We are grateful to Dr. Tingtao Zhou for designing and writing the code for the trajectory visualizations used in our analysis. This work was supported by funding: R01 NS113119 (PWS), Chen senior postdoc fellowship, and the Tianqiao and Chrissy Chen Institute for Neuroscience.

Extraction and Quantification of Volatile Sex Pheromone Responses in &lt;i&gt;C. elegans&lt;/i&gt;

The authors have no conflicts of interest to disclose.

This protocol provides a robust methodology for the extraction of volatile sex pheromones from C. elegans, along with establishing a robust chemoattraction assay to measure male chemoattraction responses. Additional information can be found in the WormLab user guide (see the Table of Materials); for a basic code to visualize worm movement trajectory, see protocol section 7.3.8.5. Several crucial steps in the protocol are important for the outcome. First, careful synchronization of worm populatio...

The interplay between chemical communication and reproductive success is a fundamental principle across the animal kingdom1,2,3,4,5,6,7,8,9,10. Sex pheromones trigger a wide array of sexually dimorphic behaviors essential for locating mates, coordinating the steps involved in finding and attracting a partner, and ultimately promoting the propagation of a species11,12,13,14,15,16,17. Significant progress has been made in understanding pheromone signaling, but the molecular mechanisms, neural circuits, and computational processes governing these interactions often remain incompletely defined18,19,20,21,22,23,24,25,26.
The nematode Caenorhabditis elegans provides a powerful model for dissecting these questions. Notably, C. elegans exhibits an unusual reproductive strategy-hermaphrodites can self-fertilize but also outcross with males27,28,29,30,31,32,33. This flexibility requires a robust communication system to signal reproductive status. C. elegans is known for its well-characterized water-soluble pheromones, the ascarosides, which play varied roles in development, behavior, and social interactions. Recent discoveries have unveiled a distinct class of volatile sex pheromones employed by nematodes. These pheromones are specifically produced by sexually mature C. elegans and C. remanei virgin females and sperm-depleted hermaphrodites, serving as an attractant for adult males29,34,35. This attractant exhibits remarkable sexual dimorphism in its production and perception. The female somatic gonad governs the synthesis of this volatile sex pheromone, and production dynamically reflects reproductive status, ceasing upon mating and resuming several hours later29,34.
Understanding nematode sex pheromone communication provides insights into the evolution of chemical communication systems, the interplay between reproductive state and behavior, and the mechanisms underlying sexually dimorphic neural processing24,26,36,37,38,39. Studies implicate the amphid neuron AWA in males as critical for pheromone detection, with the G-protein-coupled receptor SRD-1 playing a key role in pheromone detection in males24. C. elegans is well-suited for studying animal chemical communication, especially sex pheromone signaling, due to its reliance on the olfactory system for mate-searching. While much is known about ascaroside signaling, the volatile sex pheromone system offers unique opportunities for comparison25,26,36,40,41,42,43,44,45,46,47,48,49,50, 
51,52,53,54,55,56,57. Moreover, C. elegans is a powerful genetic model organism due to its fully sequenced genome, clearly defined cellular lineage, and well-characterized olfactory mutants.
However, the complete neural circuitry involved in processing this pheromone, the computations that translate its perception into targeted mate-searching behaviors, and its biosynthesis regulation remain to be fully elucidated. Further investigations into these processes are crucial for understanding the diverse mechanisms governing animal communication and reproductive behaviors. The identification of key genes involved in pheromone synthesis, secretion, and perception promises to unveil novel molecular players in animal communication.&#160;The assays&#160;described here provide a basis to address these&#160;questions.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>10 cm Petri dishes</td>
			<td>Falcon</td>
			<td>25373-100</td>
			<td>Falcon bacteriological Petri dish 100 x 15 mm</td>
		</tr>
		<tr>
			<td>6 cm Petri dishes</td>
			<td>Falcon</td>
			<td>25373-085</td>
			<td>Falcon bacteriological Petri dish 60 x 15 mm</td>
		</tr>
		<tr>
			<td>C. remanei (EM464)</td>
			<td>CGC</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Eppendorf</td>
			<td>centrifuge 5418</td>
			<td>&#160;Any brand should work.</td>
		</tr>
		<tr>
			<td>Chemoattraction assay plates</td>
			<td>Homemade solution</td>
			<td>N/A</td>
			<td>1.5% agar, 25 mM NaCl, 1.5 mM Tris-base, and 3.5 mM Tris-Cl</td>
		</tr>
		<tr>
			<td>Cholesterol</td>
			<td>Alfa Aesar</td>
			<td>57-88-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Dissecting Microscope</td>
			<td>Leica</td>
			<td>LeicaMZ75</td>
			<td>&#160;Any brand should work.</td>
		</tr>
		<tr>
			<td>E. Coli OP50</td>
			<td>CGC</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Koptec</td>
			<td>64-17-5</td>
			<td></td>
		</tr>
		<tr>
			<td>fog-2(q71) (JK574)</td>
			<td>CGC</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>him-5(e1490)(CB4088)</td>
			<td>CGC</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Household bleach</td>
			<td>Clorox Germicidal bleach concentrated</td>
			<td></td>
			<td>&#160;Bleach</td>
		</tr>
		<tr>
			<td>M9 buffer</td>
			<td>Homemade solution</td>
			<td>N/A</td>
			<td>3 g KH2PO4, 11.3 g Na2HPO4.7H2O, 5 g NaCl, H2O to 1 L. Sterilize by autoclaving. Add 1 mL 1 M MgSO4 after cool down to room temperature.</td>
		</tr>
		<tr>
			<td>Magnesium Sulfate, Anhydrous, Powder</td>
			<td>Macron</td>
			<td>M1063-500GM-EA</td>
			<td></td>
		</tr>
		<tr>
			<td>Microwave</td>
			<td>TOSHIBA</td>
			<td>N/A</td>
			<td>&#160;Any brand should work.</td>
		</tr>
		<tr>
			<td>N2</td>
			<td>CGC</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NaOH</td>
			<td>Sigma-aldrich</td>
			<td>S318-3</td>
			<td>1 M</td>
		</tr>
		<tr>
			<td>NGM plates solution</td>
			<td>Homemade solution</td>
			<td>N/A</td>
			<td>2.5 g Peptone, 18 g agar, 3 g NaCl, H2O to 1 L.Sterilize by autoclaving. Once the autoclave is done (2 h), wait until the temperature of the medium drops to 65 &#176;C. Put on a hotplate at 65 &#176;C and stir. Then add the following, waiting 5 min between each to avoid crystallization: 1 mL CaCl2 (1 M), 1 mL MgSO4 (1 M), 25 mL K3PO4 (1 M, pH=6), 1 mL Cholesterol ( 5 mg/mL in ethanol).</td>
		</tr>
		<tr>
			<td>Parafilm</td>
			<td>Bemis</td>
			<td>13-374-10</td>
			<td>Bemis Parafilm M Laboratory Wrapping Film</td>
		</tr>
		<tr>
			<td>Peptone</td>
			<td>VWR</td>
			<td>97063-324</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipet- aid</td>
			<td>Drummond Scientific&#160;</td>
			<td>4-000-100</td>
			<td>&#160;Any brand should work.</td>
		</tr>
		<tr>
			<td>Plastic paper&#160;</td>
			<td>Octago</td>
			<td>Waterproof Screen Printing Inkjet Transparency Film</td>
			<td>https://www.amazon.com/Octago-Waterproof-Transparency-Printing-Printers/dp/B08HJQWFGD</td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>Sigma-aldrich</td>
			<td>SLBP2366V</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate</td>
			<td>Spectrum</td>
			<td>7778-77-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette</td>
			<td>Eppendorf</td>
			<td>SKU: EPPR4331; MFG#: 2231300006</td>
			<td>20 - 200 &#181;L, 100 - 1000 &#181;L, any brand should work.</td>
		</tr>
		<tr>
			<td>Rotator</td>
			<td>Labnet</td>
			<td>SKU: LI-H5500</td>
			<td>&#160;Labnet H5500 Mini LabRoller with Dual Direction Rotator. Any brand should work.</td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>VWR</td>
			<td>7647-14-5</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium phosphate dibasic</td>
			<td>Sigma-aldrich</td>
			<td>SLCG3888</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-base</td>
			<td>Sigma-aldrich</td>
			<td>77-86-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-Cl&#160;</td>
			<td>Roche</td>
			<td>1185-53-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Tryptone</td>
			<td>VWR</td>
			<td>97063-390</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex</td>
			<td>Scientific industries</td>
			<td>Vortex-Genie 2</td>
			<td>&#160;Any brand should work.</td>
		</tr>
		<tr>
			<td>WormLab system&#160;</td>
			<td>MBF Bioscience</td>
			<td>N/A</td>
			<td>https://www.mbfbioscience.com/help/WormLab/Content/home.htm; https://www.mbfbioscience.com/products/wormlab/</td>
		</tr>
		<tr>
			<td>Wormpicker</td>
			<td>Homemade&#160;</td>
			<td>N/A</td>
			<td>made with platinum and glass pipet tips</td>
		</tr>
	</tbody>
</table>

volatile sex pheromone extraction and chemoattraction assay in caenorhabditis elegans

Chemical communication is vital in organismal health, reproduction, and overall well-being. Understanding the molecular pathways, neural processes, and computations governing these signals remains an active area of research. The nematode Caenorhabditis elegans provides a powerful model for studying these processes as it produces a volatile sex pheromone. This pheromone is synthesized by virgin females or sperm-depleted hermaphrodites and serves as an attractant for males.
This protocol describes a detailed method for isolating the volatile sex pheromone from several C. elegans strains (WT strain N2, daf-22, and fog-2) and C. remanei. We also provide a protocol for quantifying the male chemotaxis response to the volatile sex pheromone. Our analysis utilizes measurements such as chemotaxis index (C.I.), arrival time (A.T.), and a trajectory plot to compare male responses under various conditions accurately. This method allows for robust comparisons between males of different genetic backgrounds or developmental stages. Furthermore, the experimental setup outlined here is adaptable to investigating other chemoattraction chemicals.

Author Spotlight: Examining Volatile Sex Pheromone Influence on Male &lt;i&gt;C. elegans&lt;/i&gt; Behavior

Volatile Sex Pheromone Extraction and Chemoattraction Assay in Caenorhabditis elegans

Our research examines how the volatile sex pheromone affects male C.elegans behavior using chemotaxis assay. It aims to identify the molecular mechanism of pheromone production and the neuronal mechanism of it is perception. Individual worm to worm variability in response to pheromone, coupled with the influence of environmental factors such as temperature, humidity, and light, can introduce significant noise into the data.Moreover, the complex nature of worm behaviors complicates data interpretation. Addressing those challenges requires careful experimental design. The protocol is straight forward and highly reproducible.It is designed to optimize pheromone yet while minimizing time and resource consumption. The chemotaxis assay provides quantitative data on male attraction, enabling statistical analysis and comparison. This protocol provides a completed picture of pheromone communication.

Trajectory analysis of volatile sex pheromone perception defective strain in chemoattraction assay 
This chemoattraction assay reliably differentiates between wild-type and mutant strains of C. elegans in their response to volatile sex pheromones. Successful experiments with him-5 males consistently demonstrate robust chemotaxis towards the pheromone source. This is reflected in a high chemotaxis index (C.I.) (Figure 2), often exceeding 0.5, indicating...

This protocol establishes methods for extracting and quantifying responses to the volatile sex pheromone in C. elegans, providing tools to study chemical communication and navigation trajectory.

Chemical communication is vital in organismal health, reproduction, and overall well-being. Understanding the molecular pathways, neural processes, and ...

volatile-sex-pheromone-extraction-chemoattraction-assay

Research

JoVE Journal

Behavior

Extraction and Storage of Volatile Sex Pheromones from C. elegans and C. remanei Females

To begin, separate 200 L4 stage, fog-2 Caenorhabditis elegans virgin females one day prior to pheromone extraction. Distribute the females onto three separate six centimeter OP50 NGM plates. On the extraction day, transfer 100 virgin one-day-old fog-2 females into a micro centrifuge tube containing one milliliter of M9 buffer.After the last wash, incubate females in 100 microliters of M9 buffer for six hours at 20 degrees Celsius to allow pheromone production. Similarly, isolate 15 to 20 L4 stage Caenorhabditis remanei females onto three OP50 NGM plates. After washing, incubate five virgin females in 100 microliters of M9 buffer for six hours at 25 degrees Celsius.Centrifuge the worms at 15, 000 G for 30 to 60 seconds. Carefully transfer the supernatant containing pheromones to a clean tube. Discard the tube containing the worm pellet.Store the collected volatile sex pheromone extract at minus 80 degrees Celsius.

Large-Scale Extraction of Crude Sex Pheromones from 6-Day-Old Virgin C. elegans Hermaphrodites

After synchronizing the healthy adult Caenorhabditis Elegans Worms, wash them five times with M9 buffer. To synchronize worms at the L1 stage, rotate them in the M9 buffer for 12 to 15 hours to arrest development. Observe the arrested L1 worms onto a 10 centimeter NGM culture plate seeded with OP50 bacteria.To minimize the presence of males on a hermaphrodite plate, check the plate two days after worm release and remove any observed males. After three days of development, observe the appearance of embryos indicating that the worms have become reproductively mature adults. Wash away the embryos repeatedly with M9 buffer and let them settle until most of the adults are at the bottom of the tube.Pipette the separated adults and transfer them to a new OP50 seeded NGM plate.

Volatile Sex Pheromone Chemoattraction Assay in C. elegans

To begin, remove the culture plate containing adult hermaphrodite female worms from the incubator. After synchronizing him-5 worms, wash the worms five times with M9 buffer. Transfer the one-day-old adult males from the seeded plate to a tube containing M9 buffer.Place the worms on an unseeded NGM plate to eliminate residual bacteria and prevent interference from food during the assay. Prepare a chemoattraction assay plate with 1.5%auger, 25 millimolar sodium chloride, 1.5 millimolar Tris base, and 3.5 millimolar Tris hydrochloride. Heat the auger in the chemoattraction solution in a microwave until completely dissolved.After cooling, use a pipette to evenly distribute the chemoattraction auger solution into petri dishes. Leave the lids open in a clean area to allow the surface of the auger to dry slightly. Once the surface has dried appropriately, close the lids.To conduct the chemoattraction assay, mark three distinct spots on the lid and the underside of the petri dish. Apply two microliters of one molar sodium azide to each experimental and control spot on the plate. Pick 20 healthy and freely moving male worms with a worm picker.Under a dissecting microscope, release the worm at the starting point. Quickly add two microliters of M9 buffer to the control spot and two microliters of sex pheromone to the experimental spot on the lid. Gently close the lid and place the plate in a quiet, temperature-stable area.After 30 minutes, score the assay by counting the number of worms at each spot. For an enhanced assessment of chemotaxis, record the worms'trajectories using a camera. The chemotaxis index for him-5 males was consistently above 0.5, indicating a strong attraction to the sex pheromone source, while the chemotaxis index for SRD-1 males was around zero.Successful chemoattraction assays showed him-5 males moving closer to the pheromone source over time, with color-coded trajectories indicating time, distance, speed, straightness, and direction correctness.

799 Views.  California Institute of Technology.  This protocol establishes methods for extracting and quantifying responses to the volatile sex pheromone in C. elegans, providing tools to study chemical communication and navigation trajectory.

Extraction and Quantification of Volatile Sex Pheromone Responses in C. elegans

Summary