Autophagy is an essential, homeostatic process by which cytoplasmic materials are degraded in lysosomes.
This multi-step process involves isolation of cargo within membranes, autophagosome formation, fusion with lysosomes, degradation and recycling of cargo contents.
One key protein used to study this ‘autophagic flux’ is LC3B (microtubule-associated protein 1 light chain 3).
This protein is recruited from the cytosol, maturated and bound to the isolation membrane. This localization serves as a marker for autophagic membranes and for monitoring the process as it develops.
Chimeric proteins consisting of LC3B fused to a green fluorescent protein (GFP) and a red fluorescent protein (RFP) provide a simple means of monitoring the autophagic process.
Autophagosomes marked by an RFP::GFP::LC3 show both RFP and GFP signals. After fusion with lysosomes, GFP signals are significantly reduced due to acidic conditions, while RFP signals remain relatively stable.
