CASPAM: a triple modality biosensor for multiplexed imaging of caspase network activity

Understanding signal propagation across biological networks requires to simultaneously monitor the dynamics of several nodes to uncover correlations masked by inherent intercellular variability. To monitor the enzymatic activity of more than two components over short time scales has proven challenging. Exploiting the narrow spectral width of homoFRET-based biosensors, up to three activities can be imaged through fluorescence polarization anisotropy microscopy. We introduce CASPAM (Caspase Activity Sensor by Polarization Anisotropy Multiplexing) a single-plasmid triple-modality-reporter of key nodes of the apoptotic network. Apoptosis provides an ideal molecular framework to study interactions between its three composing pathways (intrinsic, extrinsic and effector). We characterized the biosensor performance and demonstrated the advantages that equimolar expression has both in simplifying experimental procedure and reducing observable variation, thus enabling robust data-driven modelling. Tools like CASPAM become essential to analyze molecular pathways where multiple nodes need to be simultaneously monitored.