Name: methods for imaging intracellular ph of the follicle stem cell lineage in live drosophila ovarian tissue
Uploaded: 2017-09-26T14:00:00
Description: Watch this Scientific Journal Video about Methods for Imaging Intracellular pH of the Follicle Stem Cell Lineage in Live Drosophila Ovarian Tissue at JoVE.com

We thank Bryne Ulmschneider for contributions to the protocol and Diane Barber for suggestions on the manuscript. This work was funded by a National Institute of Health grant GM116384 to T.G. Nystul and D.L. Barber.

NOTE: To measure pHi in the FSC lineage, we calculate the ratio of fluorescence intensities of pHluorin to mCherry in FSCs, pFCs, and follicle cells in physiological conditions, and convert the ratios into pHi values with standard calibration curves for each cell type7. First, live imaging experiments are performed to measure fluorescence intensities of pHluorin and mCherry in germaria dissected into a buffer containing NaHCO3, which mimics physiological conditions1</s...

<ol>
	<li>Grillo-Hill, B. K., Choi, C., Jimenez-Vidal, M., Barber, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+H++efflux+is+sufficient+to+induce+dysplasia+and+necessary+for+viability+with+oncogene+expression.">Increased H+ efflux is sufficient to induce dysplasia and necessary for viability with oncogene expression.</a> eLife. 03270, (2015).</li><li>Ulmschneider, B., Grillo-Hill, B. K., Benitez, M., Azimova, D. R., Barber, D. L., Nystul, T. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+intracellular+pH+is+necessary+for+adult+epithelial+and+embryonic+stem+cell+differentiation.">Increased intracellular pH is necessary for adult epithelial and embryonic stem cell differentiation.</a> J. Cell Biol. 215 (3), 345-355 (2016).</li><li>Han, J., Burgess, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+Indicators+for+Intracellular+pH.">Fluorescent Indicators for Intracellular pH.</a> Chemical reviews. 110 (5), 2709-2728 (2010).</li><li>Koivusalo, M., Welch, 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=Amiloride+inhibits+macropinocytosis+by+lowering+submembranous+pH+and+preventing+Rac1+and+Cdc42+signaling.">Amiloride inhibits macropinocytosis by lowering submembranous pH and preventing Rac1 and Cdc42 signaling.</a> J. Cell Biol. 188 (4), 547-563 (2010).</li><li>Choi, C. -. H., Webb, B. A., Chimenti, M. S., Jacobson, M. P., Barber, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=pH+sensing+by+FAK-His58+regulates+focal+adhesion+remodeling.">pH sensing by FAK-His58 regulates focal adhesion remodeling.</a> J. Cell Biology. 202 (6), 849-859 (2013).</li><li>Rossano, A. J., Chouhan, A. K., Macleod, G. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetically+encoded+pH-indicators+reveal+activity-dependent+cytosolic+acidification+of+Drosophila+motor+nerve+termini+in+vivo.">Genetically encoded pH-indicators reveal activity-dependent cytosolic acidification of Drosophila motor nerve termini in vivo.</a> J. Phys. 591 (7), 1691-1706 (2013).</li><li>Grillo-Hill, B. K., Webb, B. A., Barber, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ratiometric+imaging+of+pH+probes.">Ratiometric imaging of pH probes.</a> Methods in Cell Biol. 123, 429-448 (2014).</li><li>Miesenb&#246;ck, G., De Angelis, D. A., Rothman, 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=Visualizing+secretion+and+synaptic+transmission+with+pH-sensitive+green+fluorescent+proteins.">Visualizing secretion and synaptic transmission with pH-sensitive green fluorescent proteins.</a> Nature. 394 (6689), 192-195 (1998).</li><li>Kirilly, D., Xie, 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+Drosophila+ovary:+an+active+stem+cell+community.">The Drosophila ovary: an active stem cell community.</a> Cell research. 17 (1), 15-25 (2007).</li><li>Sahai-Hernandez, P., Castanieto, A., Nystul, T. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drosophila+models+of+epithelial+stem+cells+and+their+niches.">Drosophila models of epithelial stem cells and their niches.</a> Wiley interdisciplinary reviews. Dev. Biol. 1 (3), 447-457 (2012).</li><li>Losick, V. P., Morris, L. X., Fox, D. T., Spradling, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drosophila+stem+cell+niches:+a+decade+of+discovery+suggests+a+unified+view+of+stem+cell+regulation.">Drosophila stem cell niches: a decade of discovery suggests a unified view of stem cell regulation.</a> Dev. Cell. 21 (1), 159-171 (2011).</li><li>Pocha, S. M., Montell, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+and+molecular+mechanisms+of+single+and+collective+cell+migrations+in+Drosophila:+themes+and+variations.">Cellular and molecular mechanisms of single and collective cell migrations in Drosophila: themes and variations.</a> Ann Rev. of Gen. 48, 295-318 (2014).</li><li>St Johnston, D., Ahringer, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+polarity+in+eggs+and+epithelia:+parallels+and+diversity.">Cell polarity in eggs and epithelia: parallels and diversity.</a> Cell. 141 (5), 757-774 (2010).</li><li>Castanieto, A., Johnston, M. J., Nystul, T. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EGFR+signaling+promotes+self-renewal+through+the+establishment+of+cell+polarity+in+Drosophila+follicle+stem+cells.">EGFR signaling promotes self-renewal through the establishment of cell polarity in Drosophila follicle stem cells.</a> eLife. 3, (2014).</li><li>Margolis, J., Spradling, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+behavior+of+epithelial+stem+cells+in+the+Drosophila+ovary.">Identification and behavior of epithelial stem cells in the Drosophila ovary.</a> Development. 121 (11), 3797-3807 (1995).</li><li>Nystul, T. G., Spradling, 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+epithelial+niche+in+the+Drosophila+ovary+undergoes+long-range+stem+cell+replacement.">An epithelial niche in the Drosophila ovary undergoes long-range stem cell replacement.</a> Cell stem cell. 1 (3), 277-285 (2007).</li><li>Morris, L. X., Spradling, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+live+imaging+provides+new+insight+into+stem+cell+regulation+and+germline-soma+coordination+in+the+Drosophila+ovary.">Long-term live imaging provides new insight into stem cell regulation and germline-soma coordination in the Drosophila ovary.</a> Development. 138 (11), 2207-2215 (2011).</li><li>Lee, T., Luo, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mosaic+analysis+with+a+repressible+cell+marker+(MARCM)+for+Drosophila+neural+development.">Mosaic analysis with a repressible cell marker (MARCM) for Drosophila neural development.</a> Trends in neuro. 24 (5), 251-254 (2001).</li></ol>

Here, we describe a method for measuring the pHi of cells in the FSC lineage within wildtype tissue. This protocol has been developed and refined over the past five years, since we first began to study pHi in Drosophila ovarian tissue. During that time, the protocol has been used successfully by multiple investigators in our lab and on at least four different spinning disc and laser scanning microscopes. The reproducibility of our original observation, that pHi increases as cells in the FSC lineage differentiate...

Recent studies revealed a role for changes in pHi during cellular differentiation and dysplasia in vivo1,2. These studies found that pHi is remarkably consistent in cells of the same type at the same stage of differentiation, but that it changes as cells transition from one stage to another. In some cases, blocking the changes in pHi partially disrupts differentiation, suggesting that the change in pHi is not just a consequence of changes in cell fate but instead helps to promote the change in cell fate, perhaps through effects on pH-sensitive regulatory proteins or chemical reactions required for differentiation. Future studies have the potential to reveal more insight into the many different roles of pHi dynamics in vivo. However, one of the challenges of studying pHi during differentiation in vivo is obtaining accurate measurements of pHi. Unlike other features of differentiation, such as changes in cellular morphology and gene expression, pHi is a labile chemical property of the cell that is not preserved in cells that have been fixed and permeabilized with standard methods. In addition, pHi may not be stable in cells that are stressed or dying as a result of experimental manipulation. Thus, it is important to keep cells alive and as healthy as possible when measuring pHi. Several vital dyes are available that work well for measuring the pHi of cells in culture3, but in many cases they are not suitable for in vivo studies because they do not penetrate the tissue deeply or evenly enough to provide accurate measurements.
To circumvent the problem of poor dye penetration, we and others have used a genetically encoded probe, mCherry::pHluorin4,5,6,7, that can be expressed specifically in the cell types of interest and imaged in live tissue. pHluorin is a variant of GFP with a higher pKa (~ 7.0 vs. ~ 4.0) that folds more readily at higher pH; so the total fluorescence intensity emitted from a population of pHluorin molecules in the cell increases with increasing pHi8. Importantly, fluorescence is linear within the normal cytosolic range of pHi values. In contrast, the fluorescence of mCherry (pKa ~ 4.5) is insensitive to pH changes within the cytosolic range. These two reporters are covalently linked together as a single chimeric protein, encoded by a single open reading frame, so they are always present in equal amounts. Therefore, the ratio of pHluorin to mCherry fluorescence intensity provides a measurement of pHi that is normalized to the probe concentration in each cell. The ratios can then be converted to estimates of pHi values using a standard curve that is generated by obtaining the pHluorin to mCherry ratios from tissues that have been equilibrated to known pH values.
Here, we describe the methods for using mCherry::pHluorin to measure the pHi of the epithelial FSC lineage in the Drosophila ovary. This well-characterized tissue has been used to model many different aspects of epithelial biology, such as stem cell self-renewal and differentiation9,10,11, collective cell migration12, and the development and maintenance of cell polarity13,14. The follicle epithelium is produced by two FSCs that reside at the anterior edge of the tissue in a structure called the germarium15,16. These cells divide regularly during adulthood to self-renew and produce progeny, called prefollicle cells (pFCs), that can either re-enter the niche and become an FSC or differentiate into one of three different follicle cell types: polar cells, stalk cells, or main body follicle cells. We showed previously that in wildtype tissue, the pHi increases steadily during the early stages of differentiation, from a pHi of approximately 6.8 in FSCs to 7.0 in pFCs, to 7.3 in follicle cells2. Blocking this increase by RNAi knockdown of a ubiquitously expressed sodium/proton exchanger, DNhe2, severely impairs pFC differentiation, whereas increasing pHi by overexpression of DNhe2 causes a mild excess differentiation phenotype. These findings demonstrate that pHi is stably maintained in the early FSC lineage and that it can be experimentally increased or decreased in vivo. The methods described here can be used to measure pHi in either wildtype tissue or various forms of mutant tissues, including RNAi knockdown or overexpression using a Gal4 of interest, and mitotic clones.

<table>
	<tbody>
		<tr>
			<td>Fly Stocks</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>UAS-mCherry::pHluorin[1]</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>y1 w*;P{GawB}10930/CyO</td>
			<td>Bloomington Stock Center</td>
			<td>7023</td>
			<td></td>
		</tr>
		<tr>
			<td>Act-Gal4 flipout stock</td>
			<td>Bloomington Stock Center</td>
			<td>4409</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Chemicals for Buffer preparation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma Aldrich</td>
			<td>S5886</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma Aldrich</td>
			<td>P-3911</td>
			<td></td>
		</tr>
		<tr>
			<td>glucose</td>
			<td>Mallinckrodt</td>
			<td>4912</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP310</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Thermo Fisher Scientific</td>
			<td>M63</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma Aldrich</td>
			<td>C-5080</td>
			<td></td>
		</tr>
		<tr>
			<td>HCO3</td>
			<td>Sigma Aldrich</td>
			<td>S-5761</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Sigma Aldrich</td>
			<td>M-9272</td>
			<td></td>
		</tr>
		<tr>
			<td>NMDG+</td>
			<td>Sigma Aldrich</td>
			<td>M-2004</td>
			<td></td>
		</tr>
		<tr>
			<td>K2HPO4</td>
			<td>Mallinckrodt</td>
			<td>7088</td>
			<td>Use to Make KHPO4 pH 7.4</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Thermo Fisher Scientific</td>
			<td>BP362</td>
			<td>Use to Make KHPO4 pH 7.4</td>
		</tr>
		<tr>
			<td>Concanavalin A, Alexa Fluor 647 Conjugate</td>
			<td>Thermo Fisher Scientific</td>
			<td>C21421</td>
			<td>0.25 mg/ml dilution</td>
		</tr>
		<tr>
			<td>Nigericin</td>
			<td>Thermo Fisher Scientific</td>
			<td>N1495</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Dissection and mounting tools</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>2 Dumont Inox forceps (Size 5)</td>
			<td>Thermo Fisher Scientific</td>
			<td>NC9473431</td>
			<td></td>
		</tr>
		<tr>
			<td>2 23-gauge syringe needles</td>
			<td>Sigma Aldrich</td>
			<td>Z192457</td>
			<td></td>
		</tr>
		<tr>
			<td>9-well glass dissecting dish</td>
			<td>Thermo Fisher Scientific</td>
			<td>13-748B</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum Grease</td>
			<td>Dow Corning</td>
			<td>1018817</td>
			<td></td>
		</tr>
		<tr>
			<td>22 X 40 mM glass coverslips</td>
			<td>Thermo Fisher Scientific</td>
			<td>12545C</td>
			<td></td>
		</tr>
		<tr>
			<td>Round Glass Coverslips, 12mm diameter, 0.13-0.16mm thickness</td>
			<td>Ted Pella, Inc.</td>
			<td>26023</td>
			<td></td>
		</tr>
		<tr>
			<td>3-D mounting chamber</td>
			<td>custom manufactured</td>
			<td></td>
			<td>.stl and .ipt files for 3-D printer included as supplemental files</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Other equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td>Thermo Fisher Scientific</td>
			<td>13-620-183A</td>
			<td>Model: Accumet AB15</td>
		</tr>
		<tr>
			<td>Dissection microscope</td>
			<td>Olympus Corporation</td>
			<td>0H11436</td>
			<td>Model: SZ2-ST</td>
		</tr>
		<tr>
			<td>Confocal Microscope</td>
			<td>Leica Biosystems</td>
			<td></td>
			<td>SP5 or SP8 laser-scanning confocal microscope with a 40&#215; objective with a numerical aperture of 1.3</td>
		</tr>
	</tbody>
</table>

methods for imaging intracellular ph of the follicle stem cell lineage in live drosophila ovarian tissue

Changes in intracellular pH (pHi) play important roles in the regulation of many cellular functions, including metabolism, proliferation, and differentiation. Typically, pHi dynamics are determined in cultured cells, which are amenable to measuring and experimentally manipulating pHi. However, the recent development of new tools and methodologies has made it possible to study pHi dynamics within intact, live tissue. For Drosophila research, one important development was the generation of a transgenic line carrying a pHi biosensor, mCherry::pHluorin. Here, we describe a protocol that we routinely use for imaging live Drosophila ovarioles to measure pHi in the epithelial follicle stem cell (FSC) lineage in mCherry::pHluorin transgenic wild type lines; however, the methods described here can be easily adapted for other tissues, including the wing discs and eye epithelium. We describe techniques for expressing mCherry::pHluorin in the FSC lineage, maintaining ovarian tissue during live imaging, and acquiring and analyzing images to obtain pHi values.

Here we have described the process of measuring pHi in the follicle epithelium, which involves several steps. First, the ovaries are dissected from flies of the appropriate genotype using tools for dissecting and mounting (Figure 1). The ovarioles are then imaged using quantitative fluorescence microscopy and the images are analyzed to obtain measurements of pHi. For each image, the cell types of interest are identified as described in Section 3.1 (<strong cl...

Watch this Scientific Journal Video about Methods for Imaging Intracellular pH of the Follicle Stem Cell Lineage in Live Drosophila Ovarian Tissue at JoVE.com

Methods for Imaging Intracellular pH of the Follicle Stem Cell Lineage in Live Drosophila Ovarian Tissue

We provide a protocol for imaging intracellular pH of an epithelial stem cell lineage in live Drosophila ovarian tissue. We describe methods to generate transgenic flies expressing a pH biosensor, mCherry::pHluorin, image the biosensor using quantitative fluorescence imaging, generate standard curves, and convert fluorescence intensity values to pH values.

Methods for Imaging Intracellular pH of the Follicle Stem Cell Lineage in Live Drosophila Ovarian Tissue

Changes in intracellular pH (pHi) play important roles in the regulation of many cellular functions, including metabolism, proliferation, and ...

Research

JoVE Journal

Developmental Biology

Live-imaging of the Drosophila Pupal Eye

Live-imaging of the Drosophila Pupal Eye

Inherent processes of Drosophila pupal development can shift and distort the eye epithelium in ways that make individual cell behavior difficult to track ...

Assaying Blood Cell Populations of the Drosophila melanogaster Larva

Assaying Blood Cell Populations of the Drosophila melanogaster Larva

In vertebrates, hematopoiesis is regulated by inductive microenvironments (niches). Likewise, in the invertebrate model organism&#160;Drosophila ...

Isolating Hair Follicle Stem Cells and Epidermal Keratinocytes from Dorsal Mouse Skin

The hair follicle (HF) is an ideal system for studying the biology and regulation of adult stem cells (SCs). This dynamic mini organ is replenished by ...

Bioengineering of Humanized Bone Marrow Microenvironments in Mouse and Their Visualization by Live Imaging

Human hematopoietic stem cells (HSCs) reside in the bone marrow (BM) niche, an intricate, multifactorial network of components producing cytokines, growth ...

In Vitro Ovule Cultivation for Live-cell Imaging of Zygote Polarization and Embryo Patterning in Arabidopsis thaliana

In Vitro Ovule Cultivation for Live-cell Imaging of Zygote Polarization and Embryo Patterning in Arabidopsis thaliana

In most flowering plants, the zygote and embryo are hidden deep in the mother tissue, and thus it has long been a mystery of how they develop dynamically; ...

Live Imaging of Mouse Secondary Palate Fusion

The fusion of the secondary palatal shelves to form the intact secondary palate is a key process in mammalian development and its disruption can lead to ...

Preparation of Drosophila Larval and Pupal Testes for Analysis of Cell Division in Live, Intact Tissue

Preparation of Drosophila Larval and Pupal Testes for Analysis of Cell Division in Live, Intact Tissue

Experimental analysis of cells dividing in living, intact tissues and organs is essential to our understanding of how cell division integrates with ...

Imaging Intranuclear Actin Rods in Live Heat Stressed Drosophila Embryos

Imaging Intranuclear Actin Rods in Live Heat Stressed Drosophila Embryos

The purpose of this protocol is to visualize intranuclear actin rods that assemble in live Drosophila melanogaster embryos following heat stress. Actin ...

Dissection and Live-Imaging of the Late Embryonic Drosophila Gonad

Dissection and Live-Imaging of the Late Embryonic Drosophila Gonad

The Drosophila melanogaster male embryonic gonad is an advantageous model to study various aspects of developmental biology including, but not limited to, ...

Applications of Immobilization of Drosophila Tissues with Fibrin Clots for Live Imaging

Applications of Immobilization of Drosophila Tissues with Fibrin Clots for Live Imaging

Drosophila is an important model system to study a vast range of biological questions. Various organs and tissues from different developmental stages of ...