<td></td>
			<td></td>
			<td>Outer size: 25.5 x 5 x 1.4 cm, parameters of inner channels are shown in Figure 1D.</td>
		</tr>
		<tr>
			<td>Connector for aluminum blocks and tubing</td>
			<td>McMaster-Carr</td>
			<td>91355K82</td>
			<td></td>
		</tr>
		<tr>
			<td>Tygon Sanitary Silicone Tubing</td>
			<td>Tygon</td>
			<td>57296</td>
			<td>1/4&#34; ID x 3/8&#34; OD x 1/16&#34; wall</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Items and reagents for assay</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Pestle</td>
			<td>USA Scientific</td>
			<td>17361</td>
			<td>Pestle for 1.5 mL microcentrifuge tubes</td>
		</tr>
		<tr>
			<td>Thermometer</td>
			<td>Fluke</td>
			<td>51II</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermocouple</td>
			<td>Fluke</td>
			<td>K type</td>
			<td></td>
		</tr>
		<tr>
			<td>Universal microplate lid</td>
			<td>Corning</td>
			<td>6980A77</td>
			<td></td>
		</tr>
		<tr>
			<td>35 mm dish</td>
			<td>Corning</td>
			<td>9380D40</td>
			<td></td>
		</tr>
		<tr>
			<td>Labeling tape (for bidirectional gradient)</td>
			<td>Fisher Scientific</td>
			<td>15-951</td>
			<td>Fisherbrand labeling tape 2 in x 14 yds</td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Invitrogen</td>
			<td>16500500</td>
			<td>Prepare 1% solution</td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma</td>
			<td>S0389-5KG</td>
			<td>Prepare 18% solution right before starting assay</td>
		</tr>
		<tr>
			<td>Paint brush</td>
			<td>Fisher Scientific</td>
			<td>11860</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL centrifuge tubes</td>
			<td>Denville</td>
			<td>C1062-P</td>
			<td></td>
		</tr>
		<tr>
			<td>Scoopula</td>
			<td>Fisher Scientific</td>
			<td>14-357Q</td>
			<td></td>
		</tr>
		<tr>
			<td>500 mL round wide-mouth bottle</td>
			<td>Pyrex</td>
			<td>1395-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell strainer (300 mm pore)</td>
			<td>PluriSelect</td>
			<td>43-50300</td>
			<td>Optional item for larvae washing</td>
		</tr>
		<tr>
			<td>Cardboard box (vial tray)</td>
			<td>Genesee Scientific</td>
			<td>FS32-124</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Drosophila food</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Distilled water</td>
			<td></td>
			<td></td>
			<td>22,400 mL</td>
		</tr>
		<tr>
			<td>Cornmeal, yellow (extra fine mesh,flocked) 20 kg</td>
			<td>LabScientific Inc.</td>
			<td>NC0535320</td>
			<td>1,609 g</td>
		</tr>
		<tr>
			<td>Brewers yeast 100 lbs</td>
			<td>MP Biomedicals</td>
			<td>ICN90331280</td>
			<td>379 g</td>
		</tr>
		<tr>
			<td>NutriSoy&#174; Soy Flour (10 kg/unit)</td>
			<td>Genesee Scientific</td>
			<td>62-115</td>
			<td>221 g</td>
		</tr>
		<tr>
			<td>Drosophila Agar, Type II (5 kg)</td>
			<td>Genesee Scientific</td>
			<td>66-103</td>
			<td>190 g</td>
		</tr>
		<tr>
			<td>Karo light corn syrup</td>
			<td>Karo</td>
			<td></td>
			<td>1,700 mL</td>
		</tr>
		<tr>
			<td>Methyl 4-hydroxybenzoate (suspend in 200 proof ethanol)</td>
			<td>Sigma Aldrich</td>
			<td>H5501-5KG</td>
			<td>72 g/240 mL</td>
		</tr>
		<tr>
			<td>Propionic acid puriss. p.a.,&#62;99.5% (GC)</td>
			<td>Sigma Aldrich</td>
			<td>81910-1 L</td>
			<td>108 mL</td>
		</tr>
		<tr>
			<td>Phosphoric acid&#160;ACS reagent, &#8805;85 wt. % in H2O</td>
			<td>Sigma Aldrich</td>
			<td>438081-500 mL</td>
			<td>8.5 mL</td>
		</tr>
	</tbody>
</table>

a temperature gradient assay to determine thermal preferences of drosophila larvae

Many animals, including the fruit fly, Drosophila melanogaster, are capable of discriminating minute differences in&#160;environmental temperature, which enables them to seek out their preferred thermal landscape. To define the temperature preferences of larvae over a defined linear range, we developed an assay using a temperature gradient. To establish a single-directional gradient, two aluminum blocks are connected to independent water baths, each of which controls the temperature of individual blocks. The two blocks set the lower and upper limits of the gradient. The temperature gradient is established by placing an agarose-coated aluminum plate over the two water-controlled blocks so that the plate spans the distance between them. The ends of the aluminum plate that is set on the top of the water blocks defines the minimum and maximum temperatures, and the regions in-between the two blocks form a linear temperature gradient. The gradient assay can be applied to&#160;larvae of different ages and can be used to identify mutants that exhibit phenotypes, such as those with mutations affecting genes encoding TRP channels and opsins, which are required for temperature discrimination.

To establish an 18 &#176;C-28 &#176;C single-directional gradient, we set the temperatures of two water baths to 16.8 &#176;C and 31 &#176;C. We obtain the temperatures at 13 points by measuring the temperature at 26 positions within the upper and lower portions of all 6 zones, the border lines between the zones, and at the extreme ends of the agarose gel surface (Figure 2C, 2E). The temperature distribution along the gradient was nearly line...

Watch this Scientific Journal Video about A Temperature Gradient Assay to Determine Thermal Preferences of Drosophila Larvae at JoVE.com

A Temperature Gradient Assay to Determine Thermal Preferences of Drosophila Larvae

Here, we present a protocol to determine the preferred environmental temperature of Drosophila larvae using a continuous thermal gradient.

A Temperature Gradient Assay to Determine Thermal Preferences of Drosophila Larvae

Many animals, including the fruit fly, Drosophila melanogaster, are capable of discriminating minute differences in&#160;environmental temperature, which ...

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