We thank D. Braendle, C. L. Kurz and F. Monta&ntilde;ana-Sanchis for their contributions. This project was supported by grants from the ANR and the Conseil Regional PACA, and institutional funding from INSERM and the CNRS.

<ol>
	<li>Timmons, L., Fire, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Specific+interference+by+ingested+dsRNA.">Specific interference by ingested dsRNA.</a> Nature. 395, 854-854 (1998).</li><li>Kamath, R. S., Ahringer, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome-wide+RNAi+screening+in+Caenorhabditis+elegans.">Genome-wide RNAi screening in Caenorhabditis elegans.</a> Methods. 30, 313-321 (2003).</li><li>Rual, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+improving+Caenorhabditis+elegans+phenome+mapping+with+an+ORFeome-based+RNAi+library.">Toward improving Caenorhabditis elegans phenome mapping with an ORFeome-based RNAi library.</a> Genome Res. 14, 2162-2168 (2004).</li><li>Lee, S. 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+systematic+RNAi+screen+identifies+a+critical+role+for+mitochondria+in+C.+elegans+longevity.">A systematic RNAi screen identifies a critical role for mitochondria in C. elegans longevity.</a> Nat. Genet. 33, 40-48 (2003).</li><li>Hamilton, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+systematic+RNAi+screen+for+longevity+genes+in+C.+elegans.">A systematic RNAi screen for longevity genes in C. elegans.</a> Genes Dev. 19, 1544-1555 (2005).</li><li>Frand, A. R., Russel, S., Ruvkun, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+genomic+analysis+of+C.+elegans+molting.">Functional genomic analysis of C. elegans molting.</a> PLoS Biol. 3, e312-e312 (2005).</li><li>Parry, D. H., Xu, J., Ruvkun, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+whole-genome+RNAi+Screen+for+C.+elegans+miRNA+pathway+genes.">A whole-genome RNAi Screen for C. elegans miRNA pathway genes.</a> Curr. Biol. 17, 2013-2022 (2007).</li><li>O'Rourke, E. J., Conery, A. L., Moy, T. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whole-animal+high-throughput+screens:+the+C+elegans+model.">Whole-animal high-throughput screens: the C elegans model.</a> Methods Mol. Biol. 486, 57-75 (2009).</li><li>Pujol, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinct+innate+immune+responses+to+infection+and+wounding+in+the+C.+elegans+epidermis.">Distinct innate immune responses to infection and wounding in the C. elegans epidermis.</a> Curr. Biol. 18, 481-489 (2008).</li><li>Stiernagle, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maintenance+of+C.+elegans.">Maintenance of C. elegans.</a> WormBook. , 1551-8507 (2006).</li><li>Powell, J. R., Ausubel, F. M., Ewbank, J., Vivier, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Models+of+Caenorhabditis+elegans+Infection+by+Bacterial+and+Fungal+Pathogens.">Models of Caenorhabditis elegans Infection by Bacterial and Fungal Pathogens.</a> Methods Mol Biol. 415, 403-427 (2008).</li><li>Cardoso, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=XNP-1/ATR-X+acts+with+RB,+HP1+and+the+NuRD+complex+during+larval+development+in+C.+elegans.">XNP-1/ATR-X acts with RB, HP1 and the NuRD complex during larval development in C. elegans.</a> Dev. Biol. 278, 49-59 (2005).</li><li>Pujol, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anti-fungal+innate+immunity+in+C.+elegans+is+enhanced+by+evolutionary+diversification+of+antimicrobial+peptides.">Anti-fungal innate immunity in C. elegans is enhanced by evolutionary diversification of antimicrobial peptides.</a> PLoS Pathog. 4, e1000105-e1000105 (2008).</li><li>Simmer, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome-Wide+RNAi+of+C.+elegans+Using+the+Hypersensitive+rrf-3+Strain+Reveals+Novel+Gene+Functions.">Genome-Wide RNAi of C. elegans Using the Hypersensitive rrf-3 Strain Reveals Novel Gene Functions.</a> PLoS Biol. 1, e12-e12 (2003).</li><li>Couillault, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TLR-independent+control+of+innate+immunity+in+Caenorhabditis+elegans+by+the+TIR+domain+adaptor+protein+TIR-1,+an+ortholog+of+human+SARM.">TLR-independent control of innate immunity in Caenorhabditis elegans by the TIR domain adaptor protein TIR-1, an ortholog of human SARM.</a> Nat Immunol. 5, 488-494 (2004).</li><li>Morton, E., Lamitina, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+suite+of+MATLAB-based+computational+tools+for+automated+analysis+of+COPAS+Biosort+data.">A suite of MATLAB-based computational tools for automated analysis of COPAS Biosort data.</a> Biotechniques. 48, xxv-xxx (2010).</li><li>Rohlfing, A. K., Miteva, Y., Hannenhalli, S., Lamitina, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+and+physiological+activation+of+osmosensitive+gene+expression+mimics+transcriptional+signatures+of+pathogen+infection+in+C.+elegans.">Genetic and physiological activation of osmosensitive gene expression mimics transcriptional signatures of pathogen infection in C. elegans.</a> PLoS One. 5, e9010-e9010 (2010).</li><li>Lee, K. Z., Kniazeva, M., Han, M., Pujol, N., Ewbank, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+fatty+acid+synthase+fasn-1+acts+upstream+of+WNK+and+Ste20&#47;GCK-VI+kinases+to+modulate+antimicrobial+peptide+expression+in+C.+elegans+epidermis.">The fatty acid synthase fasn-1 acts upstream of WNK and Ste20&#47;GCK-VI kinases to modulate antimicrobial peptide expression in C. elegans epidermis.</a> Virulence. 1, 113-122 (2010).</li><li>Duverger, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+semi-automated+high-throughput+approach+to+the+generation+of+transposon+insertion+mutants+in+the+nematode+Caenorhabditis+elegans.">A semi-automated high-throughput approach to the generation of transposon insertion mutants in the nematode Caenorhabditis elegans.</a> Nucleic Acids Res. 35, e11-e11 (2007).</li><li>Pierce-Shimomura, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+analysis+of+crawling+and+swimming+locomotory+patterns+in+C.+elegans.">Genetic analysis of crawling and swimming locomotory patterns in C. elegans.</a> Proc. Natl. Acad. Sci. U.S.A. 105, 20982-20987 (2008).</li><li>Ruzanov, P., Riddle, 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=Deep+SAGE+analysis+of+the+Caenorhabditis+elegans+transcriptome.">Deep SAGE analysis of the Caenorhabditis elegans transcriptome.</a> Nucleic Acids Res. 38, 3252-3262 (2010).</li><li>Kurz, C. L., Ewbank, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Infection+in+a+dish:+high-throughput+analyses+of+bacterial+pathogenesis.">Infection in a dish: high-throughput analyses of bacterial pathogenesis.</a> Curr. Opin. Microbiol. 10, 10-16 (2007).</li><li>Okoli, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+antifungal+compounds+active+against+Candida+albicans+using+an+improved+high-throughput+Caenorhabditis+elegans+assay.">Identification of antifungal compounds active against Candida albicans using an improved high-throughput Caenorhabditis elegans assay.</a> PLoS One. 4, e7025-e7025 (2009).</li><li>Moy, T. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+novel+antimicrobials+using+a+live-animal+infection+model.">Identification of novel antimicrobials using a live-animal infection model.</a> Proc. Natl. Acad. Sci. U. S. A. 103, 10414-10419 (2006).</li><li>Ballestriero, F., Thomas, T., Burke, C., Egan, S., Kjelleberg, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+compounds+with+bioactivity+against+the+nematode+Caenorhabditis+elegans+by+a+screen+based+on+the+functional+genomics+of+the+marine+bacterium+Pseudoalteromonas+tunicata+D2.">Identification of compounds with bioactivity against the nematode Caenorhabditis elegans by a screen based on the functional genomics of the marine bacterium Pseudoalteromonas tunicata D2.</a> Appl. Environ. Microbiol. 76, 5710-5717 (2010).</li></ol>

The Ewbank lab collaborates with Union Biometrica and Modul-Bio.

The current protocol allows large-scale RNAi screening in C. elegans on solid media, using the level of expression of a fluorescent reporter gene as a read-out. It has been optimized with automated tools to facilitate high-throughput assays, allowing easy and fast handling of large numbers of samples, in an efficient, reliable and reproducible manner. Other methods have been described that do not rely so heavily on automated liquid sample handling 8.
	One key organizational aspect to the protocol has been the development of a robust method of sample tracking by adapting the commercial MBioLIMS software to the RNAi screen procedure in collaboration with the company ModulBio. At every stage of the procedure, plates are now identified by barcodes generated within the LIMS. As the LIMS also records the identity of the clones in each well on each plate, going from well to putative gene is simple. And beyond this, the LIMS links to the community database WormBase, allowing direct access to molecular and functional data about any given gene. The LIMS also facilitates analyses to be conducted on the plate or even chromosome and whole-genome level. For these analyses, the data is stored in a way that is entirely compatible with previously described tools such as COPAmulti 16.
	One critical experimental point in the method is the adjustment of the quantity of food relative to the number of worms. For many assays, it is essential that worms do not starve at the end of the experiment but it is also important not to have too much food at the start. We have observed that a high density of food decreases fluorescence induction in the protocol using worms carrying the pnlp-29::GFP reporter. This may reflect a diminished infection efficiency when worms are cultured in too much bacteria (BS, unpublished results). At the same time, the culture conditions of the RNAi bacteria is also important, since this determines whether dsRNA is produced at an optimal level. Some protocols for large-scale RNAi require culture of RNAi clones on agar plates prior to seeding liquid cultures 8. We obtained robust gene silencing omitting this step. We opted for growing an excess of each culture to ensure homogenous results. The protocol described in fact provides sufficient material to conduct 2 or 3 screens in parallel. In the interest of obtaining the most robust results, we favor, however, conducting screens in duplicate using independent cultures of worms, RNAi bacteria and fungal spores.
	Another critical step is related to using medium that is neither too humid nor too dry. If the plates are not dry enough, the RNAi bacteria does not dry properly and worms will swim during the assay. This can cause problems. For example, worms are not efficiently infected by D. coniospora in liquid (C. Couillault, unpublished results). On the other hand, in dry plates, the osmolarity of the culture medium increases. This has direct effects on worm physiology 17, including the induction of some antimicrobial peptide genes, such as nlp 29 18. The volume used to dispense worms and spores is critical to allow effective and rapid drying. If more than 10 &mu;L of liquid is added to fresh plates, the wells can take many hours to dry. This can mean that it is difficult to use robotic methods to add worms to the plates. For example, each worm is dispensed by the Biosort in around 1 &mu;L of liquid. We currently distribute the worms manually as that also allows us to overcome the tendency of worms in solution to sediment.
	We previously reported an adjustment of the Biosort that allowed one 96-well plate to be analyzed in 36 minutes 19. The machine's manufacturer UBI now offers a modification of the Biosort to decrease further the analysis time. With the "FastReFlex", samples are directly routed through the flow cell for analysis, bypassing the bubble-trap filter. This results in a significant reduction in the time for data acquisition; a whole plate can be analyzed in 22 min allowing around 20 plates to be treated per day. If plates were not frozen, however, there would be an 8 hour interval between the first and last ones. Given the relatively short duration of the experiment, with the infection lasting just 18 hours, this would introduce an unacceptable variable across plates. Not only does freezing plates prior to analysis resolve this problem, but it is also essential in the context of high-throughput analyses as, with the current protocol and standard liquid-handling robots, 2 people can easily process up to 50 plates a week. Currently, we routinely screen 30 plates a week, which allows a whole-genome screen to be conducted once in less than 2 months.
	One interesting feature of this protocol is the fact that it uses solid agar, allowing assays that cannot be performed in liquid culture. As worm physiology differs depending on the culture conditions 20,21, being able to perform assays on solid medium can also complement usual liquid-based screens. For certain phenotypes (e.g. movement), the analysis can be carried out directly with 96-well solid medium plates. For the current screen, however, as the Biosort cannot sample from solid medium plates, worms are first transferred to liquid before freezing. On the other hand, the COPAS Biosort permits a multiparametric quantitative analysis compatible with the measurement of many different phenotypes. It is likely that for any given screen not all the measured parameters will be the primary read-out. Nevertheless, these measurements can be useful for several reasons. They allow one to determine whether the assay ran correctly. For example, one can check on the number and size of worms in each well. Only where an RNAi clone should block growth or reproduction should there be a deviation from the expected values. Wells with less than 20 worms or/and animals 30% smaller (TOF) compared to a standard control with no effect on growth (e.g. gfp(RNAi)) can be excluded from subsequent analyses. The function of these clones can be addressed using an alternative protocol wherein worms are exposed to the RNAi bacteria after their development is well advanced 15. The different parameters can also be used to refine candidate gene (hit) selection, for example, limiting hits only to those that affect green fluorescence but not red. The precise method chosen for selecting hits will depend on the type of screen and its exact read-out. Given the complexity of the data generated from a quantitative genome-wide screen, collaboration with a statistician may be required.
	The protocol we describe can be readily adapted to other types of assays. For example, at the infection step D. coniospora could be replaced by any other pathogen able to infect on solid media. This is potentially useful as we have found that many of the virulence factors important for Serratia marcescens infection in liquid culture do not play a role during infection on solid medium (E. Pradel, personal communication). The protocol is also fully compatible with tests of chemicals compounds 22-24, or to identify compounds with bioactivity using different libraries of bacteria 25, so should find a general utility in the C. elegans research community.

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments </td>
 </tr>
 <tr>
 <td>BactoAgar </td>
 <td>BD Diagnostic Systems</td>
 <td>214010</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Ampicillin</td>
 <td>Sigma-Aldrich</td>
 <td>A9518</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>BactoPeptone</td>
 <td>BD Diagnostic Systems</td>
 <td>211677</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>CaCl2</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>AeraSeal adhesive film</td>
 <td>Dutscher</td>
 <td>760214</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Isopropyl &beta;-d-Thiogalactopyranoside (IPTG)</td>
 <td>Thermo Scientific</td>
 <td>AB-0481</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>K2HPO4</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>KH2PO4</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>MgSO4</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>NaCl</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Na2HPO4</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>NaOH</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>96 deep well plate </td>
 <td>Thermo Scientific</td>
 <td>AB-0932</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>96 well flat plate </td>
 <td>FALCON</td>
 <td>353072</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>96 well round plate </td>
 <td>FALCON</td>
 <td>353077</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Tetracycline</td>
 <td>Sigma-Aldrich</td>
 <td>T8032</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Triton X-100</td>
 <td>Any supplier</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>TECAN robot </td>
 <td>TECAN</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Liquidator96TM </td>
 <td>RAININ </td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>COPAS Biosort </td>
 <td>Union Biometrica</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>LIMS </td>
 <td>Modul-Bio</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
</tbody>
</table>

quantitative and automated high-throughput genome-wide rnai screens in c. elegans

RNA interference is a powerful method to understand gene function, especially when conducted at a whole-genome scale and in a quantitative context. In C. elegans, gene function can be knocked down simply and efficiently by feeding worms with bacteria expressing a dsRNA corresponding to a specific gene 1. While the creation of libraries of RNAi clones covering most of the C. elegans genome 2,3 opened the way for true functional genomic studies (see for example 4-7), most established methods are laborious. Moy and colleagues have developed semi-automated protocols that facilitate genome-wide screens 8. The approach relies on microscopic imaging and image analysis. 
	Here we describe an alternative protocol for a high-throughput genome-wide screen, based on robotic handling of bacterial RNAi clones, quantitative analysis using the COPAS Biosort (Union Biometrica (UBI)), and an integrated software: the MBioLIMS (Laboratory Information Management System from Modul-Bio) a technology that provides increased throughput for data management and sample tracking. The method allows screens to be conducted on solid medium plates. This is particularly important for some studies, such as those addressing host-pathogen interactions in C. elegans, since certain microbes do not efficiently infect worms in liquid culture.
	We show how the method can be used to quantify the importance of genes in anti-fungal innate immunity in C. elegans. In this case, the approach relies on the use of a transgenic strain carrying an epidermal infection-inducible fluorescent reporter gene, with GFP under the control of the promoter of the antimicrobial peptide gene nlp 29 and a red fluorescent reporter that is expressed constitutively in the epidermis. The latter provides an internal control for the functional integrity of the epidermis and nonspecific transgene silencing9. When control worms are infected by the fungus they fluoresce green. Knocking down by RNAi a gene required for nlp 29 expression results in diminished fluorescence after infection. Currently, this protocol allows more than 3,000 RNAi clones to be tested and analyzed per week, opening the possibility of screening the entire genome in less than 2 months.

Watch this Scientific Journal Video about Quantitative and Automated High-throughput Genome-wide RNAi Screens in C. elegans at JoVE.com

Quantitative and Automated High-throughput Genome-wide RNAi Screens in C. elegans

We describe a protocol using C. elegans and RNAi feeding libraries that allows automated measurement of multiple parameters such as fluorescence, size and opacity of individual worms in a population. We give one example of a screen to identify genes involved in anti-fungal innate immunity in C. elegans.

Quantitative and Automated High-throughput Genome-wide RNAi Screens in C. elegans

RNA interference is a powerful method to understand gene function, especially when conducted at a whole-genome scale and in a quantitative context. In C. ...

quantitative-automated-high-throughput-genome-wide-rnai-screens-c

Research

JoVE Journal

Biology

17.6K Views.  Université de la Méditerranée. We describe a protocol using C. elegans and RNAi feeding libraries that allows automated measurement of multiple parameters such as fluorescence, size and opacity of individual worms in a population. We give one example of a screen to identify genes involved in anti-fungal innate immunity in C. elegans.

Video: Quantitative and Automated High-throughput Genome-wide RNAi Screens in C. elegans

Development of automated imaging and analysis for zebrafish chemical screens.

We demonstrate the application of image-based high-content screening (HCS) methodology to identify small molecules that can modulate the FGF/RAS/MAPK pathway in zebrafish embryos. The zebrafish embryo is an ideal system for in vivo high-content chemical screens. The 1-day old embryo is approximately 1mm in diameter and can be easily arrayed into 96-well plates, a standard format for high throughput screening. During the first day of development, embryos are transparent with most of the major organs present, thus enabling visualization of tissue formation during embryogenesis. The complete automation of zebrafish chemical screens is still a challenge, however, particularly in the development of automated image acquisition and analysis. We previously generated a transgenic reporter line that expresses green fluorescent protein (GFP) under the control of FGF activity and demonstrated their utility in chemical screens 1. To establish methodology for high throughput whole organism screens, we developed a system for automated imaging and analysis of zebrafish embryos at 24-48 hours post fertilization (hpf) in 96-well plates 2. In this video we highlight the procedures for arraying transgenic embryos into multiwell plates at 24hpf and the addition of a small molecule (BCI) that hyperactivates FGF signaling 3. The plates are incubated for 6 hours followed by the addition of tricaine to anesthetize larvae prior to automated imaging on a Molecular Devices ImageXpress Ultra laser scanning confocal HCS reader. Images are processed by Definiens Developer software using a Cognition Network Technology algorithm that we developed to detect and quantify expression of GFP in the heads of transgenic embryos. In this example we highlight the ability of the algorithm to measure dose-dependent effects of BCI on GFP reporter gene expression in treated embryos.

We report the development of a system for automated imaging and analysis of zebrafish transgenic embryos in multiwell plates. This demonstrates the ability to measure dose dependent effects of a small molecule, BCI, on Fibroblast Growth Factor reporter gene expression and provide technology for establishing high-throughput zebrafish chemical screens.

We demonstrate the application of image-based high-content screening (HCS) methodology to identify small molecules that can modulate the FGF/RAS/MAPK ...

Genome-wide Analysis using ChIP to Identify Isoform-specific Gene Targets

Recruitment of transcriptional and epigenetic factors to their targets is a key step in their regulation. Prominently featured in recruitment are the protein domains that bind to specific histone modifications. One such domain is the plant homeodomain (PHD), found in several chromatin-binding proteins. The epigenetic factor RBP2 has multiple PHD domains, however, they have different functions (Figure 4). In particular, the C-terminal PHD domain, found in a RBP2 oncogenic fusion in human leukemia, binds to trimethylated lysine 4 in histone H3 (H3K4me3)1. The transcript corresponding to the RBP2 isoform containing the C-terminal PHD accumulates during differentiation of promonocytic, lymphoma-derived, U937 cells into monocytes2. Consistent with both sets of data, genome-wide analysis showed that in differentiated U937 cells, the RBP2 protein gets localized to genomic regions highly enriched for H3K4me33. Localization of RBP2 to its targets correlates with a decrease in H3K4me3 due to RBP2 histone demethylase activity and a decrease in transcriptional activity. In contrast, two other PHDs of RBP2 are unable to bind H3K4me3. Notably, the C-terminal domain PHD of RBP2 is absent in the smaller RBP2 isoform4. It is conceivable that the small isoform of RBP2, which lacks interaction with H3K4me3, differs from the larger isoform in genomic location. The difference in genomic location of RBP2 isoforms may account for the observed diversity in RBP2 function. Specifically, RBP2 is a critical player in cellular differentiation mediated by the retinoblastoma protein (pRB). Consistent with these data, previous genome-wide analysis, without distinction between isoforms, identified two distinct groups of RBP2 target genes: 1) genes bound by RBP2 in a manner that is independent of differentiation; 2) genes bound by RBP2 in a differentiation-dependent manner.
To identify differences in localization between the isoforms we performed genome-wide location analysis by ChIP-Seq. Using antibodies that detect both RBP2 isoforms we have located all RBP2 targets. Additionally we have antibodies that only bind large, and not small RBP2 isoform (Figure 4). After identifying the large isoform targets, one can then subtract them from all RBP2 targets to reveal the targets of small isoform. These data show the contribution of chromatin-interacting domain in protein recruitment to its binding sites in the genome.

Here we are presenting a chromatin immunoprecipitation (ChIP) procedure for genome-wide location analysis of protein isoforms that differ in a histone-binding domain. We are applying it to ChIP-Seq analysis to identify the targets of the KDM5A/JARID1A/RBP2 histone demethylase.

Recruitment of transcriptional and epigenetic factors to their targets is a key step in their regulation. Prominently featured in recruitment are the ...

High-throughput Screening and Biosensing with Fluorescent C. elegans Strains

High-throughput screening (HTS) is a powerful approach for identifying chemical modulators of biological processes. However, many compounds identified in screens using cell culture models are often found to be toxic or pharmacologically inactive in vivo1-2. Screening in whole animal models can help avoid these pitfalls and streamline the path to drug development.
C. elegans is a multicellular model organism well suited for HTS. It is small (&lt;1 mm) and can be economically cultured and dispensed in liquids. C. elegans is also one of the most experimentally tractable animal models permitting rapid and detailed identification of drug mode-of-action3.
We describe a protocol for culturing and dispensing fluorescent strains of C. elegans for high-throughput screening of chemical libraries or detection of environmental contaminants that alter the expression of a specific gene. Large numbers of developmentally synchronized worms are grown in liquid culture, harvested, washed, and suspended at a defined density. Worms are then added to black, flat-bottomed 384-well plates using a peristaltic liquid dispenser. Small molecules from a chemical library or test samples (e.g., water, food, or soil) can be added to wells with worms. In vivo, real-time fluorescence intensity is measured with a fluorescence microplate reader. This method can be adapted to any inducible gene in C. elegans for which a suitable reporter is available. Many inducible stress and developmental transcriptional pathways are well defined in C. elegans and GFP transgenic reporter strains already exist for many of them4. When combined with the appropriate transgenic reporters, our method can be used to screen for pathway modulators or to develop robust biosensor assays for environmental contaminants. 
We demonstrate our C. elegans culture and dispensing protocol with an HTS assay we developed to monitor the C. elegans cap &#x2018;n&#x2019; collar transcription factor SKN-1. SKN-1 and its mammalian homologue Nrf2 activate cytoprotective genes during oxidative and xenobiotic stress5-10. Nrf2 protects mammals from numerous age-related disorders such as cancer, neurodegeneration, and chronic inflammation and has become a major chemotherapeutic target11-13.Our assay is based on a GFP transgenic reporter for the SKN-1 target gene gst-414, which encodes a glutathione-s transferase6. The gst-4 reporter is also a biosensor for xenobiotic and oxidative chemicals that activate SKN-1 and can be used to detect low levels of contaminants such as acrylamide and methyl-mercury15-16.

High-throughput Screening and Biosensing with Fluorescent C. elegans Strains

A procedure for liquid-based culturing and dispensing of C. elegans strains expressing fluorescent reporter proteins is described that does not require expensive sorting equipment. This approach can be applied to numerous inducible C. elegans genes for drug discovery or biosensing of contaminants.

High-throughput screening (HTS) is a powerful approach for identifying chemical modulators of biological processes.  However, many compounds identified in ...

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated tools and resources for studies in this system are facilitating continued discovery of genes with more subtle phenotypes or roles. 
Here we present a generalized protocol we adapted for identifying C. elegans genes with postembryonic phenotypes of interest using RNAi2. This procedure is easily modified to assay the phenotype of choice, whether by light or fluorescence optics on a dissecting or compound microscope. This screening protocol capitalizes on the physical assets of the organism and molecular tools the C. elegans research community has produced. As an example, we demonstrate the use of an integrated transgene that expresses a fluorescent product in an RNAi screen to identify genes required for the normal localization of this product in late stage larvae and adults. First, we used a commercially available genomic RNAi library with full-length cDNA inserts. This library facilitates the rapid identification of multiple candidates by RNAi reduction of the candidate gene product. Second, we generated an integrated transgene that expresses our fluorecently tagged protein of interest in an RNAi-sensitive background. Third, by exposing hatched animals to RNAi, this screen permits identification of gene products that have a vital embryonic role that would otherwise mask a post-embryonic role in regulating the protein of interest. Lastly, this screen uses a compound microscope equipped for single cell resolution.

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

We describe a sensitized method to identify postembryonic regulators of protein expression and localization in C. elegans using an RNAi-based genomic screen and an integrated transgene that expresses a functional, fluorescently tagged protein.

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated ...

High-throughput Physical Mapping of Chromosomes using Automated in situ Hybridization

Projects to obtain whole-genome sequences for 10,000 vertebrate species1 and for 5,000 insect and related arthropod species2 are expected to take place over the next 5 years. For example, the sequencing of the genomes for 15 malaria mosquitospecies is currently being done using an Illumina platform3,4. This Anopheles species cluster includes both vectors and non-vectors of malaria. When the genome assemblies become available, researchers will have the unique opportunity to perform comparative analysis for inferring evolutionary changes relevant to vector ability. However, it has proven difficult to use next-generation sequencing reads to generate high-quality de novo genome assemblies5. Moreover, the existing genome assemblies for Anopheles gambiae, although obtained using the Sanger method, are gapped or fragmented4,6.
Success of comparative genomic analyses will be limited if researchers deal with numerous sequencing contigs, rather than with chromosome-based genome assemblies. Fragmented, unmapped sequences create problems for genomic analyses because: (i) unidentified gaps cause incorrect or incomplete annotation of genomic sequences; (ii) unmapped sequences lead to confusion between paralogous genes and genes from different haplotypes; and (iii) the lack of chromosome assignment and orientation of the sequencing contigs does not allow for reconstructing rearrangement phylogeny and studying chromosome evolution. Developing high-resolution physical maps for species with newly sequenced genomes is a timely and cost-effective investment that will facilitate genome annotation, evolutionary analysis, and re-sequencing of individual genomes from natural populations7,8.
Here, we present innovative approaches to chromosome preparation, fluorescent in situ hybridization (FISH), and imaging that facilitate rapid development of physical maps. Using An. gambiae as an example, we demonstrate that the development of physical chromosome maps can potentially improve genome assemblies and, thus, the quality of genomic analyses. First, we use a high-pressure method to prepare polytene chromosome spreads. This method, originally developed for Drosophila9, allows the user to visualize more details on chromosomes than the regular squashing technique10. Second, a fully automated, front-end system for FISH is used for high-throughput physical genome mapping. The automated slide staining system runs multiple assays simultaneously and dramatically reduces hands-on time11. Third, an automatic fluorescent imaging system, which includes a motorized slide stage, automatically scans and photographs labeled chromosomes after FISH12. This system is especially useful for identifying and visualizing multiple chromosomal plates on the same slide. In addition, the scanning process captures a more uniform FISH result. Overall, the automated high-throughput physical mapping protocol is more efficient than a standard manual protocol.

High-throughput Physical Mapping of Chromosomes using Automated in situ Hybridization

Genome assemblies based on massively parallel DNA sequencing technologies are usually highly fragmented. The development of physical chromosome maps can potentially improve genome assemblies. Here, we demonstrate innovative approaches to chromosome preparation, fluorescent in situ hybridization, and imaging that significantly increase throughput of the physical map development.

Projects to obtain whole-genome sequences for 10,000 vertebrate species1 and for 5,000 insect and related arthropod species2 are expected to take place ...

Genome-wide Gene Deletions in Streptococcus sanguinis by High Throughput PCR

Transposon mutagenesis and single-gene deletion are two methods applied in genome-wide gene knockout in bacteria 1,2. Although transposon mutagenesis is less time consuming, less costly, and does not require completed genome information, there are two weaknesses in this method: (1) the possibility of a disparate mutants in the mixed mutant library that counter-selects mutants with decreased competition; and (2) the possibility of partial gene inactivation whereby genes do not entirely lose their function following the insertion of a transposon. Single-gene deletion analysis may compensate for the drawbacks associated with transposon mutagenesis. To improve the efficiency of genome-wide single gene deletion, we attempt to establish a high-throughput technique for genome-wide single gene deletion using Streptococcus sanguinis as a model organism. Each gene deletion construct in S. sanguinis genome is designed to comprise 1-kb upstream of the targeted gene, the aphA-3 gene, encoding kanamycin resistance protein, and 1-kb downstream of the targeted gene. Three sets of primers F1/R1, F2/R2, and F3/R3, respectively, are designed and synthesized in a 96-well plate format for PCR-amplifications of those three components of each deletion construct. Primers R1 and F3 contain 25-bp sequences that are complementary to regions of the aphA-3 gene at their 5' end. A large scale PCR amplification of the aphA-3 gene is performed once for creating all single-gene deletion constructs. The promoter of aphA-3 gene is initially excluded to minimize the potential polar effect of kanamycin cassette. To create the gene deletion constructs, high-throughput PCR amplification and purification are performed in a 96-well plate format. A linear recombinant PCR amplicon for each gene deletion will be made up through four PCR reactions using high-fidelity DNA polymerase. The initial exponential growth phase of S. sanguinis cultured in Todd Hewitt broth supplemented with 2.5% inactivated horse serum is used to increase competence for the transformation of PCR-recombinant constructs. Under this condition, up to 20% of S. sanguinis cells can be transformed using ~50 ng of DNA. Based on this approach, 2,048 mutants with single-gene deletion were ultimately obtained from the 2,270 genes in S. sanguinis excluding four gene ORFs contained entirely within other ORFs in S. sanguinis SK36 and 218 potential essential genes. The technique on creating gene deletion constructs is high throughput and could be easy to use in genome-wide single gene deletions for any transformable bacteria.

Genome-wide Gene Deletions in Streptococcus sanguinis by High Throughput PCR

An efficient genome-wide single gene mutation method has been established using Streptococcus sanguinis as a model organism. This method has achieved via high throughput recombinant PCRs and transformations.

Transposon  mutagenesis and single-gene deletion are two methods applied in genome-wide  gene knockout in bacteria 1,2. Although transposon mutagenesis is ...

C. elegans Chemotaxis Assay

Many organisms use chemotaxis to seek out food sources, avoid noxious substances, and find mates. Caenorhabditis elegans has impressive chemotaxis behavior.
 The premise behind testing the response of the worms to an odorant is to place them in an area and observe the movement evoked in response to an odorant. Even with the many available assays, optimizing worm starting location relative to both the control and test areas, while minimizing the interaction of worms with each other, while maintaining a significant sample size remains a work in progress 1-10. The method described here aims to address these issues by modifying the assay developed by Bargmann et al.1. A Petri dish is divided into four quadrants, two opposite quadrants marked "Test" and two are designated "Control". Anesthetic is placed in all test and control sites. The worms are placed in the center of the plate with a circle marked around the origin to ensure that non-motile worms will be ignored. Utilizing a four-quadrant system rather than one 2 or two 1 eliminates bias in the movement of the worms, as they are equidistant from test and control samples, regardless of which side of the origin they began. This circumvents the problem of worms being forced to travel through a cluster of other worms to respond to an odorant, which can delay worms or force them to take a more circuitous route, yielding an incorrect interpretation of their intended path. This method also shows practical advantages by having a larger sample size and allowing the researcher to run the assay unattended and score the worms once the allotted time has expired.

C. elegans Chemotaxis Assay

A method of quantitatively evaluating the chemotactic response of Caenorhabditis elegans is described. A chemotactic index (CI) was employed as a way to precisely evaluate the response of worms to certain targets, and serve as a platform of comparison between strains and compounds of interest.

Many organisms use chemotaxis to seek out food sources, avoid noxious substances, and find mates.  Caenorhabditis elegans has impressive chemotaxis ...

Biochemical and High Throughput Microscopic Assessment of Fat Mass in Caenorhabditis Elegans

The nematode C. elegans has emerged as an important model for the study of conserved genetic pathways regulating fat metabolism as it relates to human obesity and its associated pathologies. Several previous methodologies developed for the visualization of C. elegans triglyceride-rich fat stores have proven to be erroneous, highlighting cellular compartments other than lipid droplets. Other methods require specialized equipment, are time-consuming, or yield inconsistent results. We introduce a rapid, reproducible, fixative-based Nile red staining method for the accurate and rapid detection of neutral lipid droplets in C. elegans. A short fixation step in 40% isopropanol makes animals completely permeable to Nile red, which is then used to stain animals. Spectral properties of this lipophilic dye allow it to strongly and selectively fluoresce in the yellow-green spectrum only when in a lipid-rich environment, but not in more polar environments. Thus, lipid droplets can be visualized on a fluorescent microscope equipped with simple GFP imaging capability after only a brief Nile red staining step in isopropanol. The speed, affordability, and reproducibility of this protocol make it ideally suited for high throughput screens. We also demonstrate a paired method for the biochemical determination of triglycerides and phospholipids using gas chromatography mass-spectrometry. This more rigorous protocol should be used as confirmation of results obtained from the Nile red microscopic lipid determination. We anticipate that these techniques will become new standards in the field of C. elegans metabolic research.

Biochemical and High Throughput Microscopic Assessment of Fat Mass in Caenorhabditis Elegans

We present robust biochemical and microscopic methods for studying Caenorhabditis elegans lipid stores. A rapid, simple, fixing-staining procedure for fluorescent lipid droplet imaging leverages the spectral properties of the lipophilic dye Nile red. We then present biochemical measurement of triglycerides and phospholipids using solid phase extraction and gas chromatography-mass spectrometry.

The nematode C. elegans has emerged as an important  model for the study of conserved genetic pathways regulating fat metabolism as  it relates to human ...

High-throughput Screening for Chemical Modulators of Post-transcriptionally Regulated Genes

Both transcriptional and post-transcriptional regulation have a profound impact on genes expression. However, commonly adopted cell-based screening assays focus on transcriptional regulation, being essentially aimed at the identification of promoter-targeting molecules. As a result, post-transcriptional mechanisms are largely uncovered by gene expression targeted drug development. Here we describe a cell-based assay aimed at investigating the role of the 3&#39; untranslated region (3&#8217; UTR) in the modulation of the fate of its mRNA, and at identifying compounds able to modify it. The assay is based on the use of a luciferase reporter construct containing the 3&#8217; UTR of a gene of interest stably integrated into a disease-relevant cell line. The protocol is divided into two parts, with the initial focus on the primary screening aimed at the identification of molecules affecting luciferase activity after 24 hr of treatment. The second part of the protocol describes the counter-screening necessary to discriminate compounds modulating luciferase activity specifically through the 3&#8217; UTR. In addition to the detailed protocol and representative results, we provide important considerations about the assay development and the validation of the hit(s) on the endogenous target. The described cell-based reporter gene assay will allow scientists to identify molecules modulating protein levels via post-transcriptional mechanisms dependent on a 3&#8217; UTR.

Here we describe a cell-based reporter gene assay as a valuable tool to screen chemical libraries for compounds modulating post-transcriptional control mechanisms exerted through 3&#8217; UTR.

Both transcriptional and post-transcriptional regulation have a profound impact on genes expression. However, commonly adopted cell-based screening assays ...

Genome-wide Mapping of Drug-DNA Interactions in Cells with COSMIC (Crosslinking of Small Molecules to Isolate Chromatin)

The genome is the target of some of the most effective chemotherapeutics, but most of these drugs lack DNA sequence specificity, which leads to dose-limiting toxicity and many adverse side effects. Targeting the genome with sequence-specific small molecules may enable molecules with increased therapeutic index and fewer off-target effects. N-methylpyrrole/N-methylimidazole polyamides are molecules that can be rationally designed to target specific DNA sequences with exquisite precision. And unlike most natural transcription factors, polyamides can bind to methylated and chromatinized DNA without a loss in affinity. The sequence specificity of polyamides has been extensively studied in vitro with cognate site identification (CSI) and with traditional biochemical and biophysical approaches, but the study of polyamide binding to genomic targets in cells remains elusive. Here we report a method, the crosslinking of small molecules to isolate chromatin (COSMIC), that identifies polyamide binding sites across the genome. COSMIC is similar to chromatin immunoprecipitation (ChIP), but differs in two important ways: (1) a photocrosslinker is employed to enable selective, temporally-controlled capture of polyamide binding events, and (2) the biotin affinity handle is used to purify polyamide&#8211;DNA conjugates under semi-denaturing conditions to decrease DNA that is non-covalently bound. COSMIC is a general strategy that can be used to reveal the genome-wide binding events of polyamides and other genome-targeting chemotherapeutic agents.

Genome-wide Mapping of Drug-DNA Interactions in Cells with COSMIC Crosslinking of Small Molecules to Isolate Chromatin

Identifying the direct targets of genome-targeting molecules remains a major challenge. To understand how DNA-binding molecules engage the genome, we developed a method that relies on crosslinking of small molecules to isolate chromatin (COSMIC).