Using an Adapted Microfluidic Olfactory Chip for the Imaging of Neuronal Activity in Response to Pheromones in Male C. Elegans Head Neurons
Summary
The use of an adapted "olfactory chip" for the efficient calcium imaging of C. elegans males is described here. Studies of male exposure to glycerol and a pheromone are also shown.
Abstract
The use of calcium indicators has greatly enhanced our understanding of neural dynamics and regulation. The nematode Caenorhabditis elegans, with its completely mapped nervous system and transparent anatomy, presents an ideal model for understanding real-time neural dynamics using calcium indicators. In combination with microfluidic technologies and experimental designs, calcium-imaging studies using these indicators are performed in both free-moving and trapped animals. However, most previous studies utilizing trapping devices, such as the olfactory chip described in Chronis et al., have devices designed for use in the more common hermaphrodite, as the less common male is both morphologically and structurally dissimilar. An adapted olfactory chip was designed and fabricated for increased efficiency in male neuronal imaging with using young adult animals. A turn was incorporated into the worm loading port to rotate the animals and to allow for the separation of the individual neurons within a bilateral pair in 2D imaging. Worms are exposed to a controlled flow of odorant within the microfluidic device, as described in previous hermaphrodite studies. Calcium transients are then analyzed using the open-source software ImageJ. The procedure described herein should allow for an increased amount of male-based C. elegans calcium imaging studies, deepening our understanding of the mechanisms of sex-specific neuronal signaling.
Introduction
Microfluidic devices provide increased access to precisely controlled environments, wherein animals, such as the nematode C. elegans, can be experimentally manipulated1. These studies include behavioral assays, calcium imaging studies, or even screenings for specific phenotypes, resulting in more exact measurements of experimental outcomes1,2,3,4,5,6. Microfluidics provide small-scale liquid conditions through which detailed experiments can be run while utilizing minimal amounts of reagents. There is a constant production of new microfluidic device designs, and the use of each varies, from arenas that allow for the natural sinusoidal motion of C. elegans in behavioral assays and neural imaging studies, to trap devices used in neural imaging and olfactory studies, to devices that allow for high-throughput phenotypic analysis in genetic screens4,5,6,7. Following the fabrication of a master mold, microfluidic devices are inexpensive to construct—given the reusability of the master—and easy to use, allowing for rapid data generation via high-throughput studies. The fabrication of devices using polymers such as polydimethylsiloxane (PDMS) allows for the creation of new devices within hours.
Calcium imaging studies use genetically encoded calcium indicators (GECIs) expressed in target cells to measure the neural dynamics of those cells in real time8,9,10,11. The transparent nature of C. elegans allows for the recording of the fluorescent levels of these proteins in live animals. Traditionally, GECIs rely on the green fluorescent protein (GFP)-based sensor GFP-Calmodulin-M13 Peptide (GCaMP), although more recent studies have adapted these sensors to allow for better signal-to-noise ratios and red-shifted excitation profiles. Following the development of GCaMP3, proteins with these specifications have varied, including sensors such as GCaMP6s and GCaMP6f (slow and fast fluorescence off-rates, respectively), as well as RFP-Calmodulin-M13 Peptide (RCaMP), which has a red-shifted activation profile. The combination of these GECIs with C. elegans cell-specific gene promoter sequences can target cells of interest, particularly sensory neurons12,13,14,15,16.
While the ease of C. elegans use in microfluidic studies is apparent, almost all studies have focused on hermaphrodites. Despite males only accounting for 0.01-0.02% of the wild type population, invaluable findings can arise from their characterization. While the physical connectome of the hermaphrodite nervous system has been fully mapped for decades17, the male connectome remains incomplete, especially in the head region of the animal18. The use of calcium imaging in males will help to generate an understanding of the male nervous system and the differences that arise between the two sexes. The smaller size of C. elegans adult males prevents effective and reliable trapping in the loading ports of traditional olfactory devices designed for larger hermaphrodites. To address this, a modified version of the Chronis Olfactory Chip19 was developed with a narrower loading port, a lower channel height, and turns in the worm loading port (which rotate the animal), allowing for the visualization of bilateral left/right neuronal pairs. This design permits: (1) the effective trapping of young adult males, (2) a more reliable orientation of the animal for the visualization of both members of bilateral paired neurons, and (3) the precise imaging of neural activity in male neurons.
Increasingly, studies show that C. elegans males respond differently than hermaphrodites to a variety of ascarosides (ascr), or nematode pheromones20,21,22,23,24. Therefore, developing an understanding of the neural dynamics and representations within the male connectome has become even more pertinent. Male C. elegans contain 87 sex-specific neurons not present in the hermaphrodite25,26, altering the connectome in as-yet undetermined ways. Being able to image these unique neural dynamics will allow us to better understand sex-specific responses and neural representations.
This protocol describes the use of a male-adapted olfactory chip for the neural imaging of male C. elegans chemosensation. The nociceptive neuron ASH responds reliably to 1 M glycerol in males, consistent with previous hermaphroditic studies27. Exposure to ascarosides may elicit responses that are variable from animal to animal, requiring a larger number of animals to be tested. The response of the male-specific CEM neurons has previously been shown, through both electrophysiology and calcium imaging studies, to respond variably to ascaroside #323.
Protocol
Representative Results
Discussion
The male-adapted olfactory chip incorporates a turn into a narrower loading port, which allows for more control of the orientation and for the efficient trapping of male C. elegans. This allows for the visualization of both the left and right members of neuronal bilateral pairs, without the need for z-stacking. This curve leads to an orientation away from vertical 100% of the time in worms where only one bilateral pair is targeted with a fluorescent marker, such as ASH (Figure 2D<st…
Divulgations
The authors have nothing to disclose.
Acknowledgements
We would like to thank Manuel Zimmer for providing us with the initial design file that was adapted for use with males; Frank Schroeder for the synthesis and supply of ascr#3; Ross Lagoy for the insight and assistance with imaging and analysis; and Laura Aurilio for the master fabrication and who, alongside Christopher Chute, contributed to the review of this manuscript. Funding for this work was provided under the National Institutes of Health grant 1R01DC016058-01 (J.S.), the National Science Foundation grant CBET 1605679 (D.R.A.), and the Burroughs Wellcome Career Award at the Scientific Interface (D.R.A.).
Materials
| Silicon Wafer | University Wafer | 452 | |
| SU-8 2035 | MicroChem | Y111070-0500L1GL | |
| Developer | MicroChem | Y020100-4000L1PE | |
| Wafer Mask | Cad/Art Services | – | Custom order. Printed at 25,000 dpi. |
| Sylgard-184 | Ellsworth Adhesives | 184 SIL ELAST KIT 0.5KG | |
| 1.0 mm Dermal Punches | Acuderm Inc. | P150 | |
| Soft Tubing | Cole-Palmer | EW-06419-01 | |
| Hard Tubing | IDEX Health & Science | 1622 | |
| Pins | New England Small Tube | NE-1027-12 | |
| Blocking Pins | New England Small Tube | 0.415/0.425" OD x .500 Long | Batch PB07027 |
| 3 mL syringes | BD | 309657 | |
| 30 mL syringes | Vitality Medical | 302832 | Used as buffer reservoirs. |
| Stainless Steel Blunt Needle 23 Gauge, Polyprolylene Luer | Component Supply Company | NE-231PL-50 | |
| Stopcocks with Luer connections; 3-way; male lock; 5 flow pattern; non-sterile | Cole-Palmer | EW-30600-07 | |
| Fisherfinest Premium Cover Glass | Fisher Scientific | 12-548-5M | |
| Mercator Control System LF-5 Plasma System | Mercator | LF-5 | |
| Scotch Tape | Scotch | BSN43575 | |
| Series 20 Chamber | Warner Instruments | P-2 | |
| Vacuum Desicator | Bel-Art Scienceware | 420250000 | 24 cm inner diameter. |
| Weigh Boats | Cole-Palmer | EW-01017-27 | |
| Classic Plus Balance | Mettler Toledo | PB1501-S/FACT | |
| Glass Pasteur Pipettes | Cole-Palmer | EW-25554-06 | |
| Transfer pipettes | Genesee Scientific | 30-202 | |
| Oven | Sheldon Manufacturing Inc | 9120993 | Model Number: 1500E. |
| 60 mm, non-vented, sharp edge Petri dishes | TriTech Research | T3308 | |
| Zeiss Axio Observer.A1 | Zeiss | – | |
| Hammamatsu Orca Flash 4.0 Digital CMOS | Hammamatsu | C11440-22CU | |
| Blue Fluorescent Light | Lumencor | SOLA SM6-LCR-SA | 24-30V/7.9A DC. |
| Illumination Adaptor | Zeiss | 423302-0000 | |
| Series 1 and 2 Miniature Inert PTFE Isolation Valve | Parker | 001-0017-900 | 3-way valve for controlling flow. |
| ValveLink8.2® | AutoMate Scientific | 01-18 | Flow Switch Controller |
| Micro Manager | Micro-Manager | – | Free software, can be downloaded at: https://www.micro-manager.org/wiki/Download_Micro-Manager_Latest_Release |
| ImageJ | ImageJ | – | Free software, can be downloaded at: https://imagej.nih.gov/ij/download.html |
| Agar, Bacteriological Grade | Apex | 9012-36-6 | |
| Peptone | Apex | 20-260 | |
| CaCl2 | VWR | BDH0224-1KG | |
| MgSO4 | Sigma-Aldrich | 230391-1kg | |
| Cholesterol | Alfa Aesar | A11470 | |
| Ethanol | Sigma-Aldrich | 270741-4L | |
| Tetramisole | Sigma-Aldrich | L9756-10(G) | Store at 4 °C. |
| Fluorescein | Sigma-Aldrich | FD2000S-250mg | Light Sensitive. Store in photoprotective vials. |
| Glycerol | Sigma-Aldrich | G6279-1L | |
| Ascaroside #3 | – | – | Synthesized in the Schroeder Lab (Cornell University). |
| NaCl | Genesee Scientific | 18-215 | |
| KH2PO4 | BDH | BDH9268.25 | |
| K2HPO4 | J.T. Baker | 3252-025 | |
| ASH GCaMP3 line | – | – | CX10979 (KyEx2865 [psra-6::GCAMP3 @ 100 ng/uL]). Developed in Bargmann lab. Provided from Albrecht Lab library. |
| CEM GCaMP6 line | – | – | JSR49 (FkEx98[ppkd-2::GCaMP::SL2::dsRED + pBX-1]; pha-1(e2123ts); him-5(e1490); lite-1(ce314)). Developed by Robyn Lints. Provided from Srinivasan Lab library. |
| E. coli (OP50) | Caenorhabditis Genetics Center | OP50 | |
| "Reservoir" | – | – | To create a Reservoir: A "30 mL syringe", is connected to a "Stopcock with Luer connections; 3-way; male lock; 5 flow pattern; non-sterile", which is connected to a "3 mL syringe" and a "Stainless Steel Blunt Needle 23 Gauge, Polyprolylene Luer". The "Stainless Steel Blunt Needle 23 Gauge, Polyprolylene Luer" is then inserted into "Soft Tubing" approximately 1/3 of the way down the needle. |
References
- Lagoy, R. C., Albrecht, D. R. Microfluidic Devices for Behavioral Analysis, Microscopy, and Neuronal Imaging in Caenorhabditis elegans. Methods Mol Biol. 1327, 159-179 (2015).
- Ben-Yakar, A., Chronis, N., Lu, H. Microfluidics for the analysis of behavior, nerve regeneration, and neural cell biology in C. elegans. Curr Opin Neurobiol. 19 (5), 561-567 (2009).
- Chronis, N. Worm chips: Microtools for C. elegans biology. Lab on a Chip. 10 (4), 432-437 (2010).
- Lee, H., Crane, M. M., Zhang, Y., Lu, H. Quantitative screening of genes regulating tryptophan hydroxylase transcription in Caenorhabditis elegans using microfluidics and an adaptive algorithm. Integr Biol (Camb). 5 (2), 372-380 (2013).
- Lockery, S. R., et al. A microfluidic device for whole-animal drug screening using electrophysiological measures in the nematode C. elegans. Lab Chip. 12 (12), 2211-2220 (2012).
- Mondal, S., et al. Large-scale microfluidics providing high-resolution and high-throughput screening of Caenorhabditis elegans poly-glutamine aggregation model. Nat Commun. 7, 13023 (2016).
- Larsch, J., Ventimiglia, D., Bargmann, C. I., Albrecht, D. R. High-throughput imaging of neuronal activity in Caenorhabditis elegans. Proc Natl Acad Sci U S A. 110 (45), E4266-E4273 (2013).
- Akerboom, J., et al. Genetically encoded calcium indicators for multi-color neural activity imaging and combination with optogenetics. Front Mol Neuro. 6, 2 (2013).
- Badura, A., Sun, X. R., Giovannucci, A., Lynch, L. A., Wang, S. S. H. Fast calcium sensor proteins for monitoring neural activity. Neurophotonics. 1 (2), 025008 (2014).
- Tatro, E. T. Brain-wide imaging of neurons in action. Front Neural Circuits. 8, 31 (2014).
- Tian, L., et al. Imaging neural activity in worms, flies and mice with improved GCaMP calcium indicators. Nat Methods. 6 (12), 875-881 (2009).
- Greene, J. S., et al. Balancing selection shapes density-dependent foraging behaviour. Nature. 539 (7628), 254-258 (2016).
- Greene, J. S., Dobosiewicz, M., Butcher, R. A., McGrath, P. T., Bargmann, C. I. Regulatory changes in two chemoreceptor genes contribute to a Caenorhabditis elegans QTL for foraging behavior. Elife. 5, (2016).
- Kim, K., et al. Two Chemoreceptors Mediate Developmental Effects of Dauer Pheromone in C. elegans. Science. 326 (5955), 994-998 (2009).
- McGrath, P. T., et al. Parallel evolution of domesticated Caenorhabditis species targets pheromone receptor genes. Nature. 477 (7364), 321-325 (2011).
- Schmitt, C., Schultheis, C., Husson, S. J., Liewald, J. F., Gottschalk, A. Specific Expression of Channelrhodopsin-2 in Single Neurons of Caenorhabditis elegans. PLoS ONE. 7 (8), e43164 (2012).
- White, J. G., Southgate, E., Thomson, J. N., Brenner, S. The Structure of the Nervous System of the Nematode Caenorhabditis elegans. Phil Trans of the Royal Soc of Lon. 314 (1165), 1 (1986).
- White, J. Q., et al. The sensory circuitry for sexual attraction in C. elegans males. Curr Biol. 17 (21), 1847-1857 (2007).
- Chronis, N., Zimmer, M., Bargmann, C. I. Microfluidics for in vivo imaging of neuronal and behavioral activity in Caenorhabditis elegans. Nat Meth. 4 (9), 727-731 (2007).
- Chute, C. D., Srinivasan, J. Chemical mating cues in C. elegans. Semin Cell Dev Biol. 33, 18-24 (2014).
- Izrayelit, Y., et al. Targeted metabolomics reveals a male pheromone and sex-specific ascaroside biosynthesis in Caenorhabditis elegans. ACS Chem Biol. 7 (8), 1321-1325 (2012).
- Ludewig, A. H., Schroeder, F. C. Ascaroside signaling in C. elegans. WormBook. , 1-22 (2013).
- Narayan, A., et al. Contrasting responses within a single neuron class enable sex-specific attraction in Caenorhabditis elegans. Proc Natl Acad Sci U S A. 113 (10), E1392-E1401 (2016).
- Srinivasan, J., et al. A blend of small molecules regulates both mating and development in Caenorhabditis elegans. Nature. 454 (7208), 1115-1118 (2008).
- Sammut, M., et al. Glia-derived neurons are required for sex-specific learning in C. elegans. Nature. 526 (7573), 385-390 (2015).
- Sulston, J. E., Albertson, D. G., Thomson, J. N. The Caenorhabditis elegans male: postembryonic development of nongonadal structures. Dev Biol. 78 (2), 542-576 (1980).
- Hilliard, M. A., et al. In vivo imaging of C. elegans ASH neurons: cellular response and adaptation to chemical repellents. The EMBO Journal. 24 (1), 63-72 (2005).
- Evans, T. C. Transformation and microinjection. WormBook. , (2006).
- Cáceres, I. d. C., Valmas, N., Hilliard, M. A., Lu, H. Laterally Orienting C. elegans Using Geometry at Microscale for High-Throughput Visual Screens in Neurodegeneration and Neuronal Development Studies. PLoS ONE. 7 (4), e35037 (2012).
- Schrodel, T., Prevedel, R., Aumayr, K., Zimmer, M., Vaziri, A. Brain-wide 3D imaging of neuronal activity in Caenorhabditis elegans with sculpted light. Nat Methods. 10 (10), 1013-1020 (2013).
- García, L. R., Portman, D. S. Neural circuits for sexually dimorphic and sexually divergent behaviors in Caenorhabditis elegans. Curr Opin Neurobiol. 38, 46-52 (2016).
- Clokey, G. V., Jacobson, L. A. The autofluorescent "lipofuscin granules" in the intestinal cells of Caenorhabditis elegans are secondary lysosomes. Mech Ageing Dev. 35 (1), 79-94 (1986).
- Coburn, C., et al. Anthranilate Fluorescence Marks a Calcium-Propagated Necrotic Wave That Promotes Organismal Death in C. elegans. PLoS Biology. 11 (7), e1001613 (2013).
- Macosko, E. Z., et al. A hub-and-spoke circuit drives pheromone attraction and social behaviour in C. elegans. Nature. 458 (7242), 1171-1175 (2009).
- Park, D., et al. Interaction of structure-specific and promiscuous G-protein-coupled receptors mediates small-molecule signaling in Caenorhabditis elegans. Proc Natl Acad Sci U S A. 109 (25), 9917-9922 (2012).
