Name: label-free imaging of lipid storage dynamics in caenorhabditis elegans using stimulated raman scattering microscopy
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Description: Watch this Scientific Journal Video about Label-Free Imaging of Lipid Storage Dynamics in Caenorhabditis elegans using Stimulated Raman Scattering Microscopy at JoVE.com

This work was supported by NIH grants R01AG045183 (M.C.W.), R01AT009050 (M.C.W.), R01AG062257 (M.C.W.), DP1DK113644 (M.C.W.), March of Dimes Foundation (M.C.W.), Welch Foundation (M.C.W.), and by HHMI investigator (M.C.W.). We thank the Caenorhabditis Genetics Center (CGC) for C. elegans strains.

1. Instrumental setup for Stimulated Raman Scattering Microscopy
NOTE: The SRS microscopy system is built upon a picosecond laser with pump integrated optical parametric oscillator and a confocal laser scanning microscope. The oscillator provides two picosecond pulse trains, including a Stokes beam at 1,064 nm and a pump beam tunable between 700&#8211;990 nm. Temporal and spatial overlapping of the two beams are achieved inside the laser. A built-in electro-optic modulator (EOM) is designed spec...

<ol>
	<li>Luppino, F. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Overweight,+obesity,+and+depression:+a+systematic+review+and+meta-analysis+of+longitudinal+studies.">Overweight, obesity, and depression: a systematic review and meta-analysis of longitudinal studies.</a> Archives of General Psychiatry. 67 (3), 220-229 (2010).</li><li>Eckel, R. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Obesity+and+type+2+diabetes:+what+can+be+unified+and+what+needs+to+be+individualized.">Obesity and type 2 diabetes: what can be unified and what needs to be individualized.</a> Diabetes Care. 34 (6), 1424-1430 (2011).</li><li>Poirier, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Obesity+and+cardiovascular+disease:+pathophysiology,+evaluation,+and+effect+of+weight+loss.">Obesity and cardiovascular disease: pathophysiology, evaluation, and effect of weight loss.</a> Arteriosclerosis, Thrombosis, and Vascular Biology. 26 (5), 968-976 (2006).</li><li>Bhaskaran, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Body-mass+index+and+risk+of+22+specific+cancers:+a+population-based+cohort+study+of+5.24+million+UK+adults.">Body-mass index and risk of 22 specific cancers: a population-based cohort study of 5.24 million UK adults.</a> Lancet. 384 (9945), 755-765 (2014).</li><li>Shen, Y., Hu, F., Min, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Raman+imaging+of+small+biomolecules.">Raman imaging of small biomolecules.</a> Annual Review of Biophysics. 48, 347-369 (2019).</li><li>Daemen, S., van Zandvoort, M., Parekh, S. H., Hesselink, M. K. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscopy+tools+for+the+investigation+of+intracellular+lipid+storage+and+dynamics.">Microscopy tools for the investigation of intracellular lipid storage and dynamics.</a> Molecular Metabolism. 5 (3), 153-163 (2016).</li><li>Syed, A., Smith, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Raman+imaging+in+cell+membranes,+lipid-rich+organelles,+and+lipid+bilayers.">Raman imaging in cell membranes, lipid-rich organelles, and lipid bilayers.</a> Annual Review of Analytical Chemistry. 10 (1), 271-291 (2017).</li><li>Thomas, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Raman+spectroscopy+of+protein+and+nucleic+acid+assemblies.">Raman spectroscopy of protein and nucleic acid assemblies.</a> Annual Review of Biophysics and Biomolecular Structure. 28, 1-27 (1999).</li><li>Evans, C. L., Xie, X. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coherent+anti-stokes+Raman+scattering+microscopy:+chemical+imaging+for+biology+and+medicine.">Coherent anti-stokes Raman scattering microscopy: chemical imaging for biology and medicine.</a> Annual Review of Analytical Chemistry. 1, 883-909 (2008).</li><li>Freudiger, C. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+biomedical+imaging+with+high+sensitivity+by+stimulated+Raman+scattering+microscopy.">Label-free biomedical imaging with high sensitivity by stimulated Raman scattering microscopy.</a> Science. 322 (5909), 1857-1861 (2008).</li><li>Hu, F., Shi, L., Min, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+imaging+of+chemical+bonds+by+stimulated+Raman+scattering+microscopy.">Biological imaging of chemical bonds by stimulated Raman scattering microscopy.</a> Nature Methods. 16 (9), 830-842 (2019).</li><li>Wang, M. C., Min, W., Freudiger, C. W., Ruvkun, G., Xie, X. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNAi+screening+for+fat+regulatory+genes+with+SRS+microscopy.">RNAi screening for fat regulatory genes with SRS microscopy.</a> Nature Methods. 8 (2), 135-138 (2011).</li><li>Wei, L., Yu, Y., Shen, Y., Wang, M. C., Min, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrational+imaging+of+newly+synthesized+proteins+in+live+cells+by+stimulated+Raman+scattering+microscopy.">Vibrational imaging of newly synthesized proteins in live cells by stimulated Raman scattering microscopy.</a> Proceedings of the National Academy of Sciences of the United States of America. 110 (28), 11226-11231 (2013).</li><li>Wei, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live-cell+imaging+of+alkyne-tagged+small+biomolecules+by+stimulated+Raman+scattering.">Live-cell imaging of alkyne-tagged small biomolecules by stimulated Raman scattering.</a> Nature Methods. 11 (4), 410-412 (2014).</li><li>Ramachandran, P. V., Mutlu, A. S., Wang, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+biomedical+imaging+of+lipids+by+stimulated+Raman+scattering+microscopy.">Label-free biomedical imaging of lipids by stimulated Raman scattering microscopy.</a> Current Protocols in Molecular Biology. 109, 31 (2015).</li><li>Srinivasan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+body+fat+in+Caenorhabditis+elegans.">Regulation of body fat in Caenorhabditis elegans.</a> Annual Review of Physiology. 77, 161-178 (2015).</li><li>Vrablik, T. L., Petyuk, V. A., Larson, E. M., Smith, R. D., Watts, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipidomic+and+proteomic+analysis+of+Caenorhabditis+elegans+lipid+droplets+and+identification+of+ACS-4+as+a+lipid+droplet-associated+protein.">Lipidomic and proteomic analysis of Caenorhabditis elegans lipid droplets and identification of ACS-4 as a lipid droplet-associated protein.</a> Biochimca Et Biophysica Acta. 1851 (10), 1337-1345 (2015).</li><li>Yu, Y., Mutlu, A. S., Liu, H., Wang, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-throughput+screens+using+photo-highlighting+discover+BMP+signaling+in+mitochondrial+lipid+oxidation.">High-throughput screens using photo-highlighting discover BMP signaling in mitochondrial lipid oxidation.</a> Nature Communications. 8 (1), 865 (2017).</li><li>Kelley, L. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live-cell+confocal+microscopy+and+quantitative+4D+image+analysis+of+anchor-cell+invasion+through+the+basement+membrane+in+Caenorhabditis+elegans.">Live-cell confocal microscopy and quantitative 4D image analysis of anchor-cell invasion through the basement membrane in Caenorhabditis elegans.</a> Nature Protocols. 12 (10), 2081-2096 (2017).</li><li>Murphy, C. T., Hu, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insulin/insulin-like+growth+factor+signaling+in+C.+elegans.">Insulin/insulin-like growth factor signaling in C. elegans.</a> WormBook. , 1-43 (2013).</li><li>Shi, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+lipid+droplet+size+and+phospholipid+composition+by+stearoyl-CoA+desaturase.">Regulation of lipid droplet size and phospholipid composition by stearoyl-CoA desaturase.</a> Journal of Lipid Research. 54 (9), 2504-2514 (2013).</li><li>Watts, J. L., Ristow, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipid+and+carbohydrate+metabolism+in+Caenorhabditis+elegans.">Lipid and carbohydrate metabolism in Caenorhabditis elegans.</a> Genetics. 207 (2), 413-446 (2017).</li><li>Kimura, K. D., Tissenbaum, H. A., Liu, Y., 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=daf-2,+an+insulin+receptor-like+gene+that+regulates+longevity+and+diapause+in+Caenorhabditis+elegans.">daf-2, an insulin receptor-like gene that regulates longevity and diapause in Caenorhabditis elegans.</a> Science. 277 (5328), 942-946 (1997).</li><li>Kwon, E. S., Narasimhan, S. D., Yen, K., Tissenbaum, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+DAF-16+isoform+regulates+longevity.">A new DAF-16 isoform regulates longevity.</a> Nature. 466 (7305), 498-502 (2010).</li><li>Chen, A. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Longevity+genes+revealed+by+integrative+analysis+of+isoform-specific+daf-16/FoxO+mutants+of+Caenorhabditis+elegans.">Longevity genes revealed by integrative analysis of isoform-specific daf-16/FoxO mutants of Caenorhabditis elegans.</a> Genetics. 201 (2), 613-629 (2015).</li><li>Lee, R. Y., Hench, 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=Regulation+of+C.+elegans+DAF-16+and+its+human+ortholog+FKHRL1+by+the+daf-2+insulin-like+signaling+pathway.">Regulation of C. elegans DAF-16 and its human ortholog FKHRL1 by the daf-2 insulin-like signaling pathway.</a> Current Biology. 11 (24), 1950-1957 (2001).</li><li>Mutlu, A. S., Gao, S. M., Zhang, H., Wang, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Olfactory+specificity+regulates+lipid+metabolism+through+neuroendocrine+signaling+in+Caenorhabditis+elegans.">Olfactory specificity regulates lipid metabolism through neuroendocrine signaling in Caenorhabditis elegans.</a> Nature Communications. 11 (1), 1450 (2020).</li><li>Chen, A. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fingerprint+Stimulated+Raman+Scattering+imaging+reveals+retinoid+coupling+lipid+metabolism+and+survival.">Fingerprint Stimulated Raman Scattering imaging reveals retinoid coupling lipid metabolism and survival.</a> Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry. 19 (19), 2500-2506 (2018).</li><li>Li, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+imaging+of+lipid+synthesis+and+lipolysis+dynamics+in+Caenorhabditis+elegans+by+Stimulated+Raman+Scattering+microscopy.">Quantitative imaging of lipid synthesis and lipolysis dynamics in Caenorhabditis elegans by Stimulated Raman Scattering microscopy.</a> Analytical Chemistry. 91 (3), 2279-2287 (2019).</li><li>Lin, C. J., Wang, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbial+metabolites+regulate+host+lipid+metabolism+through+NR5A-Hedgehog+signalling.">Microbial metabolites regulate host lipid metabolism through NR5A-Hedgehog signalling.</a> Nature Cell Biology. 19 (5), 550-557 (2017).</li><li>Fu, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+metabolic+fingerprinting+of+neutral+lipids+with+hyperspectral+stimulated+Raman+scattering+microscopy.">In vivo metabolic fingerprinting of neutral lipids with hyperspectral stimulated Raman scattering microscopy.</a> Journal of the American Chemical Society. 136 (24), 8820-8828 (2014).</li><li>Perez, C. L., Van Gilst, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+13C+isotope+labeling+strategy+reveals+the+influence+of+insulin+signaling+on+lipogenesis+in+C.+elegans.">A 13C isotope labeling strategy reveals the influence of insulin signaling on lipogenesis in C. elegans.</a> Cell Metabolism. 8 (3), 266-274 (2008).</li><li>Elle, I. C., Rodkaer, S. V., Fredens, J., Faergeman, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+for+measuring+fatty+acid+oxidation+in+C.+elegans.">A method for measuring fatty acid oxidation in C. elegans.</a> Worm. 1 (1), 26-30 (2012).</li><li>Ezcurra, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=elegans+eats+its+own+intestine+to+make+yolk+leading+to+multiple+senescent+pathologies.">elegans eats its own intestine to make yolk leading to multiple senescent pathologies.</a> Current Biology. 28 (16), 2544-2556 (2018).</li><li>Lu, F. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Label-free+DNA+imaging+in+vivo+with+stimulated+Raman+scattering+microscopy.">Label-free DNA imaging in vivo with stimulated Raman scattering microscopy.</a> Proceedings of the National Academy of Sciences of the United States of America. 112 (37), 11624-11629 (2015).</li><li>Long, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-color+vibrational+imaging+of+glucose+metabolism+using+stimulated+Raman+scattering.">Two-color vibrational imaging of glucose metabolism using stimulated Raman scattering.</a> Chemical Communications. 54 (2), 152-155 (2018).</li><li>Zhao, Z., Shen, Y., Hu, F., Min, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Applications+of+vibrational+tags+in+biological+imaging+by+Raman+microscopy.">Applications of vibrational tags in biological imaging by Raman microscopy.</a> Analyst. 142 (21), 4018-4029 (2017).</li><li>Liao, C. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+and+in+situ+spectroscopic+imaging+by+a+handheld+Stimulated+Raman+Scattering+Microscope.">In vivo and in situ spectroscopic imaging by a handheld Stimulated Raman Scattering Microscope.</a> ACS Photonics. 5 (3), 947-954 (2018).</li><li>Lee, H. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessing+cholesterol+storage+in+live+cells+and+C.+elegans+by+stimulated+Raman+scattering+imaging+of+phenyl-Diyne+cholesterol.">Assessing cholesterol storage in live cells and C. elegans by stimulated Raman scattering imaging of phenyl-Diyne cholesterol.</a> Scientific Reports. 5, 7930 (2015).</li><li>Wang, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+lipid+metabolism+in+live+Caenorhabditis+elegans+using+fingerprint+vibrations.">Imaging lipid metabolism in live Caenorhabditis elegans using fingerprint vibrations.</a> Angewandte Chemie (International Edition in English). 53 (44), 11787-11792 (2014).</li><li>Chen, W. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectroscopic+coherent+Raman+imaging+of+Caenorhabditis+elegans+reveals+lipid+particle+diversity.">Spectroscopic coherent Raman imaging of Caenorhabditis elegans reveals lipid particle diversity.</a> Nature Chemical Biology. 16 (10), 1087-1095 (2020).</li><li>Freudiger, C. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stimulated+Raman+Scattering+microscopy+with+a+robust+fibre+laser+source.">Stimulated Raman Scattering microscopy with a robust fibre laser source.</a> Nature Photonics. 8 (2), 153-159 (2014).</li><li>Brinkmann, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Portable+all-fiber+dual-output+widely+tunable+light+source+for+coherent+Raman+imaging.">Portable all-fiber dual-output widely tunable light source for coherent Raman imaging.</a> Biomedical Optics Express. 10 (9), 4437-4449 (2019).</li></ol>

In defense against obesity and its associated metabolic disorders, important research efforts have been implemented to better understand the regulatory mechanisms of lipid homeostasis. For quantitative detection of lipid molecules in biological samples, label-free imaging by SRS microscopy has been proven to be a reliable alternative to biochemical assays and other staining methods. Our group and others have revealed novel biological mechanisms in lipid metabolic regulation by combining the use of C. elegans and...

Obesity has become a global health problem threatening one third of the population around the world, and it presents a serious medical concern, given its association with poor mental health1 and deadly diseases including diabetes2, cardiovascular diseases3 and some types of cancer4. Study of lipid metabolism is essential to better understand the biological problems behind obesity. Rapid and specific quantification of lipid storage entails the detection of fatty acids and their derivatives, as well as sterol-containing metabolites, with high sensitivity and preferably with spatial information. Lipids are challenging targets to image because they lack intrinsic fluorescence and cannot be easily fluorescently tagged. The fluorescent tags are often larger than the lipid molecules and, therefore, can be chemically invasive and impractical for in vivo applications. Label-free or minimal labeling strategy is necessary to preserve the hydrophobic structure of the lipid molecules5. Recent developments in imaging technologies have created exciting opportunities for label-free imaging of lipids in living cells, tissues, and organisms.
Traditional approaches for lipid storage analyses in biological samples include biochemical assays and staining protocols with lipophilic dyes. Biochemical quantification assays involving mass spectrometry (MS) are unmatched in their molecular resolvability, but they require very large sample amounts and sample preparation usually takes several hours, limiting their application for real-time imaging of living systems5. Another major limitation of these assays is the lack of spatial information. On the other hand, lipophilic dyes such as Oil Red O and Sudan Black provide tissue and cellular distribution of lipid storage organelles and compared to MS techniques, these staining methods are also low in cost and easy to perform. However, these staining protocols require fixation, which can impact the hydrophobic nature of the lipid droplets, generate artificial changes in their structure and result in inconsistencies between experiments6. The technical difficulties associated with biochemical and staining techniques have led to the search for label-free methods to image lipid molecules and to the rapid increase in the usage of coherent Raman scattering (CRS) microscopy in lipid imaging.
The Raman effect was first recognized by Raman and Krishnan, where they reported that upon interacting with a photon, a molecule can generate scattered light with no change in wavelength (called Rayleigh scattering) or rarely with an altered wavelength (called Raman scattering) and this change in wavelength is characteristic of the functional chemical groups within the molecule7. When the chemical bonds within a molecule get excited to a higher vibrational energy level by an incident photon, called pump photon, the energy of the scattered photon, called the Stokes photon, become lower. Otherwise, the chemical bonds can reach a lower vibrational energy level if they are originally at a higher level, and the scattered photon gain energy to be the anti-Stokes photon. The frequency difference between the incident and scattered photons is known as the Raman shift. Each chemical bond within a molecule has a characteristic and quantifiable Raman shift. For example, the CH2 bond has a Raman shift of 2,845 cm-1, which is abundant in fatty acid chains8. This spontaneous Raman signal is generally very weak, which has vastly limited the imaging speed in conventional spontaneous Raman microscopy. Over the years, various approaches have been developed to increase the imaging speed and sensitivity of spontaneous Raman microscopy. Coherent Raman scattering microscopy, including Coherent Anti-Stokes Raman Scattering (CARS) microscopy and Stimulated Raman Scattering (SRS) microscopy, is the most recent progress. CARS and SRS have slightly different working principles, but both are label-free techniques that have live imaging capability, can yield spatial and temporal information on lipid storage dynamics, and only require small sample size. CARS microscopy suffers from non-resonant background, which comes from various non-linear processes, and CARS signals also have non-linear relationship with the molecule concentration, which together complicate the quantification process9. Unlike CARS microscopy, SRS microscopy does not generate non-resonant background signals and offers linear dependence on the concentration of the molecule of interest. Thus, currently SRS microscopy is more widely used for lipid imaging.
In SRS microscopy, the weak spontaneous Raman signals can be amplified when excited by two synchronized laser beams with their frequency difference matching the chemical bond vibrational frequency. The molecule will experience an enhanced transition to an excited state due to coherent excitation. As a result, the rate of Stokes photon generation is boosted. Consequently, the intensity of the transmitted &#8220;Stokes&#8221; beam increases (stimulated Raman gain, SRG) and the intensity of the transmitted &#8220;pump&#8221; beam decreases (stimulated Raman loss, SRL). Detection of SRG or SRL signals underlies the basis for Stimulated Raman Scattering (SRS) microscopy imaging of molecules with specific chemical bonds10. If the frequency difference between the two laser beams does not match the vibrational frequency of the chemical bond within a molecule of interest, neither SRG nor SRL signals will be generated. The imaging speed of SRS microscopy is around 2 &#956;sec per pixel or 1 second per frame, which is much faster than spontaneous Raman microscopy11. Typical lateral resolution for SRS microscopy is diffraction limited and around 300 nm. In addition, the two-photon optical processes of SRS microscopy allow for volumetric 3D imaging of relative thick tissue samples and the imaging depth could reach 300&#8211;500 &#956;m. Overall, SRS microscopy presents an efficient, label-free imaging technique to detect specific biomolecules, especially lipids.
Lipid droplets are single-membrane organelles, which are the main cellular storage site for neutral lipids, including the triacylglycerols (TAGs) and cholesterol esters (CEs). CH2 bonds in the fatty acid chains of these lipid molecules generate strong SRS signals at 2,845 cm-1 when excited8, thus enabling the detection and quantification of storage lipid levels in intact cells, tissue sections and even whole organisms12,13,14,15. In particular, C. elegans are useful for lipid imaging studies owing to their transparency. Like mammals, C. elegans also store lipids in lipid droplets and the synthesis and degradation pathways of lipid molecules are highly conserved16. In this protocol, we will provide the working principle of SRS microscopy, its fundamental setup and describe the methods for its use in lipid imaging in C. elegans.

<table>
	<tbody>
		<tr>
			<td>A/D converter</td>
			<td>Olympus</td>
			<td>Analog Unit</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>GeneMate</td>
			<td>3119</td>
			<td>For making agarose pads</td>
		</tr>
		<tr>
			<td>Alignment tool - adapter</td>
			<td>Thorlabs</td>
			<td>SM1A4</td>
			<td>For mounting the tool on scope</td>
		</tr>
		<tr>
			<td>Alignment tool - target</td>
			<td>Thorlabs</td>
			<td>VRC2SM1</td>
			<td>For viewing IR laser</td>
		</tr>
		<tr>
			<td>Alignment tool - tube</td>
			<td>Thorlabs</td>
			<td>SM1L40</td>
			<td>Length can vary</td>
		</tr>
		<tr>
			<td>Autocorrelator (Optional)</td>
			<td>APE</td>
			<td>pulseCheck</td>
			<td></td>
		</tr>
		<tr>
			<td>Bandpass filter</td>
			<td>minicircuits</td>
			<td>BBP-21.4+ if modulated at 20MHz or KR Electronics 2724 if modulated at 8 MHz</td>
			<td>For signal with modulation frequency filtering</td>
		</tr>
		<tr>
			<td>BNC cables</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dissection microscope</td>
			<td>Nikon</td>
			<td>SMZ800</td>
			<td>For handling and picking worms for imaging</td>
		</tr>
		<tr>
			<td>Dodecane</td>
			<td>Sigma-Aldrich</td>
			<td>44010</td>
			<td>Used for calibration of the SRS signal</td>
		</tr>
		<tr>
			<td>Filter</td>
			<td>Chroma Technology</td>
			<td>890/220 CARS</td>
			<td>For removing Stokes beam</td>
		</tr>
		<tr>
			<td>General purpose laboratory labeling tape</td>
			<td>VWR</td>
			<td>89097</td>
			<td>For making agarose pads</td>
		</tr>
		<tr>
			<td>Glass coverslips</td>
			<td>VWR</td>
			<td>48393-106</td>
			<td>For covering worms for imaging</td>
		</tr>
		<tr>
			<td>Glass microscope slide</td>
			<td>VWR</td>
			<td>16004-422</td>
			<td>For making agarose pads</td>
		</tr>
		<tr>
			<td>Laser scanning microscope</td>
			<td>Olympus</td>
			<td>FV3000</td>
			<td></td>
		</tr>
		<tr>
			<td>Lens</td>
			<td>Thorlabs</td>
			<td>L1: AC254-050-B 
			L2: AC254-075-B</td>
			<td>For beam expander</td>
		</tr>
		<tr>
			<td>Lock-in amplifier</td>
			<td>Zurich</td>
			<td>HF2LI</td>
			<td></td>
		</tr>
		<tr>
			<td>Lowpass filter</td>
			<td>minicircuits</td>
			<td>BLP-1.9+</td>
			<td>For power supply noise suppression</td>
		</tr>
		<tr>
			<td>Mirrors</td>
			<td>Thorlabs</td>
			<td>BB1-E03</td>
			<td>For relay and periscope</td>
		</tr>
		<tr>
			<td>Objective</td>
			<td>Olympus</td>
			<td>UPlanSAPO 20x 0.75, UPlanSAPO 60XW 1.20</td>
			<td></td>
		</tr>
		<tr>
			<td>Photodiode</td>
			<td>Thorlabs</td>
			<td>FDS1010</td>
			<td></td>
		</tr>
		<tr>
			<td>Picosecond laser source</td>
			<td>APE</td>
			<td>picoEmerald</td>
			<td></td>
		</tr>
		<tr>
			<td>Power supply</td>
			<td>TEKPOWER</td>
			<td>TP1342U</td>
			<td>For photodiode, reversed 50V voltage</td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>Sigma</td>
			<td>S2002</td>
			<td>For anaesthesizing the worms</td>
		</tr>
		<tr>
			<td>Worm picker</td>
			<td>WormStuff</td>
			<td>59-AWP</td>
			<td></td>
		</tr>
	</tbody>
</table>

label-free imaging of lipid storage dynamics in caenorhabditis elegans using stimulated raman scattering microscopy

Lipid metabolism is a fundamental physiological process necessary for cellular and organism health. Dysregulation of lipid metabolism often elicits obesity and many associated diseases including cardiovascular disorders, type II diabetes, and cancer. To advance the current understanding of lipid metabolic regulation, quantitative methods to precisely measure in vivo lipid storage levels in time and space have become increasingly important and useful. Traditional approaches to analyze lipid storage are semi-quantitative for microscopic assessment or lacking spatio-temporal information for biochemical measurement. Stimulated Raman scattering (SRS) microscopy is a label-free chemical imaging technology that enables rapid and quantitative detection of lipids in live cells with a subcellular resolution. As the contrast is exploited from intrinsic molecular vibrations, SRS microscopy also permits four-dimensional tracking of lipids in live animals. In the last decade, SRS microscopy has been widely used for small molecule imaging in biomedical research and overcome the major limitations of conventional fluorescent staining and lipid extraction methods. In the laboratory, we have combined SRS microscopy with the genetic and biochemical tools available to the powerful model organism, Caenorhabditis elegans, to investigate the distribution and heterogeneity of lipid droplets across different cells and tissues and ultimately to discover novel conserved signaling pathways that modulate lipid metabolism. Here, we present the working principles and the detailed setup of the SRS microscope and provide methods for its use in quantifying lipid storage at distinct developmental timepoints of wild-type and insulin signaling deficient mutant C. elegans.

Insulin signaling is an important endocrine pathway that impacts development, reproduction, lifespan, and metabolism. In worms, insulin signaling consists of about 40 insulin-like peptide ligands, insulin-like growth factor receptor ortholog DAF-2, downstream PI3K/AKT kinase cascade, and the FoxO transcription factor ortholog, DAF-1620. daf-2 mutants, that lack the insulin receptor, have more lipid droplets in their intestine,&#160;the worm lipid storage tissue21<s...

Watch this Scientific Journal Video about Label-Free Imaging of Lipid Storage Dynamics in Caenorhabditis elegans using Stimulated Raman Scattering Microscopy at JoVE.com

Label-Free Imaging of Lipid Storage Dynamics in Caenorhabditis elegans using Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy allows selective, label-free imaging of specific chemical moieties and it has been effectively employed to image lipid molecules in vivo. Here, we provide a brief introduction to the principle of SRS microscopy and describe methods for its use in imaging lipid storage in Caenorhabditis elegans.

Label-Free Imaging of Lipid Storage Dynamics in Caenorhabditis elegans using Stimulated Raman Scattering Microscopy

Lipid metabolism is a fundamental physiological process necessary for cellular and organism health. Dysregulation of lipid metabolism often elicits ...

Stimulated Raman scattering microscopy is a chemical imaging technology that enables the rapid and quantitative detection of lipids and allows the tracking of lipids in live animals in a label-free manner. The most important advantage of SRS microscopy over traditional lipid detection techniques is that it is label-free and therefore, is not as sustainable to photo bleaching as other fluorescence and staining matters. The use of SRS microscopy in conjunction with the genetic and biochemical tools available for model organisms, particularly Caenorhabditis elegans provides a powerful framework for studying normal regulators of lipid biology and metabolism.To feed laser beams into the SRS microscope, first, set the periscope to lift the beam from a picosecond light source exit to the infrared laser input port on the scanner of the microscope and open the laser control software to start the lasers. Lower the pump laser power to 50 milliwatts and set the pump signal to 750 nanometers. Use a beam expander to adjust the beam diameter to fit the back aperture of the microscope objectives.Use two relay mirrors, M1 and M2, to guide the laser beam to the periscope and set the nods of the periscope at the center of the tuning range. Select the initial position and angle of each mirror such that the laser beam approximately hits the center of the mirror to launch the beam into the microscope and use an empty port on the objective turret of the microscope to perform the course alignment. Place the power meter probe at the objective port to measure the power of the transmitted light and set the scanner of the microscope at the highest zoom, 50X.Measure the power of the transmitted light with the focused laser beam spot and optimize the knobs of mirrors M1 and M2 iteratively to achieve the highest transmitted laser power. Use the alignment tool to perform the fine alignment of the transmitted light to make sure the light is passing through the center of the objective and place the fluorescence target alignment cap on the empty objective seat. Adjust the knobs of the first steering mirror, M1, to center the laser beam spot and introduce the extension tube with the alignment cap on the other end to an empty objective seat for monitoring the laser beam spot.Then, tune the knobs of the second steering mirror, M2, to center the laser beam spot again on the other end of the extension tube. To set up the SRS detection module, place a beam splitter cube after the condenser to direct the transmitted laser to the photo diode module. To set up the electronics connection, use a built-in electro optic modulator at 20 megahertz inside the picosecond tune-able laser to modulate the intensity of the Stokes beam and feed the output signal of the photo diode into the lock-in amplifier for demodulation of the stimulated Raman loss.Then, feed the lock-in amplifier output into the analog box of the microscope to convert the electrical analog signal to a digital signal. To optimize the imaging conditions, add five microliters of oleic acid to a mini microscope slide chamber and cover the sample with a cover slip. Place the sample onto the microscope stage and use the edge of the pad to locate and focus on the droplet.Adjust the condenser for Kohler illumination and use an infrared sensor card and infrared viewer to check whether the pump beam path is still correct. Confirm that the delay stage is set to zero femtoseconds and set the pump beam wavelength to 795.8 nanometers. Set the power of the pump beam to 50 milliwatts and set the Stoke beam to 100 milliwatts.Open the shutter for both the beams, as well as the main shutter of the laser. Scan the sample and check the image on the computer screen. Change the display mode to high low and adjust the range to see an approximately 50%saturation.Check whether the saturation is centered in the image, carefully adjusting the steering mirrors inside the picosecond tune-able laser system for optimized overlap of the pump and the Stokes to maximize the image intensity and to center the peak intensity as necessary. Before each imaging session, add 100 microliters of warm 2%agarose to a clean glass slide placed between support slides with two layers of laboratory tape and quickly place a second slide on top of the first slide. Gently pressed to create a thin, even, agarose pad and allow the agarose to cool.To mount the worms for imaging, place a four to five microliter drop of anesthetic agent per 10 to 20 worms onto a cover slip and use a dissection microscope to pick the worms to be imaged, placing the worms onto the droplet of anesthesia as they are collected. When all of the worms have been collected, cover the worms with the glass slide with the agarose pad. For imaging, mount the worm sample with the cover slip facing the objective lens and direct the bright field light source to the eyepiece to locate the worms.Bring the worms into focus and adjust the condenser position accordingly. Adjust the laser powers by setting the pump laser power to 200 milliwatts and the IR power to 400 milliwatts. Set the lock-in amplifier for demodulation of the worm SRS signal.Begin scanning the first worm at a fast scanning rate, adjusting the fine focus to find the area of interest. When the signal has been optimized, switch to a slower scanning rate and a higher pixel resolution to obtain the SRS image and save the image in a format that enables high resolution. When all of the samples have been imaged, place the laser source on standby and turn off all of the associated equipment.To analyze the images, open the files in ImageJ and select analyze and set measurements to select the properties to be analyzed. Use the polygon selection tool to outline the region of the worm intestine to be quantified and click analyze and measure again. The measurements will appear in the results window.When all of the worms have been outlined, copy and paste the measurements for each of the worms in a given genotype into a spreadsheet. For the background measurement value, select an area in the vicinity of the worm that does not have any SRS signal and subtract the background mean gray value from the measurement for each individual worm to calculate the average and standard deviation of the background subtracted mean gray values from all of the worms in a given genotype or test group. These values can then be normalized to the average of the control group.In this representative analysis, the intestinal lipid levels in age-synchronized wild type worms and daf-2 mutants lacking the insulin receptor were quantified during adulthood. As expected, a decline in lipid levels is observed in wild type worms, starting at day one and continuing until day nine of adulthood. The lipid levels in daf-2 mutants, however, increase until they are five days old, at which point they remain constant at about 2.5 to three fold higher than the wild type.Daf-16 inactivation suppresses the increase in lipid levels of daf-2 mutants. Expression of the daf-16a a or daf-16b isoform in the daf-2, daf-16 double mutants does not restore the lipid levels. The expression of the daf-16d/f/h isoform, however, is sufficient to restore the lipid levels in daf-2, daf-16 double mutants to the levels observed in daf-2 single mutants.These results indicate that the daf-16d/f/h isoform specifically modulates lipid metabolism in daf-2 mutant worms. It is important to use the same laser power for pump and Stokes beams throughout the imaging session and to include a control group in every six and four consistent quantification. In addition to quantifying lipid storage, SRS microscopy can be coupled with bioorthogonal tags, such as the deuterium, and implemented to visualize the dynamics of lipid incorporation, synthesis and degradation.SRS microscopy permits multiplexing and can be implemented to image multiple biomolecules in different subcellular compartments. So-called hyperspectral SRS microscopy has a great future in exploring the metabolic dynamics.

label-free-imaging-lipid-storage-dynamics-caenorhabditis-elegans

Research

JoVE Journal

Biology

Label-free in situ Imaging of Lignification in Plant Cell Walls

Meeting growing energy demands safely and efficiently is a pressing global challenge. Therefore, research into biofuels production that seeks to find cost-effective and sustainable solutions has become a topical and critical task. Lignocellulosic biomass is poised to become the primary source of biomass for the conversion to liquid biofuels1-6. However, the recalcitrance of these plant cell wall materials to cost-effective and efficient degradation presents a major impediment for their use in the production of biofuels and chemicals4. In particular, lignin, a complex and irregular poly-phenylpropanoid heteropolymer, becomes problematic to the postharvest deconstruction of lignocellulosic biomass. For example in biomass conversion for biofuels, it inhibits saccharification in processes aimed at producing simple sugars for fermentation7. The effective use of plant biomass for industrial purposes is in fact largely dependent on the extent to which the plant cell wall is lignified. The removal of lignin is a costly and limiting factor8 and lignin has therefore become a key plant breeding and genetic engineering target in order to improve cell wall conversion.
Analytical tools that permit the accurate rapid characterization of lignification of plant cell walls become increasingly important for evaluating a large number of breeding populations. Extractive procedures for the isolation of native components such as lignin are inevitably destructive, bringing about significant chemical and structural modifications9-11. Analytical chemical in situ methods are thus invaluable tools for the compositional and structural characterization of lignocellulosic materials. Raman microscopy is a technique that relies on inelastic or Raman scattering of monochromatic light, like that from a laser, where the shift in energy of the laser photons is related to molecular vibrations and presents an intrinsic label-free molecular "fingerprint" of the sample. Raman microscopy can afford non-destructive and comparatively inexpensive measurements with minimal sample preparation, giving insights into chemical composition and molecular structure in a close to native state. Chemical imaging by confocal Raman microscopy has been previously used for the visualization of the spatial distribution of cellulose and lignin in wood cell walls12-14. Based on these earlier results, we have recently adopted this method to compare lignification in wild type and lignin-deficient transgenic Populus trichocarpa (black cottonwood) stem wood15. Analyzing the lignin Raman bands16,17 in the spectral region between 1,600 and 1,700 cm-1, lignin signal intensity and localization were mapped in situ. Our approach visualized differences in lignin content, localization, and chemical composition. Most recently, we demonstrated Raman imaging of cell wall polymers in Arabidopsis thaliana with lateral resolution that is sub-&mu;m18. Here, this method is presented affording visualization of lignin in plant cell walls and comparison of lignification in different tissues, samples or species without staining or labeling of the tissues.

Label-free in situ Imaging of Lignification in Plant Cell Walls

A method based on confocal Raman microscopy is presented that affords label-free visualization of lignin in plant cell walls and comparison of lignification in different tissues, samples or species.

Meeting growing energy demands safely and efficiently is a pressing global challenge. Therefore, research into biofuels production that seeks to find ...

Differential Imaging of Biological Structures with Doubly-resonant Coherent Anti-stokes Raman Scattering (CARS)

Coherent Raman imaging techniques have seen a dramatic increase in activity over the past decade due to their promise to enable label-free optical imaging with high molecular specificity 1. The sensitivity of these techniques, however, is many orders of magnitude weaker than fluorescence, requiring milli-molar molecular concentrations 1,2. Here, we describe a technique that can enable the detection of weak or low concentrations of Raman-active molecules by amplifying their signal with that obtained from strong or abundant Raman scatterers. The interaction of short pulsed lasers in a biological sample generates a variety of coherent Raman scattering signals, each of which carry unique chemical information about the sample. Typically, only one of these signals, e.g. Coherent Anti-stokes Raman scattering (CARS), is used to generate an image while the others are discarded. However, when these other signals, including 3-color CARS and four-wave mixing (FWM), are collected and compared to the CARS signal, otherwise difficult to detect information can be extracted 3. For example, doubly-resonant CARS (DR-CARS) is the result of the constructive interference between two resonant signals 4. We demonstrate how tuning of the three lasers required to produce DR-CARS signals to the 2845 cm-1 CH stretch vibration in lipids and the 2120 cm-1 CD stretching vibration of a deuterated molecule (e.g. deuterated sugars, fatty acids, etc.) can be utilized to probe both Raman resonances simultaneously. Under these conditions, in addition to CARS signals from each resonance, a combined DR-CARS signal probing both is also generated. We demonstrate how detecting the difference between the DR-CARS signal and the amplifying signal from an abundant molecule's vibration can be used to enhance the sensitivity for the weaker signal. We further demonstrate that this approach even extends to applications where both signals are generated from different molecules, such that e.g. using the strong Raman signal of a solvent can enhance the weak Raman signal of a dilute solute.

Differential Imaging of Biological Structures with Doubly-resonant Coherent Anti-stokes Raman Scattering CARS

A combination of three single wavelength short-pulsed lasers is used to generate coherent anti-Stokes Raman scattering (CARS) and doubly-resonant CARS (DR-CARS). The difference between these signals provides enhanced sensitivity for otherwise difficult to detect coherent Raman signals, enabling imaging of weak Raman scatterers.

Coherent Raman imaging techniques have seen a dramatic increase in activity over the past decade due to their promise to enable label-free optical imaging ...

Time-lapse Microscopy of Early Embryogenesis in Caenorhabditis elegans

Caenorhabditis elegans has often been used as a model system in studies of early developmental processes. The transparency of the 
embryos, the genetic resources, and the relative ease of transformation are qualities that make C. elegans an excellent model for early embryogenesis. Laser-based 
confocal microscopy and fluorescently labeled tags allow researchers to follow specific cellular structures and proteins in the developing embryo. For example, 
one can follow specific organelles, such as lysosomes or mitochondria, using fluorescently labeled dyes. These dyes can be delivered to the early embryo by means 
of microinjection into the adult gonad. Also, the localization of specific proteins can be followed using fluorescent protein tags. Examples are presented here 
demonstrating the use of a fluorescent lysosomal dye as well as fluorescently tagged histone and ubiquitin proteins. The labeled histone is used to visualize 
the DNA and thus identify the stage of the cell cycle. GFP-tagged ubiquitin reveals the dynamics of ubiquitinated vesicles in the early embryo. Observations 
of labeled lysosomes and GFP:: ubiquitin can be used to determine if there is colocalization between ubiquitinated vesicles and lysosomes. A technique for 
the microinjection of the lysosomal dye is presented. Techniques for generating transgenenic strains are presented elsewhere (1, 2). For imaging, embryos 
are cut out of adult hermaphrodite nematodes and mounted onto 2% agarose pads followed by time-lapse microscopy on a standard laser scanning confocal 
microscope or a spinning disk confocal microscope. This methodology provides for the high resolution visualization of early embryogenesis.

Time-lapse Microscopy of Early Embryogenesis in Caenorhabditis elegans

This article describes a technique for the visualization of the early events of embryogenesis in the nematode Caenorhabditis elegans.

Caenorhabditis elegans has often been used as a model system in studies of early developmental processes.  The transparency of the 
embryos, the genetic ...

Basic Caenorhabditis elegans Methods: Synchronization and Observation

Research into the molecular and developmental biology of the nematode Caenorhabditis elegans was begun in the early seventies by Sydney Brenner and it has since been used extensively as a model organism 1. C. elegans possesses key attributes such as simplicity, transparency and short life cycle that have made it a suitable experimental system for fundamental biological studies for many years 2. Discoveries in this nematode have broad implications because many cellular and molecular processes that control animal development are evolutionary conserved 3.
C. elegans life cycle goes through an embryonic stage and four larval stages before animals reach adulthood. Development can take 2 to 4 days depending on the temperature. In each of the stages several characteristic traits can be observed. The knowledge of its complete cell lineage 4,5 together with the deep annotation of its genome turn this nematode into a great model in fields as diverse as the neurobiology 6, aging 7,8, stem cell biology 9 and germ line biology 10. 
An additional feature that makes C. elegans an attractive model to work with is the possibility of obtaining populations of worms synchronized at a specific stage through a relatively easy protocol. The ease of maintaining and propagating this nematode added to the possibility of synchronization provide a powerful tool to obtain large amounts of worms, which can be used for a wide variety of small or high-throughput experiments such as RNAi screens, microarrays, massive sequencing, immunoblot or in situ hybridization, among others. 
Because of its transparency, C. elegans structures can be distinguished under the microscope using Differential Interference Contrast microscopy, also known as Nomarski microscopy. The use of a fluorescent DNA binder, DAPI (4',6-diamidino-2-phenylindole), for instance, can lead to the specific identification and localization of individual cells, as well as subcellular structures/defects associated to them.

Basic Caenorhabditis elegans Methods: Synchronization and Observation

The easiness of maintaining and propagating the nematode C. elegans make it a nice model organism to work with. The possibility of synchronizing worms allows the work with a significant amount of subjects at the same developmental stage, what facilitates the study of one particular process in many animals.

Research into the molecular and developmental biology of the nematode Caenorhabditis elegans was begun in the early seventies by Sydney Brenner and it has ...

Using Caenorhabditis elegans as a Model System to Study Protein Homeostasis in a Multicellular Organism

The folding and assembly of proteins is essential for protein function, the long-term health of the cell, and longevity of the organism. Historically, the function and regulation of protein folding was studied in vitro, in isolated tissue culture cells and in unicellular organisms. Recent studies have uncovered links between protein homeostasis (proteostasis), metabolism, development, aging, and temperature-sensing. These findings have led to the development of new tools for monitoring protein folding in the model metazoan organism Caenorhabditis elegans. In our laboratory, we combine behavioral assays, imaging and biochemical approaches using temperature-sensitive or naturally occurring metastable proteins as sensors of the folding environment to monitor protein misfolding. Behavioral assays that are associated with the misfolding of a specific protein provide a simple and powerful readout for protein folding, allowing for the fast screening of genes and conditions that modulate folding. Likewise, such misfolding can be associated with protein mislocalization in the cell. Monitoring protein localization can, therefore, highlight changes in cellular folding capacity occurring in different tissues, at various stages of development and in the face of changing conditions. Finally, using biochemical tools ex vivo, we can directly monitor protein stability and conformation. Thus, by combining behavioral assays, imaging and biochemical techniques, we are able to monitor protein misfolding at the resolution of the organism, the cell, and the protein, respectively.

Using Caenorhabditis elegans as a Model System to Study Protein Homeostasis in a Multicellular Organism

To study the relationship between protein homeostasis, stress and aging, we monitored changes in protein folding by following protein dysfunction, protein localization in the cell and protein stability at the organismal, cellular and protein levels, using the genetically tractable metazoan Caenorhabditis elegans as a model system.

The folding and assembly of proteins is essential for protein function, the long-term health of the cell, and longevity of the organism. Historically, the ...

Quantification of Lipid Abundance and Evaluation of Lipid Distribution in Caenorhabditis elegans by Nile Red and Oil Red O Staining

Caenorhabditis elegans is an exceptional model organism in which to study lipid metabolism and energy homeostasis. Many of its lipid genes are conserved in humans and are associated with metabolic syndrome or other diseases. Examination of lipid accumulation in this organism can be carried out by fixative dyes or label-free methods. Fixative stains like Nile red and oil red O are inexpensive, reliable ways to quantitatively measure lipid levels and to qualitatively observe lipid distribution across tissues, respectively. Moreover, these stains allow for high-throughput screening of various lipid metabolism genes and pathways. Additionally, their hydrophobic nature facilitates lipid solubility, reduces interaction with surrounding tissues, and prevents dissociation into the solvent. Though these methods are effective at examining general lipid content, they do not provide detailed information about the chemical composition and diversity of lipid deposits. For these purposes, label-free methods such as GC-MS and CARS microscopy are better suited, their costs notwithstanding.

Quantification of Lipid Abundance and Evaluation of Lipid Distribution in Caenorhabditis elegans by Nile Red and Oil Red O Staining

Nile red staining of fixed Caenorhabditis elegans is a method for quantitative measurement of neutral lipid deposits, while oil red O staining facilitates qualitative assessment of lipid distribution among tissues.

Caenorhabditis elegans is an exceptional model organism in which to study lipid metabolism and energy homeostasis. Many of its lipid genes are conserved ...

Oligomerization Dynamics of Cell Surface Receptors in Living Cells by Total Internal Reflection Fluorescence Microscopy Combined with Number and Brightness Analysis

Despite the importance and ubiquity of receptor oligomerization, few methods are applicable for detecting clustering events and measuring the degree of clustering. Here, we describe an imaging approach to determine the average oligomeric state of mEGFP-tagged-receptor homocomplexes in the membrane of living cells. The protocol is based on Total Internal Reflection Fluorescence (TIRF) microscopy combined with Number and Brightness (N&#38;B) analysis. N&#38;B is a method similar to fluorescence-correlation spectroscopy (FCS) and photon counting histogram (PCH), which are based on the statistical analysis of the fluctuations of the fluorescence intensity of fluorophores diffusing in and out of an illumination volume during an observation time. In particular, N&#38;B is a simplification of PCH to obtain information on the average number of proteins in oligomeric mixtures. The intensity fluctuation amplitudes are described by the molecular brightness of the fluorophore and the average number of fluorophores within the illumination volume. Thus, N&#38;B considers only the first and second moments of the amplitude distribution, namely, the mean intensity and the variance. This is, at the same time, the strength and the weakness of the method. Because only two moments are considered, N&#38;B cannot determine the molar fraction of unknown oligomers in a mixture, but it only estimates the average oligomerization state of the mixture. Nevertheless, it can be applied to relatively small time series (compared to other moment methods) of images of live cells on a pixel-by-pixel basis, simply by monitoring the time fluctuations of the fluorescence intensity. It reduces the effective time-per-pixel to a few microseconds, allowing acquisition in the time range of seconds to milliseconds, which is necessary for fast oligomerization kinetics. Finally, large cell areas as well as sub-cellular compartments can be explored.

We describe an imaging approach for the determination of the average oligomeric state of mEGFP-tagged-receptor oligomers induced by ligand binding in the plasma membrane of living cells. The protocol is based on Total Internal Reflection Fluorescence (TIRF) microscopy combined with Number and Brightness (N&#38;B) analysis.

Despite the importance and ubiquity of receptor oligomerization, few methods are applicable for detecting clustering events and measuring the degree of ...

Rapid Antimicrobial Susceptibility Testing by Stimulated Raman Scattering Imaging of Deuterium Incorporation in a Single Bacterium

To slow and prevent the spread of antimicrobial resistant infections, rapid antimicrobial susceptibility testing (AST) is in urgent need to &#65279;quantitatively determine the &#65279;antimicrobial effects on pathogens. &#65279;It typically takes days to complete the AST by conventional methods based on the long-time culture, and they do not work directly for clinical samples. Here, we report a rapid AST &#65279;method enabled by stimulated Raman scattering (SRS) imaging of deuterium oxide (D2O) metabolic incorporation. Metabolic incorporation of D2O into biomass and the metabolic activity inhibition upon exposure to antibiotics at the single bacterium level are monitored by SRS imaging. The&#65279; single-cell metabolism inactivation concentration (SC-MIC) of bacteria upon exposure to antibiotics can be obtained after a total of 2.5 h of sample preparation and detection. Furthermore, this rapid AST method is directly applicable to bacterial samples in complex biological environments, such as urine or whole blood. SRS metabolic imaging of deuterium incorporation is transformative for rapid single-cell phenotypic AST in the clinic.

This protocol presents rapid antimicrobial susceptibility testing (AST) assay within 2.5 h by single-cell-stimulated Raman scattering imaging of D2O metabolism. This method applies to bacteria in the urine or whole blood environment, which is transformative for rapid single-cell phenotypic AST in the clinic.

To slow and prevent the spread of antimicrobial resistant infections, rapid antimicrobial susceptibility testing (AST) is in urgent need to ...

Automating Aggregate Quantification in Caenorhabditis elegans

A rise in the prevalence of neurodegenerative protein conformational diseases (PCDs) has fostered a great interest in this subject over the years. This increased attention has called for the diversification and improvement of animal models capable of reproducing disease phenotypes observed in humans with PCDs. Though murine models have proven invaluable, they are expensive and are associated with laborious, low-throughput methods. Use of the Caenorhabditis elegans nematode model to study PCDs has been justified by its relative ease of maintenance, low cost, and rapid generation time, which allow for high-throughput applications. Additionally, high conservation between the C. elegans and human genomes makes this model an invaluable discovery tool. Nematodes that express fluorescently tagged tissue-specific polyglutamine (polyQ) tracts exhibit age- and polyQ length-dependent aggregation characterized by fluorescent foci. Such reporters are often employed as proxies to monitor changes in proteostasis across tissues. Manual aggregate quantification is time-consuming, limiting experimental throughput. Furthermore, manual foci quantification can introduce bias, as aggregate identification can be highly subjective. Herein, a protocol consisting of worm culturing, image acquisition, and data processing was standardized to support high-throughput aggregate quantification using C. elegans that express intestine-specific polyQ. By implementing a C. elegans-based image processing pipeline using CellProfiler, an image analysis software, this method has been optimized to separate and identify individual worms and enumerate their respective aggregates. Though the concept of automation is not entirely unique, the need to standardize such procedures for reproducibility, elimination of bias from manual counting, and increase throughput is high. It is anticipated that these methods can drastically simplify the screening process of large bacterial, genomic, or drug libraries using the C. elegans model.

Automating Aggregate Quantification in Caenorhabditis elegans

The following protocol describes the development and optimization of a high-throughput workflow for worm culturing, fluorescence imaging, and automated image processing to quantify polyglutamine aggregates as an assessment of changes in proteostasis.

A rise in the prevalence of neurodegenerative protein conformational diseases (PCDs) has fostered a great interest in this subject over the years. This ...

Super-Resolution Microscopy of the Synaptonemal Complex Within the Caenorhabditis elegans Germline

During meiosis, homologous chromosomes must recognize and adhere to one another to allow for their correct segregation. One of the key events that secures the interaction of homologous chromosomes is the assembly of the synaptonemal complex (SC) in meiotic prophase I. Even though there is little sequence homology between protein components within the SC among different species, the general structure of the SC has been highly conserved during evolution. In electron micrographs, the SC appears as a tripartite, ladder-like structure composed of lateral elements or axes, transverse filaments, and a central element. 
However, precisely identifying the localization of individual components within the complex by electron microscopy to determine the molecular structure of the SC remains challenging. By contrast, fluorescence microscopy allows for the identification of individual protein components within the complex. However, since the SC is only ~100 nm wide, its substructure cannot be resolved by diffraction-limited conventional fluorescence microscopy. Thus, determining the molecular architecture of the SC requires super-resolution light microscopy techniques such as structured illumination microscopy (SIM), stimulated-emission depletion (STED) microscopy, or single-molecule localization microscopy (SMLM). 
To maintain the structure and interactions of individual components within the SC, it is important to observe the complex in an environment that is close to its native environment in the germ cells. Therefore, we demonstrate an immunohistochemistry and imaging protocol that enables the study of the substructure of the SC in intact, extruded Caenorhabditis elegans germline tissue with SMLM and STED microscopy. Directly fixing the tissue to the coverslip reduces the movement of the samples during imaging and minimizes aberrations in the sample to achieve the high resolution necessary to visualize the substructure of the SC in its biological context.

Super-Resolution Microscopy of the Synaptonemal Complex Within the Caenorhabditis elegans Germline

Super-resolution microscopy can provide a detailed insight into the organization of components within the synaptonemal complex in meiosis. Here, we demonstrate a protocol to resolve individual proteins of the Caenorhabditis elegans synaptonemal complex.

During meiosis, homologous chromosomes must recognize and adhere to one another to allow for their correct segregation. One of the key events that secures ...