Name: the replica set method: a high-throughput approach to quantitatively measure caenorhabditis elegans lifespan
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Funding for this work described in this manuscript was provided by: the University of Rochester Office of The Provost and the School of Medicine and Dentistry Dean&#39;s Office via the Health Sciences Center for Computational Innovation (HSCCI); the Ellison Medical Foundation New Scholars in Aging Fellowship (AG-NS-0681-10) The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

1. Traditional Method for Scoring C. elegans Longevity
<ol>
	<li>Preparation of reagents
	<ol>
		<li>Identify genes to be inactivated via feeding-based RNAi. Purchase transformed stocks of HT115 E. coli2 containing the RNAi clone of interest. Alternatively, subclone the cDNA of the gene of interest into the multicloning site of the L4440 plasmid. 
		NOTE: HT115 is an RNase III-deficient E. coli strain with IPTG-inducible T7 polymerase activity, wh...

<ol>
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Both the traditional and replica set methods require the synchronization of chronologically aged animals. We include a method that synchronizes animals using hypochlorite treatment of gravid adults, where only fertilized eggs with the gravid adult survive treatment. These embryos hatch in liquid suspension and developmentally arrest at the first larval stage (L1). After seeding L1 animals onto food (e.g. E. coli expressing dsRNA to a gene of interest), animals resume development. Synchronizing L1 animal...

One of the most transformative technological advancements towards understanding the genetic basis of aging was the development of feeding-based RNAi in C. elegans1; prior to the experimental use of RNAi, many phenotypes of aging were not genetically tractable. Feeding-based RNAi is achieved through the production of dsRNA within E. coli that matches an endogenous C. elegans mRNA: IPTG induces bidirectional transcription across an insert of either C. elegans cDNA or a portion of an open reading frame within a plasmid2. When C. elegans feed upon intact E. coli, dsRNA produced by bacteria is transported from the lumen into intestinal cells via the SID-2 transmembrane protein3, and then distributed through the rest of the animal via SID-14. Within each cell, exogenous dsRNA is processed by the Dicer complex into siRNA, which interact with a mature mRNA via complementary base pairing to create a new siRNA-mRNA duplex. This duplex is recognized by the RISC complex and cleaved, thereby degrading the endogenous mRNA5. Thus, by merely changing the plasmid insert, one can inactivate the function of nearly any gene within the C. elegans genome. This discovery led to the creation of several large feeding-based RNAi libraries- collections of transformed E. coli stocks that can be combined to achieve coverage of approximately 86% of known C. elegans genes6,7.
Since the advancement of feeding-based RNAi, comprehensive screens in C. elegans have led to the discovery of more than 900 genes that alter lifespan when inactivated (as evidenced by the RNAi-phenotype associations curated in WormBase), which we refer to as gerogenes. A role for the majority of gerogenes in longevity control was discovered through feeding-based RNAi in just a few seminal reports (see Figure 1A and Supplemental File 1 for details). In some cases, these gerogenes have been identified based on measuring the viability at a single or a few time points, which fails to provide a quantifiable measure of the change in lifespan with RNAi treatment. In other cases, these genes have been quantitatively assessed for changes in lifespan, as well as additional age-associated phenotypes. For instance, we previously identified 159 genes that were necessary for both normal and increased lifespan of animals with decreased insulin/IGF-1 signaling, and quantified changes in healthspan. Of these, 103 gene inactivations result in a progeric phenotype, as loss resulted in one or more signs of premature aging8.
While some gerogenes have been associated with 100 or more studies (e.g. daf-16, daf-2, sir-2.1), over 400 gerogenes have 10 or fewer citations (Figure 1B, and Supplemental File 2). Thus, while comprehensive feeding-based RNAi screens have discovered and cursorily characterized hundreds of putative gerogenes, how these genes function in longevity control, and the genetic interrelationships between these gene products remain poorly studied. Full longitudinal analysis for age-associated phenotypes is a prerequisite for identifying genetic interactions between gerogenes (e.g. epistatic interactions, asynthetic interactions, etc.). Gaining deeper insight into the genetic interrelationships between gerogenes requires a high-throughput quantitative method, which also leverages the advantages of feeding-based RNAi.
The most common surrogate measure of aging is lifespan. The traditional approach for measuring C. elegans mortality tracks the deaths of individual animals over time within a small population sample. A relatively small number of animals are followed over time and periodically are gently prodded with either a platinum wire or eyelash, with movement as an indicator of viability (Figure 2A). This method has been widely used, as it provides straightforward, direct measurements of the average and the maximum lifespan. However, this traditional method is time consuming and relatively low-throughput, which limits the number of animals and conditions that can simultaneously be measured in a controlled manner. A recent simulation study found that many C. elegans lifespan studies do not assay a large enough number of animals to be able to reliably detect small changes between conditions9. Furthermore, this traditional method involves repeatedly handling the same cohort of animals over time, which in turn can introduce contamination, and can damage or kill increasingly fragile, aged animals.
We have developed an alternative &#34;Replica Set&#34; methodology for measuring C. elegans lifespan. To this end, a large population of age-synchronized, isogenic animals are divided into a number of small populations (or replicas). Enough replica samples are generated to cover each time point in the planned experiment. At each observation time point, one of the replicas is scored for the number of living, dead and censored animals, then animals within that replicate are discarded. Thus, over the expected lifespan of the population as a whole, a series of independent subpopulations are periodically sampled (Figure 2B). In using replica sets there is no repeated prodding of animals and no repeated exposure to potential environmental contamination. The viability observed at the one-time point is completely independent of every other observation, which minimizes handling and increases throughput by at least an order of magnitude. This has allowed us to quantitate changes in lifespan for hundreds of RNAi clones simultaneously8,10.
Here we present detailed protocols for conducting C. elegans lifespan via both the Replica Set and traditional methods for scoring C. elegans longevity. We demonstrate that similar results are obtained between the methods. We have developed software to assist in the graphical analysis of lifespan data generated through either approach, which we freely provide under a GPL V3 license (See Table of Materials). &#34;WormLife&#34; is written in R11, and includes a graphical user interface (GUI) for plotting data, which has been tested in Mac OS and Linux. Lastly, we compare and contrast the limitations of each method and highlight other considerations when choosing between approaches to measure quantitative changes in C. elegans lifespan.

<table border="0" cellpadding="0" cellspacing="0" width="1120">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">IPTG (isopropyl beta-D-1-thigalactopyranoside)</td>
			<td style="width:108px;">Gold Bio</td>
			<td style="width:119px;">12481C100</td>
			<td style="width:527px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">FuDR (5-Fluoro-2&#39;-deoxyuridine)</td>
			<td style="width:108px;">Alfa Aesar</td>
			<td>L16497</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:367px;">24 Well Culture Plates</td>
			<td style="width:108px;">Greiner Bio-One</td>
			<td style="width:119px;">#662102</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">Retangular non-treated single-well plate, 128x86mm</td>
			<td style="width:108px;">Thermo-Fisher</td>
			<td style="width:119px;">242811</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:367px;">600 &#181;L 96-well plates</td>
			<td style="width:108px;">Greiner Bio-One</td>
			<td style="width:119px;">#786261</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:367px;">2mL 96-well plates</td>
			<td style="width:108px;">Greiner Bio-One</td>
			<td style="width:119px;">#780286</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">Air-permeable plate seal</td>
			<td style="width:108px;">VWR</td>
			<td style="width:119px;">60941-086</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">96-pin plate replicator</td>
			<td style="width:108px;">Nunc</td>
			<td style="width:119px;">250520</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">bacto-peptone</td>
			<td style="width:108px;">VWR</td>
			<td style="width:119px;">90000-368</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">bacteriological agar</td>
			<td style="width:108px;">Affymetrix/USB</td>
			<td style="width:119px;">10906</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:367px;">C. elegans RNAi clone library in HT115 bacteria- Ahringer</td>
			<td style="width:108px;">Source Bioscience</td>
			<td style="width:119px;">C. elegans RNAi Collection (Ahringer)</td>
			<td>See also Kamath et. al, Nature 2003.</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:367px;">C. elegans RNAi clone library in HT115 bacteria- Vidal</td>
			<td style="width:108px;">Source Bioscience</td>
			<td style="width:119px;">C. elegans ORF-RNAi Resource (Vidal)</td>
			<td>See also Rual et. al, Genome Research 2004. This library is also available from Dharmacon.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">WormLife- Software for Replica Set Survival Analysis</td>
			<td style="width:108px;">Samuelson Lab</td>
			<td style="width:119px;">N/A</td>
			<td>https://github.com/samuelsonlab-urmc/wormlife</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">L4440 Empty Vector Plasmid</td>
			<td style="width:108px;">Addgene</td>
			<td style="width:119px;">1654</td>
			<td>https://www.addgene.org/1654/</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">Wormbase</td>
			<td style="width:108px;"></td>
			<td style="width:119px;"></td>
			<td>http://www.wormbase.org/&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">OASIS</td>
			<td style="width:108px;"></td>
			<td style="width:119px;"></td>
			<td>https://sbi.postech.ac.kr/oasis2/&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:367px;">Graphpad Prism</td>
			<td style="width:108px;"></td>
			<td style="width:119px;"></td>
			<td>https://www.graphpad.com/scientific-software/prism/&#160;</td>
		</tr>
	</tbody>
</table>

the replica set method: a high-throughput approach to quantitatively measure caenorhabditis elegans lifespan

The Replica Set method is an approach to quantitatively measure lifespan or survival of Caenorhabditis elegans nematodes in a high-throughput manner, thus allowing a single investigator to screen more treatments or conditions over the same amount of time without loss of data quality. The method requires common equipment found in most laboratories working with C. elegans and is thus simple to adopt. The approach centers on assaying independent samples of a population at each observation point, rather than a single sample over time as with traditional longitudinal methods. Scoring entails adding liquid to the wells of a multi-well plate, which stimulates C. elegans to move and facilitates quantifying changes in healthspan. Other major benefits of the Replica Set method include reduced exposure of agar surfaces to airborne contaminants (e.g. mold or fungus), minimal handling of animals, and robustness to sporadic mis-scoring (such as calling an animal as dead when it is still alive). To appropriately analyze and visualize the data from a Replica Set style experiment, a custom software tool was also developed. Current capabilities of the software include plotting of survival curves for both Replica Set and traditional (Kaplan-Meier) experiments, as well as statistical analysis for Replica Set. The protocols provided here describe the traditional experimental approach and the Replica Set method, as well as an overview of the corresponding data analysis.

In the development of any new methodology, it is imperative that the new method recapitulates accepted results from previous approaches and meets the standard within a field. We have previously shown empirically that the Replica Set and traditional methods for assaying C. elegans lifespan produce similar results20. Wild-type C. elegans (N2) maintained at 20 &#176;C typically live between 20 and 25 days, which we observed with both the traditional ...

Watch this Scientific Journal Video about The Replica Set Method: A High-throughput Approach to Quantitatively Measure Caenorhabditis elegans Lifespan at JoVE.com

The Replica Set Method: A High-throughput Approach to Quantitatively Measure Caenorhabditis elegans Lifespan

Here we describe the Replica Set method, an approach to quantitatively measure C. elegans lifespan/survival and healthspan in a high-throughput and robust manner, thus allowing screening of many conditions without sacrificing data quality. This protocol details the strategy and provides a software tool for analysis of Replica Set data.

The Replica Set Method: A High-throughput Approach to Quantitatively Measure Caenorhabditis elegans Lifespan

The Replica Set method is an approach to quantitatively measure lifespan or survival of Caenorhabditis elegans nematodes in a high-throughput manner, thus ...

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