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Autophagy (Greek for “self-eating”) is a process by which cytoplasmic material, including organelles, are targeted to lysosomes for degradation. Autophagy is a dynamic process which involves autophagosome synthesis, delivery of materials to be degraded to the lysosome, and degradation of autophagic substrates inside the lysosome. Historically, methods for studying autophagy focused on counting the number of autophagosomes. This approach, however, has inherent limitations because it turns a dynamic process into a static measurement and it provides limited information about what materials or organelles are being targeted for autophagy. The development of several fluorescent autophagy reporters now allows for the measurement of autophagic flux, or the changes in autophagic activity, and are a more reliable indicator of autophagic activity. The aim of this post is to provide an overview of four autophagy biosensors currently available from Addgene.

Kinases: they regulate many proteins, with ~1/3 of human proteins predicted to be phosphorylated on at least one site. Phosphorylation is particularly important for regulating signal transduction and measuring kinase activity at the single-cell level can aid in drawing connections between signaling activity and cell phenotype. One method for monitoring live single-cell kinase activity is FRET, but FRET reporters are challenging to design and difficult to multiplex. The Covert Lab provides an alternative tool with their Kinase Translocation Reporters (KTRs) whose cellular localization serves as a proxy measurement of kinase activity. The key advantage of KTRs is that they are easy to create and simple to multiplex.

Oliver Griesbeck of the Max Planck Institute for Neurobiology has been working on genetically encoded indicators of calcium and other small molecules since the very beginnings of the field. Those engineered sensors were designed to replace synthetic calcium dyes, which had been in use since the 1980s.

“Synthetic dyes were the standard in the field, but there is one problem: how to get that into the cells of interest,” Griesbeck said. Because they are chemical compounds, they have to be applied or injected, and they don’t always end up where you want them to go.

Griesbeck is motivated by a particular interest in monitoring the activity and biochemistry of living neurons in an effort to understand the connection between molecular- and cellular-level events and behavior. It’s a problem that he considers “one of the greatest challenges of neuroscience.”