Name: dietary supplementation of polyunsaturated fatty acids in caenorhabditis elegans
Uploaded: 2013-11-29T16:00:00
Description: Watch this Scientific Journal Video about Dietary Supplementation of Polyunsaturated Fatty Acids in Caenorhabditis elegans at JoVE.com

We thank Chris Webster for performing the preliminary experiments shown in Figure 3 of the representative results and Jason Watts and Chris Webster for helpful comments on the manuscript. Funding for this study was provided by a grant from the National Institutes of Health (USA) (R01DK074114) to JLW. Some nematode strains used in this work were provided by the Caenorhabditis Genetics Center, which is funded by the NIH Office of Research Infrastructure Programs (P40 OD010440).

Polyunsaturated fatty acids are sensitive to heat, light and oxygen. Therefore, care must be taken when preparing fatty acid supplementation plates such that fatty acids are not exposed to excess heat and light. NGM media containing 0.1% Tergitol (NP-40) is autoclaved and partially cooled, after which fatty acid sodium salts are added with constant stirring. The plates are allowed to dry in the dark. Uptake of fatty acids by C. elegans cultured on these plates can then be monitored by gas chromatography.
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Here we describe a method of supplementation of C. elegans with dietary unsaturated fatty acids. As mentioned above, care must be taken in the preparation of PUFA supplemented plates because the reactive nature of the double bonds in PUFAs causes these fatty acids to be sensitive to oxidation through heat and light11. To avoid oxidation, it is important to add the PUFA to the liquid agar medium after the media has cooled to 55 &#176;C and stores plates in a dark environment.
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Fatty acids are essential structural components of membranes as well as efficient energy storage molecules. Additionally, fatty acids can be cleaved from cellular membranes by lipases and be enzymatically modified to produce signaling effectors1. Naturally occurring polyunsaturated fatty acids (PUFAs) contain two or more cis double bonds. The omega-3 fatty acids and the omega-6 fatty acids are distinguished from each other based on the positions of double bonds with respect to the methyl end of the fatty acid. Healthy diets require both omega-6 and omega-3 fatty acids. However, Western diets are particularly rich in omega-6 fatty acids and poor in omega-3 fatty acids. A high omega-6 to omega-3 fatty acid ratio is associated with increased risk of cardiovascular and inflammatory diseases, however, the precise beneficial and detrimental functions of specific fatty acids are not well understood2. The roundworm Caenorhabditis elegans is useful in studying fatty acid function because it synthesizes all of the enzymes necessary to produce a range of omega-6 and omega-3 fatty acids, including an omega-3 desaturase, an activity that is absent in most animals3,4 . Mutants lacking fatty acid desaturase enzymes fail to produce specific PUFAs, leading to a range of developmental and neurological defects4-6.
To study the physiological effects of dietary fatty acids, we have developed a biochemical assay compatible with genetic analysis using both mutant and RNAi knock-down techniques in C. elegans. Supplementation with specific PUFAs is achieved by adding a fatty acid sodium salt solution to the agar medium prior to pouring. This results in PUFA uptake by the E. coli food source, where it accumulates in the bacterial membranes. C. elegans ingest the PUFA-containing bacteria, and this dietary supplementation is sufficient to rescue the defects of PUFA-deficient mutants. Supplementation of most fatty acids has no detrimental effects on wild type animals, however, specific omega-6 fatty acids, especially dihomo-gamma linolenic acid (DGLA, 20:3n-6) cause a permanent destruction of C. elegans germ cells7,8 .
Gas chromatography is used to monitor the uptake of the supplemented fatty acid in the bacterial food source (either OP50 or HT115) as well as in the nematodes. The addition of the detergent Tergitol (NP-40) in the media allows for even distribution of fatty acids through the entire plate and more efficient uptake of the fatty acids by the E. coli and the nematodes. We have found that unsaturated fatty acids are readily taken up by bacteria and C. elegans, but the uptake of saturated fatty acids is much less efficient. This article will describe step-by-step how to supplement the agar media with fatty acids, as well as how to monitor fatty acid uptake in the nematode using gas chromatography.

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		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Bacto-Agar</td>
			<td style="width:128px;">Difco</td>
			<td style="width:155px;">214010</td>
			<td style="width:275px;"></td>
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		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Tryptone</td>
			<td style="width:128px;">Difco</td>
			<td style="width:155px;">211705</td>
			<td style="width:275px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:208px;">NaCl</td>
			<td style="width:128px;">J.T. Baker</td>
			<td style="width:155px;">3624-05</td>
			<td style="width:275px;"></td>
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		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Tergitol</td>
			<td style="width:128px;">Sigma</td>
			<td style="width:155px;">NP40S-500mL</td>
			<td style="width:275px;"></td>
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			<td height="22" style="height:22px;width:208px;">Cholesterol</td>
			<td style="width:128px;">Sigma</td>
			<td style="width:155px;">C8667-25G</td>
			<td style="width:275px;">(5 mg/mL in ethanol)</td>
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			<td height="22" style="height:22px;width:208px;">MgSO4</td>
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			<td style="width:128px;">J.T. Baker</td>
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			<td height="42" style="height:42px;width:208px;">Sodium dihomogamma linolenate</td>
			<td style="width:128px;">NuCHEK</td>
			<td style="width:155px;">S-1143</td>
			<td style="width:275px;"></td>
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		<tr height="42">
			<td height="42" style="height:42px;width:208px;">Warm sterile Millipore water</td>
			<td style="width:128px;"></td>
			<td style="width:155px;"></td>
			<td style="width:275px;"></td>
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			<td height="42" style="height:42px;width:208px;">Sterile water for collecting worms</td>
			<td style="width:128px;"></td>
			<td style="width:155px;"></td>
			<td style="width:275px;"></td>
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		<tr height="42">
			<td height="42" style="height:42px;width:208px;">Nuclease-free Water for DGLA stock solution</td>
			<td style="width:128px;">Ambion</td>
			<td style="width:155px;">AM9932</td>
			<td style="width:275px;"></td>
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			<td height="42" style="height:42px;width:208px;">Ampicillin</td>
			<td style="width:128px;">Fisher Scientific</td>
			<td style="width:155px;">BP1760-25</td>
			<td style="width:275px;">100 mg/ml in water (for RNAi plates)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:208px;">Isopropyl-beta-D-thiogalactopyranoside (IPTG)</td>
			<td style="width:128px;">Gold Biotechnology</td>
			<td style="width:155px;">12481C100</td>
			<td style="width:275px;">1 M in water (for RNAi plates)</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:208px;">HSO4</td>
			<td style="width:128px;">J.T. Baker</td>
			<td style="width:155px;">9681-03</td>
			<td style="width:275px;"></td>
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		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Methanol</td>
			<td style="width:128px;">Fisher Scientific</td>
			<td style="width:155px;">A452-4</td>
			<td style="width:275px;"></td>
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			<td height="22" style="height:22px;width:208px;">Hexane</td>
			<td style="width:128px;">Fisher Scientific</td>
			<td style="width:155px;">H302-4</td>
			<td style="width:275px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">diamindinophenylindole (DAPI)</td>
			<td style="width:128px;">Sigma</td>
			<td style="width:155px;">D9542</td>
			<td style="width:275px;"></td>
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			<td height="42" style="height:42px;width:208px;">VectaShield</td>
			<td style="width:128px;">Vector Laboratories</td>
			<td style="width:155px;">H-1000</td>
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			<td height="22" style="height:22px;width:208px;">Glass Flask</td>
			<td style="width:128px;">Corning</td>
			<td style="width:155px;">4980-2L</td>
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			<td height="42" style="height:42px;width:208px;">Autoclaveable Glass bottles with stirbars</td>
			<td style="width:128px;">Fisherbrand</td>
			<td style="width:155px;">FB-800</td>
			<td></td>
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			<td height="42" style="height:42px;width:208px;">Autoclaveable Glass Graduated Cylinder</td>
			<td style="width:128px;">Fisherbrand</td>
			<td style="width:155px;">08-557</td>
			<td></td>
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		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Stir Plate</td>
			<td style="width:128px;">VWR</td>
			<td style="width:155px;">97042-642</td>
			<td></td>
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		<tr height="42">
			<td height="42" style="height:42px;width:208px;">Waterbath at 55+ &#176;C</td>
			<td style="width:128px;">Precision Scientific Inc.</td>
			<td style="width:155px;">66551</td>
			<td></td>
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			<td height="22" style="height:22px;width:208px;">Screwcap Brown Glass Vial</td>
			<td style="width:128px;">Sun SRI</td>
			<td style="width:155px;">200 494</td>
			<td></td>
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			<td height="22" style="height:22px;width:208px;">Argon gas tank</td>
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			<td height="22" style="height:22px;width:208px;">Automated Pipette aid</td>
			<td style="width:128px;">Pipette-Aid</td>
			<td style="width:155px;">P-90297</td>
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			<td height="42" style="height:42px;width:208px;">Sterile Serological Pipettes (25 ml)</td>
			<td style="width:128px;">Corning</td>
			<td style="width:155px;">4489</td>
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			<td height="22" style="height:22px;width:208px;">Bunsen Burner</td>
			<td style="width:128px;">VWR</td>
			<td style="width:155px;">89038-534</td>
			<td></td>
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			<td height="22" style="height:22px;width:208px;">Dissection microscope</td>
			<td style="width:128px;">Leica</td>
			<td style="width:155px;">TLB3000</td>
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		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Silanized glass tube</td>
			<td style="width:128px;">Thermo Scientific</td>
			<td style="width:155px;">STT-13100-S</td>
			<td>for FAMEs derivitization</td>
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			<td height="22" style="height:22px;width:208px;">Clinical tabletop centrifuge</td>
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			<td height="22" style="height:22px;width:208px;">GC Crimp Vial</td>
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			<td style="width:155px;">200 232</td>
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			<td height="22" style="height:22px;width:208px;">GC Vial cap</td>
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			<td style="width:155px;">200 100</td>
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			<td height="22" style="height:22px;width:208px;">Gas Chromatograph</td>
			<td style="width:128px;">Agilent</td>
			<td style="width:155px;">7890A</td>
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			<td height="22" style="height:22px;width:208px;">Mass Spectrometry Detector</td>
			<td style="width:128px;">Agilent</td>
			<td style="width:155px;">5975C</td>
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		<tr height="22">
			<td height="22" style="height:22px;width:208px;">Column for gas chromatography</td>
			<td style="width:128px;">Suppelco</td>
			<td style="width:155px;">SP 2380</td>
			<td>30 m x 0.25 mm fused silica capillary column</td>
		</tr>
	</tbody>
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dietary supplementation of polyunsaturated fatty acids in caenorhabditis elegans

Fatty acids are essential for numerous cellular functions. They serve as efficient energy storage molecules, make up the hydrophobic core of membranes, and participate in various signaling pathways. Caenorhabditis elegans synthesizes all of the enzymes necessary to produce a range of omega-6 and omega-3 fatty acids. This, combined with the simple anatomy and range of available genetic tools, make it an attractive model to study fatty acid function. In order to investigate the genetic pathways that mediate the physiological effects of dietary fatty acids, we have developed a method to supplement the C. elegans diet with unsaturated fatty acids. Supplementation is an effective means to alter the fatty acid composition of worms and can also be used to rescue defects in fatty acid-deficient mutants. Our method uses nematode growth medium agar (NGM) supplemented with fatty acidsodium salts. The fatty acids in the supplemented plates become incorporated into the membranes of the bacterial food source, which is then taken up by the C. elegans that feed on the supplemented bacteria. We also describe a gas chromatography protocol to monitor the changes in fatty acid composition that occur in supplemented worms. This is an efficient way to supplement the diets of both large and small populations of C. elegans, allowing for a range of applications for this method.

Supplementation of the C. elegans diet is limited by the ability of the bacterial food source to uptake and incorporate fatty acid into the bacterial membrane. To determine the ability of E. coli OP50 to assimilate various fatty acids into its membranes, OP50 was plated onto media with no supplement, 0.1 mM and 0.3 mM concentrations of stearic acid (18:0), sodium oleate (18:1n-9), and sodium DGLA (20:3n-6). Plates were dried at room temperature for 2 days in the dark, and incubated at 20 &#176;C for 3 d...

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Dietary Supplementation of Polyunsaturated Fatty Acids in Caenorhabditis elegans

Caenorhabditis elegans is a useful model to explore the functions of polyunsaturated fatty acids in development and physiology. This protocol describes an efficient method of supplementing the C. elegans diet with polyunsaturated fatty acids.

Dietary Supplementation of Polyunsaturated Fatty Acids in Caenorhabditis elegans

Fatty acids are essential for numerous cellular functions. They serve as efficient energy storage molecules, make up the hydrophobic core of membranes, ...

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Biology

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