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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Disclosures
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

To detect healthy cells in whole animals that contain low levels of caspase activity, the highly sensitive biosensor designated CaspaseTracker was generated for Drosophila. Caspase-dependent biosensor activity is detected in long-lived healthy cells throughout the internal organs of adult animals reared under optimized conditions in the absence of death stimuli.

Abstract

Caspases are the key mediators of apoptotic cell death via their proteolytic activity. When caspases are activated in cells to levels detectable by available technologies, apoptosis is generally assumed to occur shortly thereafter. Caspases can cleave many functional and structural components to cause rapid and complete cell destruction within a few minutes. However, accumulating evidence indicates that in normal healthy cells the same caspases have other functions, presumably at lower enzymatic levels. Studies of non-apoptotic caspase activity have been hampered by difficulties with detecting low levels of caspase activity and with tracking ultimate cell fate in vivo. Here, we illustrate the use of an ultrasensitive caspase reporter, CaspaseTracker, which permanently labels cells that have experienced caspase activity in whole animals. This in vivo dual color CaspaseTracker biosensor for Drosophila melanogaster transiently expresses red fluorescent protein (RFP) to indicate recent or on-going caspase activity, and permanently expresses green fluorescent protein (GFP) in cells that have experienced caspase activity at any time in the past yet did not die. Importantly, this caspase-dependent in vivo biosensor readily reveals the presence of non-apoptotic caspase activity in the tissues of organ systems throughout the adult fly. This is demonstrated using whole mount dissections of individual flies to detect biosensor activity in healthy cells throughout the brain, gut, malpighian tubules, cardia, ovary ducts and other tissues. CaspaseTracker detects non-apoptotic caspase activity in long-lived cells, as biosensor activity is detected in adult neurons and in other tissues at least 10 days after caspase activation. This biosensor serves as an important tool to uncover the roles and molecular mechanisms of non-apoptotic caspase activity in live animals.

Introduction

Caspases are cysteine proteases that mediate apoptotic cell death by cleaving many intracellular proteins after key aspartate residues. For example, initiator caspases activate effector caspases, derepress DNA nucleases, cleave cytoskeletal components and alter the lipid composition of cell membranes to rapidly dismantle cells and stimulate their recognition and engulfment by neighboring cells that dispose of the cell corpses.1-4 It is estimated that billions of cells die per day in the human body, and apoptosis is an important mechanism of chemotherapy-induced tumor cell death.5 A different set of caspases can cause cell death by distinct non-ap....

Protocol

1. Preparation of CaspaseTracker Flies

  1. To prepare CaspaseTracker (DQVD) flies for experiments, perform this cross: UBI-CaspaseTracker x G-TRACE (UAS-RFP; UAS-FLP; Ubi>Stop>GFP-nls), by transferring 7-10 virgin female (or male) flies carrying the caspase biosensor substrate mCD8-DIAP1-Gal4 driven by the ubiquitin promoter35 together with the same number of male (or female) G-TRACE flies, which have the second chromosome CyO balancer to avoid lethality of the homozygous comb.......

Representative Results

There are two key components that allow CaspaseTracker to detect caspase activity in normal healthy cells (Figure 1a). The first of these is a 146 amino acid caspase-cleavable polypeptide modeled after the caspase biosensor Apoliner (Figure 1b).28 This polypeptide is derived from DIAP1 (Drosophila inhibitor of apoptosis) containing a single naturally occurring caspase site that is cleaved during apoptosis typically by the caspase DrICE.......

Discussion

Here we illustrate the construction and inner workings of CaspaseTracker that facilitate detection of widespread basal caspase activity in healthy tissues. The critical steps for detecting non-apoptotic caspase activity in vivo are: 1) generating flies with the biosensor transgene, 2) verifying caspase-specific reporter function with appropriate controls, 3) practicing dissection techniques to observe all internal organ systems of adult Drosophila, and 4) distinguishing biosensor activity from autofluor.......

Disclosures

The authors have nothing to disclose.

Acknowledgements

We thank Polan Santos and Darren Obbard for Drosophila illustrations in Fig. 2a, Marcelo Jacobs-Lorena for use of the JHMRI insectary. This work was supported by the Life Science Research Foundation fellowship (H.L.T.), University Grants Committee of the Hong Kong AoE/B-07/99 (M.C.F.), and NIH grants NS096677, NS037402 and NS083373 (J.M.H.). Ho Lam Tang is a Shurl and Kay Curci Foundation Fellow of the Life Sciences Research Foundation.

....

Materials

NameCompanyCatalog NumberComments
CONSUMABLES AND REAGENTS
VectashieldVector ProductsH-1000Mounting medium
ForcepsTed Pella#505 (110mm, #5)Dumont tweezer biology grade, stainless steel
Hanging Drop SlidesFisher Scientific12-565BGlass slides
Hoechst 33342Molecular ProbesH1399DNA stain
Alexa Fluor 633 PhalloidinMolecular ProbesA22284Actin stain
Rat-Elav-7E8A10 anti-elav antibody Developmental Studies Hybridoma Bank (DSHB)Antibody Registry ID:  AB_528218 Stain for Drosophla pan-neuronal ELAV
Cleaved caspase-3 (Asp175) antibodyCell Signaling Technology#9661Stain for active fragment of caspase-3
ProLong Gold antifade reagentLife TechnologiesP36934to preserve fluorophores 
ProLong Diamond Antifade MountantLife TechnologiesP36961to preserve fluorophores 
SylGard 182 Silicone Elastomer KitDow Corning Product code: 0001023934for dissection plates
EQUIPMENT
LSM780 confocal microscopeCarl ZeissN/AImaging
Carl Zeiss Stereomicroscope Stemi 2000 Carl ZeissN/ADrosophila dissection
AmScope Fiber Optic Dual Gooseneck Microscope Illuminator, 150WAmScopeWBM99316 Light source

References

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