Correlative light and electron microscopy

Autophagy is an intracellular degradative pathway that is essential for cellular homeostasis. Efficient autophagy ultimately relies on the ability of the cell to form autophagosomes, and the efficiency of lysosomal enzymes and lipid hydrolases contained within the autolysosome to degrade sequestered cytosolic material and organelles and recycle these nutrients back to the cytosol. Several assays and techniques to monitor autophagy are available, and these can be quantitative or qualitative, biochemical or morphological. Here we describe a method for monitoring the autophagic process that is based on morphology and the application of both light and electron microscopy, called correlative light and electron microscopy, or CLEM. CLEM provides an advance over either technique (light or electron microscopy) alone and can be performed on any cell or tissue sample, which can be grown or mounted on a gridded coverslip or support compatible with light microscopy. CLEM gives a broad low magnification overview of the cell, allowing an assessment of both spatial and temporal events, as well as providing high-resolution information about individual autophagosomes or single compartments.