The authors thank Bryan T. Vinyard of the USDA, Agricultural Research Service, Henry A. Wallace Beltsville Agricultural Research Center, Biometrical Consulting Service, Beltsville, MD for statistical analyses. This work was supported in part by a grant to J.C.D. from the Deployed War Fighter Protection (DWFP) Research Program funded by the Department of Defense through the Armed Forces Pest Management Board (AFPMB).

1. Rearing Ae. aegypti adults
<ol>
	<li>Hatch eggs in approximately &#190; inch water in shallow tray. Overcrowding will reduce the size of adults.</li>
	<li>Rear larvae at 25 &#176;C (12-hL:12-hD) and feed with ground fish food. 
	NOTE: Overfeeding may reduce survival rates.</li>
	<li>Remove pupae individually by Pasteur pipette daily and transfer to plastic dishes (9 cm &#215; 5.5 cm) inside small containment buckets with fine mesh lids, thus establishing 24 hr&#160;age groupings.</li>
	<li>Feed adult m...

<ol>
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C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gustatory+receptor+neuron+responds+to+DEET+and+other+insect+repellents+in+the+yellow-fever+mosquito,+Aedes+aegypti.">Gustatory receptor neuron responds to DEET and other insect repellents in the yellow-fever mosquito, Aedes aegypti.</a> Naturwiss. 100 (3), 269-273 (2013).</li><li>Sparks, J. T., Vinyard, B. T., Dickens, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gustatory+receptor+expression+in+the+labella+and+tarsi+of+Aedes+aegypti.">Gustatory receptor expression in the labella and tarsi of Aedes aegypti.</a> Insect Biochem. Mol. Biol. 43 (12), 1161-1171 (2013).</li><li>Kent, L. B., Walden, K. K. O., Robertson, H. 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+Gr+family+of+candidate+gustatory+and+olfactory+receptors+in+the+yellow-fever+mosquito+Aedes+aegypti.">The Gr family of candidate gustatory and olfactory receptors in the yellow-fever mosquito Aedes aegypti.</a> Chem. Senses. 33 (1), 79-93 (2008).</li><li>Ramsk&#246;ld, D., Wang, E. T., Burge, C. B., Sandberg, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+abundance+of+ubiquitously+expressed+genes+revealed+by+tissue+transcriptome+sequence+data.">An abundance of ubiquitously expressed genes revealed by tissue transcriptome sequence data.</a> PLoS Comput. Biol. 5 (12), e1000598 (2009).</li><li>Wagner, G. P., Kin, K., Lynch, V. 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The most challenging aspect of recording action potentials from gustatory sensilla is deciding which responses are &#8220;normal.&#8221; When employing single gustatory sensillum tip recording the first time for a given insect species, the total number and sensitivities of the gustatory receptor neurons (GRNs) are likely unknown. Many preliminary recordings are first required to decide the range and concentrations of chemicals to test. In this instance, we began with the observation that a single GRN responded to low con...

Compounds like DEET, Picaridin, Citronellal and IR3535 have been shown to effectively repel mosquitoes, including the important disease vector Aedes aegypti1,2. We record action potentials from sensory neurons associated with specific gustatory sensilla to determine the cells involved with mosquito repellency. Coupled with downstream sequencing of expressed genes in these tissues, we may identify the genes most likely mediating the responses of these cells in order to screen new compounds for improved repellency capabilities.
RNA-seq is a powerful tool, quickly becoming standard for tracking temporal and spatial changes in gene expression. RNA-seq analyses of insect chemosensory appendages and organs have been used to uncover molecular receptors in several insect species3-5, greatly improving on conventional PCR-based searches gene by gene6. Insects represent the most diverse animal class, presenting many opportunities to study the connection between genes and unique phenotypes. RNA-seq technology can be employed on any living insect tissue. Likewise, electrophysiological recording from sensory cells within uniporous gustatory sensilla can be achieved in many different insect species. The pairing of these two techniques allows researchers to narrow the set genes involved in an observed chemosensory phenotype. Different species will present specific challenges, but may inform the connection between chemosensory receptor genes and a chemosensory adaptation. The size and morphology of chemosensory sensilla is variable and may require extensive troubleshooting when recording action potentials to reduce noise and identify repeatable signals. Dissections of chemosensory organs may be trivial or delicate and time consuming, depending on morphology and size of the insect. Recovery of high-quality RNA may require some troubleshooting as well, such as avoiding certain pigments during tissue collection.
While demonstrating the effects of repellent compounds through behavioral trials is direct and informative, this approach is time intensive and broad with respect to mechanism of action. Electrophysiology coupled with RNA-seq allows for more specific analyses of what drives avoidance behaviors in insects. Once the &#8220;toolkit&#8221; of chemical discrimination has been identified in an insect species, more specific attempts to improve on known repellents are possible. Receptors and associated proteins in sensory cells responsible for these behaviors may be expressed heterologously for direct chemical screening. Furthermore, molecular modeling can predict which chemicals will elicit strong responses from these receptors7.
The snapshot of all active genes in a narrow set of chemosensory tissues may also be useful in identifying similar genes in other species. Using sequence homology and expression similarities, researchers may form sets of molecular receptors most likely mediating responses to repellents that are broadly effective on insects. We present the following protocol to aid researchers in deconstructing insect chemosensory pathways and to persuade more to delve into the neuroethology of non-model and economically important insects.

<table border="0" cellpadding="0" cellspacing="0" width="1272">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Name of Material/ Equipment</td>
			<td style="width:367px;">Company</td>
			<td style="width:189px;">Catalog Number</td>
			<td style="width:467px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Glass capillary</td>
			<td style="width:367px;">A-M Systems</td>
			<td style="width:189px;">628000</td>
			<td>Standard, 1.5mm X 0.86mm, 4&#34;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Silver wire</td>
			<td style="width:367px;">A-M Systems</td>
			<td style="width:189px;">7875</td>
			<td>.015&#34; bare</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Tungsten wire</td>
			<td style="width:367px;">Alfa Products</td>
			<td style="width:189px;">369</td>
			<td>0.127mm diameter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Fine forceps</td>
			<td style="width:367px;">Fine Science Tools</td>
			<td style="width:189px;">11252</td>
			<td>#5SF Inox</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Refridgerated stage</td>
			<td style="width:367px;">BioQuip Products</td>
			<td style="width:189px;">1429</td>
			<td>Chill Table</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Preamplifier</td>
			<td style="width:367px;">Syntech</td>
			<td style="width:189px;">Taste Probe</td>
			<td style="width:467px;">preamplifier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Software for electrophysiology</td>
			<td style="width:367px;">Syntech</td>
			<td style="width:189px;">Autospike</td>
			<td style="width:467px;">software for electrophysiology</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;">TetraMin fish food</td>
			<td style="width:367px;">Tetra</td>
			<td style="width:189px;">Tropical fish food granules</td>
			<td>fish food ground to fine powder</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TRIzol</td>
			<td>Life Technologies</td>
			<td>15596-026</td>
			<td>RNA isolation reagent</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RNeasy Plus Mini Kit</td>
			<td>Qiagen</td>
			<td style="width:189px;">74136</td>
			<td style="width:467px;">includes gDNA eliminator and RNeasy spin columns</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nanodrop spectrophotometer</td>
			<td>Nano Drop Products</td>
			<td style="width:189px;">ND-1000</td>
			<td>tabletop spectrometer</td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:251px;">R statistics</td>
			<td style="width:367px;">freeware (created by Robert Gentleman and Ross Ihaka)</td>
			<td>www.r-project.org</td>
			<td>Use the lm function of the stats package and the equiv.boot function of the equivalence package in the R computing environment.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">1.5ml tube rack</td>
			<td style="width:367px;">Evergreen</td>
			<td style="width:189px;">240-6388-030</td>
			<td>Pour liquid nitrogen into a few empty wells to freeze and grind tissue.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">1.5mL collection tubes with pestle</td>
			<td style="width:367px;">Grainger</td>
			<td style="width:189px;">6HAX6</td>
			<td>RNase free</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Centrifuge</td>
			<td style="width:367px;">Thermo Scientific</td>
			<td style="width:189px;">11178160</td>
			<td>Spin down frozen tissue to keep at bottom of 1.5 mL tube.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Primer-BLAST Primer Designing tool</td>
			<td style="width:367px;">NCBI</td>
			<td style="width:189px;">n/a</td>
			<td></td>
		</tr>
	</tbody>
</table>

physiological recordings and rna sequencing of the gustatory appendages of the yellow-fever mosquito aedes aegypti

Electrophysiological recording of action potentials from sensory neurons of mosquitoes provides investigators a glimpse into the chemical perception of these disease vectors. We have recently identified a bitter sensing neuron in the labellum of female Aedes aegypti that responds to DEET and other repellents, as well as bitter quinine, through direct electrophysiological investigation. These gustatory receptor neuron responses prompted our sequencing of total mRNA from both male and female labella and tarsi samples to elucidate the putative chemoreception genes expressed in these contact chemoreception tissues. Samples of tarsi were divided into pro-, meso- and metathoracic subtypes for both sexes. We then validated our dataset by conducting qRT-PCR on the same tissue samples and used statistical methods to compare results between the two methods. Studies addressing molecular function may now target specific genes to determine those involved in repellent perception by mosquitoes. These receptor pathways may be used to screen novel repellents towards disruption of host-seeking behavior to curb the spread of harmful viruses.

The trace recordings of action potentials from Ae. aegypti gustatory sensilla (Figure 1) demonstrate the effectiveness of direct stimulation with a range of chemicals. This technique can be used to quantify responses to any stimulating chemical by counting spikes of a given amplitude and duration over a reasonable time range (generally less than 500 ms). Trace recordings must be readily reproducible under a given set of experimental conditions. Otherwise, the observed physiological responses may...

Watch this Scientific Journal Video about Physiological Recordings and RNA Sequencing of the Gustatory Appendages of the Yellow-fever Mosquito Aedes aegypti at JoVE.com

Physiological Recordings and RNA Sequencing of the Gustatory Appendages of the Yellow-fever Mosquito Aedes aegypti

Using two methods to estimate gene expression in the major gustatory appendages of Aedes aegypti, we have identified the set of genes putatively underlying the neuronal responses to bitter and repulsive compounds, as determined by electrophysiological examination.

Physiological Recordings and RNA Sequencing of the Gustatory Appendages of the Yellow-fever Mosquito Aedes aegypti

Electrophysiological recording of action potentials from sensory neurons of mosquitoes provides investigators a glimpse into the chemical perception of ...

physiological-recordings-rna-sequencing-gustatory-appendages-yellow

Research

JoVE Journal

Biology

8.0K visualizações.  United States Department of Agriculture.  O uso de dois métodos para estimar a expressão do gene nos principais apêndices gustativas de Aedes aegypti, identificamos o conjunto de genes putativamente subjacentes às respostas neuronais para compostos amargos e repulsivas, conforme determinado pelo exame eletrofisiológico. 