Funding from the Kansas Agricultural Experiment Station and K-State Arthropod Genomics Center to KYZ supported the original development of chitosan/dsRNA-mediated gene silencing in A. gambiae19.The A. gambiae work described here was supported in part by R01-AI095842 from NIH/NIAID to KM. Development of chitosan/siRNA-mediated gene silencing in A. aegypti20,21 was supported by NIH/NIAID Award R01-AI081795 to MDS. The contents of this study are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.

1. Mosquito Species and Rearing
<ol>
	<li>Maintain A. gambiae G3 and A. aegypti&#160;Liverpool IB12 strains (used in the representative studies below) or other strains of interest according to standard lab practice or as described previously23,24.</li>
</ol>
2. dsRNA and siRNA Design and Production
<ol>
	<li>Design primers to construct long dsRNA templates specific to the gene of interest. Use the E-RNAi tool25. Produce dsRNA according to the method of c...

<ol>
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D., Wong, S., Ryan, C. P., Whyard, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oral+delivery+of+double-stranded+RNA+in+larvae+of+the+yellow+fever+mosquito,+Aedes+aegypti:+implications+for+pest+mosquito+control.">Oral delivery of double-stranded RNA in larvae of the yellow fever mosquito, Aedes aegypti: implications for pest mosquito control.</a> J Insect Sci. 13, 69 (2013).</li><li>Lopez-Martinez, G., Meuti, M., Denlinger, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rehydration+driven+RNAi:+a+novel+approach+for+effectively+delivering+dsRNA+to+mosquito+larvae.">Rehydration driven RNAi: a novel approach for effectively delivering dsRNA to mosquito larvae.</a> Journal of medical entomology. 49 (1), 215-218 (2012).</li><li>Scott, J. G., 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=Towards+the+elements+of+successful+insect+RNAi.">Towards the elements of successful insect RNAi.</a> Journal of insect physiology. 59 (12), 1212-1221 (2013).</li><li>Coy, M. R., 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=Gene+silencing+in+adult+Aedes+aegypti+mosquitoes+through+oral+delivery+of+double-stranded+RNA.">Gene silencing in adult Aedes aegypti mosquitoes through oral delivery of double-stranded RNA.</a> J Appl Entomol. 136 (10), 741-748 (2012).</li><li>Zhang, X., Zhang, J., Zhu, K. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chitosan/double-stranded+RNA+nanoparticle-mediated+RNA+interference+to+silence+chitin+synthase+genes+through+larval+feeding+in+the+African+malaria+mosquito+(Anopheles+gambiae).">Chitosan/double-stranded RNA nanoparticle-mediated RNA interference to silence chitin synthase genes through larval feeding in the African malaria mosquito (Anopheles gambiae).</a> Insect molecular biology. 19 (5), 683-693 (2010).</li><li>Mysore, K., Flannery, E. M., Tomchaney, M., Severson, D. 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R., Choong, P. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chitosan-mediated+orally+delivered+nucleic+acids:+a+gutful+of+gene+therapy.">Chitosan-mediated orally delivered nucleic acids: a gutful of gene therapy.</a> Journal of drug targeting. 16 (4), 257-261 (2008).</li><li>An, C., Budd, A., Kanost, M. R., Michel, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+a+regulatory+unit+that+controls+melanization+and+affects+longevity+of+mosquitoes.">Characterization of a regulatory unit that controls melanization and affects longevity of mosquitoes.</a> Cellular and molecular life sciences : CMLS. 68 (11), 1929-1939 (2011).</li><li>Clemons, A., Mori, A., Haugen, M., Severson, D. 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The authors have nothing to disclose.

The chitosan/interfering RNA nanoparticle methodology described herein has been used to effectively target genes during larval development in A. gambiae (Figures&#160;2, 3) and A. aegypti (Figures 4, 5,&#160;6, Tables 1, 2). Chitosan nanoparticles can be prepared with either long dsRNA or siRNA, both of which have been used successfully in mosquitoes as evidenced by the representative results described herein. Synthesis of dsRNA is less...

Blood feeding vector mosquitoes of the Anopheline and Aedine genera transmit disease-causing agents responsible for several of the worst scourges of humankind. An estimated 3.4 billion people are at risk for contracting malaria, which is responsible for over one-half million deaths annually worldwide. Malaria results from infection by Plasmodiumsp. parasites, which are transmitted to people through the bites of infected mosquitoes of the Anopheles genus, including the principal African vector Anopheles gambiae (<a href="http://www.who.int/topics/malaria/en/">http://www.who.int/topics/malaria/en/</a>, 2014)1. Aedes aegypti is the primary mosquito vector for dengue virus, which causes dengue fever, a nonspecific febrile illness that is the most widespread and significant arboviral disease in the world. Dengue virus is presently a threat to &#62;2.5 billion people in the tropics, with a yearly incidence of approximately 50 million cases resulting in ~24,000 deaths annually (<a href="http://www.cdc.gov/dengue/">http://www.cdc.gov/dengue/</a>, 2014)2. Despite the devastating global impact of mosquito-borne illnesses on human health, effective means of preventing and treating these diseases are lacking. Mosquito control is presently the best method of disease prevention.
The potential for controlling arthropod-borne diseases by the genetic manipulation of vector insects has been recognized for over four decades3. Transgenic strains of A. aegypti engineered to have a repressible female-specific flightless phenotype have recently made the potential for using transgenic vector control strategies a reality4-6. These advancements have challenged researchers to identify novel genetic targets for vector control and additional means of manipulating gene function in vector mosquitoes. Alteration of gene expression during development, as was the case in female-flightless mosquitoes4, may promote the elucidation of novel vector control strategies. However, largely due to technical challenges, the functions of very few genes have been characterized during development of A. gambiae, A. aegypti, or other mosquito species.
Since its discovery in C. elegans7, RNA interference (RNAi), which is conserved in animals, plants, and microorganisms, has been extensively used for functional genetic studies in a wide variety of organisms, including insects8,9. The RNAi pathway is initiated by Dicer, which cleaves long dsRNA into short 20-25 nucleotide-long siRNAs that function as sequence-specific interfering RNA. siRNAs silence genes that are complementary in sequence by promoting transcript turnover, cleavage, and disruption of translation9. Long dsRNA molecules (typically 300-600 bp) or custom siRNAs targeting a particular sequence can be used in the research laboratory for silencing any gene of interest. By managing when interfering RNA is delivered, researchers can control the time at which gene silencing initiates. This advantage is useful as it can be used to overcome challenges such as developmental lethality or sterility, which can hinder the production and maintenance of strains bearing heritable mutations, an expensive and labor-intensive process that is not yet available in all insect species. Although the degree of gene silencing by RNAi can vary from gene to gene, tissue to tissue, and animal to animal, RNAi is widely used for functional analysis of genes in mosquitoes and other insects8,9.
Three interfering RNA delivery strategies have been used in mosquitoes: microinjection, soaking/topical application, and ingestion. For a detailed history and comparison of the use of these three techniques in insects, please refer to Yu et al8. We have successfully used microinjection10 as a means of delivering siRNAs to target developmental genes in A. aegypti embryos, larvae, and pupae11-14. However, this labor-intensive delivery strategy requires both a microinjection setup and a skilled hand. Moreover, microinjection is stressful to the organism, a confounding factor, particularly when behavioral phenotypes will be assessed. Finally, microinjection delivery cannot be extended to the field for vector control. As an alternative, soaking the organism in interfering RNA solution has also become a popular means of inducing gene silencing, as it is convenient and requires little equipment or labor. Soaking has primarily been applied in insect cell line studies8, but in a recent study, knockdown was achieved in A. aegypti larvae immersed in a solution of dsRNA15, which the animals appeared to be ingesting. However, for studies involving analysis of multiple experimental groups or phenotypes, soaking is rather costly. Lopez-Martinez et al.16 described rehydration driven RNAi, a novel approach for interfering RNA delivery that involves dehydration in saline solution and rehydration with a single drop of water containing interfering RNA. This approach does cut the costs associated with whole animal immersion, but is more expensive than microinjection and may be limited in its application to species that can tolerate high osmotic pressures. Moreover, it is difficult to envision how immersion or dehydration/rehydration immersion methodology could be adapted for vector control in the field. For these reasons, for post-embryonic studies, delivery of interfering RNA with ingested food is a viable alternative strategy.
Although ingestion-based strategies do not work in all insect species, perhaps most notably Drosophila melanogaster, oral delivery of interfering RNA mixed with food has promoted gene silencing in a variety of insects8,17, including A. aegypti adults18. We described chitosan nanoparticle-mediated RNAi in A. gambiae larvae19 and have successfully applied this approach for reduction of gene expression in A. aegypti larvae20,21. Here, methodology for this RNAi procedure, which involves entrapping of interfering RNA by the polymer chitosan, is detailed. Chitosan/interfering RNA nanoparticles are formed by self-assembly of polycations with interfering RNA through the electrostatic forces between positive charges of the amino groups in chitosan and negative charges carried by the phosphate groups on the backbone of interfering RNA19. The procedure described is compatible with both long dsRNA molecules (hereafter referred to as dsRNA) or double stranded siRNA (hereafter referred to as siRNA). Following synthesis, chitosan/interfering RNA nanoparticles are mixed with larval food and delivered to larvae through oral ingestion. This methodology is relatively inexpensive, requires little equipment and labor19, and facilitates high-throughput analysis of multiple phenotypes, including analysis of behaviors20,21. This methodology, which can be adapted for gene silencing studies in other insects, including other disease vectors and insect agricultural pests, could potentially be used for gene silencing in a variety of other animal species. Moreover, chitosan, an inexpensive, non-toxic and biodegradable polymer22, could potentially be utilized in the field for species-specific mosquito control.

<table border="0" cellpadding="0" cellspacing="0" width="1429">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Name of Reagent/Equipment</td>
			<td style="width:243px;">Company</td>
			<td style="width:177px;">Catalog Number</td>
			<td style="width:663px;">Comments/Descriptions</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">0.02 ml pipetteman</td>
			<td>Rainin</td>
			<td>PR20</td>
			<td>for resuspension of interfering RNA</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">0.2 ml pipetteman</td>
			<td>Rainin</td>
			<td>PR200</td>
			<td>for resuspension of interfering RNA and preparation of interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">0.5 ml graduated tube&#160;</td>
			<td>Fischer Scientific</td>
			<td>05-408-120</td>
			<td>for aliquoting resuspended interfering RNA</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 ml pipetteman</td>
			<td>Rainin</td>
			<td>PR1000</td>
			<td>for resuspension of interfering RNA and preparation of interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1.5 ml graduated tube&#160;</td>
			<td>Fischer Scientific</td>
			<td>05-408-046</td>
			<td>for preparation of interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1M Sodium Acetate, pH 4.5</td>
			<td>TEKnova</td>
			<td>S0299</td>
			<td>to prepare sodium acetate buffer</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Acetic Acid, AIRSTAR. ACS, USP, FCC Grade</td>
			<td>BDH</td>
			<td>VWR BDH3092-500MLP</td>
			<td>to prepare sodium acetate buffer</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Agarose Genetic Technology Grade</td>
			<td>MP Biomedicals LLC.</td>
			<td>800668</td>
			<td>to coat prepared interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Centrifuge</td>
			<td>Eppendorf AG</td>
			<td>5415D</td>
			<td>to pellet interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Chitosan, from shrimp shells</td>
			<td>Sigma-Aldrich</td>
			<td>C3646-25G</td>
			<td>to combine with interfering RNA for prepararation of interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dry Yeast</td>
			<td>Universal Food Corp</td>
			<td>NA</td>
			<td>to prepare mosquito larval food with interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">E-RNAi tool</td>
			<td>German Cancer Research Center</td>
			<td>NA</td>
			<td>for design of dsRNA; http://www.dkfz.de/signaling/e-rnai3//</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">goldfish food</td>
			<td>Wardley</td>
			<td>Goldfish FLAKE FOOD</td>
			<td>to prepare mosquito larval food with interfering RNA/nanoparticles</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Heated water bath</td>
			<td>Thermo Scientific</td>
			<td>51221048</td>
			<td>to heat the interfering RNA/nanoparticles at 55oC</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ice</td>
			<td>not applicable</td>
			<td>not applicable</td>
			<td>for thawing interfering RNA and preparation of interfering RNA/nanoparticles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ice bucket</td>
			<td>Fisher Scientific</td>
			<td>02-591-44</td>
			<td>for storage of ice used during the procedure</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">liver powder</td>
			<td>MP Biomedicals LLC.</td>
			<td>900396</td>
			<td>to feed mosquito larvae post interfering RNA/nanoparticle treatment</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Microwave oven</td>
			<td>A variety of vendors</td>
			<td>not applicable</td>
			<td>to prepare 2% agarose solution</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">petridish (100X15 mm)</td>
			<td>Fischer Scientific</td>
			<td>875713</td>
			<td>interfering RNA/nanoparticle feeding chamber for larvae</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">pH meter</td>
			<td>Mettler Toledo</td>
			<td>S220</td>
			<td>for preparation of buffers</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Razor blade</td>
			<td>Fischer Scientific</td>
			<td>12-640</td>
			<td>to divide the interfering RNA/nanoparticle pellet for feedings</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">siRNA</td>
			<td>Thermo Scientific/Dharmacon</td>
			<td>custom</td>
			<td>for preparation of siRNA/nanoparticles</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">Sodium Sulfate, Anhydrous (Na2SO4)</td>
			<td>BDH/distributed by VWR</td>
			<td>VWR BDH0302-500G</td>
			<td>to prepare 50mM sodium sulfate solution in which the interfering RNA will be resuspended</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Thermometer</td>
			<td>VWR</td>
			<td>61066-046</td>
			<td>to measure the water bath temperature</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tooth picks</td>
			<td>VWR</td>
			<td>470146-908</td>
			<td>for stirring during interfering RNA/nanoparticle food preparation and cutting gel pellets</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Ultralow freezer</td>
			<td>A variety of vendors</td>
			<td>not applicable</td>
			<td>for storage of interfering RNA aliquots and interfering RNA/nanoparticles at -80oC</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Vortex mixer</td>
			<td>Fischer Scientific</td>
			<td>02-216-108</td>
			<td>for preparation of chitosan/interfering RNA</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Weight paper</td>
			<td>Fischer Scientific</td>
			<td>NC9798735</td>
			<td>to divide the interfering RNA/nanoparticle pellet for feedings</td>
		</tr>
	</tbody>
</table>

chitosan/interfering rna nanoparticle mediated gene silencing in disease vector mosquito larvae

Vector mosquitoes inflict more human suffering than any other organism&#8212;and kill more than one million people each year. The mosquito genome projects facilitated research in new facets of mosquito biology, including functional genetic studies in the primary African malaria vector Anopheles gambiae and the dengue and yellow fever vector Aedes aegypti. RNA interference- (RNAi-) mediated gene silencing has been used to target genes of interest in both of these disease vector mosquito species. Here, we describe a procedure for preparation of chitosan/interfering RNA nanoparticles that are combined with food and ingested by larvae. This technically straightforward, high-throughput, and relatively inexpensive methodology, which is compatible with long double stranded RNA (dsRNA) or small interfering RNA (siRNA) molecules, has been used for the successful knockdown of a number of different genes in A. gambiae and A. aegypti larvae. Following larval feedings, knockdown, which is verified through qRT-PCR or in situ hybridization, can persist at least through the late pupal stage. This methodology may be applicable to a wide variety of mosquito and other insect species, including agricultural pests, as well as other non-model organisms. In addition to its utility in the research laboratory, in the future, chitosan, an inexpensive, non-toxic and biodegradable polymer, could potentially be utilized in the field.

A. gambiae: 
Chitosan/dsRNA nanoparticles are formed due to the electrostatic interaction between amino groups of chitosan and the phosphate groups of dsRNA. The efficiency of dsRNA incorporation into nanoparticles is usually above 90% as measured by depletion of dsRNA from the solution. Atomic force microscopy images show that chitosan-dsRNA particle size averages 140 nm in diameter, ranging from 100-200 nm (Figure 1).
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Watch this Scientific Journal Video about Chitosan/Interfering RNA Nanoparticle Mediated Gene Silencing in Disease Vector Mosquito Larvae at JoVE.com

Chitosan/Interfering RNA Nanoparticle Mediated Gene Silencing in Disease Vector Mosquito Larvae

Here we describe a procedure for inhibiting gene function in disease vector mosquitoes through the use of chitosan/interfering RNA nanoparticles that are ingested by larvae.

Vector mosquitoes inflict more human suffering than any other organism&#8212;and kill more than one million people each year. The mosquito genome projects ...

chitosaninterfering-rna-nanoparticle-mediated-gene-silencing-disease

Research

JoVE Journal

Biology

14.1K Views.  Kansas State University. Here we describe a procedure for inhibiting gene function in disease vector mosquitoes through the use of chitosan/interfering RNA nanoparticles that are ingested by larvae.