Apical caspase reporters uncover unknown stages of apoptosis and enable ready visualization of undead cells

Abstract

The caspase-mediated regulation of many cellular processes, including apoptosis, justifies the substantial interest in understanding all of the biological features of these enzymes. To complement functional assays, it is critical to identify caspase-activating cells in live tissues. Our work describes new caspase-reporters that, for the first time, provide direct information concerning the initial steps of the caspase activation cascade in Drosophila tissues. One of our caspase-sensors has capitalized on the rapid subcellular localization change of a fluorescent marker to uncover novel cellular apoptotic events. These refer to the actin-mediated positioning of the nucleus before cell delamination. The other construct has benefited from a caspase-induced nuclear translocation of a QF transcription factor. This feature enables the genetic manipulation of caspase-activating cells, whilst showing the spatio-temporal patterns of apical caspase activation. Collectively, our sensors offer new experimental opportunities that are already illuminating unknown aspects of caspase-dependent processes in apoptotic and non-apoptotic cellular scenarios.\n\nSummary statementWe describe a novel set of caspase sensors that directly detect early caspase activation. The exclusive features of our reporters uncovered unknown stages of apoptosis and properties of caspase-activating cells.