We would like to thank our student researchers over the years. In particular, Nina Meyer, Sibylle Mayer, Juliane Kaim, and Laura Jaggy, whose data have been utilized in this protocol as representative results. Research of our group presented here was funded by grants from the Deutsche Forschungsgemeinschaft (Hu 839/2-4, Hu 839/7-1) to Armin Huber.

1. General considerations
<ol>
	<li>Use Drosophila stocks expressing a permanently rhabdomerally located fluorescence protein for morphological analysis (e.g., TRP::eGFP, eGFP::NINAC) and translocating proteins for analyses regarding protein trafficking (e.g., TRPL::eGFP, Arr2::eGFP).</li>
	<li>Predetermine light exposure conditions of selected flies for the experimental approach.
	<ol>
		<li>For dark-adaptation, keep the flies in dark boxes for the desired period at 25 &#176;C. For illuminati...

<ol>
	<li>Wang, X., Huang, T., Bu, G., Xu, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dysregulation+of+protein+trafficking+in+neurodegeneration.">Dysregulation of protein trafficking in neurodegeneration.</a> Molecular Neurodegeneration. 9. 9, 31 (2014).</li><li>Schopf, K., Huber, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane+protein+trafficking+in+Drosophila+photoreceptor+cells.">Membrane protein trafficking in Drosophila photoreceptor cells.</a> European Journal of Cell Biology. 96 (5), 391-401 (2017).</li><li>Hardie, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+photoreceptor+array+of+the+dipteran+retina.">The photoreceptor array of the dipteran retina.</a> Trends in Neurosciences. 9, 419-423 (1986).</li><li>Wang, T., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phototransduction+and+retinal+degeneration+in+Drosophila.">Phototransduction and retinal degeneration in Drosophila.</a> Pfl&#252;gers Archiv - European Journal of Physiology. 454 (5), 821-847 (2007).</li><li>Xiong, B., Bellen, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rhodopsin+homeostasis+and+retinal+degeneration:+lessons+from+the+fly.">Rhodopsin homeostasis and retinal degeneration: lessons from the fly.</a> Trends in Neurosciences. 36 (11), 652-660 (2013).</li><li>B&#228;hner, 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=Light-regulated+subcellular+translocation+of+Drosophila+TRPL+channels+induces+long-term+adaptation+and+modifies+the+light-induced+current.">Light-regulated subcellular translocation of Drosophila TRPL channels induces long-term adaptation and modifies the light-induced current.</a> Neuron. 34 (1), 83-93 (2002).</li><li>Cronin, M. A., Lieu, M. -. H., Tsunoda, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two+stages+of+light-dependent+TRPL-channel+translocation+in+Drosophila+photoreceptors.">Two stages of light-dependent TRPL-channel translocation in Drosophila photoreceptors.</a> Journal of Cell Science. 119, 2935-2944 (2006).</li><li>Meyer, N., Joel-Almagor, T., Frechter, S., Minke, B., Huber, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subcellular+translocation+of+the+eGFP-tagged+TRPL+channel+in+Drosophila+photoreceptors+requires+activation+of+the+phototransduction+cascade.">Subcellular translocation of the eGFP-tagged TRPL channel in Drosophila photoreceptors requires activation of the phototransduction cascade.</a> Journal of Cell Science. 119, 2592-2603 (2006).</li><li>Oberegelsbacher, C., Schneidler, C., Voolstra, O., Cerny, A., Huber, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Drosophila+TRPL+ion+channel+shares+a+Rab-dependent+translocation+pathway+with+rhodopsin.">The Drosophila TRPL ion channel shares a Rab-dependent translocation pathway with rhodopsin.</a> European Journal of Cell Biology. 90 (8), 620-630 (2011).</li><li>Wagner, K., Smylla, T. K., Lampe, M., Krieg, J., Huber, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phospholipase+D+and+retromer+promote+recycling+of+TRPL+ion+channel+via+the+endoplasmic+reticulum.">Phospholipase D and retromer promote recycling of TRPL ion channel via the endoplasmic reticulum.</a> Traffic. , (2021).</li><li>Franceschini, N., Kirschfeld, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Les+ph&#233;nom&#233;nes+de+pseudopupille+dans+l'oeil+compose+de+Drosophila.">Les ph&#233;nom&#233;nes de pseudopupille dans l'oeil compose de Drosophila.</a> Kybernetik. 9 (5), 159-182 (1971).</li><li>Pichaud, F., Desplan, C. <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+visualization+approach+for+identifying+mutations+that+affect+differentiation+and+organization+of+the+Drosophila+ommatidia.">A new visualization approach for identifying mutations that affect differentiation and organization of the Drosophila ommatidia.</a> Development. 128 (6), 815-826 (2001).</li><li>Smylla, T. K., Wagner, K., Huber, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+fluorescent+proteins+for+functional+dissection+of+the+Drosophila+visual+system.">Application of fluorescent proteins for functional dissection of the Drosophila visual system.</a> International Journal of Molecular Sciences. 22 (16), (2021).</li><li>Meyer, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+the+light-dependent+translocation+of+the+ion+channel+TRPL+in+the+photoreceptors+of+Drosophila+melanogaster:+Dissertation+for+obtaining+the+academic+degree+Dr.+rer.+nat.">Mechanisms of the light-dependent translocation of the ion channel TRPL in the photoreceptors of Drosophila melanogaster: Dissertation for obtaining the academic degree Dr. rer. nat.</a> University of Karlsruhe (TH). , (2005).</li><li>Meyer, N., Oberegelsbacher, C., D&#252;rr, T. D., Sch&#228;fer, A., Huber, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+eGFP-based+genetic+screen+for+defects+in+light-triggered+subcelluar+translocation+of+the+Drosophila+photoreceptor+channel+TRPL.">An eGFP-based genetic screen for defects in light-triggered subcelluar translocation of the Drosophila photoreceptor channel TRPL.</a> Fly. 2 (1), 36-46 (2008).</li><li>Zheng, L., Carthew, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lola+regulates+cell+fate+by+antagonizing+Notch+induction+in+the+Drosophila+eye.">Lola regulates cell fate by antagonizing Notch induction in the Drosophila eye.</a> Mechanisms of Development. 125 (1-2), 18-29 (2008).</li><li>Hibbard, K. L., O'Tousa, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+role+for+the+cytoplasmic+DEAD+box+helicase+Dbp21E2+in+rhodopsin+maturation+and+photoreceptor+viability.">A role for the cytoplasmic DEAD box helicase Dbp21E2 in rhodopsin maturation and photoreceptor viability.</a> Journal of Neurogenetics. 26 (2), 177-188 (2012).</li><li>Huang, Y., Xie, J., Wang, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Fluorescence-based+genetic+screen+to+study+retinal+degeneration+in+Drosophila.">A Fluorescence-based genetic screen to study retinal degeneration in Drosophila.</a> PloS One. 10 (12), 0144925 (2015).</li><li>Zhao, H., Wang, J., Wang, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+V-ATPase+V1+subunit+A1+is+required+for+rhodopsin+anterograde+trafficking+in+Drosophila.">The V-ATPase V1 subunit A1 is required for rhodopsin anterograde trafficking in Drosophila.</a> Molecular Biology of the Cell. 29 (13), 1640-1651 (2018).</li><li>Xiong, 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=ER+complex+proteins+are+required+for+rhodopsin+biosynthesis+and+photoreceptor+survival+in+Drosophila+and+mice.">ER complex proteins are required for rhodopsin biosynthesis and photoreceptor survival in Drosophila and mice.</a> Cell Death and Differentiation. 27 (2), 646-661 (2020).</li><li>Zhao, H., Wang, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PE+homeostasis+rebalanced+through+mitochondria-ER+lipid+exchange+prevents+retinal+degeneration+in+Drosophila.">PE homeostasis rebalanced through mitochondria-ER lipid exchange prevents retinal degeneration in Drosophila.</a> PLoS Genetics. 16 (10), 1009070 (2020).</li><li>Cerny, A. 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=The+GTP-+and+phospholipid-binding+protein+TTD14+regulates+trafficking+of+the+TRPL+ion+channel+in+Drosophila+photoreceptor+cells.">The GTP- and phospholipid-binding protein TTD14 regulates trafficking of the TRPL ion channel in Drosophila photoreceptor cells.</a> PLoS Genetics. 11 (10), 1005578 (2015).</li><li>Richter, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+and+functional+analyses+of+TRP+ion+channels+in+the+photoreceptor+cells+of+Drosophila+melanogaster:+Dissertation+for+obtaining+the+academic+degree+Dr.+rer,+nat.">Structural and functional analyses of TRP ion channels in the photoreceptor cells of Drosophila melanogaster: Dissertation for obtaining the academic degree Dr. rer, nat.</a> University of Karlsruhe (TH). , (2007).</li><li>Gambis, A., Dourlen, P., Steller, H., Mollereau, B. <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+in+vivo+imaging+of+photoreceptor+apoptosis+and+development+in+Drosophila.">Two-color in vivo imaging of photoreceptor apoptosis and development in Drosophila.</a> Developmental Biology. 351 (1), 128-134 (2011).</li><li>Hardie, R. C., Liu, C. -. H., Randall, A. S., Sengupta, S. <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+tracking+of+phosphoinositides+in+Drosophila+photoreceptors.">In vivo tracking of phosphoinositides in Drosophila photoreceptors.</a> Journal of Cell Science. 128 (23), 4328-4340 (2015).</li><li>Chakrabarti, 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=A+dPIP5K+dependent+pool+of+phosphatidylinositol+4,5+bisphosphate+(PIP2)+is+required+for+G-protein+coupled+signal+transduction+in+Drosophila+photoreceptors.">A dPIP5K dependent pool of phosphatidylinositol 4,5 bisphosphate (PIP2) is required for G-protein coupled signal transduction in Drosophila photoreceptors.</a> PLoS Genetics. 11 (1), 1004948 (2015).</li></ol>

The applicability of fluorescence proteins and simplicity of screening by DPP imaging and retinal water immersion microscopy has been proven to be successful by many groups12. Strategies similar to the ones presented here have been used in several genetic screens to detect defects in rhodopsin expression levels, homeostasis, retinal organization, or cellular integrity with the help of Rh1::eGFP17,18,19<su...

By delivering and removing proteins to and from the plasma membrane, membrane protein trafficking in neurons controls the plasma membrane equipment with receptors as well as ion channels and, as a result, regulates neuronal function. Misregulation or defects in protein trafficking typically have detrimental effects on cells and result in neuronal degeneration. In humans, this may cause neurodegenerative diseases such as Alzheimer&#39;s and Parkinson&#39;s disease or Retinitis pigmentosa1. Photoreceptors in the compound eye of Drosophila melanogaster have become an in vivo model system for studying membrane protein trafficking2.&#160;This is not only due to the genetic versatility of Drosophila that allows effective genetic screens, but also because all essential components of the light-absorbing photoreceptor membrane are characterized in great detail and efficient microscopic techniques are available that can be applied to the fly eye. These techniques are the focus of this article.
In Drosophila photoreceptor cells, the apical plasma membrane forms a densely packed stack of microvilli along one side of the cell, termed rhabdomere. The rhabdomeres of photoreceptor cells R1-6 are arranged in a characteristic trapezoidal pattern while photoreceptor cells R7 and R8 form a single rhabdomere in the center of this trapezoid3. Membrane protein trafficking is needed for a regulated turnover of rhabdomeral membrane proteins such as rhodopsin and the light-activated TRP (transient receptor potential) and TRPL (TRP-like) ion channels to assure the proper amount of these phototransduction proteins in the rhabdomere. Photoreceptor membrane proteins are synthesized in the endoplasmic reticulum and transported via the Golgi apparatus to the rhabdomere. Following activation of rhodopsin by light, a rhodopsin molecule can either become inactivated by absorption of a second photon or can be removed from the rhabdomere by clathrin-mediated endocytosis. Endocytosed rhodopsin either becomes degraded in the lysosome or is recycled back to the rhabdomere4,5. The ion channel TRPL is also internalized following activation of the phototransduction cascade and undergoes a light-dependent translocation between the rhabdomere (where it is located when flies are kept in the dark) and an ER-enriched storage compartment in the cell body (to which it is transported within several hours upon illumination)6,7,8,9,10. In contrast to endocytosed rhodopsin, only small amounts of TRPL are degraded via the endolysosomal pathway, and the majority is stored intracellularly instead and recycled back to the rhabdomere upon dark adaptation6. TRPL can thus be used for analyzing light-triggered trafficking of plasma membrane proteins. Drosophila photoreceptor cells are also employed for studying neuronal degeneration. Photoreceptor cell degeneration is frequently determined by assessing the structure of rhabdomeres, which disintegrate as a result of degenerative processes5.
In order to study the subcellular localization of TRPL and rhodopsin in photoreceptor cells or photoreceptor cell degeneration, two fluorescence microscopy methods that differ with respect to analysis speed and resolution have been applied here. A very fast, non-invasive method that can be used for genetic screens but with a limited spatial resolution is the detection of fluorescence in the deep pseudopupil (DPP). The DPP is an optical phenomenon of arthropod compound eyes whose geometric origin has been explained in detail by Franceschini and Kirschfeld in 197111. In short, on several optical planes below the retina overlay-images of rhabdomeres from adjacent ommatidia can be observed. On a focal plane through the center of the eye&#39;s curvature, these superimposed projections form an image that resembles the trapezoidal layout of rhabdomeres in a single ommatidium only orders of magnitude larger. This phenomenon can also be observed independently of exogenous expression of fluorescence proteins (e.g. TRPL::eGFP8), which nonetheless make the DPP easier to detect (Figure&#160;1A-A&#39;&#39;)12. A second non-invasive method is water immersion microscopy that relies on imaging fluorescently tagged proteins after optically neutralizing the eyes&#39; dioptric apparatus with water (Figure&#160;1B-C&#39;&#39;)12. Using the water immersion method, the relative amount of TRPL::eGFP in the rhabdomeres or cell body can be assessed quantitatively for individual photoreceptor cells. Furthermore, non-translocating fluorescence-tagged proteins can be utilized to evaluate rhabdomeral integrity and to determine the time course of a potential degeneration in a quantitative manner, as described here.
While recordings of the DPP are by far the easiest and fastest of these methods to perform, the spatial resolution of data they generate is limited. In addition, there are numerous reasons why a DPP may be absent, which are not necessarily discernible by DPP imaging itself. Since the DPP represents a summation of several ommatidia, information about individual cells is lost. Thus, low-resolution DPP imaging serves an important function in screening large numbers of flies but should generally be followed by higher resolution recordings by way of water immersion microscopy. Water immersion micrographs allow interpretations about individual cells, developmental defects, eye morphology, protein mislocalization or retinal degeneration as well as quantification of these effects. This Protocol describes these two techniques in detail.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/63375/63375fig01.jpg" /> 
Figure 1: Overview of microscopy variations for the Drosophila eye presented in this Protocol. Schematic representations and exemplary micrographs of (A-A&#39;&#39;) fluorescent deep pseudopupil (DPP) imaging, (B-B&#39;&#39;) lethal water immersion microscopy of fluorescent rhabdomeres, and (C-C&#39;&#39;) non-lethal water drop microscopy of fluorescent rhabdomeres. Scale bar (A&#39;&#39;): 100 &#181;m. Scale bars (B&#39;&#39;-C&#39;&#39;): 10 &#181;m. The figure has been modified from reference13. <a href="https://www.jove.com/files/ftp_upload/63375/63375fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>15 mL centrifuge tube</td>
			<td>Greiner Bio-One</td>
			<td>188271</td>
			<td></td>
		</tr>
		<tr>
			<td>CO2 anaesthesia fly pad</td>
			<td>Flystuff</td>
			<td>59-172</td>
			<td></td>
		</tr>
		<tr>
			<td>Cold light lamp (KL 1500 LCD)</td>
			<td>Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fiji/ImageJ</td>
			<td>NIH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence microscope with UV lamp, camera, filter set and software (AxioImager.Z1m, Axiocam 530 mono, 38 HE, ZEN2 blue edition)</td>
			<td>Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescent tube (Lumilux T8, L 30W/840, 4000 K, G13) 
			[1750 Lux, Ee470nm = 298 &#181;W cm-2, Ee590nm = 215 &#181;W cm-2] 
			and [760 Lux, Ee470nm = 173 &#181;W cm-2, Ee590nm = 147 &#181;W cm-2]</td>
			<td>Osram</td>
			<td>4050300518039</td>
			<td></td>
		</tr>
		<tr>
			<td>Laboratory pipette (20-200 &#181;L)</td>
			<td>Eppendorf</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Object slide</td>
			<td>Roth</td>
			<td>0656.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dish (94 mm)</td>
			<td>Greiner Bio-One</td>
			<td>633102</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette tips (200 &#181;L)</td>
			<td>Labsolute</td>
			<td>7695844</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasticine (Blu-Tack)</td>
			<td>Bostik</td>
			<td>30811745</td>
			<td></td>
		</tr>
		<tr>
			<td>Stereo microscope (SMZ445)</td>
			<td>Nikon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Stereo microscope with UV lamp, camera, filer set and software (MZ16F, MC170 HD, GFP3, LAS 4.12)</td>
			<td>Leica</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

studying membrane protein trafficking in drosophila photoreceptor cells using egfp-tagged proteins

Membrane protein trafficking regulates the incorporation and removal of receptors and ion channels into the plasma membrane. This process is fundamentally important for cell function and cell integrity of neurons. Drosophila photoreceptor cells have become a model for studying membrane protein trafficking. Besides rhodopsin, which upon illumination becomes internalized from the photoreceptor membrane and is degraded, the transient receptor potential-like (TRPL) ion channel in Drosophila exhibits a light-dependent translocation between the rhabdomeral photoreceptor membrane (where it is located in the dark) and the photoreceptor cell body (to which it is transported upon illumination). This intracellular transport of TRPL can be studied in a simple and non-invasive way by expressing eGFP-tagged TRPL in photoreceptor cells. The eGFP fluorescence can then be observed either in the deep pseudopupil or by water immersion microscopy. These methods allow detection of fluorescence in the intact eye and are therefore useful for high-throughput assays and genetic screens for Drosophila mutants defective in TRPL translocation. Here, the preparation of flies, the microscopic techniques, as well as quantification methods used to study this light-triggered translocation of TRPL are explained in detail. These methods can be applied also for trafficking studies on other Drosophila photoreceptor proteins, for example, rhodopsin. In addition, by using eGFP-tagged rhabdomeral proteins, these methods can be used to assess the degeneration of photoreceptor cells.

Transgenic Drosophila flies expressing a TRPL::eGFP fusion protein under the control of the rhodopsin 1 promoter have been generated. In these flies, TRPL::eGFP is expressed in photoreceptor cells R1-6 of the compound eye and displays an illumination-dependent localization. When flies are kept in the dark, TRPL::eGFP is incorporated into the outer rhabdomeres. After illumination for several hours, TRPL translocates into the cell body where it is stored in an ER-enriched compartment.8...

Watch this Scientific Journal Video about Studying Membrane Protein Trafficking in Drosophila Photoreceptor Cells Using eGFP-Tagged Proteins at JoVE.com

Studying Membrane Protein Trafficking in Drosophila Photoreceptor Cells Using eGFP-Tagged Proteins

Here, non-invasive methods are described for localization of photoreceptor membrane proteins and assessment of retinal degeneration in the Drosophila compound eye using eGFP fluorescence.

Studying Membrane Protein Trafficking in Drosophila Photoreceptor Cells Using eGFP-Tagged Proteins

Membrane protein trafficking regulates the incorporation and removal of receptors and ion channels into the plasma membrane. This process is fundamentally ...

GFP-tagged photoreceptor proteins, like the ion channel TRPL GFP, allow us to study protein transport in neurons using noninvasive techniques. This method can also be used to monitor photoreceptor degeneration. Thus, the molecular basis of hereditary diseases resulting in blindness in humans can be studied in the Drosophila eye.Cellular localization of GFP-tagged proteins can be assessed by observing the fluorescence in the deep pseudopupil or by water-immersion microscopy. Both methods allow fast determination of the localization of visual proteins and observing structural defects of rhabdomeres due to the degeneration of photoreceptor cells. To obtain high-quality images, the most important aspect is the orientation of the fly eye.While performing this technique, one should focus on ommatidia located slightly towards the eye's periphery. I will be demonstrating the procedure of DPP imaging, while the two techniques using water-immersion microscopy will be demonstrated by my colleague, Dr.Krystina Wagner, and Matthias Zeger, a PhD student in our group. To begin deep pseudopupil, or DPP, imaging, anesthetize one-to three-day-old flies, and position one of them in the center of the microscope objective on its side so that either the left or right eye is facing the objective precisely radially.Increase the magnification to fit the entire eye, and center the central ommatidia of the eye. If possible, decrease the depth of field of the microscope by adjusting the double-iris diaphragm to a shallow setting. Next, switch on the microscope UV lamp at maximum intensity.Then, select the fluorescence filter set of the microscope according to the fluorescence protein expressed in the eyes, and set the light path toward the microscope-mounted camera. Using the live imaging feature within the software, adjust the image brightness to a setting that detects only specific signals from the eye by raising the exposure time and gain value. Readjust the microscope focus into the eye to generate the superimposed image of the DPP.Then, take a snapshot of the fluorescent DPP. To prepare a fly in a lethal variation, adhere a piece of Plasticine onto an object slide and another piece into the center of a Petri dish. Fill the Petri dish with ice-chilled distilled water and some ice flakes.Then, put one ice-anesthetized fly under a stereo microscope on top of the Plasticine-coated object slide. Turn the fly on its back, and pierce an insect pin through the center of the thorax. Fix the pin horizontally on the Plasticine-coated object slide, and orient either the left or the right eye of the fly upward.Then, carefully fix the object slide with its Plasticine-free side facing down in the Petri dish, preventing rotation of the fly head. Ensure that the fly eye is covered with water. Alternatively, to prepare a fly in a non-lethal variation, transfer the ice-anesthetized fly head first into a 200-microliter pipette tip, and carefully push the fly toward the tip with compressed air.Then, using a scalpel, cut off the pipette tip just in front of the head, and using tweezers carefully push the fly a few millimeters into the pipette tip. Cut off the pipette tip again, and push the fly back toward the tip with the compressed air so that only the head of the fly protrudes from the pipette tip. After adhering a piece of Plasticine onto an object slide, press the pipette tip into it so that the left or the right eye faces upward.Ensure that the eye is oriented correctly under the microscope. For image acquisition, select a water-immersion objective. In the case of a non-lethal variation, use a laboratory pipette to adhere a large drop of chilled water to the underside of the water-immersion objective.Carefully place the object slide with the prepared fly onto the microscope stage. Then, lower the water-immersion objective manually until it contacts the water surface or the fly's eye touches the drop. Then, switch the light path toward the microscope camera, and generate a live image.Readjust the focus for the camera, and evaluate the orientation of the eye, considering that the eye must face the microscope objective radially. Use the lookup table software to detect oversaturation. In the case of non-pigmented flies, adjust the exposure time such that the brightest pixels are just below the saturation limit for every image.Record an image, and save it as a raw file to archive all corresponding metadata of the recording. Then, export the image in a tif format. To quantify relative eGFP fluorescence in the rhabdomeres of water-immersion micrographs, adjust ImageJ settings by clicking on Analyze, then Set Measurements, and check only the box for Mean gray value.Import the tif image by clicking on File, then Open. Choose a representative region of the image in focus, and enlarge it to 200 to 300%by repeatedly pressing Control and together. Next, select the Oval tool, and while pressing the Shift key generate a circular selection in the image that is significantly smaller than one fluorescent rhabdomere.Then, look for the exact size displayed below the toolbar in the ImageJ main window. To measure the fluorescence intensities within the circular selection, move the circle to the first rhabdomere with the arrow keys on the keyboard, and click Analyze, then Measure. A result window listing the measured gray value will pop up.Continue with measurements of rhabdomeres two to six, and also measure the background signal. In the case of non-pigmented flies, make additional measurements of the corresponding cell body areas. Measure the fluorescence of two more ommatidia, resulting in three technical replicates.Mark the analyzed ommatidia by using the Pencil tool, and save this image for documentation. Select and copy the measured gray values from the result window, and paste them into spreadsheet software for further calculations. Sort the fluorescence intensity values according to their origin into the categories rhabdomere, cell body, and background, and calculate the mean intensity from each category.Then, calculate the relative amount of eGFP present in the rhabdomere using the first formula for non-pigmented eyes and the second for pigmented eyes. Alternatively, to quantify eye morphology by eGFP fluorescence in water-immersion micrographs, choose three adjacent ommatidia in a representative region of the image that is in focus. Evaluate the 18 rhabdomeres of the selection individually according to their eGFP intensity, edge sharpness, and contrast with respect to the surrounding background signal.Finally, score the clearly visible rhabdomeres with a value of two, weekly visible rhabdomeres with a value of one, and absent rhabdomeres with a value of zero to generate a degeneration index. In transgenic Drosophila flies expressing an eGFP TRPL fusion protein, rhabdomeral fluorescence disappears in light due to translocation of the eGFP TRPL. This allows for performing a genetic screen to identify mutants defective in the internalization of the eGFP TRPL.In control flies, eGFP TRPL translocates out of the rhabdomeres into the cell body after 16 hours of illumination, resulting in a significant decrease of rhabdomeral fluorescence compared to the dark-adapted state. The second dark incubation raises the rhabdomeral fluorescence again towards the initial value. However, in the TRPL translocation defective mutant vps35MH20, the fluorescence pattern does not change drastically after 16 hours of illumination and a subsequent dark adaptation for 24 hours.This quantification method can detect a statistically highly significant recycling defect. White-eyed flies allow the detection of fluorescence signals from both rhabdomere and cell body. In contrast, in red-eyed flies, fluorescence signals are only detectable in rhabdomeres but not in the cell body.Regarding the quantification of retinal degeneration, eGFP TRP fluorescence can be assessed over the course of several weeks. When kept in a 12-hour light, 12-hour dark cycle for two weeks, the degeneration index declined in mutant flies but not in control flies. In this protocol, one needs to differentiate between pigmented and non-pigmented eyes.Since pigmentation affects the fluorescent signal, quantitative water-immersion microscopy has been optimized for both cases individually. DPP imaging and water-immersion microscopy are high-throughput methods with limited resolution. To investigate subcellular localization, we recommend immunofluorescence microscopy on tissue sections.For a detailed analysis of degenerative phenotypes, electron microscopy can be performed.

studying-membrane-protein-trafficking-drosophila-photoreceptor-cells

Research

JoVE Journal

Biology

2.6K ビュー.  University of Hohenheim. GFPタグ付き光受容体タンパク質は、イオンチャネルTRPL GFPと同様に、非侵襲的技術を用いてニューロンにおけるタンパク質輸送を研究することを可能にする。この方法は、感光体の変性を監視するためにも使用することができる。したがって、ヒトの失明をもたらす遺伝性疾患の分子基盤をショウジョウバエの眼で研究することができる。GFPタグ付きタンパク質の?...

ビデオ: Studying Membrane Protein Trafficking in Drosophila Photoreceptor Cells Using eGFP-Tagged Proteins

Studying Aggression in Drosophila (fruit flies)

Aggression is an innate behavior that evolved in the framework of defending or obtaining resources. This complex social behavior is influenced by genetic, hormonal and environmental factors. In many organisms, aggression is critical to survival but controlling and suppressing aggression in distinct contexts also has become increasingly important. In recent years, invertebrates have become increasingly useful as model systems for investigating the genetic and systems biological basis of complex social behavior. This is in part due to the diverse repertoire of behaviors exhibited by these organisms. In the accompanying video, we outline a method for analyzing aggression in Drosophila whose design encompasses important eco-ethological constraints. Details include steps for: making a fighting chamber; isolating and painting flies; adding flies to the fight chamber; and video taping fights. This approach is currently being used to identify candidate genes important in aggression and in elaborating the neuronal circuitry that underlies the output of aggression and other social behaviors.

Studying Aggression in Drosophila fruit flies

Aggression is an innate behavior that evolved in the framework of defending or obtaining resources.  This complex social behavior is influenced by ...

Staining of Proteins in Gels with Coomassie G-250 without Organic Solvent and Acetic Acid

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents (Methanol, Ethanol or 2-Propanol) and acetic acid are used for fixation, staining and destaining of proteins in a gel after SDS-PAGE. To speed up the procedure, heating the staining solution in the microwave oven for a short time is frequently used. This usually results in evaporation of toxic or hazardous Methanol, Ethanol or 2-Propanol and a strong smell of acetic acid in the lab which should be avoided due to safety considerations. In a protocol originally published in two patent applications by E.M. Wondrak (US2001046709 (A1), US6319720 (B1)), an alternative composition of the staining solution is described in which no organic solvent or acid is used. The CBB is dissolved in bidistilled water (60-80mg of CBB G-250 per liter) and 35 mM HCl is added as the only other compound in the staining solution. The CBB staning of the gel is done after SDS-PAGE and thorough washing of the gel in bidistilled water. By heating the gel during the washing and staining steps, the process can be finished faster and no toxic or hazardous compunds are evaporating. The staining of proteins occurs already within 1 minute after heating the gel in staining solution and is fully developed after 15-30 min with a slightly blue background that is destained completely by prolonged washing of the stained gel in bidistilled water, without affecting the stained protein bands.

A short protocol for protein staining with Coomassie Brilliant Blue (CBB) G-250 in polyacrylamide gels is described without using organic solvents or acetic acid as in the classical staining procedures with CBB.

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents ...

Crystallizing Membrane Proteins for Structure Determination using Lipidic Mesophases

A detailed protocol for crystallizing membrane proteins by using lipidic mesophases is described. This method has variously been referred to as the lipidic cubic phase or in meso method. The method has been shown to be quite versatile in that it has been used to solve X-ray crystallographic structures of prokaryotic and eukaryotic proteins, proteins that are monomeric, homo- and hetero-multimeric, chromophore-containing and chromophore-free, and alpha-helical and beta-barrel proteins. Recent successes using in meso crystallization are the human engineered beta2-adrenergic and adenosine A2a G protein-coupled receptors. Protocols are presented for reconstituting the membrane protein into the monoolein-based mesophase, and for setting up crystallizations in the manual mode. Additional steps in the overall process, such as crystal harvesting, are to be addressed in future video articles. The time required to prepare the protein-loaded mesophase and to set up a crystallization plate manually is about one hour.

Herein is described the procedure implemented in the Caffrey Membrane Structural and Functional Biology Group to set up manually crystallization trials of membrane proteins in lipidic mesophases.

A detailed protocol for crystallizing membrane proteins by using lipidic mesophases is described. This method has variously been referred to as the ...

Crystallization of Membrane Proteins in Lipidic Mesophases

Membrane proteins perform critical functions in living cells related to signal transduction, transport and energy transformations, and, as such, are implicated in a multitude of malfunctions and diseases. However, a structural and functional understanding of membrane proteins is strongly lagging behind that of their soluble partners, mainly, due to difficulties associated with their solubilization and generation of diffraction quality crystals. Crystallization in lipidic mesophases (also known as in meso or LCP crystallization) is a promising technique which was successfully applied to obtain high resolution structures of microbial rhodopsins, photosynthetic proteins, outer membrane beta barrels and G protein-coupled receptors. In meso crystallization takes advantage of a native-like membrane environment and typically produces crystals with lower solvent content and better ordering as compared to traditional crystallization from detergent solutions. The method is not difficult, but requires an understanding of lipid phase behavior and practice in handling viscous mesophase materials. Here we demonstrate a simple and efficient way of making LCP and reconstituting a membrane protein in the lipid bilayer of LCP using a syringe mixer, followed by dispensing nanoliter portions of LCP into an assay or crystallization plate, conducting pre-crystallization assays and harvesting crystals from the LCP matrix. These protocols provide a basic guide for approaching in meso crystallization trials; however, as with any crystallization experiment, extensive screening and optimization are required, and a successful outcome is not necessarily guaranteed.

The protocols describe the essential steps for obtaining diffraction quality crystals of a membrane protein starting from reconstitution of the protein in a lipidic cubic phase (LCP), finding initial conditions with LCP-FRAP pre-crystallization assays, setting up LCP crystallization trials and harvesting crystals.

Membrane proteins perform critical functions in living cells related to signal transduction, transport and energy transformations, and, as such, are ...

Protein Membrane Overlay Assay: A Protocol to Test Interaction Between Soluble and Insoluble Proteins in vitro

Validating interactions between different proteins is vital for investigation of their biological functions on the molecular level. There are several methods, both in vitro and in vivo, to evaluate protein binding, and at least two methods that complement the shortcomings of each other should be conducted to obtain reliable insights. 
For an in vivo assay, the bimolecular fluorescence complementation (BiFC) assay represents the most popular and least invasive approach that enables to detect protein-protein interaction within living cells, as well as identify the intracellular localization of the interacting proteins 1,2. In this assay, non-fluorescent N- and C-terminal halves of GFP or its variants are fused to tested proteins, and when the two fusion proteins are brought together due to the tested proteins&#x2019; interactions, the fluorescent signal is reconstituted3-6. Because its signal is readily detectable by epifluorescence or confocal microscopy, BiFC has emerged as a powerful tool of choice among cell biologists for studying about protein-protein interactions in living cells 3. This assay, however, can sometimes produce false positive results. For example, the fluorescent signal can be reconstituted by two GFP fragments arranged as far as 7 nm from each other due to close packing in a small subcellular compartment, rather that due to specific interactions7.
Due to these limitations, the results obtained from live cell imaging technologies should be confirmed by an independent approach based on a different principle for detecting protein interactions. Co-immunoprecipitation (Co-IP) or glutathione transferase (GST) pull-down assays represent such alternative methods that are commonly used to analyze protein-protein interactions in vitro. However, iIn these assays, however, the tested proteins must be readily soluble in the buffer that supportsused for the binding reaction. Therefore, specific interactions involving an insoluble protein cannot be assessed by these techniques.
 Here, we illustrate the protocol for the protein membrane overlay binding assay, which circumvents this difficulty. In this technique, interaction between soluble and insoluble proteins can be reliably tested because one of the proteins is immobilized on a membrane matrix. This method, in combination with in vivo experiments, such as BiFC, provides a reliable approach to investigate and characterize interactions faithfully between soluble and insoluble proteins. In this article, binding between Tobacco mosaic virus (TMV) movement protein (MP), which exerts multiple functions during viral cell-to-cell transport8-14, and a recently identified plant cellular interactor, tobacco ankyrin repeat-containing protein (ANK) 15, is demonstrated using this technique.

Protein Membrane Overlay Assay: A Protocol to Test Interaction Between Soluble and Insoluble Proteins in vitro

Testing protein-protein interaction is indispensable for dissection of protein functionality. Here, we introduce an in vitro protein-protein binding assay to probe a membrane-immobilized protein with a soluble protein. This assay provides a reliable method to test interaction between an insoluble protein and a protein in solution.

Validating interactions between different proteins is vital for investigation of their biological functions on the molecular level.  There are several ...

Use of a Robot for High-throughput Crystallization of Membrane Proteins in Lipidic Mesophases

Structure-function studies of membrane proteins greatly benefit from having available high-resolution 3-D structures of the type provided through macromolecular X-ray crystallography (MX). An essential ingredient of MX is a steady supply of ideally diffraction-quality crystals. The in meso or lipidic cubic phase (LCP) method for crystallizing membrane proteins is one of several methods available for crystallizing membrane proteins. It makes use of a bicontinuous mesophase in which to grow crystals. As a method, it has had some spectacular successes of late and has attracted much attention with many research groups now interested in using it. One of the challenges associated with the method is that the hosting mesophase is extremely viscous and sticky, reminiscent of a thick toothpaste. Thus, dispensing it manually in a reproducible manner in small volumes into crystallization wells requires skill, patience and a steady hand. A protocol for doing just that was developed in the Membrane Structural &amp; Functional Biology (MS&amp;FB) Group1-3. JoVE video articles describing the method are available1,4. 
The manual approach for setting up in meso trials has distinct advantages with specialty applications, such as crystal optimization and derivatization. It does however suffer from being a low throughput method. Here, we demonstrate a protocol for performing in meso crystallization trials robotically. A robot offers the advantages of speed, accuracy, precision, miniaturization and being able to work continuously for extended periods under what could be regarded as hostile conditions such as in the dark, in a reducing atmosphere or at low or high temperatures. An in meso robot, when used properly, can greatly improve the productivity of membrane protein structure and function research by facilitating crystallization which is one of the slow steps in the overall structure determination pipeline. 
In this video article, we demonstrate the use of three commercially available robots that can dispense the viscous and sticky mesophase integral to in meso crystallogenesis. The first robot was developed in the MS&amp;FB Group5,6. The other two have recently become available and are included here for completeness.	
An overview of the protocol covered in this article is presented in Figure 1. All manipulations were performed at room temperature (~20 &deg;C) under ambient conditions.

Herein is described a robotic approach to high-throughput crystallization of membrane proteins in lipidic mesophases for use in structure determination using macromolecular X-ray crystallography. Three robots capable of handling the viscous and sticky protein-laden mesophase integral to the method are introduced.

Structure-function studies of membrane proteins greatly benefit from having available high-resolution 3-D structures of the type provided through ...

Harvesting and Cryo-cooling Crystals of Membrane Proteins Grown in Lipidic Mesophases for Structure Determination by Macromolecular Crystallography

An important route to understanding how proteins function at a mechanistic level is to have the structure of the target protein available, ideally at atomic resolution. Presently, there is only one way to capture such information as applied to integral membrane proteins (Figure 1), and the complexes they form, and that method is macromolecular X-ray crystallography (MX). To do MX diffraction quality crystals are needed which, in the case of membrane proteins, do not form readily. A method for crystallizing membrane proteins that involves the use of lipidic mesophases, specifically the cubic and sponge phases1-5, has gained considerable attention of late due to the successes it has had in the G protein-coupled receptor field6-21 (<a href="http://www.mpdb.tcd.ie" target="_blank">www.mpdb.tcd.ie</a>). However, the method, henceforth referred to as the in meso or lipidic cubic phase method, comes with its own technical challenges. These arise, in part, due to the generally viscous and sticky nature of the lipidic mesophase in which the crystals, which are often micro-crystals, grow. Manipulating crystals becomes difficult as a result and particularly so during harvesting22,23. Problems arise too at the step that precedes harvesting which requires that the glass sandwich plates in which the crystals grow (Figure 2)24,25 are opened to expose the mesophase bolus, and the crystals therein, for harvesting, cryo-cooling and eventual X-ray diffraction data collection.
The cubic and sponge mesophase variants (Figure 3) from which crystals must be harvested have profoundly different rheologies4,26. The cubic phase is viscous and sticky akin to a thick toothpaste. By contrast, the sponge phase is more fluid with a distinct tendency to flow. Accordingly, different approaches for opening crystallization wells containing crystals growing in the cubic and the sponge phase are called for as indeed different methods are required for harvesting crystals from the two mesophase types. Protocols for doing just that have been refined and implemented in the Membrane Structural and Functional Biology (MS&amp;FB) Group, and are described in detail in this JoVE article (Figure 4). Examples are given of situations where crystals are successfully harvested and cryo-cooled. We also provide examples of cases where problems arise that lead to the irretrievable loss of crystals and describe how these problems can be avoided. In this article the Viewer is provided with step-by-step instructions for opening glass sandwich crystallization wells, for harvesting and for cryo-cooling crystals of membrane proteins growing in cubic and in sponge phases.

Herein is described procedures implemented in the Caffrey Membrane Structural and Functional Biology Group to harvest and cryo-cool membrane protein crystals grown in lipidic cubic and sponge phases for use in structure determination using macromolecular X-ray crystallography.

An important route to understanding how proteins function at a mechanistic level is to have the structure of the target protein available, ideally at ...

Intravital Microscopy for Imaging Subcellular Structures in Live Mice Expressing Fluorescent Proteins

Here we describe a procedure to image subcellular structures in live rodents that is based on the use of confocal intravital microscopy. As a model organ, we use the salivary glands of live mice since they provide several advantages. First, they can be easily exposed to enable access to the optics, and stabilized to facilitate the reduction of the motion artifacts due to heartbeat and respiration. This significantly facilitates imaging and tracking small subcellular structures. Second, most of the cell populations of the salivary glands are accessible from the surface of the organ. This permits the use of confocal microscopy that has a higher spatial resolution than other techniques that have been used for in vivo imaging, such as two-photon microscopy. Finally, salivary glands can be easily manipulated pharmacologically and genetically, thus providing a robust system to investigate biological processes at a molecular level.
In this study we focus on a protocol designed to follow the kinetics of the exocytosis of secretory granules in acinar cells and the dynamics of the apical plasma membrane where the secretory granules fuse upon stimulation of the beta-adrenergic receptors. Specifically, we used a transgenic mouse that co-expresses cytosolic GFP and a membrane-targeted peptide fused with the fluorescent protein tandem-Tomato. However, the procedures that we used to stabilize and image the salivary glands can be extended to other mouse models and coupled to other approaches to label in vivo cellular components, enabling the visualization of various subcellular structures, such as endosomes, lysosomes, mitochondria, and the actin cytoskeleton.

Intravital microscopy is a powerful tool that enables imaging various biological processes in live animals. In this article, we present a detailed method for imaging the dynamics of subcellular structures, such as the secretory granules, in the salivary glands of live mice.

Here we describe a procedure to image subcellular structures in live rodents that is based on the use of confocal intravital microscopy. As a model organ, ...

The Tomato/GFP-FLP/FRT Method for Live Imaging of Mosaic Adult Drosophila Photoreceptor Cells

The Drosophila eye is widely used as a model for studies of development and neuronal degeneration. With the powerful mitotic recombination technique, elegant genetic screens based on clonal analysis have led to the identification of signaling pathways involved in eye development and photoreceptor (PR) differentiation at larval stages. We describe here the Tomato/GFP-FLP/FRT method, which can be used for rapid clonal analysis in the eye of living adult Drosophila. Fluorescent photoreceptor cells are imaged with the cornea neutralization technique, on retinas with mosaic clones generated by flipase-mediated recombination. This method has several major advantages over classical histological sectioning of the retina: it can be used for high-throughput screening and has proved an effective method for identifying the factors regulating PR survival and function. It can be used for kinetic analyses of PR degeneration in the same living animal over several weeks, to demonstrate the requirement for specific genes for PR survival or function in the adult fly. This method is also useful for addressing cell autonomy issues in developmental mutants, such as those in which the establishment of planar cell polarity is affected.

The Tomato/GFP-FLP/FRT Method for Live Imaging of Mosaic Adult Drosophila Photoreceptor Cells

The Tomato/GFP-FLP/FRT method involves visualizing mosaic photoreceptor cells in living Drosophila. It can be used to follow individual photoreceptor cell fates in the retina for days or weeks. This method is ideal for studies of retinal degeneration and neurodegenerative diseases or photoreceptor cell development.

The Drosophila eye is widely used as a model  for studies of development and neuronal degeneration. With the powerful mitotic  recombination technique, ...

Easy Measurement of Diffusion Coefficients of EGFP-tagged Plasma Membrane Proteins Using k-Space Image Correlation Spectroscopy

Lateral diffusion and compartmentalization of plasma membrane proteins are tightly regulated in cells and thus, studying these processes will reveal new insights to plasma membrane protein function and regulation. Recently, k-Space Image Correlation Spectroscopy (kICS)1&#160;was developed to enable routine measurements of diffusion coefficients directly from images of fluorescently tagged plasma membrane proteins, that avoided systematic biases introduced by probe photophysics. Although the theoretical basis for the analysis is complex, the method can be implemented by nonexperts using a freely available code to measure diffusion coefficients of proteins. kICS calculates a time correlation function from a fluorescence microscopy image stack after Fourier transformation of each image to reciprocal (k-) space. Subsequently, circular averaging, natural logarithm transform and linear fits to the correlation function yields the diffusion coefficient. This paper provides a step-by-step guide to the image analysis and measurement of diffusion coefficients via kICS.
First, a high frame rate image sequence of a fluorescently labeled plasma membrane protein is acquired using a fluorescence microscope. Then, a region of interest (ROI) avoiding intracellular organelles, moving vesicles or protruding membrane regions is selected. The ROI stack is imported into a freely available code and several defined parameters (see Method section) are set for kICS analysis. The program then generates a &#34;slope of slopes&#34; plot from the k-space time correlation functions, and the diffusion coefficient is calculated from the slope of the plot. Below is a step-by-step kICS procedure to measure the diffusion coefficient of a membrane protein using the renal water channel aquaporin-3 tagged with EGFP as a canonical example.

This paper provides a step by step guide to the fluctuation analysis technique k-Space Image Correlation Spectroscopy (kICS) for measuring diffusion coefficients of fluorescently labeled plasma membrane proteins in live mammalian cells.

Lateral diffusion and compartmentalization of plasma membrane proteins are tightly regulated in cells and thus, studying these processes will reveal new ...