Name: optical quantification of intracellular ph in drosophila melanogaster malpighian tubule epithelia with a fluorescent genetically-encoded ph indicator
Uploaded: 2017-08-11T12:30:00
Description: Watch this Scientific Journal Video about Optical Quantification of Intracellular pH in Drosophila melanogaster Malpighian Tubule Epithelia with a Fluorescent Genetically-encoded pH Indicator at JoVE.

This work was supported by NIH DK092408 and DK100227 to MFR. AJR was supported by T32-DK007013. The authors wish to thank Dr. Julian A.T. Dow for the CapaR-GAL4 and c724-GAL4 Drosophila stocks. We also thank Jacob B. Anderson for assistance maintaining experimental fly crosses.

All steps in this protocol comply with the Mayo Clinic (Rochester, MN) animal use guidelines.
1. Fly Husbandry
<ol>
	<li>Raise flies and set crosses according to standard husbandry29. 
	NOTE: Fluorescent reporter expression by the GAL4/UAS system is proportional to temperature and thus rearing temperature can be adjusted to alter expression level. While high expression levels often lead to a better signal-to-noise ratio this condition is also associated with incr...

The success of quantification of pHi in Drosophila MTs depends entirely on the health of extracted MTs and the quality of mounting and dissection (Figure A&#160;-&#160;C). Thus, the careful handling of tissue as described is imperative. Slides freshly coated in PLL substantially aid MT mounting as they tend to be much more adhesive than slides which have previously been exposed to solution. Careful mounting will also aid in identification of distinct ...

The goal of this protocol is to describe quantification of intracellular pH (pHi) using a Genetically-Encoded pH-Indicator (GEpHI) and demonstrate how this method can be used to assess basolateral H+ transport in a model insect (D. melanogaster) renal structure, the Malpighian tubule (MT). MTs serve as the excretory organs of the fruit fly and are functionally similar to the mammalian nephron in several key respects1. MTs are arranged as 2 pairs of tubules (anterior and posterior) in the thorax and abdomen of the fly. The single-cell epithelial tube of each MT is composed of metabolically active principal cells with distinct apical (luminal) and basolateral (hemocoel) polarity as well as intercalated stellate cells. Anterior MTs are composed of 3 morphologically, functionally, and developmentally distinct segments, notably the initial dilated segment, transitional segment, and secretory main segment, which joins to the ureter2. At the cellular scale trans-epithelial ion transport into the lumen is accomplished by an apical plasma membrane V-ATPase3 and an alkali-metal/H+ exchanger as well as a basolateral Na+-K+-ATPase4, inward-rectifier K+ channels5, Na+-driven Cl&#8722;/HCO3&#8722; exchanger (NDAE1)6, and Na+-K+-2Cl&#8722; cotransporter (NKCC; Ncc69)7, while stellate cells mediate Cl- and water transport8,9. This complex but accessible physiologic system provides excellent opportunities for investigation of endogenous ion transport mechanisms when combined with the diverse genetic and behavioral toolsets of Drosophila.
The rationale for this protocol was to describe a genetically malleable system for studying epithelial ion transport with potential for integration from cell to behavior and export of tools to other model systems. Expression of pHerry10, a GEpHI derived from a fusion of green pH-sensitive super-ecliptic pHluorin11,12 (SEpH) and red pH-insensitive mCherry13, in MTs permits quantification of H+ transport in single MT cells through the high K+/nigericin calibration technique14. As many ion transporters move H+ equivalents, quantification of intracellular pHi serves as a functional representation of ion movement via a variety of transporters. The Drosophila MT model system also offers powerful genetic tools in tissue-specific transgene15 and RNA interference (RNAi)16 expression, which can be combined with cellular imaging and whole-organ assays17,18,19 of tubule function to create a robust toolset with vertical integration from molecules to behavior. This stands in contrast to many other protocols for assessing epithelial biology, as historically such measurements have relied on intricate and daunting micro-dissection, sophisticated ion-selective electrodes20,21, and expensive pH-sensitive dyes22 with restrictive loading requirements and poor cellular specificity in heterogeneous tissues. GEpHIs have been used to extensively measure pHi in a variety of cell types23. Early work exploited the inherent pH-sensitivity of Green Fluorescent Protein (GFP) to monitor pHi in cultured epithelial cells24 but the past two decades have seen GEpHIs used in neurons25, glia26, fungi27, and plant cells28. The combination of the potential for cellular targeting of genetic constructs through the GAL4/UAS expression system15 and the physiologic accessibility of the Drosophila MT make this an ideal preparation for investigations of pHi regulation and epithelial ion transport.
pHi regulation has been studied for decades and is vital to life. The MT preparation offers a robust model to teach physiology of pHi regulation but also perform sophisticated investigations of pHi regulation ex vivo and in vivo. This protocol describes quantification of H+ movement across the basolateral membrane of the epithelial cells of the Drosophila MT using the NH4Cl pulse acid loading technique21, but as the pH-indicator is genetically encoded, these methods and their theoretical framework can be applied to any preparation amenable to transgenesis and live-imaging.

<table>
	<tbody>
		<tr>
			<td>Poly-L-Lysine Solution</td>
			<td>Sigma-Aldrich</td>
			<td>P4832</td>
			<td>Store at 4 &#176;C, can be reused.</td>
		</tr>
		<tr>
			<td>Nigericin Sodium Salt</td>
			<td>Sigma-Aldrich</td>
			<td>N7143</td>
			<td>CAUTION: Handle with gloves. Store as aliquots of 20 mM stock solution in DMSO at 4 &#176;C.</td>
		</tr>
		<tr>
			<td>Adhesive Perfusion Chamber Covers, adhesive size 1 mm, chamber diameter &#215; thickness 9 mm &#215; 0.9 mm, ports diameter 1.5 mm</td>
			<td>Sigma-Aldrich</td>
			<td>GBL622105</td>
			<td>Can be substituted as needed to match perfusion system.</td>
		</tr>
		<tr>
			<td>Sylgard 184 Silicone Elastomer Kit</td>
			<td>Ellsworth Adhesives</td>
			<td>184 SIL ELAST KIT 0.5KG</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>Helping Hands Soldering Stands</td>
			<td>Harbor Freight Tools</td>
			<td>60501</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>Open Gravity-fed Perfusion System with Valve Controller, 8 to 1 Manifold and Reserviors</td>
			<td>Bioscience Tools</td>
			<td>PS-8S</td>
			<td>Any comparable perfusion system can be used.</td>
		</tr>
		<tr>
			<td>Flow Regulator</td>
			<td>Warner Instruments</td>
			<td>64-0221</td>
			<td>Can be substituted as needed to match perfusion system.</td>
		</tr>
		<tr>
			<td>Schneider&#39;s Medium</td>
			<td>Fisher Scientific</td>
			<td>21720024</td>
			<td>Store at 4 &#176;C in sterile aliquots.</td>
		</tr>
		<tr>
			<td>#5 Inox Steel Forceps</td>
			<td>Fine Science Tools</td>
			<td>11252-20</td>
			<td>Can be substituted based on experimenter comfort.</td>
		</tr>
		<tr>
			<td>35 mm x 10 mm polystyrene Petri dish</td>
			<td>Corning Life Sciences</td>
			<td>Fisher Scientific 08-757-100A</td>
			<td>Exact brand and size are unimportant.</td>
		</tr>
		<tr>
			<td>75 x 25 mm Microscope Slides</td>
			<td>Corning Life Sciences</td>
			<td>2949-75X25</td>
			<td>Exact brand and size can vary as long as perfusion wells are compatible.</td>
		</tr>
		<tr>
			<td>Filimented Borosilicate Capillary Glass, ID 1.5 mm, OD 0.86 mm, thickness 0.32 mm</td>
			<td>Warner Instruments</td>
			<td>64-0796</td>
			<td>Filiment not necessary, glass can be substituted to match perfusion tubing and perfusion wells.</td>
		</tr>
		<tr>
			<td>Tygon Tubing, ID 1/16 inch, OD 1/8 inch, thickness 1/32 inch</td>
			<td>Fisher Scientific</td>
			<td>14-171-129</td>
			<td>Available from multiple vendors, can be substituted to match perfusion system.</td>
		</tr>
		<tr>
			<td>Vacuum Silicone Grease</td>
			<td>Sigma-Aldrich</td>
			<td>Z273554</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>Plastic Flow Control Clamp</td>
			<td>Fisher Scientific</td>
			<td>05-869</td>
			<td>Available from multiple vendors, sterility not required</td>
		</tr>
		<tr>
			<td>Glass rods, 5 mm diameter</td>
			<td>delphiglass.com</td>
			<td>9198</td>
			<td>Exact size is personal preference, multiple vendors available</td>
		</tr>
		<tr>
			<td>PAP Hydrophobic Pen</td>
			<td>Sigma-Aldrich</td>
			<td>Z377821</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>Sealing Film</td>
			<td>Sigma-Aldrich</td>
			<td>P7668</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>15 mL Falcon tube</td>
			<td>BD Falcon</td>
			<td>352096</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>50 mL Falcon tube</td>
			<td>BD Falcon</td>
			<td>352070</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>HEPES; 4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid</td>
			<td>Sigma-Aldrich</td>
			<td>H3375</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>MES; 4-Morpholineethanesulfonic acid monohydrate</td>
			<td>Sigma-Aldrich</td>
			<td>69892</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>TAPS; N-[Tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid</td>
			<td>Sigma-Aldrich</td>
			<td>T5130</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>10x/0.45 Air Objective</td>
			<td>Zeiss</td>
			<td>000000-1063-139</td>
			<td>Comparable objectives can be substituted. 40x objectives can be used for single cell imaging.</td>
		</tr>
		<tr>
			<td>Dissecting Stereoscope</td>
			<td>Zeiss</td>
			<td>Discovery.V8</td>
			<td>Any dissecting stereoscope can be used.</td>
		</tr>
		<tr>
			<td>UAS-pHerry transgenic Drosophila melagnogaster</td>
			<td>Available from Romero Lab</td>
			<td></td>
			<td>First published: Citation 10</td>
		</tr>
		<tr>
			<td>capaR-GAL4 driver line Drosophila melagnogaster</td>
			<td>Available from Romero Lab</td>
			<td></td>
			<td>First published: Citation 32</td>
		</tr>
		<tr>
			<td>c724-GAL4 driver line Drosophila melagnogaster</td>
			<td>Available from Romero Lab</td>
			<td></td>
			<td>First published: Citation 2</td>
		</tr>
		<tr>
			<td>Monochromatic High Sensitivity Digital Camera</td>
			<td>Zeiss</td>
			<td>Axiocam 506 mono</td>
			<td>Exact brand and model can vary, can be replaced with any monochromatic high-sensitivity camera suited to live cellular imaging.</td>
		</tr>
		<tr>
			<td>GFP/FITC filter set, 470/40 nm ex., 515 nm longpass em., 500 nm dichroic</td>
			<td>Chroma</td>
			<td>CZ909</td>
			<td>Any GFP/FITC filer set can be substituted.</td>
		</tr>
		<tr>
			<td>RFP/TRITC filter set, 546/10 nm ex., 590 nm longpass em., 565 nm dichroic</td>
			<td>Chroma</td>
			<td>CZ915</td>
			<td>Any GFP/FITC filer set can be substituted.</td>
		</tr>
		<tr>
			<td>Inverted Epifluoescent Microscope</td>
			<td>Zeiss</td>
			<td>Axio Observer Z.1</td>
			<td>Any comparable microscope with motorized filter switching can be used. Upright microscopes can be used with open perfusion baths and water-immersion objectives.</td>
		</tr>
		<tr>
			<td>Statistical Analysis Software</td>
			<td>Microcal</td>
			<td>Origin 6.0</td>
			<td>Any software with comparable functionality can be substituted</td>
		</tr>
		<tr>
			<td>Image Analysis Software</td>
			<td>National Institutes of Health</td>
			<td>ImageJ 1.50i</td>
			<td>Any software with comparable functionality can be substituted</td>
		</tr>
		<tr>
			<td>Image Acquisition Software</td>
			<td>Zeiss</td>
			<td>Zen 1.1.2.0</td>
			<td>Any software with comparable functionality can be substituted</td>
		</tr>
		<tr>
			<td>Single-edged Carbon Steel Razor Blade</td>
			<td>Electron Microscopy Sciences</td>
			<td>71960</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>Microscopy Slide Folder</td>
			<td>Fisher Scientific</td>
			<td>16-04</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>Bunsen Burner</td>
			<td>Fisher Scientific</td>
			<td>50-110-1231</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>Polystrene Drosophila Rearing Vials with Flugs</td>
			<td>Genesee Scientific</td>
			<td>32-109BF</td>
			<td>Comparable items can be substituted.</td>
		</tr>
		<tr>
			<td>2.5 L Laboratory Ice Bucket</td>
			<td>Fisher Scientific</td>
			<td>07-210-129</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>NMDG; N-Methyl-D-glucamine</td>
			<td>Sigma-Aldrich</td>
			<td>M2004</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>200 uL barrier pipette tips</td>
			<td>MidSci</td>
			<td>AV200</td>
			<td>Available from multiple vendors.</td>
		</tr>
		<tr>
			<td>200 uL variable volume pipette</td>
			<td>Gilson Incorporated</td>
			<td>PIPETMAN P200</td>
			<td>Available from multiple vendors.</td>
		</tr>
	</tbody>
</table>

optical quantification of intracellular ph in drosophila melanogaster malpighian tubule epithelia with a fluorescent genetically-encoded ph indicator

Epithelial ion transport is vital to systemic ion homeostasis as well as maintenance of essential cellular electrochemical gradients. Intracellular pH (pHi) is influenced by many ion transporters and thus monitoring pHi is a useful tool for assessing transporter activity. Modern Genetically Encoded pH-Indicators (GEpHIs) provide optical quantification of pHi in intact cells on a cellular and subcellular scale. This protocol describes real-time quantification of cellular pHi regulation in Malpighian Tubules (MTs) of Drosophila melanogaster through ex vivo live-imaging of pHerry, a pseudo-ratiometric GEpHI with a pKa well-suited to track pH changes in the cytosol. Extracted adult fly MTs are composed of morphologically and functionally distinct sections of single-cell layer epithelia, and can serve as an accessible and genetically tractable model for investigation of epithelial transport. GEpHIs offer several advantages over conventional pH-sensitive fluorescent dyes and ion-selective electrodes. GEpHIs can label distinct cell populations provided appropriate promoter elements are available. This labeling is particularly useful in ex vivo, in vivo, and in situ preparations, which are inherently heterogeneous. GEpHIs also permit quantification of pHi in intact tissues over time without need for repeated dye treatment or tissue externalization. The primary drawback of current GEpHIs is the tendency to aggregate in cytosolic inclusions in response to tissue damage and construct over-expression. These shortcomings, their solutions, and the inherent advantages of GEpHIs are demonstrated in this protocol through assessment of basolateral proton (H+) transport in functionally distinct principal and stellate cells of extracted fly MTs. The techniques and analysis described are readily adaptable to a wide variety of vertebrate and invertebrate preparations, and the sophistication of the assay can be scaled from teaching labs to intricate determination of ion flux via specific transporters.

Healthy tissues and proper identification of anterior MTs are vital to the success of this protocol. During dissection, care should be taken to not directly touch the MTs and to only handle them by the ureter as gripping the MTs directly will lead to breakage (Figure 4A&#160;-&#160;B). When MTs are swept flat onto the slide, the tubules must be touched as little as possible and excess motion avoided as this will damage the si...

Watch this Scientific Journal Video about Optical Quantification of Intracellular pH in Drosophila melanogaster Malpighian Tubule Epithelia with a Fluorescent Genetically-encoded pH Indicator at JoVE.

Optical Quantification of Intracellular pH in Drosophila melanogaster Malpighian Tubule Epithelia with a Fluorescent Genetically-encoded pH Indicator

Cellular ion transport can often be assessed by monitoring intracellular pH (pHi). Genetically Encoded pH-Indicators (GEpHIs)&#160;provide optical quantification of intracellular pH in intact cells. This protocol details the quantification of intracellular pH through cellular ex vivo live-imaging of Malpighian tubules of Drosophila melanogaster with pHerry, a pseudo-ratiometric genetically encoded pH-indicator.

Optical Quantification of Intracellular pH in Drosophila melanogaster Malpighian Tubule Epithelia with a Fluorescent Genetically-encoded pH Indicator

Epithelial ion transport is vital to systemic ion homeostasis as well as maintenance of essential cellular electrochemical gradients. Intracellular pH ...

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