This work was supported by a Marie Curie Reintegration Grant (IRG249084). We thank all members of the Kurant laboratory. We also thank E. Suss-Toby at the Interdepartmental Bioimaging facility for excellent technical support.

To follow the dynamics of apoptotic cell clearance in vivo two populations of cells must be labeled: phagocytic cells and apoptotic cells.
To mark phagocytic cell populations we use a Drosophila line containing the simu-cytGFP marker, which labels exclusively phagocytic cells in the embryo: macrophages, glia and ectoderm8. One can use different markers for phagocytic cells, including lines containing a hemocyte-specific Gal4 driver (crq-Gal4) or glia-specific Gal4 driver (repo-Gal4) and a genetically encoded fluorescent reporter under UAS control (uas-GFP).
To monitor apoptotic cells during apoptotic cell clearance we use different apoptosis/phagocytosis markers. Annexin V (Molecular Probes) serves as an early marker for apoptotic cells 10; Phiphilux (OncoImmunin) is a fluorogenic caspase-3 substrate, which is used as a later apoptosis marker, and LysoTracker (Molecular Probes) works as a phagosome marker. We inject these reagents using the microinjection system PicoPump PV 820.
1. Getting Ready
<ol>
	<li>Heptane glue: 
	Unroll double sided tape and put as much as you can in a scintillation vial, fill with heptane, seal the vial with Parafilm, and rock for 24 hr. Add heptane if the glue is too thick.</li>
	<li>We allow the flies to lay on a pre-warmed grape juice agar plate + yeast paste for 2 hr, and then transfer the plate to 25 &deg;C for 10-12 hr (depends on the desired stage) prior to microinjection and time lapse recordings of injected embryos. We collect embryos from the agar plates maintained at 25 &deg;C, thus providing embryos from stage 15 or 16 of development.</li>
	<li>Needle preparation: 
	To prepare needles for injection, we use a 'Sutter instrument' needle puller and thin walled glass filaments (FHC Capillary tubing). The tip of the pooled capillary is broken to a diameter of 0.5-2 &mu;m.</li>
	<li>Coverslip with glue: 
	Using a pipette tip disperse a drop of the heptane glue in one line in the middle of the coverslip. Let it dry for a few seconds. Prepare a few of these coverslips.</li>
</ol>
2. Embryo Preparation
<ol>
	<li>Collect embryos from agar plates and transfer them to a cell strainer (SPL Life Sciences) using a clean paint brush and running water. The strainer is held over a beaker to collect waste water.</li>
	<li>Wash embryos in the cell strainer using water until all the yeast paste is removed.</li>
	<li>Dry out the excess water by wiping the outside of the strainer using Kimwipes.</li>
	<li>Place the cell strainer in a clean Petri dish and add enough 50% bleach to cover embryos in the cell strainer. Dechorionate the embryos for 2 min occasionally (2-3 times) stirring them.</li>
	<li>Rinse with water extensively until embryos loose the bleach odor.</li>
	<li>Place the cell strainer into a clean Petri dish and cover the embryos with water to prevent drying up.</li>
	<li>Before starting embryos setting, load 1 &mu;l of the desired reagent into two needles (sometimes a needle can be clogged). It takes about 5 min for the liquid to reach the tip of the needle.</li>
	<li>Cut a rectangular piece of grape juice agar and place it on a microscope slide. Transfer dechorionated embryos from the Petri dish to the agar piece using a clean paint brush.</li>
	<li>Under a fluorescent dissection microscope select properly staged embryos expressing the GFP marker using a wet paint brush and place each embryo close to the edge of the agar piece in a row one after another (Figure 1A). The embryos should be placed with their ventral side up for imaging phagocytosis by glia in the Central Nervous System (CNS).</li>
	<li>Set up about 10 embryos in one row.</li>
	<li>Attach the embryos to a coverslip coated in the middle with a strip of the heptane glue (Figure 1B, C).</li>
	<li>Place the coverslip in the dehydration chamber for about 5 min (this depends on the humidity of the room and the amount to be injected).</li>
	<li>After drying up cover the embryos with halocarbon oil 700 (Sigma) to avoid further dehydration.</li>
	<li>Place the coverslip on a microscope slide with the embryos facing up. You may put a drop of water on the slide to prevent moving of the coverslip. Embryos are now ready for injection. Injection location is typically on the lateral side in the middle of the embryo.</li>
</ol>
3. Embryo Injection
<ol>
	<li>Attach the needle to a micromanipulator.</li>
	<li>To break the needle tip put the edge of the coverslip in the field of view and adjust the needle to the same focal plane. Very carefully move the coverslip until it hits the needle tip and breaks it.</li>
	<li>Focusing on the embryos, place the needle into the oil and make sure you get a liquid drop from the needle. It means the needle tip has been broken well.</li>
	<li>Without touching the needle holder move the embryo into the needle and inject a drop into the embryo. Move the embryo away and proceed to the next one until all the embryos are injected.</li>
</ol>
4. Imaging
We image the embryos on an inverted confocal microscope with a 40X or 100X objective. We look for a nicely positioned embryo with the CNS in the middle, which shows strong GFP expression and a good labeling of apoptotic cells following injection.
For time lapse recordings of live embryos we usually choose 5 or 6 confocal slices (2 &mu;m thick each). Afterwards, we make a projection of 3 slices (6 &mu;m thickness) in order to observe whole cells.
We use markers for apoptotic cells which are stable and do not bleach easily. To avoid GFP bleaching we make recordings in intervals of 60 sec.
In some cases embryos may start rolling during the time of video recording. Therefore, we take a look once in a while at the recording in order to stop and start over if necessary.

<ol>
	<li>Kinchen, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+model+to+die+for:+signaling+to+apoptotic+cell+removal+in+worm,+fly+and+mouse.">A model to die for: signaling to apoptotic cell removal in worm, fly and mouse.</a> Apoptosis. 15, 998-1006 (2010).</li><li>Kinchen, J. M., Ravichandran, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phagosome+maturation:+going+through+the+acid+test.">Phagosome maturation: going through the acid test.</a> Nat. Rev. Mol. Cell Biol. 9, 781-795 (2008).</li><li>Kinchen, J. M., Ravichandran, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phagocytic+signaling:+you+can+touch,+but+you+can't+eat.">Phagocytic signaling: you can touch, but you can't eat.</a> Curr. Biol. 18, 521-524 (2008).</li><li>Stuart, L. M., Ezekowitz, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phagocytosis:+elegant+complexity.">Phagocytosis: elegant complexity.</a> Immunity. 22, 539-550 (2005).</li><li>Lauber, K., Blumenthal, S. G., Waibel, M., Wesselborg, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clearance+of+apoptotic+cells:+getting+rid+of+the+corpses.">Clearance of apoptotic cells: getting rid of the corpses.</a> Mol. Cell. 14, 277-287 (2004).</li><li>Henson, P. M., Hume, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptotic+cell+removal+in+development+and+tissue+homeostasis.">Apoptotic cell removal in development and tissue homeostasis.</a> Trends Immunol. 27, 244-250 (2006).</li><li>Kurant, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keeping+the+CNS+clear:+glial+phagocytic+functions+in+Drosophila.">Keeping the CNS clear: glial phagocytic functions in Drosophila.</a> Glia. 59, 1304-1311 (2011).</li><li>Kurant, E., Axelrod, S., Leaman, D., Gaul, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Six-microns-under+acts+upstream+of+Draper+in+the+glial+phagocytosis+of+apoptotic+neurons.">Six-microns-under acts upstream of Draper in the glial phagocytosis of apoptotic neurons.</a> Cell. 133, 498-509 (2008).</li><li>Mergliano, J., Minden, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Caspase-independent+cell+engulfment+mirrors+cell+death+pattern+in+Drosophila+embryos.">Caspase-independent cell engulfment mirrors cell death pattern in Drosophila embryos.</a> Development. 130, 5779-5789 (2003).</li><li>van den Eijnde, S. 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=Cell+surface+exposure+of+phosphatidylserine+during+apoptosis+is+phylogenetically+conserved.">Cell surface exposure of phosphatidylserine during apoptosis is phylogenetically conserved.</a> Apoptosis. 3, 9-16 (1998).</li></ol>

The authors declare that they have no competing financial interests.

Apoptotic cell clearance is a critical last stage of apoptosis, which is highly dynamic. Therefore real time studies of the process are of utmost importance. Here we describe a protocol that enables monitoring of apoptotic cell clearance in living developing Drosophila embryos. In this procedure, two populations of cells must be marked using specific markers: apoptotic cells and phagocytes. The simu-cytGFP reporter is suitable for monitoring phagocytic macrophages, glia and ectoderm simultaneously in the same embryo, which makes it possible to follow different phagocytic cell populations at the same time. This is a great advantage for studying 'professional' and 'non-professional' clearance concurrently, comparing specific aspects of the process such as rate, specificity and degradation ability. A disadvantage of this approach is that simu-cytGFP marker is expressed extremely strongly in macrophages and much weaker in glia, which could be tricky to adjust in the same movie. However, one can image apoptotic cell clearance by macrophages separately from this process in the CNS, by driving GFP expression with specific Gal4s (crq-Gal4 for macrophages and repo-Gal4 for glia).
Different markers for apoptotic cells reflecting specific molecular and morphological alterations are of great value for understanding the dynamics and reversibility of apoptosis and cell clearance. Moreover, real time recordings of apoptotic cell clearance using these markers add additional information about mutant phenotypes, which could not be achieved by using conventional immunohistochemistry techniques in fixed embryos.
The most difficult step of the described protocol, when imaging the developing CNS, is the extremely precise positioning of the embryos before injection. Even a slight move of the coverslip during attachment of the prepared embryos to the glue could change their position, which would not be appropriate for imaging the CNS. The embryo attaching step should be done with maximum attention.
Development of additional markers for specific stages in apoptosis and phagocytosis would be extremely desirable for finer dissection and possible manipulation of apoptotic cell clearance. The protocol presented here serves as a good basis for future development.

The proper elimination of unwanted or aberrant cells through apoptosis and subsequent phagocytosis is crucial for embryonic development as well as for tissue homeostasis in the adult. Phagocytosis of apoptotic cells or apoptotic cell clearance is a highly dynamic process which proceeds in four steps: (1) recruitment of phagocytes to the apoptotic cell ('find-me'), (2) recognition of the cell as a target for phagocytosis ('eat-me') and (3) engulfment, followed by (4) phagosome maturation and degradation of the apoptotic particle1-5. There are two types of phagocytes: 'professional' macrophages and immature dendritic cells, and the 'non-professional' tissue-resident neighboring cells, which are crucial for apoptotic cell clearance during metazoan development6,7 .
In Drosophila development, the elimination of superfluous cells through apoptosis occurs in three main phases, first in the mid to late embryo, then in the mid pupa, and again in the early adult. During embryogenesis apoptotic particles are removed by 'professional' phagocytes, macrophages, and by the 'non-professional' ectoderm and glia8,9 .
In our previous work we have identified a phagocytic receptor, Six-microns-under (SIMU), which is expressed exclusively in phagocytic cells during embryogenesis. Using the simu promoter we generated a specific marker for phagocytic cell populations (simu-cytGFP) which enables us to monitor macrophages, ectoderm and glia simultaneously in a live developing embryo8. In addition, by using specific markers for apoptotic cells in different stages of apoptosis, we are able to follow the dynamics of apoptotic cell clearance in vivo.

<table border="1">
 <tbody>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>Reagent</td>
 </tr>
 <tr>
 <td>Annexin V </td>
 <td>Molecular Probes</td>
 <td>A35108</td>
 <td></td>
 </tr>
 <tr>
 <td>PhiPhiLux G2D2</td>
 <td>OncoImmunin</td>
 <td>A304R2G-5</td>
 <td></td>
 </tr>
 <tr>
 <td>LysoTracker</td>
 <td>Molecular Probes</td>
 <td>L-7528</td>
 <td></td>
 </tr>
 <tr>
 <td>Halocarbon oil 700</td>
 <td>Sigma</td>
 <td>H8898</td>
 <td></td>
 </tr>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>Material</td>
 </tr>
 <tr>
 <td>Capillary tubing</td>
 <td>FHC </td>
 <td>30-30-0</td>
 <td></td>
 </tr>
 <tr>
 <td>Cell Strainer</td>
 <td>SPL</td>
 <td>93100</td>
 <td></td>
 </tr>
 <tr>
 <td>Paintbrush</td>
 <td></td>
 <td></td>
 <td></td>
 </tr>
 </tbody>
</table>

live imaging of apoptotic cell clearance during drosophila embryogenesis

The proper elimination of unwanted or aberrant cells through apoptosis and subsequent phagocytosis (apoptotic cell clearance) is crucial for normal development in all metazoan organisms. Apoptotic cell clearance is a highly dynamic process intimately associated with cell death; unengulfed apoptotic cells are barely seen in vivo under normal conditions. In order to understand the different steps of apoptotic cell clearance and to compare 'professional' phagocytes - macrophages and dendritic cells to 'non-professional' - tissue-resident neighboring cells, in vivo live imaging of the process is extremely valuable. Here we describe a protocol for studying apoptotic cell clearance in live Drosophila embryos. To follow the dynamics of different steps in phagocytosis we use specific markers for apoptotic cells and phagocytes. In addition, we can monitor two phagocyte systems in parallel: 'professional' macrophages and 'semi-professional' glia in the developing central nervous system (CNS). The method described here employs the Drosophila embryo as an excellent model for real time studies of apoptotic cell clearance.

Representative frames from a movie in which apoptotic cells are labeled with Annexin V, and glia, ectoderm and macrophages are labeled with simu-cytGFP are shown in Figure 2. Each frame is a projection of 3 slices 2 &mu;m each.
The embryo of stage 15 is properly positioned showing the embryonic CNS in the middle with well labeled glia (g). Macrophages (m), which are mostly outside the CNS, show strong cytoplasmic GFP expression. Ectodermal cells are also labeled with cytoplasmic GFP (e). Many Annexin V positive cells are seen inside and outside the CNS. To follow the engulfment event is not easy. We highlighted one event with a white rectangle where a glial cell is engulfing an apoptotic particle. Note the probing behavior of the glial cell: touching the apoptotic particle a few times without engulfing it and then ending up with engulfment of the Annexin V labeled apoptotic cell (Figure 2).
Additional markers for different apoptotic stages could be used with the same procedure.
<img src="/files/ftp_upload/50151/50151fig1.jpg" alt="Figure 1" /> 
Figure 1. Schematic representation of embryo preparation for microinjections. A. A microscopic slide containing a piece of agar on which embryos are transferred after dechorionation. About 20 embryos are placed in line, close to the edge of the agar piece, with their ventral side up, for imaging the CNS. B. A coverslip containing a strip of heptane glue in the middle. C. The coverslip from B with embryos attached to the heptane glue strip.
<img src="/files/ftp_upload/50151/50151fig2.jpg" alt="Figure 2" /> 
Figure 2. Dynamic analysis of apoptotic cell clearance. Time-lapse recordings of apoptotic cell clearance in a stage 15 embryo. Glia (g), macrophages (m) and ectoderm (e) are labeled with simu-cytGFP (green). Apoptotic cells are marked with the fluorescent Annexin V (red). A. Selected frames from a representative movie are shown. A glial cell engulfing an apoptotic cell is depicted by a rectangle. B. Close up views of the marked rectangle.

Watch this Scientific Journal Video about Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis at JoVE.com

Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

Here we describe an effective method for studying dynamics of apoptotic cell clearance in vivo. This method employs live Drosophila embryos as a powerful model for monitoring phagocytosis of apoptotic cells using specific labeling of apoptotic cells and phagocytes.

Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

The  proper elimination of unwanted or aberrant cells through apoptosis and  subsequent phagocytosis (apoptotic cell clearance) is crucial for normal  ...

live-imaging-apoptotic-cell-clearance-during-drosophila

Nanyang Technological University

Research

JoVE Journal

Biology

13.4K Views.  Technion-Israel Institute of Technology. Here we describe an effective method for studying dynamics of apoptotic cell clearance in vivo. This method employs live Drosophila embryos as a powerful model for monitoring phagocytosis of apoptotic cells using specific labeling of apoptotic cells and phagocytes.

Video: Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

Live Imaging of Glial Cell Migration in the Drosophila Eye Imaginal Disc

Glial cells of both vertebrate and invertebrate organisms must migrate to final target regions in order to ensheath and support associated neurons. While recent progress has been made to describe the live migration of glial cells in the developing pupal wing (1), studies of Drosophila glial cell migration have typically involved the examination of fixed tissue. Live microscopic analysis of motile cells offers the ability to examine cellular behavior throughout the migratory process, including determining the rate of and changes in direction of growth. Paired with use of genetic tools, live imaging can be used to determine more precise roles for specific genes in the process of development. Previous work by Silies et al. (2) has described the migration of glia originating from the optic stalk, a structure that connects the developing eye and brain, into the eye imaginal disc in fixed tissue. Here we outline a protocol for examining the live migration of glial cells into the Drosophila eye imaginal disc. We take advantage of a Drosophila line that expresses GFP in developing glia to follow glial cell progression in wild type and in mutant animals.

Here we describe a protocol to examine the migration of glial cells into the developing Drosophila eye using live microscopic analysis paired with GFP tagged glial cells.

Glial cells of both vertebrate and invertebrate organisms must migrate to final target regions in order to ensheath and support associated neurons.  While ...

Live Cell Imaging of F-actin Dynamics via Fluorescent Speckle Microscopy (FSM)

In this protocol we describe the use of Fluorescent Speckle Microscopy (FSM) to capture high-resolution images of actin dynamics in PtK1 cells. A unique advantage of FSM is its ability to capture the movement and turnover kinetics (assembly/disassembly) of the F-actin network within living cells. This technique is particularly useful in deriving quantitative measurements of F-actin dynamics when paired with computer vision software (qFSM).  We describe  the selection, microinjection and visualization of fluorescent actin probes in living cells. Importantly, similar procedures are applicable to visualizing other macomolecular assemblies. FSM has been demonstrated for microtubules, intermediate filaments, and adhesion complexes.  

Live Cell Imaging of F-actin Dynamics via Fluorescent Speckle Microscopy FSM

Selection, microinjection, and imaging of fluorescently-labeled F-actin via fluorescent speckle microscopy (FSM).

In this protocol we describe the use of Fluorescent Speckle Microscopy (FSM) to capture high-resolution images of actin dynamics in PtK1 cells. A unique ...

Live Imaging Of Drosophila melanogaster Embryonic Hemocyte Migrations

Many studies address cell migration using in vitro methods, whereas the physiologically relevant environment is that of the organism itself. Here we present a protocol for the mounting of Drosophila melanogaster embryos and subsequent live imaging of fluorescently labeled hemocytes, the embryonic macrophages of this organism. Using the Gal4-uas system1 we drive the expression of a variety of genetically encoded, fluorescently tagged markers in hemocytes to follow their developmental dispersal throughout the embryo. Following collection of embryos at the desired stage of development, the outer chorion is removed and the embryos are then mounted in halocarbon oil between a hydrophobic, gas-permeable membrane and a glass coverslip for live imaging. In addition to gross migratory parameters such as speed and directionality, higher resolution imaging coupled with the use of fluorescent reporters of F-actin and microtubules can provide more detailed information concerning the dynamics of these cytoskeletal components.

Live Imaging Of Drosophila melanogaster Embryonic Hemocyte Migrations

Drosophila hemocytes disperse over the entirety of the developing embryo. This protocol demonstrates how to mount and image these migrations using embryos with fluorescently labelled hemocytes.

Many studies address cell migration using in vitro methods, whereas the physiologically relevant environment is that of the organism itself. Here we ...

Preparation of Developing and Adult Drosophila Brains and Retinae for Live Imaging

The Drosophila brain and visual system are widely utilized model systems to study neuronal development, function and degeneration. Here we show three preparations of the brain and visual system that cover the range from the developing eye disc-brain complex in the developing pupae to individual eye and brain dissection from adult flies. All protocols are optimized for the live culture of the preparations. However, we also present the conditions for fixed tissue immunohistochemistry where applicable. Finally, we show live imaging conditions for these preparations using conventional and resonant 4D confocal live imaging in a perfusion chamber. Together, these protocols provide a basis for live imaging on different time scales ranging from functional intracellular assays on the scale of minutes to developmental or degenerative processes on the scale of many hours.

Preparation of Developing and Adult Drosophila Brains and Retinae for Live Imaging

This protocol describes three Drosophila preparations: 1) adult brain dissection, 2) adult retina dissection and 3) developing eye disc- brain complexes dissection. Emphasis is laid on special preparation techniques and conditions for live imaging, although all preparations can be used for fixed tissue immunohistochemistry.

The Drosophila brain and visual system are widely utilized model systems to study neuronal development, function and degeneration. Here we show three ...

A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis

Gene function during embryogenesis is typically defined by loss-of-function experiments, for example by targeted mutagenesis (knockout) in the mouse. In the zebrafish model, effective reverse genetic techniques have been developed using microinjection of gene-specific antisense morpholinos. Morpholinos target an mRNA through specific base-pairing and block gene function transiently by inhibiting translation or splicing for several days during embryogenesis (knockdown). However, in vertebrates such as mouse or zebrafish, some gene functions can be obscured by these approaches due to the presence of another gene that compensates for the loss. This is especially true for gene families containing sister genes that are co-expressed in the same developing tissues. In zebrafish, functional compensation can be tested in a relatively high-throughput manner, by co-injection of morpholinos that target knockdown of both genes simultaneously. Likewise, using morpholinos, a genetic interaction between any two genes can be demonstrated by knockdown of both genes together at sub-threshold levels. For example, morpholinos can be titrated such that neither individual knockdown generates a phenotype. If, under these conditions, co-injection of both morpholinos causes a phenotype, a genetic interaction is shown. Here we demonstrate how to show functional redundancy in the context of two related GATA transcription factors. GATA factors are essential for specification of cardiac progenitors, but this is revealed only by the loss of both Gata5 and Gata6. We show how to carry out microinjection experiments, validate the morpholinos, and evaluate the compensated phenotype for cardiogenesis.

Gene function can be obscured in loss-of-function experiments if there is compensation by another gene. The zebrafish model provides a relatively high-throughput means to reveal such functional redundancy in living embryos.

Gene function during embryogenesis is typically defined by loss-of-function experiments, for example by targeted mutagenesis (knockout) in the mouse. In ...

Live Imaging of Cell Extrusion from the Epidermis of Developing Zebrafish

Homeostatic maintenance of epithelial tissues requires the continual removal of damaged cells without disrupting barrier function. Our studies have found that dying cells send signals to their live neighbors to form and contract a ring of actin and myosin that ejects it out from the epithelial sheet while closing any gaps that might have resulted from its exit, a process termed cell extrusion1. The optical clarity of developing zebrafish provides an excellent system to visualize extrusion in living epithelia. Here we describe a method to induce and image extrusion in the larval zebrafish epidermis. To visualize extrusion, we inject a red fluorescent protein labeled probe for F-actin into one-cell stage transgenic zebrafish embryos expressing green fluorescent protein in the epidermis and induce apoptosis by addition of G418 to larvae. We then use time-lapse imaging on a spinning disc confocal microscope to observe actin dynamics and epithelial cell behaviors during the process of apoptotic cell extrusion. This approach allows us to investigate the extrusion process in live epithelia and will provide an avenue to study disease states caused by the failure to eliminate apoptotic cells.

Dying cells are extruded from epithelial tissues by concerted contraction of neighboring cells without disrupting barrier function. The optical clarity of developing zebrafish provides an excellent system to visualize extrusion in living epithelia. Here we describe methods to induce and image extrusion in the larval zebrafish epidermis at cellular resolution.

Homeostatic maintenance of epithelial tissues requires the continual removal of damaged cells without disrupting barrier function.  Our studies have found ...

Preparing Individual Drosophila Egg Chambers for Live Imaging

Live cell imaging is an important technique applied to a number of Drosophila tissues used as models to investigate topics such as axis specification, cell differentiation and organogenesis 1. Correct preparation of the experimental samples is a crucial, often neglected, step. The goal of preparation is to ensure physiological relevance and to establish optimal imaging conditions. To maintain tissue viability, it is critical to avoid dehydration, hypoxia, overheating or medium deterioration 2. 
 The Drosophila egg chamber is a well established system for examining questions relating, but not limited, to body patterning, mRNA localization and cytoskeletal organization 3,4. For early- and mid-stage egg chambers, mounting in halocarbon oil is good for survival in that it allows free diffusion of oxygen, prevents dehydration and hypoxia and has superb optical properties for microscopy. Imaging of fluorescent proteins is possible through the introduction of transgenes into the egg chamber or physical injection of labeled RNA, protein or antibodies 5-7. For example, addition of MS2 constructs to the genome of animals enables real time observation of mRNAs in the oocyte 8. These constructs allow for in vivo labeling of mRNA through utilization of the MS2 bacteriophage RNA stem loop interaction with its coat protein 9. 
 Here, we present a protocol for the extraction of ovaries as well as isolating individual ovarioles and egg chambers from the female Drosophila. For a detailed description of Drosophila oogenesis see Allan C. Spradling (1993, reprinted 2009) 10.

Preparing Individual Drosophila Egg Chambers for Live Imaging

The Drosophila egg chamber is an excellent model for studying the mechanisms of mRNA localization. In order to capture the dynamic events that underpin the processes of localization, rapid high resolution imaging of live tissue is required. Here, we present a protocol for dissection and imaging of live samples with minimal disruption.

Live cell imaging is an important technique applied to a number of Drosophila tissues used as models to investigate topics such as axis specification, ...

Live Imaging of GFP-labeled Proteins in Drosophila Oocytes

The Drosophila oocyte has been established as a versatile system for investigating fundamental questions such as cytoskeletal function, cell organization, and organelle structure and function. The availability of various GFP-tagged proteins means that many cellular processes can be monitored in living cells over the course of minutes or hours, and using this technique, processes such as RNP transport, epithelial morphogenesis, and tissue remodeling have been described in great detail in Drosophila oocytes1,2.
The ability to perform video imaging combined with a rich repertoire of mutants allows an enormous variety of genes and processes to be examined in incredible detail. One such example is the process of ooplasmic streaming, which initiates at mid-oogenesis3,4. This vigorous movement of cytoplasmic vesicles is microtubule and kinesin-dependent5 and provides a useful system for investigating cytoskeleton function at these stages.
Here I present a protocol for time lapse imaging of living oocytes using virtually any confocal microscopy setup.

Live Imaging of GFP-labeled Proteins in Drosophila Oocytes

A protocol for live imaging of GFP-tagged proteins or autofluorescent structures in individual Drosophila oocytes is described.

The  Drosophila oocyte has been established as a versatile system for investigating  fundamental questions such as cytoskeletal function, cell ...

4D Imaging of Protein Aggregation in Live Cells

One of the key tasks of any living cell is maintaining the proper folding of newly synthesized proteins in the face of ever-changing environmental conditions and an intracellular environment that is tightly packed, sticky, and hazardous to protein stability1. The ability to dynamically balance protein production, folding and degradation demands highly-specialized quality control machinery, whose absolute necessity is observed best when it malfunctions. Diseases such as ALS, Alzheimer's, Parkinson's, and certain forms of Cystic Fibrosis have a direct link to protein folding quality control components2, and therefore future therapeutic development requires a basic understanding of underlying processes. Our experimental challenge is to understand how cells integrate damage signals and mount responses that are tailored to diverse circumstances.
The primary reason why protein misfolding represents an existential threat to the cell is the propensity of incorrectly folded proteins to aggregate, thus causing a global perturbation of the crowded and delicate intracellular folding environment1. The folding health, or "proteostasis," of the cellular proteome is maintained, even under the duress of aging, stress and oxidative damage, by the coordinated action of different mechanistic units in an elaborate quality control system3,4. A specialized machinery of molecular chaperones can bind non-native polypeptides and promote their folding into the native state1, target them for degradation by the ubiquitin-proteasome system5, or direct them to protective aggregation inclusions6-9.
In eukaryotes, the cytosolic aggregation quality control load is partitioned between two compartments8-10: the juxtanuclear quality control compartment (JUNQ) and the insoluble protein deposit (IPOD) (Figure 1 - model). Proteins that are ubiquitinated by the protein folding quality control machinery are delivered to the JUNQ, where they are processed for degradation by the proteasome. Misfolded proteins that are not ubiquitinated are diverted to the IPOD, where they are actively aggregated in a protective compartment.
Up until this point, the methodological paradigm of live-cell fluorescence microscopy has largely been to label proteins and track their locations in the cell at specific time-points and usually in two dimensions. As new technologies have begun to grant experimenters unprecedented access to the submicron scale in living cells, the dynamic architecture of the cytosol has come into view as a challenging new frontier for experimental characterization. We present a method for rapidly monitoring the 3D spatial distributions of multiple fluorescently labeled proteins in the yeast cytosol over time. 3D timelapse (4D imaging) is not merely a technical challenge; rather, it also facilitates a dramatic shift in the conceptual framework used to analyze cellular structure.
We utilize a cytosolic folding sensor protein in live yeast to visualize distinct fates for misfolded proteins in cellular aggregation quality control, using rapid 4D fluorescent imaging. The temperature sensitive mutant of the Ubc9 protein10-12 (Ubc9ts) is extremely effective both as a sensor of cellular proteostasis, and a physiological model for tracking aggregation quality control. As with most ts proteins, Ubc9ts is fully folded and functional at permissive temperatures due to active cellular chaperones. Above 30 &deg;C, or when the cell faces misfolding stress, Ubc9ts misfolds and follows the fate of a native globular protein that has been misfolded due to mutation, heat denaturation, or oxidative damage. By fusing it to GFP or other fluorophores, it can be tracked in 3D as it forms Stress Foci, or is directed to JUNQ or IPOD.

Cellular viability depends on timely and efficient management of protein misfolding. Here we describe a method for visualizing the different potential fates of a misfolded protein: refolding, degradation, or sequestration in inclusions. We demonstrate the use of a folding sensor, Ubc9ts, for monitoring proteostasis and aggregation quality control in live cells using 4D microscopy.

One of the key tasks of any living cell is maintaining the proper folding of newly synthesized proteins in the face of ever-changing environmental ...

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, ...