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Method Article

Imaging Intranuclear Actin Rods in Live Heat Stressed Drosophila Embryos

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DOI:

10.3791/61297

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May 15th, 2020

 ,  , 
1Integrative Molecular and Biomedical Sciences, Baylor College of Medicine, 2Department of Cell and Molecular Biology, School of Molecular and Cellular Biology, University of Illinois at Urbana-Champaign, 3Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine

In This Article

Summary

The goal of this protocol is to inject Rhodamine-conjugated globular actin into Drosophila embryos and image intranuclear actin rod assembly following heat stress.

Abstract

The purpose of this protocol is to visualize intranuclear actin rods that assemble in live Drosophila melanogaster embryos following heat stress. Actin rods are a hallmark of a conserved, inducible Actin Stress Response (ASR) that accompanies human pathologies, including neurodegenerative disease. Previously, we showed that the ASR contributes to morphogenesis failures and reduced viability of developing embryos. This protocol allows the continued study of mechanisms underlying actin rod assembly and the ASR in a model system that is highly amenable to imaging, genetics and biochemistry. Embryos are collected and mounted on a coverslip to prepare them for injection. Rhodamine-conjugated globular actin (G-actinRed) is diluted and loaded into a microneedle. A single injection is made into the center of each embryo. After injection, embryos are incubated at elevated temperature and intranuclear actin rods are then visualized by confocal microscopy. Fluorescence recovery after photobleaching (FRAP) experiments may be performed on the actin rods; and other actin-rich structures in the cytoplasm can also be imaged. We find that G-actinRed polymerizes like endogenous G-actin and does not, on its own, interfere with normal embryo development. One limitation of this protocol is that care must be taken during injection to avoid serious injury to the embryo. However, with practice, injecting G-actinRed into Drosophila embryos is a fast and reliable way to visualize actin rods and can easily be used with flies of any genotype or with the introduction of other cellular stresses, including hypoxia and oxidative stress.

Introduction

This protocol describes how to inject G-actinRed to visualize the assembly of intranuclear actin rods in heat-stressed embryos that are undergoing an inducible Actin Stress Response (ASR)1. We developed this protocol to aid studies of the ASR, which in embryos leads to disrupted morphogenesis and reduced viability, and in adult human cell types is associated with pathologies including renal failure2, muscle myopathies3, and Alzheimer’s and Huntington’s Disease4,5,6,7,8. This ASR is induced by numerous cellular stresses, including heat shock9,10,11, oxidative stress4,6, reduced ATP synthesis12, and abnormal Huntingtin or β-amyloid oligomerization4,5,6,7,9,13,14,15,16. A hallmark of the ASR is the assembly of aberrant actin rods in either the cytoplasm or nucleus of affected cells, which is driven by stress-induced hyperactivation of an actin interacting protein, Cofilin1,5,6,10. Unfortunately, key knowledge gaps remain regarding the ASR. For example, the function of the actin rods is not known. We do not understand why rods form in the cytoplasm of some cell types, but the nucleus of others. Nor is it clear whether the ASR is protective or maladaptive for cells or embryos undergoing stress. Finally, we still do not know the detailed mechanisms underlying Cofilin hyperactivation or actin rod assembly. Thus, this protocol provides a rapid and versatile assay to probe the ASR by visualizing actin rod formation and dynamics in the highly tractable experimental system of the living fruit fly embryo.

The protocol to microinject G-actinRed into living Drosophila embryos was initially developed to study the dynamics of normal cytoplasmic actin structures17 during tissue building events. In those studies, we found that G-actinRed injection did not adversely affect early developmental processes in the embryo, including cytokinesis or gastrulation17,18. We then modified the protocol, adapting the embryo handling and G-actinRed injection to allow imaging of actin rods in heat stressed embryos undergoing the ASR1. Other methods besides G-actinRed injection can be used to visualize actin in embryos. These methods rely on expressing fluorescent proteins (FPs) tagged to actin or to domains of actin binding proteins, such as Utrophin-mCherry, Lifeact, F-tractin-GFP, and Moesin-GFP (reviewed in19). However, using these FP probes requires caution because they can stabilize or disrupt some actin structures, do not equally label all actin structures20, and in the case of actin-GFP, are highly overexpressed – problematic for the analysis of rod assembly which is not only stress dependent but also actin concentration dependent1. Thus, G-actinRed is the preferred probe for rod studies in fly embryos, and the large size of the embryo allows its easy injection.

The workflow of this protocol is similar to other well-established microinjection techniques that have been used for injecting proteins, nucleic acids, drugs, and fluorescent indicators into Drosophila embryos21,22,23,24,25,26,27. However, following the microinjection of G-actinRed here, embryos are exposed to mild heat stress to induce the ASR and intranuclear actin rod assembly. For labs with access to flies and an injection rig, this method should be readily implementable and adaptable for specific lines of study in regard to the ASR, including its induction by different stresses or modulation in distinct genetic backgrounds.

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Protocol

1. Prepare embryo collection cups and apple juice agar plates

  1. Five days prior to the injection experiment, construct28 or procure at least two small embryo collection cups. Make fresh 60 mm apple juice agar plates to be used with small collection cups28. Store plates in plastic boxes covered with damp paper towels at 4 °C.
    NOTE: Small embryo collection cups, populated with fly numbers as described in step 1.3, will provide sufficient embryo numbers per experiment, while also ensuring that embryo handling and injection can be done in a short enough time to allow imaging of early developmental stages.
  2. Warm apple juice plates to 18 °C and add a dab of yeast paste to the center of the plate. Yeast paste is a simple paste of active yeast and distilled water.
  3. To promote the most generous egg laying, set up collection cups with flies 2 days prior to the experiment. Add at least 100 females and 50 male flies to the collection cups, and top with a prepared apple juice plate (Figure 1, step 1). On the days leading up to the injection experiment change the apple juice plates at least twice each day, once in the morning and once in the evening.
    NOTE: The best injection and imaging results are obtained when embryo collection cups are kept at 18 °C with a 12 h light on/light off cycle.

2. Prepare a working stock solution of G-actinRed for microinjection

NOTE: This preparation only makes 2 μL of a 5 mg/mL working stock of G-actinRed, so if users are unaccustomed to the microinjection technique, it is advantageous to skip to step 3 and practice the microinjections with a neutral pH buffer to conserve precious working stock. The 10 μg stock of G-actinRed from the vendor can be stored in its original packaging in a 16 oz screw top jar with ~500 g of desiccant at 4 °C for up to 6 months.

  1. Prepare a G-buffer stock solution in advance: 5 mM Tris-HCl, 0.2 mM CaCl2, pH 8.0. Filter and store at room temperature.
  2. On the day of injections, prepare 1 mL of a G-buffer working solution in a fresh snap cap microcentrifuge tube on ice using the G-buffer stock from step 2.1, supplemented with the following at the indicated final concentrations: 1 mM dithiothreitol (DTT) and 0.2 mM ATP, pH 8.0.
    NOTE: The 1 mL volume of G-buffer working solution is more than what is needed for an experiment but simplifies the preparation. Excess can be discarded after the experiment or users can scale down according to their preference.
    1. Keeping the 10 μg G-actinRed stock on ice, first add 1 μL of filtered, distilled water to the top of the pink droplet of G-actinRed inside the tube.
    2. Next, add 1 μL of the cold, freshly prepared G-buffer working solution from step 2.2. Pipet up and down ~20 times to mix well with the pipette volume set to 1 μL. The G-actinRed stock will now be at the final dilution of 5 mg/mL.
  3. Incubate the prepared G-actinRed for 30 min on ice undisturbed.
  4. Centrifuge the prepared G-actinRed at 16,000 x g for 20 min at 4 °C in a microcentrifuge to remove any precipitate.
  5. Carefully pipet 1.5 μL of the supernatant into a fresh snap cap microcentrifuge tube on ice, avoiding the dark pink pellet.
  6. Store the prepared G-actinRed supernatant on ice for up to 6 h until ready to load into a microneedle.
    NOTE: Microneedles can be pulled from capillary tubes in advance on a micropipette puller, then stored at room temperature on a strip of modeling clay in a 100 x 20 mm Petri dish. Suggested parameters for microneedle pulling can be found in the Pipette Cookbook29.

3. Collect embryos and mount for injection

  1. Allow flies to lay embryos for 30 min on apple juice plates with yeast paste at 18 °C.
  2. While flies are laying, pre-warm an apple juice agar plate without yeast paste to room temperature, cut out a 4 cm x 1 cm rectangular wedge of apple juice agar with a razor blade, and place on a 25 mm x 75 mm glass slide.
    1. Harvest plate from the 30 minute collection and dechorionate embryos by pouring fresh bleach, diluted 1:1 with distilled water, onto the plate and swirling the plate for 1 min, as described in28 (Figure 1, step 2).
      NOTE: Different brands of bleach are sold at different concentrations. The bleach used here is 6% sodium hypochlorite from the bottle and is diluted to a final concentration of 3% sodium hypochlorite. Other bleach brands at slightly lower concentrations will work equally well.
    2. Pour the bleach and dechorionated embryos into a collection basket (a 70 μm cell strainer) and rinse the plate twice with distilled water from a squirt bottle, adding these washes to the collection basket.
    3. Vigorously rinse the dechorionated embryos in the collection basket with distilled water until no yeast clumps are visible and the basket leaves no pink marks from excess bleach when blotted on a paper towel.
  3. Using a paintbrush with bristles dampened with distilled water, transfer dechorionated and washed embryos from the collection basket onto the prepared apple juice agar wedge on the glass slide.
  4. Use a pair of fine tip tweezers or a dissecting needle to arrange ten embryos in a straight line along the long axis of the rectangular agar wedge (Figure 1, step 3). Arrange the embryos head-to-tail, such that their anterior pole is facing to the right and dorsal side is facing the researcher (Figure 1, step 3, magnified).
  5. Cut off 0.5 cm of the end of a P200 pipette tip with a razor blade and dip into the “embryo glue” (described in28). Generously coat a region 5 mm in width (Figure 1, step 4) along the long edge of a 24 mm x 50 mm rectangular coverslip, and let dry, glue side up. Drying will take ~30 s and is complete once the entire glue-coated region appears matte rather than wet or shiny.
    NOTE: Prepare “embryo glue” at least 48 h in advance. Add n-Heptane to strips of double-sided tape in a scintillation vial as described in28.
  6. Once the “embryo glue” has dried, gently place the coverslip glue side down on top of the row of aligned embryos on the agar, leaving 2-3 mm of space between the edge of the coverslip and the row of embryos.
    NOTE: Sticking the embryos too close to the edge of the coverslip may lead to the embryos drying out too much during the course of the experiment.
  7. Flip the coverslip over so that the embryos are now facing up. They should be stuck in a line along one long edge of the coverslip, and their ventral region facing the closest edge of the coverslip (Figure 1, step 4, magnified).
  8. Desiccate the embryos by placing the coverslip with embryos gently on top of 150 g of fresh blue desiccant stored in a 16 oz screw top jar. Tightly screw on the lid and incubate for 8-10 min (Figure 1, step 5).
  9. After desiccation, remove the coverslip from the desiccant jar and tape each short side of the coverslip to a microscope slide, embryo side up, with two 4 cm2 pieces of double-sided tape so that the embryo coverslip will fit onto the injection stage (Figure 1, step 6).
  10. Add 2-3 drops of Halocarbon 27 oil with a Pasteur pipette to cover the aligned embryos and protect them from further dehydration (Figure 1, step 6).

4. Inject and heat stress embryos to promote actin rod formation

NOTE: All injections are done in a temperature-controlled room at 18 °C.

  1. Prepare humid incubation chambers from a glass Petri dish at least 100 mm x 20 mm in size and line the chamber with twists of lab tissue wipers dampened with distilled water (Figure 1, step 8). Pre-warm the incubation chambers at 32 °C or the desired incubation temperature prior to injecting embryos.
  2. Open the airflow valve for the microinjector and turn on the microinjector (compressed air or house air with a pressure of at least 90 psi is suitable).
  3. While embryos are desiccating, backload the previously prepared G-actinRed supernatant into the microneedle using a micro loader tip. Set the pipette to draw up 1-1.5 μL.
    NOTE: Because of the viscosity of the actin, loading volumes may not be accurate and there may be enough actin left to load at least one to two more microneedles. Up to 60 embryos can be injected per loaded microneedle if the microneedle is calibrated properly and does not become clogged during the course of the experiment.
  4. Attach the microneedle to the needle holder and tighten the screw. Connect the air tube to the microinjector and ensure that the backflow pressure on the microneedle equilibrates to 30 hPa.
  5. Calibrate the microinjector settings to expel a 100 μm diameter bubble of G-actinRed (~500 pL) on a slide micrometer. Rotate the pressure knob (500-1500 hPa) and injection pulse time knob (0.1-0.5 s) on the microinjector to get the right bubble size. Adjust these settings each time a new microneedle is loaded to account for variability in actin viscosity and microneedle tip size.
    NOTE: The prepared G-actinRed is viscous and there may be air in the tip of the microneedle that should be expelled before injecting embryos. If the G-actinRed does not readily expel from the tip of the microneedle, gently break the microneedle tip against the edge of the slide micrometer.
  6. Place the slide with mounted embryos onto the microscope stage.
    NOTE: Every injection set up will be different, so researchers will have to adjust their injection method accordingly. Here the embryos are moved with respect to a stationary microneedle, injecting each embryo by running the embryo into the microneedle.
  7. Adjust the micromanipulator stage and focus of the 10x objective on the light microscope so that the embryos are visible. The embryos are in the correct focal plane when the outlines of the vitelline membrane are sharpest and the embryo appears largest. Choose embryos to inject that are in the correct developmental stage, so that by the time the post-injection incubation is complete, most of the clutch reaches the desired developmental stage (e.g., inject embryos at Bownes’ stage 2-330 in order to observe rods at cellularization after heat stress at 32 °C).
  8. Use the microneedle controls to bring the needle into the same focal plane as the embryos.
    NOTE: If the microneedle catches on the coverslip while moving the stage or microneedle, then the microneedle is too close to the slide and is not in the correct focal plane. The microneedle should be parallel to the coverslip, and not at a significant angle (Figure 1, step 7).
  9. Insert the microneedle into the embryo so that it hits the embryo in the middle of its ventral region, at the embryo “equator”. Trigger injection with the foot pedal or “inject” button when the microneedle tip is visible inside the middle of the embryo (Figure 1, step 7).
  10. Inject the G-actinRed once and slowly remove the microneedle. Move the stage and repeat for each embryo of the appropriate developmental stage.
    NOTE: Expansion of the embryo is normal as the G-actinRed is injected and a bit of cytoplasm may leak out of the embryo.
  11. After all the embryos have been injected, place the slide with the embryos in the prepared humid incubation chamber and close the lid (Figure 1, step 8). If trying to obtain embryos that reach cellularization, heat stress the embryos at 32 °C for 60-75 min in the humid incubation chamber.
    NOTE: Incubation times are noted that allow visualization of rods in cellularizing heat stressed embryos. The incubation time will be longer for non heat stress control embryos because development will be slower at a lower temperature31. These control embryos can be incubated in humid chambers at temperatures such as 18 °C or 25 °C, depending on design of the specific experiment and the question to be asked. The minimum incubation time necessary for the G-actinRed to diffuse throughout the embryo is 30 min.

5. Image actin rods in heat stressed embryos by confocal microscopy

  1. While the embryos are being heat stressed, turn on the confocal microscope and select the 561 nm laser channel.
  2. Move the objective lens (25x, 40x or 63x recommended) to the working position.
  3. If imaging heat stressed embryos, then set the heated stage incubator to achieve an internal temperature of 32 °C. A point-and-shoot or infrared thermometer can be used to check the temperature at or near the objective.
  4. Remove the slide with injected embryos from the humid incubation chamber after incubation is complete (Figure 1, step 9).
  5. Working quickly, gently pry off the double-sided tape pieces that were used to adhere the coverslip with mounted embryos to the slide (Figure 1, step 9).
    CAUTION: Be gentle during these steps as coverslips can easily shatter if too much force is applied.
  6. Stick two 2.5 cm long pieces of double-sided tape together and cut the tape in half lengthwise to make two strips, 2.5 x 0.5 cm long (Figure 1, step 10).
  7. Stick two-thirds of the length of each tape strip onto the first coverslip, flanking each side of the embryos in Halocarbon 27 oil (Figure 1, step 10, orange), leaving one-third of the tape strips hanging off the edge of the first coverslip where the embryos are stuck. Use gloved hands and be careful not to touch the embryos during this step.
  8. Gently place a second rectangular coverslip on top of the tape strips to sandwich the embryos between the coverslips (Figure 1, step 10, blue). Align the 25 mm edges but keep the 50 mm edges offset from one another by 1 cm in width.
    NOTE: This second coverslip’s full surface will become the new imaging surface that will face the objective lens, so take care not to get fingerprints or Halocarbon 27 oil on this second coverslip surface. The offset is necessary so that extra Halocarbon 27 oil can be added to evenly immerse the embryos. If needed, add Halocarbon 27 oil at the seam where the two coverslips meet at the top of the sandwich and it will coat the embryos by capillary action (see dashed lines in Figure 1, step 10).
  9. Gently tap down on the areas of the coverslip that are directly on top of the tape strips with the blunt side of a razorblade to get the coverslip to adhere to the tape.
  10. Flip the coverslip sandwich over and place on a lab tissue wiper to keep the imaging surface clean and carry to the confocal microscope (Figure 1, step 11). Ensure that the tape is completely stuck to both coverslips before imaging.
  11. Confirm that the heated stage is at temperature and if using an inverted microscope, add immersion liquid onto the selected objective lens.
  12. Place the coverslip sandwich onto the stage carefully to ensure that the new imaging surface (2nd coverslip) is the one touching the immersion liquid (Figure 1, step 11).
    NOTE: If needed, adhere the coverslip sandwich to the stage with two small pieces of double-sided tape to prevent unnecessary movement during imaging if the coverslips do not fit well in the heated stage.
  13. Focus on an embryo that is in cellularization (Bownes stage 4a30) or desired developmental stage using either transmitted light or fluorescence.
  14. Once an embryo has been brought into focus, switch to the laser acquisition mode on the confocal microscope and adjust laser power and gain, frame size, tiling, and projection settings as desired.
  15. Take surface-view images through the focal planes of the embryo’s nuclei to find intranuclear actin rods. Rods should appear in multiple orientations as bright streaks or dots inside the comparatively dark nuclei (Figure 2A, 2C).

6. Alternative imaging experiments

  1. Perform FRAP to investigate actin turnover along the length of intranuclear actin rods or in cytoplasmic actin structures, such as the tips of the plasma membrane furrows during cellularization.
  2. In the imaging software, choose a rectangular region around furrow tips or actin rods in which to acquire the experiment.
  3. Choose a small square region of the center of an actin rod within the rectangular acquisition region to bleach. Ensure that the tips of the actin rod are visible and do not get bleached during the course of the experiment to allow for accurate tracking of the rod inside the nucleus.
  4. Set the bleach laser to iterate 50x and set the bleach laser power to maximum.
  5. Choose a time course to acquire images every second for a total up to 120 s at maximum pixel dwell speed and set the laser to bleach after the first two seconds of image acquisition.
  6. Quantify the data to determine the half-time of fluorescence recovery1.

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Results

A schematic workflow of embryo handling is depicted in Figure 1, and a timetable for a typical experiment is presented in Table 1. An estimate for a good experimental outcome is that for every 10 embryos injected, at least half of the embryos viewed will be at the correct developmental stage, undamaged, and exhibit a robust ASR with heat stress at 32 °C. This ASR will be evidenced by the assembly of intranuclear actin rods as shown in the representative surface view image of...

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Discussion

The significance of this method is that it utilizes the well-established protocol of microinjection in Drosophila embryos21,22,23,24,25,26,27 to enable new research regarding the ASR and accompanying actin rod assembly. A major advantage of injecting G-actinRed into live ...

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Disclosures

No conflicts of interests declared.

Acknowledgements

The authors gratefully acknowledge the work of Liuliu Zheng and Zenghui Xue, who helped pioneer this technique in the Sokac lab, as well as Hasan Seede who helped with the analysis. The work for this study is funded by a grant from NIH (R01 GM115111).

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
Adenosine triphosphate (ATP)Millipore-SigmaA23835GComponent of G buffer
Apple juice, Mott's, 64 fl ozMott's014800000344Component of apple juice plates
Bacto AgarBD214010Component of apple juice plates
Bleach, PureBright Germicidal, 6.0% sodium hypochloriteKIK International059647210020For dechorionating embryos
Calcium chlorideMillipore-SigmaC1016500GComponent of G buffer
Cell strainer, 70 μmFalcon352350For collecting dechorionated embryos
Confocal microscope, LSM 880 34-channel with AiryscanZeiss0000001994956For imaging intranuclear actin rods
DesiccantDrierite24001For desiccating embryos
Dissecting microscope, Stemi 508 Stereoscope with 8:1 zoomZeiss4350649000000For arranging embryos on agar wedge
Dissecting needle, 5 inFisher Scientific08965AFor arranging embryos on agar wedge
Dithiothreitol (DTT)Fisher ScientificBP1725Component of G buffer
Double-sided Tape, Scotch Permanent, 0.5 in x 250 in3M021200010323For making embryo glue
Embryo collection cageGenessee Scientific59100For housing adult flies and collecting embryos
Fine tip tweezers, Dumont Tweezer, Style 5Electron Microscopy Sciences72701DFor arranging embryos on agar wedge
Glass capillaries, Borosillicate glass, thin 1 mm x 0.75 mmWorld Precision Instruments, Inc.TW1004For microneedles
Halocarbon oil 27Millipore-SigmaH8773100MLFor hydration of embryos
Heated stage incubatorZeiss4118579020000, 4118609020000, 4118609010000For confocal imaging
Lab Tissue Wipers, KimWipesKimberly-Clark34155Lab tissue wipers
Light microscope, Invertoskop 40C Inverted Phase contrast microscope, refurbishedZeissDiscontinuedInjection microscope
Methyl-4-hydroxybenzoateMillipore-SigmaH36471KGComponent of apple juice plates
Microinjector, FemtoJet4xEppendorf5253000025Microinjector
Micro loader tips, epT.I.P.S. 20 μLEppendorf5242956003For loading microneedles
Micromanipulator and injection stage with x,y,z dials for needle adjustmentBernard Instruments, Inc (Houston, TX)CustomFor performing microinjections
Micropipette puller, Model P-97, Flaming/BrownSutter InstrumentsP97For pulling capillary tubes to make microneedles
Microscope cover glass 24x50-1.5Fisher Scientific12544EFor mounting embryos
Microscope slides, Lilac Colorfrost, Precleaned, 25 x 75 x 1mmFisher Scientific22037081For mounting embryos for injection
n-HeptaneFisher ScientificH3601Component of embryo glue
Objective, 10xZeissDiscontinued10x objective for injection microscope
Objective, C-Apochromat 40x/1,2 W Korr. FCSZeiss421767997171140x water objective for confocal
Objective, LD LCI Plan-Apochromat 25x/0.8 Imm Cor DIC M27 for oil, water, silicone oil or glycerine immersion (D=0-0.17mm) (WD=0.57mm at D=0.17mm)Zeiss420852987100025x mixed immersion objective for confocal
Objective, Plan-Apocrhomat 63x/1.40 Oil DIC f/ELYRAZeiss420782990079963x oil objective for confocal
Paintbrush, Robert Simmons Expression E85 Pointed Round size 2Daler-Rowney038372016954For transferring embryos
Paper towels, Kleenex C-fold paper towels, whiteKimberly-Clark884266344845For blotting cell strainer
Pasteur pipette, 5 3/4 inFisher Scientific1367820AFor covering embryos with oil
Petri dish, glass, 100 x 20 mmCorning3160102For humid incubation chamber
Petri dish, plastic, 60 x 15 mmVWR25384092For apple juice plates
Pipette, Eppendorf Reference 0.5-10 μLEppendorf2231000604For loading the microneedle
Pipette tip, xTIP4 250 μLBiotix63300006For adding embryo glue to coverslip
Razor bladeVWR55411050For cutting agar wedge, tape, pipette tips
Rhodamine-conjugated globular actin, human platelet (non-muscle; 4x10 μg)Cytoskeleton, Inc.APHR-AG-actin^Red
Scintillation vial, 20 mL Glass borosillicate with polyethylene liner and urea capsFisher Scientific033377For making embryo glue
Screw top jar, 16 ozNalgene000194414195For desiccating embryos
Stage micrometerElectron Microscopy Sciences602104PGFor calibrating volume of G-actin injection
SucroseMillipore-Sigma840971KGComponent of apple juice plates
Trizma baseMillipore-SigmaT15031KGComponent of G buffer
Yeast, Lesaffre Yeast Corporation Yeast, Red Star Active Dry, 32 ozLesaffre Yeast Corporation117929157002Component of yeast paste

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